L7: Cells

Question 1

Reason for different types of cells

Answer 1

1. Transcription regulation at promoter
2. Epigenetic changes
   - Acetylation (activate gene transcription)/deacetylation (deactivate) of Histone
   - Methylation of DNA

Question 2

Components of nucleus

Answer 2

1. Nucleolus
2. Nuclear membrane (double membrane)
3. Heterochromatin
4. Euchromatin (active in gene transcription)

Chromatin = DNA + histone

Question 3

Function of nucleolus

Answer 3

1. ribosomal RNA synthesis and transcription (ribosomal protein imported from cytoplasm)
2. Processing and assembly of ribosomes

Prominent during interphase

Question 4

Rough ER function

Answer 4

Protein synthesis, well-developed in secretory cell

Membranous sheets, tubular network

Question 5

Smooth ER function

Answer 5

1. Calcium storage and release (sarcoplasmic reticulum)
2. Lipid metabolism and detoxification
3. Steroid hormone production

Question 6

Golgi apparatus function

Answer 6

1. Modifications and packaging of proteins
   - Glycosylation
   - Proteolysis into active form
   - Sorting of protein for exocytosis
2. Lysosome formation
3. Recycling of cell membrane
4. Lipid are only for incorporation into vesicles

(Cis (forming) and trans (exit) surface)

Question 7

Nucleic acid staining

Answer 7

Basophilic, therefore stained by basic dye (blue dye / haematoxylin dye)

Question 8

Mitochondria features

Answer 8

1. Double membrane
   Outer: Permeable to many substances by non-specific channel proteins
   Inner: folded into cristae, contain respiratory chain enzymes
   Intermembranous space: Cytochrome C
   Matrix: Citric acid cycle enzymes, fatty acid oxidation, store calcium
2. Circular DNA (maternal origin)
   Encodes proteins for oxidative phosphorylation, mitochondrial protein encoded by nuclear genes and transported into mitochondria

Question 9

Types of cytoskeleton

Answer 9

1. Microfilament (Actin) (最細)
2. Intermediate filaments (structural)
3. Microtubules (地鐵路軌) (最大)

Question 10

Functions of Microfilament

Answer 10

1. Cell movement
2. Cytokinesis
3. Microvilli
4. Stress fibres

(actin: two forms: G-actin and F-actin)

Question 11

Functions of Microtubules (present in all cells except RBC)

Answer 11

1. Intracellular transport: movement of organelles, vesicles
2. Chromosome separation (by microtubules from centrosome)
3. Cilia

Alpha and beta: Microtubules
Gamma: Centrosome

Question 12

Functions of intermediate filament

Answer 12

Structural support, cell shape and rigidity

Question 13

Types of intermediate filament

Answer 13

• 1. Tonofilament / Cytokeratin (epithelial cells)
• 2. Desmin filament (muscle)
• 3. Vimentin (fibroblasts)
     
     4. Neurofilament (neurone)
     5. Glial filament (GFAP) (glial cells)
     6. Nuclear lamin
• = important

Question 14

Microtubule motor protein

Answer 14

1. Kinesins (towards +ve end)
2. Dyneins (towards -ve end)

(火車在路軌)

Question 15

Purpose of membrane fluidity

Answer 15

Allow lateral diffusion for membrane protein

Breaks and tears sealed spontaneously

Question 16

3 types of membrane lipids

Answer 16

1. Phospholipid
2. Cholesterol (stabilise membrane mechanically)
3. Glycolipid (outer side of membrane)

Question 17

Function of membrane proteins

Answer 17

1. Transport molecules in and out
2. Receptors for signalling
3. Attach cells to ECM
4. Attach cytoskeleton filament to cell membrane
5. Enzymatic activity, cell attachment and communication

Question 18

Function of membrane carbohydrates (glycocalyx)

Answer 18

1. Antigen (Cell type and blood group)
2. Histocompatibility complex
3. Adhesion

Question 19

4 types of endocytic vesicles

Answer 19

1. Phagosomes (largest)
2. Clathrin-coated vesicles
3. Caveolae (smallest, high affinity to cholesterol)
4. Uncoated vesicles

Question 20

Function of exocytosis

Answer 20

1. Secretion (from trans face of Golgi)

2. Recycling of cell membrane

Question 21

What is endosome

Answer 21

• Sorting compartment along endocytic pathway
• Early, recycling, multivesicular, late endosome
• Fuse directly with lysosome and low pH activate lysosomal acid hydrolases
• Endosome pH affects the fate of transported ligand

Question 22

Describe nuclear membrane

Answer 22

Two concentric membrane
Outer: continuous with ER
Inner: attached to lamins of nuclear matrix

Question 23

Describe cell cycle

Answer 23

• G1 —> S —> G2 —> M —> G1
• G0 for non-dividing cells
• Interphase: G1, S, G2
• Regulated by cyclin dependent kinase (cdks) which is activated by cyclin

Question 24

Describe mitosis

Answer 24

1. Prophase: condensed chromosome
2. Prometaphase: break down of nuclear membrane, attachments of chromosome at kinetochore to spindle microtubules
3. Metaphase: Alignment at equatorial plane
4. Anaphase: Separation to two poles
5. Telophase: Chromatids separate from microtubules, reformation of nuclear membrane
6. Cytokinesis: Cleavage into two cells by aggregation of actin-myosin belt

Question 25

Describe Centrosome

Answer 25

1. A pair of centrioles which located at spindle pole and organisation of spindle fibres 2. Duplicate once each cell cycle 3. Segregation of chromosome

Question 26

What are lysosome

Answer 26

1. High content of acidic hydrolytic enzyme 2. Numerous in macrophage and neutrophil 3. From Golgi (primary), fusion with endosome (secondary), fusion with phagosome (phagolysosome)

Question 27

What are perixosomes

Answer 27

Contain oxidative enzyme for oxidative detoxification Numerous in hepatocyte Beta-oxidation to break down fatty acids