Chapter 5 - DNA and Chromosomes

Question 1

A

Answer 1

A-T base pair

Question 2

B

Answer 2

G-C base pair

Question 3

C

Answer 3

deoxyribose

Question 4

D

Answer 4

phosphodiester bonds

Question 5

E

Answer 5

purine base

Question 6

F

Answer 6

pyrimidine base

Question 7

A DNA strand has a polarity because its two ends contain different bases.

Answer 7

False

Question 8

G-C base pairs are more stable than A-T base pairs.

Answer 8

True

Question 9

1. The two polynucleotide chains in the DNA double helix are held together by ____________ between the bases on the different strands. All the bases are therefore on the outside/ inside of the double helix, with the sugar-phosphate backbones on the outside/ inside.

Answer 9

hydrogen bonds; inside; outside

Question 10

A ____________ is often defined as a segment of DNA that contains the instructions for making a particular protein or RNA molecule.

Answer 10

gene

Question 11

______________is the total amount of genetic information carried in the complete set of chromosomes in an organism.

Answer 11

genome

Question 12

Each DNA molecule is packaged in a separate ___________________ and the total genetic information stored in the chromosomes of an organism is said to constitute its __________.

Answer 12

chromosome; genome

Question 13

Each chromosome contains a single long DNA molecule. True or False?

Answer 13

True

Question 14

Each human cell contains about _________ of DNA; yet the cell nucleus is only _________ in diameter. Tucking all this material into such a small space is the equivalent of trying to fold 40km (24miles) of extremely fine thread into a tennis ball.

Answer 14

2m; 5-8 um

Question 15

Two copies of each of H2A, H2B, H3, and H4 form a ______ around which the double-stranded DNA helix is twice.

Answer 15

nucleosome core particle

Question 16

Histones are relatively small proteins with a very high proportion of positively charged amino acids: positive charge helps the histones bind tightly to DNA. True or False?

Answer 16

True

Question 17

In living cells nucleosomes are packed upon one another to generate regular arrays in which the DNA is more highly condensed, usually in the form of a 30nm fiber. True or false?

Answer 17

True

Question 18

By light microscopy there are two types of chromatin in interphase nuclei of higher eukaryotic cells: a highly condensed form called _______________ and all the rest, which is less condensed, called __________________

Answer 18

heterochromatin; eurochromatin

Question 19

During interphase, the chromosomes are extended as long, thin, tangled threads of DNA in the nucleus and cannot be easily distinguished in the light microscope. We refer to chromosomes in this extended state as _________________.

Answer 19

interphase

Question 20

Chromosomes from nearly all cells are visible during mitosis, where they coil up to form much more condensed structures , called __________________

Answer 20

mitotic chromosome

Question 21

In eukaryotic _______, DNA is complexed with proteins to form ____. The paternal and maternal copies of human Chromosome 1 are _____, whereas the paternal copy of Chromosome 1 and the maternal copy of Chromosome 3 are nonhomologous chromosomes. Cytogeneticists can determine large-scale chromosomal abnormalities by looking at a patient’s ______.

Answer 21

chromosomes; chromatin; homologous; karyotype

Question 22

The display of the 46 human chromosomes at mitosis is called the human ___

Answer 22

karyotype

Question 23

1. Given the sequence of one strand of a DNA helix (below), provide the sequence of the complementary strand and label the 5′ and 3′ ends.

5′-GCATTCGTGGGTAG-3′

Answer 23

5′-CTACCCACGAATGC-3′

Be careful with the polarity!

Question 24

The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body.

How many centromeres are in each cell? What is the main function of the centromere?

Answer 24

46; distribution of chromosomes to daughter cells via mitosis

Question 25

The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body. ## Footnote How many telomeres are in each cell? What is their main function?

Answer 25

92; protection and enable completion replication

Question 26

The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body. ## Footnote How many replication origins are in each cell? What is their main function?

Answer 26

\>200; these DNA sequences direct the initiation of DNA synthesis needed to replicate chromosomes.

Question 27

Each chromosome is a single molecule of ____ whose extraordinarily long length can be compacted by as much as \_\_\_-fold during ___ and tenfold more during \_\_\_\_\_.

Answer 27

DNA; 1000; interphase; mitosis

Question 28

This is accomplished by binding to ______ that help package the DNA in an orderly manner so it can fit in the small space delimited by the \_\_\_\_\_\_.

Answer 28

proteins; nuclear envelope

Question 29

The structure of the DNA–protein complex, called \_\_\_\_\_\_\_\_\_\_, is highly ________ over time.

Answer 29

chromatin; dynamic

Question 30

A cell can regulate its chromatin structure- temporarily decondensing or condensing particular regions of its chromosomes – using ____ and enzymes that ________ histone tails in various ways.

