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Biology 1406 > Chapter 16 > Flashcards

Chapter 16 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

In 1953, James Watson and Francis Crick introduced an

A

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

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2
Q

DNA, the substance of inheritance, is

A

the most celebrate molecule of our time

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3
Q

Hereditary information is encoded in

A

DNA and reproduced in all cells of the body

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4
Q

This DNA program directs the

A

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

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5
Q

DNA is the

A

genetic material

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6
Q

Early in the 20th century,

A

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

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7
Q

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

A

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

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8
Q

The key factor in determining the genetic material was

A

choosing appropriate experimental organisms

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9
Q

The role of DNA in heredity was first discovered by

A

studying bacteria and the viruses that infect them

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10
Q

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

A

Frederick Griffith in 1928

the mouse guy

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11
Q

Frederick Griffith worked with

A

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

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12
Q

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

A

some living cells became pathogenic

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13
Q

Griffith called this phenomenon

A

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

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14
Q

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

A

the transforming substance was DNA

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

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15
Q

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

A

only DNA worked in transforming harmless bacteria into pathogenic bacteria.

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

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16
Q

Evidence that viral DNA can

A

program cells

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17
Q

More evidence for DNA as the genetic material came from

A

studies of viruses that infect bacteria

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18
Q

Such viruses, called bacteriophages (or phages), are

A

widely used in molecular genetics research

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19
Q

Bacteria is only made of

A

DNA and protein

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20
Q

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

A

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

the blender experiment

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21
Q

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

A

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

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22
Q

Alfred Hershey and Martha Chase concluded that

A

the injected DNA of the phage provides the genetic information

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23
Q

It was known that DNA is a

A

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

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24
Q

In 1950, Edwin Chargaff reported that

A

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))

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25
Q

Two findings became known as Chargaff’s Rules:

A
  • 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

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26
Q

The bases for Chargaff’s rules was not understood until

A

the discovery of the double helix

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27
Q

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

A

determine how its structure accounts for its role in heredity

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28
Q

Maurice Wilkins and Rosalind Franklin were using a technique called

A

X-ray Crystallography to study molecule structure

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29
Q

Rosalind Franklin produced a picture of the

A

DNA molecule using this X-ray Crystallography technique

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30
Q

Scientists use X-ray crystallography to

A

determine a protein’s structure

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31
Q

Another method is

A

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

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32
Q

Bioinformatics uses computer programs to

A

predict protein structure from amino acid sequences

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33
Q

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

A

deduce that DNA was helical

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34
Q

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

A

width of the helix and the spacing of the nitrogenous bases

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35
Q

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

A

two strands, forming a double helix

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36
Q

James Watson and Francis Crick built models of a

A

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

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37
Q

Rosalind Franklin had concluded that there were

A

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

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38
Q

James Watson built a model in which the

A

backbones were antiparallel (their subunits run in opposite directions)

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39
Q

At first, James Watson and Francis Crick thought the

A

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

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40
Q

Instead, pairing a purine with a pyrimidine resulted in a

A

uniform width consistent with the X-ray data

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41
Q

James Watson and Francis Crick reasoned that the

A

pairing was more specific, dictated by the base structures

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42
Q

James Watson and Francis Crick determined that

A

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

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43
Q

The Watson-Crick model explains Chargaff’s rules:

A

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

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44
Q

Many proteins work together in

A

DNA replication and repair

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45
Q

The relationship between structure and function is

A

manifest in the double helix

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46
Q

James Watson and Francis Crick noted that

A

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

47
Q

The Basic Principle:

A

Base pairing to a template strand

48
Q

Since the two strands of DNA are complementary,

A

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

49
Q

In DNA replication,

A

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

50
Q

DNA replication occurs in the

A

S phase of interphase

51
Q

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

A

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
Q

Competing models were the

A

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

53
Q

Experiments by Matthew Meselson and Franklin Stahl supported the

A

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

54
Q

The copying of DNA is remarkable in its

A

speed and accuracy.

