Download Science 103: Outline 17

Science 103 Spring 2006 Outline 16: Transcription, Translation, and Mutation
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Transcription, Translation & Mutation
P 572-579
PROTEIN SYNTHESIS
DNARNAProtein = The Central Dogma
1. Gene Expression
Expressing a gene = Synthesizing the corresponding protein.
Involves 2 steps:
(a) Transcription
(b) Translation
2. Transcription
(a) Overall Process
Gene (DNA) 
(b) Functions
(i)
(ii)
(c) Location
(d) Process
A single-stranded RNA copy of the DNA is made by RNA polymerase:
(i) RNA pol binds to and moves down the DNA, separating the strands.
(ii) As it goes, it pairs complementary nucleotides with ONE strand, the template strand
(*NOT coding strand as in the book!)  making a copy of the information in the gene:
eg. DNA:
RNA:
ATCGGCTTCAA
(iii) When it reaches a termination site, the RNA detaches and the DNA re-zips.
(iv) mRNA passes out of the nucleus through the ______________________.
Figure 25.14
3. Translation
(a) Overall Process
(b) Location
(c) Classes of RNA Used
(i) mRNA
(ii) Transfer RNA (tRNA)
An adapter molecule that picks up a specific amino acid and pairs to the
complementary sequence of nucleotides on the mRNA.
(iii) Ribosomal RNA (rRNA)
Ribosomes =
(d) Genetic Code
(i) Description
(ii) Codon
Table 25.3
(e) Process
Figures
(i) mRNA binds to the ribosome.
(ii) The first tRNA (carrying its amino acid) with the anticodon corresponding to the first
codon (always AUG) binds.
(iii) The second tRNA (with amino acid) with the anticodon corresponding to the second
codon binds.
(iv) A peptide (covalent) bond forms between the 2 amino acids and the first amino acid
detaches from its tRNA.
(iv) Ribosome moves one codon to the right.
(v) A tRNA (plus amino acid) with the anticodon corresponding to the third codon binds
and the first tRNA (empty) leaves.
(v) The ribosomes move down the mRNA until they reach a stop codon. The ribosomes
detach from the mRNA and the protein is released.
4. Fate of Proteins
Where in the cell would translation occur if a protein is to be:
(a) Secreted?
(b) Used in cell?
5. Translate the Following mRNA sequence:
mRNA
Protein
UGAUAUGACGUCGCAGCAAAGUUAAGGAGGGCC
Mutation
1. Description
2. Somatic Mutations
3. Germ-Line Mutations
(Only when genetic change occurs in germ-line cells will it be passed on to
offspring).
(a) Importance
(b) Do All Mutations in Germ-Lines Increase Genetic Fitness?
4. Effect on Evolution
5. Evolution Rate
Examples of Mutation
Point Mutations
Alterations in one or a few base pairs.
1. Insertion
Example:
Polypeptide chain
DNA
RNA
Mutated DNA
RNA
Polypeptide chain
Consequences?
2. Deletion
Leucine Proline Stop
AAT AGG TAT T
Example:
DNA
AAT GGT ATT

AAG GTA TT
RNA
Polypeptide chain
Consequences?
3. Base Substitution
Eg.
Figure 25.16
Example 1:
DNA
AAT GGT ATT

AAC GGT ATT
RNA
Polypeptide chain
Consequences?
Example 2:
DNA
RNA
Polypeptide chain
Consequences?
AAA GGT ATT