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a level biology > nucleic acids > Flashcards

nucleic acids Flashcards

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

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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’)

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25
Q

what are the base pairing rules for adenine + thymine ?

A

they form 2 hydrogen bonds

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26
Q

what are the base pairing rules for cytosine + guanine ?

A

they form 3 hydrogen bonds

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27
Q

what is the base pairing rule known as ?

A

complementary base pairing

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28
Q

how do purines and pyrimidines pair together ?

A
  • a small purine always joins to a large pyrimidine
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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

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30
Q

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

A

in the form of a code

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31
Q

what does ribonucleic acid (RNA) do ?

A

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

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32
Q

why can’t DNA leave the nucleus ?

A

it is long and to large

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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

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34
Q

what is messenger RNA ?

A

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

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35
Q

which pentose sugar is used in RNA ?

A

ribose

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36
Q

which base is replaced with what ?

A

thymine with uracil

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37
Q

what are the bonds in RNA nucleotides ?

A

phosphodiester bonds

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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

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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

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40
Q

why do cells divide ?

A

growth
repair of tissues

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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)

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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
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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

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44
Q

which bonds are broken when the 2 DNA strands separate ?

A

hydrogen bonds holding complementary bases together

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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

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46
Q

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

A

phosphodiester bonds

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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
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48
Q

what does DNA helicase do during DNA replication ?

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

how does helicase unwind the DNA ?

A

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

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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

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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
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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

how do organisms pass genetic information from one generation to the next ?

A

via genetic code

56
Q

what is genetic code ?

A

the sequence of bases in DNA which are the instructions for the sequences of amino acids in the production of proteins

57
Q

why is the production of proteins important ?

A

they are the foundations for the different physical and biochemical characteristics of living things

58
Q

where are the instructions to build up proteins that DNA carries contained ?

A

in the sequences of bases along the chain of nucleotides which make up the 2 strands of DNA

59
Q

what is the code in the base sequences called ?

A

a triplet code

60
Q

what is a triplet code ?

A

a sequence of 3 bases, called a codon

61
Q

what is a codon ?

A

a sequence of 3 bases

62
Q

what is a gene ?

A

a section of DNA that contains the complete sequence of codons to code for an entire protein

63
Q

the genetic code is universal - what does this mean ?

A

all organisms use it

64
Q

how many codons are possible to make ?

A

64
( 4 bases - 4x4x4)

65
Q

what types of codons are there ?

A

start codon
stop codon

66
Q

what is the start codon ?

A

the codon which signals the start of a sequence which codes for proteins

67
Q

if the codon is in the middle of a gene what does it code for ?

A

amino acid methionine

68
Q

what do stop codons do ?

A
  • they don’t code for any amino acids
  • they signal the end of a sequence
69
Q

why are start codons important ?

A

to ensure the codons are read from base 1 not bases 2/3 so the genetic code does not overlap

70
Q

how is the genetic code degenerate ?

A

there are lots more codons than amino acids so amino acids can be coded for by more than 1 codon

71
Q

where does protein synthesis happen ?

A

ribosomes

72
Q

how is protein syntheisis happening in the ribosomes a problem for DNA ?

A

it is too large to leave the nucleus

73
Q

how do we solve the problem of DNA being too large to leave the nucleus in protein synthesis ?

A

bases sequences of genes are copied and transported to the site of protein synthesis via transcriptions

74
Q

what happens during transcription -

A

produces shorter molecules of RNA

75
Q

what is the process of transcription ?

A

1 - a section of DNA with the desired gene unwinds & unzips beginning the start of a codon
2 - hydrogen bonds are broken
3 - only 1/2 strands of DNA contains desired gene
4- the other strand is complementary & the template strand
5 - free RNA nucleotides pair with complementary bases on antisense strand
6 - phosphodiester bonds are formed between RNA molecules via RNA polymerase
7 - transcription stops at the end of a gene
8 - completed short strand is mRNA
- mRNA detaches from DNA & leaves nucleus
9 - DNA double helix reforms and mRNA goes to ribosome

76
Q

which enzyme is involved in unzipping the DNA strand ?

A

helicase

77
Q

what is the sense strand ?

A

the section and strand of DNA which contains the correct protein code

78
Q

what is the antisense strand ?

A

the strand which has the complementary bases to the sense strand

79
Q

what is the antisense strand also known as ?

A

the template strand

80
Q

what does the template strand allow ?

A

for the complementary RNA strand to carry the same bases as the sense strand

81
Q

the free RNA nucleotides pair with the complementary bases on the antisense strand, which bases are different from DNA ?

A

thymine is swapped with uracil

82
Q

which enzyme forms the phosphodiester bonds between the RNA molecules ?

A

RNA polymerase

83
Q

which type of RNA forms the short strand of DNA ?

A

messenger RNA

84
Q

after transcription, what happens ?

A

translation

85
Q

how are ribosomes structured ?

A

there is 1 larger subunit and 1 smaller subunit composed of equal amounts of protein

86
Q

what does ribosomal RNA do ?

