Campbell Biology Chapter 16

Watson and Crick

discovered the structure of DNA as double helix in 1953

DNA replication

process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission

Griffith

1928, Accidentally discovered transformation by combining a heat killed virulent strain of bacteria with a live non virulent strain while studying pneumonia.

transformation

(genetics) modification of a cell or bacterium by the uptake and incorporation of exogenous DNA

Avery

1944 - experiments on the strains of a cell that led to the discovery that DNA was the transforming factor not the protein

bacteriophage

a virus that infects bacteria

virus

an infectious particle made only of a strand of DNA or RNA surrounded by a protein coat

Hershey and Chase

Identified DNA to be genetic material through experiments with bacteriophages

Chargaff's rules

1. number of adenines = number of thymines

number of cytosines = number of guanines

2. species differ in the number of relative amounts of bases

double helix

twisted-ladder shape of DNA, formed by two nucleotide strands twisted around each other

antiparallel

Parallel, but running in opposite directions. The 5' end of one strand of DNA aligns with the 3' end of the other strand in a double-helix.

semiconservative model

Type of DNA replication in which the replicated double helix consists of one old strand, derived from the old molecule, and one newly made strand.

conservative model

The two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix

dispersive model

each strand of both daughter molecules contains a mixture of old and newly synthesized DNA

origin of replication

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing.

helicase

an enzyme that untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands

single strand binding proteins

Proteins that bind to and stabilize the signle strands of DNA exposed when helicase unwinds the double helix in preparation for replication.

primer

An already existing RNA chain bound to template DNA to which DNA nucleotides are added during DNA synthesis.

primase

An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

DNA polymerase

An enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain.

leading strand

the new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5' to 3' direction

lagging strand

A discontinuously synthesized DNA strand that elongates in a direction away from the replication fork.

Okazaki fragments

Short fragments of DNA that are a result of the synthesis of the lagging strand during DNA replication.

DNA polymerase I

Enzyme. Removes RNA primers and replaces them with the appropriate nucleotides during DNA replication.

DNA polymerase III

using parental DNA as a template synthesize DNA strand by covalently adding nucleotides to the 3' end of a preexisting DNA or RNA primer

DNA ligase

Joins 3' end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand

mismatch repair

enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors

nuclease

An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.

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

The tandemly repetitive DNA at the end of a eukaryotic chromosome's DNA molecule that protects the organism's genes from being eroded during successive rounds of replication.

telomerase

catalyzes the lengthening of telomeres in eukaryotic germ cells, thus restoring their original length and compensating for the shortening that occurs during DNA replication

histone

A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in its chromatin structure.

nucleosome

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

nucleoid

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

chromatin

Combination of DNA and protein molecules, in the form of long, thin fibers, making up the genetic material in the nucleus of a eukaryotic cell

heterochromatin

Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed

euchromatin

an uncoiled form that is the site of active transcription of DNA into RNA