Chapter 16: DNA

Question 1

when did the role of DNA in heredity first appear ?

Answer 1

by studying bacteria and the viruses that infect them

Question 2

what replication processes are suggested to be structurally similar?

Answer 2

eukaryotes and prokaryotes

Question 2

what is a virus ?

Answer 2

DNA (sometimes RNA) enclosed by a protective coat, often simply protein

Question 2

what are the origins of replication ?

Answer 2

where replication begins, the 2 DNA strands are separated, opening up a replication “bubble”

Question 3

what is transformation ?

Answer 3

a change in genotype and phenotype due to assimilation of foreign DNA

Question 4

what are helices ?

Answer 4

enzymes that untwist the double helix at the replication forks

Question 5

what is a replication fork ?

Answer 5

at the end of each replication bubble, a y-shapped region where parental DNA strands are being unwound

Question 6

what is topoisomerase?

Answer 6

relieves the strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands

Question 6

what are single-strand binding proteins

Answer 6

proteins that bind to and stabilize single-stranded DNA

Question 7

what is the original nucleotide chain for a new DNA strand ? what is it synthesized by ?

Answer 7

the initial chain is a short RNA primer and it synthesized by primase

Question 8

what are DNA polymerases ?

Answer 8

enzymes that catalyze the synthesis of a new DNA at a replication fork

Question 9

how does the lagging strand elongate ?

Answer 9

the DNA polymerase must work in the direction away from the replication fork

Question 10

what are Okazaki fragments ?

Answer 10

the lagging strand that is synthesized as a series of segments, they’re joined together by DNA ligase

Question 10

what occurs during the mismatch repair of DNA ?

Answer 10

repair enzymes replace incorrectly paired nucleotides that have evaded the proofreading process

Question 10

what are telomeres ? what do they do ?

Answer 10

1. special nucleotide sequences at the end of eukaryotic chromosomal DNA molecules
2. they postpone the erosion of genes near the ends of DNA molecules

Question 10

what occurs during the nucleotide excision repair ?

Answer 10

a nuclease cuts out and replaces damaged stretched of DNA

Question 10

what do telomeres not do ?

Answer 10

they don’t prevent the shortening of DNA molecules

Question 11

what could the shortening of telomeres might do ?

Answer 11

protect cells from cancerous growth by limiting the number of cell divisions

Question 12

what is chromatin ?

Answer 12

a complex protein where DNA is precisely combined

Question 12

what are histones responsible for ?

Answer 12

helps DNA stay organized and compacted inside the nucleus.
1. organizes DNA
2. regulate gene expression
3. form chromatin

Question 13

what is a nucleosome made of ?

Answer 13

is composed of DNA wound twice around a core of eight histones, two each of the four main histone types

Question 14

what is euchromatin ?

Answer 14

loosely packed chromatin

Question 15

what is heterochromatin ?

Answer 15

highly condensed inactive DNA

Question 16

what is the affect of densely packed heterochromatin

Answer 16

it difficult for the cell to express genetic information coded in these regions

Question 16

what changes do histones go through ? what effects does it have ?

Answer 16

Histones can undergo chemical modifications that result in changes in chromatin condensation, resulting to multiple effects on gene expression

Question 17

what was Griffin's experiment, and purpose ?

Answer 17

he worked with 2 strains of bacterium, 1 pathogenic 1 harmless. when he mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became pathogenic. called this TRANSFORMATION.

Question 18

what are bacteriophages / phages, and what were they used for ?

Answer 18

they are viruses that infect bacteria 1. been used as tools by researches in molecular genetics 2. helped prove that DNA is genetic matieral

Question 19

what was the Hershey & Chase experiment ? what did they conclude ?

Answer 19

showed that one only of the 2 components of T2 (DNA or protein) enters an E. coil cell during infection. concluded that the injected DNA of the phage provides the genetic information

Question 20

what were Chargaff's base pairing rules ?

Answer 20

1. the base composition of DNA varies between species 2. in any species the # of A and T bases is equal and the number of G and C bases is equal

Question 21

what is DNA's structure ?

Answer 21

nucleotide that has 2 outer deoxyribose sugar phosphate backbones, and the nitrogenous bases paired inside.

Question 22

what DNA bases are purines ?

Answer 22

Adenine (A) and Guanine (G)

Question 23

what DNA bases are pyrimidines ?

Answer 23

Cytosine (C) Thymine (T) and Uracil (U)

Question 24

what were the 3 proposed DNA molecules ?

Answer 24

1. semiconservative model 2. conservative model 3. dispersive model

Question 25

what did the semiconservative model ?

Answer 25

it predicted 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

Question 26

what did the conservative model say?

Answer 26

that the two parent strands rejoin

Question 27

what did the dispersive model say ?

Answer 27

that each strand is a mix of old and new