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CELS191 > DNA replication > Flashcards

DNA replication Flashcards

1
Q

What is semi-conservative DNA replication?

A

Semiconservative replication would produce two copies that each contained one of the original strands and one new strand

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2
Q

What is direction of DNA synthesis?

A

DNA or RNA is always synthesised in the 5’ to 3’ direction

- The 3rd OH carbon group is very reactive, and nucleotides are added to it

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3
Q

What way does the parental stand run?

A

In the 3’ to 5’ direction

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4
Q

What are origins of replication?

A

Where replication originates along the chromosome
- Multiple origins of replication along the chromosomes (want to pull the two DNA strands apart to expose the DNA template so two H bonds is origin to allow this to be easier)

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5
Q

What does DNA polymerase 3 do?

A

Progressive addition of new nucleotides in the 5’ to 3’ direction
- Needs a 3’ OH group to start

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6
Q

What does primase do?

A

Provides a starting point for nucleotide addition (origin of replication)
- Provides the primer that has a 3’ OH group

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7
Q

What does helicase do?

A

Unwinds the helical double strand (to give parental templates)

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8
Q

What does topoisomerase do?

A

Release of tension generated by unwinding the DNA helix

- Rejoins DNA strands

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9
Q

What does single stranded DNA binding protein do?

A

Function 1: protect the DNA from being degraded by other enzymes.

Function 2: Keep the DNA single stranded (keep them from snapping back together)

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10
Q

What does DNA polymerase 1 do?

A

Carries out two activity:
- RNase H is an endonuclease enzyme that recognises DNA:RNA hybrids and degrades the RNA part (RNase activity)

  • Synthesises DNA by adding nucleotides (complementary to the parental DNA template of the lagging strand (DNA polymerase activity)
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11
Q

What does DNA ligase do?

A

Joining of ends of newly synthesised fragments together (creates phosphodiester bonds)

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12
Q

What type of bond links Okazaki fragments?

A

Phosphodiester

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13
Q

When can errors be corrected during DNA synthesis?

A
  • During replication, using an EXOnuclease

- After replication, using a endonuclease

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14
Q

How does exonuclease work?

A

DNA chopping enzyme which can only chop nucleotides off the ends (either from 3’ or 5’ end depending on the type)

  • Activity of DNA pol 3 (proofreading of bases against template during DNA replication)
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15
Q

How does endonuclease work?

A
  • Works when a incorrect base is not removed by pol 3 during DNA replication, when radiation occurs or when bases are chemically modified
    Section of the DNA is removed and is replaced by DNA pol, ligase then joins the strands again.
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16
Q

What happens if a error is not corrected?

A

Strand then carries the error and it is used as a template - errors carries on and becomes permeant (mutation)

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17
Q

What is PCR?

A

Polymerase chain reaction

  • Allows many copies of a particular DNA region
  • There will be a rapid exponential increase of DNA molecules
  • Method is driven by different temperatures
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18
Q

What is the DNA templates roll in PCR?

A

DNA molecule to which complementary nucleotides can be matched to
make identical copies via DNA synthesis

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19
Q

What is the primers role in PCR?

A

Provides a free ‘3 OH group, the chemical group that is essential to initiate DNA synthesis
Defines the region of the DNA molecule to be replicated

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20
Q

What is DNA polymerase’s role in PCR?

A

Enzyme which adds nucleotides, (complementary to the DNA template),
and joins them together forming a phosphodiester bond

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21
Q

What are dNTPs role in PCR?

A 
Free nucleotides (equal amount of A, G, C and G) - the building blocks
used by the DNA polymerase)
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22
Q

What happens during disjunction?

A

Chromosomes don’t seperate properly during meiosis, happens during meiosis 1 and 2

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23
Q

What happens in disjunction in meiosis 1?

A

Homologous pairs don’t disjoin, so both go into some meiosis 1 product

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24
Q

What happens in disjunction in meiosis 2?

A

1 product will have to many chromosomes and 1 will have too little

25
Q

What is polyploidy?

A

The possession of multiple sets of chromosomes
- Chromosomes don’t pair up properly during meiosis as they are not exact homologs of each other, so they double to make an exact homologous

26
Q

What is deletion?

A

A deletion removes chromosomal segment

27
Q

What is an inversion?

A

An inversion reverses a segment within a chromosome

28
Q

What is a duplication?

A

A duplication repeats a segment

29
Q

What is a translocation?

A

A translocation moves a segment from one chromosome to a nonhomologous chromosome

30
Q

What is a meiosis synapse?

A

Recognising pieces that are homologous to each other.

If one is flipped around they can’t pair up properly, which can lead to deletions and insertions - In crossing over.

31
Q

Are there barr bodies present in XY individuals? Why/why not?

A

No, as they only have one X chromosome.
There sex chromosomes are different and so can remain active at the same time - no need to condense one, so shows no barr body

32
Q

Are there barr bodies present in XX individuals? Why/why not?

A

Yes, as they have more then one X chromosome. This means that one needs to be inactivated in order for proper development.

