chapter 16

Question 1

What are Chargaff’s rules?

Answer 1

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

Question 2

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

Answer 2

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)

Question 3

What is a chromosome?

Answer 3

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

Question 4

Where are chromosomes found in eukaryotes?

Answer 4

nucleus

Question 5

Where are chromosomes found in prokaryotes?

Answer 5

nucleoid

Question 6

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

Answer 6

Hydrogen bond

Question 7

nucleotide

Answer 7

molecule that consists of a pentose sugar, a nitrogenous base, and one phosphate

Question 8

nucleoside triphosphate

Answer 8

molecule that consists of a pentose sugar, a nitrogenous base, and three phosphates

Question 9

deoxyribose

Answer 9

a pentose sugar with one fewer oxygens than ribose

Question 10

purine

Answer 10

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

Question 11

pyrimidine

Answer 11

a nitrogenous base made of a six-member ring

Question 12

Describe the sugar-phosphate backbone of a nucleic acid

Answer 12

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

Question 13

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

Answer 13

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); Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication

Question 14

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

Answer 14

The 3’ (3 carbon) end because DNA polymerases can only attach nucleotides to this end.

Question 15

For both the leading and lagging strand, helicase…

Answer 15

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

Question 16

What is at each end of the replication bubble

Answer 16

replication forks where replication is occurring.

Question 17

What happens as the replication bubble grows?

Answer 17

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

Question 18

What is the initial nucleotide strand?

Answer 18

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

Question 19

What can primase start?

Answer 19

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

Question 20

How long is the primer?

Answer 20

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

Question 21

What does the 3’ end serve as?

Answer 21

the starting point for the new DNA strand.

Question 22

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

Answer 22

DNA polymerases

Question 23

What can’t DNA polymerases do?

Answer 23

initiate synthesis of a polynucleotide.

Question 24

What can DNA polymerases do?

Answer 24

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.

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

Okazaki fragments

Answer 27

The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase.

Question 28

Helicase

Answer 28

enzyme that untwists the double helix at the replication forks

Question 29

Topoisomerase

Answer 29

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

Question 30

DNA polymerase III

Answer 30

enzyme that elongates the DNA strands

Question 31

DNA polymerase I

Answer 31

enzyme that removes the RNA primer and replaces it with DNA

Question 32

Primase

Answer 32

an enzyme that can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template

Question 33

DNA ligase

Answer 33

enzyme that binds together fragments of DNA

Question 34

single strand binding proteins

Answer 34

proteins that bind to and stabilize single-stranded DNA

Question 35

Adenine

Answer 35

Purine, nitrogenous base represented by the letter A

Question 36

Guanine

Answer 36

Purine, nitrogenous base represented by the letter G

Question 37

Cytosine

Answer 37

Pyrimidine, nitrogenous base represented by the letter C

Question 38

Thymine

Answer 38

Pyrimidine, nitrogenous base represented by the letter T

Question 39

Purine

Answer 39

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

Question 40

Pyrimidines

Answer 40

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

Question 41

Elongation

Answer 41

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

Question 42

Histone

Answer 42

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