Answer 30

chromatin remodeling complex; modify

Question 31

The loosing of chromatin to a more decondensed state allows proteins involved in \_\_\_\_\_, \_\_\_\_\_\_\_\_, and _______ to gain access to the necessary DNA sequences.

Answer 31

gene expression; DNA replication; DNA repair

Question 32

Some forms of chromatin have a pattern of histone tail modification that causes the DNA to become so highly condensed that its genes cannot be expressed to produce RNA; such condensation occurs on all chromosomes during mitosis and in the _______________ of interphase chromosomes.

Answer 32

heterochromatin

Question 33

Interphase chromosomes contain both darkly staining \_\_\_\_\_and more lightly staining \_\_\_\_.

Answer 33

heterochromatin; euchromatin

Question 34

Genes that are being transcribed are thought to be packaged in a ____ condensed type of euchromatin.

Answer 34

less

Question 35

Nucleosome core particles are separated from each other by stretches of ____ DNA.

Answer 35

linker

Question 36

A string of nucleosomes coils up with the help of _______ to form the more compact structure of the ___ .

Answer 36

histone H1; 30-nm fiber

Question 37

A __________ model describes the structure of the 30-nm fiber.

Answer 37

zigzag

Question 38

The 30 nm chromatin fiber is further compacted by the formation of ____ that emanate from a central \_\_\_\_\_\_.

Answer 38

loops; axis

Question 39

Describe the mechanism by which heterochromatin can spread, once it has been established in one region of the chromosome.

Answer 39

Once the initial H3 lysine 9 methylation is established on core histone octamers in one region, the modification attracts a specific set of proteins and other histone-methylating enzymes. These enzymes create the same modification on adjacent histone octamers, which continue to recruit more heterochromatin-specific proteins and enzymes, creating a wave of heterochromatin spreading along the chromosome.

Question 40

Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the “histone code.” Which of the following patterns will probably lead to gene silencing?

Answer 40

lysine 9 methylation

Question 41

DNA and its associated proteins

Answer 41

chromatin

Question 42

basic unit of chromatin packing

Answer 42

nucleosomes

Question 43

Nucleosomes consist of ____ pairs of histones, which is ___ total.

Answer 43

4; 8

Question 44

\_\_\_\_ are highly conserved, small, positively charged proteins.

Answer 44

Histones

Question 45

Histones are ___ bp of DNA.

Answer 45

147

Question 46

\_\_\_\_ chromosomes are the most condensed.

Answer 46

mitotic

Question 47

\_\_\_ chromosomes are the less condensed.

Answer 47

interphase

Question 48

Nucleosomes are further packed into 30 nm fibers via what two ways?

Answer 48

1- Interactions between histone tails; 2- Binding of histone H1

Question 49

Histone-modifying enzymes work in concert with the chromatin-remodeling complexes to ____ and ____ stretches of chromatin, allowing local chromatin structure to change rapidly according to the needs of the cell.

Answer 49

condense; relax

Question 50

The pattern of histone modification indicates the status of the nearby \_\_\_\_.

Answer 50

chromatin

Question 51

What are the two levels of interphase chromatin condensation?

Answer 51

Heterochromatin; Euchromatin

Question 52

2 co-centric lipid bi-layers

Answer 52

nuclear envelope

Question 53

allows exchange between cytoplasm and nucleus

Answer 53

nuclear pores

Question 54

the mesh of intermediate filaments that support the nucleus

Answer 54

nuclear lamina

Question 55

example of "biochemical neighborhood"

Answer 55

nucleolus

Question 56

What contains the genes that encode ribosomal RNAs?

Answer 56

nucleolus

Question 57

The process of sorting human chromosome pairs by size and morphology is called karyotyping. A modern method employed for karyotyping is called chromosome painting. How are individual chromosomes “painted”?

Answer 57

Chromosome painting relies on the specificity of DNA complementarity. Because unique sequences for each chromosome are known, short DNA molecules matching a set of these sites can be designed for each chromosome. Each set is labeled with a specific combination of fluorescent dyes and then allowed to hybridize (form base pairs) with the two homologous chromosomes that contain the unique sequences being targeted

Question 58

One of the two X chromosomes is inactivated in the cells of mammalian females by ______________ formation

Answer 58

heterochromatin

Question 59

Each female cell contains two X chromosomes, whereas male cells contain one X and one Y. Because a double dose of X-chromosome products would be lethal, one of these two chromosomes becomes condensed into \_\_\_\_\_\_\_\_\_\_\_\_\_\_early in embryonic development. Thereafter, the condensed and inactive state of that X chromosome is inherited in all of the many descendants of those cells.

Answer 59

heterochromatin