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Finals Cytogenetics > U6: Molecular Basis of Inheritance > Flashcards

U6: Molecular Basis of Inheritance Flashcards

1
Q
  • the two chemical components of chromosomes - _______ and ___________- emerged as the leading
    candidates for the genetic material
A

DNA and protein

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2
Q

Once _______________ group showed that genes exist as parts of chromosomes, the two chemical components of chromosomes – DNA and protein- emerged as the leading candidates for the genetic material

A

Thomas Hunt Morgan’s

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3
Q

Year for Frederick Griffith experiment / study

A

1928

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4
Q

British medical officer who was trying to develop a vaccine against pneumonia

A

Frederick Griffith

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5
Q

Frederick Griffith was studying this type of bacterium; a bacterium that causes pneumonia in mammals

A

Streptococcus pneumoniae

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6
Q

Explain the experiment of Frederick Griffith

A

Frederick Griffith studied two strains of the bacterium Streptococcus pneumoniae. The S (smooth) strain can cause pneumonia in mice; it is pathogenic because the cells have an outer capsule that protects them from an animal’s immune system. Cells of the R (rough) strain lack a capsule and are nonpathogenic. To test for the trait of pathogenicity, Griffith injected mice with the two strains

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7
Q

How many strains did Griffith have in his experiment? What are these strains?

A

Griffith had two strains (varieties) of the bacterium, one pathogenic (disease-causing) and one nonpathogenic (harmless)

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8
Q

hypothesized that nucleic acid might be Griffith’s “transforming principle”

A

OSWALD AVERY, MACLYN MCCARTY, and COLIN MACLEOD

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9
Q

Give the conclusion of Griffith’s experiment

A

The living R bacteria had been transformed into pathogenic S bacteria by an unknown, heritable substance from the dead S cells that enabled the R cells to make capsules

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10
Q

they observed that treating broken open type S bacteria with protease- an enzyme that dismantles protein- did not prevent the transformation of a nonvirulent to a virulent strain, but treating such bacteria with deoxyribose-nuclease (or DNase), an enzyme dismantles DNA only, did disrupt transformation

A

OSWALD AVERY, MACLYN MCCARTY, and COLIN MACLEOD

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11
Q

What year did OSWALD AVERY, MACLYN MCCARTY, and COLIN MACLEOD confirmed that DNA is the transforming principle of the bacteria?

A

1944

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12
Q

A virus that infects bacteria; also called a phage.

A

Bacteriophages

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13
Q

Other term for bacteriophages

A

Phage

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14
Q

[True or False]
→ viruses are much simpler than cells
→ a virus is little more than DNA (or sometimes RNA) enclosed by a protective coat, which is often simply protein

A

Both statements are true

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15
Q

In _________, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2.

A

1952

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16
Q

In 1952, who performed experiments showing that
DNA is the genetic material of a phage
known as T2.?

A

Alfred Hershey and Martha Chase

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17
Q

Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as _________. This is one of the many phages that infect Escherichia coli (E. coli).

A

T2

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18
Q

A bacterium that normally lives in the intestines of mammals and is a model organism for molecular biologists

A

E. coli

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19
Q

DNA was known to be a polymer of nucleotides, each having three components: a nitrogenous (nitrogen-containing) base, a pentose sugar called deoxyribose, and a phosphate group

A

CHARGAFF’S RULE

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19
Q

Further evidence that DNA is the genetic material came from the laboratory of biochemist _______________.

A

Erwin Chargaff

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20
Q

Erwin Chargaff reported that the base composition of DNA varies from one species to another.

Give the percentage of DNA nucleotides with base A in the following organisms:

  1. Sea urchin
  2. Human
  3. E. coli
A

Chargaff found that :
- 32.8% of sea urchin DNA nucleotides have the base A
- 30.4% of human DNA nucleotides have base A and
- 24.7% of the DNA nucleotides from the bacterium E. coli have the base A

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21
Q

Give Chargaff’s Rule

A

CHARGAFF’S RULE:
1. DNA base composition varies between species.
2. For each species, the percentages of A and T bases are roughly equal, as those of G and C bases.

