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Cell & Tissue Biology > Exam #1: Cell Biology III > Flashcards

Exam #1: Cell Biology III Flashcards

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1
Q

What are the five endocytotic pathways?

A

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

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2
Q

Macropinocytosis

A
  • 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
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3
Q

Clathrin-mediated endocytosis

A
  • 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
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4
Q

Non-coat-mediated endocytosis

A
  • Simple invagination of the plasma membrane

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

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5
Q

Caveolae-mediated endocytosis

A
  • Caveolin protein mediates pinocytosis

- Associated with endocytosis of Simian Virus 40

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6
Q

Phagocytosis

A
  • 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
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7
Q

What are the two requirements for endocytosis?

A

1) Energy (ATP)

2) Ca++

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8
Q

Dynamin

A

GTPase required to pinch off the vesicle in clathrin mediated endocytosis

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9
Q

Adaptin

A

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

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10
Q

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

A

Neurotransmitters

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11
Q

How does an LDL receptor defect lead to atherosclerosis?

A
  • LDL receptors are required for clathrin-mediated endocytosis of cholesterol
  • LDL mutation impairs binding to adaptin/cargo
  • Less cholesterol is brought into the cell
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12
Q

What are the three modes of secretion from the cell?

A
  • Exocytosis
  • Porocytosis
  • Exosomes & Exosome-like vesicles
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13
Q

Exocytosis

A
  • 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
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14
Q

Porocytosis

A

Quantal release of neurotransmitters

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15
Q

Exosomes

A
  • Secretory products released into the extracellular environment, surrounded in plasma membrane
  • Can function to discard unneeded membrane proteins
  • E.g. reticulocyte (RBC) discarding transferrin
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16
Q

What are the two pathways of exocytosis?

A
  • Constitutive

- Regulated

17
Q

Constitutive exocytosis

A
  • Continuous secretory process

- Product not stored in secretory granules

18
Q

Regulated exocytosis

A
  • Secretory product IS STORED in granules

- Released in response to signal

19
Q

Describe the staining of ribosomes.

A
  • Ribosomes are basophilic b/c of negatively charged phosphate groups
  • Use Hematoxylin
  • Stains blue
20
Q

Where are ribosomes synthesized?

A

Nucleoli

21
Q

What are the two subunits of the eukaryotic ribosome?

A
  • Large, 60S

- Small, 40S

22
Q

Where do ribosomes synthesize proteins?

A

Cytoplasm

23
Q

What are the two different forms of a ribosome?

A

1) Individual granule i.e. discrete ribosomal subunits

2) Polyribosomes, mRNA + ribosome

24
Q

Where are polyribosomes found?

A
  • Free in the cytoplasm (polysome)

- Bound to the ER

25
Q

Where are ribosomes not found?

A

Mature RBCs

26
Q

Polysome (free ribosome)

A
  • Free ribosome in cytoplasm with pearl on a necklace appearance
  • Function in protein synthesis for use within the cell
27
Q

rER Characteristics

A
  • Rough Endoplasmic Reticulum
  • Basophilic
  • Forms intracellular network of cisternae
  • Continuous with nuclear envelope
  • Polyribosomes attached
28
Q

How are exported proteins produced?

A
  • Signal recognition sequence
  • Signal recognition peptide, SRP, recognizes sequence
  • Binds to SRP Receptor & places ribosome in translocon
  • Signal peptidase removes signal sequence
29
Q

rER Functions

A

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

30
Q

ER Stress

A
  • Unfolded/misfolded proteins in ER cisternae

- Protein must be folded properly to traffic to the golgi

31
Q

Unfolded Protein Response

A
  • Chaperone synthesis increased
  • Decreased synthesis of proteins
  • Misfolded proteins exported from ER & polyubiquinated in cytosol for proteosome degradation
  • Caspases activated for apoptosis if needed
32
Q

Alpha1-Antitrypsin Deficiency

A
  • Enzyme forms but is misfolded & accumulated in the ER

- Implicated in emphysema

33
Q

sER Characteristics

A
  • Lacks polyribosomes (hence smooth)
  • Acidophilic
  • Continuous with rER
  • Cisternae have more tubular appearance than rER
34
Q

Functions of sER

A

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

35
Q

Von Gierke’s Disease

A
  • Defect in glucose 6-phosphatase or glucose 6-phosphate transporter in sER that leads to glycogen accumulation
  • Sx= hepatomegaly, hypoglycemia, & increased lactate
36
Q

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

A

Increase in cytochrome p450 enzymes

37
Q

Malignant Hypertermia

A
  • 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
38
Q

Pharmacologic treatment for Malignant Hyperthermia

A
  • Dantrolene

- Ryanodine-1 Receptor Antagonist

Cell & Tissue Biology (25 decks)

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