Download Protein Synthesis PowerPoint - Scotts Valley High School

Protein Synthesis
Transcription and Translation
The Central Dogma
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The information encoded with the DNA
nucleotide sequence of a double helix is
transferred to a mRNA molecule.
The mRNA molecule travels out of the
nucleus and attaches to a ribosome
Using the RNA nucleotide sequence and the
genetic code, the ribosome assembles a
protein
The Central Dogma (brief)

DNA is copied to
mRNA

mRNA is used as
blueprint to make
protein
DNA  Protein:
in 3 easy steps!
1.
Transcription
2.
RNA modification
3.
Translation
Genes and DNA

A gene is a specific sequence of
DNA nucleotides

For each specific protein used by
a cell, there is a specific DNA
sequence (gene) located on a
chromosome
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1 gene  1 polypeptide
RNA Structure
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RNA (ribonucleic acid) are nucleotides very
similar to DNA
Nitrogenous bases include Cytosine,
Guanine, Adenine, and Uracil (instead of
Thymine)
Form three basic structures
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mRNA – messenger RNA
rRNA – ribosomal RNA
tRNA – transfer RNA
RNA vs DNA

RNA has an oxygen on
the 2’ carbon of the
ribose sugar
RNA
vs DNA

RNA is single
stranded, DNA is
double stranded

GCAT vs CUGA
Types of RNA molecules

mRNA (messenger):

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rRNA (ribosomal):
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Relays DNA sequence information to ribosome
Combines with proteins to form ribosomes
tRNA (transfer):
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Acts as bridge between nucleotide sequence and
growing polypeptide chain
Transcription


The process by which the nucleotide base sequence
of a DNA molecule is copied into a mRNA molecule
3 steps:

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Initiation
Elongation
Termination
Proteins required:
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RNA polymerase
Transcription factors
RNA Polymerase

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Creates a mRNA
molecule
complimentary to
template strand of DNA
Works in the 5’ 3’
direction
Requires transcription
factors to begin its work
Initiation
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Proteins called
transcription factors
bind to DNA region
upstream from gene
Proteins bind to region
called promoter
RNA polymerase
attaches to double helix
at beginning of gene
Elongation

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RNA polymerase
creates a mRNA
molecule with bases
complimentary to the
template strand
Template strand =
Anti-sense strand
Termination


RNA
polymerase
reaches end of
gene and
detaches from
double helix
mRNA transcript
is released
Animations

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Transcription showing full complex
Transcription – cool sounds
Sense or Anti-sense?

The sense strand of a gene has the same
base sequence as the mRNA transcript
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The anti-sense strand is used as the template
Transcript Modification
Before a mRNA transcript exits the nucleus
it is modified in 3 three (tres) ways…

1.
2.
3.
Addition of 5’ cap
Addition of poly-A tail
Removal of introns
5’ cap and poly-A tail
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Protective cap is placed
on 5’ end
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A long repetitive
sequence of adenine
nucleotides are added
to 3’ end, also for
protection
mRNA splicing
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Not all of a transcribed DNA sequence will be
translated
Genes are composed of introns and exons
Introns are removed from mRNA transcripts by
splicosomes
Transcription Review
1.
2.
3.
4.
How is RNA polymerase similar to DNA
polymerase III? How are they different?
Will the mRNA transcript have the same
nucleotide sequence as the sense or antisense strand of DNA?
How are RNA and DNA different?
Name 3 things that happen during mRNA
modification.
Translation
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messenger RNA (mRNA) is decoded at a ribosome
to produce a specific polypeptide according to the
rules specified by the genetic code.
4 steps:
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Activation
Initiation
Elongation
Termination
Requires:
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Ribosomes (rRNA + proteins), mRNA, tRNA, and amino
acids
Activation
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Amino acid is joined
with the correct tRNA
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Reaction catalyzed by
aminoacyl-tRNAsynthetase
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Occurs continuously
tRNA - transfer
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Specified amino acids are
attached to tRNA
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each anti-codon corresponds
to the amino acid specified by
the genetic code
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Each tRNA has an anti-codon
(3 nucleotides)
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Anti-codon region base pairs
with mRNA trascript
Initiation
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Small ribosome subunit recognizes start sequence
on mRNA and binds to it
Start codon, AUG, is recognized by tRNA carrying a
Methionine amino acid
Large subunit completes the complex
Elongation
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Ribosome moves down the mRNA in a 5’ 3’
direction
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Every three mRNA nucleotides another amino acid
is added to the growing polypeptide
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3 steps:
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Codon recognition
Peptide bond formation
Translocation
Elongation: Codon Recognition

When the appropriate tRNA anticodon H-bonds
to a mRNA codon at the ribosomal complex
Elongation:
Peptide Bond Formation

A peptide bond is
created between
polypeptide chain
and new amino acid

polypeptide is
transferred to
incoming tRNA
Elongation:
Translocation
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Ribosome shifts 3
nucleotides (reading
frame) down mRNA
transcript
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tRNA unattached to
polypeptide is
released
Elongation
Codon
Recognition
Translocation
Peptide Bond
Formation
Termination
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The end of the mRNA coding sequence is reached
Stop codon is recognized by a release factor
Ribosome complex dissociates, protein is released
The Genetic Code
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Each codon corresponds to a specific
amino acid
Degenerate
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64 possible codons
only 20 amino acids
Several codons can code for the same
amino acid
Ex. CCU, CCA, CCG, CCC = Proline
Universal
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The same genetic code is used by all living
organisms
The Genetic Code
Animations
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Translation
Translation – no sound,
basic
Summary
Genetic information is encoded in the sequence of the
DNA double helix. To access this information, the
DNA sequence must be copied, or "transcribed", by
enzymes known as RNA polymerases. The resulting
messenger RNA (mRNA) molecules carry the
genetic information to the protein-synthesizing
machinery, where it is used to define the amino-acid
sequence, and therefore the structure and function,
of proteins.