Chapter 16

Question 1

Frederick Griffith

Answer 1

began search for genetic material in 1928

Question 2

Griffith’s experiment

Answer 2

a pathogenic and a harmless strain of bacteria

heat kill pathogenic = harmless

mix with living harmless = living become pathogenic

called this transformation

Question 3

transformation

Answer 3

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

Question 4

Where did evidence for DNA as genetic material come from?

Answer 4

Studies of viruses that infect bacteria

Question 5

bacteriophages

Answer 5

viruses that infect bacteria (often simply protein)

Question 6

Hershey and Chase

Answer 6

showed that DNA is the genetic material of a phage known as T2 (not the protein)

Question 7

Chargaff’s rules

Answer 7

The base composition of DNA varies between species

In any species the number of A and T bases are equal and the number of G and C bases are equal.

Question 8

Wilkins and Franklin

Answer 8

X-ray crystallography to study molecular structure

Picture of DNA

Question 9

Watson and Crick

Answer 9

DNA helical with 2 antiparallel strands

2 outer sugar-phosphate backbones (nitrogenous bases inside) [A-T and G-C]

Question 10

Why does the pairing of pyrimidine and purine make sense?

Answer 10

It gives a uniform width to the DNA

Question 11

semiconservative model of replication

Answer 11

when a double helix replicates, each daughter molecule will have one old strand (derived from the parent molecule) and one newly made strand

Question 12

Competing models of replication at the time of Watson and Crick

Answer 12

conservative (old strands rejoin)

dispersive (each strand is mix of old and new)

Question 13

How did Meselson and Franklin support the semiconservative model?

Answer 13

old strands - heavy N
new strands - light N

first replication = hybrid DNA (not conservative)

second replication = 2 light and 2 hybrid (not dispersive)

Question 14

origin of replication

Answer 14

where replication begins (euk may have 100s or 1000s)

2 strands are separated, opening a replication “bubble”

Question 15

From which direction does replication begin?

Answer 15

Both directions

Question 16

replication fork

Answer 16

At the end of each replication bubble: a Y-shaped region where new DNA strands are elongating

Question 17

helicases

Answer 17

enzymes that untwist the double helix at the replication forks

Question 18

single-strand binding proteins

Answer 18

bind to and stabilize single-stranded DNA

Question 19

topoisomerase

Answer 19

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

Question 20

RNA primer

Answer 20

DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to an existing 3’ end

Question 21

primase

Answer 21

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, creating short primer (5-10 nucleotides long)

Question 22

DNA polymerases

Answer 22

enzyme that catalyze the elongation of new DNA at a replication fork

Question 23

Nucleoside triphosphates

Answer 23

“building blocks”

partly cause the reactivity of nucleotides

Question 24

Which direction does a new DNA strand elongate?

Answer 24

Only 5’ to 3’

Question 25

leading and lagging strand

Answer 25

DNA will synthesize a leading strand moving toward the replication fork and a lagging strand moving away from the replication fork

Question 26

Okazaki fragments

Answer 26

synthesize the lagging strand, joined together by DNA ligase

Question 27

What if there are incorrect nucleotides? What is done to prevent/fix that?

Answer 27

DNA polymerase proofread new DNA and replace any incorrect nucleotides

Question 28

mismatch repair

Answer 28

other enzymes can remove and replace incorrectly paired nucleotides

Question 29

What can change DNA?

Answer 29

``` harmful exposure (cigarette smoke and X-rays) spontaneous change (mutations for natural selection) ```

Question 30

nuclease

Answer 30

cuts out and removes damaged stretches of DNA

Question 31

telomeres

Answer 31

special nucleotide sequences at the end of euk chromosomal DNA do not prevent shortening of DNA, but do postpone erosion of genes near the ends of DNA molecules

Question 32

What might the shortening of telomeres be linked to?

Answer 32

Aging

Question 33

telomerase

Answer 33

catalyzes the lengthening of telomeres in germ cells

Question 34

Why might the shortening of telomeres be helpful?

Answer 34

Could prevent cancerous growth by limiting the number of cell divisions

Question 35

nucleoid

Answer 35

where the "supercoiled" DNA of bacteria is found

Question 36

chromatin

Answer 36

in euk cell, combines DNA precisely with proteins

Question 37

histones

Answer 37

proteins responsible for the first level of packing in chromatin

Question 38

heterochromatin

Answer 38

highly condensed chromatin even in interphase (difficult to express genetic information coded in these regions)

Question 39

euchromatin

Answer 39

loosely packed chromatin

Question 40

Replicating the ends of DNA molecules is not a problem for prokaryotes because…

Answer 40

They have circular chromosomes.