A

maintain the structural stability of the protein synthesis sequence and plays a biochemical role of catalysing the reaction

87
Q

how is rRNA formed ?

A

by the ribosomal subunits

88
Q

what does the mRNA do after leaving the nucleus ?

A

it binds to the specific site on a small ribosome subunit
- the ribosome holds the mRNA in position whilst it is decoded into a sequence of amino acids

89
Q

what is tRNA used for ?

A

used for the translation of mRNA

90
Q

what is the structure of tRNA ?

A
  • composed of a strand of RNA folded into 3 bases
91
Q

what are the 3 bases which fold into RNA called ?

A

the anticodon

92
Q

what are the steps of translation ?

A
  • anticodon binds to the complementary codon on mRNA via base pairing rules
  • tRNA carries the amino acid corresponding to that codon
  • when tRNA anticodons bind to complementary codons amino acids are brought together in the correct sequence forming the primary structure of protein coded for by mRNA
  • amino acids are added one at a time
  • ribosomes act as a binding site for mRNA and tRNA catalyse the assembly of proteins
93
Q

summaries translation ?

A
  • mRNA binds to small subunits on ribosomes at its start codon
  • tRNA with complementary anticodon binds to start codon - this tRNA carries methionine
  • another tRNA with anticodon carries the corresponding amino acid to corresponding codon on mRNA
  • first amino acid transfers to amino acid forming a peptide bond
  • ribosomes move along mRNA releasing tRNA forming proteins
94
Q

what is the start codon ?

A

AUG

95
Q

what enzyme catalyses the peptide bonds which form between tRNA called in translation ?

A

peptidyl transferase

96
Q

what happens at the end of translation ?

A
  • amino acids are added to the chain of amino acids each time until the ribosome reaches the end of mRNA at the stop codon
  • polypeptide is released
97
Q

in translation, what stage of the protein is formed ?

A

amino acids join together to form the primary structure which fold into the secondary and tertiary structure

98
Q

what do the folding and the bonds of the protein determined by ?

A

the sequence of amino acids in the primary structure

99
Q

how are proteins made so they can be simultaneously identical ?

A

many ribosomes follow on mRNA behind the first

100
Q

what do cells need energy for ?

A
  • synthesis
  • transport
  • movement
101
Q

how do cells need synthesis ?

A

e.g, large molecules such as proteins

102
Q

why do cells need transport , e.g

A

pumping molecules or ions across cell membranes by active transport

103
Q

give an example of when movement is used in cells ?

A

protein fibres in muscles fibres which cause contraction

104
Q

what does ATP stand for ?

A

adenosine triphosphate

105
Q

how is ATP structured ?

A

3 phosphate groups
pentose sugar - ribose
nitrogenous base

106
Q

what is the base always in atp ?

A

adenine

107
Q

what is ATP used for ?

A

energy transfer in all cells and living things

108
Q

what is ATP known as ?

A

universal energy currency

109
Q

how is energy released ?

A

when bonds are formed

110
Q

energy is needed to break bonds however only a small amount why is this useful ?

A

not a lot of energy is needed to break the bond holding the last phosphate group, but lots of energy is released

111
Q

what do the released phosphate groups do (ATP)?

A

undergo bond formation - 30.6 KJ energy released

112
Q

what type of reaction released energy ?

A

hydrolysis

113
Q

hydrolysis of ATP is coupled with energy requiring reactions - what does this mean ?

A

it happens simultaneously with energy requiring reactions

114
Q

what is ATP hydrolysed into ?

A

adenine diphosphate + a phosphate ion

115
Q

why isn’t ATP a good long term memory store ?

A

instability of phosphate bonds in atp

116
Q

what are better stores of energy ?

A

fats and carbohydrates

117
Q

why are fats and carbohydrates better stores of energy ?

A

energy released in the breakdown of these molecules create ATP via phosphorylation

118
Q

what is phosphorylation ?

A

a phosphate molecule is reattached to an ADP molecule

119
Q

what kind of reaction is phosphorylation ?

A

condensation reaction

120
Q

why don’t cells store large amounts of ATP ?

A

it is instable

121
Q

why is ATP rapidly formed ?

A

phosphorylation

122
Q

what kind of store is ATP ?

A

a good immediate energy store

123
Q

what are the properties of ATP ?s

A

small
water soluble
contains bonds between phosphates with intermediate energy
releases energy in small quantities
easily regenerated

124
Q

why is ATP being small good ?

A

moves easily in and out of cells

125
Q

why is ATP being water soluble good ?

A

energy requiring processes often happen in aqueous environments

126
Q

why is it being a good intermediate energy source good ?

A

large enough to be useful for cellular reactions
not too large so energy is wasted as heat

127
Q

why is atp releasing energy in small quantities good ?

A

quantities are suitable to most cellular needs
energy isn’t wasted as heat

128
Q

why is atp being easily regenerated good ?

A

it can be recharged with energy

a level biology (6 decks)

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