DNA, RNA, and Protein Synthesis

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DNA, RNA, and Protein Synthesis

• Chapter 12 and 13

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Chap 12 Terms

• Transformation
• Bacteriophage
• Base pairing
• Nucleotides
• Nucleic acids
• Nitrogenous bases
• Antparallel strands
• Replication
• Replication fork
• DNA Polymerase
• Helicase
• Telomease
• Ligase
• Semi conservative

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Do you know?

• What determines how a protein will function?
• three-dimensional shape of the protein
• Why is it important that new cells have same DNA
  as the parent cell?
• the cells may develop properties that would not
  be beneficial to the organism as a whole

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Objectives??

• Relate how Griffiths bacterial experiments
  showed that a hereditary factor was involved in
  transformation
• Summarize how Averys experiments led his group
  to conclude that DNA is responsible for
  transformation in bacteria
• Describe how Hershey and Chases experiments led
  to the conclusion that DNA, not protein, is the
  hereditary molecules in viruses

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Discovery of DNA

• From his studies with pea plants, Mendel
  concluded that hereditary factors determine many
  of an organisms traits. But what were these
  hereditary factors? How did these molecules store
  hereditary information? Scientists believed that
  if they could answer these questions, they could
  und4erstand how cell pass on characteristics to
  their descendants. The answers these questions
  began to emerge during an epidemic of pneumonia
  in London in the 1920s.

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Experiments

• Three experiments that led to the discovery of
  DNA and RNA
• 1. Griffiths
• 2. Averys
• 3. Hershey-Chase experiments
• Studies involved bacteria (bacteriophages or
  phages) and viruses (DNA head, protein body)

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Griffiths experiments

• 1928- studied bacteria Streptococcus pneumoniae
  (pneumonia)
• Trying to develop a vaccine against virulent
  strain (disease-causing)
• Virulent bacterium is surrounded by a capsule
  made of polysaccharides that protect it from a
  body's defense systems

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Griffiths exp cont

• Two strains of bacteria
• 1. S strain smooth-edged colonies, ill
• 2. R stain- rough colonies, lacks a capsule,
  does not cause pneumonia
• Had a series of 4 exp fig 10-2 (BIO)
• R cells ? mouse alive
• S cells ? mouse dies
• Kills S cells with heat ? mouse lives
• Kills S cells with heat and mix with R cells?
  mouse dies (transformation occurs)

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Griffiths exp cont

• Results or conclusion
• Heat-killed virulent bacterial cells release a
  hereditary factor that transfers the disease-
  causing the healthy cells to be harmful
• The transfer of genetic material from one cell
  to another is called transformation
• (holt video)

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Heat Factor?

• DNA can tolerate temperature near 90C without
  being altered. Proteins are denatured (broken
  down) at about 60C.
• What effect temperature had on Griffiths works?
• A The DNA was not altered and became
  incorporated into the DNA of the living bacteria

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DNA Technology

• Griffith manipulated genes with out knowing it.
  Today this manipulation of genes is known as
  genetic engineering or recombinant DNA
  Technology.
• Transformation is a modern-day genetic
  engineering technique.
• Examples bacteria used to introduce foreign
  genes into plant cells, producing plants with
  desirable traits (Genetic modified)

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Avery's Experiments

• 1940s wanted to test whether the transforming
  agent in Griffiths exp was protein, RNA, DNA
• Used enzymes separately to id which part
• Results
• Cells missing protein and RNA able to transform R
  cells into s cells ? mice die
• Cells missing DNA did not transform? mice lived
• DNA is responsible for transformation in bacteria

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Radioactivity review?