33
Q

What are the specific stop codons?

A

UAA, UAG and UGA

34
Q

What is the specific start codon?

A

AUG

35
Q

What is tRNA?

A

Transfer RNA

  • A single-strand RNA
  • 70-80 nucleotides in length
  • At least one tRNA for each amino acids
  • Each tRNA has a region which can bind an amino acid AND a region which can interact with mRNA
36
Q

How is a tRNA charged?

A

An enzyme recognises both a specific amino acids and the correct tRNA for this amino acids and joins them together with a covalent bond

37
Q

What is translation?

A

The process of synthesising proteins from mRNA instructions

38
Q

What is the anatomy of a ribosome?

A

Has a small and a large subunit

- Within the large subunit there are three binding sites for tRNA (E,P,A)

39
Q

What happens in the initiation stage of Translation?

A

The small ribosomal subunits finds the initiation AUG codon on the mRNA. The AUG codon is positioned in the P site of the small ribosomal subunit.

  • A tRNA ‘charged’ with the amino acid Methionine binds to the P site
  • The large ribosomal subunit attaches above small subunit
40
Q

What happens during elongation of Translation?

A
  1. A charged tRNA, with an anticodon complementary to the A codon lands in the A site
  2. The ribosome will break the bond that binds the amino acids to the tRNA in the P site, transfer the amino acid to the newly arrived amino acid (attached to the tRNA in the A site) and form a peptide bond between them.
    - While the tRNAs are bound to the mRNA (in the P and A sites), the ribosome moves three nucleotides down the mRNA

The tRNA with the growing amino acid chain up in the P site (was in the A site) so that the chain of amino acids can exit through the tunnel above the P site
‘Uncharged’ tRNA in the E site (was in the P site)
3. In the E site, the ‘uncharged’ tRNS detaches from its anticodon and is expelled. A new ‘charged’ tRNA with an anticodon complementary to the next A site codon enters the ribosome at the A site and the process is repeated.

41
Q

What happens in termination of translation?

A
  1. When the ribosome reaches a stop codon, a protein called release factor enters the A site
  2. The release factor breaks the bonds between the P site tRNA (using water) and the final amino acid. This causes the polypeptide chain to detach from its tRNA and the newly made polypeptide is released
  3. The small and large ribosomal subunit dissociate from the mRNA and each other.
42
Q

How do we predict genotypes in a population?

A

p^2 + 2pq + q^2 = 1
q = recessive allele
p = dominant allele

43
Q

Why might we need to estimate frequencies of genotypes in a population?

A
  1. To predict how many individuals will inherit a genetic disease
  2. To estimate the proportion of individuals who are ‘carriers’ of a genetic disease
44
Q

What is genetic drift?

A

A random change in allele frequencies due to randomness

- More evident in smaller populations

45
Q

What is the bottleneck effect?

A

Population reduction of bottleneck effect occurs (natural disasters e.g. disease, earthquake)

some allele are completely lost, some alleles now rare - due to only some individuals surviving

46
Q

What is the founder effect?

A

A small number is introduced Reduced genetic diversity due to small amount of alleles in new population

Some alleles won’t be transferred from the large population to small population
Some alleles may be in very big frequencies

47
Q

What is stabilising selection?

A

Reduces variation but does not change the mean

Favours the average, decreases the extremes

48
Q

What is directional selection?

A

Changes the mean value towards on extreme - far left or far right

49
Q

What is disruptive selection?

A

Favours the two extremes producing two peaks

50
Q

What is a Cline?

A

The gradual geographic change in genetic/ phenotypic composition
- Natural selection acting differently in different geographical areas

51
Q

What is migration?

A

An individual from another population successfully mates (i.e. contributes gametes) to the gene pool

  • Brings new alleles
  • Charges proportions of existing alleles
  • Makes two populations more similar
52
Q

What is the 3 steps of PCR?

A

Denaturation, Annealing and extension

53
Q

What happens during Denaturation in PCR?

A

Temperature is increased to separate DNA strands

54
Q

What happens during Annealing in PCR?

A

Temperature is decreased to allows primers to base pair to complementary DNA template

55
Q

What happens during Extension in PCR?

A

Polymerase extends primer to from a new DNA strand

  • An exponential increase in DNA molecules
  • Adds complementary bases in the 5’ to 3’ direction
56
Q

What is familial down syndrome and what is it caused by?

A

Translocation of an extra chromosome 21 onto one of the acrocentric chromosomes, usually chromosome 14. Carriers of this translocation phenotypically normal by produce a variety of gametes which can give rise to downs syndrome, normal or more carrier zygotes (as well as zygote lethality)

57
Q

What is downs syndrome caused by?

A

A trisomy - three copies of chromosome 21 instead of two

- Happens via disjunction

58
Q

What is turners syndrome?

A

Only has one sex chromosome (XO)

- Causes by disjunction

59
Q

What is Klinefelters syndrome?

A

Has an extra X chromosome (XXY)

- Caused by disjunction

CELS191 (15 decks)

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