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1.6Chemistry of Life

Nucleic Acids — AP BIOLOGY Revision Notes & Topical Questions

5 min read 8 parts Lesson 6 of 7 1 quiz

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1.6 Nucleic Acids — Notes — AP BIOLOGY notes: Describe the structure and function of DNA and RNA.Polynucleotide — DNA and RNA are polymers made of many nucleotide monomers linked in a chainNucleotide = a five-carbon (pentose) sugar, a phosphate group and a nitrogenous baseDNA has…

  • Base pairing
  • Pairing rule
  • Information
  • Pyrimidine
  • Antiparallel
  • Phosphodiester bond

Part 1 of 6Nucleotides and polynucleotides

Polynucleotide
  • DNA and RNA are polymers made of many nucleotide monomers linked in a chain
Nucleotide
Nucleotide a five-carbon (pentose) sugar, a phosphate group and a nitrogenous base
  • DNA has deoxyribose sugar and the bases adenine, guanine, cytosine and thymine.
  • RNA has ribose sugar and the bases adenine, guanine, cytosine and uracil.
Bases
  • Bases purines (A, G) have two rings and pyrimidines (C, T, U) have one ring
Reminder
  • Reminder nucleic acids are polymers of nucleotides, not polymers of bases

Part 2 of 63′ and 5′ ends

3′ end
  • 3′ end the end with a terminal hydroxyl (–OH) group on carbon 3 of a sugar
5′ end
  • 5′ end the end with a terminal phosphate group on carbon 5 of a sugar
Synthesis
  • Synthesis new nucleotides are always added to the 3′ end of the growing strand, forming strong covalent (phosphodiester) bonds
Backbone
  • Backbone covalent phosphodiester bonds join the phosphate of one nucleotide to the sugar of the next to form a sugar–phosphate backbone

Part 3 of 6DNA structure

DNA structure
Shape
  • DNA is an antiparallel double helix, with the two strands running in opposite 5′ to 3′ orientations
Base pairing
  • Base pairing the bases are joined by hydrogen bonds
  • Adenine pairs with thymine (A–T) through 2 hydrogen bonds.
  • Cytosine pairs with guanine (C–G) through 3 hydrogen bonds.
Pairing rule
  • Pairing rule a purine always pairs with a pyrimidine, which keeps the width of the helix constant
Strength
  • Strength regions with more G–C pairs need more energy to separate because they have more hydrogen bonds
Information
  • Information the sequence of bases stores genetic information

Part 4 of 6RNA structure

RNA structure
Strands
  • RNA is usually single-stranded
Folding
  • RNA can fold, held by base pairing
  • Adenine pairs with uracil (A–U) instead of thymine.
  • Cytosine pairs with guanine (C–G) as in DNA.
Types
  • Types mRNA, tRNA and rRNA take part in protein synthesis

Part 5 of 6Comparing DNA and RNA

FeatureDNARNA
Pentose sugarDeoxyriboseRibose
Nitrogenous basesA, T, C, GA, U, C, G
Base pairingA–T, C–GA–U, C–G
Typical structureDouble-stranded antiparallel double helixUsually single-stranded
Synthesis direction5′ to 3′ (nucleotides added to the 3′ end)5′ to 3′ (nucleotides added to the 3′ end)
Sugar–phosphate backboneCovalent phosphodiester bondsCovalent phosphodiester bonds
  • ATP
    • it is a modified nucleotide that carries energy

Part 6 of 6More from the specification

More from the specification
Carbohydrate
  • A molecule of carbon, hydrogen and oxygen, including sugars, starch, glycogen and cellulose.
Fatty acid
  • A hydrocarbon chain with a carboxyl group.
Primary structure
  • The sequence of amino acids in a polypeptide.
Glycosidic bond
  • The covalent link between two sugar units made by condensation.
Dehydration
  • Drying out of a specimen.
Glucose
  • A simple sugar; the unit that starch, glycogen and cellulose are built from.
Polypeptide
  • A chain of three or more amino acids.
Starch
  • An insoluble polysaccharide of glucose used by plants for energy storage.
Lipids
  • Concentrated energy, insulation, cell membranes.
Hydrolysis
  • A reaction that splits a molecule by adding water.
Glycogen
  • The polysaccharide in which glucose is stored in animals.

Key terms

TermMeaning
NucleotideA five-carbon sugar, a phosphate and a nitrogenous base.
PurineA double-ring base: A and G.
PyrimidineA single-ring base: C, T and U.
AntiparallelRunning in opposite 5′ to 3′ directions.
Phosphodiester bondCovalent bond linking nucleotides in the backbone.
Complementary base pairingA–T (A–U in RNA) and C–G.

Avoid these mistakes

1
Describing DNA or RNA as polymers of bases — they are polymers of nucleotides.
2
Saying RNA contains thymine — it contains uracil.
3
Saying A–T and C–G have equal numbers of hydrogen bonds — A–T has 2 and C–G has 3.
4
Forgetting that the two DNA strands are antiparallel.

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