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Biology A level > 2.1.3 nucleotides and nucleic acids > Flashcards

2.1.3 nucleotides and nucleic acids Flashcards

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1
Q

what is a nucleotide made from

A

a nitrogenous base
a pentose sugar
a phosphate group

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2
Q

what are nucleotides

A

the monomers of DNA and RNA

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3
Q

what bases can be found in DNA

A

adenine, thymine, cytosine, guanine

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4
Q

what pentose sugar is in DNA

A

deoxyribose

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5
Q

what is a purine base

A

contains 2 carbon nitrogen rings joined together

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6
Q

what bases are purines

A

adenine and guanine

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7
Q

what is a pyramidal base

A

only contains 1 carbon nitrogen ring so they are smaller

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8
Q

what bases are pyramidal

A

thymine and cytosine

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9
Q

what is the pentose sugar in RNA

A

ribose

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10
Q

what base is different in RNA

A

thymine is uracil instead

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11
Q

how is energy released from ATP

A

the phosphate bond stores energy that is released when ATP is broken down into ADP and Pi

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12
Q

what does ATP and ADP stand for

A

ATP - adenine triphosphate
ADP - adenine diphosphate

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13
Q

what are the bonds between nucleotides

A

phosphodiester bonds

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14
Q

what is the chain of sugar and phosphates called

A

the sugar-phosphate backbone

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15
Q

what is the structure of DNA

A

a double stranded helix

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16
Q

how are the two DNA strands joined together

A

hydrogen bonds between complementary bases (complementary base pairs)

17
Q

how many hydrogen bonds between A and T

A

2

18
Q

how many hydrogen bonds between C and G

A

3

19
Q

how is the helix shape formed

A

antiparallel strands twist the DNA

20
Q

how do we purify DNA

A

break up cells in sample
add detergent (break down cell membranes), salt (binds to DNA and clumps it together) and distilled water to the sample
heat in a water bath at 60 degrees for 15 mins to stop enzymes working
then add to ice bath to cool then filter
add protease to break down proteins and RNAase to break down RNA
drop ethanol down the side forming a layer on top, DNA forms a white precipitate

21
Q

what is semi conservative replication

A

half the strand in each copy are from the original piece of DNA

22
Q

how does DNA copy itself

A

DNA helicase breaks hydrogen bonds between strands
each original strand acts as a template for a new strand. free floating nucleotides join to exposed bases by complementary base pairing
nucleotides of new strand are joined by DNA polymerase to make phosphodiester bonds between nucleotides and hydrogen bonds form between strands

23
Q

what is a gene

A

a sequence of DNA nucleotides that codes for the sequence of amino acids in a polypeptide

24
Q

how many bases codes for a single amino acid

A

3 it is called a triplet

25
Q

what is mRNA

A

messenger RNA
it is made in the nucleus it carries the genetic code from DNA in the nucleus to the cytoplasm for translation

26
Q

what is tRNA

A

transfer RNA
found in the cytoplasm it has an amino acid binding site at one end of the sequence of 3 base pairs at the other end called an anticodon

27
Q

what is rRNA

A

ribosomal RNA
forms the two subunits in a ribosome and catalyses the formation if peptide bonds between amino acids

28
Q

why is the genetic code said to be non overlapping

A

each base triplet is read in sequence separate from the triplet before and after it. base triplets do not share bases

29
Q

why is the genetic code said to be degenerate

A

there are more possible combinations of triplets than there are amino acids this means that some amino acids are coded for by multiple codons.
there are also start and stop codons at the ends of the codons

30
Q

why is the genetic code said to be universal

A

the same specific codons code for the same amino acids in all living things

31
Q

what is the first stage of protein synthesis

A

transcription

32
Q

what is the purpose in transcription

A

an mRNA copy of a gene is made in the nucleus

33
Q

what are the steps of transcription

A

RNA polymerase breaks the hydrogen bonds separating the strands. one of the strands and the DNA molecule is used as a template
the RNA polymerase lines up free RNA nucleotides alongside the template using complementary base pairing (U is used instead of T)
RNA nucleotides bond to make an mRNA molecule
hydrogen bonds reform between DNA strands

34
Q

what is the second stage of protein synthesis

A

translation

35
Q

what is the purpose in translation

A

amino acids are joined together to make a polypeptide

36
Q

what are the steps of transcription

A

mRNA attaches to a ribosome
tRNA carries amino acids to ribosome
a tRNA molecule with a complementary anticodon to the start codon and attaches itself by complementary base pairing
a peptide bond forms between each amino acid and tRNA moves away.
this continues until stop codon
polypeptide moves away from ribosome when done.

Biology A level (13 decks)

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