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22
Q

suggested a triple helix structure for DNA
→ this was incorrect

A

LINUS PAULING

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23
Q

bombarded DNA with X-rays using a technique called X-ray diffraction, then deduced the overall structure of the molecule from the patterns in which the X-rays were deflected

A

MAURICE WILKINS AND ROSALIND FRANKLIN

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24
Q

How many hours did Franklin took in order to obtain photo 51 of the B form in May of 1952?

A

100 hours

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25
Q

[Scientist]
→ ____________ : provided a pivotal clue to deducing the three-dimensional structure of DNA. She distinguished two forms of DNAa dry, crystalline “A” form, and the wetter type seen in cells, the “B” form.

A

Rosalind Franklin

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26
Q

______ and _________ were certain of the sugar-phosphate backbone largely from photo 51, and turned their attention to the bases

A

Watson and Crick

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27
Q

opposing orientation of the two nucleotide chains in the DNA molecule

A

Antiparallelism

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28
Q

adenine and thymine number of H bonds

A

2 hydrogen bonds

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29
Q

[WHAT YEAR]
→ Watson and Crick surprised the scientific world with a succinct, one-page paper that reported their molecular model of the DNA: the double helix, which has since become the symbol of molecular biology

A

APRIL 1953

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30
Q

Rosalind Franklin had died of _____________ at the age of 37 in 1958 and was thus ineligible for the prize) [Nobel Prize can only be awarded to living person

A

ovarian cancer

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31
Q

[DNA REPLICATION ALTERNATIVE MODELS]
→ the two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix

A

CONSERVATIVE MODEL

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32
Q

[DNA REPLICATION ALTERNATIVE MODELS]
→ two strands of the parental molecule separate, and each functions as a template for synthesis of new, complementary strand

A

SEMICONSERVATIVE MODEL

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33
Q

(DNA REPLICATION ALTERNATIVE MODELS)
→ each strand of both daughter molecules contains a** mixture of old and newly** synthesized DNA

A

DISPERSIVE MODEL

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34
Q

After two years of preliminary work at the California Institute of Technology in the late 1950s, _________ AND _______________ devised a clever experiment that distinguished between the three DNA Replication models

A

Matthew Meselson and Franklin Stahl

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35
Q

site where replication of chromosomal DNA begins

A

ORIGINS OF REPLICATION

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36
Q

like many other bacterial chromosomes, is circular and has a single origin

A

Escherichia coli chromosome

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37
Q

short stretches of DNA having a specific sequence of nucleotides

A

ORIGINS OF REPLICATION

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38
Q
A

Eukaryotic chromosome

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38
Q

Y-shaped region where the parental strands of DNA are being unwound

A

REPLICATION FORK

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39
Q
A
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40
Q

Some of the proteins involved in the initiation of DNA replication.

A

Helicases
Single-strand binding proteins
Topoisomerase
Primase

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41
Q

are enzymes that untwist the double helix at the replication forks, separating the two parental strands and making them available as template strands.

A

Helicases

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42
Q

→ bind the unpaired DNA strands, keeping them from repairing
→ the untwisting of the double helix causes tighter twisting and strain ahead the replication fork

A

Single-strand binding proteins

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43
Q

→ is an enzyme that helps relieve this strain by breaking, swivelling, and rejoining DNA strands

A

TOPOISOMERASE

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44
Q

→ RNA chain synthesized by primase
→ generally, 5-10 nucleotides long

A

PRIMER

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45
Q

[Primer]
→ the new DNA strand will start from the _____________ end of the RNA primer

A

3’

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46
Q

→ catalyzes the synthesis of new DNA by adding nucleotides to a preexisting chain

A

DNA POLYMERASES

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47
Q

True or False
Escherichia coli: DNA polymerase III and DNA polymerase I

A

T

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48
Q

HELICASES are enzymes that untwist the double helix at the replication forks, separating the two parental strands and making them available as ____________

A

template strands

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49
Q

[True or False]
- E. coli chromosome is circular and has a single origin

A

True

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50
Q

[True or False]
Watson and Crick’s model predicts that when a double helix replicates, each of the two daughter molecules will have one old strand, from the parental molecule, and one newly made strand.

