DNA: The

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Chapter 16 The Molecular Basis of Inheritance

• DNA The
• Genetic Material

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Intro to DNA Video

• http//www.youtube.com/watch?vbVk0twJYL6Yfeature
  youtube_gdata_player

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Just a thought

• Make a stack of books totaling
• about 10,000 pages.
• That stack of books represents
• only about one-fiftieth of the information
• contained in the DNA of
• every human cell.
• Correlate this with the amount of information
• required to code for a human being.

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Quick Review1. What is the structure of a
chromosome?2. Define the term gene.3.
Identify the stage in the cell cycle in which DNA
is copied.4. What are mutations?5. Summarize
Mendels theory of heredity.
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• Answers
• 1. A chromosome consists of two replicated
  strands of DNA tightly coiled around proteins.
• The two strands, called chromatids, are attached
  at a point called a centromere.
• 2. A gene is a segment of DNA that codes for a
  protein or RNA molecule.
• 3. A cells DNA is copied during the synthesis
  (S) phase.
• 4. When chromosomes break, the broken pieces can
  detach completely or can reattach in various
  ways. Therefore, the chromosome is changed, or
  mutated.

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• 5. (a) For each inherited trait, an individual
  has two copies of the gene, one from each parent.
  
• (b) There may be alternative versions of genes.
• (c) When two different alleles occur together,
  one of them may be completely expressed, while
  the other may have no observable effect on the
  organisms appearance.
• (d) When gametes are formed, the alleles for each
  gene in an individual separate independently of
  one another, and when gametes unite during
  fertilization, each gamete contributes one
  allele.

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Vocabulary

• 1. DNA /double helix,
• 2. Nucleosome
• 3. Semi conservative replication,
• 4. DNA polymerase,
• 5. Okazaki fragment

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Vocabulary

1. vaccine
2. virulent
3. transformation
4. bacteriophage
5. double helix
6. nucleotide
7. deoxyribose
8. base-pairing rules
9. complementary base pair
10. DNA replication
11. DNA helicase
12. replication fork
13. DNA polymerase

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• 1. What are the two chemical components of
  chromosomes?

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• DNA and protein

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Chapter DNA The Genetic Material

• 1. Identifying the Genetic Material
• A. Transformation
• B. Viral Genes and DNA

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2. Why did researchers originally think that
protein was the genetic material?
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• Until the 1940s, the case for proteins seemed
  stronger, especially since biochemists had
  identified them as a class of macromolecules with
  great heterogeneity (uniformity) and
  specificity of function, essential requirements
  for the hereditary material.
• Also, little was known about nucleic acids, whose
  physical and chemical properties seemed far too
  uniform to account for the multitude of specific
  inherited traits exhibited by every organism.

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Identifying the Genetic Material

• The experiments of Griffith and of Avery yielded
  results that suggested DNA was the genetic
  material.

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• Frederick Griffith--Discovery of the Transforming
  Principle (Video Clip)

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Griffiths Discovery of Transformation
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The capsule killed, non capsule did not!
Heat-killed capsule, did not KILL! BUT A MIX OF
THE 2 DID!
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3. Distinguish between the virulent and
non-virulent strains of Streptococcus pneumoniae
studiedby Frederick Griffith.
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• The virulent strains ( with capsules) are
  pathogenic (disease-causing), whereas the
  nonvirulent strains ( no capsule) are
  nonpathogenic (harmless).

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4. What was the purpose of Griffiths studies?
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• Griffith was attempting to develop a vaccine
  against pneumonia.

