Chromosomes

Question 1

Describe the structure of a chromosome.

Answer 1

Two sister linear chromatids which are held together by the centromere.

Question 2

What are the ends of the chromosomes known as?

Answer 2

Telomeres

Question 3

What are the functions of telomeres?

Answer 3

They protect the chromosome ends from degradation in the cell and also potentially from inappropriate repair.

Question 4

What are heterochromatins?

Answer 4

Large amounts of DNA in the eukaryotic genome that is not active.

Question 5

How is euchromatin characterised?

Answer 5

By the ability to be expressed

Question 6

Why does the entire genome need to get replicated?

Answer 6

So that a complete copy of the DNA can be passed to each of the daughter cells.

Question 7

What is the DNA synthesis reaction carried out by?

Answer 7

DNA polymerase

Question 8

What direction does DNA polymerase synthesis DNA?

Answer 8

In a five prime to three prime direction due to the anti parallel nature.

Question 9

So the replication can stay in the same direction, how do the second strand (lagging strand) get replicated?

Answer 9

In short fragments known as Okazaki Fragments

Question 10

What enzyme stitches the shorter fragments together in DNA replication?

Answer 10

Ligase

Question 11

What is the end replication problem?

Answer 11

RNA primers get removed in the lagging strand so the fragments can join together.
However, at the end, the removal of a primer leaves a gap meaning this could lead to degradation and loss of DNA.

Question 12

What is the solution to the end replication problem?

Answer 12

Expression of the enzyme telomerase which adds repeats and resynthesizes and fills in the end of DNA during DNA replication.

Question 13

G1=?
S=?
G2?
M+?

Answer 13

G1=growth phase
S=replication of DNA
G2=cells grow and prepare to divide
M= mitosis

Question 14

Name the order of the five stages of mitosis

Answer 14

Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 15

Describe prophase.

Answer 15

Chromosomes condense
Nuclear membrane disappears
Spindle fibres form from the centriole

Question 16

Describe metaphase

Answer 16

Chromosomes aligned at the equator of the cell
Attached by fibre to each centriole
Maximum condensation of chromosome

Question 17

Describe anaphase

Answer 17

Sister chromatids separate at centromere
Separate longitudinally
Move to opposite ends of cell

Question 18

Describe telophase.

Answer 18

New nuclear membranes form
Each cell contains 46 chromosomes (diploid)

Question 19

Describe cytokinesis.

Answer 19

Cytoplasm separates
Two new daughter cells

Question 20

What is the centromere?

Answer 20

Constricted region joining sister chromatids

Question 21

What are centromeres characterised by?

Answer 21

Repetitive DNA sequences
->like satellite DNA

Question 22

What are centromeres the site of?

Answer 22

The kinetochore which is a protein complex that binds to microtubules.

Question 23

What is the kinetochore required for?

Answer 23

Required for chromosome separation during cell division.

Question 24

What stages of the cell cycle make up interphase?

Answer 24

G1, S, G2

Question 25

Describe the structure and genes of Heterochromatin.

Answer 25

-Condensed structure -Silenced genes

Question 26

Describe the structure and genes of Euchromatin

Answer 26

-Open structure -Active genes

Question 27

What percentage of our DNA is protein coding?

Answer 27

2%

Question 28

What is chromatin?

Answer 28

DNA protein assembly into which our DNA is assembled and packaged to make it possible to fit it within the nucleus

Question 29

What is the central component of chromatin.

Answer 29

Histone proteins

Question 30

Why are histones well suited to packaging DNA?

Answer 30

They are positively charged and the phosphate backbone is negatively charged.

Question 31

What are the four main histone particles called?

Answer 31

Histone 3 Histone 4 Histone 2A Histone 2B

Question 32

What does Histone 1 do?

Answer 32

Binds to the base of the nucleosome and helps to hold DNA in place.

Question 33

What charge do histones have?

Answer 33

Positive

Question 34

Describe how DNA gets wrapped up into chromosomes.

Answer 34

-Short region of DNA double helix wrapped around nucleosomes -These then get assembled into a chromatid fibre -Chromatid fibres become attached to a scaffold complex so that the fibre is assembled in a series of loops on a chromatin scaffold -DNA condensed

Question 35

Give some of the purposes of the packaging of DNA

Answer 35

-Negatively charged DNA neutralised by positive charged histone proteins -DNA takes up less space -Inactive DNA can be folded into inaccessible locations until required -Inactive chromatin characterised by specific histone convalent modification (e.g. methylation)

Question 36

What side of the chromosome is known as the P side?

Answer 36

The shorter side P= petite arm

Question 37

Which side of the chromosome is known as the Q arm?

Answer 37

The longer side Contains more DNA

Question 38

Give an example of a chromosome in which the P arm is so small that it doesn't have any function.

Answer 38

Chromosome 21

Question 39

Describe simply the process of chromosome analysis

Answer 39

-Blood sample taken -Want to separate off the white blood cells through incubation. -Cells put on slide and stained -Photographed -Chromosomes assembled into a karyotype

Question 40

What does a karyotype show?

Answer 40

All the chromosomes lined up in their pairs

Question 41

In each chromosome pair, how many strands of DNA are there?

Answer 41

4

Question 42

Define metacentric.

Answer 42

The centromere constriction is close to the centre of the the chromosome

Question 43

Define sub-metacentric.

Answer 43

Centromere is displaced from the centre of the chromosome.

Question 44

Define acrocentric.

Answer 44

Q arm is so small that it doesn't consist of any functional DNA.

Question 45

Name the stain which can be used to highlight the differences in chromosomes.

Answer 45

Giemsa

Question 46

Name four type of FISH (Fluorescent in situ hybridisation) probes

Answer 46

Unique sequence probes Centromeric probes Whole chromosome probes Telomeric probes

Question 47

Why are centromeric probes useful?

Answer 47

Useful for determining chromosome number

Question 48

Why are telomeric probes useful?

Answer 48

Useful for detecting subtelomeric rearrangements Often present in children with unexplained mental retardation

Question 49

Where would you find satellite DNA?

Answer 49

Centromeres Telomeres

Question 50

What type of DNA is used for finger printing?

Answer 50

Minisatellite DNA