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IMMS lectures > dna function, structure & replication > Flashcards

dna function, structure & replication Flashcards

1
Q

what are the uses of DNA in pathology

A

genetic disease
viruses
cancer

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2
Q

what are the uses of DNA in diagnostics

A

mutation analysis
microbiology
forensic medicine

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3
Q

what are the uses of DNA in therapy

A

DNA as drug target
gene therapy
risk assessment

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4
Q

what are the uses of DNA in biotechnology

A

production of biomedicines,
delivery vectors
gene production

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5
Q

describe DNA in prokaryotes

A

no nuclear membrane
arranged often in a single chromosome
circular

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6
Q

describe DNA in prokaryotes

A

no nuclear membrane
arranged often in a single chromosome
circular

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7
Q

describe DNA in eukaryotes

A

is in the nucleus & some in mitochondria
DNA is bound to proteins (chromatin complex)
different appearance according to the function

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8
Q

what are the 2 functions of DNA

A
  • acts as a template and regulator for transcription and protein synthesis
  • is the genetic material, structural basis of heredity and genetic diseases
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9
Q

what did gregor mendel do

A

he demonstrated the ‘granular’ nature of inheritance
traits were not passed on by simple blending but in a quantitative process

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10
Q

what did walter sutton do

A

he analysed the interesting movement of chromosomes during mitosis and meoisis
he demonstrated metaphase alignment of chromosomes and segregation during mitosis
and
the homologous pairing of chromosomes and crossing over (chiasma) during meiosis

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11
Q

what did oswald avery, colin macleod and maclyn mccarty do

A

they transformed one strain of bacteria into another by transferring genetic information
chemically they were able to show that the only compound transferred was nucleic acid

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12
Q

what did alfred hershey and martha chase do

A

they radiolabelled a bacterial virus with either 35S or 32P
they analysed the copies of virus made by the infected bacterium and showed that only the 32P labelled viral material was replicated

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13
Q

what is the difference between heterochromatin and euchromatin

A

heterochromatin is more condensed and is not active in gene expression whereas euchromatin is more open

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14
Q

describe prokaryotic DNA

A

supercoiled
circular chromosome
2.5 x106 kDa
4 x106 bases
2mm linear

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15
Q

describe eukaryotic DNA

A

complex packaging
(22x2) + X,Y or X,X
4 x109 kDa
3 x109bp
2m linear

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16
Q

is DNA replication conservative or semi-conservative and why

A

semi-conservative
because a new DNA molecule is composed of one old strand and one new strand

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17
Q

describe the process of DNA replication

A
  1. Prior to cell division, topoisomerase unwinds DNA and DNA helicase separates DNA apart to expose two single DNA strands and create two replication forks. DNA replication takes place simultaneously at each fork.
  2. SSB’s (single-strand binding protein) coat the single DNA strands to prevent re-
    annealing or ‘snapping back together’. (so they keep it open)
  3. The primate enzyme then uses the original DNA sequence on the parent strand to synthesise a short RNA primer. Primers are necessary since DNA polymerase can only extend a nucleotide chain, not start one
  4. DNA polymerase begins to synthesise a new DNA (via complementary base pairing using free floating nucleotides) strand by extending an RNA primer in the 5’ to 3’ direction. Each parental strand is copied by one DNA polymerase.
  5. As replication proceeds,
    RNAse H recognises RNA primers bound to the DNA template and removes the primers by hydrolysing the RNA
  6. DNA polymerase can then
    fill the gap left by RNAse H
  7. DNA replication process
    completed when the ligase enzyme joins the short DNA pieces (Okazaki fragments) together into one continuous strand.
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18
Q

which enzymes and proteins are involved in DNA replication

A

Topoisomerase

DNA helicase

DNA polymerase:

Primer

Single strand binding protein (SSB)
Primase enzyme

RNAse H

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19
Q

what does topoisomerase do in DNA replication

A

Unwinds the double helix by relieving the supercoils

20
Q

what does DNA helicase do in DNA replication?