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What happened?5. Use this figure to summarize
the experiment in which Griffith became aware
that hereditaryinformation could be transmitted
between two organisms in an unusual manner.
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• information could be transmitted between two
  organisms in an unusual manner.
• Griffith studied two strains of the bacterium
  Streptococcus pneumoniae. Bacteria of the S
  (smooth) strain can cause pneumonia in mice they
  are pathogenic because they have an outer capsule
  that protects them from an animals defense
  system. Bacteria of the R (rough) strain lack a
  capsule and are nonpathogenic.
• To test for the trait of pathogenicity, Griffith
  injected mice with the two strains. Griffith
  concluded that the living R bacteria had been
  transformed into pathogenic S bacteria by an
  unknown, heritable substance from the dead S
  cells that allowed the R cells to make capsules.

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Transformation

• Something in the heat-killed bacteria that once
  were able to produce a capsule that caused them
  to kill the mice was able to transform the once
  non-virulent bacteria into capsule producing,
  virulent ones!
• But what was that something????

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6. Define transformation.
A change in genotype and phenotype due to the
assimilation of external DNA by a cell. When the
external DNA is from a member of a different
species, transformation results in horizontal
gene transfer.
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Griffith 1928

• 1. What happened to the normally non-virulent
  rough bacteria when mixed with the virulent
  smooth heat killed ones?
• 2. Based on what happened to the bacteria, what
  was Griffiths experiment called?
• 3. At the end of Griffiths experiment, did
  scientists know if DNA or proteins caused the
  changes?

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Griffith 1928

• 1. What happened to the normally non-virulent
  rough bacteria when mixed with the virulent
  smooth heat killed ones? they became virulent
• 2. Based on what happened to the bacteria, what
  was Griffiths experiment called? the
  transforming experiment
• 3. At the end of Griffiths experiment, did
  scientists know if DNA or proteins caused the
  changes? _no

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Averys experiment

• DNA destroying enzymes helped support the fact
  that it was the DNA not proteins that were the
  transforming factors!

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• 7. What did Oswald Avery determine to be the
  transforming factor?
• Explain his experimental approach.

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• DNA !
• Avery broke open the heat-killed pathogenic
  bacteria and extracted the cellular contents. He
  treated each of three samples with an agent that
  inactivated one type of molecule, and then tested
  the sample for its ability to transform live
  nonpathogenic bacteria.
• Only when DNA was allowed to remain active did
  transformation occur.

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Avery 1944

• 4. Avery attempted to do what?
• 5. Did people accept Averys results?
  
  
  

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Avery 1944

• 4. Avery attempted to do what? identify if the
  substance was protein or DNA
• 5. Did people accept Averys results?
  
  
  NO

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• Hershey and Chase used the bacteriophage T2 and
  radioactive labels to show that viral genes are
  made of DNA, not protein.

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• Alfred Hershey and Martha Chase--Acceptance
  within scientific community of DNA as genetic
  material (Video Clip)

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bacteriophage

• 8. Sketch a T2 bacteriophage and label its head,
  tail sheath, tail fiber, and DNA.

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• 9. How does a bacteriophage destroy a bacterial
  cell?

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• The T4 phage uses its tail fibers to bind to
  specific receptor sites on the outer surface of
  an E. coli cell. The sheath of the tail
  contracts, injecting the phage DNA into the cell
  and leaving an empty capsid outside.
• .

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• The cells DNA is hydrolyzed. The phage DNA
  directs production of phage proteins and copies
  of the phage genome by host and viral enzymes,
  using components within the cell.

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• Three separate sets of proteins self-assemble to
  form phage heads, tails, and tail fibers. The
  phage genome is packaged inside the capsid as the
  head forms. The phage directs production of an
  enzyme that damages the bacteria cell wall,
  allowing fluid to enter. The cell swells, and
  finally bursts, releasing 100 to 200 phage
  particles

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The Hershey-Chase Experiment
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Hershey and Chase

• More evidence it is DNA!

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• Radioactive (heavy forms) were provide for the
  phages to incorporate into their structures
• Sulfur in protein 35 S
• Phosphorus in DNA 32 P

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• The radioactive sulfur remained outside with the
  protein coat of the virus.
• The radioactive Phosphorus went inside the
  bacteria and showed that the DNA was the
  component that went inside and produced more
  viral proteins.

