Topic 9 – Nucleic Acids & DNA Replication

Vocabulary flashcards covering key terms and definitions from the lecture on nucleic acids, DNA/RNA structure, and DNA replication.

Nucleic Acid

A biological polymer (DNA or RNA) composed of nucleotide monomers that stores or transmits genetic information.

Nucleotide

The monomer of nucleic acids; consists of a 5-carbon sugar, a phosphate group, and a nitrogenous base.

DNA (Deoxyribonucleic Acid)

Double-stranded nucleic acid made of deoxyribonucleotides; stores hereditary information in cells.

RNA (Ribonucleic Acid)

Single-stranded nucleic acid made of ribonucleotides; acts as a messenger or catalyst in protein synthesis.

Deoxyribose

The 5-carbon sugar in DNA that lacks an oxygen at the 2' carbon (C₅H₁₀O₄).

Ribose

The 5-carbon sugar in RNA that has an –OH at the 2' carbon (C₅H₁₀O₅).

Phosphate Group

The component of a nucleotide that is identical in DNA and RNA and links sugars to form the backbone.

Nitrogenous Base

Aromatic base (A, G, C, T, or U) attached to the 1' carbon of the sugar in a nucleotide.

Purine

Double-ring nitrogenous base; includes adenine and guanine.

Pyrimidine

Single-ring nitrogenous base; includes cytosine, thymine, and uracil.

Adenine

A purine base that pairs with thymine in DNA and uracil in RNA via two hydrogen bonds.

Guanine

A purine base that pairs with cytosine via three hydrogen bonds.

Cytosine

A pyrimidine base that pairs with guanine via three hydrogen bonds.

Thymine

A pyrimidine base found only in DNA; pairs with adenine via two hydrogen bonds.

Uracil

A pyrimidine base found only in RNA; replaces thymine and pairs with adenine.

Complementary Base Pairing

Specific hydrogen bonding of A-T (or A-U) and G-C that allows accurate DNA replication.

Hydrogen Bond

Weak attraction between complementary bases that holds the two DNA strands together.

Double Helix

The twisted-ladder structure formed by two complementary DNA strands.

5′ End

The end of a nucleic acid strand with a free phosphate on the 5′ carbon of the sugar.

3′ End

The end of a nucleic acid strand with a free hydroxyl on the 3′ carbon of the sugar.

Antiparallel Strands

Orientation of DNA strands running in opposite 5′→3′ directions.

Sugar-Phosphate Backbone

The repeating chain of sugars and phosphates that forms the exterior of DNA or RNA.

Semi-Conservative Replication

DNA replication mechanism in which each daughter molecule contains one parental and one new strand.

Origin of Replication

Specific DNA sequence where replication begins; eukaryotes have many, bacteria usually one.

Replication Fork

Y-shaped region where parental DNA strands are unwound and new strands synthesized.

Helicase

Enzyme that unzips DNA by breaking hydrogen bonds between bases.

DNA Polymerase

Enzyme that adds nucleotides to a growing DNA strand and proofreads for errors.

Primase

Enzyme that synthesizes short RNA primers needed to start DNA synthesis on the lagging strand.

Leading Strand

New DNA strand synthesized continuously toward the replication fork in a 5′→3′ direction.

Lagging Strand

New DNA strand synthesized discontinuously away from the fork in short fragments.

Okazaki Fragment

Short DNA segment produced on the lagging strand during replication.

Ligase

Enzyme that seals nicks between Okazaki fragments to create a continuous DNA strand.

DNA Proofreading

Error-correcting function of DNA polymerase that reduces mutation rate to about 1 in several billion bases.

Mutation

Permanent change in DNA nucleotide sequence; can arise from replication errors.

Topoisomerase

Enzyme that relieves torsional stress ahead of the replication fork by cutting and rejoining DNA.

Gyrase

A type of topoisomerase in bacteria that removes supercoils to allow replication.

Supercoiling

Highly twisted state of bacterial circular DNA that must be relaxed for replication.

High-Fidelity Replication

The accurate copying of ~3 billion human nucleotides with very few errors.

Energy Difference in Base Pairs

G-C pairs require more energy to separate than A-T pairs because they have three hydrogen bonds.

Binary Fission

Asexual division in bacteria requiring complete DNA replication before cell splits.