Transcript DNA Transcription & Protein Translation

Warm ups:
1.
What are the four bases that make up DNA?
2.
What is a mutation?
3. List the different types of mutations…
DNA Transcription & Protein
Translation
Today’s Objectives
1. To explain how DNA and RNA
code for proteins and determine traits.
2. To investigate and understand
common mechanisms of protein
synthesis.
Making Proteins
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
DNA directs the formation of proteins by the
ribosomes of the cell.
RNA – Ribonucleic acid. The molecule that
carries information from nucleus (DNA) to
ribosomes
RNA is different for DNA:

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RNA only has one side of the ladder shape
RNA’s sugar is ribose (DNA's deoxyribose)
RNA has the nucleotide base Uracil (U) in
place of Thymine (RNA also contains the other
three bases: A, C and G).
When forming base pairs, C links with G, but A
links with U (no T)
Transcription
1.
DNA must be copied to messenger RNA
(mRNA)
What would be the mRNA strand that is copied from the
DNA strand below? Remember, RNA has U instead of T
DNA
Sequence
G
A
C
U
U
A
mRNA
Sequence
2. mRNA goes from nucleus to the ribosomes
in cytoplasm
Transcription
3. mRNA complements known as codons
–
Only 3 nucleotide “letters” long
Transcription – Step I
A C G T A T C G C G T A
T G C A T A G C G C A T
Template DNA Strands
Transcription – Step II
A C G T A T C G C G T A
U G C A U A G C G C A U
Template DNA is Matched Up with
Complementary mRNA Sequences
Transcription – Step III
A C G U A U C G C G U A
U G C A U A G C G C A U
mRNA leaves nucleus
and goes to ribosomes
A new complementary RNA strand is
made (rRNA)
Protein Translation
1. mRNA leaves the cell nucleus goes to
ribosome
2. mRNA code is translated into a transfer RNA
(tRNA) code which, in turn, is transferred into a
protein sequence.
Protein Translation
3. Each set of 3 mRNA bases (codons) will pair with a
complimentary tRNA base triplet (called an anticodon).
4. Each tRNA is specific to an amino acid, as tRNA's
are added to the sequence, amino acids are linked
together by peptide bonds, eventually forming a protein
that is later released by the tRNA.
5. Codon code is specific, but redundant!
 20 amino acids
 64 triplet (codon) combinations
Protein translation - example

Using the mRNA strand we obtained above, we generated the
following amino acids
mRNA codon

UUA
After the processes of transcription and translation are complete,
we are left with a protein that consists of the chain:
–
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GAC
Aspartic Acid - Leucine
Although our 'protein' is only 2 amino acids in length, proteins
normally consist of hundreds or thousands of amino acids.
tRNA structure
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3-base code (triplet) is an “anticodon”
Protein molecule
Attached amino acid that is carried from
cytoplasm to ribosomes
Protein Synthesis
1. Start: Ribosome binds to mRNA at start
codon
2. Elongation:
–
–
–
tRNA complexes bind to mRNA codon by forming
complementary base pairs with the tRNA
anticodon
The ribosome moves from codon to codon along
the mRNA.
Amino acids are added one by one
3. Release: release factor binds to the stop
codon
Exit slip
1.
2.
3.
List the three types of RNA?
What does RNA stand for?
What organelle in the cell is the place for
protein production?