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• 10. How did Hershey and Chase label viral DNA
  and viral protein so that they could be
  distinguished? Explain why they chose each
  radioactive tag in light of the chemical
  composition of DNA and protein.

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• Hershey and Chase used radioactive isotopes of
  sulfur to tag protein in one batch of T2 and a
  radioactive isotope of phosphorus to tag DNA in a
  second batch.
• Because proteins, but not DNA, contain sulfur,
  radioactive sulfur atoms were incorporated only
  into the protein of the phage.

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• DNA stores the information that tells cells which
  proteins to make and when to make them.

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• 11. Describe the means by which Hershey and Chase
  established that only the DNA of a phage enters
  an E. coli cell.
• What conclusions did these scientists draw based
  on these observations?

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• Separate samples of the non-radioactive E. coli
  cells were allowed to be infected by the protein
  labeled and DNA-labeled batches of T2.
• The researchers then tested the two samples
  shortly
• after the onset of infection to see which type of
  moleculeprotein or DNAhad entered the bacterial
  cells and would therefore be capable of
  reprogramming them.
• Hershey and Chase found that the phage of DNA
  entered the host cells but the phage protein did
  not.
• Hershey and Chase concluded that the DNA injected
  by the phage must be the molecule carrying the
  genetic information that makes the cells produce
  new viral DNA and proteins.

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Hershey and Chase 1952

• 6. What is a bacteriophage?
• 7. Radioactive phosphorous was used to identify
  DNA because _________does not contain phosphorous
  but DNA does.
• 8. They could then trace the path of the
  radioactive phosphorous and found that it ended
  up in the transformed______________
• 9. Radioactively labeled Protein did not enter
  the bacteria at all but_____________________

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Hershey and Chase 1952

• 6. What is a bacteriophage? A virus that
  infects bacterial cells.
• 7. Radioactive phosphorous was used to identify
  DNA because protein_does not contain phosphorous
  but DNA does.
• 8. They could then trace the path of the
  radioactive phosphorous and found that it ended
  up in the transformed bacteriums DNA
• 9. Radioactively labeled Protein did not enter
  the bacteria at all but remained outside the
  cell.

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• 10. Which experiments led to the discovery of
  DNA as the genetic material?

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• 10. Which experiments led to the discovery of
  DNA as the genetic material?
• All of them, Griffiths, Avery and Hershey and
  Chases were needed to get to the idea that DNA
  and not Protein was the genetic material. It was
  ultimately Hershey and Chases experiment that
  demonstrated that it was DNA and not protein that
  transmitted the genetic material.

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• 1. In 1928, the experiments of Griffith
  demonstrated transformation of
• a. R bacteria into S bacteria.
• b. S bacteria into R bacteria.
• c. heat-killed S bacteria into R bacteria.
• d. S bacteria into heat-killed R bacteria.
• 2. In 1952, Hershey and Chase used the
  bacteriophage T2 to determine that genetic
  material is made of which of the following?
• a. protein c. DNA
• b. RNA d. 35S
• 3. A microorganism that is virulent is
• a. able to cause disease. c. a bacteriophage.
• b. transformed. d. harmless.

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• 4. Averys experiments showed that
• a. DNA is responsible for transformation.
• b. proteins are responsible for transformation.
• c. bacteriophages are responsible for
  transformation.
• d. virulent bacteria are responsible for
  transformation.
• 5. Hershey and Chase injected phages with
• a. S bacteria. c. radioactive isotopes.
• b. R bacteria. d. vaccines.
• 6. Hershey and Chase found that T2
  bacteriophages
• a. inject their DNA into host cells.
• b. cause host cells to produce viral DNA and
  proteins.
• c. keep most of their viral proteins outside the
  host cell.
• d. All of the above

