Chapter 13: The Molecular Basis of Inheritance

DNA

Deoxyribonucleic acid, a self-replicating material present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information.

DNA replication

The process in which DNA makes a duplicate copy of itself.

Transformation

A change in genotype and phenotype due to assimilation of foreign DNA.

Bacteriophage

A virus that infects bacteria

Chargoff's rules

Amount of adenine equaled the amount of thymine and cytosine equaled the amount of guanine regardless of the species studied; base composition varies between species.

Double-helix

Two strands of nucleotides wound about each other; structure of DNA

Watson and Crick

Determine double-helix structure of DNA.

Nucleotide

A building block of DNA, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group.

Deoxyribose

A five-carbon sugar that is a component of DNA nucleotides

Nitrogen base

Carbon ring structure found in DNA or RNA that contains one or more atoms of nitrogen; includes adenine, guanine, cytosine, thymine, and uracil

Phosphate group

A chemical group consisting of a phosphorus atom bonded to four oxygen atoms

Antiparallel

The opposite arrangement of the sugar-phosphate backbones in a DNA double helix.

Sugar-phosphate backbone

In a polynucleotide (DNA or RNA strand), the alternating chain of sugar and phosphate to which nitrogenous bases are attached.

Hydrogen bond

Attraction between a slightly positive hydrogen atom and a slightly negative atom.

3' and 5' ends

DNA is antiparallel; the 3' end has a terminal phosphate group; the 5' end has a terminal hydroxyl group. DNA can only add nucleotides to the 3' end.

Purine

A nitrogenous base that has a double-ring structure; one of the two general categories of nitrogenous bases found in DNA and RNA; either adenine or guanine

Pyrimidine

A nitrogenous base that has a single-ring structure; one of the two general categories of nitrogenous bases found in DNA and RNA; either cytosine or thymine.

Adenine (A)

The base that pairs with Thymine in DNA

Guanine (G)

The base that pairs with Cytosine in DNA

Thymine (T)

The base that pairs with Adenine in DNA

Cytosine (C)

The base that pairs with Guanine with DNA

Complementary base pairing

Hydrogen bonding between particular bases; in DNA, thymine (T) pairs with adenine (A), and guanine (G) pairs with cytosine (C); in RNA, uracil (U) pairs with A, and G pairs with C

Semiconservative replication model

The process in which the DNA molecule uncoils and separates into two strands. Each original strand becomes a template on which a new strand is constructed, resulting in two DNA molecules identical to the original DNA molecule, each with one parental strand from the original molecule and one newly-synthesized daughter strand.

Origin of replication

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides where the two D N A strands are separated, opening up a replication "bubble"

Replication fork

a Y-shaped region where the parental strands of D N A are being unwound

Helicases

Enzymes that untwist the double helix at the replication forks

Single-strand binding proteins

Bind to and stabilize single-stranded D N A so they do not reform hydrogen bonds between nitrogenous bases of nucleotides.

Topoisomerase

Relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining D N A strands

Primer

A short stretch of RNA with a free 3' end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication

Primase

Starts an RNA chain with a single RNA nucleotide and adds RNA nucleotides one at a time using the parental DNA as a template; builds the RNA primer

Leading strand

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction.

Continuous replication

The uninterrupted replication of DNA in the 5' to 3' direction using a 3' to 5' template strand.

DNA polymerase III

Catalyze the elongation of new DNA at a replication fork by adding nucleotides to the 3′ end of a preexisting chain of nucleotides, usually the RNA primer. Attaches nucleotides based on complementary base-pairing of template strand.

Lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' to 3' direction away from the replication fork.

Discontinuous replication

Replication in which a DNA strand is formed in short lengths that are synthesized in the direction opposite of DNA unwinding.

Okazaki fragments

Short fragments of DNA that are a result of the synthesis of the lagging strand during DNA replication. Must be attached together by covalent bonds.

DNA polymerase I

Removes the RNA primer and replaces it with DNA

Ligase

An enzyme that connects two fragments of DNA along one strand to make a single molecule by covalently bonding fragments together.

Mismatch repair

The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

Nuclease

A DNA cutting enzyme that excises damaged DNA.

Nucleotide excision repair

A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.

Telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes.

Telomerase

An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.

Nucleoid

A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated.

Chromatin

Substance found in eukaryotic chromosomes that consists of DNA tightly coiled around histones

Histones

Protein molecules around which DNA is tightly coiled in chromatin

Nucleosome

Bead-like repeating structure in eukaryotic chromatin, composed of a short length of DNA wrapped around a core of histone proteins

Heterochromatin

DNA that is densely packed around histones. The genes in heterochromatin are generally inaccessible to enzymes and are turned off.

Euchromatin

The less condensed form of eukaryotic chromatin that is available for transcription.