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Biology - mr ellis > module 2 - 3.9 DNA replication and the genetic code > Flashcards

module 2 - 3.9 DNA replication and the genetic code Flashcards

1
Q

what are the 4 requirements for DNA to be a genetic molecule?

A
  1. must carry information (this is the genetic code)
  2. must replicate (this is DNA replication)
  3. must allow for the information to change (this is mutation)
  4. must control the phenotype (this is gene expression using protein synthesis)
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2
Q

where is DNA information stored?

A

in the sequence of nitrogenous bases

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3
Q

the sequence of A, C, T, and G encodes information in the form of what to make what?

A

encodes information in the form of genes to make proteins

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4
Q

when are most genes only accessible?

A

when DNA is unwound (chromatin)

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5
Q

why is extreme accuracy of DNA replication necessary?

A

in order to preserve the integrity of the genome in successive generations

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6
Q

in eukaryotes, when does DNA replication occur?

A

during the S phase of the cell cycle (stationary phase)

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7
Q

what is the S phase?

A

when the cell is doing its job

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8
Q

what is the replication rate like in prokaryotes/ eukaryotes?

A

prokaryotes - faster rate, lower fidelity (accuracy)
eukaryotes - slower rate, higher fidelity (accuracy)

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9
Q

what is semi-conservative DNA replication?

A
  • one strand of a double helix is passed on unchanged to each daughter cell
  • ‘conserved’ strand acts as a template for synthesis of a new, complementary strand by DNA POLYMERASE
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10
Q

what is N14?

A

non-radioactive isotope of nitrogen

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11
Q

what is N15?

A

radioactive isotope of nitrogen

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12
Q

where does DNA replication begin?

A

at the origin (methionine)

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13
Q

what is the origin within prokaryotic cells?

A

single circular DNA molecule or chromosome and so single origin of DNA replication

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14
Q

where is the origin within eukaryotic cells?

A

eukaryotic cells have multiple, linear DNA molecules/ chromosomes & each DNA molecule has multiple origins of DNA replication

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15
Q

where does DNA replication always go from and to?

A

5’ to 3’ direction

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16
Q

what does DNA polymerase require before synthesis can be initiated?

A

a free 3’ hydroxyl group

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17
Q

what is the difference between the old and new DNA strand to do with the way they are read?

A

the new DNA template strand is read in a 3’ to 5’ direction, whereas the old strand is read from 5’ to 3’ direction

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18
Q

why is DNA replication discontinuous?

A

the DNA forms complementary fragments of the DNA molecule from 5’ to 3’ on the new strand
(synthesises in sections)

19
Q

why is DNA replication continuous?

A

the DNA forms its complementary strand from 3’ to 5’ continuously on the new strand

20
Q

how are complimentary base pairs paired together?

A

collision theory

21
Q

what is the enzyme that untwists the DNA?

A

helicase

22
Q

what is DNA polymerase in a DNA molecule?

A

the active site

23
Q

where does DNA replication happen?

A

a replication fork

24
Q

what is a replication fork?

A

the structure that forms within the long helical DNA during DNA replication

25
Q

what is a replication fork created by?

A

helicases, which break the hydrogen bonds holding the 2 DNA strands together in the helix

26
Q

what happens once the hydrogen bonds are broken?

A

causes 2 strands of DNA and has 2 branching ‘prongs’

27
Q

what happens when the 2 strands then serve as a template for the leading and lagging strands?

A

strands will be created as DNA polymerase which matches complementary nucleotides to the templates

28
Q

what happens when the helicase unwinds the DNA at the replication fork? what does this result in?

A

the DNA ahead is forced to rotate
results in a build up of twists and tension in the DNA ahead

29
Q

what are topoisomerases?

A
  • enzymes that temporarily break the strands of DNA, relieving tension caused by unwinding 2 strands of DNA helix
  • they add negative supercoils to DNA helix
30
Q

what does primase do?

A
  • creates short strands of RNA complementary to DNA strand
  • allows DNA polymerase to bind to DNA and begin replicating it
31
Q

what happens if you have a purine + purine?

A

base pair too thin

32
Q

what happens if you have pyrimidine + pyrimidine?

A

base pair too wide

33
Q

how many mistakes does DNA polymerase make?

A

1 in every billion base pairs copied

34
Q

what does DNA polymerase do?

A

proof-reads the base pairs, corrects mistakes in the newly synthesised DNA

35
Q

what happens when an incorrect base pair is recognised?

A

the DNA polymerase moves backwards by one base pair of a DNA

36
Q

what does the 3’-5’ exonuclease activity of the DNA polymerase allow?

A

allows the incorrect base pairs to be exercised

37
Q

what is a mutation within DNA?

A

mistakes lead to random and spontaneous changes in the base sequence of the newly synthesised strand

38
Q

what are the differences between polypeptides and proteins?

A

polypeptides: chain of amino acids
proteins: chain of amino acids, virtually all enzymes are proteins, functional molecules

39
Q

what is the genetic code?

A

set of rules used by all living cells to translate the information encoded in genetic material, into proteins

40
Q

how is translation accomplished?

A
  • by the ribosome which links to amino acids in an order specified by mRNA
  • uses tRNA molecules to carry amino acids
41
Q

what are 4 features of the genetic code?

A
  • it is a triplet code (codon)
  • it is universal among all living organisms
  • it is a degenerate code (more codes than needed)
  • it establishes the reading frame
42
Q

where does is reading frame always set within polypeptides?

A

methionine (ATG)

43
Q

what is the degenerate code?

A
  • the redundancy of the genetic code (more codes than needed)
  • the genetic code has redundancy but no variation
44
Q

how is the reading frame defined/started?

A
  • defined/started by the initial triplet of nucleotides where translation starts
  • frame is a run of SUCCESSIVE, NON-OVERLAPPING CODONS

Biology - mr ellis (76 decks)

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