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• ______ 7. radioactive sulfur and phosphorous
• ______ 8. transformation
• ______ 9. bacteriophage
• ______10. vaccine
• a. discovered by Griffith
• b. infects bacteria
• c. used in the Hershey and Chase experiments
• d. helps protect the body against future
  infections by specific disease-causing agents

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GENETIC MATERIAL answers

• 1. a 6. d
• 2. c 7. c
• 3. a 8. a
• 4. a 9. b
• 5. c 10. d

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2. The Structure of DNA

• A. A Winding Staircase
• B. Discovering DNAs Structure

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• Erwin Chargaff--DNA is not equal for all species
  and ratio of bases varies among species (Video
  Clip)

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Chargaffs data
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12. What are Chargaffs rules? How did he arrive
at them?
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Chargaffs rules are

• 1. The base composition varies between species.
• 2. Within a species, the number of A and T bases
  are equal and the number of G and C bases are
• equal.
• Chargaff analyzed the base composition of DNA
  from a number of different organisms. He reported
  that the base composition of DNA varies from one
  species to another. He also noticed a peculiar
  regularity in the ratios of nucleotide bases. In
  the DNA of each species he studied, the number of
  adenines approximately equaled the number of
  thymines, and the number of guanines
  approximately equaled the number of cytosines

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13. List the three components of a nucleotide.
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• Phosphate, Sugar (deoxyribose for DNA ribose for
  RNA), Nitrogenous base

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nucleotide
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• 1. What is a nucleotide composed of?
• 2. What scientist looked at the data that
  analyzed the amount of guanine equaled the amount
  of cytosine and the amount of thymine equaled the
  amount of adenine and what conclusion did he draw
  from this?.

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• 1. What is a nucleotide composed of? Sugar,
  nitrogen base and a phosphate group
• 2. What scientist looked at the data that
  analyzed the amount of guanine equaled the amount
  of cytosine and the amount of thymine equaled the
  amount of adenine and what conclusion did he draw
  from this? Chargaff/ these nitrogen bases must
  be paired up in the structure.

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Watson and Crick
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• 14. Who are the two men who built the first
  molecular model of DNA and shared the 1962 Nobel
  Prize for discovery of its structure?

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• James Watson and Francis Crick

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X ray diffraction of DNAby Rosalind Franklin
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• 15. What was the role of Rosalind Franklin in the
  discovery of the double helix?

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• Rosalind Franklin, a very accomplished X-ray
  crystallographer, conducted critical experiments
  resulting in the photograph that allowed Watson
  and Crick to deduce the double-helical structure
  of DNA.

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• 3. X-ray diffraction was used to help determine
  what about DNA?
• 4. Who are the 2 scientists who put all of the
  info together to describe the structure of DNA?

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• 3. X-ray diffraction was used to help determine
  what about DNA? the double helix shape
• 4. Who are the 2 scientists who put all of the
  info together to describe the structure of DNA?
  Watson and Crick

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DNA Structure

• Chromatin--Chromosomes and DNA subunits (Video
  Clip)

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Purines and Pyrimidinestwo types of nitrogen
bases in DNA and RNA

• Purinesdouble rings. Adenine and Guanine
• Pyrimidines single rings. Thymine, Cytosine and
  Uracil which replaces Thymine in RNA

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bonding

• G triple hydrogen bonds to C
• A double hydrogen bonds to T
• These un zip in DNA replication

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• 17. How did Watson and Cricks model explain the
  basis for Chargaffs rules?

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• Watson and Crick built models of a double helix
  that would matched the X-ray measurements and
  what was known about the chemistry of DNA,
  including Chargaffs rule of base equivalences.
  Through trial and error, Watson and Crick deduced
  that the nitrogenous bases of the double helix
  are paired in specific combinationsadenine (A)
  with thymine (T), and guanine (G) with cytosine
  (C)and they reflected these findings in their
  model.
• Whenever one strand of a DNA molecule has an A,
  the partner strand has a T. And a G in one strand
  is always paired with a C in the complementary
  strand. Therefore, in the DNA of any organism,
  the amount of adenine equals the amount of
  thymine, and the amount of guanine equals the
  amount of cytosine.

