DNA & Protein Synthesis

1
DNA Protein Synthesis

• Gene to Protein

2
Nucleic Acids and Protein Synthesis

• All functions of a cell are directed from some
  central form of information.
• This "biological program" is called the Genetic
  Code. - The way cell store information regarding
  it's structure and function.

3
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

4
Griffith Experiment

• 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

5
Avery, McCarty MacLeod

• Tried to determine the nature of this
  transforming agent. Eg. Was it protein or DNA?
• Degraded chromosomes with enzymes which destroyed
  proteins or DNA
• Samples with Proteins destroyed would still cause
  transformation in bacteria indicating genetic
  material was DNA

6
Hershey-Chase

• 1 virus was "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.

7
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 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.

8
DNA Structure

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

9
Nucleotides

• DNA is formed by Nucleotides
• These are made from 3 components
• A 5-Carbon Sugar
• A Nitrogenous base
• A Phosphate group

10
Nucleotide types

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

11
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)

12
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
13
DNA Replication

• DNA has unique ability to make copies of itself
• This is a major "driving force" of living things.
• Does so through the process of DNA Replication.
• Complex process
• DNA "Unzips itself" forming two strands with an
  exposed Nucleotide.
• An nucleotide which forms the appropriate
  Base-pair bonds with the exposed nucleotide.
  This is facilitated by the enzyme DNA Polymerase.
• The process moves down the DNA molecule, and once
  complete, results in two identical DNA strands.
• 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 attached to a segment of the strand by
  enzyme primase.
• Transcription now continues in the 5'?3'
  direction forming an okazaki fragment. Until it
  reaches the next fragment.
• The two fragments are joined by DNA ligase

14
DNA Replication
15
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.

16
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 complimentary base pair.
• This releases a long strand of Messenger RNA
  (mRNA) which is an important component of protein
  synthesis.

17
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

18
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.

19
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.

20
Ribosome

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

21
Protein Synthesis

• Protein synthesis is a complex, many step
  process, it is as follows.
• An mRNA strand binds to the large small
  subunits of a ribosome in the cytoplasm of the
  cell
• This occurs at the AUG (initiation) codon of the
  strand.
• A tRNA molecule with an attached amino acid binds
  to the mRNA strand.
• Note This occurs with complimentary codons
  anti-codons.
• Another tRNA binds to the adjacent codon of the
  mRNA
• A peptide bond is formed between the amino acids
• 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 is
  reached.
• The completed polypeptide is then released.

22
Replication Problem

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

23
Answer

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

24
RNA Transcription Problem

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

25
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

26
Codon / Anticodon

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

27
Answer

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

28
Protein Translation

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

29
Protein Translation / Answer

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

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