Exam #1: Cell Biology III

Question 1

What are the five endocytotic pathways?

Answer 1

1) Macropinocytosis
2) Clathrin- mediated endocytosis
3) Non-coat-mediated endocytosis
4) Caveolae-mediated endocytosis
5) Phagocytosis

Question 2

Macropinocytosis

Answer 2

• Actin based process
• Nonspecific ingestion of fluids & solutes
• Can be triggered by bacteria e.g. Salmonella
• Examples: thyroid cells & dendritic cells of the immune system

Question 3

Clathrin-mediated endocytosis

Answer 3

• Occurs at clathrin coated pits
• Can be mediated by receptors e.g. LDL/cholesterol
• Dynamin (GTPase) pinches off vesicles
• Coated pits contain cargo receptors & adaptin protein
• Coated vesicles form and then quickly become uncoated

Question 4

Non-coat-mediated endocytosis

Answer 4

• Simple invagination of the plasma membrane

- Associated with endocytosis of cholera toxin & Shiga (Dysentary)

Question 5

Caveolae-mediated endocytosis

Answer 5

• Caveolin protein mediates pinocytosis

- Associated with endocytosis of Simian Virus 40

Question 6

Phagocytosis

Answer 6

• Ingestion of large particles that is mediated by receptors
• Actin-dependent
• Results in formation of a phagosome
• Phagosomes fuse with lysosomes
• Associated with endocytosis of non-biologic material e.g. latex or asbestos

Question 7

What are the two requirements for endocytosis?

Answer 7

1) Energy (ATP)

2) Ca++

Question 8

Dynamin

Answer 8

GTPase required to pinch off the vesicle in clathrin mediated endocytosis

Question 9

Adaptin

Answer 9

Protein that associates with the intracellular portion of the cargo receptor in clathrin mediated endocytosis

Question 10

What is non-receptor clathrin mediated endocytosis used to bring into the cell?

Answer 10

Neurotransmitters

Question 11

How does an LDL receptor defect lead to atherosclerosis?

Answer 11

• LDL receptors are required for clathrin-mediated endocytosis of cholesterol
• LDL mutation impairs binding to adaptin/cargo
• Less cholesterol is brought into the cell

Question 12

What are the three modes of secretion from the cell?

Answer 12

• Exocytosis
• Porocytosis
• Exosomes & Exosome-like vesicles

Question 13

Exocytosis

Answer 13

• Bulk secretion of cellular synthetic products e.g. proteins/enzymes, hormones, & neurotransmitters
• Secretory vesicles are formed by Golgi that fuse with plasma membrane
• COP (Coat Protein) directed inside the cell

Question 14

Porocytosis

Answer 14

Quantal release of neurotransmitters

Question 15

Exosomes

Answer 15

• Secretory products released into the extracellular environment, surrounded in plasma membrane
• Can function to discard unneeded membrane proteins
• E.g. reticulocyte (RBC) discarding transferrin

Question 16

What are the two pathways of exocytosis?

Answer 16

• Constitutive

- Regulated

Question 17

Constitutive exocytosis

Answer 17

• Continuous secretory process

- Product not stored in secretory granules

Question 18

Regulated exocytosis

Answer 18

• Secretory product IS STORED in granules

- Released in response to signal

Question 19

Describe the staining of ribosomes.

Answer 19

• Ribosomes are basophilic b/c of negatively charged phosphate groups
• Use Hematoxylin
• Stains blue

Question 20

Where are ribosomes synthesized?

Answer 20

Nucleoli

Question 21

What are the two subunits of the eukaryotic ribosome?

Answer 21

• Large, 60S

- Small, 40S

Question 22

Where do ribosomes synthesize proteins?

Answer 22

Cytoplasm

Question 23

What are the two different forms of a ribosome?

Answer 23

1) Individual granule i.e. discrete ribosomal subunits

2) Polyribosomes, mRNA + ribosome

Question 24

Where are polyribosomes found?

Answer 24

• Free in the cytoplasm (polysome)

- Bound to the ER

Question 25

Where are ribosomes not found?

Answer 25

Mature RBCs

Question 26

Polysome (free ribosome)

Answer 26

- Free ribosome in cytoplasm with pearl on a necklace appearance - Function in protein synthesis for use within the cell

Question 27

rER Characteristics

Answer 27

- Rough Endoplasmic Reticulum - Basophilic - Forms intracellular network of cisternae - Continuous with nuclear envelope - Polyribosomes attached

Question 28

How are exported proteins produced?

Answer 28

- Signal recognition sequence - Signal recognition peptide, SRP, recognizes sequence - Binds to SRP Receptor & places ribosome in translocon - Signal peptidase removes signal sequence

Question 29

rER Functions

Answer 29

1) Synthesis of proteins for secretion, membrane proteins & lysosomal proteins 2) Synthesis of enzymes associated with sER 3) Modification of proteins

Question 30

ER Stress

Answer 30

- Unfolded/misfolded proteins in ER cisternae | - Protein must be folded properly to traffic to the golgi

Question 31

Unfolded Protein Response

Answer 31

- Chaperone synthesis increased - Decreased synthesis of proteins - Misfolded proteins exported from ER & polyubiquinated in cytosol for proteosome degradation - Caspases activated for apoptosis if needed

Question 32

Alpha1-Antitrypsin Deficiency

Answer 32

- Enzyme forms but is misfolded & accumulated in the ER | - Implicated in emphysema

Question 33

sER Characteristics

Answer 33

- Lacks polyribosomes (hence smooth) - Acidophilic - Continuous with rER - Cisternae have more tubular appearance than rER

Question 34

Functions of sER

Answer 34

1) Cholesterol Homeostasis 2) Steroid Synthesis 3) Synthesis of Phospholipids 4) Glycogenolysis 5) Detoxification of Drugs 6) Storage, release, & uptake of Ca++ in striated muscle

Question 35

Von Gierke's Disease

Answer 35

- Defect in glucose 6-phosphatase or glucose 6-phosphate transporter in sER that leads to glycogen accumulation - Sx= hepatomegaly, hypoglycemia, & increased lactate

Question 36

Effect of protracted drug and/or alcohol use on the sER?

Answer 36

Increase in cytochrome p450 enzymes

Question 37

Malignant Hypertermia

Answer 37

- Mutant ryanodine-1 receptors that allow excessive Ca++ movement from sER into cytoplasm in response to anesthesia - Increases sER-Ca++ pump that consumes large quantities of ATP - ATP consumption gives off heat

Question 38

Pharmacologic treatment for Malignant Hyperthermia

Answer 38

- Dantrolene | - Ryanodine-1 Receptor Antagonist