Transcript Molecular Genetics

Molecular
Genetics
Protein
Synthesis
Protein Synthesis
 Traits
are end products of metabolic
processes regulated by enzymes
(proteins)
 A gene is a DNA segment that
encodes a particular polypeptide
 Gene expression is the process in
which proteins are assembled from
the information contained in DNA
Messenger RNA
 Single-stranded
 Codons
(triplet code)
 64 codons, 20 AA
Transfer RNA
 3’
end carries amino acid
 Anticodon pairs with mRNA
– 3rd nucleotide can “wobble”
– Thus can pair with more than 1 codon
– Only 45 tRNAs (bind to 61 AA codons)
Aminoacyl-tRNA
tRNA/amino
acid
complex
Aminoacyl tRNA
synthetases use ATP
to power the
attachment of an
amino acid
– Unique for each tRNA
Ribosomal RNA
 Assembled
with proteins in nucleolus
to build ribosome subunits
 2 subunits (large, small)
 3 binding sites (A, P, E)
Transcription

Initiation
– RNA poly binds to promoter site (TATA)
– DNA unzipped by RNA poly

Elongation
– RNA poly unzips & assembles mRNA
– Builds in 5’ → 3’ direction

Termination
– RNA poly reaches termination sequence (polyA)
– Pre-mRNA & transcription factors released
Transcription
mRNA Processing
Before mRNA leaves the nucleus:
1. Addition of 5’ Cap (-P-P-P-G-5’) GTP
- For stability and ribosome attachment
2. Addition of 3’ Poly-A Tail (-A-A-A…A-A-3’) ~200
A’s
- For stability and crossing the nuclear envelope
3. RNA Splicing of exons and introns
- Exons “express”, Introns “intervening”
- snRNP’s delete introns
(small nuclear ribonucleoproteins)
- Alternative splicing allows different mRNA’s to be
made from the same pre-mRNA transcript
Translation
1.
2.
3.
Initiation
Elongation
Termination
Powered
by GTP
Initiation
Elongation
TRANSLOCATION = movement of tRNA from A to P site
Elongation
Termination
Post-translational Modification
Folding
Lipid groups
added for
membrane
localization
Cofactors added
for enhanced
enzymatic
function
Glycosylation
(sugar groups)
Ubiquitin
(destruction at
proteasome)