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nucleic acids Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Describe the structure of a nucleotide

A
  • A phosphate group
  • Nitrogen-containing base
  • Pentose sugar
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2
Q

Name the pentose sugar in DNA and RNA

A
  • DNA: deoxyribose
  • RNA: ribose
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3
Q

State the role of DNA in living cells

A
  1. Base sequence of genes codes for functional RNA and amino acid sequence for polypeptides
  2. Genetic information determines inherited characteristics and influences the structure and function of organisms
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4
Q

State the role of mRNA, RNA and tRNA in living cells

A
  1. mRNA = complementary sequence to 1 gene from DNA with introns spliced out, codons can be translated into a polypeptide by ribosomes
  2. rNA = component of ribosomes
  3. tRNA = supplies complementary amino acids 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 of 2 polynucleotide strands
  • Contains deoxyribose
  • Hydrogen bonds between complementary purine and pyrimidine base pairs on opposite strands
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7
Q

Name the complementary base pairs in DNA

A

adenine + thymine
guanine + cytosine

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8
Q

Which bases are purines and which are pyrimidines?

A

Adenine and guanine = 2 ring purine bases

Thymine and cytosine = 1 ring pyrimidine bases

(Purines are larger than pyrimidines because they have a two-ring structure while pyrimidines only have a single ring)

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9
Q

Name the complementary base pairs in RNA and their bonds

A

2 hydrogen bonds between adenine and uracil

3 hydrogen bonds between guanine and cytosine

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10
Q

Describe how the structure of DNA is adapted for its functions

A
  1. Sugar phosphate backbone and many hydrogen bonds provide stability
  2. Long molecule so stores a lot of information
  3. Helix is compact for storage in the nucleus
  4. Base sequence of triplets codes for amino acids
  5. Double-stranded for semi-conservative replication
  6. Complementary base pairings for accurate replication
  7. Weak hydrogen bonds so strands separate for replication
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11
Q

Describe the structure of messenger RNA (mRNA)

A
  • Long ribose polynucleotide
  • Contains uracil instead of thymine
  • Single-stranded and linear so has no complementary base pairs
  • Codon sequence is complementary to exons of 1 gene from 1 DNA strand
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12
Q

Describe how the structure of mRNA makes it adaptable to its function

A
  1. Breaks down quickly so no excess polypeptide forms
  2. Ribosomes can move along strands and tRNA can bind exposed bases
  3. Can be translated into a specific polypeptide by ribosomes
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13
Q

Describe the structure of transfer RNA (tRNA)

A
  • Single strand of 80 nucleotides
  • Folded into a clover shape
  • Anticodon on one end, amino acid binding site on the other
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14
Q

What is the function of an anticodon on tRNA

A

Anticodon binds to complementary mRNA codon

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15
Q

Why is DNA replication described as semi-conservative

A
  • Strands from the original DNA molecule act as a template
  • New DNA molecule contains 1 old strand and 1 new strand
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16
Q

Outline the process of semi-conservative DNA replication

A
  1. DNA helices break hydrogen bonds between bases which unwinds the double helix producing 2 strands that act as templates
  2. Free-floating DNA nucleotides are attracted to the exposed bases via specific complementary base pairing, and hydrogen bonds form between these
  3. DNA polymerase joins adjacent nucleotides on a new strand by condensation which creates phosphodiester bonds
17
Q

Describe the Meselson-Stahl experiment

A
  1. Bacteria were grown in a medium containing heavy isotope 15N for many generations
  2. Some bacteria were moved to a medium containing light isotope 14N, and samples were extracted after 1 and 2 cycles of DNA replication
  3. Centrifugation formed a pellet, and heavier DNA bases settles closer to the bottom of the tube

biology (46 decks)

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