1
Q
two properties of the plasma membrane
A
- fluidity and mosaicism
- selective permeability
2
Q
selective permeability
A
to allow some substances to cross more easily than others
3
Q
cellular membranes are fluid mosaics of
A
lipids and proteins
4
Q
amphipathic
A
the plasma membrane consists of hydrophilic “heads” and hydrophobic “tails”
5
Q
phospholipids form two structures in an aqueous environment
A
micelles and liposomes
6
Q
micelles
A
single layer spherical structure
7
Q
liposomes
A
bilayer spherical structures
8
Q
3 types of membrane lipids
A
- phospholipids
- glycolipids
- sterols (cholesterol)
9
Q
2 types of phospholipids
A
- phosphoglycerides
- phosphosphingolipids
10
Q
composition of a phosphoglyceride
A
glycerol + 2 fatty acids + phosphate + organic molecule
11
Q
composition of a phosphosphingolipid
A
sphingosine + 1 fatty acid + phosphate + organic molecule
12
Q
their basis is glycerol
A
phosphoglycerides
13
Q
examples of phosphoglycerides
A
- phosphatidyl-choline
- phosphatidyl-ethanolamine
- phosphatidyl-serine
- phosphatidyl-inositol
14
Q
their basis is sphingosine
A
phosphosphingolipids
15
Q
example of phosphosphingolipid
A
sphingomyelin
(only in animal cell membrane)
16
Q
glycolipids
A
sugar + lipids (glycosylated lipids)
17
Q
glyosphingolipids
A
sphingosine + 1 fatty acid + sugar residue(s)
18
Q
examples of glycosphingolipids
A
- cerebrosides
- gangliosides
19
Q
monosaccharide glycosphingolipid
A
cerebrosides
20
Q
oligosaccharide glycosphingolipid
A
ganglioside
21
Q
sialic acid (NANA)
A
N-acetyl neuraminic acid
22
Q
types of sterols
A
- cholesterol (animal cell membrane)
- phytosterols (plant cell membrane)
- ergosterols (fungal and protozoal cell membranes)
23
Q
membrane protein categories
A
- integral
- peripheral
24
Q
types of integral proteins
A
- transmembrane proteins: completely span out the membrane
- lipid-bound protein: attached to a membrane lipid
25
2 types of secondary structure
(transmembrane proteins)
- α-helical structure: e.g. growth factor receptors (EGFR), insulin, membrane immunoglobulins
- β-pleated sheet structure (β-barrel): e.g. bacterial porin
26
the hydrophobic region of transmembrane proteins contains
non-polar amino acids
27
EGFR
- epidermal growth factor receptor
- overexpressed in cancers (ex:breast)
- single-pass transmembrane protein with α-helical structure
28
integral lipid-bound proteins
attached to the plasma membrane through a covalent bond with a lipid molecule
29
2 types of attachment (in lipid-bound proteins)
1. directly attached: to the lipids at the internal side of the plasma membrane
2. indirectly attached: to the phosphatidyl-inositol at the external site of the plasma membrane through an oligosaccharide chain
30
peripheral proteins
loosely bound to the surface of the membrane
31
example of an internal membrane protein (peripheral protein)
erythrocyte spectrin
32
six major functions of membrane proteins
- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachment to the cytoskeleton and ECM
33
membrane carbohydrates
- located on the external side of the cell membrane
- interact with the surface molecules of other cells facilitating cell-cell recognition
34
3 types of membrane-associated carbohydrates
- glycoproteins: carbohydrates covalently bonded to proteins
- glycolipids: carbohydrates covalently bonded to proteins
- proteoglycans: proteins covalently linked to carbohydrates
35
membrane-associated carbohydrate found in both membrane and ECM
glycoproteins
36
membrane-associated carbohydrate found in ECM only
proteoglycans
37
membrane-associated carbohydrate found in membrane only
glycolipids
38
glycocalyx
carbohydrate cover on the external side of the cell membrane protecting the cell surface from mechanical/chemical damage
39
examples of hydrophobic molecules
CO2, O2, hydrocarbons
40
examples of hydrophilic molecules
sugars, ions
41
2 types of transport proteins
- channel proteins
- carrier proteins
42
aquaporins
- special channel proteins
- transports water
43
channel vs carrier proteins
channel - transport proteins using a hydrophilic channel
carrier - transport proteins that bind to molecules and change shape to shuttle them across
44
example of a carrier protein
glucose transporters (GLUT)
45
active transport
transport of a substance across a membrane that requires energy investment
46
passive transport
transport of a substance across a membrane with no energy investment
47
2 types of passive transport
1. diffusion - movement of solute molecules across the plasma membrane down their concentration gradient
2. osmosis - movement of solvent (water) molecules across the plasma membrane against the solute concentration
48
facilitated diffusion
passive transport by transport proteins
(movement of molecules is always down their concentration gradient)
49
some diseases are caused by malfunctions in specific transport proteins
- cystic fibrosis
- cystinuria
50
cystic fibrosis
- mutation in chloride ion channel protein
- viscous secretions in respiratory tract causes pulmonary infections
51
cystinuria
(kidney disease)
- mutations in a renal membrane carrier protein
- prevention of cysteine reabsorption into the blood
- cysteine concentrates in urine then forms kidney stones (crystals)
52
tonicity
the ability of a solution to cause a cell to gain or lose water
53
an animal cell will _____ in a hypotonic solution and _____ in a hypertonic solution
lyse, shrivel
54
plant cells in a hypotonic environment become _____, become _____ in an isotonic environment, and become _____ in a hypertonic environment
turgid, flaccid, plasmolyzed
55
plant cells are happier in a _____ environment, while animal cells are happier in a _____ environment
hypotonic, isotonic
56
molecules move against their concentration gradient through
active transport
57
membrane protein used for active transport
ion pumps
58
example of an ion pump
sodium/potassium (Na+/K+) pump
59
steps of Na+/K+ pump
1. cytoplasmic Na+ binds to the sodium-potassium pump
2. Na+ binding stimulates phosphorylation by ATP
3. phosphorylation causes the protein to change its conformation, expelling Na+ to the outside
4. extracellular K+ binds to protein, triggering release of the phosphate group
5. loss of phosphate group, restores protein's original conformation
6. K+ is released, Na+ sites are receptive again, cycle repeats
60
electrogenic pumps
transport proteins that generate voltage across a membrane (create membrane potential)
ex: H+ pump
61
cotransport
passive transport of H+ to the inside of the cell by diffusion coupled in active transport of sucrose
62
bulk transport of large macromolecules across the plasma membrane using transport vesicles occurs by
exocytosis and endocytosis
63
3 types of endocytosis
- pinocytosis
- phagocytosis
- receptor-mediated endocytosis
64
phagocytosis
"cellular eating"
the intake of solid/insoluble material by the cell or ingestion of whole cells
65
pinocytosis
"cellular drinking"
the intake of liquid or soluble material by the cell
66
receptor-mediated endocytosis
the intake of specific molecules selected by a receptor
ex: binding of ligands to receptors triggers vesicle formation
67
ligand
a molecule that binds specifically to a receptor molecule
68
example of receptor-mediated endocytosis
cholesterol uptake by hepatocytes
1. cholesterol circulates to blood bound to liposomes
2. the cell takes in the lipoproteins-cholesterol vesices
3. cholesterol is released in the liver cell
biology med 103
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