The Cell, Cell Division and Cancer

Question 1

State three functions of the smooth endoplasmic reticulum.

Answer 1

1. Synthesis of phospholipids and cholesterol
2. Provides the enzymes that control glycogen breakdown when glycogen is to be used for energy [e.g. glucose-6-phosphatase, which converts glucose-6-phosphate to glucose].
3. Provides enzymes that are capable of detoxifying substances.

Question 2

Hyaluronic acid and chondroitin sulphate are saccharide polymers produced by the Golgi apparatus. List some of their functions. (4)

Answer 2

1. They are the major components of proteoglycans secreted in mucus and other glandular secretions.
2. They are the major components of the ground substance.
3. They are principal components of the organic matrix in both cartilage and bone.
4. They are important in cell activities such as migration and proliferation.

Question 3

(a) State two key differences between peroxisomes and lysosomes.
(b) Name one disorder associated with peroxisomes.

Answer 3

(a) (1) Peroxisomes form by self replication/budding off from smooth ER, whereas lysosomes are formed by breaking off from the Golgi apparatus. (2) The enzymes contained in peroxisomes are oxidases whereas those contained in lysosomes are hydrolases.
(b) Zellweger syndrome; caused by deficiency in peroxisomal enzymes. It is characterizied by severe muscular impairment, liver and kidney lesions and disorganisation of the central and peripheral nervous systems. Electron microscopy reveals empty peroxisomes in liver and kidney cells of these patients.

Question 4

Name three bactericidal agents present in lysosomes that can kill phagocytized bacteria before they cause cellular damage.

Answer 4

(1) lysozyme (dissolves bacterial cell wall)
(2) lysoferrin (binds iron and other substances before they can promote bacterial growth)
(3) acid at a pH of 5 which activates the hydrolases and inactivates bacterial metabolic systems

Further notes:
Iron is a vital cofactor that enables a wide range of metabolic activities. It serves as a cofactor in electron carrying proteins, and is also important for RNA and DNa metabolism. Iron is essential for bacterial physiological processes such as DNA replication, transcription, metabolism and energy generation via respiration.

Question 5

State four functions of mitochondria.

Answer 5

1. Oxidative phosphorylation
2. Heat production
3. Calcium storage
4. Apoptosis

Question 6

What is the function of the glycocalyx?

Answer 6

It protects the cell from mechanical and chemical damage.

Question 7

Name three types of cell junctions.

Answer 7

1. Occluding junctions
2. Anchoring junctions
3. Communicating junctions

Question 8

What is the function of occluding junctions, and give an example.

Answer 8

They seal cells together in an epithelial sheet in a way that prevent even small molecules from leaking from one side of the sheet to the other e.g. tight junctions.

Question 9

What are some differences between euchromatin and heterochromatin?

Answer 9

1. Euchromatin is transcriptionally active whereas heterochromatin is transcriptionally inactive.
2. Euchromatin is lightly stained under nuclear stains whereas heterochromatin is darkly stained.
3. Euchromatin is present in both prokaryotes and eukaryotes whereas heterochromatin is present only in eukaryotes.
4. In euchromatin, the DNA is lightly compressed with the histone proteins whereas in heterochromatin, the DNA is compressed tightly with histone proteins.

Question 10

What is the role of the communicating junctions, and give an example.

Answer 10

They mediate the passage of chemical or electrical signals from one interacting cell to its partner e.g. gap junctions.

Question 11

What comprises the cell cytoplasm?

Answer 11

Organelles
Inclusions
Cytoskeleton
Cytosol

Question 12

What is the difference in the shape and number of chromosomes in prokaryotic and eukaryotic cells?

Answer 12

Prokaryotic cells typically have a single circular chromosome while eukaryotic cells have multiple linear chromosomes.

Question 13

Are mitotic spindles that partition chromosomes into the daughter cells and intermediate filaments found in prokaryotes?

Answer 13

No.

Question 14

Frequency of cell division varies by cell type. Which cells do not divide at all after maturity, remaining permanently in G0?

Answer 14

mature nerve cells and muscle cells
[Diagram]: the Cell Cycle

Question 15

What are the two irreversible events in cell cycle?

Answer 15

✔ replication of genetic material
✔ separation of sister chromatids

Question 16

Checkpoints assess if key cellular processes have been completed correctly. List the 3 checkpoints, and what is being checked at each.

Answer 16

G1/S checkpoint (start or restriction point) - can DNA synthesis begin?
G2/M checkpoint
- has DNA synthesis been completed correctly?
- commitment to mitosis
Spindle checkpoint/M checkpoint - are all chromosomes attached to spindle? can sister chromatids separate correctly?

Question 17

G1/S checkpoint is the most critical checkpoint. It is the primary decision point/restriction point. What happens if the cell at that checkpoint doesn’t receive “GO” signal?

Answer 17

It exits cycle and switches to G0 phase, the non-dividing, differentiated state.

Note:
Liver cells are in G0, but can be “called back” to cell cycle by external cues

Question 18

What are cyclins, and cyclin-dependent kinases?

Answer 18

Cyclins are regulatory proteins controlling the cell cycle. Cyclin-dependent kinases (Cdk) phosphorylates cellular proteins. The Cdk-cyclin complex triggers passage through different stages of cell cycle.

Question 19

Name one disorder associated with cilia.

Answer 19

Kartagener syndrome

Further notes:
Kartagener syndrome, also known as ciliary dyskinesia syndrome or primary ciliary dyskinesia (PCD), is a rare genetic disease that affects cellular elements such as cilia and flagella. Clinical features:
➤ Lung problems: The main symptom is lung dysfunction. Cilia in the respiratory tract don’t work properly, leading to difficulty in clearing debris and fluid from the lungs.
➤ Sinus and Ear Issues: Frequent sinus infections, chronic coughing, and middle ear infections are common.
➤ Reproductive Problems: In men, infertility occurs due to poorly motile sperm. Women may experience ectopic pregnancies.
➤ Reversed Organs: Kartagener syndrome may cause reversed internal organs (situs inversus), where organs are on the opposite side of the body from their normal position.