Protein Synthesis Transcription and Translation. The Central Dogma The information encoded with the...
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Transcript of Protein Synthesis Transcription and Translation. The Central Dogma The information encoded with the...
![Page 1: Protein Synthesis Transcription and Translation. The Central Dogma The information encoded with the DNA nucleotide sequence of a double helix is transferred.](https://reader036.fdocuments.us/reader036/viewer/2022062518/56649ea25503460f94ba58cc/html5/thumbnails/1.jpg)
Protein Synthesis
Transcription and Translation
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The Central Dogma
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
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The Central Dogma (brief)
DNA is copied to mRNA
mRNA is used as blueprint to make protein
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DNA Protein: in 3 easy steps!
1. Transcription
2. RNA modification
3. Translation
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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
1 gene 1 polypeptide
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RNA Structure
RNA (ribonucleic acid) are nucleotides very similar to DNA
Nitrogenous bases include Cytosine, Guanine, Adenine, and Uracil (instead of Thymine)
Form three basic structures mRNA – messenger RNA rRNA – ribosomal RNA tRNA – transfer RNA
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RNA vs DNA RNA has an oxygen on
the 2’ carbon of the ribose sugar
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RNA vs DNA
RNA is single stranded, DNA is double stranded
GCAT vs CUGA
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Types of RNA molecules
mRNA (messenger): Relays DNA sequence information to ribosome
rRNA (ribosomal): Combines with proteins to form ribosomes
tRNA (transfer): Acts as bridge between nucleotide sequence and
growing polypeptide chain
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Transcription
The process by which the nucleotide base sequence of a DNA molecule is copied into a mRNA molecule
3 steps: Initiation Elongation Termination
Proteins required: RNA polymerase Transcription factors
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RNA Polymerase
Creates a mRNA molecule complimentary to template strand of DNA
Works in the 5’ 3’ direction
Requires transcription factors to begin its work
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Initiation
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
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Elongation
RNA polymerase creates a mRNA molecule with bases complimentary to the template strand
Template strand = Anti-sense strand
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Termination
RNA polymerase reaches end of gene and detaches from double helix
mRNA transcript is released
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Animations
Transcription showing full complex Transcription – cool sounds
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Sense or Anti-sense?
The sense strand of a gene has the same base sequence as the mRNA transcript
The anti-sense strand is used as the template
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Transcript Modification
Before a mRNA transcript exits the nucleus it is modified in 3 three (tres) ways…
1. Addition of 5’ cap
2. Addition of poly-A tail
3. Removal of introns
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5’ cap and poly-A tail
Protective cap is placed on 5’ end
A long repetitive sequence of adenine nucleotides are added to 3’ end, also for protection
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mRNA splicing 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
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Transcription Review
1. How is RNA polymerase similar to DNA polymerase III? How are they different?
2. Will the mRNA transcript have the same nucleotide sequence as the sense or anti-sense strand of DNA?
3. How are RNA and DNA different?
4. Name 3 things that happen during mRNA modification.
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Translation
messenger RNA (mRNA) is decoded at a ribosome to produce a specific polypeptide according to the rules specified by the genetic code.
4 steps: Activation Initiation Elongation Termination
Requires: Ribosomes (rRNA + proteins), mRNA, tRNA, and amino
acids
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Activation
Amino acid is joined with the correct tRNA
Reaction catalyzed by aminoacyl-tRNA-synthetase
Occurs continuously
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tRNA - transfer
Specified amino acids are attached to tRNA
each anti-codon corresponds to the amino acid specified by the genetic code
Each tRNA has an anti-codon (3 nucleotides)
Anti-codon region base pairs with mRNA trascript
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Initiation
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
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Elongation
Ribosome moves down the mRNA in a 5’ 3’ direction
Every three mRNA nucleotides another amino acid is added to the growing polypeptide
3 steps: Codon recognition Peptide bond formation Translocation
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Elongation: Codon Recognition
When the appropriate tRNA anticodon H-bonds to a mRNA codon at the ribosomal complex
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Elongation: Peptide Bond Formation
A peptide bond is created between polypeptide chain and new amino acid
polypeptide is transferred to incoming tRNA
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Elongation: Translocation
Ribosome shifts 3 nucleotides (reading frame) down mRNA transcript
tRNA unattached to polypeptide is released
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Elongation
Translocation
Codon Recognition
Peptide Bond Formation
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Termination
The end of the mRNA coding sequence is reached Stop codon is recognized by a release factor Ribosome complex dissociates, protein is released
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The Genetic Code
Each codon corresponds to a specific amino acid
Degenerate 64 possible codons only 20 amino acids Several codons can code for the same
amino acid Ex. CCU, CCA, CCG, CCC = Proline
Universal The same genetic code is used by all living
organisms
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The Genetic Code
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Animations
Translation Translation – no sound,
basic
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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.
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