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Biology A Level Content > 2.1.3 Nucleotides and Nucleic Acids > Flashcards

2.1.3 Nucleotides and Nucleic Acids Flashcards

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1
Q

What is DNA?

A

Deoxyribonucleic acid

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2
Q

What is the structure of DNA?

A
  • A polymer made up of repeating units called nucleotides
  • Each nucleotide consists of a common sugar, a phosphate group and one of four bases (either A, T, C or G)
  • There is complementary base pairing where A and T pair up and C and G pair up
  • Antiparallal
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3
Q

What does antiparallel mean?

A
  • Chains are running in opposite directions
  • One runs in the 5’3’ direction and the other in the 3’5’ direction
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4
Q

What is the structure of a DNA nucleotide?

A
  • Contains deoxyribose sugar
  • H on carbon 2
  • Nitrogenous base can be either A, T, C or G
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5
Q

What is the structure of an RNA nucleotide?

A
  • Contains ribose sugar
  • OH on carbon 2
  • Nitrogenous base can be either A, U, C or G
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6
Q

What are purines?

A
  • Contain 2 carbon-nitrogen rings
  • A and C
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7
Q

What are pyrimidines?

A
  • Contain 1 carbon-nitrogen ring
  • T and C
  • A purine base will always pair with a pyrimidine base
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8
Q

What are the differences between RNA and DNA?

A
  • RNA contains ribose and DNA contains deoxyribose
  • RNA contains uracil and DNA contains thymine
  • RNA is single stranded and DNA is double stranded
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9
Q

How are polynucleotides formed?

A
  • Phosphodiester bond
  • Between the phosphate group of one nucleotide and the deoxyribose sugar of the next
  • Catalysed by DNA polymerase
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10
Q

How do two single polynucleotide strands join together to make a double helix?

A
  • Hydrogen bonding between base pairs
  • Complementary base pairing is A-T and C-G
  • There are 2 hydrogen bonds between A and T and three hydrogen bonds between C and G
  • Two antiparallel polynucleotide strands twist to form a double helix
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11
Q

What is ATP?

A
  • Adenosine triphosphate
  • Chemical energy needed to fuel biological activities
  • Must be produced continually
  • Energyi food molecules is transferred to molecules of ATP by respiration
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12
Q

What is the structure of ATP?

A
  • Contains adenine, ribose and 3 phosphates
  • The phosphates are joined by a phosphoanhydride bond
  • Adding a phosphate group is called phosphorylation
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13
Q

How is ATP formed?

A
  • Made when adenosine diphosphate (ADP) is bonded to a third inorganic phosphate (Pi) using the energy released from glucose
  • With ATP synthase enzyme
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14
Q

What is the role of ATP?

A
  • Stores most of the energy in the third bond of the molecule in small manageable amounts
  • Energy is released when that bond is broken
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15
Q

How is energy released from ATP?

A
  • Phosphoanhydride bond between the second and third phosphate is hydrolysed
  • By ATPase enzyme
  • Forms ADP and inorganic phosphate
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16
Q

What does semi-conservative replication mean?

A
  • New DNA molecule comprises of one original and one new strand
  • Each strand of DNA acts as a template strand
17
Q

What is the process of semi-conservative replication?

A
  • DNA helicase causes two strands to separate by breaking the H bonds between the polynucleotide strands
  • The helix separates to form 2 single strands
  • Each original strand acts as a template and free nucleotides are attracted to exposed complementary bases
  • Nucleotides and bases are joined together by DNA polymerase to form sugar phosphate backbone as hydrogen bonds form between bases
  • 2 identical strands are formed as all nucleotides are joined to form a complete polynucleotide
  • Each strand retains half the original DNA (semi-conservative)
18
Q

What were the three possible theories for DNA replication?

A

Conservative = one molecule of both original strands and one molecule of two new strand
Semi-conservative = two DNA molecules with one original and one new strand
Dispersive = two DNA molecules that are a mixture of parental and daughter DNA

19
Q

What is the evidence for semi-conservative replication?

A

In 1958, Matthew Meselsohn and Franklin Stahl demonstrated that DNA replication was semi-conservative through an experiment using E.coli bacteria

20
Q

What were the details of the experiment to prove semi-conservative replication?

A
  • E.coli bacteria were grown in a medium containing a heavy isotope of nitrogen (15N)
  • The bacteria used 15N to make the purine and pyrimidine bases
  • The bacteria were then moved to a medium containing 14N
21
Q

What are the results from the semi-conservative replication experiment?

A
  • Used density gradient centrifugation to separate molecules into bands
  • Parental generation was the heaviest
  • 1st generation was lighter
  • 2nd generation had two bands (one lighter and one same as 1st generation)
  • 3rd generation had a thicker lightest band and thinner intermediate band
22
Q

What is the explanation of the results from the semi-conservative replication experiment?

A
  • Parental generation had both strands made with 15N
  • 1st generation had 2 DNA molecules with one strand of 15N and one strand of 14N
  • 2nd generation had 4 DNA molecules where some DNA was made of 2 strands of 14N and some made of 14N and 15N
23
Q

What are genes?

A
  • Each gene contains a different sequence of bases
  • Codes for a particular polypeptide
  • Each gene is on a fixed position (locus) on a strand of DNA
24
Q

What is the triplet code?

A
  • The sequence of 3 bases is the code for one particular amino acid
  • The order of bases controls the order that the amino acids are assembled to produce a particular protein
25
Q

What is a triplet?

A

Each amino acid on a protein is coded for by a sequence of 3 nucleotide bases on mRNA called a codon

26
Q

What does degenerate mean?

A

There is usually more than on codon that codes for each amino acid

27
Q

What does non-overlapping mean?

A

Each base sequence is only read once

28
Q

What does universal code mean?

A

The same codon codes for the same amino acid in all organisms

29
Q

What is the structure of tRNA?

A
  • Clover shaped
  • One strand folded back on itself
  • Anti-codon is complimentary to the codon on the mRNA
  • Amino acid is attached at the amino acid activation site, is specific and is determined by the anti-codon
30
Q

What is the process of transcription?

A
  1. DNA helicase separates the two strands of DNA by breaking the hydrogen bonds
  2. RNA polymerase moves along one of the strands of DNA (template strand) causing RNA nucleotides to align with complimentary bases and join together with a phosphodiester bond
  3. As RNA polymerase moves along, the DNA strands rejoin behind it
31
Q

What starts and stops translation?

A

Start and stop codons

32
Q

What is the process of translation?

A
  1. One end of the mRNA attaches to the ribosome
  2. A tRNA molecule that has a complementary anticodon also attaches to the ribosome
  3. A second tRNA molecule binds to the next codon
  4. The ribosome moved along the mRNA and joins the two amino acids together by a peptide bond (catalysed by rRNA)
  5. This continues until a stop codon is reached

Biology A Level Content (7 decks)

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