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Mpharm 1 > PH1123 - Membranes > Flashcards

PH1123 - Membranes Flashcards

1
Q

where is cholesterol found and its function? (2)

A
  • sits on the inner and outer membrane

- reduces degree of fluidity and regulates rigidity

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2
Q

where are there many drug targets?

A
  • proteins on the plasma membrane
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3
Q

what are lipid rafts?

A
  • rich collections cholesterol and sphingolipids and other similar lipids with or without associated proteins that serve as attachment points for other biomolecules
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4
Q

what do lipid rafts do? (2)

A
  • cell signalling

- endocytic pathways

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5
Q
  • cell signalling

- endocytic pathways

A
  • separate environments to optimize the course of chemical reactions
  • incompatible processes can go on simultaneously inside the same cell
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6
Q

what is the first stage of endocytosis?

A
  • part of the membrane falls into the cytoplasm of the cell
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7
Q

how do secretory vesicles release their contents?

A
  • exocytosis
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8
Q

what is endocytosis?

A
  • the taking in of matter by a living cell by invagination of its membrane to form a vacuole
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9
Q

what molecules are endocytosis used for? (3)

A
  • cell uptake of extracellular nutrients
  • cell recovery through endocytic recycling
  • cholesterol homeostasis
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10
Q

what are the different endocytic pathways? (5)

A
  • macropinocytosis
  • clathrin coated vesicles
  • clathrin independent endocytosis
  • cavaeolae; platform is lipid raft
  • phagocytosis
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11
Q

what is clathrin? (2)

A
  • triskeleton composed of three clathrin heavy chains and three light chains which form a polyhedral lattice around the vesicle
  • protein that plays a major role in the formation of coated vesicles
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12
Q

what are adaptins?

A
  • they link clathrin to receptors in coated vesicles
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13
Q

where do the molecules go to after fusion in clathrin endocytosis? (3)

A
  • to early endosome (pH6.5)
  • then late endosome (pH 5.5)
  • then lysosome H+ enters (pH 4.5)
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14
Q

how does clathrin endocytosis work? (5)

A
  • cargo binds to cargo receptor
  • adaptin links clathrin to receptors in coated vesicles
  • vescicle forms and fission occurs
  • uncoating (opening/splitting of complex) occurs and are transported via transport vesicles
  • fusion and sorting endosome
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15
Q

in the acidic cell stomach what is inside and what is the optimum pH? (4)

A
  • nucleases (break up DNA)
  • proteinases (break up proteins)
  • lipases (break up lipids)
  • optimum pH is low (4.5)
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16
Q

what is receptor mediated endocytosis? (4)

A
  • tranferrin (ion carrying molecule) binds to transferrin receptor
  • epidermal growth factor (EGF) binding to EGF receptor
  • LDL binding to LDL receptor (endocytic pathway traversed by receptor and ligand)
  • all these rely on clathrin mediated endocytosis
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17
Q

what is the condition when you have too little iron?

A

anaemia

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18
Q

what is the condition when you have too much iron?

A
  • haemochromatosis
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19
Q

what is the function of iron in cells? (3)

A
  • cofactor in enzymes necessary for metabolic processes
  • essential element for blood production and important for haemoglobin and myoglobin
  • iron transports oxygen in blood from lungs to tissues
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20
Q

how does iron get into cells? (7)

A
  • transferrin (ligand) binds and transports iron in blood serum
  • transferrin-receptor complexes concentrate in clathrin coated pits and are internalized in an endycotic vesicle
  • the clathrin coat is removed and the complexes are directed into an endosome
  • the pH in the endosome drops to pH 6 due to the action of (H+)-ATPase pump
  • the pH drop weakens the affinity of transferrin for iron, leading to Fe3+ dissociation from the protein where Fe3+ is reduced to Fe2+
  • as the pH drops the affinity of the receptor for apotransferrin increases
  • remains bound to the receptor in the endosome, the complex recycles to the cell surface and ready for another round of iron uptake
21
Q

how does receptor mediated endocytosis of epidermal growth factor work (EGF)? (2)

A
  • lLigand binding to the receptor’s extracellular domain leads to dimerization (joining) of adjacent EGFR monomers which activates the cytoplasmic tyrosine kinase domains
  • after ligand binding and receptor activation the EGFRs are endocytosed and recycled or directed to lysosomes for degradation
22
Q

what happens if there is no regulation of epidermal growth factor? (2)

A
  • binding of an EGF ligand to the receptor’s extracellular domain initiates signal transduction pathways that regulate cell proliferation and differentiation
  • over-expression and aberrant activity of EFGR is involved in the development of cancer
23
Q

what is HER2 a target for?