• Radioactive elements have unstable nuclei that
  emit alpha and beta particles or energy as gamma
  rays.
• Emissions make it easier for scientists to detect
  and trace the path of the radioactive elements as
  they interact with other materials or transformed
  during metabolic processes
• (Radioactive isotopes, increase neutrons, and
  the mass of the element)

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Hershey-Chase Experiment

• ?They wanted to know if DNA or Protein was the
  hereditary material viruses transfer when viruses
  enter a bacterium
• Bacteriophages or phages are viruses that infect
  bacteria (Holt video)
• EXP
• Used radioactive isotope sulfur (35S) to label
  protein and radioactive isotope phosphorus
  (32P)to label DNA
• Infected the cells
• Blended? separated the phage from bacteria
• Results
• Viral DNA and little protein entered bacteria ?
  concluded that DNA is the hereditary molecule in
  the viruses
• (Honors 10.A)

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Key Questions

• Evaluate the contributions of Franklin and
  Wilkins in helping Watson and crick discover
  DNAs double helix structures
• Describe the 3 parts of a nucleotide
• Summarize the role of covalent and hydrogen bonds
  in the structure of DNA
• Relate the role of the base-paring rules to the
  structure of DNA

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DNA

• By the early 1950s, most biologist accepted DNA
  as the hereditary material. However, they still
  lacked an understanding of DNAs structure or how
  this molecule could replicate, store, and
  transmit hereditary information and direct cell
  function. These mysteries would soon begin to
  unravel at Cambridge university in England.

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DNA is a double-stranded Helix

• Pauling, Wilkins, Franklin- were first
• They used x-ray diffraction
• Watson saw an x-ray produced by Franklin and was
  able to figure out the basic shape of DNA to be a
  helix (fig 10-5 bio)
• Watson and Crick began trying to construct a
  double helix w/ uniform diameter that would
  confirm Franklins data
• 1962 W and C received the Nobel Prize in Medicine
  and Franklin died in 1958 never to receive the
  award currently recognized at Cambridge

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http//www.accessexcellence.org/RC/AB/BC/Rosalind_
Franklin.php http//www.blinkx.com/video/rosalind-
franklin-dna-discoveries-in-science-and-art/A3fUh_
J7RZ77E7Njdd7zcA
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DNA Nucleotides

• DNA is a nucleic acid made of two long chains of
  Polymers made of monomers which is made of
  nucleotides
• Nucleotide is made of 3 parts
• 1. 5-carbon sugar (deoxyribose)
• 2. Phosphate group
• 3. Nitrogenous base

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Bonds hold DNA together

• DNA looks like a spiral staircase
• Covalent bonds and hydrogen bonds
• Nitrogenous bases
• 4 types
• a. Purines- contain double ring of carbon
• 1. Adenine
• 2. Guanine
• b. Pyrimidines- have a single ring of carbon
• 3. Thymine
• 4. Cytosine

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Complementary Bases

• 1949- Chargaff observed percentages of A T, C G
• Base-paring rules- single strand pairs up with
  second strand to make a double strand
• Complementary base pairs- A T, C G
• Base sequence- order of nitrogenous bases on a
  chain

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DNA model

• Looks like a ladder
• Sugar-phosphate is the handrails
• Base pairs are steps
• Draw in the complementary base pairs to
• AACCTGACTGGACAC

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DNA replication Key Questions

• Summarize the process of DNA replication
• Identify the role of enzyme in the replication of
  DNA
• Describe how complementary base paring guides DNA
  replication
• Compare the number of replication forks in
  prokaryotic and eukaryotic cells during DNA
  replication
• Describe how errors are corrected during DNA
  replication

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Q and A

• Q Why do you think gives DNA its stability even
  though the hydrogen bonds between the nitrogenous
  bases are easily broken?.
• A Strong covalent bonds connect the sugar and
  phosphate groups of the DNA backbone

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DNA Replication

• Watson and Cricks discovery of the double helix
  structure of DNA caused great excitement in the
  scientific community. Scientists realized that
  this model could explain simply and elegantly how
  DNA can replicate exactly each time a cell
  divides, this is a key feature of hereditary
  material.