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• 16. Distinguish between the structure of
  pyrimidines and purines.
• Explain why adenine bonds only to thymine.

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• Pyrimidinescytosine (C), thymine (T), and uracil
  (U)are characterized by a six-membered ring.
• Purinesadenine (A) and guanine (G)are
  characterized by a six-membered ring fused to a
  five-membered ring.

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• Always pairing a purine with a pyrimidine results
  in a uniform diameter in the double helix.

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• Additionally, each base has chemical side groups
  that can form hydrogen bonds with its appropriate
  partner.
• Adenine can form two hydrogen bonds with thymine
  and only thymine. Adenine bonds only with thymine
  because adenine is a purine, and thymine is a
  pyrimidine.

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• 18. Given that the DNA of a certain fly species
  consists of 27.3 adenine and 22.5 guanine, use
  Chargaffs rules to deduce the percentages of
  thymine and cytosine.

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• 18. Given that the DNA of a certain fly species
  consists of 27.3 adenine and 22.5 guanine, use
  Chargaffs rules to deduce the percentages of
  thymine and cytosine.
• 27.6 thymine
• 22.5 cytosine

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19. Name the five nitrogenous bases, and put a
checkmark in the correct column for each
base.Also indicate if the base is found in DNA
(D), RNA (R), or both (B).
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• 20. What DNA base is complementary to adenine?
• What DNA base is complementary to guanine?

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• 20. What DNA base is complementary to adenine?
  Thymine
• What DNA base is complementary to guanine?
  Cytosine

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• Describe the structure of DNA relative to each of
  the following. Indicate the distance in the
  correct location on the figure as well.
• a. distance across molecule
• b. distance between nucleotides
• c. distance between turns
• d. components of the backbone
• e. components of the rungs

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• a. distance across molecule 1 nm
• b. distance between nucleotides 0.34 nm
• c. distance between turns 3.4 nm
• d. components of the backbone sugar-phosphate
• e. components of the rungs A T G C
• I will not ask these on the test!

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5 and 3 ends

• Organic molecules are numbered by the carbons!

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Antiparallel

• Go in opposite directions 5 to 3 on one side 3 to
  5 on the other!

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• 22. Explain what is meant by 5' and 3' ends of
  the nucleotide.

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• The two free ends of the polymer are distinctly
  different from each other. One end has a
  phosphate attached to a 5' carbon, and the other
  has a hydroxyl group on the 3' carbon. We refer
  to these as the 5' end and the 3' end
  respectively.

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• 23. What do we mean when we say the two strands
  of DNA are antiparallel?

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• Their subunits run in opposite directions.

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DNA replication
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DNA replication Video

• http//www.youtube.com/watch?vzdDkiRw1PdUfeature
  youtube_gdata_player

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Semi conservative

• Half is original half is new.
• The method of DNA replication had to be
  determined. Several tests were done to figure
  this out

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Matthew Meselson and Franklin Stahl

• 1958 determined that the method of DNA
  replication was semi-conservative based on
  Nitrogen that was radioactive and heavier so it
  formed bands at different heights after
  centrifugation. The multiple generations of
  replications demonstrated the method had to be
  semi-conservative due to the intermediate bands
  produced.

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• 24. What is the semiconservative model of
  replication?

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• Type of DNA replication in which the replicated
  double helix consists of one old strand, derived
  from the parental molecule, and one newly made
  strand

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• 26. How did Meselson and Stahl create heavy DNA
  for their experiments?

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• Meselson and Stahl cultured E. coli for several
  generations in a medium containing nucleotide
  precursors labeled with a heavy isotope of
  nitrogen, 15N.

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• 27. Use Figure 16.11 to explain how Meselson and
  Stahl confirmed the semiconservative
• mechanism of
• DNA replication.

