Session 2: Characteristics, structure & functions of a cell

Question 1

Define membranous and non-membranous organelles and give examples.

Answer 1

Membranous organelles: organelles that are surrounded by a plasmamembrane and are isolated from the cytosol, e.g mitochondria

Non-membranous organelles: organelles that are not surrounded by a plasmamembrane and are in direct contact w/ cytosol, e.g ribosomes, microtubuli

Question 2

List the different cytoplasmic organelles that occur and state the function of each.

Answer 2

Endoplasmic Reticulum: contain large amounts of protein

Golgi apparatus: transported substances from the ER are processed to form lysosomes, transport vesicles, etc.

Lysosomes: serve as the intracellular digestive system

Peroxisomes: oxidizes substances that might be poisonous to the cell

Secretory vesicles: store protein proenzymes

Mitochondria: powerhouse of the cell

Cytoskeleton( filament and tubular structures): provides rigid, physical structures for certain parts of the cell

Nucleus: control centre of the cell

Nuclear membrane: large complexes of protein molecules attached at the edges of the pores

Nucleolus: some synthesised RNA is stored

Question 3

List the different cytoplasmic organelles that occur and state the function of each.

Answer 3

Endoplasmic Reticulum: contain large amounts of protein

Golgi apparatus: transported substances from the ER are processed to form lysosomes, transport vesicles, etc.

Lysosomes: serve as the intracellular digestive system

Peroxisomes: oxidizes substances that might be poisonous to the cell

Secretory vesicles: store protein proenzymes

Mitochondria: powerhouse of the cell

Cytoskeleton( filament and tubular structures): provides rigid, physical structures for certain parts of the cell

Nucleus: control centre of the cell

Nuclear membrane: large complexes of protein molecules attached at the edges of the pores

Nucleolus: some synthesised RNA is stored here

Question 4

Describe the structure of a cell membrane.

Answer 4

• Double layer of phospholipid molecules
• Cholesterol
• Integral and peripheral proteins
• Contains lipids, carbohydrates and functional proteins

Question 5

What are the 4 functions of the cell membrane?

Answer 5

1. Physical isolation - acts as a barrier
2. Regulates exchange with the external environment - diffusion, osmosis, phagocytosis
3. Monitors the environment - extracellular fluid composition & chemical signals
4. Structural support - anchors cells and tissues

Question 6

Explain the 4 steps of endocytosis.

Answer 6

1. Receptors accumulate on the cell membrane
2. Receptors bind to target molecules
3. Target molecules form vesicle-like invagination on plasmamembrane
4. Proteins and receptors are pulled into the forming vesicle

Question 7

Explain exocytosis

Answer 7

Substances (proteins and receptors) exit the cell

Question 8

What is the functional role of endosomes in a cell?

Answer 8

Sort and recycle proteins internalized by endocytosis

Question 9

Describe the 3 functions of lysosomes?

Answer 9

1. Intracellular digestion
   * break down molecules
   * attack bacteria
   * recycle basic components of broken down damaged
   organelles
   * ejects waste by exocytosis
2. Autolysis of tissue
3. Defends the body against certain bacterial invaders

Question 10

Define the term primary lysosome.

Answer 10

Formed by Golgi and inactive enzymes

Question 11

Define the term secondary lysosome.

Answer 11

• Lysosome fused with phagosome or damaged organelle
• Digestive enzymes activated
• Toxic chemicals isolated

Question 12

Define the term residual body.

Answer 12

Vesicles containing indigestible material

Question 13

Define autophagy.

Answer 13

Processs that maintains normal functioning of the cell by protein degradation and turnover of the dstroyed cell organelles for new cell formation.

Question 14

Define heterophagy.

Answer 14

Digestion of a substance in the cell’s environment through pinocytosis or phagocytosis.

Question 15

What is the function of the rough-surfaced endoplasmic reticulum?

Answer 15

Exporting in protein synthesis

Question 16

In what type of cells would the rER be well-developed and why?

Answer 16

…

Question 17

What are the 9 functions of the smooth-surfaced endoplasmic reticulum?

Answer 17

1. Absorbed fatty acids are resynthesized
2. Transcellular transport of fats
3. Lipoprotein synthesis
4. Role in muscle contraction
5. Secretion of Cl- ions
6. Synthesie steroid hormones
7. Oxidation to detoxify poisonous substances
8. Break down of glycogen
9. Triglyceride synthesis

Question 18

What are the functions of the

Answer 18

1. Connected w/ protein production
2. Protein undergo changes in sacculae
3. Produce secretory vesicles, enzymes, hormones
4. Add carbohydrates to proteins (glycoproteins)

Question 19

Describe the basic structure of mitochondria.

Answer 19

• Have smooth outer membrane and folded inner membrane(cristae)
• Matrix around the cristae

Question 20

What are the functions of mitochondria?

Answer 20

Produces energy needed for the functioning and survival of the cell by:

• houses the chains of enzymes responsible for cell respiration
• require O2 & organic substrates
• generate CO2 & ATP

Question 21

What are the 4 functions of peroxisomes?

Answer 21

1. Breaks down fatty acids and organic compounds
2. Contains oxidases and regulates H2O2 levels
3. Site of urate oxidase
4. Possibly responsible for gluconeogenesis

Question 22

What is the function of microtubules?

Answer 22

1. Attach to the centrosome
2. Anchor organelles and strengthen cells
3. Change cell shape
4. Move vesicles within the cell
5. Form spindle apparatus

Question 23

What are the structural differences between basal bodies and centrioles?

Answer 23

A centriole is surrounded by cytoplasm AND basal bodies have no cytoplasm surrounding it

Question 24

Describe the 4 pathways for the ingestion of particles by a cell.

Answer 24

• Diffusion- substances move thru cell membrane pores
• Active transport- actual carrying of substances by a physical protein structure that penetrates all the way thru the mebrane
• Pinocytosis- ingestion of minute particles that form vesicles of ECF
• Phagocytosis- ingestion of large particles

Question 25

Describe the pathway for the digestion of particles by a cell.

Answer 25

* Lysosomes attach to the vesicle * A digestive vesicle is formed inside the cytoplasm * The proteins, carbs, lipids, etc are hydrolyzed

Question 26

Describe the pathway of secretion of particles by a cell.

Answer 26

The residual body with indigestible substances is excreted externally through exocytosis.

Question 27

Describe the synthesis and secretion of proteins by a cell.

Answer 27

* Proteins are synthesized by ribosomes | * Synthesized proteins are extruded to the cytosol by ribosomes

Question 28

Describe the pathway for the synthesis of proteins for intracellular use.

Answer 28

Some synthesized proteins are extruded to the ER by ribosomes into the endoplasmic matrix.

Question 29

Define autodigestion.

Answer 29

The digestion of tissue by enzymes produced by the organism itself.

Question 30

Explain the various ways of passage through the cell membrane.

Answer 30

- Diffusion - Active transport - Phagocytosis - Pinocytosis