Mitotic Chromosome Structure

Question 1

Where is hereditary information found in eukaryotic cells? What form does hereditary information take?

Answer 1

hereditary information in the form of genes is found along many linear DNA molecules

Question 2

What is a chromosome?

Answer 2

an individual DNA molecule + associated histone + non-histone proteins

Question 3

What allows a chromosome to have 2 arms?

Answer 3

a centromere

Question 4

What is a centromere?

Answer 4

a point on a chromosome where the spindle fibers attach during mitosis and meiosis

Question 5

What is chromatin?

Answer 5

the complex of DNA and histone proteins that make up a chromosome

Question 6

T or F: the appearance and arrangement of the chromatin in the nucleus is the same at all stages of the cell cycle

Answer 6

FALSE! it differs at different stages of the cycle

Question 7

What is the most dominant component of an interphase nucleus?

Answer 7

chromatin - it makes up 80-90% of the nuclear mass

Question 8

How does the chromatin appear in the interphase nucleus?

Answer 8

fine, intertwined fibers or threads

Question 9

What are the two classifications of interphase nuclear chromatin?

Answer 9

euchromatin

heterochromatin

Question 10

How is the interphase nuclear chromatin divided into the two classifications?

Answer 10

based on its appearance and possible activity level

Question 11

Describe the structure of euchromatin

Answer 11

the interphase nuclear chromatin that appears as loosely packed threads

Question 12

How does euchromatin appear under an electron microscope?

Answer 12

it is less densely stained and appears as if the threads are dispersed

Question 13

What is the transcription activity level of euchromatin?

Answer 13

transcriptionally active

Question 14

Describe the structure of heterochromatin

Answer 14

densely packed mass around the periphery of the nucleus

Question 15

How does heterochromatin appear under an electron microscope?

Answer 15

densely stained

Question 16

What is the transcription activity level of heterochromatin?

Answer 16

inactive

Question 17

When are chromosomes at their most condensed and compact state?

Answer 17

during metaphase of mitosis or meiosis

Question 18

When can chromosomes be visualized with a light microscope?

Answer 18

during metaphase

Question 19

What are the stages of the cell cycle

Answer 19

G1
S
G2
Mitosis or meiosis 
C

Question 20

What occurs during the G1 phase of the cell cycle?

Answer 20

gap phase

growth or regular cell function - anything that isn’t cell division

Question 21

What occurs during the S phase of the cell cycle?

Answer 21

DNA synthesis

duplication of DNA

Question 22

Describe the structure of chromosomes at metaphase of mitosis

Answer 22

two identical sister chromatids attached at their centromeres

Question 23

How do the centromeres appear at metaphase of mitosis?

Answer 23

narrowed or constricted areas along the length of the chromosome

Question 24

What is another term for centromeres?

Answer 24

primary constriction

Question 25

How do researchers see and count the number of chromosomes in a single cell?

Answer 25

by preparing a slide with cells held at metaphase and exposing them to a hypotonic solution to burst the cells and release the chromosomes

Question 26

What is karyotyping?

Answer 26

determining the chromosomal complement of cells by staining and taking a picture of released chromosomes from a cell and pairing them with their homologue and arranging them according to size and structure

Question 27

How are the characteristic morphology of metaphase chromosomes determined?

Answer 27

by their size and location of centromere

Question 28

What are the 4 classifications of chromosomes?

Answer 28

metacentric submetacentric acrocentric telocentric

Question 29

Describe metacentric chromosomes

Answer 29

chromosomes with a centromere that is equidistant between the 2 arms and the 2 arms are of equal length

Question 30

Describe submetacentric chromosomes

Answer 30

chromosomes with an off centered centromere (slightly different arm lengths)

Question 31

Describe acrocentric chromosomes

Answer 31

chromosomes with a centromere that is closer to one end than to the other (very different arm lengths)

Question 32

Describe telocentric chromosomes

Answer 32

chromosomes with the centromere AT the end of the chromosome

Question 33

Which 2 types of chromosomes have 2 arms of unequal lengths?

Answer 33

submetacentric acrocentric

Question 34

How are two unequal arms of submetacentric or acrocentric chromosomes classified?

Answer 34

the shorter arm = the p arm the longer arm = the q arm

Question 35

Which arm is the p arm?

Answer 35

the shorter arm can remember as p for 'petite' arm

Question 36

Which arm is the q arm?

Answer 36

the longer arm can remember that p = petite and q comes after p

Question 37

the movement of sister chromatids of each chromosome pair toward the poles of cell depends on what?

Answer 37

the development of a kinetochore on each centromere

Question 38

Where are kinetochores located?

Answer 38

on centromeres of chromosomes

Question 39

Where do sister chromatids separate from?

Answer 39

their centromeres

Question 40

Describe a kinetochore

Answer 40

a large multiprotein complex that appears in the EM as a plate-like trilaminar structure

Question 41

How does a kinetochore appear in an EM?

Answer 41

as a plate-like trilaminar structure

Question 42

How many centromeres are there in a chromosome consisting of 2 sister chromatids?

Answer 42

2

Question 43

How many kinetochores are there in a chromosome consisting of 2 sister chromatids?

Answer 43

2

Question 44

Where do microtubule spindle fibers attach on a sister chromatid? What stages of mitosis does this occur?

Answer 44

to its kinetochore on its centromere during prophase and metaphase

Question 45

What does the kinetochore do during anaphase?

Answer 45

it climbs the microtubule while digesting it along the way and this pulls the sister chromatid along with it

Question 46

T or F: the kinetochore is providing the force that pulls sister chromatids apart and towards the poles, NOT the spindle fiber microtubules

Answer 46

true

Question 47

What is another term for the secondary constriction?

Answer 47

Nuclear Organizer Region (NOR)

Question 48

Describe the NOR/secondary constriction

Answer 48

a large cluster of repeating rRNA genes that marks the site of nucleolar formation during interphase

Question 49

What does secondary constriction/NOR do to the appearance of a metaphase chromosome?

Answer 49

the NOR can be so narrow that it makes the distal portion of an arm appear to be completely detached from the rest of the chromosome

Question 50

What is a satellite?

Answer 50

the distal portion of a metaphase chromosome that appears to be separated from the chromosome because of the NOR/secondary constriction

Question 51

T or F: every species has the same number of NORs/secondary constrictions on their chromosomes

Answer 51

false! it varies from species to species

Question 52

How many NORs do human chromosomes have?

Answer 52

5 pairs

Question 53

Which human chromosomes have NORs?

Answer 53

13, 14, 15, 21, 22

Question 54

What are telomeres?

Answer 54

the ends of linear chromosomes

Question 55

What are telomeres made of?

Answer 55

long stretches of repetitive nucleotide sequences covered with protein complexes

Question 56

What are the 3 major function of telomeres?

Answer 56

1. to protect the chromosome from fusing with other chromosomes 2. to protect transcriptionally valuable DNA from being lost 3. preventing uncontrolled cell division (cancer) due to telomere loss initiating apoptosis

Question 57

What happens to telomeres with every round of cell division?

Answer 57

they shorten by a few hundred base pairs

Question 58

How is the total number of cell division limited? Why?

Answer 58

by the length of telomeres because they shorten with every round of cell division

Question 59

How do telomeres prevent uncontrolled cell division?

Answer 59

the loss of telomeres (after rounds of cell division) initiates apoptosis