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• Meselson and Stahl transferred their heavy DNA
  to a medium with lighter isotope, 14N. A sample
  was taken after DNA replicated once another
  sample was taken after DNA replicated again. They
  extracted DNA from the bacteria in the samples
  and then centrifuged each DNA sample to separate
  DNA of different densities.
• Meselson and Stahl compared their results to
  those predicted by each of the three models
  (conservative, semiconservative, and dispersive).
  

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• The first replication in the 14N medium produced
  a band of hybrid DNA. This result eliminated the
  conservative model.
• The second replication produced both light and
  hybrid DNA, a result that refuted the dispersive
  model and supported the semiconservative model.
  They therefore concluded that DNA replication is
  semiconservative.

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• 28. Define the origins of replication.

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• Site where the replication of a DNA molecule
  begins, consisting of a specific sequence of
  nucleotides

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• 29. Distinguish between the leading and the
  lagging strands during DNA replication.

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• The leading strand is the new complementary DNA
  strand synthesized continuously along the
• template strand toward the replication fork in
  the mandatory 5' to 3' direction.
• The lagging strand is a discontinuously
  synthesized DNA strand that elongates by means of
  Okazaki fragments, each synthesized in a 5' to 3'
  direction away from the replication fork.

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DNA is packaged into chromosomes
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• Histones are positively charged, and DNA is
  negatively charged.
• Without histones the DNA could not fit into the
  nucleus!
• Heterochromatin is highly condensed, whereas
  euchromatin is less compact.

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The Structure of DNA

• DNA is made of two strands of nucleotides twisted
  into the form of a double helix.

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• 1. Why does DNA have to replicate every time a
  cell divides?
• 2. When does DNA replication occur in the cell
  cycle?

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• 1. Why does DNA have to replicate every time a
  cell divides?
• Because every cell needs the instructions to make
  proteins that the DNA contains.
• 2. When does DNA replication occur in the cell
  cycle?
• S phase of interphase

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• Each nucleotide in DNA is made of the sugar
  deoxyribose, a
• phosphate group, and
• one of four nitrogen bases.
• The four nitrogen bases found in DNA nucleotides
  are
• adenine (A),
• thymine (T),
• guanine (G),
• and
• cytosine (C).

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• The two strands of DNA are complementaryeach A
  on one strand pairs with a T on the opposite
  strand, and each G on one strand pairs with a C
  on the opposite strand.

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• 5. Describe the structure of DNA in detail, use
  a diagram to help.

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• 5. Describe the structure of DNA in detail, use
  a diagram to help. The sides are made up of the
  sugar deoxy ribose and the phosphate groups
  bonded covalently together the rungs are the
  nitrogen bases with cytosine and guanine bonded
  with hydrogen bonds across from each other and
  thymine and Adenine across from each other. The
  entire thing is in a double helix and runs 3 to
  5 anti parallel.

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The Replication of DNA

• A. The Roles of Enzymes in DNA Replication
• Summarize the steps of DNA replication

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Bozeman Biology video DNA replication

• http//www.youtube.com/watch?vFBmO_rmXxIw

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• B. The Rate of Replication
• To go fast, there are multiple replication forks!

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The Replication of DNA

• Before a cell divides, it copies its DNA by a
  process called DNA replication. ( s phase)
• In DNA replication, enzymes work to unwind and
  separate the double helix and add complementary
  nucleotides to the exposed strands.

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• The result of DNA replication is two exact copies
  of the cells original DNA.
• Each new double helix is composed of one original
  DNA strand and one new DNA strand.
• .

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• DNA polymerase proofreads DNA during its
  replication so that very few errors occur

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• 30. What is the direction of synthesis of the new
  strand?

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• 5' to 3' direction

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• 31. What are Okazaki fragments? How are they
  welded together?

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• Okazaki fragments are short segments of DNA
  synthesized away from the replication fork on a
  template strand during DNA replication. Many such
  segments are joined together by the enzyme DNA
  ligase to make up the lagging strand of newly
  synthesized DNA.

