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a level biology > nucleic acids > Flashcards

nucleic acids Flashcards

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1
Q

what are nucleic acids ?

A

large molecules found in cell nuclei

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2
Q

what are the 2 types of nucleic acids ?

A

DNA
RNA

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3
Q

what is the overall roles of RNA and DNA ?

A

storage and transfer roles of genetic information
the synthesis of polypeptides

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4
Q

what is the overall structure of nucleic acids ?

A
  • contain carbon hydrogen oxygen nitrogen and phosphorus
  • large polymers formed from nucleotides linked together in a chain
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5
Q

what is the structure of a nucleotide ?

A
  • made up of a pentose monosaccharide (5 carbon atoms)
  • phosphate group
  • nitrogenous base
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6
Q

what is a nitrogenous base ?

A

a complex organic molecule containing 1/2 carbon rings + nitrogen

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7
Q

how are nucleotides linked together ?

A
  • condensation reactions
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8
Q

how do the nucleotides link together ?

A
  • phosphate group of a 5th carbon of a pentose sugar covalently bonds with the hydroxyl group of the 3rd carbon of pentose sugar of another nucleotide
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9
Q

what bonds form between nucleotides ?

A

phosphodiester bonds

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10
Q

what do the polynucleotides form ?

A

a long strong sugar backbone with a base attached to each sugar

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11
Q

what reaction reverses polynucleotides being linked together ?

A

hydrolysis reaction

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12
Q

what is the sugar in DNA ?

A

deoxyribose

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13
Q

how many bases in the nucleotides of DNA ?

A

4

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14
Q

what 2 groups are the bases split into ?

A

purines
pyrimidines

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15
Q

what are pyrimidines ?

A

smaller bases with single ring carbon structures

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16
Q

what are purines ?

A

larger bases with double ring carbon structures

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17
Q

which bases are pyrimidines ?

A

thymine
cytosine

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18
Q

which bases are purines ?

A

adenine
guanine

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19
Q

how is DNA a double helix ?

A

it is made up of 2 strands of polynucleotides coiled into a helix

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20
Q

how are the 2 strands of DNA held together ?

A

hydrogen bonds between bases (ladder rungs)

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21
Q

strands of DNA are described as antiparallel, what does this mean ?

A

the 2 strands run in opposite directions

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22
Q

what does the pairing between bases allow DNA to do ?

A

be copied and transcribed

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23
Q

how do the bases pair ?

A

adenine + thymine
guanine + cytosine

24
Q

each strand of DNA has a phosphate group (5’) at one end. what is the other group at the other end ?

A

hydroxyl (3’)

25
Q

what are the base pairing rules for adenine + thymine ?

A

they form 2 hydrogen bonds

26
Q

what are the base pairing rules for cytosine + guanine ?

A

they form 3 hydrogen bonds

27
Q

what is the base pairing rule known as ?

A

complementary base pairing

28
Q

how do purines and pyrimidines pair together ?

A
  • a small purine always joins to a large pyrimidine
29
Q

why does a small purine always bind to a larger pyrimidine ?

A

to maintain a constant distance between the DNA backbones - parallel polynucleotide chains

30
Q

how does the sequence of bases along DNA carry genetic information ?

A

in the form of a code

31
Q

what does ribonucleic acid (RNA) do ?

A

play a role in the transfer of genetic information from DNA to proteins

32
Q

why can’t DNA leave the nucleus ?

A

it is long and to large

33
Q

how do we overcome the issue of DNA not being able to leave the nucleus ?

A

a short section of the long DNA molecule corresponding to the desired gene is transcribed into mRNA

34
Q

what is messenger RNA ?

A

a polymer composed of nucleotide monomers - a shorter replication of the desired gene needed from the DNA

35
Q

which pentose sugar is used in RNA ?

A

ribose

36
Q

which base is replaced with what ?

A

thymine with uracil

37
Q

what are the bonds in RNA nucleotides ?

A

phosphodiester bonds

38
Q

why are RNA molecules used to transfer genetic information ?

A

they are small enough to leave the nuclear pores and travel to the ribosomes in the cytoplasm where protein synthesis occurs

39
Q

what happens to RNA molecules after protein synthesis ?

A

they are degraded in the cytoplasm
phosphodiester bonds are hydrolysed and RNA nucleotides are released and reused

40
Q

why do cells divide ?

A

growth
repair of tissues

41
Q

what is produced from cell division ?

A

2 daughter cells which are genetically identical to the parent cells and each other (identical base sequence)

42
Q

what happens in preparation of DNA replication to the strands of DNA ?

A
  • 2 strands of DNA unwinds and unzips
  • separated strands become template strands
43
Q

what is a template strand ?

A

a single strand of DNA which acts as a template for the creation of a new double strand DNA molecule

44
Q

which bonds are broken when the 2 DNA strands separate ?

A

hydrogen bonds holding complementary bases together

45
Q

what happens to the complementary strands of DNA ?

A

free DNA nucleotides pair with the complementary bases which have been exposed and hydrogen bonds form

46
Q

when complementary base pairing in DNA replication had occurred how do new nucleotides join to other nucleotides ?

A

phosphodiester bonds

47
Q

what is semi conservative replication and how does this happen with DNA replication ?

A
  • 2 molecules of DNA are produced each with 1 new and 1 original strand from the original DNA
48
Q

what does DNA helicase do during DNA replication ?

A
  • helps to unwinds the 2 separate strand of DNA
49
Q

how does helicase unwind the DNA ?

A

it travels along the DNA backbone, catalysing reactions that break the hydrogen bonds (unzipping)

50
Q

what does DNA polymerase do in DNA replication ?

A

catalyse the formation of phosphodiester bonds between free nucleotides which pair with newly exposed bases

51
Q

what is continuous replication ?

A
  • DNA polymerase moves along the template strand in the same direction
  • it can only bind to the 3’ end so moves in a 3-5 direction
  • DNA only unzips in 1 direction so DNA polymerase has to replicate each of the template strands in opposite directions
  • strand which is unzipped from the 3’ end is continuously replicated as strands unzip
52
Q

what is discontinuous replication ?

A
  • the other strand is unzipped from the 5’ end so DNA polymerase and has to wait until a section of that strand has been unzippped then work back along that strand
  • DNA is joined in sections which are then joined
53
Q

how does a mutation occur ?

A

sequences of bases aren’t matched correctly
random
spontaneous

54
Q

what could happen if there is a mutation ?

A

an incorrect sequence may occur in a newly copied strand

55
Q
A

a level biology (4 decks)

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