Chapter 16 Flashcards Preview

Biology 1406 > Chapter 16 > Flashcards

Flashcards in Chapter 16 Deck (114):
1

In 1953, James Watson and Francis Crick introduced an

elegant double-helical model for the structure of deoxyribonucleic acid, or DNA

2

DNA, the substance of inheritance, is

the most celebrate molecule of our time

3

Hereditary information is encoded in

DNA and reproduced in all cells of the body

4

This DNA program directs the

development of biochemical, anatomical, physiological, and (to some extent) behavioral traits

5

DNA is the

genetic material

6

Early in the 20th century,

the identification of the molecules of inheritance loomed as a major challenge to biologists

7

When T.H. Morgan's group showed that genes are located on chromosomes,

the two components of chromosomes---DNA and protein--- became candidates for the genetic material

8

The key factor in determining the genetic material was

choosing appropriate experimental organisms

9

The role of DNA in heredity was first discovered by

studying bacteria and the viruses that infect them

10

The discovery of the genetic role of DNA began with research by

Frederick Griffith in 1928

(the mouse guy)

11

Frederick Griffith worked with

two strains of a bacterium, one pathogenic (bad) and one harmless

12

When Griffith mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain,

some living cells became pathogenic

13

Griffith called this phenomenon

transformation, now defined as a change in genotype and phenotype due to assimilation of foreign DNA

14

In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that

the transforming substance was DNA

(they figured out Griffith (the mouse guys) experiment.)
((DNA is transforming bacteria causing mice to die??))

15

Their (Oswald Avery, Maclyn McCarty, and Colin MacLeod) conclusion was based on experimental evidence that

only DNA worked in transforming harmless bacteria into pathogenic bacteria.

Many biologists remained skeptical, mainly because little was known about DNA.

16

Evidence that viral DNA can

program cells

17

More evidence for DNA as the genetic material came from

studies of viruses that infect bacteria

18

Such viruses, called bacteriophages (or phages), are

widely used in molecular genetics research

19

Bacteria is only made of

DNA and protein

20

In 1952, Alfred Hershey and Martha Chase performed experiments showing that

DNA is the genetic material of a phage known as T2.

(the blender experiment)

21

To determine this, Alfred Hershey and Martha Chase designed an experiment showing that

only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection

22

Alfred Hershey and Martha Chase concluded that

the injected DNA of the phage provides the genetic information

23

It was known that DNA is a

polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate group

24

In 1950, Edwin Chargaff reported that

DNA composition varies from one species to the next.

This evidence of diversity made DNA a more credible candidate for the genetic material

((DNA Rules))

25

Two findings became known as Chargaff's Rules:

-The base composition of DNA varies between species
--Humans have 30.3% A (adenine)
--E. coli has 26% A (adenine)

-In any species the number of A and T bases are equal and the number of G and C bases are equal

26

The bases for Chargaff's rules was not understood until

the discovery of the double helix

27

After DNA was accepted as the genetic material, the challenge was to

determine how its structure accounts for its role in heredity

28

Maurice Wilkins and Rosalind Franklin were using a technique called

X-ray Crystallography to study molecule structure

29

Rosalind Franklin produced a picture of the

DNA molecule using this X-ray Crystallography technique

30

Scientists use X-ray crystallography to

determine a protein's structure

31

Another method is

nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization

32

Bioinformatics uses computer programs to

predict protein structure from amino acid sequences

33

Rosalind Franklin's X-ray crystallographic images of DNA enabled James Watson to

deduce that DNA was helical

34

The X-ray images also enabled James Watson to deduce the

width of the helix and the spacing of the nitrogenous bases

35

The pattern in the photo suggested that the DNA molecule was made up of

two strands, forming a double helix

36

James Watson and Francis Crick built models of a

double helix to conform to the X-rays and chemistry of DNA

37

Rosalind Franklin had concluded that there were

two outer sugar-phosphate backbones, with the nitrogenous bases paired in the molecule's interior

38

James Watson built a model in which the

backbones were antiparallel (their subunits run in opposite directions)

39

At first, James Watson and Francis Crick thought the

bases paired like with like (A with A, and so on), but such pairings did not result in a uniform width

40

Instead, pairing a purine with a pyrimidine resulted in a

uniform width consistent with the X-ray data

41

James Watson and Francis Crick reasoned that the

pairing was more specific, dictated by the base structures

42

James Watson and Francis Crick determined that

adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C)

43

The Watson-Crick model explains Chargaff's rules:

in any organism the amount of A=T, and the amount of G=C

44

Many proteins work together in

DNA replication and repair

45

The relationship between structure and function is

manifest in the double helix

46

James Watson and Francis Crick noted that

the specific base pairing suggested a possible copying mechanism for genetic material.

47

The Basic Principle:

Base pairing to a template strand

48

Since the two strands of DNA are complementary,

each strand acts as a template for building a new strand in replication

49

In DNA replication,

the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules

50

DNA replication occurs in the

S phase of interphase

51

James Watson and Francis Crick's semiconservative model of replication predicts that

when a double helix replicates, each daughter molecule will have one old strand (derived or "conserved" from the parent molecule) and one newly made strand

((half old stuff and half new stuff))

52

Competing models were the

conservative model (the two parent strands rejoin) and the dispersive model (each strand is a mix of old and new)

53

Experiments by Matthew Meselson and Franklin Stahl supported the

semiconservative model ((half old stuff and half new stuff))

54

The copying of DNA is remarkable in its

speed and accuracy.

