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Protein Synthesis:

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Translating the Genetic Message. General steps in protein synthesis. The ... Role of ATP in supplying energy for reactions. Typical. A B A-B. A ATP A~P ADP ... – PowerPoint PPT presentation

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Title: Protein Synthesis:


1
Lecture 15 Protein Synthesis Translation of
the Genetic Message Chapter 12
2
Translating the Genetic Message
  • General steps in protein synthesis.
  • The genetic code.
  • Chain initiation.
  • Chain elongation.
  • Chanin termination.

3
Aminoacyl-tRNA
mRNA aminoacyl-tRNA bind to ribosome
4
The genetic code Triplet Nonoverlapping Commaless
Degenerate Universal
5
Why 3 bases? 20 amino acids 1 base ? 4 amino
acids
2 bases ? 42 16 amino acids
3 bases ? 43 4 x 4 x 464
6
Nonoverlapping
7
Commaless
8
Degenerate 1 amino acid may have more than
1 codon. Leucine has 6
However, a particulr codon only codes for 1
amino acid not ambiguous CUU only codes for
leucine.
3 stop codons
9
Universal all organisms have the same code.
10
(No Transcript)
11
How do we know which triplet codes for which
amino acid?
Poly-U UUUUU ? phenylalanine
ACACACA ? alternating threonine and histidine.
Reading frames.
12
General Characteristics of the Code
  • Certain protections against mutaition.
  • For 32 codons coding for 8 amno acids, the
  • third base is irrelevant.
  • A U in the second place means it codes for a
  • hydrophobic amino acid.

13
Formation of an Amino-acyl tRNA
14
t-RNA
15
Amino acid Attached here.
tRNA
Anticodon loop
16
Formation of aminoacyl-tRNA
Why is the ATP needed?
17
ATP adenine-ribose-phosphate-phosphate-phosphat
e
Break bonds release energy.
18
Role of ATP in supplying energy for reactions.
Typical A B ? A-B
A ATP ? AP ADP AP ADP P ? A-B P
Adenine-ribose-PPP
19
Amino acid activation.
aa tRNA ? aa-tRNA
aa ATP ? aa-AMP PPi
aa-AMP tRNA ? aa-tRNA
Adenine-ribose-PPP
20
Amino acid ATP?aminoacyl-AMP PPi
aminoacyl-AMP tRNA ? aminoacyl-tRNA

AMP
Amino acid ATP ? aminoacyl-tRNA
AMP PPi
Both steps catalyzed by An aminoacyl-tRNA
synthetase 1 per aa.
21
Protein synthesis occurs on ribosomes. The
prokaryotic ribosome has two subunits 30s and
50s
22
30s
23
50s ribosomal subunit
24
30s 50s form the 70s ribosome
25
Chain initiation formyl methionine Two
methionine tRNAs tRNAmet all methionines
inside the protein. met tRNAmet ?
met-tRNAmet
26
tRNAfmet
fmet formyl methionine
makes
fmet-tRNAfmet N-terminal amino acid
in prokaryotes. Made in two steps.
27
Chain initiation formalmethionine
28
Chain initiation formalmethionine
fmet-tRNAfmet
tetrahydrofolate
29
What happens to met-tRNAmet? Nothing. No formal
group added.
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