Transcript Lecture 18: Powerpoint

Biology 102
Gene Regulation and Expression
Part 2
Lecture outline
1. Translation




Review of what translation is
Types of RNA and their functions
Overview of translation
Details of translation
2. Information flow through cell
Review: Information Flow
DNA=>mRNA=>Protein
Three Types of RNA (review)
mRNA
A G A U G C G A G U U A U GG
catalytic site
Large
subunit
1
Ribosome
contains rRNA
2
Small
subunit
Transfer RNA
Met
tRNA docking sites
Attached amino acid
anticodon
U G
A
Translation: An Overview
Translation: Initiation

A tRNA with an attached methionine amino acid
binds to a small ribosomal subunit, forming an
initiation complex.
Translation: Initiation (2)

The initiation complex
binds to end of mRNA
and travels down until it
encounters an AUG
codon in the mRNA.

The anticodon of the
tRNA in the initiation
complex forms base
pairs with the AUG
codon.
Translation: Initiation (3)

The large
ribosomal subunit
binds to the small
subunit, with the
mRNA between the
two subunits.

The methionine
tRNA is in the first
tRNA site on the
large subunit.
Translation: Elongation 1
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The second tRNA enters
the second tRNA site
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The tRNA that binds must
be able to match its
anticodon (CAA in this
example) to base pair with
the codon (GUU in this
example) in the mRNA.

tRNAs with a CAA
anticodon carry an
attached valine amino
acid, which was added to it
by enzymes in the
cytoplasm.
Translation: Elongation 2

The catalytic site
on the large
subunit catalyzes
the formation of a
peptide bond
linking the amino
acids

The two amino
acids are now
attached to the
tRNA in the second
binding position.
Translation:
Elongation 3

The "empty" tRNA is
released and the
ribosome moves
down the mRNA, one
codon to the right.

The tRNA that is
attached to the two
amino acids is now in
the first tRNA binding
site and the second
tRNA binding site is
empty.
Translation: Elongation 4

Another tRNA enters the
second tRNA binding site
carrying its attached amino
acid.

The tRNA has an anticodon
that pairs with the codon.
(Here, the CAU mRNA codon
pairs with a GUA tRNA
anticodon.)

The tRNA molecule carries
the amino acid histidine
(his).
Translation: Elongation 5

The catalytic site forms
a new peptide bond, in
this example, between
the valine and the
histidine.
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A three-amino acid
chain is now attached to
the tRNA in the second
tRNA binding site.
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The empty tRNA in the
first site is released and
the ribosome moves one
codon to the right.
Translation:
Termination

Binding of tRNAs, &
formation of peptide bonds
continues.
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Ribosome reaches STOP
codon (UAG).
Protein "release factors"
signal the ribosome to
release the protein.
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The mRNA is also released
and large & small subunits
separate.
Review: From DNA to amino acid chain
gene
G
C
A
T
G
G
G
A
G
T
template
DNA strand
etc.
T
(a) complementary
DNA strand
C
G
T
A
C
C
C
T
C
A
A
etc.
G
U
U
etc.
codons
(b) mRNA
G
C
A
U
G
G
G
A
anticodons
(c) tRNA
U
A
C
C
C
U
C
A
A
etc.
amino acids
(d) protein
Methionine
Glycine
Valine
etc.
(Cytoplasm)
(Nucleus)
Overview of
Information Flow within
the cell
DNA
1 Transcription
rRNA mRNA tRNA
+ Proteins
Ribosomes mRNA
Inactive
Protein
Active
Protein
Substrate
tRNA
tRNA-AA
2 Translation
3 Modification
Amino
4 Degradation Acids
Product
The End