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Chapter 17: From Gene
to Protein
Objectives
1.
To understand the central dogma
2.
To understand the process of transcription
3.
To understand the purpose and structure of RNA
4.
To understand the process of translation
5.
To understand the types of mutations that can occur
The Central Dogma is based on the triplet code
Three basic stages of transcription
1. Initiation (No primer needed)
2. Elongation (5’ to 3’)
3. Termination
Important vocabulary
1. “Upstream”
3. RNA Polymerase
5. Promotor
7. Transcription Unit
2. “Downstream”
4. Template Strand
6. Terminator
Difference between Prokaryotic
and Eukaryotic Cells
1.
2.
Use of transcription help RNA Poly II
attach
Eukaryotic cells use more then one type
3.
of Polymerase use of a transcription
complex
Use of a TATA box
Eukaryotic Pre-mRNA needs to be modified before
leaving nucleus in two main stages
1.
Alteration of the
ends
-Aid in Export of mRNA
-Help protect from enzymes
-Help in attachment to
Ribosomes
2.
Gene splicing
-Cut out Introns (Noncoding RNA)
-Splice Exons (RNA that is expressed)
-Use of spliceosomes ”Cut and Paste”
*Consist of small nucear ribonucleicproteins
**Recognize sequences in introns
Evolutionary significance
1.
2.
3.
RNA has catalytic role (snRNA) in Eukaryotic Cells and in protozoan (p. 336) Why can RNA
act as an enzyme (Ribozyme)?
Alternative RNA splicing --- One exon codes for one domain of a protein (p. 336)
Introns allow for more crossing over without disrupting domain coding = new proteins
sequences.
Translation Overview
-mRNA brings code (codon or
triplet) to ribosomes
-tRNA with anticodon brings a
specific amino acid to
ribosomes
-Polypeptide bonds are made
between amino acids
Structure and Function on tRNA
-tRNA is transcribed in
the nucleus
-tRNA contains an anticodon that is antiparallel to the codons
-Uses an enzyme
aminoacyl-tRNA
synthetase to bond a
specific amino acid to
the 3’ end
Two processes responsible
accurate translation
1.
2.
tRNA specically
carries one amino
acid
The anti-codon
matches mRNA in
the ribosomes
(Wobble exists in the
third base of the
triplet which allows
for some flexibility)
Ribosomal Structure
Building a Polypeptide
1.
Initiation
-start codon
-Large ribosomal sub-unit
-rRNA is thought be be responsible
for structure
2.
Elongation
- A site -- P site -- E site
-anti-codon recognizes codon
-Peptide bond formed between P
and A site
-tRNA is translocated from A to P
site and the empty tRNA exits the
ribosome
3.
Termination
-Release factor bonds to the stop
codon
Base-pair substitutions
1.
Missense - change one amino
acid to another.
2.
Nonsense - Changes codon to stop
codon terminating translation.
Insertions and
Deletions
Result in frameshift
mutations