Unit 3 Lecture 4 10/24/22

Question 1

In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of __________, or __________

Answer 1

deoxyribonucleic acid or DNA

Question 2

__________information is encoded in DNA and reproduced in all cells of the body (DNA replication)

Answer 2

heredity

Question 3

The two components of chromosomes—__________ and __________—became candidates for the genetic material

Answer 3

1.DNA
2.Protein

Question 4

Viruses that infect bacteria are called __________

Answer 4

bacteriophages

Question 5

Griffith worked with two strains of a bacterium, one __________ and one __________

Answer 5

1.pathogenic
2.harmless

Question 6

He called this phenomenon __________, now defined as a change in genotype and phenotype due to assimilation of foreign DNA

Answer 6

transformation

Question 7

Later work by Oswald Avery and others identified the transforming substance as __________

Answer 7

DNA

Question 8

Many biologists remained skeptical, mainly because little was known about DNA and they thought __________were better candidates for the genetic material

Answer 8

Proteins

Question 9

To determine this, they designed an experiment showing that only the __________of the T2 phage, and not the __________, enters an E. coli cell during infection

Answer 9

1.DNA
2.protein

Question 10

It was known that DNA is a polymer of __________, each consisting of a nitrogenous base, a sugar, and a phosphate group

Answer 10

Nucleotides

Question 11

Two findings became known as __________

Answer 11

Chargaff’s rules

Question 12

The base composition of DNA ____________________

Answer 12

varies between species

Question 13

In any species the number of __________bases is equal, and the number of __________bases is equal

Answer 13

A and T
G and C

Question 14

The basis for these rules was not understood until the discovery of the __________

Answer 14

double helix

Question 15

Maurice Wilkins and Rosalind Franklin were using a technique called ____________________to study molecular structure

Answer 15

X-ray Crystallography

Question 16

The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a __________

Answer 16

double helix

Question 17

Franklin had concluded that there were two outer __________________________, with the ____________________ paired in the molecule’s interior

Answer 17

1.sugar-phosphate backbones
2.nitrogenous bases

Question 18

Watson built a model in which the backbones were __________ (their subunits run in opposite directions)

Answer 18

antiparallel

Question 19

Instead, pairing a __________with a __________ resulted in a uniform width consistent with the X-ray data

Answer 19

1.purine
2.pyrimidine

Question 20

They determined that __________paired only with __________, and __________ paired only with __________

Answer 20

1&2.adenine with thymine
3&4.guanine with cytosine

Question 21

The __________ explains __________: in any organism the amount __________, and the amount of __________

Answer 21

Watson-Crick model
Chargaff’s rules
A=T
G=C

Question 22

The relationship between structure and function is manifest in the __________

Answer 22

Double helix

Question 23

Watson and Crick noted that the specific base pairing suggested a possible __________for genetic material

Answer 23

Copying mechanism

Question 24

Watson and Crick’s __________of replication predicts 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

Answer 24

Semiconservative model

Question 25

Competing models were the __________ (the two parent strands rejoin) and the __________ (each strand is a mix of old and new)

Answer 25

conservative model dispersive model

Question 26

Experiments by Matthew Meselson and Franklin Stahl supported the __________

Answer 26

Semiconservative model

Question 27

Replication begins at particular sites called ____________________, where the two DNA strands are separated, opening a ____________________

Answer 27

origins of replication replication bubble

Question 28

At each end of a bubble is a ____________________, a Y-shaped region where the parental strands of DNA are being unwound

Answer 28

replication fork

Question 29

__________are enzymes that untwist the double helix at the replication forks

Answer 29

Helicases

Question 30

____________________bind to and stabilize single-stranded DNA

Answer 30

single-strand binding proteins

Question 31

__________ relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strands

Answer 31

Topoisomerase

Question 32

__________replication bubbles form and eventually fuse, speeding up the copying of DNA

Answer 32

Multiple

Question 33

__________cannot initiate synthesis of a polynucleotide; they can only add nucleotides to an already existing chain base-paired with the template

