Chapter 16: molecular basis of inheritance

Question 1

Frederick Griffith

Answer 1

studied strains of streptococcus and discovered transformation
- treated mice with pathogenic S strain, nonpathogenic R strain, heat-killed S strain
- found that heat-killed S cells and living R cells killed mice

Question 2

transformation

Answer 2

change in genotype/phenotype due to assimilation of external DNA by cell

Question 3

Avery, McCarty, MacLeod

Answer 3

found that transforming agent was DNA

Question 4

bacteriophages

Answer 4

virus that infects bacteria

Question 5

virus

Answer 5

DNA enclosed by protective coat (mostly protein)

Question 6

Hershey & Chase

Answer 6

used radioactive sulfur and phosphorus to trace protein/DNA of T2 phages that infect bacteria. found that phages inject DNA and so DNA carries hereditary material

Question 7

Chargaff’s rules

Answer 7

1. base composition varies between species
2. A = T, G = C

Question 8

double helix

Answer 8

DNA has 2 strands in a helix shape

Question 9

antiparallel

Answer 9

two sugar-phosphate backbones go in opposite directions

Question 10

purines

Answer 10

adenine and guanine

Question 11

pyrimidines

Answer 11

thymine and cytosine

Question 12

base pairing in DNA

Answer 12

• 2 hydrogen bonds between A and T
• 3 hydrogen bonds between G and C

Question 13

semiconservative model

Answer 13

each daughter DNA has template parent strand and one newly made strand

Question 14

conservative model

Answer 14

two parental strands reassociate after acting as templates for new strands

Question 15

dispersive model

Answer 15

each strand of both daughter molecules has mixture of both parent and newly synthesized DNA

Question 16

Meselsohn & Stahl

Answer 16

cultured bacteria with heavy isotope 15N (nitrogen) and then transferred to medium with 14N (lighter). centrifuged DNA samples from bacteria to separate DNA of different densities

Question 17

origins of replication

Answer 17

short stretches of DNA with specific sequences where DNA replication starts

Question 18

replication fork

Answer 18

region where parental strands of DNA are unwound in a replication bubble (eukaryotes)

Question 19

helicase

Answer 19

separate DNA at replication forks

Question 20

single-strand binding proteins

Answer 20

keeps DNA apart in replication

Question 21

topoisomerase

Answer 21

relieves tension ahead of replication fork in DNA

Question 22

primer

Answer 22

RNA chain used in initiation of DNA synthesis

Question 23

DNA polymerases

Answer 23

catalyze synthesis of DNA by adding nucleotides to preexisting chain in 5-3 direction
- adds nucleotriphosphate, which loses 2 phosphate as pyrophosphate
- hydrolysis of pyrophosphate to 2 molecules of inorganic phosphate is coupled exergonic reaction that helps drive polymerization reaction

Question 24

primase

Answer 24

synthesizes RNA primer

Question 25

leading strand

Answer 25

strand elongated continuously in 5-3 direction

Question 26

lagging strand

Answer 26

strand elongated in fragments away from replication fork in 5-3 direction

Question 27

Okazaki fragments

Answer 27

segments of lagging strand. 1000-2000 bp long in E. coli, 100-200 bp long in eukaryotes

Question 28

DNA polymerase 3

Answer 28

adds nucleotides

Question 29

DNA polymerase 1

Answer 29

replaces RNA primer with DNA

Question 30

DNA ligase

Answer 30

joins sugar-phosphate backbones of Okazaki fragments

Question 31

mismatch repair

Answer 31

other enzymes remove/replace incorrectly paired nucelotides

Question 32

nuclease

Answer 32

DNA-cutting enzyme

Question 33

nucleotide excision repair

Answer 33

nuclease cuts damaged DNA and DNA polymerse/ligase fills in gap

Question 34

xeroderma pigmentosum

Answer 34

defect in nucleotide excision repair enzyme. sensitive to sunlight (cause UV rays can cause thymine dimers)

Question 35

telomeres

Answer 35

special nucleotide sequences at the ends of eukaryotic chromosomal DNA molecules that protects it
- not needed in circular prokaryote DNA

Question 36

telomerase

Answer 36

catalyzes lengthening of telomeres in eukaryotic germ cells

Question 37

nucleoid

Answer 37

dense region of bacteria in bacterium not membrane-enclosed

Question 38

chromatin

Answer 38

complex of DNA and protein

Question 39

histones

Answer 39

proteins involved in DNA packing in chromatin. about 100 amino acids, 1/5 of which are positively charged (to bind to negative DNA).
- H2A, H2G, H3, H4: used in nucleosomes

Question 40

nucleosome/ 10 nm fiber

Answer 40

basic unit of DNA packing. DNA wound twice around protein core of 2 molecules each of four main histone types.
- N terminus (amino end) of each histone extends outwards (histone tail)

Question 41

linker DNA

Answer 41

“string” between beads of nucleosomes

Question 42

30 nm fiber

Answer 42

packing because of interactions between histone tails of nucleosome and linker DNA on nucleosomes on either side.
- prevalent in interphase nucleus

Question 43

looped domains (300 nm fiber)

Answer 43

30 nm fiber forms loops (looped domains) to chromosome scaffold of proteins, which has some topoisomerase and H1 histones.

Question 44

metaphase chromosomes

Answer 44

looped domains coil in mitotic chromosome (1400 nm)

Question 45

heterchromatin

Answer 45

highly condensed interphase chromatin

Question 46

ucrhomatin

Answer 46

more dispersed chromatin. easily transcribed because DNA is more accessible