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• topoisomerase stabilizes the intact double helix.
  It also relieves strain in the DNA ahead of the
  replication forkhelicase unwinds the double
  helix
• A short RNA primer is added by primase in the 5'
  to 3' direction

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• Helicase unwinds the parental double helix.
  (Green) at the replication fork
• 2. Molecules of single-stranded binding protein
  stabilize the unwound template strands.( grey)

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• 3. The leading strand is synthesized continuously
  in the 5' to 3' direction by DNA polymerase III
  after being primed by primase. ( orange)
• 4. Primase begins synthesis of the RNA primer for
  the lagging strand. (pink)
• 5. DNA polymerase III synthesizes discontinuously
  the lagging strand in the 5' to 3' direction.
• 6. DNA polymerase I removes all the RNA primer
  sections and replaces them with DNA nucleotides (
  yellow)
• 7.

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• 6. DNA polymerase I removes all the RNA primer
  sections and replaces them with DNA nucleotides (
  yellow)
• 7. The replacement of the primer with DNA leaves
  the new DNA nucleotides with a free 3' end. DNA
  ligase joins the free 3' end to its adjacent 5'
  end, forming a continuous and unbroken strand of
  DNA on both the leading and lagging strands.

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• 33. Label the following figures. Include 3' and
  5' strands, RNA primer, primase, SSBP,
  topoisomerase, helicase, leading strand, lagging
  strand, DNA pol I, DNA pol III, DNA ligase,
  parental DNA, and new DNA On the second figure,
  also add arrows to indicate the direction of
  synthesis.

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• topoisomerase stabilizes the intact double
  helix.helicase unwinds the double helix
• A short RNA primer is added by primase in the 5'
  to 3' direction

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• 34. Put it all together! Make a detailed list of
  the steps that occur in the synthesis of a new
  strand.
• 1. Helicase unwinds the parental double helix.
• 2. Molecules of single-stranded binding protein
  stabilize the unwound template strands.
• 3. The leading strand is synthesized continuously
  in the 5' ? 3' direction by DNA polymerase III
  after being primed by primase.
• 4. Primase begins synthesis of the RNA primer for
  the lagging strand.
• 5. DNA polymerase III synthesizes discontinuously
  the lagging strand in the 5' ? 3' direction.
• 6. DNA polymerase I removes all the RNA primer
  sections and replaces them with DNA nucleotides.
• 7. The replacement of the primer with DNA leaves
  the new DNA nucleotides with a free 3' end. DNA
  ligase joins the free 3' end to its adjacent 5'
  end, forming a continuous and unbroken strand of
  DNA on both the leading and lagging strands.

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Enzymes for repair and proofreading
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• Prokaryotes have a single circular chromosome and
  eukaryotes have DNA packaged into several
  chromosomes that are found in the nucleus.

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• 6. Describe how the DNA is packaged into a
  chromosome in a eukaryote and compare this to the
  prokaryotic chromosome._

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• 6. Describe how the DNA is packaged into a
  chromosome in a eukaryote and compare this to the
  prokaryotic chromosome._ DNA is in chromosomes in
  eukaryotic cells which means it is wrapped around
  proteins called histones into units called
  nucleosomes to make chromosomes. In the
  prokaryotic cell the DNA is in a circular strand.

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• 3. What enzyme first unwinds the DNA helix? _
• 4. What type of bond must be broken to unzip
  the double helix ?
• 5. Leading and lagging strands are built using
  what enzyme?
• 6. The strands are bonded together to form 2 new
  strands each made up of one original and one new
  side. What is the name of the enzyme used to bond
  the strands together?
  

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• 3. What enzyme first unwinds the DNA helix? _
• DNA Helicase
• 4. What type of bond must be broken to unzip
  the double helix ?
• hydrogen_
• 5. Leading and lagging strands are built using
  what enzyme?
• DNA polymerase
• 6. The strands are bonded together to form 2 new
  strands each made up of one original and one new
  side. What is the name of the enzyme used to bond
  the strands together?
  
