BIOL253 - Lecture 1

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  • Created by: Katherine
  • Created on: 28-03-17 15:58
What are the features of a prokaryotic cell?
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What and when were Fred Griffith's experiments?
Used Streptococcus pneumoniae - material isolated from heat killed virulent bacteria could transform non virulent bacteria into a virulent form 'transforming principle'
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What and when were 0swald Avery, Colin MacLeod and Macyln McCarty's experiments?
Took the heat killed bacteria and fractionated it into different compoents - demonstrated that it's the nucleic acid which are thee transforming principle.
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Avery proved that transforming activity is destroyed when...
nucleic acids are treated with deoxyribonuclease (digests DNA), but not ribonuclease (digests RNA)
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Avery identified Griffith's transforming principle as...
DNA
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What and when were Alred Hersey and Martha Chase's experiments?
Used a virus that infects bacteria (bacteriophage) and labelled it with either radioactive sulphur or radioactive Phosphorus (35S or 32P). Only 32P was detected in the bacteria and in the progeny. 35S never actually entered the bacteria.
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How does the work of Hershey and Chase confirm DNA as genetic material?
It shows that only the nucleic acids get into the bacteria.
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Nucleic acids are polymers of what...
nucelotides
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What are polynucleotides?
Nucleotides linked together with a phosphodiester bond between the 3' OH of one sugar and the phosphate attached to the 5' hydroxyl of the next sugar.
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What is the repeating?
The sugar phosphate backbone.
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What are the sugars present in DNA and RNA?
Deoxyribse and Ribose - these are different are ribose has an extra O.
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What are the nitrogenous bases present in RNA and DNA?
cytosine, thymine, uracil, adenine and guanine
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What are the bases?
They are planar rings that are typically uncharged under physiological conditions.
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What is base tautomerisation?
Where a proton moves to a different place within the base structure.
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When does tautomerisation have an effect?
When the DNA is being replicated at the point
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How many rare bases are there at common time?
100000 bases.
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What are the implication of tautomeres?
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What is a nucleoside?
A base plus sugar.
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What is a nucleotide?
A base plus sugar plus phosphate
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The physpahete roupe are slinked to the
C5' of the sugar
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A base is joined to a sugar by a...
Glycosidic bond betwen the C1' of the sugar and the N1 of a pyrimidine or N9 of a purine.
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Nucleotides have additional biological functions, such as..
Energy storage (ATP) and molecular transport.
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What did Chargaff do?
Took nucleic acids and hydrolysed them to break them up into bits, looked at the proportion of everything in different organisms.
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What did Chargaff find?
Found that the amount of purines was always the same as the amount of pyrimidines. (A+G=C+T
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The amount of Guanine =
the amount of cytosine
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What was the work of Rosalind Franklin?
Fibres of DNA and direct X rays through the fibres = determined structure. Diffraction pattern and these DNA fibres were prepared at DNA humidity.
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What did the images show?
The spacing of the lines suggested the dimension of the helix (3.4nm) and approx 10bp/turn. 0.34nm rise per bp.
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What did Franklin's data suggest?
That there were two molecules intertwined.
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What did Watson and Crick do?
Suggested a theory for the complementary base pairing in C+G, A+T.
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Ho
2 Hydrogen bonds so easier to break apart.
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C+G?
3 Hydrogen Bonds
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What are the key features of B-DNA?
Two complementary DNA strands are antiparallel. Two polynucleotide strands wrap round each other in a right handed helix (clockwise). Hydrophilic sugar phasphate is out theo utside - hydrophobic bases on inside. Stability of helix is due to helical.
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What does Van der Waals interaction do?
It stabilizes the interactions - important for stability of DNA
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When was the structure of B-DNA confirmed?
1980
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How was the structure of BDNA confirmed?
Crystal structure of B DNA was characterised The Helix diameter is 2nm. 10.5 bp in on complete turn of helix. Bp are 0.34nm apart.
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In B-DNA the helix forms a...
Major groove and a minor groove. These govern interactions with other molecules.
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The major groove is..
rich in chemical information. Much more than the minor groove. the chemical singaures allow chemical identification of what the actual bp si.
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The minor groove is...
information poor so this is where non sequence specific proteisn bind.
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DNA is predominantly in...
the B configoration in cells.
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What are the features of High humidity B DNA
Right handed helix, 10.5bp/turn, predominant conformation in cells
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What are the features of Low humidity A DNA
Right handed helix, even sized grooves, Can be induced by DNA binding proteins
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What are the features of Z DNA (Alternating pyrimidine/purine).
Left handed helix, 12bp/turn induced by methylation of cytosine, torisonal stress and high salt conc.
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Give examples of non B DNA structures formed by genomic repetitive sequences.
Cruciform, Slipped structure, Quadroplex
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What are the seq requirements of Cruciform?
Inverted repeats
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what are the seq requiremens of slipped structure?
Direct repeats
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What are the seq requirements of quadruplex structure?
Oligo (G)n tracts
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What happens to DNA wehn you isolate it from cells?
It's not relaxed - it is supercoiled.
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What s relaxed DNA?
Open, uncoiled circular DNA.
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What is super coiled DNA
DNA undertension so it twists in on itself
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How do you generate supercoils?
A circular molecule is cut and held at one end while the other is twisted. When the 2 ends are reattached, the DNA twists to restore the preferred number of base/turn. This causes the DNA to wrap itself around in a coiled structure.
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Can super coiling be quantified?
Yes
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What is the LK?
The linking number - the number of times one strand wraps around the other - for circular DNA and constrained linear molecules this is fixed
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What is the Tw number?
Twist - the number of turns in a DNA fragment (+1 per 360 twist)
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What is the Wr number?
Writhe - describes the number of supercoils and can be positive or negative.
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What is the super coiling equation?
Lk = Tw + Wr
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Many biological processes require...
DNA strand separation - this is facilitated by negative supercoiling
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What happens in negative supercoiling?
Uninding the supercoils opens up the DNA strand
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What do topoisomerases do?
They introduce or remove supercoils from DNA in an energy requiring process by temporarily breaking DNA and twisting it
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What are the features of Watson and Crick's model?
Two polynucleotide chains wound around each other in a right haned helix, chains antiparallel, sugar phosphate backbones on outside, bases held by H bonds, base stacking contributes to helix stability, bases 0.34nm apart, helix diameter 2nm
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Because of base H-bonding, the opposite sugar phosphate backbones are not equaly spaced, what does this result in?
Major and minor groove
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Card 2

Front

What and when were Fred Griffith's experiments?

Back

Used Streptococcus pneumoniae - material isolated from heat killed virulent bacteria could transform non virulent bacteria into a virulent form 'transforming principle'

Card 3

Front

What and when were 0swald Avery, Colin MacLeod and Macyln McCarty's experiments?

Back

Preview of the front of card 3

Card 4

Front

Avery proved that transforming activity is destroyed when...

Back

Preview of the front of card 4

Card 5

Front

Avery identified Griffith's transforming principle as...

Back

Preview of the front of card 5
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