A

T

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51
Q

Watson and Crick’s model predicts that when a double helix replicates, each of the two daughter molecules will have one old strand and one newly made strand. This __________ can be distinguished from a __________ of replication, in which the two parental strands somehow come back together after the process. It was shown to be correct experimentally by __________.

A

Semi-conservative model; conservative model; Matthew Meselson and Franklin Stahl

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52
Q

Explain the model for DNA replication (Basic Concept)

A

(a) The parental molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C.

(b) First, the two DNA strands are separated. Each parental strand can now serve as a template for a new, complementary strand.

c) Nucleotides complementary to the parental strand are connected to form the sugar-phosphate backbones of the new “daughter” strands.

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53
Q

Purine + Purine in DNA = __________

A

Too wide

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54
Q

Pyrimidine + Pyrimidine in DNA = __________

A

Too narrow

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55
Q

[TRUE OR FALSE]
- Purine + pyrimidine: width consistent with X-ray data

A

TRUE

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55
Q

Adenine can form __________ hydrogen bonds with thymine and only thymine

A

2

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56
Q

Guanine forms _________ hydrogen bonds with cytosine and only cytosine.

A

3

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56
Q

[Determine what DNA Model]
All four strands of DNA following replication have a mixture of old and new DNA

A

Dispersive model

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57
Q

What are the three alternative models? Explain each.

A

(a) Conservative model.
(b) Semiconservative model
(c) Dispersive model.

58
Q

The two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix.

A

Conservative model.

59
Q

Watson’s and Crick’s model of a double helix was supported by what following information? Explain.

A
  • Rosalind Franklin concluded the sugar-phosphate backbones were on the outside of the DNA molecule and the nitrogenous bases in the molecule’s interior.
  • The two sugar-phosphate backbones are anti-parallel (their subunits run in opposite directions).
  • A pairs with T, and G pairs with C due to hydrogen bonds between them and a uniform diameter.
60
Q

What was the additional evidence that DNA was the genetic material?

  • It came from studies of viruses that infect bacteria; these viruses are called __________
A

Bacteriophages

61
Q

Explain the synthesis of the Lagging Strand

A
  1. Primase joins RNA nucleotides into a primer.
  2. DNA pol III adds DNA nucleotides to the primer, forming Okazaki fragment 1.
  3. After reaching the next RNA primer, DNA pol III detaches.
  4. Fragment 2 is primed. Then, DNA pol III adds DNA nucleotides, detaching when it reaches the fragment 1 primer.
  5. DNA pol I replaces the RNA with DNA, adding nucleotides to the 3’ end of fragment 2 (and, earlier, of fragment 1).
  6. DNA ligase forms a bond between the newest DNA and the DNA of fragment 1.
  7. The lagging strand in this region is now complete.
62
Q

These are enzymes that proofread each nucleatide against its template as soon as it is covalently bonded to the growing strand.

A

DNA Polymerases

63
Q

[True or False]
Errors in a completed DNA molecule are high because, during DNA replication, DNA topoisomerase proofreads each nucleotide against its template as soon as it is covalently bonded to the growing strand.

A

False:
Errors in a completed DNA molecule are LOW because during DNA replication, DNA polymerases proofread each nucleotide against its template as soon as it is covalently bonded to the growing strand.

64
Q

Little more than DNA or sometimes RNA, is enclosed by a protective coat, which is often simply protein.

A

Virus

65
Q

[Determine what model]
The two strands of the parental molecule separate, and each functions as a template for the synthesis of a new, complementary strand.

A

Semiconservative model.

66
Q

[Determine what model]
Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA

A

Dispersive model.

67
Q

Who conducted this experiment?

(2) cultured E. coli for several generations in a medium containing nucleotide precursors labeled with a heavy isotope of nitrogen, 15N. They then transferred the bacteria to a medium with only 14N, a lighter isotope. They took one sample after the first DNA replication and another after the second replication. They extracted DNA from the bacteria in the samples and then centrifuged each DNA sample to separate DNA of different densities

Conclusion: The result eliminated the conservative model. They therefore concluded that DNA replication is semiconservative.

