Biol 4 Lecture: From Gene to Protein (Ch 17)
© copyright 2006 Marta D. de Jesus
useful sites from Univ of Ariz.:
from Fall 2001 -> http://www.blc.arizona.edu/courses/181gh/
from Spring 2002 -> http://www.blc.arizona.edu/marty/181/index.html
I. How does DNA affect phenotype? History of discovery
A. Archibold/bald Garrod (1909)
alkaptonuria
B. George Beadle & Edward Ephrussi (1930’s)
Drosophila eye color
C. George Beadle & Edward Tatum (early 1940’s)
Neurospora
1gene-1 enzyme hypothesis
D. Overview: information flow (again)
II. Transcription
A. Structure
B. When does this happen?
C. 3 main kinds of RNA
1. messenger RNAs (mRNA)
2. transfer RNAs (tRNA)
3. ribosomal RNAs (rRNA)
D. How is it made? Transcription
Musical analogy
RNA polymerase
transcription unit
4. Steps:
a. initiation
promoter
initiator site
upstream
b. elongation
c. termination & release
E. major differences between prokaryotes & eukaryotes
1. in prokaryotes:
Pribnow box
2. in eukaryotes:
TATA box
UPE {eg: CA(A)T box}
enhancers
activators
transcription factors
termination & release
AATAAA
post-transcriptional modifications/RNA processing
5’ end
3’ end
introns & exons
pre-mRNA = hnRNA
small nuclear RNAs (snRNAs)
small nuclear riboproteins (snRNPs)
spliceosomes
ribozymes
why are euk. genes like this
alternative RNA splicing
III. Translation
A. foreign language analogy
B. what is it saying?
1. codons
redundancy or degeneracy
not ambiguity
1961: Marshall Nirenberg & JH Matthaei
Nobel Prize 1968: Nirenberg, Khorana & Holley
C. How is a protein built?
1. ribosomes
a. large & small subunits
b. have 3 sites for tRNAs
(ribosome structure: http://www.rcsb.org/pdb/molecules/pdb10_1.html)
2. tRNAs carrying amino acids
aminoacyl-tRNA synthetases
tRNA structure
anticodon
3. mRNA
D. Steps:
1. initiation
reading frame
initiation complex
2. chain elongation
a. codon recognition
b. peptide bond formation
c. translocation
3. chain termination
release factor
E. polyribosomes/polysomes
F. chaperone proteins
G. post-translational modifications
1. individual amino acids
2. signal sequences of protein: “zip codes” (Gunter Blobel, Nobel Prize 1999)
a. proteins for the RER
1) signal sequence/peptide
2) signal-recognition particle (SRP)
b. other signal peptides
2. further editing can also occur
IV. How accurate do all these processes have to be?
A. mutation
B. point mutation
1. base-pair substitution
a. silent
b. missense
c. nonsense
2. frameshift mutation
a. base-pair insertion
b. base-pair deletion
C. larger DNA changes
1. chromosomal
2. transposon
Barbara McClintock 1983 Nobel Prize
3. viruses
D. is mutation always bad?
E. How to test chemicals for mutation-causing ability
1. for mutagens: Ames test
2. for carcinogens