• DNA Ligase

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Replication forks
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• 7. How does this process make sure that the
  original information in the DNA is maintained in
  all new cells?
• 8. Why is this process important in terms of not
  making changes in the nitrogen base order? _
• 9. How is the process of DNA replication in
  eukaryotes different from that of prokaryotes?

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• 7. How does this process make sure that the
  original information in the DNA is maintained in
  all new cells?
• The original strands are used as templates to
  make the new copies,
• 8. Why is this process important in terms of not
  making changes in the nitrogen base order? _
• If changes in the nitrogen bases are made the
  instructions are changes resulting in different
  proteins and this is called a mutation!__
• 9. How is the process of DNA replication in
  eukaryotes different from that of prokaryotes?
• In eukaryotes, the process starts in many places
  and they then connect so that large amounts of
  DNA can be copies all at once. In prokaryotes it
  is a circular process starting in 2 places and
  then connecting in the middle.

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• 36. What is a thymine dimer? How might it occur?
  How is it repaired?

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• A thymine dimer is the covalent linking of
  thymine bases that are adjacent on a DNA strand,
  causing the DNA to buckle and interfere with DNA
  replication. In order to repair this damage, a
  nuclease enzyme cuts the damaged DNA strand, and
  the damaged section is removed. DNA polymerase
  fills in the missing nucleotides, and DNA ligase
  seals the free end of the new DNA to the old DNA,
  making the strand complete

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Thymine Dimer
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• 37. Make a sketch of a chromosome and label the
  telomeres.

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telomeres
167

• 38. Explain telomere erosion and the role of
  telomerase.

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• Telomeres provide their protective function by
  postponing the erosion of genes located near the
  ends of DNA molecules.
• Telomeres become shorter during every round of
  replication.

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• Telomeric DNA tends to be shorter in dividing
  somatic cells of older individuals and in
• cultured cells that have divided many times.
  Importantly, some cell genomes (such as germ
• cells) must persist virtually unchanged from an
  organism to its offspring over many generations.
  In order to accomplish this, an enzyme called
  telomerase catalyzes the lengthening of telomeres
  in eukaryotic germ cells, thus restoring their
  original length and compensating for the
  shortening that occurs during DNA replication.

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• 39. Why are cancer cells immortal even though
  most body cells have a limited life span?
• .

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• Researchers have found telomerase activity in
  cancerous somatic cells, suggesting that its
  ability to stabilize telomere length may allow
  these cancer cells to persist

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• 40. On the following diagram, identify the
  following 30-nm fiber, metaphase chromosome,
  double
• helix, histone proteins, nucleosomes, protein
  scaffold, and looped domains (300-nm fiber).
• See pages 320-321 in your text for the labeled
  figure.

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• 41. Distinguish between heterochromatin and
  euchromatin.

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• Heterochromatin is eukaryotic chromatin that
  remains highly compacted during interphase and is
  generally not transcribed. Euchromatin is a less
  condensed form of eukaryotic chromatin that is
  available for transcription. Heterochromatin is
  highly condensed, whereas euchromatin is less
  compact.

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Protein production Vocabulary

• 1. mRNA
• 2. rRNA
• 3. tRNA
• 4. Transcription
• 5. RNA polymerase
• 6. Intron
• 7. Exon
• 8. Codon
• 9. Translation
• 10. Gene regulation
• 11. Operon
• 12. Mutation
• 13. Mutagen

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links

• A very useful game to help comprehend DNA
  replicationhttp//www.studystack.com/matching-15
  9604
• A beneficial video about how DNA replication
  workshttp//www.youtube.com/watch?v4jtmOZaIvS0
  
• A quick video on DNA damage and
  repairhttp//www.youtube.com/watch?vnPS2jBq1k48
  featurerelated