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Biology Exam 3 > Chapter 16 > Flashcards

Chapter 16 Flashcards

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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
Q

DNA polymerase III

A

the enzyme that elongates the DNA strands

26
Q

DNA polymerase I

A

the enzyme that removes the RNA primer and replaces it with DNA

27
Q

Primase

A

an enzyme that can start an RNA chain from scratch and adds RNA nucleotides

28
Q

DNA ligase

A

the enzyme that binds together fragments of DNA

29
Q

Single strand binding proteins

A

proteins that bind to and stabilize single-stranded DNA

30
Q

Describe the process of the repair of replication mistakes in DNA.

A

repair enzymes correct errors in base pairing

31
Q

Why do linear chromosomes get shorter with each replication?

A

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
Q

Telomeres

A

nucleotide sequences at the ends of eukaryotic chromosomal DNA molecules that postpone the erosion of genes near the ends of DNA molecules.

33
Q

Telomerase

A

catalyzes the lengthening of telomeres in germ (gamete) cells.

34
Q

How do telomeres prevent the erosion of genes?

A

Telomeres are noncoding DNA that can be eroded because they don’t control the production of any proteins.

35
Q

How does telomerase prevent the erosion of genes?

A

Telomerase adds telomeres to the end of DNA strands.

36
Q

Compare euchromatin and heterochromatin.

A

Euchromatin is loosely packed chromatin whereas heterochromatin is highly condensed chromatin

37
Q

Euchromatin

A

found in the area of the chromosome where gene expression is actively occurring.

38
Q

Heterochromatin

A

Heterochromatin is formed for gene regulation and chromosome protection

39
Q

Adenine

A

Purine, nitrogenous base represented by the letter A

40
Q

Guanine

A

Purine, nitrogenous base represented by the letter G

41
Q

Cytosine

A

Pyrimidine, nitrogenous base represented by the letter C

42
Q

Thymine

A

Pyrimidine, nitrogenous base represented by the letter T

43
Q

Purine

A

a nitrogenous base made of a six-member ring fused to a five-member ring; includes adenine and guanine

44
Q

Pyrimidines

A

a nitrogenous base made of a six-member ring; includes cytosine and thymine

45
Q

Elongation

A

lengthening of the DNA molecule through the addition of nucleotides to the 3’ end

46
Q

Histone

A

proteins that, together with DNA, make up chromatin; responsible for protection and condensation of the DNA

47
Q

Complementary base pairs

A

G and C
T and A

(Straight letters together and curvy letters together)

48
Q

What does helicase do for both the leading and lagging strand?

A

it binds to the origin of replication and separates the strands, generating a replication bubble.

49
Q

What is at each end of the replication bubble?

A

replication forks where replication is occurring.

50
Q

What happens as the replication bubble grows?

A

single-strand binding proteins stabilize the newly separated strands and keep them from reattaching.

51
Q

What is the initial nucleotide strand?

A

a short RNA primer that is attached to the DNA strand by an enzyme called primase.

52
Q

What can primase start?

A

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

53
Q

How long is the primer?

A

The primer is short (5-10 nucleotides long).

54
Q

What does the 3’ end serve as?

A

the starting point for the new DNA strand.

55
Q

During DNA synthesis, enzymes called ___ ________ catalyze the elongation of new DNA at a replication fork.

A

DNA polymerases

56
Q

What can’t DNA polymerases do?

A

initiate synthesis of a polynucleotide.

57
Q

What can DNA polymerases do?

A

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
Q

What does DNA polymerase do along one template strand of DNA?

A

DNA polymerase synthesizes a leading strand continuously, moving away from the origin of replication and toward the replication fork.

59
Q

What must DNA polymerase do to elongate the other new strand (lagging strand)?

A

DNA polymerase must work in the direction away from the replication fork and toward the origin of replication.

60
Q

Okazaki fragments

A

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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