Cell Nucleus & Cell Division

Question 1

What is the distinguishing feature of eukaryotic cells?

Answer 1

Nucleus

Question 2

Where does chromatin tend to be found in the nucleus?

Answer 2

At periphery

Question 3

What is the nucleolus?

Answer 3

Region where DNA coding for rRNA is localised

Site of synthesis and assembly of ribosomal subunits

Question 4

Where is the DNA coding for rRNA found?

Answer 4

At the ends of 5 different chromosome pairs

Question 5

What supports the inner nuclear membrane?

Answer 5

Nuclear lamina (meshwork of lamins)

Question 6

What is the function of the nuclear pores?

Answer 6

Allow communication/exchange across nuclear envelope

Question 7

What kind of molecules can pass through nuclear pores via diffusion?

Answer 7

<9nm

Water-soluble

Question 8

How do nuclear proteins pass into the nucleus?

Answer 8

Nuclear localisation sequence binds to a cytoplasmic nuclear import receptor to deliver the protein into the nucleus

GTP hydrolysis

Question 9

What is a nuclear localisation sequence?

Answer 9

Short sequence of basic amino acids, predominantly lysine and arginine

Question 10

How can you unravel the structure of chromatin experimentally?

Answer 10

Reduce salt concentration

Question 11

What is the length of the longest human chromosome (unravelled)?

Answer 11

8.5cm

Question 12

How many of each histone protein is present in a nucleosome?

Answer 12

2 x H2A

2 x H2B

2 x H3

2 x H4

Question 13

How far apart are nucleosomes spaced?

Answer 13

200bp intervals - 146 around nucleosome itself and ~50bp between

Question 14

Which histone protein aids the coiling of nucleosomes into 30nm fibres?

Answer 14

H1

Question 15

What is the structure of the chromatin of euchromatin?

Answer 15

30nm fibres

Question 16

What features are essential in a functional eukaryotic chromosome?

Answer 16

At least one origin of replication

Centromere

Telomeres at each end

Question 17

What is a centromere?

Answer 17

Special DNA sequence which functions during cell division

Question 18

What are the functions of a centromere?

Answer 18

Helps hold replicated daughter chromatids together until separation/anaphase

Enables assembly of the kinetochore which attaches the chromosome to the mitotic spindle

Question 19

What are telomeres?

Answer 19

Tandem repeats of short, G-rich sequences

Act as origins of replication

Question 20

What is the repeating sequence in human telomeres?

Answer 20

GGGTTA

Question 21

What are the functions of the telomeres?

Answer 21

Prevent chromosome fusion

Protect chromosomes from losing important genetic material

Question 22

Explain how telomeres protect genetic material.

Answer 22

DNA polymerase is unable to copy to the end of a linear chromosome

Telomeres extend sequences so all important genetic material is copied

Question 23

What does telomerase do and where is it expressed?

Answer 23

Adds multiple hexanucleotide repeats to the ends of chromosomes to preserve telomeres

Germ cells and cancer cells

Question 24

What is the karyotype?

Answer 24

Number, size and shape of the chromosome complement

Question 25

Why are some cells polyploid?

Answer 25

Repeated DNA replication with no intervening cell division

Question 26

What is an aneuploid cell?

Answer 26

Cells containing abnormal chromosome number

Question 27

What is heteroploidy?

Answer 27

Extra fragments of chromosomes

Question 28

How long does mitosis and cytokinesis take?

Answer 28

~1 hour

Question 29

What is the name given to the period between one mitosis and the next?

Answer 29

Interphase

Question 30

How long does interphase last?

Answer 30

~4 hours

Question 31

What happens during S phase?

Answer 31

DNA replication

Question 32

When does regulation of the cell cycle primarily occur?

Answer 32

G1

Question 33

How do protein growth factors affect the cell cycle?

Answer 33

In absence of protein growth factors, cell leaves cycle in G1 at restriction point and enters resting stage/G0 Waits for growth factors and re-enters at R

Question 34

What part of the cytoskeleton is mitosis dependent on?

Answer 34

Microtubules

Question 35

What part of the cytoskeleton is cytokinesis dependent on?

Answer 35

Actin

Question 36

What is karyokinesis?

Answer 36

Division of nucleus

Question 37

What is cytokinesis?

Answer 37

Division of cytoplasm

Question 38

What are the stages of mitosis?

Answer 38

Prophase Prometaphase Metaphase Anaphase Telophase

Question 39

What happens during prophase? (4)

Answer 39

Chromosomes condense Nucleolus disappears Cytoplasmic microtubules break down Spindle begins to form

Question 40

What happens during prometaphase?

Answer 40

Nuclear envelope breaks down Chromosomes attach to spindle via kinetochores

Question 41

What happens during metaphase?

Answer 41

Chromosomes line up on spindle

Question 42

What happens during anaphase?

Answer 42

Sister chromatids separate Cytokinesis begins

Question 43

What happens during cytokinesis?

Answer 43

Ring of actin and myosin contracts to form cleavage furrow Contracts until cytoplasm separates

Question 44

What happens during telophase? (5)

Answer 44

Spindle disappears Nuclear envelope reforms Chromosomes decondense Nucleolus reforms Cytoplasmic microtubules reform

Question 45

What does a centrosome contain?

Answer 45

2 centrioles at right angles to each other

Question 46

Where is the centrosome located during interphase?

Answer 46

Adjacent to nucleus

Question 47

What are the dimensions of a centriole?

Answer 47

0.5 x 0.2um cylinder

Question 48

What is the wall of a centriole made up of?

Answer 48

9 triplets of microtubules

Question 49

When does centriole duplication occur?

Answer 49

Interphase

Question 50

Describe centriole duplication.

Answer 50

Procentriole grows out of base of mother centriole at right angle By late G2, procentriole is full length but still attached

Question 51

How was the mitotic promoting factor discovered?

Answer 51

Fusion of mitotic cell with interphase cell which caused interphase cell to enter mitosis prematurely

Question 52

What is the mitotic promoting factor?

Answer 52

Cyclin-dependent kinase Complex of Cdk1 (catalytic) and cyclin B (regulatory)

Question 53

Explain how mitotic promoting factor works.

Answer 53

Cdk1 is only active when there is enough cyclin B present Cyclin B accumulates steadily during interphase, peaking at M Degradation of cyclin B required to exit mitosis - occurs when chromatids separate

Question 54

What is S-phase promoting factor?

Answer 54

Cyclin-dependent kinase Complex of Cdk2 and cyclin E or A

Question 55

Briefly describe what occurs during meiosis. (6)

Answer 55

DNA replication Homologous chromosomes pair up to form bivalents Crossing over Homologous chromosomes separate at anaphase 1 Sister chromatids separate at anaphase 2 4 genetically-different haploid cells produced

Question 56

What are chiasmata?

Answer 56

Sites of crossing over

Question 57

What is crossing over?

Answer 57

Exchanging of random segments between homologous chromosomes

Question 58

What is the purpose of meiosis? (3)

Answer 58

Random assortment of maternal and paternal chromosomes Recombination of maternal and paternal chromosomes Infinite number of possible genetic combinations