Ch 16: The Molecular Basis of Inheritance

DNA replication

the process by which a DNA molecule is copied, and how cells repair the DNA

bacteriophages/phages

viruses that infect bacteria

virus

DNA enclosed by a protective coat, often just made of protein

double helix

two strands in a helical pattern

antiparallel

the subunits of DNA run in opposite directions

semiconservative model

each daughter nucleotide of DNA will have one old and one new strand

origins of replication

short sections of DNA with a specific nucleotide sequence where replication begins

replication fork

the Y-shaped region at the end of the replication bubble where parental strands are being unwound

helicases

enzymes that untwist the double helix, separating the parental strands

single-stranded binding proteins

after parental strands separate, these bind to unpaired DNA strands, keeping them from re-pairing

topoisomerase

an enzyme which breaks, swivels, and rejoins DNA strands to relieve strain caused by untwisting during replication

primer

a short RNA strand that is initially produced to initiate DNA synthesis

primase

the enzyme that synthesizes primers

DNA polymerase I

an enzyme which replaces the RNA nucleotides in the primer with DNA nucleotides

DNA polymerase III

an enzyme which catalyzes the synthesis of DNA by adding nucleotides to the existing chain

leading strand

• the strand that is synthesized continuously

• only one primer required

lagging strand

• synthesized discontinuously

• composed of okazaki fragments

okazaki fragments

• the fragments of the lagging strand

• each fragment is primed separately

DNA ligase

an enzyme which attaches okazaki fragments together

mismatch repair

when mistakes by polymerase are fixed by other enzymes

nucleotide excision repair

a damaged segment is cut out by nuclease and the gap is filled with nucleotides using the undamaged strand as a template

nuclease

a DNA cutting enzyme which fixes damaged or incorrect DNA segments

telomeres

• special nucleotide sequences at the end of DNA

• consist of multiple repetitions of a short nucleotide sequence, not genes

• acts as a buffer zone

• prevents staggered ends from setting of error signals

• postpones erosion of genes near the end of DNA

• shorten during each replication

telomerase

• an enzyme which catalyzes the lengthening of telomeres in eukaryotic germ cells

• not active in most human somatic cells

• restores original length of telomeres after replication

nucleoid

a dense, uncontained region of DNA in bacteria

chromatin

in eukaryotic cells, the complex of DNA and protein within the nucleus

histones

• a protein responsible for the first level of DNA packing in chromatin

• has a polar bond with the negatively charged DNA

• similar among eukaryotes

nucleosomes

• the “beads” on the “string” of chromatin

• the “string” is called linker DNA

• the basic unit of DNA packing

• DNA winds twice around a protein composed of two histone types

heterochromatin

• the interphase chromatin visible as irregular clumps under a light microscope

• inaccessible to transcription

• these genes are unexpressed

euchromatin

less densely condensed chromatin whose genes are expressed

Frederick Griffith

• determined that DNA from one organism can transform the DNA of another organism

• injected pathogenic and non-pathogenic viruses in mice

Thomas Hunt Morgan

• discovered that chromosomes are the hereditary molecule

• fruit fly experiments

Avery, McCarty, and MacLeod

• determined that DNA was the transforming agent in bacteriophages

• inactivated potential hereditary material and observed which bacteriophages could still transform bacteria

Alfred Hershey and Martha Chase

• determined that DNA was the hereditary material

• radioactively tagged DNA and protein

• found that DNA from bacteriophages entered the bacteria, but protein did not

Watson and Crick

• determined the double helix structure of DNA

• with help from Rosalind Franklin