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Transcript 
1
BIOLOGY PRESENTATIONS
FOR A-LEVEL, IN MULTIMEDIA
JAMES BOWLES, 2001
LEFT CLICK OR PRESS SPACE
BAR TO ADVANCE, PRESS P BUTTON
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2
‘A’ Level Biology
Protein Synthesis
The Genetic Code
The sequence of bases
determines the order of
amino acids in a protein
3
The Genetic Code
4
The code is read in Triplets of
bases
U A AGC G UA U UGGC A U
This gives 64 combinations of
the 4 bases
The Genetic Code
5
Each triplet is read as a discrete
unit
U A AGC G UA U UGGC A U
It is a non-overlapping code
The Genetic Code
6
It is a Degenerate code
G U U
G U C
G U A
G U G
Valine
Most amino acids have more than
one triplet coding for them
The Genetic Code
There is also punctuation in the
code
U A A
U A G
U GA
Stop code
7
The Genetic Code
The code is universal
Codons
code for
the same
amino acid
in all
organisms
8
Protein Synthesis
9
Protein synthesis occurs in three
stages:
1.Transcription
2.Activation of Amino Acids
3.Translation
Transcription
Part of the DNA molecule
unwinds
10
Transcription
11
RNA polymerase attaches at a
start codon
Transcription
12
RNA polymerase moves along
the DNA catalysing the
production of mRNA
Transcription
13
At the stop codon the RNA
polymerase and mRNA detach
from the DNA
14
Activation of Amino
Acids
Met
U A C
Amino Acids
combine with
tRNA
15
Activation of Amino
Acids
Met
U A C
This process
utilises
specific
enzymes and
ATP is
hydrolysed
Translation
16
A ribosome
attaches to a
length of
mRNA
A U GGC G UA U UGGC A U
Translation
Met
17
Met
Met
Met
Met
tRNA with
corresponding
anticodon
fits
U A C
A in
C the ribosome
U
U A C
U A U
C A C
A U GGC G UA U UGGC A U
Translation
Ala
Ala
Met
Ala
18
Ala
A second piece
of tRNA fits
C Ginto
C the
G C ribosome
C
C GC
U A CC G C
A U GGC G UA U UGGC A U
Translation
Met
19
Ala
A peptide bond
forms between
the amino acids
U A CC G C
A U GGC G UA U UGGC A U
Translation
Met
Ala
20
The
ribosome
moves
along one
codon
U A CC G C
A U GGC G UA U UGGC A U
Translation
Met
Ala
21
The first
piece of
tRNA is
released
C GC
A U GGC G UA U UGGC A U
Translation
Met
Ala
22
The 1st
amino acid
remains in
place
C GC
A U GGC G UA U UGGC A U
TranslationTyr
Met
Ala
Tyr
23
Tyr
Tyr
The process
is repeated
A U A
A U A
A U A
C GCA U A
A U GGC G UA U UGGC A U
24
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