There is only 1 mistake in 10 billion nucleotides

55
Q

More than a dozen enzymes and other proteins participate in

A

DNA replication

56
Q

Replication begins at particular sites called

A

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

57
Q

A eukaryotic chromosome may have

A

hundreds or even thousands of origins of replication

58
Q

Replication proceeds in

A

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

59
Q

At the end of each replication bubble is a

A

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

60
Q

Helicases are

A

enzymes that untwist the double helix at the replication forks

61
Q

Single-strand binding proteins

A

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

62
Q

Topoisomerase

A

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

63
Q

DNA polymerases cannot initiate synthesis of a

A

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

64
Q

The initial nucleotide strand is a short

A

RNA primer

65
Q

An enzyme called primase can start an

A

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

66
Q

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

A

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

67
Q

Enzymes called DNA polymerases III catalyze the

A

elongation of new DNA at a replication fork

68
Q

Most DNA polymerases III require

A

a primer and a DNA template strand

69
Q

The rate of elongation is about

A

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

70
Q

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

A

nucleoside triphosphate

71
Q

dATP supplies adenine to DNA and is

A

similar to the ATP of energy metabolism

72
Q

The difference is in their sugars:

A

dATP has deoxyribose while ATP has ribose

73
Q

As each monomer of dATP joins the DNA strand,

A

it loses two phosphate groups as molecule of pyrophosphate

74
Q

The antiparallel structure of the double helix affects

A

replication

75
Q

DNA polymerases (III??) add

A

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
Q

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

A

leading strand continuously, moving toward the replication fork

77
Q

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

A

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

78
Q

The lagging strand is synthesized as a series of fragments called

A

Okazaki fragments, which are joined together by DNA ligase

79
Q

The proteins that participate in DNA replication form a

A

large complex, a “DNA replication machine”

80
Q

The DNA replication machine may be

A

stationary during the replication process

81
Q

Recent studies support a model in which

A

DNA polymerase molecules “reel in” parental DNA and “extrude” newly made daughter DNA molecules

82
Q

DNA polymerases I proofread newly made

A

DNA, replacing any incorrect nucleotides

83
Q

In mismatch repair of DNA,

A

repair enzymes correct errors in base pairing

(during duplication)

84
Q

DNA can be damaged by

A

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

85
Q

In nucleotide excision repair,

A

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
Q

Error rate after proofreading repair is

A

low but not zero

87
Q

Sequence changes may become permanent and

A

can be passed on to the next generation

88
Q

These changes (mutations) are the source of the

A

genetic variation upon which natural selection operates

89
Q

Limitations of DNA polymerase create problems for the

A

linear DNA of eukaryotic chromosomes

90
Q

The usual replication machinery provides no way to

A

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
Q

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

A

telomeres

92
Q

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

A

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

93
Q

It has been proposed that the shortening of telomeres is

A

connected to aging

94
Q

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

A

essential genes would eventually be missing from the gametes they produce

95
Q

An enzyme called telomerase catalyzes the

A

lengthening of telomeres in germ cells

96
Q

The shortening of telomeres might protect cells from

A

cancerous growth by limiting the number of cell divisions

(once it gets the shortest, it can signal apoptosis)

97
Q

There is evidence of telomerase activity in

A

cancer cells, which may allow cancer cells to persist

98
Q

A chromosome consists of a

A

DNA molecule packed together with proteins

99
Q

The bacterial chromosome is a

A

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

100
Q

Eukaryotic chromosomes have

A

linear DNA molecules associated with a large amount of protein

101
Q

In a bacterium,

A

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

(prokaryote)

102
Q

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

A

the nucleus of eukaryotic cells

103
Q

Chromosomes fit into the nucleus through an

A

elaborate, multilevel system of packing

104
Q

Histones are

A

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

105
Q

DNA winds around

A

histones to form nucleosome “beads”

106
Q

Nucleosomes are

A

strung together like beads on a string by linker DNA

107
Q

Chromatin undergoes changes in

A

packing during the cell cycle

108
Q

At interphase, some chromatin is organized into a

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
Q

Though interphase chromosomes are not highly condensed,

A

they still occupy specific restricted regions in the nucleus

110
Q

Most chromatin is loosely packed in the

A

nucleus during interphase and condenses prior to mitosis

111
Q

Loosely packed chromatin is called

A

euchromatin

112
Q

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

A

heterochromatin

113
Q

Dense packing of the heterochromatin makes it

A

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

114
Q

Histones can undergo chemical modifications that result in

A

changes in chromatin organization

Biology 1406 (53 decks)

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