Session 3: Nuclear structure, cell cycle and cell division

Question 1

Briefly describe the 4 functions of the nucleus.

Answer 1

1. Controls all cytoplasmic and nuclear activities
2. Carries genetic material
3. DNA replication
4. Plays a role in protein synthesis

Question 2

Can a human cell perform a useful function w/o a nucleus? Explain and give examples.

Answer 2

Yes, red blood cells can perform useful functions w/o a nucleus.

Question 3

Name three types of cells that have more than one nuclues.

Answer 3

1. Syncytium (skeletal muscle cells)
2. Fungi
3. Species of protozoa

Question 4

Describe the shape and size of the nucleus, as well as its components and their functions.

Answer 4

• NUCLEUS
  Shape: Membrane-lined compartment
  Function: all 4 functions mentioned above
• NUCLEAR ENVELOPE
  Shape: double membrane surrounding nucleus w/ perinuclear cisternal space (contains lamina and pores)
  Function: provides a selective membrane barrier between the nuclear compartment and cytoplasm
• NUCLEOLUS
  Shape: non-membranous region of the nucleus that contains heterochromatin and rRNA
  Function: Site of rRNA synthesis and initial ribosomal assembly
• CHROMATIN
  Shape: a complex of DNA and proteins
  Function: carries genetic material
• NUCLEOPLASM
  Shape: Material enclosed by the nuclear envelope
  Function: suspends chromatin and nucleolus

Question 5

Describe the composition, appearance, and organization of chromatin.

Answer 5

Composition:

• a complex of DNA and proteins
• smallest unit = nucleosomes
• nucleosomes make up the chromatin fibrils

Appearance and organization:
- During cell division
  * appear as chromosomes 
  * each chromosome has 2 chromatids joined together 
    by a centromere
- During telophase 
  * heterochromatin forms the nucleolus
  * euchromatin -loosely arranged chromatin fibers

Question 6

Describe the structure of a chromosome from DNA to a chromosome.

Answer 6

• short region of DNA double helix
• “beads on a string” form chromatin
• chromatin fiber of packed nucleosomes
• extended scaffold form
• condensed scaffold form
• metaphase chromosome

Question 7

Explain gonosomes.

Answer 7

Sex chromosomes that determine the gender of the individual.
Only 1 pair is responsible

Question 8

Explain the Barr body.

Answer 8

One inactive spiralised, condensed X chromosome visible as a large dot. Only visible in females and used for sex determination.

Question 9

Describe the karyotype of man.

Answer 9

Description of chromosomal makeup of an individual according to:
- #
- size
- shape
- type 
 - emitted fluorescent colour
- organisation
of chromosomes in a somatic cell.

• 46 chromsomes
• 22 autosome apirs and 1 gonosome pair

Question 10

What are the 3 importances of karyotype studies.

Answer 10

1. Cytogenetic testing for chromosomal abnormality disorders
2. Prenatal sex determination in foetuses
3. Prenatal screening of certain genetic disorders

Question 11

What are the morphological characteristics of a smear that enable one to accurately determine sex?

Answer 11

1. Barr body

2. Y chromosome

Question 12

Briefly describe the structure, composition, and function of a nucleolus.

Answer 12

Structure: non-membranous part of a nucleus made of fibrillar centre and material and granular material.

Composition: ribosomal particles

Function: site of rRNA synthesis and initial ribosomal activity

Question 13

Explain the 3 classifications of cells into cell populations w/ regard to their level and characteristics of mitotic activity.

Answer 13

Static cell populations

• no mitotic activity
• cells no longer divide
• e.g neurons

Stable cell populations

• can divide but only stimulated by injury/disease
• divide episodically
• e.g endothelial cells

Renewing cell populations

• regular mitotic activity
• occurs slowly ( smooth muscle in hollow organs) and rapidly ( epithelial cells in the skin)

Question 14

Describe the events and checkpoints of each phase of the cell cycle.

Answer 14

G1 phase:

• cell performs its normal functions
• G1 DNA damage checkpoint
• Restriction checkpoint

S phase:

• DNA is doubled
• S DNA damage checkpoint

G2 phase:

• cell prepares for cell division
• G2 DNA damage checkpoint
• Unreplicated DNA checkpoint

M phase:

• karyokinesis and cytokinesis
• no checkpoints

Question 15

Define necrosis and examples of where it occurs.

Answer 15

A process of cell death caused by exposure to unfavorable environments, like low pH.

Question 16

Describe the process of necrosis.

Answer 16

Cells are exposed to unfavourable physical and chemical conditions.
Cell death is initiated by viruses.
Characterised by swelling and lysis.

Question 17

Define apoptosis.

Answer 17

Programmed cell death where the cells that are no longer needed are eliminated from the organism.

Question 18

Describe the process of apoptosis.

Answer 18

It’s a physiological process where no longer needed cells are eliminated from the organism.
Death is initiated by the cells.
Characterized by autodigestion.

Question 19

Define atrophy and give physiological and pathological examples of it.

Answer 19

The wasting of cells.
Physiological: shrinking of tonsils during adolescence.
Pathological: muscular dystrophy.

Question 20

Define hypertrophy and give physiological and pathological examples of it.

Answer 20

The cells increase in size.
Physiological: muscular hypertrophy as a result of strength training.
Pathological: hypertrophy of the clitoris ass. w/ general ambiguity.

Question 21

Define hyperplasia and give physiological and pathological examples of it.

Answer 21

Proliferation (renewal) of cells as a result of a specific stimulus.
Physiological: replacing damaged liver cells.
Pathological: hyperplasia is always physiological.

Question 22

Define neoplasia and give physiological and pathological examples of it.

Answer 22

The formation or presence of new, abnormal growth of tissue.
Physiological: all neoplasia is pathological.
Pathological: any type of cancer.