Answer 33

DNA polymerases

Question 34

The initial nucleotide strand is a short __________

Answer 34

RNA primer

Question 35

The enzyme __________starts an RNA chain from a single RNA nucleotide and adds RNA nucleotides one at a time using the parental DNA as a template

Answer 35

Primase

Question 36

Enzymes called __________catalyze the elongation of new DNA at a replication fork

Answer 36

DNA polmerases

Question 37

The rate of elongation is about __________ per second in bacteria and __________in human cells

Answer 37

500 nucleotides 50 per second

Question 38

__________is used to make DNA and is similar to the ATP of energy metabolism

Answer 38

dATP

Question 39

The difference is in the sugars: dATP has __________, while ATP has __________

Answer 39

Deoxyribose Ribose

Question 40

As each monomer nucleotide joins the DNA strand, it loses two phosphate groups as a molecule of __________

Answer 40

Pyrophosphate

Question 41

The __________structure of the double helix affects replication

Answer 41

antiparallel

Question 42

Along one template strand of DNA, the __________synthesizes a __________continuously, moving toward the replication fork

Answer 42

DNA polymerase Leading strand

Question 43

To elongate the other new strand, called the __________, DNA polymerase must work in the direction __________from the replication fork

Answer 43

lagging strand away

Question 44

The lagging strand is synthesized as a series of segments called __________

Answer 44

Okazaki fragments

Question 45

After formation of Okazaki fragments, __________ removes the __________and replaces the nucleotides with DNA

Answer 45

DNA polymerase 1 RNA primer

Question 46

The remaining gaps are joined together by DNA __________

Answer 46

ligase

Question 47

__________proofread newly made DNA, replacing any incorrect nucleotides

Answer 47

DNA polymerases

Question 48

In nucleotide__________, a __________cuts out and replaces damaged stretches of DNA

Answer 48

excision repair nuclease

Question 49

Error rate after proofreading repair is low but __________zero

Answer 49

not

Question 50

These changes __________are the source of the genetic variation upon which __________operates

Answer 50

mutations natural selection

Question 51

Limitations of DNA polymerase create problems for the __________of eukaryotic chromosomes

Answer 51

linear DNA

Question 52

Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called __________

Answer 52

telomeres

Question 53

__________ do not prevent the shortening of DNA molecules, but they do postpone it

Answer 53

Telomeres

Question 54

It has been proposed that the shortening of telomeres is connected to __________

Answer 54

aging

Question 55

An enzyme called __________ catalyzes the lengthening of telomeres in germ cells Telomerase is not active in most human somatic cells

Answer 55

telomerase

Question 56

The bacterial chromosome is a double-stranded, __________ DNA molecule associated with a __________ amount of protein

Answer 56

circular small

Question 57

Eukaryotic chromosomes have __________ DNA molecules associated with a __________ amount of protein

Answer 57

linear large

Question 58

In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the __________

Answer 58

nucleoid

Question 59

__________, a complex of DNA and protein, is found in the nucleus of eukaryotic cells

Answer 59

Chromatin

Question 60

__________ fit into the nucleus through an elaborate, multilevel system of packing

Answer 60

Chromosomes

Question 61

__________ undergoes striking changes in the degree of packing during the course of the cell cycle

Answer 61

Chromatin

Question 62

At __________, most of the chromatin is compacted into a 30-nm fiber, which is folded further in some areas by looping

Answer 62

interphase

Question 63

This condensed chromatin is called __________; the more dispersed, less compacted chromatin is called __________

Answer 63

heterochromatin euchromatin

Question 64

Dense packing of the heterochromatin makes it largely __________ to the machinery responsible for transcribing genetic information

Answer 64

inaccessible

Question 65

Complementary base pairing of DNA is the basis for __________, the base pairing of one strand of a nucleic acid to another, complementary sequence

Answer 65

nucleic acid hybridization

Question 66

__________ forms the foundation of virtually every technique used in __________, the direct manipulation of genes for practical purposes

Answer 66

nucleic acid hybridization genetic engineering