Transcript MOLECULAR GENETICS

MOLECULAR GENETICS
Translation
Definition
Formation of a polypeptide from mRNA
using the genetic code.
TRANSLATION
Genetic Code
Definition
Code used to translate the genetic language
into the language of proteins.
Language
RNA Alphabet
Four letters (nucleotides): A, C, G, and U
Proteins
Twenty amino acids
Fig. 24.10
TRANSLATION
Genetic Code
Codons
Definition
Three adjacent nucleotide bases on
mRNA that code for a single amino
acid or termination.
TRANSLATION
Genetic Code
Codons
Types
Start Codon
Special codon (AUG) that signifies where
translation should start.
Stop Codon
Codons that stop translation (UAA, UAG, UGA).
Message Codons
Reading frame codons that determine the
specific amino acid sequence .
Message
What amino acid is coded
for by the codon AUG
TRANSLATION
Initiation
1) Small ribosomal unit attaches to mRNA.
2) Initiator tRNA with correct anticodon
(UAC) and amino acid (Methionine)
attaches to the start codon (AUG) on
the mRNA at the P-site of the ribosome.
3) Large ribosomal subunit joins small
subunit.
TRANSLATION
Elongation
1) The second tRNA with the correct anticodon
attaches to the message codon at the A-site
on the ribosome.
2) A peptide bond is formed between the Methionine
and second amino acid.
3) The bond between Methionine and tRNA
is broken at the P-site.
TRANSLATION
Elongation
4) The Ribosome pulls the mRNA one codon
5) The tRNA in the P-site is moved into the E-site and the
tRNA in the A-site is moved into the P-site. The A-site is
empty.
6) A new tRNA comes into the A-site and matches up with
the mRNA message condon.
7) The tRNA in the E-site exits to find a new amino acid
8) This continues until the Reading Frame is read.
TRANSLATION
Termination
1) The ribosome A-site is occupied by a Stop Codon
at the end of the reading frame.
2) A “Release Factor” protein binds to the Stop
Codon.
3) The tRNA and protein detach from ribosome.
4) The ribosomal subunits dissociate.
POLYRIBOSOME
Definition
A single mRNA being translated by several
ribosomes.
TRANSLATION
Medical Significance
Retrovirus Replication
HIV
1) Stores genetic information in the form of RNA
2) Copies its RNA into DNA by “reverse transcription”
within the cell.
3) DNA is inserted into the host cell genome.
4) The cell transcripts DNA to RNA then translates
this to reproduce itself.
HIV VIRUS
TRANSLATION
Medical Significance
AZT
1) Is an analogue of DNA nucleotides.
2) Does not allow formation of phosphodiester
for synthesis of new strands of DNA or RNA.
3) Prevents viral replication but does not kill it.
3’
5’
No Hydroxyl
EXERCISE 5
PG. 55