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Biology 1406 > Chapter 16 > Flashcards

Chapter 16 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
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

Biology 1406 (53 decks)

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