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How DNA Replication occurs

• Process by which DNA is copied in a cell before a
  cell divides by mitosis, meiosis, or binary
  fission
• The two nucleotide strands of the original double
  helix separate along the strands
• Strands become templates to make new
  complementary strands
• Two identical DNA (double helix) separate and
  move to new cell during division

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Steps of replication

• Helicases- enzyme that separate the DNA strands,
  move along the molecule breaking the H-Bond
  between the complementary nitrogenous bases, a
  Y-shaped region is formed called the replication
  fork
• DNA polymerase adds complementary nucleotides
• DNA poly completes strand and falls off
• DNA ligase links the pieces together
• Get two identical DNA molecules
• This is called a semi-conservative replication-
  keeps one of the original (conserved)

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Prokaryotic DNA Replication

• In most prokaryotes, DNA replication does not
  start until regulatory proteins bind to a single
  starting point on the chromosome. This triggers
  the beginning of DNA replication.
• Replication in most prokaryotic cells starts
  from a single point and proceeds in two
  directions until the entire chromosome is copied.

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Eukaryotic DNA Replication

• Eukaryotic chromosomes are generally much bigger
  than those of prokaryotes.
• In eukaryotic cells, replication may begin at
  dozens or even hundreds of places on the DNA
  molecule, proceeding in both directions until
  each chromosome is completely copied.

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Chapter 13 Key Terms

• RNA
• mRNA
• rRNA
• tRNA
• Transcription
• Translation
• RNA Polymerase
• Genetic code
• Translation
• Anticodon
• Condon
• Polypeptide
• Gene expression
• Mutations
• Point mutation
• Fram shift
• mutatgens

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Protein Synthesis

• Characteristics such as hair color are largely
  determined by genetic factors. But how does
  inheriting a particular form of a gene result in
  the appearance of a specific hair color? The
  structure of DNA helps explain how genes function
  in making proteins that determine traits in an
  organism.

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Misconception

• Different cells, same DNA
• You might think that because cells in the same
  organism appear different and have different
  functions, the cells must have different DNA.
• The first fertilized egg undergoes DNA
  replication and then mitosis and then repeated to
  give every cell in the body the same DNA.
  (except for when crossing over takes place during
  meiosis to create gametes)
• other factors determine which genes are used
  for the cells specific function

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Key Questions

• Outline the flow of genetic information in cells
  from DNA to protein
• Compare the structure of RNA To DNA
• Summarize the process of transcription
• Describe the importance of the genetic code
• Compare the role of mRNA, rRNA, tRNA in
  translation
• Id the importance of learning about the human
  genome

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Flow of genetic info

• Gene- segment of DNA that is located on a
  chromosome and codes for a specific trait
• Process in Eukaryotic cells
• DNA ? transcription? RNA? translation ? protein
• Transcription- DNA acts as a template for the syn
  of RNA

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Flow of genetic info cont

• 2. translation- RNA directs the assembly of
  proteins
• 3. Protein synthesis- proteins are formed based
  on information in DNA and carried out by RNA
  (gene expression)
• DNA (double stranded)? RNA (single)? Protein
• Proteins are responsible for protecting the
  body against infections and carrying oxygen in
  red blood cells

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RNA Structure and Function

• RNA is a nucleic acid made up of nucleotides
• 4 major differences from DNA
• 1. contain the sugar ribose not deoxyribose
• 2. contains the nitrogenous base uracil not
  thymine
• 3. single stranded not double
• 4. usually much shorter in length

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3 types of RNA

1. mRNA- messenger- single stranded molecules that
   carries the instructions from a gene to make a
   protein (carries a message)
2. rRNA- ribosomal- part of the structure of
   ribosome, ribosomes are made of rRNA and many
   proteins
3. tRNA- transfer- transfers amino acids to the
   ribosome to make protein

