DNA

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DNA GenesChapter 12

• DNA, RNA, Protein Synthesis

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DNA Molecule of HeredityA. Structure

• DNA (polymer) is a long molecule made up of
  Nucleotides (monomers)
• A Nucleotide consists of
• Deoxyribose (a 5-carbon sugar)
• a phosphate group
• One of 4 Nitrogenous bases (contain nitrogen)
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)

PURINES
PYRIMIDINES

• The nitrogenous bases of DNA (purines double
  ring / pyrimidines single ring)

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DNA

• Deoxyribonucleic acid
• Deoxyribose is sugar
• Nitrogenous bases
• Adenine binds with Thymine
• Cytosine binds with Guanine

One nucleotide of DNA
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Structure of DNA (cont.)

• DNA is like a twisted ladder
• Rungs complementary base pairs (AT, GC)
• Uprights deoxyribose and phosphate groups
• Your Turn Match this DNA base sequence with its
  correct complementary DNA bases
• T-C-G-A-A-C-T
• A-G-C-T-T-G-A

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DNA.who cares
Is used to catch criminals
Is used to determine the paternity of Children
on shows such as
Is used to make genetically modified food
Is used to compare similarities between species
Is used to make antibiotics and vaccines
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History Griffith and Transformation

• Year 1928
• Examined 2 strains of pneumonia bacteria
• Rough
• Smooth
• Injected mice with bacteria to see if they would
  develop pneumonia
• Discovered transformation
• Took the heat killed bacteria and combined it
  with the harmless bacteria, and mice developed
  pneumonia

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History Avery DNA

• 1944
• Used Griffiths experiment. He wanted to know
  which molecule in the heat-killed bacteria was
  important in transformation
• Avery used enzymes to discover that DNA was the
  molecule that allowed transformation to happen

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History Hershey-Chase

• 1952
• The Hershey-Chase experiment used viruses known
  as bacteriophages.
• Question Wanted to know which part of the virus,
  protein or DNA, entered the infected core of
  bacterium. Preformed the experiment by using
  radioactive markers
• Concluded, that the genetic material was DNA

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B. History
Source of DNA A T G C
Streptococcus 29.8 31.6 20.5 18.0
Yeast 31.3 32.9 18.7 17.1
Herring 27.8 27.5 22.2 22.6
Human 30.9 29.4 19.9 19.8

• . CHARGAFF (1949) discovered that the of
  Cytosine and Guanine were about the same in DNA
  the same was true about Adenine and Thymine
• This suggests BASE PAIRING.. that C bonds with
  G and A bonds with T!

Purines
Pyrimidines
Phosphate group
Deoxyribose
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History (cont.)

• 2. Wilkins and Franklin(1952) took X-Ray
  photographs of DNA which suggested a twisted,
  helical structure, 2 strands, and bases in the
  center
• 3. Watson and Crick (1953) using all the
  research to date, discovered the structure for
  DNA A DOUBLE HELIX (with sugar-phosphate
  backbones and bases on the inside held together
  by H bonds)

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More DNA info

• DNA contains information that determines an
  organisms function and appearance
• Some DNA codes for proteins
• DNA is located within genes (sections of a
  chromosome) inside of the nucleus of every cell

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Wait a minute
Does that shape remind you of any other shape you
may have seen before?
How about this portion of an apple?
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DNA Flo Rider Featuring T-Pain-less
Shawty got them apple bottom genes with the DNA
(NA)
Nucleotides twisted that way
They start to fold (they start to fold)
Next thing you know
Shawty got chro mo so o o o o omes
The As bond with the Ts and the Cs bond with
the Gs (with the Gs)
Hydrogen bonds in the double helix
They start to fold (they start to fold)
Next thing you know
Shawty got chro mo so o o o o omes
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DNA Replication

• DNA opens up and makes a complete copy of itself
  necessary during mitosis and meiosis
• New nucleotides float in and pair in a
  complementary fashion A to T, C to G and vice
  versa

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Figure 16.7 A model for DNA replication the
basic concept (Layer 1)
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Figure 16.7 A model for DNA replication the
basic concept (Layer 2)
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Figure 16.7 A model for DNA replication the
basic concept (Layer 3)
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Figure 16.7 A model for DNA replication the
basic concept (Layer 4)
Semi-conservative process
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C. DNA Replication making more DNA during the
S Phase of the Cell Cycle (in the nucleus)

• 1. The enzyme helicase unwinds DNA double helix
  (breaks hydrogen bonds btwn. bases) a
  replication fork is created.
• (Each old DNA strand will act as a template for
  2 new strands to be added on)
• 2. Enzyme called DNA Polymerase binds to
  replication fork and adds free nucleotides to
  each old strand of DNA
• 3. DNA Polymerase remains attached until 2 new
  DNA strands are created it proofreads the
  strands to minimize error in the process.

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Chromosome Structure
Nucleosome
Chromosome
DNA double helix
Coils
Supercoils
Histones
DNA Animation
Go to Section
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DNA Replication (cont.)

