BIOB11H3 Lecture Notes - Lecture 4: Molecular Biology, Ribosomal Rna, Uracil

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Published on 14 Oct 2011
School
UTSC
Department
Biological Sciences
Course
BIOB11H3
Professor
1
Lecture 4
Introduction to Transcription
rRNA synthesis & maturation
SPs: Figs 11-4, 6, 7, 9, 12, 13, 14
Vocabulary: core enzyme/sigma factor/holoenzyme/
TATA box/consensus sequence/!-amanitin/ribosome/
nucleolus/nucleolar organizer region (NOR)/
Beadle and Tatum Experiment (1940s)
Laid foundation of biochemical genetics
Support for ‘one gene/one enzyme’ hypothesis
B&T awarded Nobel prize in 1958
Fig 11-1
Demonstrates a deficiency in vitamin biosynthesis
In this case: mutation in gene encoding protein
involved in making the vitamin pantothenic acid
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2
A B C D
Enz1 Enz2 Enz3
Generic biochemical pathway
If Enz2 gene mutated, then providing cells with C will
‘rescue’, but providing A and B will not.
X
Beadle & Tatum proposed: “One gene-one enzyme” hypothesis
pantothenic acid=C
=Co-enzyme A
Fig 11-2
Transcription: DNA makes RNA
1.5’ to 3’ (strand being
synthesized)
2. unwinding DNA
creates topological
stress.
Supercoiling alleviates
torsional stress:also
see Fig 13-6.
3. NTP hydrolysis
provides energy
4. Many polymerases
can act simultaneously.
Fig 11-4
5’
3’
3’
5’
Fig 11-6
5 subunits
Random initiation sites
Initiation occurs at proper sites
Prokaryotic
Transcription
NTP- nucleotide triphosphates (ATP, GTP, etc.)
on the same gene
sigma factor- interacts with the core enzyme to make a
holoenzyme-- and the molec interacts with the
template and initiate synthesis at the proper sites
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Document Summary

Sps: figs 11-4, 6, 7, 9, 12, 13, 14. Beadle and tatum experiment (1940s: laid foundation of biochemical genetics, support for one gene/one enzyme" hypothesis, b&t awarded nobel prize in 1958. In this case: mutation in gene encoding protein involved in making the vitamin pantothenic acid. If enz2 gene mutated, then providing cells with c will. Rescue", but providing a and b will not. Beadle & tatum proposed: one gene-one enzyme hypothesis. 5" to 3" (strand being synthesized: unwinding dna creates topological stress. Supercoiling alleviates torsional stress:also see fig 13-6: ntp hydrolysis provides energy, many polymerases can act simultaneously. Consensus sequences located at -35 and -10 in prokaryotic genes. Pol i sensitivity to !-amanitin rnas large (rrnas) insensitive. Pol iii moderately sensitive small rnas (5s, trnas) Nucleolus: clusters" of rrna genes and the site of ribosome assembly. Rna size can be estimated based on sedimentation of the molecule during centrifugation.