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Transcription

• Process in which genetic instructions in a gene
  are transcribed or rewritten into an RNA molecule
• Steps
• RNA polymerase binds to promoter. The promoter
  initiates transcription
• Adds free RNA nucleotides that are complementary
  to the nucleotides on one of the DNA strands, DNA
  strands rewind
• RNA poly reaches the terminal signal, makes the
  end of that gene, or a stop signal or stop codon

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The genetic code

• Is the term that rules how a sequence of
  nitrogenous bases in nucleotides corresponds to a
  particular amino acid
• The genetic code, three adjacent nucleotides in
  mRNA specify an amino acid in a polypeptide
• Each 3-nucleotide sequence in mRNA encodes for a
  amino acid or signifies a start or stop signal
  called a codon 10.1tab
• (Start is AUG) (stop are UAA, UAG, UGA)

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Translation- making of protein

• Protein structure- one or more polypeptides,
  chains of AA linked by peptides bonds
• Over 20 AA found in proteins of living things
• AA are arranged to specific sequence
• Shape always equals function

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5 Steps of translation

1. Initiation- tRNA and mRNA bind, on the tRNA is
   the anticodon (3 nucleotides on RNA that
   complements codon in mRNA)
2. Elongation-the next AA binds to the codon,
   peptide bonds form between adjacent amino acids
3. Elongation cont- first tRNA leaves and leaves it
   AA, elongating the chain
4. Termination- stop codon is reached
5. Disassembly- new polypeptide is released

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Human Genome

• 3.2 billion base pair in the 23 human chromosomes
• Take one person almost 10yrs to read the total
  sequence aloud
• Bioinformatics- uses pc to compare different DNA
  sequences, aids in interpretation
• Ability to treat diseases in the future

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Review Answers

• Transcription
• Nucleus
• Steps
• RNA Polymerase binds DNA unwinds
• mRNA starts to form
• DNA and mRNA are released

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Review Cont

• Translation
• Cytoplasm
• Steps
• initiation tRNA binds to mRNA
• Elongation first peptide bond forms
• Elongation polypeptide chain grows
• Termination protein is complete

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DNA errors in replication

• Errors are rare- like typing this book 1000xs
  with out mistakes
• DNA polymerase have repair enzymes that proofread
  the strands and repair it
• Mutation are changes in the nucleotide sequence
  of DNA molecule
• Environmental factors can also disrupt or damage
  DNA
• Studying DNA replication is one good way to
  understand and treat some cancers

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Mutations

• Change in the nucleotide-base sequence of a gene
  or DNA molecule
• Germ-cell occurs in an organisms gametes, can
  be passed on to an offspring
• Somatic-cell body cell and can affect the
  organism, skin cancer, leukemia, can not be
  inherited!!
• Lethal mutations- cause death before birth
• Can mutations be beneficial to the individual?

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Chromosome Mutations

• Two ways
• 1. change in structure of chromosome
• 2. adding or loosing a chromosome
• Deletion- loss of a piecd of a chromosome due to
  breakage
• Inversion- segments breaks off, flips around and
  reattaches
• Translocation- breaks off and reattaches to non
  homologous chromosome
• Nondisjunction- chromosome fails to separate from
  its homologous during meiosis, get and extra copy
  (trisomy 21)

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Gene Mutations

• Point mutations- substitution, addition, or
  removal of single nucleotide
• Substitution- one nucleotide replaces another
• Frameshift mutation- it just shifts down- creates
  new amino acids
• Insertion mutations- addition of a gene and
  framshift occurs
• ATCGA

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Answers to Review

• Replication
• ATGCAGTACGGTGGGCTG
• TRANSCRIPTION
• AUG-CAG-UAC-GGU-GGG-CUG
• TRANSLATION
• MET START- GLU-TYR-GLY-GLY-LEU..

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MUTATIONS

• TACGTCATGCCACCCGAC
• 1. Change C to G
• substitution- no start codon
• TAG? AUC
• 2. Remove T- deletion
• AUG- CAG-UCG-GUG-GGC-UG
• START-LEU-SER-VAL-ALA- X