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Biology pt2 > 1.5 Nucleic Acids, 1.6 ATP > Flashcards

1.5 Nucleic Acids, 1.6 ATP Flashcards

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1
Q

What does a nucleotide consist of?

A
  • Phosphate group
  • Pentose sugar
  • Nitrogen containing base
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2
Q

Name the pentose sugars in DNA and RNA

A
  • DNA: deoxyribose
  • RNA: ribose
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3
Q

State the role of DNA in living cells

A
  • Base sequences of genes codes for functional RNA and amino acid sequence of polypeptides
  • Genetic information determines inherited characteristics = influences structure and 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 (non coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes
  • rRNA: component of ribosomes (along with proteins)
  • 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 (sugar-phosphate backbone)

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6
Q

Describe the structure of DNA

A
  • Double helix of 2 polynucleotide strands (deoxyribose)
  • H-bonds between complementary purine and pyrimidine base pairs on opposite strands: adenine+thymine, guanine+cytosine
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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: adenine+thymine
  • 3 H-bonds between: guanine+cytosine
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9
Q

Name the complementary base pairs in RNA

A
  • 2 H-bonds between adenine+uracil
  • 3 H-bonds between guanine+cytosine
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10
Q

Relate the structure of DNA to its functions

A
  • Sugar-phosphate backbone and 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 strands separate for replication
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11
Q

Describe structure of mRNA

A
  • Long ribose polynucleotide (but shorter than DNA)
  • Contains uracil instead of thymine
  • Single stranded and linear (no complementary base pairing)
  • Codon sequence is complementary to exons of 1 gene from 1 DNA strand
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12
Q

Relate structure of mRNA to its function

A
  • Breaks down quickly so no excess polypeptide forms
  • Ribosome can move along strand and tRNA can bind to exposed bases
  • Can be translated into 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 (some paired bases)
  • 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 a few components

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16
Q

Why is DNA replication describe as ‘semi-conservative’?

A
  • Strands from original DNA molecule act as a template
  • New DNA molecule contains one old strand and one new strand
17
Q

Outline the process of semi-conservative DNA replication

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

Describe the Meselson-Stahl experiment

A
  • Bacteria was grown in a medium containing heavy isotope 15N for many generations
  • Some bacteria was removed to a medium containing light isotope 14N. Samples were extracted after 1 and 2 cycles of DNA replication
  • Centrifugation formed a pellet. Heavier DNA (15N bases) settled closer to the bottom of the tube
19
Q

Describe the structure of ATP

A

Nucleotide derivative of adenine with 3 phosphate groups

20
Q

What does ATP hydrolase catalyse?

A

ATP hydrolase catalysed ATP->ADP+Pi

21
Q

Explain the role of ATP in cells

A
  • Energy released is coupled to metabolic reactions
  • Phosphate group phosphorylates compounds to make them more reactive
22
Q

How is ATP resynthesised in cells

A
  • ATP synthase catalyses condensation reaction between ADP and Pi
  • During photosynthesis and respiration
23
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 pt2 (33 decks)

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