A

Matthew Meselson and Franklin Stahl

68
Q

(Scientists) concluded that DNA replication is semiconservative

A

Matthew Meselson
Franklin Stahl

69
Q

How many DNA molecules does a human somatic cell contain?

A

46 DNA molecules in its nucleus

70
Q

_____________ breaks, swivels, and rejoins the parental DNA ahead of the replication fork, relieving the strain caused by unwinding

A

Topoisomerase

71
Q

synthesizes RNA primers, using the parental DNA as a template

A

Primase

72
Q

______ unwinds and separates the parental DNA strands.

A

helicase

73
Q

[TRUE OR FALSE]
DNA cannot initiate the synthesis of a polynucleotide; they can only add DNA nucleotides to the end of an already existing chain that is base-paired with the template strand.

A

true

73
Q

___________ stabilize the unwound parental strands

A

Single-strand binding proteins

74
Q

The rate of elongation is about ____________ nucleotides per second in bacteria and ___________ per second in human cells.

A

500; 50

75
Q

What is the nucleotide that is used to make DNA?

A

dATP(Deoxyadenosine triphosphate)

76
Q

DNA polymerases can add nucleotides only to the free ____________ of a primer or growing DNA strand, never to the ___________

A

3′ end; 5′ end

77
Q

A new DNA strand can elongate only in the _____________ direction.

A

5′ —-> 3′

78
Q

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5’ to 3’ direction.

A

Leading strand

79
Q

How many primers are required for DNA pol III to synthesize the entire leading strand?

A

1 primer

80
Q

DNA pol III must work along the other template strand in the direction away from the replication fork. The DNA strand elongating in this direction is called the ____________________.

A

lagging strand

81
Q

The ___________ strand is synthesized discontinuously, as a series of segments

A

Lagging strand

82
Q

The segments of the lagging strand are called ___________________.

A

Okazaki fragments

83
Q

The segments of the lagging strand are called Okazaki fragments, after________________, the Japanese scientist who discovered them.

A

Reiji Okazaki

84
Q

Okazaki Fragments Length

E.coli :
Eukaryotes:

A

The fragments are about 1,000-2,000 nucleotides long in E. coli and 100-200 nucleotides long in eukaryotes

85
Q

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3’ end of a new DNA fragment to the 5’ end of a growing chain.

A

DNA ligase

86
Q

catalyzes the synthesis of new DNA by adding nucleotides to a preexisting chain

A

DNA POLYMERASES

87
Q

[Determine the DNA Polymerases]
Escherichia coli

A

DNA polymerase III and DNA polymerase I

88
Q

[Determine the DNA Polymerases]
Eukaryotes

A

At least 11 different DNA polymerases

89
Q

[TRUE OR FALSE]
→ The only difference between the ATP of energy metabolism and dATP, the adenine nucleotide used to make DNA, is the sugar component, which is deoxyribose in the building block of DNA but ribose in ATP.

A

TRUE

90
Q

joins the sugar-phosphate backbones of all the Okazaki fragment into a continuous DNA strand

A

DNA Ligases

91
Q

[TRUE OR FALSE]
Synthesis of the leading strand and synthesis of the lagging strand does not occur concurrently. They have different rates.

A

False;
Synthesis of the leading strand and synthesis of the lagging strand occur concurrently and at the same rate

92
Q

The lagging strand is so named because its synthesis is?

A

The lagging strand is so named because its synthesis is delayed slightly relative to the synthesis of the leading strand.

93
Q

The lagging strand is so named because its synthesis is delayed slightly relative to the synthesis of the leading strand.

