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Lecture 3

BIOB11H3 Lecture Notes - Lecture 3: Absorbance, 5.8S Ribosomal Rna, 18S Ribosomal Rna


Department
Biological Sciences
Course Code
BIOB11H3
Professor
Dan Riggs
Lecture
3

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BIOB11: Molecular Aspects
Lecture 3: Introduction to Transcription: rRNA Synthesis & Maturation
Beadle & Tatum Experiment (1940s)
-laid foundation of biochemical genetics
-support for “one gene/one enyzme” hypothesis
-awarded Nobel prize in 1958
-demonstrates deficiency in vitamin biosynthesis
*In this case: mutation in gene encoding protein
involved in making the vitamin pantothenic acid
*if Enz2 gene mutated, no Enz2 to convert B to
C; and providing cells with C will “rescue”, but
providing A & B will not rescue
-the results of B & T’s experiment led to:
>one gene-one enzyme hypothesis
Transcription of DNA for RNA
1.) Synthesis from 5’ to 3’
2.) Unwinding DNA creates topological stress
>supercoiling alleviates this stress
>topoisomerases remove supercoils
3.) Nucleoside TriPhosphate (NTP) hydrolysis
provides energy
>acts like ATP
4.) Many polymerases can act simultaneously
<Prokayotic Transcription
<Random Initiation Sites
<Initiation occurs at
proper sites
<Sigma Factor binds to
sequences @ -10/-35 to
correctly position RNA
polymerase
<Initiation start site = +1
t
Wild-type
Neurospora
Irradiate with X-rays or
ultraviolet light
Minimal medium
Grow on
supplemented medium
Spores produced by
meiosis followed by
a single mitosis
Mutants are able to
grow on supplemented
medium, but not on
minimal medium
Test growth
capability
Minimal medium
+ vitamins
Minimal medium supplemented with:
Folic
acid
InositolCholinep-Amino
benzoic
acid
Pyridoxine Control on
minimal
medium
ThiamineRiboflavinNiacinPantothenic
acid
Minimal medium
+ amino acids
Spores Meiosis
12
3
4
5
W
ild-typ
e
Neurospora
Ir
3
Test
g
cap
f
ollowed by
e
mitosi
s
G
row on
supplemented medium
M
2
w
th
ity
g
ro
w
a
bil
4
with:
p
plementedmedium
s
s
u
p
M
ini
m
m
al
A B C D
Enz1 Enz2 Enz3
Generic biochemical pathway
X
pantothenic acid=C
=Co-enzyme A
Fig 11-4
5
3 5
3
t
+
Core enzyme
Loose association between DNA
and core enzyme. RNA chains that
are begun are not initiated at proper sites.
+
Complete enzyme (holoenzyme)
Initiation
start site
Sigma (σ) factor
–35 –10
Association of complete enzyme
with DNA at proper site and
opening of double helix
Loss of sigma factor as
RNA chain is elongated
5'
(a)
(b)
(c)
(d)
Fig 11-7
Consensus sequences located at -35
and -10 in prokaryotic genes
TATA box
Arrangement of elements in a bacterial promoter
5’
3’
5’
3’
‘promoter region’
Lots of nomenclature here and remember that
DNA is an antiparallel helix
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