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A-level Biology > Chapter 3 - Nucleic Acids > Flashcards

Chapter 3 - Nucleic Acids Flashcards

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1
Q

what are nucleotides composed of

A
  • one phosphate group
  • one pentose sugar
  • one organic nitrogenous base
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2
Q

how are the subunits joined to form a nucleotide molecule

A

covalent bonds

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3
Q

DNA vs. RNA nucleotide number of strands

A

DNA: 2
RNA: 1

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4
Q

DNA vs. RNA nucleotide pentose sugar

A

DNA: deoxyribose
RNA: ribose

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5
Q

DNA vs. RNA nucleotide bases

A

DNA: A, T, C, G
RNA: A, U, C, G

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6
Q

what is a purine, name the bases

A
  • 2 nitrogen containing rings
    adenine and guanine
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7
Q

what is a pyramidine, name the bases

A
  • 1 nitrogen containing ring
    cystosine, thymine, uracil
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8
Q

what is a nucleotide

A

the monomer from which nucleic acids are made

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9
Q

what are the complementarty base pairs

A

cytosine and guanine
adenine and thyamine (DNA)
adenine and uracil (RNA)

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10
Q

how are the complementary base pairs joined

A

weak hydrogen bonds

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11
Q

how many hydrogen bonds between complementary base pairs

A

A-T (2)
C-G (3)

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12
Q

how are polynucleotides formed

A
  • condensation reaction
  • phosphdiester bond forms between the 5’ phosphate group of one nucleotide and the 3’ hydroxyl group on the sugar of another
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13
Q

describe the structure of DNA

A
  • polymer of nucleotides
  • 2 antiparallel helical chains of nucleotides linked by hydrogen bonds between complementary base pairs
  • coiled to form a double helix
  • stable structure
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14
Q

what is the importance of complementary base pairing

A
  • same distance between each pair of bases
  • allows faithful DNA replication
  • high fidelity of replication: bases can only pair with a specific other base
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15
Q

define high fidelity of replication

A

making an accurate copy

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16
Q

when is DNA replicated

A

interphase

17
Q

why is DNA replication semi-conservative

A
  • one original strand that acts as a template
  • one newly formed strand
  • 50-50
18
Q

what method did meselson and stahl use to separate DNA by its density

A

centrifugation

19
Q

what enzymes are involved in DNA replication

A
  • DNA helicase
  • DNA polymerase
20
Q

role of helicase in DNA replication

A
  • unwinds the double helix
  • breaks hydrogen bonds between complementary base pairs
  • separates the 2 strands
21
Q

what happens once the strands of DNA have been ‘unzipped’

A
  • both strands are used as templates
  • complementary base pairing occurs between template strands and free nucleotides
22
Q

role of DNA polymerase in DNA replication

A

joins adjacent nucleotides by phosphodiester bonds formed in condensation reactions

23
Q

what is mutation

A
  • replication errors
  • incorrect sequence of nucleotides when bases arent exactly matched
24
Q

what is the triplet code

A

3 bases code for an amino acid

25
Q

why is it the triplet code, not doublet?

A

enough combinations to code for the 20 needed amino acids

26
Q

why is the genetic code universal

A

same 4 DNA bases in all organisms

27
Q

how is the genetic code degenerate

A

more than one triplet codes for the same amino acid

28
Q

how is the genetic code non-overlapping

A
  • start codon AUG
  • each triplet only read once, dont share bases
29
Q

significance of AUG

A

ensures the code is read from base 1, not 2 or 3

30
Q

function of base sequence in DNA

A

stores genetic information

31
Q

function of large size and helix of DNA

A

large size: can store alot of genetic info
helix: compact

32
Q

what is ATP

A
  • adenosine triphosphate
  • used for energy transfer in all cells of all living things
33
Q

structure of ATP

A
  • nitrogenous base (always adenine)
  • pentose sugar (ribose)
  • three phosphate groups
34
Q

how does ATP release energy

A
  • more energy is released than used when the weak bond holding the last phosphate group is broken as it free phosphate undergoes other reactions involving bond formation
35
Q

hydrolysis of ATP

A

ATP + H2O —> ADP + Pi + energy

36
Q

why isnt ATP a good long-term energy store

A

unstable phosphate bonds mean cells dont store alot of ATP

37
Q

how is ATP reformed

A

phosphorylation of ADP

38
Q

properties of ATP

A
  • small (in+out cells)
  • bonds between phosphate have immediate energy
  • easily regenerated
  • releases small quant energy, none wasted as heat
  • water soluble

A-level Biology (16 decks)

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