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AQA AS Biology > Section 1 - Unit 2: Nucleic Acids > Flashcards

Section 1 - Unit 2: Nucleic Acids Flashcards

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1
Q

Explain why new nucleotides can only be added in a 5’ to 3’ direction (4 marks)

A
  • DNA polymerase
  • Is specific
  • And is only complementary to the 5’ end of the strand
  • The shapes of 5’ end and 3’ end are different
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2
Q

Describe the role of DNA polymerase in DNA replication (1 mark)

A
  • Joins nucleotides (to form new strand)
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3
Q

Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA (2 marks)

A
  • Prokaryotic DNA is circular vs eukaryotic DNA is linear

- Prokaryotic DNA is not associated with proteins/histones vs eukaryotic DNA is

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4
Q

Using your knowledge of DNA structure and function, explain how although humans and animals have very similar percentages of each base in their DNA, they are very different organisms (2 marks)

A
  • Have different genes

- So bases are in a different sequence

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5
Q

Explain how the events that take place during interphase and mitosis lead to the production of two genetically identical cells (4 marks)

A
  • DNA replicated
  • Due to complementary base-pairing
  • Two sister chromatids are produced
  • Each chromatid moves to opposite ends of the poles
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6
Q

Explain how the structure of DNA is related to its functions (6 marks)

A
  • Sugar-phosphate backbone provides strength/ protects hydrogen bonds
  • Long, large molecule to store lots of information
  • Double helix so compact
  • Base sequence allows information to be stored
  • Double stranded so replication can occur semi-conservatively
  • Weak hydrogen bonds for strand separation
  • Many hydrogen bonds for stability
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7
Q

Explain why DNA helicase is important in DNA replication (2 marks)

A
  • Separates the double helix

- So that nucleotides can attach

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8
Q

Describe and explain how the structure of DNA results in accurate replication (4 marks)

A

Any four from:

  • Two strands therefore semi-conservative replication is possible
  • Hydrogen bonds holds strands together
  • Hydrogen bonds are weak so strands can separate
  • Base sequence acts as template
  • A with T, C with G
  • DNA is one parent and one new strand;
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9
Q

Describe the role of the sequence of bases on one strand of DNA (1 mark)

A
  • Determines sequence of amino acids
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10
Q

Describe how the two strands of a DNA molecule are held together (1 mark)

A
  • Hydrogen bonds
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11
Q

Describe one advantage of DNA molecules having two strands (1 mark)

A
  • Stability/Protects Bases/Replication
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12
Q

Describe how, after the parent DNA strands separate, the second strand of DNA is formed (3 marks)

A

Any 3 from:

  • Semi-conservative replication
  • Complementary base pairing
  • Hydrogen bonding of bases
  • Condensation of nucleotides
  • DNA polymerase involved
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13
Q

Describe how the proportion of DNA that contained 15N changed at each division when bacteria were grown on the 14N medium (2 marks)

A
  • Decreases by 50%

- At every generation

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14
Q

Give two ways doctors could use base sequences to compare different types of viruses (2 marks)

A
  • Compare DNA base sequence

- Compare mRNA base sequence

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15
Q

Explain why the replication of DNA is described as semi-conservative (2 marks)

A
  • Each strand acts as a template

- DNA is composed of one new strand and one original/parent strand

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16
Q

Explain how DNA replicates (4 marks)

A
  • Hydrogen bonds broken
  • Semi-conservative replication
  • Nucleotides line up - specific base pairing
  • DNA polymerase
17
Q

Define homologous chromosomes (3 marks)

A
  • Two chromosomes
  • With same genes
  • At same loci
18
Q

Describe how ATP is resynthesised in cells (2 marks)

A
  • From ADP and phosphate
  • By ATP synthase
  • During respiration/photosynthesis
19
Q

Give two ways in which the hydrolysis of ATP is used in cells (2 marks)

A
  • To provide energy for other reactions

- To add phosphate to other substances and make them more reactive/ change their shape

20
Q

Explain some uses of phosphate in the body (5 marks)

A
  • Used to make RNA
  • Used to make DNA
  • Used to make ATP/ADP
  • Used to make membranes
  • Used for phosphorylation
21
Q

Give two ways in which ATP is a suitable energy source for cells to use (2 marks)

A
  • Releases relatively small amount of energy

- Releases energy instantaneously

22
Q

Explain why ATP is useful in many biological processes (4 marks)

A
  • Releases energy in small amounts
  • Broken down in a single step/energy available rapidly
  • Adds phosphate to substances and makes them more reactive/lowers their Ae
  • Can be reformed/made again
23
Q

Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis (5 marks)

A
  • In the dark no ATP production in photosynthesis
  • So some tissues are unable to photosynthesise/produce ATP
  • ATP cannot be moved from cell to cell/stored
  • Plant uses more ATP than produced in photosynthesis
  • ATP for active transport
24
Q

Write a simple equation to show how ATP is synthesised from ADP (1 mark)

A
  • ADP + Pi → ATP
25
Q

Explain why it is necessary for humans to synthesise such a large amount of ATP (3 marks)

A
  • ATP is unstable
  • ATP cannot be stored / is an immediate source of energy
  • Required in active transport
  • ATP only releases a small amount of energy at a time
26
Q

Give two advantages of ATP as an energy storage molecule within a cell (2 marks)

A
  • Cannot pass out of cell
  • Quickly broken down
  • Releases small amounts of energy
27
Q

State what happens to the energy which is not incorporated into ATP when glucose is respired (1 mark)

A
  • It is released as heat
28
Q

Describe the role of DNA polymerase in the semi-conservative replication of DNA (2 marks)

A
  • Joins (adjacent DNA) nucleotides
  • Catalyses condensation reactions
  • Catalyses formation of phosphodiester bonds
29
Q

Describe how an enzyme can be phosphorylated

A
  • Attachment of Pi to enzyme

- Which comes from hydrolysis of ATP

AQA AS Biology (14 decks)

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