PH1123 - Membranes Flashcards
(48 cards)
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
2
Q
where are there many drug targets?
A
- proteins on the plasma membrane
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
4
Q
what do lipid rafts do? (2)
A
- cell signalling
- endocytic pathways
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
6
Q
what is the first stage of endocytosis?
A
- part of the membrane falls into the cytoplasm of the cell
7
Q
how do secretory vesicles release their contents?
A
- exocytosis
8
Q
what is endocytosis?
A
- the taking in of matter by a living cell by invagination of its membrane to form a vacuole
9
Q
what molecules are endocytosis used for? (3)
A
- cell uptake of extracellular nutrients
- cell recovery through endocytic recycling
- cholesterol homeostasis
10
Q
what are the different endocytic pathways? (5)
A
- macropinocytosis
- clathrin coated vesicles
- clathrin independent endocytosis
- cavaeolae; platform is lipid raft
- phagocytosis
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
12
Q
what are adaptins?
A
- they link clathrin to receptors in coated vesicles
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)
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
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)
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
17
Q
what is the condition when you have too little iron?
A
anaemia
18
Q
what is the condition when you have too much iron?
A
- haemochromatosis
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
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
what are triglycerides transported by?
- b globulins
26
what is cholesterol transported by?
- b globulins
27
what are phospholipids transported by?
- a globulins
28
what are free fatty acids transported by?
albumin
29
what is the receptor mediated endocytosis of LDL receptors? (4)
- 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
what is autophagy?
- eating from the inside
31
what usually goes through autophagy?
- old and damaged organelles are wrapped in membrane and delivered to the lysosomes for degradation
32
what is the secretory pathway? (2)
- a series of steps a cell uses to move proteins out of the cell
- deliver membrane proteins like tranferrin receptors and LDL receptors
33
what are soluble proteins that are excreted via exocytosis? (2)
- insulin (hormone)
| - pepsin
34
what are small molecules that are excreted via exocytosis? (3)
- neurotransmitters
- acetycholine
- noradrenaline
35
how do proteins travel from the ER to the extracellular fluid in vesicles? (3)
- budding of vesicle from ER
- at golgi modification of proteins occur
- vesicle fuses with plasma membrane to release contents
36
what is apoptosis? (2)
- programmed cell death
| - allows removal of specific cells for various reasons
37
what are the two pathways of apoptosis? (2)
- intrinsic (cell decides) pathways
| - extrinsic (told by other cells) pathways
38
what is the intrinsic pathway of apoptosis? (2)
- cellular stress
- regulation of BCL-2 proteins by transcriptional and post-transcriptional mechanisms
- cell death
39
what is the process of apoptosis? (4)
- pro-apoptotic stimulus
- execution
- engulfment
- clearance
40
what happens to red blood cells in a hypotonic solution? (2)
- 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
what happens to red blood cells in a hypertonic solution? (2)
- higher concentration of solutes in solution compared to cell (less water potential outside cell)
- cell shrinks and dies
42
what is the difference between an ion channel and an ion pump? (2)
- 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
what are nicotinic acetylcholine receptors an example of?
- ionotropic receptors (ligand-gated ion channels)
44
what are g proteins? (3)
- 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
what are g protein coupled receptors? (2)
- don't have ion channels but G-proteins
| - have 2 domains where intracellular binds to G-proteins and extracellular binds to neurotransmitters
46
what is signal transduction? (2)
- the mechanism whereby a command is executed within a cell
| - an external signal generates an intracellular message
47
what are examples of signal transduction? (4)
- 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
what is a symport and an example? (2)
- two molecules working together driving each other from one place to another
- glucose-Na+ coupled transport
