DNA Replication and Repair Flashcards
DNA
deoxyribonucleic acid; the cell’s genetic material; has a double helix structure and each strand has a sugar phosphate backbone with nitrogenous base pairs; has a negative charge due to phosphate group
gene
a specific portion of a cell’s DNA
chromosome
a single large DNA molecule and it’s associated proteins, containing many genes; stores and transmits genetic information
genome
all the genetic information encoded in a cell or virus
gene expression
transcription and, in the case of proteins, translation, to yield the product of a gene; a gene is expressed when its biological product is present and active
nucleotide
monomer of nucleic acids (DNA and RNA); consists of a nitrogenous base, a 5-carbon sugar, and a phosphate group
nucleoside
is a nucleotide without the phosphate group
nitrogenous bases
part of a nucleotide; purines (A,G) and pyrimidines (T/U,C)
base pairing
pairing of purines wth pyrimidine A&T/U, G&C via hydrogen bonding
DNA denaturation and annealing/hybridization
denaturation: when DNA is melted (about 90 degrees C) the base pairs separate making single strands of DNA; annealing/hybridization: the strands come back together and base pairs match up again
semiconservative model
the parent DNA strand gives one originial strand to each new DNA molecule and one new complementary strand; in contrast to the conservative model (the parent DNA molecule is conserved, and a new DNA has none of the original DNA) and the dispersice model (both strands are a mixture of new and old)
origins of replication
the places along the DNA molecule where the two strands open up and start the replication process
replication fork
the Y-shaped region where the parental strands of DNA are being unwound
helicases
enzymes that untwist the double helix at the replicaiton forks, separating the two partenal strands and making them available as template strands; causes strain ahead of the replicaiton fork
single-strand binding proteins
proteins that bind to the sinle-stranded (unpaired) DNA strands, keeping them from re-pairing
topoisomerase
enzyme that helps relieve strain caused by the untwisting of the DNA by breaking, swiveling, and rejoining DNA strands
primer and primase
primer: the initial nucleotide chain of RNA that occurs before DNA synthesis happens; primase: the enzyme that synthesizes the primer
DNA polymerases
enzymes that catalyze the synthesis of new DNA by adding nucleotides to the preexisting chain (primer RNA chain or DNA chain)
which end are new nucleotides added to?
the 3’ end
which direction does DNA synthesis move down the template strand?
3’ to 5’
leading strand
the part of the synthesized complement DNA that is continuous (just one primer) and elongated away from the origin of replication
lagging strand
the part of the synthesized complement DNA that is segmented (multiple primers, segments are called Okazaki fragments) and each segment is elongated toward from the origin of replication
DNA pol III
enzyme that adds new nucleotides
DNA pol I
enzyme that replaces the intermediate primer RNA nucleotides in the lagging strand with DNA
DNA ligase
enzyme that joins the sugar-phospate backbones of the Okazaki segments in the lagging strand
proofreading
DNA polymerases proofread the nucleotide sequence
mismatch repair
other enzymes remove and replace incorrectly paired nucleotides
nuclease
a DNA-cutting enzyme that can remove a segment of DNA strand (ie to remove damage)
nucleotide excision repair
a DNA repair system where a segement of damaged DNA is removed by nuclease, filled in by DNA polymerase, and has the 3’ end sealed by DNA ligase
shortening of the ends of linear DNA molecules
then ends of a DNA molecule become shorter and staggered because the 5’ end of the daughter DNA molecule can never be completely replicated since DNA can only be added to the 3’ end
telomeres
special nucleotide sequences (TTAGGG repeated) at the ends of DNA in eukaryotes that acts as a buffer zone to protect agaist the effects of DNA shortening; may play a role in limiting the number of divisions a cell can undergo
telomerase
an enzyme that catalyzes the lengthing of telomeres in eukaryotic germ cells (cancer cells too possibly)
chromatin
all DNA + associated proteins that package/order the DNA
histones
positively charged proteins responsible for the first level of DNA (negatively charged) packing in chromatin; histones group together and DNA wraps around creating nucleosomes
nuclesosomes
beads of DNA wrapped around histones
fiber (chromatin)
structure of nucleosomes condensed into a fiber
looped domains (chromatin)
structure of chromatin fiber that is looped into a thicker fiber
metaphase chromosome
the condensed chromatin structure, looped domains futher folded and coiled; particular genes always end up in the same places
heterochromatin
clumped chromatin during interphase; less accessible for gene expression; in contrast to euchromatin
euchromatin
dispersed chromatin during interphase; more accessible for gene expression