There is only 1 mistake in 10 billion nucleotides

55

More than a dozen enzymes and other proteins participate in

DNA replication

56

Replication begins at particular sites called

origins of replication, where the two DNA strands are separated, opening up a replication "bubble"

57

A eukaryotic chromosome may have

hundreds or even thousands of origins of replication

58

Replication proceeds in

both directions from each origin, until the entire molecule is copied

59

At the end of each replication bubble is a

replication fork, a Y-shaped region where new DNA strands are elongating

60

Helicases are

enzymes that untwist the double helix at the replication forks

61

Single-strand binding proteins

bind to and stabilize single-stranded DNA (keeps the strands apart)

62

Topoisomerase

corrects "overwinding" ahead of replication forks by breaking, swiveling, and rejoining DNA strands

63

DNA polymerases cannot initiate synthesis of a

polynucleotide; they can only add nucleotides to the 3' end

64

The initial nucleotide strand is a short

RNA primer

65

An enzyme called primase can start an

RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template

66

The primer is short (5-10 nucleotides long), and the

3' end serves as the starting point for the new DNA strand

67

Enzymes called DNA polymerases III catalyze the

elongation of new DNA at a replication fork

68

Most DNA polymerases III require

a primer and a DNA template strand

69

The rate of elongation is about

500 nucleotides per second in bacteria and 50 per second in human cells

70

Each nucleotide that is added to a growing DNA strand is a

nucleoside triphosphate

71

dATP supplies adenine to DNA and is

similar to the ATP of energy metabolism

72

The difference is in their sugars:

dATP has deoxyribose while ATP has ribose

73

As each monomer of dATP joins the DNA strand,

it loses two phosphate groups as molecule of pyrophosphate

74

The antiparallel structure of the double helix affects

replication

75

DNA polymerases (III??) add

nucleotides only to the free 3' end of a growing strand; therefore, a new DNA strand can elongate only in the 5' to 3' direction

76

Along one template strand of DNA, the DNA polymerase synthesizes a

leading strand continuously, moving toward the replication fork

77

To elongate the other new strand, called the lagging strand,

DNA polymerase must work in the direction away from the replication fork

78

The lagging strand is synthesized as a series of fragments called

Okazaki fragments, which are joined together by DNA ligase

79

The proteins that participate in DNA replication form a

large complex, a "DNA replication machine"

80

The DNA replication machine may be

stationary during the replication process

81

Recent studies support a model in which

DNA polymerase molecules "reel in" parental DNA and "extrude" newly made daughter DNA molecules

82

DNA polymerases I proofread newly made

DNA, replacing any incorrect nucleotides

83

In mismatch repair of DNA,

repair enzymes correct errors in base pairing

((during duplication))

84

DNA can be damaged by

exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes

85

In nucleotide excision repair,

a nuclease cuts out and replaces damaged stretches of DNA

((not during duplication. this is when DNA is damaged by exposure to harmful stuff))

86

Error rate after proofreading repair is

low but not zero

87

Sequence changes may become permanent and

can be passed on to the next generation

88

These changes (mutations) are the source of the

genetic variation upon which natural selection operates

89

Limitations of DNA polymerase create problems for the

linear DNA of eukaryotic chromosomes

90

The usual replication machinery provides no way to

complete the 5' ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends.

This is not a problem for prokaryotes, most of which have circular chromosomes.

91

Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called

telomeres

92

Telomeres do not prevent the shortening of DNA molecules, but they

do postpone the erosion of genes near the ends of DNA molecules

93

It has been proposed that the shortening of telomeres is

connected to aging

94

If chromosomes of germ cells became shorter in every cell cycle,

essential genes would eventually be missing from the gametes they produce

95

An enzyme called telomerase catalyzes the

lengthening of telomeres in germ cells

96

The shortening of telomeres might protect cells from

cancerous growth by limiting the number of cell divisions
((once it gets the shortest, it can signal apoptosis))

97

There is evidence of telomerase activity in

cancer cells, which may allow cancer cells to persist

98

A chromosome consists of a

DNA molecule packed together with proteins

99

The bacterial chromosome is a

double-stranded, circular DNA molecule associated with a small amount of protein

100

Eukaryotic chromosomes have

linear DNA molecules associated with a large amount of protein

101

In a bacterium,

the DNA is "supercoiled" and found in a region of the cell called the nucleoid

(prokaryote)

102

Chromatin, a complex of DNA and protein, is found in

the nucleus of eukaryotic cells

103

Chromosomes fit into the nucleus through an

elaborate, multilevel system of packing

104

Histones are

proteins that are responsible for the first level of DNA packing in chromatin

105

DNA winds around

histones to form nucleosome "beads"

106

Nucleosomes are

strung together like beads on a string by linker DNA

107

Chromatin undergoes changes in

packing during the cell cycle

108

At interphase, some chromatin is organized into a

10-nm fiber, but much is compacted into a 30-nm fiber, through folding and looping

(don't need to know the sizes and lengths of these)

109

Though interphase chromosomes are not highly condensed,

they still occupy specific restricted regions in the nucleus

110

Most chromatin is loosely packed in the

nucleus during interphase and condenses prior to mitosis

111

Loosely packed chromatin is called

euchromatin

112

During interphase a few regions of chromatin (centromeres and telomeres) are highly condensed into

heterochromatin

113

Dense packing of the heterochromatin makes it

difficult for the cell to express genetic information coded in these regions

114

Histones can undergo chemical modifications that result in

changes in chromatin organization