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Biology Exam 3 > Chapter 16 > Flashcards

Chapter 16 Flashcards

1
Q

What are Chargaff’s rules?

A

1) The base composition of DNA varies between species

2) 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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2
Q

How did Chargaff’s second rule contribute to the construction of a model for the DNA molecule?

A

The Watson-Crick model explains Chargaff’s rules: in any organism, the amount of A = T, and the amount of G = C, from this Watson and Crick determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C)

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3
Q

How did the x-ray diffraction images produced by Wilkins and Franklin contribute to the construction of Watson and Crick’s model of DNA?

A

Franklin concluded that there were two outer sugar-phosphate backbones, with the nitrogenous bases paired in the molecule’s interior; Franklin’s X-ray crystallographic images of DNA enabled Watson and Crick to deduce that DNA was helical and made up of two strands, forming a double helix

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4
Q

What is a chromosome?

A

a piece of genetic material composed of chromatin (DNA and proteins)

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5
Q

Where are chromosomes found in eukaryotes?

A

In the nucleus

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6
Q

Where are chromosomes found In prokaryotes?

A

in the nucleoid

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7
Q

What type of chemical bond joins two nucleotides on the same strand of DNA?

A

covalent bond

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8
Q

What type of bond forms between the nucleotides of complementary strands of DNA?

A

hydrogen bond

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9
Q

Nucleotide structure

A

a pentose sugar, a nitrogenous base, and one phosphate

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10
Q

Nucleoside structure

A

a pentose sugar, a nitrogenous base, and three phosphates

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11
Q

Deoxyribose structure

A

a pentose sugar with one fewer oxygens than ribose

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12
Q

Purine structure

A

a nitrogenous base made of a six-member ring fused to a five-member ring

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13
Q

Pyrimidine structure

A

a nitrogenous base made of a six-member ring

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14
Q

Describe the process by which a nucleoside triphosphate is added to an elongating strand of DNA.

A

nucleoside triphosphate is added to the 3’ end by a DNA polymerase. During this process, two phosphates are broken off of the nucleoside triphosphate

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15
Q

Describe the sugar-phosphate backbone of a nucleic acid.

A

The backbone is made up of alternating pentose sugars and phosphates. The phosphates on the 5 carbon of one nucleotide are bonded to the 3 carbon of another nucleotide.

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16
Q

Describe the antiparallel, complementary, double-helix nature of DNA.

A

Watson and Crick built models of a double helix in which the backbones were antiparallel (their subunits run in opposite directions); The two strands of the double helix are complementary: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)

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17
Q

What is the semi-conservative model of DNA replication?

A

states that when a double helix replicates, each daughter molecule will have one old strand and one newly made strand

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18
Q

How does the semiconservative model of DNA replication compare to the conservative and dispersive models?

A

In the conservative model, the two parent strands rejoin and in the dispersive model, each strand is a mix of old and new

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19
Q

Which model of DNA replication is correct?

A

Semiconservative

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20
Q

To which end of the DNA strand can additional nucleotides be attached? Why?

A

3’ (3 carbon) end; DNA polymerases can only attach nucleotides to this end

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21
Q

Circular chromosome

A

has one origin of replication, so will form one replication bubble with one replication fork at each end of the bubble.

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22
Q

Linear chromosome

A

Linear chromosomes have hundreds to thousands of origins of replication and will form hundreds to thousands of replication bubbles with one replication fork at each end of the bubble.

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23
Q

Helicase

A

enzyme that untwists the double helix at the replication forks

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24
Q

Topoisomerase

A

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

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25
DNA polymerase III
the enzyme that elongates the DNA strands
26
DNA polymerase I
the enzyme that removes the RNA primer and replaces it with DNA
27
Primase
an enzyme that can start an RNA chain from scratch and adds RNA nucleotides
28
DNA ligase
the enzyme that binds together fragments of DNA
29
Single strand binding proteins
proteins that bind to and stabilize single-stranded DNA
30
Describe the process of the repair of replication mistakes in DNA.
repair enzymes correct errors in base pairing
31
Why do linear chromosomes get shorter with each replication?
The usual replication machinery provides no way to complete the 5' ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends
32
Telomeres
nucleotide sequences at the ends of eukaryotic chromosomal DNA molecules that postpone the erosion of genes near the ends of DNA molecules.
33
Telomerase
catalyzes the lengthening of telomeres in germ (gamete) cells.
34
How do telomeres prevent the erosion of genes?
Telomeres are noncoding DNA that can be eroded because they don't control the production of any proteins.
35
How does telomerase prevent the erosion of genes?
Telomerase adds telomeres to the end of DNA strands.
36
Compare euchromatin and heterochromatin.
Euchromatin is loosely packed chromatin whereas heterochromatin is highly condensed chromatin
37
Euchromatin
found in the area of the chromosome where gene expression is actively occurring.
38
Heterochromatin
Heterochromatin is formed for gene regulation and chromosome protection
39
Adenine
Purine, nitrogenous base represented by the letter A
40
Guanine
Purine, nitrogenous base represented by the letter G
41
Cytosine
Pyrimidine, nitrogenous base represented by the letter C
42
Thymine
Pyrimidine, nitrogenous base represented by the letter T
43
Purine
a nitrogenous base made of a six-member ring fused to a five-member ring; includes adenine and guanine
44
Pyrimidines
a nitrogenous base made of a six-member ring; includes cytosine and thymine
45
Elongation
lengthening of the DNA molecule through the addition of nucleotides to the 3' end
46
Histone
proteins that, together with DNA, make up chromatin; responsible for protection and condensation of the DNA
47
Complementary base pairs
G and C T and A (Straight letters together and curvy letters together)
48
What does helicase do for both the leading and lagging strand?
it binds to the origin of replication and separates the strands, generating a replication bubble.
49
What is at each end of the replication bubble?
replication forks where replication is occurring.
50
What happens as the replication bubble grows?
single-strand binding proteins stabilize the newly separated strands and keep them from reattaching.
51
What is the initial nucleotide strand?
a short RNA primer that is attached to the DNA strand by an enzyme called primase.
52
What can primase start?
an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template.
53
How long is the primer?
The primer is short (5-10 nucleotides long).
54
What does the 3’ end serve as?
the starting point for the new DNA strand.
55
During DNA synthesis, enzymes called ___ ________ catalyze the elongation of new DNA at a replication fork.
DNA polymerases
56
What can’t DNA polymerases do?
initiate synthesis of a polynucleotide.
57
What can DNA polymerases do?
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.
58
What does DNA polymerase do along one template strand of DNA?
DNA polymerase synthesizes a leading strand continuously, moving away from the origin of replication and toward the replication fork.
59
What must DNA polymerase do to elongate the other new strand (lagging strand)?
DNA polymerase must work in the direction away from the replication fork and toward the origin of replication.
60
Okazaki fragments
The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase.

Biology Exam 3 (6 decks)

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