• Diagram of DNA Replication

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DNA ? ProteinA. RNA

• RNA Ribonucleic Acid used to make proteins /
  Single-stranded
• -RNA (polymer) made of nucleotides
  (monomer)
• -Ribose 5 C sugar Phosphate group N
  Base
• 4 bases
• Cytosine (C)
• Guanine (G)
• Adenine (A)
• Uracil (U) NO THYMINE in RNA!
• 3 types of RNA
• 1. messenger RNA (mRNA) single stranded
• transmits info from DNA to protein syn.
• 2. transfer RNA (tRNA) - single stranded/
• 20 or more varieties ea. w/ ability to bond to
  only
• 1 specific AA
• 3. ribosomal RNA (rRNA) globular / major
• component of ribosome

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B. Protein Synthesis (overview)

• 2 Stages in making proteins
• Transcription using DNA template to make mRNA
  strand
• Translation using mRNA strand to create
  polypeptides

DNA
RNA
Protein
Transcription
Translation
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1. Transcription

• The Goal of Transcription is to produce a
  single-stranded mRNA helix that contains
  information from DNA to make proteins
• How its done (This happens in the Nucleus!)
• 1. DNA strand unwinds/unzips complementary DNA
  strands
• 2. Enzyme called RNA Polymerase binds to DNA
  promoter regions and plugs in complementary
  RNA nucleotides to the DNA template.
• Example DNA Template ATTGGCAGT
• new RNA Strand UAACCGUCA

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Transcription (cont.)
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Transcription (cont.)

• 3. Once produced, this pre-mRNA strand breaks
  away when RNA polymerase reaches a sequence of
  bases on DNA that act as a stop sign.
• The finished product (mRNA) moves out of the
  Nucleus through a nuclear pore into the
  cytoplasm.
• 4. 2 DNA complementary strands rejoin

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2. The Genetic Code

• How do we get proteins from mRNA strands?
• The mRNA strand must be read in groups of 3
  nucleotides, called a CODON.
• Different Codons translate for different Amino
  acids.

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Codons in mRNA
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Codons in mRNA

• Start codon AUG (Methionine)
• Stop codons UAA, UAG, and UGA
• Example
• mRNA Strand
• U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G
• methionine glycine threonine cysteine
  phenylalanine STOP

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3. Translation

• The Goal of Translation is to translate these
  mRNA codons into their amino acids to form a
  polypeptide.
• How its done
• 1. mRNA strand attaches to a ribosome (rRNA)
• 2. Each mRNA codon passes through ribosome
• 3. Free-floating Amino Acids from cytosol are
  brought to ribosome by tRNA
• 4. Each tRNA has an anticodon to match up to mRNA
  codons
• 5. Amino Acids are joined as tRNA keeps bringing
  them
• 6. Polypeptide chain grows until stop codon is
  reached

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Translation (cont.)

• Translation

1st. mRNA strand attaches to a ribosome (rRNA)
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Translation (cont.)

• Translation

2nd, Each mRNA codon passes through ribosome
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Translation (cont.)
3rd, Free-floating Amino Acids from cytosol are
brought to ribosome by tRNA

• Translation

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Translation (cont.)

• Translation

4th, Each tRNA has an anticodon to match up to
mRNA codons
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Translation (cont.)

• Translation

5th, Amino Acids are joined as tRNA keeps
bringing them
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Translation (cont.)

• Translation

. Polypeptide chain grows until stop codon is
reached
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Genetic Changes MutationsA. Types of
Mutations

• 1. Gene Mutations changes in nucleotides
• Point Mutations
• Frameshift mutations
• 2. Chromosome Mutations changes in or
  structure of chromosome
• Deletion
• Insertion/Duplication
• Inversion
• Translocation

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1. Gene Mutations

• a. Point Mutation the substitution, addition or
  removal of a single nucleotide
• b. Frameshift Mutations types of point
  mutations that shift the reading frame of the
  genetic message

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Example of Point Mutation
Induced Point mutation in growth hormone gene
causes semi-dominant dwarfism obesity
image borrowed from www.science.ngfn.de/6_164.htm

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B. Chromosome Mutations

• 1. Deletion
• 2. Insertion/Duplication
• 3. Inversion
• 4. Translocation.

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• A chromosomal mutation involves changes in the
  number or structure of chromosomes. Chromosomal
  mutations may change the locations of genes on
  chromosomes and even the number of copies of some
  genes.
• Deletion involves the loss of all or part of a
  chromosome.
• The opposite of a deletion is a
• Duplication, in which a segment of a chromosome
  is repeated.
• When part of a chromosome becomes oriented in the
  reverse of its usual direction, the result is an
  Inversion.
• A Translocation occurs when part of one
  chromosome breaks off and attaches to another,
  non-homologous, chromosome. In most cases,
  nonhomologous chromosomes exchange segments so
  that two translocations occur at the same time.

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• A chromosomal mutation involves changes in the
  number or structure of chromosomes. Chromosomal
  mutations may change the locations of genes on
  chromosomes and even the number of copies of some
  genes.
• Deletion involves the loss of all or part of a
  chromosome.
• The opposite of a deletion is a
• Duplication, in which a segment of a chromosome
  is repeated.
• When part of a chromosome becomes oriented in the
  reverse of its usual direction, the result is an
  Inversion.
• A Translocation occurs when part of one
  chromosome breaks off and attaches to another,
  non-homologous, chromosome. In most cases,
  nonhomologous chromosomes exchange segments so
  that two translocations occur at the same time.

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Gene Regulation in Prokaryotes
The lac operon enables the production of
lactose-processing enzymes in E. coli, but only
when needed.

• In the absence of lactose, the repressor protein
  binds to the operator on DNA and inhibits
  transcription of lactose-processing enzymes.

• In the presence of lactose, the repressor is
  inhibited from binding with the operator this
  all ows transcription to take place to produce
  lactose-processing enzymes.