A

TRUE

94
Q

____________ forms a bond between the newest DNA and the DNA of fragment 1.

A

DNA ligase

95
Q

__________ begins synthesis of the RNA primer for the fifth Okazaki fragment.

A

Primase

96
Q

Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides added to 3’ end of adjacent fragment

A

DNA pol I

97
Q

synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand

A

Primase

98
Q

relieves overwinding strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands

A

Topoisomerase

99
Q

Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand

A

DNA poll III

100
Q

Joins Okazaki fragments of lagging strand;

on leading strand, joins 3’ end of DNA that replaces primer to rest of leading strand DNA

A

DNA Ligase

101
Q

[Proofreading and Repairing of DNA]
→ During DNA replication, many ____________________ proofread each nucleotide against its template as soon as it is covalently bonded to the growing strand

A

DNA polymerases

102
Q

_________________________ : enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors

A

Mismatched pair

103
Q

[TRUE OR FALSE]
Mismatched nucleotides sometimes evade proofreading by a DNA polymerase

A

TRUE

104
Q

The various proteins that participate in DNA replication actually form a single large complex, a “DNA replication machine.”

A

The DNA Replication Complex

105
Q

A segment of the strand containing the damage is cut out (excised) by a DNA cutting enzyme _________________and the resulting gap is then filled in with nucleotides, using the undamaged strand as a template

A

NUCLEASE

106
Q

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

A

telomeres

107
Q

Telomeres become __________ during every round of replication. Thus, as expected, telomeric DNA tends to be __________ in dividing somatic cells of older individuals and in cultured cells that have divided many times.

A

shorter; shorter

108
Q

[PROOFREADING AND REPAIRING DNA]
→ Enzymes involved in filling the gap are DNA polymerase and DNA ligase - one such DNA repair system is called ___________

A

NUCLEOTIDE EXCISION REPAIR

109
Q

WHAT ARE INVOLVED IN THE NUCLEOTIDE EXCISION REPAIR

A

DNA polymerase and DNA ligase

110
Q

Enzymes that are involved in filling the gap of damaged segment of the strands are:

A

DNA polymerase and DNA ligase

111
Q

Permanent changes that are perpetuated through successive replications are called?

A

Mutations

112
Q

Because repair of damaged DNA is so important to the survival of an organism, it is no surprise that many different DNA repair enzymes have evolved. Almost ______________ are known in E. coli, and about _________ have been identified so far in humans

A

100 AND 170

113
Q

Explain Nucleotide excision repair of DNA damage.

A
  1. Teams of enzymes detect and repair damaged DNA, such as this thymine dimer (often caused by ultraviolet radiation), which distorts the DNA molecule.
  2. A nuclease enzyme cuts the damaged DNA strand at two points, and the damaged section is removed.
  3. Repair synthesis by a DNA polymerase fills in the missing nucleotides, using the undamaged strand as a template.
  4. DNA ligase seals the free end of the new DNA to the old DNA, making the strand complete
114
Q

Caused by an inherited defect in a nucleotide excision repair enzyme.

Individuals with ______ are hypersensitive to sunlight; mutations in their skin cells caused by ultraviolet light are left uncorrected, often resulting in skin cancer

A

Xeroderma pigmentosum (XP)

115
Q

Without sun protection, children who have XP can develop skin cancer by age ______.

A

10

116
Q

A disorder that signified the importance of DNA repair enzyme.

A

Xeroderma pigmentosum (XP)

117
Q

[TRUE OR FALSE]
Mutations can change the phenotype of an organism. And if they occur in germ cells, which give rise to gametes, mutations can be passed on from generation to generation

A

True

118
Q

For linear DNA, such as the DNA of eukaryotic chromosomes, the usual replication machinery cannot complete the __________________ of daughter DNA strands.

A

5′ ends of daughter DNA strands.

Note: This is another consequence of the fact that a DNA polymerase can add nucleotides only to the 3′ end of a preexisting polynucleotide

119
Q

True or False: Most prokaryotes have a circular chromosome, with no ends, so the shortening of DNA does not occur.

A

True

120
Q

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

A

Telomeres

121
Q

In each human telomere, for example, the six-nucleotide sequence ____________ is repeated between ___________ and __________ times.