A
  • herceptin
24
Q

why do fats need specialised transport?

A
  • they are hydrophobic
25
Q

what are triglycerides transported by?

A
  • b globulins
26
Q

what is cholesterol transported by?

A
  • b globulins
27
Q

what are phospholipids transported by?

A
  • a globulins
28
Q

what are free fatty acids transported by?

A

albumin

29
Q

what is the receptor mediated endocytosis of LDL receptors? (4)

A
  • LDL contains chloesterol and cholesterol esters and binds to LDL receptors
  • invagination of LDL to form a clathrin coated vesicle
  • lysosomes fuse with the vesicle and hydrolyses it where LDL falls off the receptor at low pH
  • free cholesterol is released and the endosome is recycled
30
Q

what is autophagy?

A
  • eating from the inside
31
Q

what usually goes through autophagy?

A
  • old and damaged organelles are wrapped in membrane and delivered to the lysosomes for degradation
32
Q

what is the secretory pathway? (2)

A
  • a series of steps a cell uses to move proteins out of the cell
  • deliver membrane proteins like tranferrin receptors and LDL receptors
33
Q

what are soluble proteins that are excreted via exocytosis? (2)

A
  • insulin (hormone)

- pepsin

34
Q

what are small molecules that are excreted via exocytosis? (3)

A
  • neurotransmitters
  • acetycholine
  • noradrenaline
35
Q

how do proteins travel from the ER to the extracellular fluid in vesicles? (3)

A
  • budding of vesicle from ER
  • at golgi modification of proteins occur
  • vesicle fuses with plasma membrane to release contents
36
Q

what is apoptosis? (2)

A
  • programmed cell death

- allows removal of specific cells for various reasons

37
Q

what are the two pathways of apoptosis? (2)

A
  • intrinsic (cell decides) pathways

- extrinsic (told by other cells) pathways

38
Q

what is the intrinsic pathway of apoptosis? (2)

A
  • cellular stress
  • regulation of BCL-2 proteins by transcriptional and post-transcriptional mechanisms
  • cell death
39
Q

what is the process of apoptosis? (4)

A
  • pro-apoptotic stimulus
  • execution
  • engulfment
  • clearance
40
Q

what happens to red blood cells in a hypotonic solution? (2)

A
  • the concentration of solutes inside the cell is higher (lower water potential inside the cell) than the outside
  • osmosis will occur from outside of cell into the cell and cause it to swell and then burst
41
Q

what happens to red blood cells in a hypertonic solution? (2)

A
  • higher concentration of solutes in solution compared to cell (less water potential outside cell)
  • cell shrinks and dies
42
Q

what is the difference between an ion channel and an ion pump? (2)

A
  • an ion channels allows ion to rush down gradients of concentration or electrical potential (PASSIVE)
  • an ion pump actively (uses ATP) pushes ions against a gradient and therefore further build up the gradient (ACTIVE)
43
Q

what are nicotinic acetylcholine receptors an example of?

A
  • ionotropic receptors (ligand-gated ion channels)
44
Q

what are g proteins? (3)

A
  • proteins bind GTP rather than ATP
  • they are active when bound to GTP and inactive when bound to GDP
  • can hydrolyse GTP to GDP
45
Q

what are g protein coupled receptors? (2)

A
  • don’t have ion channels but G-proteins

- have 2 domains where intracellular binds to G-proteins and extracellular binds to neurotransmitters

46
Q

what is signal transduction? (2)

A
  • the mechanism whereby a command is executed within a cell

- an external signal generates an intracellular message

47
Q

what are examples of signal transduction? (4)

A
  • how an action potential casues transmitter release
  • how acetylcholine phosphorylates ion channels
  • how hormone release is controlled (eg insulin)
  • how agonists modify cell growth (eg EGF)
48
Q

what is a symport and an example? (2)

A
  • two molecules working together driving each other from one place to another
  • glucose-Na+ coupled transport

Mpharm 1 (59 decks)

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