DNA

1
DNA Protein Synthesis

• From Gene to Protein

2
Nucleic Acids and Protein Synthesis

• All functions of a cell are directed from some
  central form of information (DNA).
• This "biological program" is called the Genetic
  Code.
• This is the way cells store information regarding
  their structure and function.

3
History of DNA

• Composition and Structure

4
History

• For years the source of heredity was unknown.
  This was resolved after numerous studies and
  experimental research by the following
  researchers
• Fredrick Griffith
• He was studying effects of 2 strains of an
  infectious bacteria, the "smooth" strain was
  found to cause pneumonia death in mice. The
  "rough" strain did not. He conducted the
  following experiment

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Griffith Experiment
Bacteria Strain injected into mouse Result
Smooth Strain Mouse dies
Rough strain Mouse Lives
Heat-Killed Smooth strain Mouse lives
Rough Strain Heat killed smooth strain MOUSE DIES

• The last condition was unusual, as he predicted
  that the mouse should live
• Concluded that some unknown substance was
  Transforming the rough strain into the smooth one

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Avery, McCarty MacLeod
Tried to determine the nature of this
transforming agent.

• Was it protein or DNA?
• They Degraded chromosomes with enzymes that
  destroyed proteins or DNA
• The Samples with Proteins destroyed would still
  cause transformation in bacteria indicating
  genetic material was DNA

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Hershey-Chase

• ONE virus was radioactively "tagged" with 32P on
  it's DNA
• The OTHER was "tagged" 35S on it's protein coat.
• Researchers found the radioactive P in the
  bacteria, indicating it is DNA, not protein being
  injected into bacteria.

8
Watson Crick

• The constituents of DNA had long been known.
  Structure of DNA, however was not.
• In 1953, Watson Crick published findings based
  on X-ray analysis (Rosalind Franklin) and other
  data that DNA was in the form of a "Double
  Helix".
• Their findings show us the basic structure of DNA
  which is as follows.

9
DNA Structure

• The Double Helix

10
DNA Structure

• DNA is Formed of in a "Double Helix" - like a
  spiral staircase

11
Nucleotides

• DNA is formed by Nucleotides
• These are made from three components
• 5-Carbon or pentose Sugar
• Nitrogenous base
• Phosphate group

12
Types of Nucleotides

• For DNA There are 4 different Nucleotides
  categorized as either Purines (Double rings) or
  Pyrimidines (Single ring). These are usually
  represented by a letter. They Are
• Adenine (A)
• Cytosine (C)
• Guanine (G)
• Thymine (T)

Guanine
13
Base Pairing

• Each "Rung" of the DNA "staircase" is formed by
  the linking of 2 Nucleotides through Hydrogen
  Bonds.
• These Hydrogen bonds form only between specific
  Nucleotides. This is known as Base Pairing. The
  rules are as follows
• Adenine (A) will ONLY bond to Thymine (T) (by 2
  hydrogen bonds)
• Cytosine (C) will ONLY bond to Guanine (G) (by 3
  hydrogen bonds)

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Central Dogma of Genetics

• DNA to Protein Synthesis

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Central Dogma of Genetics

• Central Dogma holds that genetic information is
  expressed in a specific order. This order is as
  follows

There are some apparent exceptions to
this. Retroviruses (eg. HIV) are able to
synthesize DNA from RNA
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DNA Replication

• DNA has unique ability to make copies of itself
• The process is called DNA Replication.
• First, the enzyme Helicase unwinds the parental
  DNA
• DNA "Unzips itself" by breaking the weak hydrogen
  bonds between base pairs forming two TEMPLATE
  strands with exposed Nucleotides

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DNA Replication

• The place where helicase attaches and opens DNA
  is called the Replication Fork

REPLICATION FORK
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DNA Replication

• Helicase enzymes may attach to multiple sites on
  the DNA strand forming Replication Bubbles which
  makes replication faster

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DNA Replication

• Single-strand binding proteins attach STABILIZE
  the 2 parental strands
• DNA polymerase attaches to the 3 end of the 5
  to 3 parental strand
• DNA polymerase attaches FREE nucleotides to the
  complementary nucleotide on the parental DNA
• This new strand is synthesized continuously 5 to
  3 (LEADING)

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Replication Bubble

• DNA is synthesized from the Origin of Replication
  within a replication bubble
• Towards fork continuous replication
• Away from fork discontinuous replication
  (fragments)

Origin of Replication
Origin of Replication
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DNA Replication

• Since DNA polymerase can only add nucleotides to
  the 3 end of the parental strand, the parental
  5 to 3 strand must be replicated in fragments
  that must later be joined together (LAGGING)

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DNA Replication

• Transcription proceeds continuously along the
  5'?3' direction (This is called the leading
  strand)
• Proceeds in fragments in the other direction
  (called the lagging strand) in the following way
• RNA primer is attached to a segment of the strand
  by the enzyme primase.

