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Biology A-Level > Nucleic Acids and ATP > Flashcards

Nucleic Acids and ATP Flashcards

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1
Q

Describe the structure of a nucleotide.

A

Phosphate group, pentose sugar, nitrogen-containing base

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2
Q

Name the pentose sugars in DNA & RNA.

A

DNA: deoxyribose
RNA: ribose

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3
Q

State the role of DNA in living cells.

A

Base sequence of genes codes for functional RNA & amino sequence of polypeptides.
Genetic information determines inherited characteristics = influences structure & function of organisms

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4
Q

State the role of RNA in living cells.

A

mRNA: complementary sequence to 1 gene from DNA with introns spliced out. Codons can be translated into a polypeptide by ribosomes
rRNA: component of ribosomes
tRNA: supplies complementary amino acid to mRNA codons during translation

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5
Q

How do polynucleotides form?

A

Condensation reactions between nucleotides form strong phosphodiester bonds.

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6
Q

Describe the structure of DNA

A

Double helix
H-bonds between complementary base pairs

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7
Q

Which bases are purine and which are pyrimidine?

A

A&G = 2-ring purine bases
T&C&U= 1-ring pyrimidine bases

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8
Q

Name the complementary base pairs in DNA.

A

2 H bonds between A & T
3 H bonds between G & C

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9
Q

What base changes in RNA?

A

T to U

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10
Q

Relate the structure of DNA to its functions.

A
  • sugar-phosphate backbone & many H-bonds provide stability
  • long molecule stores lots of information
  • helix is compact for storage in nucleus
  • base sequence of triplets codes for amino acids
  • double-stranded for semi conservative replication
  • complementary base pairing for accurate replication
  • weak H-bonds break so strand separate for replication
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11
Q

Describe the structure of messenger RNA.

A

-long ribose polynucleotide (shorter than DNA)
-contains uracil instead of thymine
- single stranded and linear
- codon sequence is complementary to exons of 1 gene from 1 DNA strand

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12
Q

Relate the structure of messenger RNA to its functions.

A
  • Breaks down quickly so no excess polypeptide forms
  • ribosome can move along strand & tRNA can bind to exposed bases
  • can be translated into a specific polypeptide by ribosomes
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13
Q

Describe the structure of tRNA.

A
  • single strand of about 80 nucleotides.
  • folded into clover shape
  • anticodon on one end, amino acid binding site on the other:
    a) anticodon binds to complementary mRNA codon
    b) amino acid corresponds to anticodon
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14
Q

Order DNA, mRNA and tRNA according to increasing length.

A

tRNA, mRNA, DNA

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15
Q

Why did scientists initially doubt that DNA carried the genetic code?

A

Chemically simple molecule with few components.

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16
Q

Why is DNA replication described as semi-conservative?

A
  • strands from original DNA molecule act as a new template
  • new DNA molecule contains 1 old strand and 1 new strand
17
Q

Outline the process of semi-conservative DNA replication.

A
  1. DNA helicase breaks h-bonds between base pairs
  2. Each strand acts as a template
  3. Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
  4. DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
  5. H-bonds reform
18
Q

Describe the Meselson-Stahl experiment.

A
  1. Bacteria grown in medium containing isotope 15N
  2. Some bacteria were removed to a medium containing light isotope 14N. Samples were extracted after 1&2 cycles of DNA replication
  3. Centrifugation formed a pellet. Heavier DNA settled closer to bottom of tube
19
Q

Describe the structure of adenosine triphosphate (ATP)

A

Nucleotide derivative of adenine with 3 phosphate groups.

20
Q

Explain the role of ATP in cells.

A

ATP hydrolase catalyses ATP —> ADP + Pi
- energy released is coupled to metabolic reactions
- phosphate group phosphorylates compounds to make them more reactive

21
Q

How is ATP resynthesised in cells?

A
  • ATP synthase catalyses condensation reaction between ADP + Pi
  • during photosynthesis & respiration
22
Q

Explain why ATP is suitable as the ‘energy currency’ of cells.

A
  • high energy bonds between phosphate groups
  • small amounts of energy released at a time = less energy wasted as heat
    -single step hydrolysis = energy available quickly
  • readily resynthesised

Biology A-Level (17 decks)

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