Translation

1
Translation
2
Translation

• The final product of gene expression is a
  polypeptide chain of amino acids whose sequence
  was prescribed by the genetic code.

3
The Players

1. mRNA transcribed from genomic DNA
2. Transfer RNA (tRNA) to transport amino acids
3. Ribosome to read mRNA, align amino acids
   attached to tRNA and create the peptide bonds
   between adjacent amino acids

4
Ribosome

• Two subunits composed of protein and ribosomal
  RNA (rRNA)
• The rRNA is a structural component of the
  ribosome subunits

5
The Ribosome (Eukaryote)
40S
18S RNA 33 proteins
80S
60S
28S RNA 49 proteins
6
tRNA

• tRNAs are small, extremely stable RNA structures
  shaped like a cloverleaf due to internal base
  pairing
• They are almost identical in both prokaryotes and
  eukaryotes
• They contain a number of posttranscriptional
  modifications, including non-traditional bases
  (other than (A, U, G and C)

7
tRNA
8
tRNA

• The amino acid attaches to the 3 end of the tRNA
• tRNA can base pair with the codon in mRNA at the
  anticodon on the tRNA

9
Charging tRNA with an Amino Acid

• An individual tRNA is specific for a single amino
  acid. (There are at least 20 different tRNAs)
• Charging is the process of covalently attaching
  an amino acid to the tRNA
• Charging is accomplished by aminoacyl tRNA
  synthetases, each of which is specific for an
  amino acid.

10
Prokaryotes vs. Eukaryotes

• The process is essentially the same, but somewhat
  more complicated in eukaryotes.
• What I am showing you is the process for
  prokaryotes, but at the end Ill talk a little
  bit about eukaryotes.

11
Steps in Translation

1. Initiationthe two subunits of the ribosome come
   together and the start codon on the mRNA in the
   ribosome is aligned to set the reading frame
2. ElongationCharged tRNAs attach and peptide bonds
   form between the amino acids
3. Termination

12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
Prokaryotes vs. Eukaryotes
19
Prokaryotes vs. Eukaryotes

• Prokaryotes
• Translation takes place directly after
  transcription
• mRNA is not modified
• Transcription and translation take place in the
  same area

20
(No Transcript)
21
3
5
22
Prokaryotes vs. Eukaryotes

• Eukaryotes
• Transcript is modified before leaving the nucleus
  (5 cap and 3 poly-A tail)
• Modifications increase translation efficiency and
  lifespan of the mRNA
• Translation takes place on ribosomes located in
  the rough endoplasmic reticulum (translation is
  physically separated from transcription)

23
Eukaryotes
24
Prokaryotes vs. Eukaryotes

• Influence on gene expression forms the basis of
  function in many antibiotics.
• The purpose is to impair function in the
  prokaryote without disrupting function in
  eukaryotes.

25
Antibiotics

1. Tetracycline Blocks attachment of the AA-tRNA to
   the A site in the ribosome
2. Erythromycin Blocks the movement of the ribosome
   down the mRNA
3. Streptomycin Blocks formation of the initiation
   complex and causes miscoding
4. Rifamycin Blocks transcription by blocking
   binding of RNA polymerase