A

Separates the DNA apart, by breaking hydrogen bonds between bases, exposing nucleotides

21
Q

what does DNA polymerase do in DNA replication

A

Reads 3’ to 5’ and synthesises DNA on daughter strand 5’ to 3’ - creates DNA by working in paris to make 2 new strands of DNA. Starts at a primer

22
Q

what does a primer do in DNA replication

A

a short strand of DNA that is the start point for DNA synthesis as DNA polymerases can only add nucleotides on to an existing strand of DNA

23
Q

what does Single strand binding protein (SSB) do in DNA replication

A

keeps two strands of DNA apart whilst synthesis of new DNA occurs - prevents annealing to form double stranded DNA

24
Q

what does primase enzyme do in DNA replication

A

RNA polymerase that synthesises the short RNA primers needed to start the strand replication process

25
Q

what does RNAse H do in DNA replication

A

removes the RNA primers that previously began the DNA strand synthesis

26
Q

how fast is DNA replication

A

about 700 - 1000 bp per second

27
Q

how does DNA polymerase read the template strand

A

from 3’ to 5’

28
Q

how is DNA synthesised on the daughter strand

A

from 5’ to 3’

29
Q

why can DNA only be synthesised from 5’ to 3’

A

because DNA polymerase reads the template strand from 3’ to 5’
thus DNA is synthesised on the daughter strand from 5’ to 3’ since DNA runs antiparallel, the daughter strand is synthesised from 5’ to 3’ since phosphate at the 5’ is used by enzyme as a source of energy for reaction to occur (ACTIVATION ENERGY)

at one end of the molecule is an unreacted oxygen (3’) whereas at 5’ end there is a phosphate group thus DNA can only be synthesised from 5’ to 3’ since if it was 3’ to 5’ there would be no phosphate group available to provide the energy for the reaction to occur

30
Q

in what direction does the leading strand of DNA run

A

runs 3’ to 5’ towards the fork and is made continuously

31
Q

in what direction does the lagging strand of DNA run

A

runs 5’ to 3’ away from the fork and is made in small pieces called Okazaki fragments.

32
Q

what does a polymerase chain reaction (PCR) aim to do

A

to synthesise fragments of DNA
Its the basis for forensic testing

33
Q

how long does one cycle of PCR take

A

5 - 20 mins

34
Q

what are primers

A

short synthetic pieces of DNA that have complementary bases to DNA you are trying to synthesise/amplify

35
Q

outline the process of PCR

A
  • obtain region of DNA to be amplified
  • heat to separate strands
  • cool and add primers
  • add heat stable DNA polymerase
  • heat and cool (with primers and DNA polymerase present)
  • repeat heating and cooling cycle
  • multiple heating and cooling cycles
36
Q

what sources can damage our genomes

A

chemical
radiation
spontaneous insertion of incorrect bases during replication

37
Q

how does ionising radiation damage DNA

A

can damage bases
cause breaks in phosphate bonds

38
Q

how does UV damage DNA

A

damages bases
in particular the formation of thymine dimers

39
Q

how can DNA be repaired

A

base or nucleotide excision
mismatch repair

40
Q

give 2 drugs which inhibit nucleotide synthesis

A

methotrexate
5-fluorouacil

41
Q

give 2 drugs which inhibit DNA polymerase

A

cytosine arabinoside
acyclovir

42
Q

give 2 drugs which damage DNA templates

A

cyclophosphamide
cysplatin

43
Q

give 1 drug which inhibits DNA topoisomerase

A

doxorubicin

44
Q

what is the structure of a nucleotide

A

nitrogenous base
phosphate group
sugar

45
Q

what are the bonds between phosphate and sugar called

A

phosphodiester bonds

46
Q

what do phosphate bonds in nucleotides provide

A

energy

IMMS lectures (22 decks)

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