Module 5—The Molecular Basis of Inheritance

Question 1

Friedrich Miescher

Answer 1

accidentally isolated DNA for the first time

Question 2

Albrecht Kossel

Answer 2

discovered 4 nitrogenous bases

Question 3

Phoebus Levene

Answer 3

tetranucleotide hypothesis - incorrect belief that the pattern of bases repeated, making DNA unlikely to be the genetic information

Question 4

Griffith experiment

Answer 4

first demonstration of heredity by something abiotic (DNA from dead cells)

combination of dead pathogenic cells with live harmless cells yielded pathogenic cells (“transformation”)

Question 5

Avery, Macleod & McCarty

Answer 5

showed DNA to be the molecule assimilated into a “transformed” cell

destroying DNA prevented transference, but destroying RNA & protein did not

Question 6

Hershey & Chase

Answer 6

showed that DNA is the genetic material

radiolabelled DNA and protein of phage T2; labels showed DNA in E. coli, but not protein

Question 7

radiolabelling of phage protein

Answer 7

radioactive sulfur

Question 8

radiolabelling of phage DNA

Answer 8

radioactive phosphorus

Question 9

deoxyribose vs ribose

Answer 9

ribose has OH groups at 2’ and 3’

deoxyribose has H at 2’ position instead of OH

Question 10

purines

structure

Answer 10

2 rings

adenine & guanine

Question 11

pyrimidines

structure

Answer 11

1 ring

cytosine, thymine, uracil

Question 12

Chargaff

Answer 12

found that base composition of DNA varies between species, but all species have equal ratios of A to T, and C to G

Question 13

Franklin & Wilkins

Answer 13

produced x-ray crystallography images of DNA helical pattern

Question 14

Watson & Crick

Answer 14

deduced structure of DNA:

• double helix structure
• double strand
• complementary base pairing (only A + T and C + G provided uniform width)
• antiparallel backbones

Question 15

3 forms of DNA

Answer 15

A form

B form

Z form

Question 16

most important/normal form of DNA

Answer 16

B form

Question 17

2 areas of DNA where base pairs are accessible

Answer 17

major & minor grooves

Question 18

diameter of DNA

Answer 18

2 nm

Question 19

each base is ___ nm apart

Answer 19

3.4

Question 20

DNA makes a complete turn every ___ bases, or every ____ nm

Answer 20

10

34

Question 21

dehydration of DNA produces…

Answer 21

A form

no grooves; tighly wound

Question 22

tension on DNA produces…

Answer 22

Z form

left handed

transient

Question 23

2 DNA strands are linked by…

Answer 23

hydrogen bonds between base pairs

Question 24

bonds between stacked base bairs

Answer 24

van der waals

Question 25

___ H bonds between A & T

Answer 25

2

Question 26

___ H bonds between C & G

Answer 26

3

Question 27

correct model of duplication

Answer 27

semiconservative

daughter molecule composed of a new one and an old one

Question 28

Meselson & Stahl

Answer 28

tested semiconservative model of duplication & found it to be correct

Question 29

location of DNA duplication

Answer 29

the replication bubble

Question 30

at the center of the replication bubble

Answer 30

origin of replication

Question 31

where two ends of the replication bubble meet

Answer 31

replication fork

Question 32

helicase

Answer 32

unwinds parental double helix at replication forks

Question 33

single strand binding proteins

Answer 33

bind to strand of parental DNA just inside bubble

keep hydrogen bonds from reforming

Question 34

topoisomerase

Answer 34

relieves overwinding strain ahead of replication forks (outside of bubble)

breaks, swivels and rejoins strands

Question 35

primase

Answer 35

lays down RNA primers at 5’ ends of leading strand and Okazaki fragments

Question 36

DNA pol III

Answer 36

synthesizes new DNA strands by adding new nucleotides to the primers

Question 37

DNA pol I

Answer 37

removes primers & replaces them with DNA nucleotides

Question 38

DNA ligase

Answer 38

joins Okazaki fragments

joins 3’ end of former primer location to the rest of the leading strand

Question 39

DNA polymerization direction

Answer 39

5’ → 3’

Question 40

new nucleotides added to…

Answer 40

OH group at 3’ location on deoxyribose

Question 41

free nucleotide

structure

bond name

what is released after binding to new strand? purpose?

Answer 41

DATP

has 3 phosphates

binds to DNA strand by phosphodiester linkage

pyrophosphate (two PO₄) released, providing energy to “pay” for synthesis of large polymer

Question 42

complex of all DNA duplication enzymes

Answer 42

DNA replication machine

Question 43

trombone model

Answer 43

DNA replication complex is anchored/stationary in the nucleus

DNA is passed through it and duplicated

1 helix enters, 2 helices exit

Question 44

mismatch repair occurs during..

Answer 44

duplication

Question 45

steps of mismatch repair

Answer 45

enzymes detect mismatched base pairs

nuclease excises damaged segment

DNA pol fills in missing nucleotides correctly

ligase seals the free end (3’)

Question 46

repair enzymes discovered in humans

Answer 46

107

Question 47

problem for eukaryotes that prokaryotes do not have

solution

Answer 47

duplication leads to degeneration of the ends of chromosomes - loss of genes

telomerases lay down telomeres (RNA templates)

telomeres postpone erosion of chromasomes by providing a buffer region that can safely be lost

Question 48

first level of DNA packing

Answer 48

histones

Question 49

help control nucleosome position/packing

Answer 49

H1 histones

histone tails

Question 50

organize chromatin into dense loops during division

Answer 50

condensins

Question 51

condenses are activated by…

Answer 51

mitotic cyclin-cdk complexes

Question 52

period of greatest chromosome density

Answer 52

metaphase

Question 53

densely packed chromatin

Answer 53

heterochromatin

Question 54

loosely packed chromatin

Answer 54

euchromatin

Question 55

suggests order in the organization of the genome during interphase

Answer 55

fluorescent labelling