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DNA Replication

• Transcription now continues in the 5'?3'
  direction forming an okazaki fragment. Until it
  reaches the next fragment.
• The two fragments are joined by the enzyme DNA
  ligase
• Two, new, identical DNA strands are now formed

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DNA Replication
26
Protein Synthesis

• Transcription and Translation

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RNA Transcription

• The cell does not directly use DNA to control the
  function of the cell.
• DNA is too precious and must be kept protected
  within the nucleus.
• The Cell makes a working "Photocopy" of itself to
  do the actual work of making proteins.
• This copy is called Ribonucleic Acid or RNA.
• RNA differs from DNA in several important ways.
• It is much smaller
• It is single-stranded
• It does NOT contain Thymine, but rather a new
  nucleotide called Uracil which will bind to
  Adenine
• Contains ribose, not deoxyribose sugar

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RNA Transcription

• RNA is produced through a process called RNA
  Transcription.
• Similar to DNA Replication.
• Small area of DNA "Unzips" exposing Nucleotides
• This area is acted on by an enzyme called RNA
  Polymerase, which binds nucleotides (using
  uracil) to their complementary base pair.
• This releases a long strand of Messenger RNA
  (mRNA) which is an important component of protein
  synthesis.

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RNA Transcription
30
Protein Synthesis The Genetic Code

• The Sequence of nucleotides in an mRNA strand
  determine the sequence of amino acids in a
  protein
• Process requires mRNA, tRNA ribosomes
• Polypeptide chains are synthesized by linking
  amino acids together with peptide bonds

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mRNA

• Each three Nucleotide sequence in an mRNA strand
  is called a "Codon
• Each Codon codes for a particular amino acid.
• The codon sequence codes for an amino acid using
  specific rules. These specific codon/amino acid
  pairings is called the Genetic Code.

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tRNA

• There is a special form of RNA called Transfer
  RNA or tRNA.
• Each tRNA has a 3 Nucleotide sequence on one end
  which is known as the "Anitcodon"
• This Anticodon sequence is complimentary to the
  Codon sequence found on the strand of mRNA
• Each tRNA can bind specifically with a particular
  amino acid.

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Ribosome

• Consists of two subunits made of protein rRNA
• Large subunit
• Small subunit
• Serves as a template or "work station" where
  protein synthesis can occur.

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Protein Synthesis

• First, an mRNA strand binds to the large small
  subunits of a ribosome in the cytosol of the cell
• This occurs at the AUG (initiation) codon of the
  strand.
• The ribosome has 3 binding sites for codons --- E
  (exit site), P, and A (entry site for new tRNA)
• The ribosome moves along the mRNA strand

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Protein Synthesis

• An anticodon on tRNA binds to a complementary
  codon on mRNA.
• The tRNA carrying an amino acid enters the A site
  on the ribosome
• The ribosome moves down the mRNA so the tRNA is
  now in the P site and another tRNA enters the A
  site
• A peptide bond is formed between the amino acids
  and the ribosome moves down again
• The first tRNA is released, and another tRNA
  binds next to the second, another peptide bond is
  formed.
• This process continues until a stop codon (UAG)
  is reached.
• The completed polypeptide is then released.

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Protein Synthesis
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Replication Problem

• Given a DNA strand with the following nucleotide
  sequence, what is the sequence of its
  complimentary strand?
• 3- TACCACGTGGACTGAGGACTCCTCTTCAGA -5

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Answer

• Given a DNA strand with the following nucleotide
  sequence, what is the sequence of its
  complimentary strand?
• 3- TACCACGTGGACTGAGGACTCCTCTTCAGA -5
• 5- ATGGTGCACCTGACTCCTGAGGAGAAGTCT -3

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RNA Transcription Problem

• Given a DNA strand with the following nucleotide
  sequence, what is the sequence of its
  complimentary mRNA strand?
• 3- TACCACGTGGACTGAGGACTCCTCTTCAGA -5

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ANSWER

• Given a DNA strand with the following nucleotide
  sequence, what is the sequence of its
  complimentary mRNA strand?
• 3- TACCACGTGGACTGAGGACTCCTCTTCAGA -5
• 3- AUGGUGCACCUGACUCCUGAGGAGAAGUCU -5

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Codon / Anticodon

• Given a mRNa strand with the following nucleotide
  sequence, what are the sequence (anticodons) of
  its complimentary tRNA strands?
• 3- AUGGUGCACCUGACUCCUGAGGAGAAGUCU -5

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Answer

• Given a mRNA strand with the following nucleotide
  sequence, what are the sequence (anticodons) of
  its complimentary tRNA strands?
• 3- AUGGUGCACCUGACUCCUGAGGAGAAGUCU -5
• 3 UACCACGUGGAUGAGGACUCCUCUUCAGA -5

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Protein Translation

• Given the following sequence of mRNA, what is the
  amino acid sequence of the resultant polypeptide?
• AUGGUGCACCUGACUCCUGAGGAGAAGUCU

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Protein Translation / Answer

• Given the following sequence of mRNA, what is the
  amino acid sequence of the resultant polypeptide?
• AUGGUGCACCUGACUCCUGAGGAGAAGUCU

Met-val-his-leu-thr-pro-glu-glu-lys-ser
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