DNA Replication and Repair

Question 1

DNA

Answer 1

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

Question 2

gene

Answer 2

a specific portion of a cell’s DNA

Question 3

chromosome

Answer 3

a single large DNA molecule and it’s associated proteins, containing many genes; stores and transmits genetic information

Question 4

genome

Answer 4

all the genetic information encoded in a cell or virus

Question 5

gene expression

Answer 5

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

Question 6

nucleotide

Answer 6

monomer of nucleic acids (DNA and RNA); consists of a nitrogenous base, a 5-carbon sugar, and a phosphate group

Question 7

nucleoside

Answer 7

is a nucleotide without the phosphate group

Question 8

nitrogenous bases

Answer 8

part of a nucleotide; purines (A,G) and pyrimidines (T/U,C)

Question 9

base pairing

Answer 9

pairing of purines wth pyrimidine A&T/U, G&C via hydrogen bonding

Question 10

DNA denaturation and annealing/hybridization

Answer 10

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

Question 11

semiconservative model

Answer 11

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)

Question 12

origins of replication

Answer 12

the places along the DNA molecule where the two strands open up and start the replication process

Question 13

replication fork

Answer 13

the Y-shaped region where the parental strands of DNA are being unwound

Question 14

helicases

Answer 14

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

Question 15

single-strand binding proteins

Answer 15

proteins that bind to the sinle-stranded (unpaired) DNA strands, keeping them from re-pairing

Question 16

topoisomerase

Answer 16

enzyme that helps relieve strain caused by the untwisting of the DNA by breaking, swiveling, and rejoining DNA strands

Question 17

primer and primase

Answer 17

primer: the initial nucleotide chain of RNA that occurs before DNA synthesis happens; primase: the enzyme that synthesizes the primer

Question 18

DNA polymerases

Answer 18

enzymes that catalyze the synthesis of new DNA by adding nucleotides to the preexisting chain (primer RNA chain or DNA chain)

Question 19

which end are new nucleotides added to?

Answer 19

the 3’ end

Question 20

which direction does DNA synthesis move down the template strand?

Answer 20

3’ to 5’

Question 21

leading strand

Answer 21

the part of the synthesized complement DNA that is continuous (just one primer) and elongated away from the origin of replication

Question 22

lagging strand

Answer 22

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

Question 23

DNA pol III

Answer 23

enzyme that adds new nucleotides

Question 24

DNA pol I

Answer 24

enzyme that replaces the intermediate primer RNA nucleotides in the lagging strand with DNA

Question 25

DNA ligase

Answer 25

enzyme that joins the sugar-phospate backbones of the Okazaki segments in the lagging strand

Question 26

proofreading

Answer 26

DNA polymerases proofread the nucleotide sequence

Question 27

mismatch repair

Answer 27

other enzymes remove and replace incorrectly paired nucleotides

Question 28

nuclease

Answer 28

a DNA-cutting enzyme that can remove a segment of DNA strand (ie to remove damage)

Question 29

nucleotide excision repair

Answer 29

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

Question 30

shortening of the ends of linear DNA molecules

Answer 30

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

Question 31

telomeres

Answer 31

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

Question 32

telomerase

Answer 32

an enzyme that catalyzes the lengthing of telomeres in eukaryotic germ cells (cancer cells too possibly)

Question 33

chromatin

Answer 33

all DNA + associated proteins that package/order the DNA

Question 34

histones

Answer 34

positively charged proteins responsible for the first level of DNA (negatively charged) packing in chromatin; histones group together and DNA wraps around creating nucleosomes

Question 35

nuclesosomes

Answer 35

beads of DNA wrapped around histones

Question 36

fiber (chromatin)

Answer 36

structure of nucleosomes condensed into a fiber

Question 37

looped domains (chromatin)

Answer 37

structure of chromatin fiber that is looped into a thicker fiber

Question 38

metaphase chromosome

Answer 38

the condensed chromatin structure, looped domains futher folded and coiled; particular genes always end up in the same places

Question 39

heterochromatin

Answer 39

clumped chromatin during interphase; less accessible for gene expression; in contrast to euchromatin

Question 40

euchromatin

Answer 40

dispersed chromatin during interphase; more accessible for gene expression