A

TTAGGG
100
1000 times

122
Q

G rich tail

A

TTAGGG (Telomeres)

123
Q

GIVE PROTECTIVE FUNCTION OF TELOMERES

A
  1. Specific proteins associated with telomeric DNA prevent the staggered ends of the daughter molecule from activating the cell’s systems for monitoring DNA damage.
  2. Telomeric DNA acts as a kind of buffer zone that provides some protection against the organism’s gene shortening, somewhat like how the plastic-wrapped ends of a shoelace slow down its unravelling
124
Q

Specific proteins associated with ________ prevent the staggered ends of the daughter molecule from activating the cell’s systems for monitoring DNA damage.

A

telomeric DNA

125
Q

sequences consist of short tandem repeats that contribute to the stability and integrity of chromosomes

A

Telomeric DNA

126
Q

sequences consist of short tandem repeats that contribute to the stability and integrity of chromosomes

A

Telomeric DNA

127
Q

acts as a kind of buffer zone that provides some protection against the organism’s gene shortening

A

telomeric DNA

128
Q

[True or False]
Telomeres does not prevent the erosion of genes near the ends of chromosomes; they merely postpone it.

A

TRUE

129
Q

Telomeres become ______ during every round of replication

A

shorter

130
Q

Telomeric DNA tends to be _____________ in dividing somatic cells of older individuals and in cultured cells that have divided many times

A

shorter

131
Q

Conditions wherein telomeres become shorter:

A

→ Telomeres become shorter during every round of replication
→ Telomeric DNA tends to be shorter in dividing somatic cells of older individuals and
→ Telomeric DNA in cultured cells that have divided many times

132
Q

discovered an enzyme called telomerase that catalyzes the lengthening of telomeres in eukaryotic germ cells

A

ELIZABETH BLACKBURN and JACK SZOSTAK

133
Q

ELIZABETH BLACKBURN and JACK SZOSTAK
→ discovered an enzyme called _______________ that catalyzes the lengthening of telomeres in eukaryotic germ cells

A

Telomerase

134
Q

[TRUE OR FALSE]
→ Telomerase is NOT active in most human somatic cells, but its activity varies from tissue to tissue.

→ The activity of germ cells results in telomeres of minimum length in zygote.

A

First statement is true; second is false

→ Telomerase is not active in most human somatic cells, but its activity varies from tissue to tissue.
→ The activity of germ cells results in telomeres of maximum length in zygote

135
Q

[True or False]
Normal shortening of telomeres may protect organisms from cancer by limiting the number of divisions that somatic cells can undergo.

A

TRUE

136
Q

Telomerase activity is abnormally ___________ in cancerous somatic cells, suggesting that its ability to stabilize telomere length may allow these cancer cells to persist.

A

high

137
Q

In E. coli, the chromosomal DNA consists of about 4.6 million nucleotide pairs, representing about ______________ genes.

A

4,400 genes

138
Q

In E. coli, the chromosomal DNA consists of about ___________ nucleotide pairs, representing about 4,400 genes.

A

4.6 million

138
Q

Proteins called _________ are responsible for the first level of DNA packing in chromatin.

A

histones

138
Q

More than a fifth of a histone’s amino acids are ___________ charged (____ or ______) and therefore bind tightly to the negatively charged DNA.

A

positively charged ; (lysine or arginine)

138
Q

[NUCLEOSOME]

The “string” between beads is called

A

Linker DNA

138
Q

A nucleosome consists of DNA wound ____________ around a protein core of eight histones.

A

twice

139
Q

This dense region of DNA in a bacterium, called the ______________, is not bounded by membrane

A

nucleoid

139
Q

Each eukaryotic chromosome contains a single linear DNA double helix that, in humans, averages about ____________ nucleotide pairs.

A

1.5 * 10^8 nucleotide pairs

140
Q

complex of DNA and protein, called ___________

A

chromatin

141
Q

_____________ is a process by which nucleases cut out and other enzymes replace damaged stretches of DNA.

A

Nucleotide Excision Repair (NER)

141
Q

The Meselson-Stahl experiment showed that DNA replication is _________________________

: The parental molecule unwinds, and each strand then serves as a template for the synthesis of a new strand according to base-pairing rules

A

semiconservative

Finals Cytogenetics (8 decks)

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