BIOC 3560 Final Exam

Some biological membrane examples? (2)

plasma and organelle

Functions of cellular membranes? (4)

1) permeability barrier/compartmentalization
2) communication - action potentials
3) energy conversion - inner mito membrane
4) surface recognition - A,B,O blood

Composition of typical plasma membrane? (3 percentages)

45% = lipid (long acyl chains+polar head groups)
50% = protein
5% = carbohydrate

Membrane lipids are _____

amphipathic (hydrophobic and hydrophilic)

Components of membrane lipids? (3)

1) phospholipids
2) glycolipids
3) cholesterol

What is a phospholipid?

polar "head" group joined by phosphodiester link

Types of phospholipids? (2)

1) Phosphoglycerides (glycerophospholipids)
2) sphingolipids (named after the Sphinx)

What makes up phosphoglycerides?

-backbone=glycerol
-2 fatty acids in ester link
-head group derived from alcohol
-CHARGED and HYDROPHOBIC

What makes up sphingolipids?

-backbone=sphingosine
-1 fatty acid in amide link
-head group=choline (sphingomyelin)

What makes up glycolipids?

-backbone=sphingosine
-1 fatty acid in amide link
-carbohydrate "head" group

Cholesterol head group? Nucleus? Side chain?

-major animal cell sterol
-planar fused rings + alkyl side chain + OH (polar head group) + steroid nucleus
-FLAT, PLANAR, mostly HYDROPHOBIC (fixed rings=stability)

What are storage lipids?

triacylglycerols (neutral)

How do glycerophospholipids gain membrane fluidity?

C=C always cis (kinked)

Sphingolipids are similar in shape to _____

glycerolipids

_______ are part of the ABO blood type system

glycosphingolipids

Cholesterol is a precursor for _____

steroid hormones

Chemical properties/forms of lipids in membranes? (3)

1) monolayers
2) micelles
3) bilayers/liposomes

What are monolayers?

-are at air-water interface formed by many types of lipids
-air is hydrophobic (NP), interacts with hydrophobic acyl chains

What are micelles?

detergents and lipids with one acyl "tail"

What are bilayers/liposomes?

-non polar tails associate in interior
-very stable, 3nm thick
-basic matrix of all biological membranes
-impermeable to ions and polar molecules

Shape of individual micelle units?

wedge-shaped (cross-section of head greater than that of side chain)

Shape of individual bilayer units?

cylindrical (cross-section at head equals that of side chain)

_______

different membranes have different _____ compositions

function

______ is a major component of plasma membrane

cholesterol

______ is a major lipid in all membranes

phosphatidylcholine

Functions of membrane proteins? (5)

1) transporters and channels (30% of overall body E)
2) receptors
3) structural components
4) adhesion proteins
5) surface antigens

Types of membrane protein? (2)

1) peripheral membrane proteins (sits on membrane)
2) integral membrane proteins (sits in membrane)

Types of integral membrane proteins?

1) covalently attached lipid anchor
2) transmembrane domain

____, _____, and ____ have critical structural and functional roles in cell membranes

lipids, proteins, carbohydrates

What do peripheral membrane proteins interact with? Types of interaction (2)?

-with polar head groups of membrane lipids
-electrostatic interactions + hydrogen bonds

Annexin is an example of?

adhesion protein

C14 FA function?

signalling for apoptosis

What makes up transmembrane domain? What do they interact with?

-alpha helix
-hydrophobic amino acids
-interacts with fatty acyl chains

If pH change or chelator removes a membrane protein = _________

peripheral protein

If detergent or phospholipase removes a membrane protein = _______

integral protein

What does a chelator do?

removes Ca2+ (which would remove protein)

What is a Hydropathy plot?

-allows for the visualization of hydrophobicity over the length of a peptide sequence
-a hydropathy scale which is based on the hydrophobic and hydrophilic properties of the 20 amino acids is used

Example of single-spanning membrane protein?

-glycophorin A
-sugars on RBCs keeps them from sticking to capillaries

Example of multi-spanning membrane protein?

-bacterioriorhodopsin
-7 transmembrane segments

What do outer membrane proteins do?

(OMP) bind bacteria to our cells

What amino acids at interface in membrane proteins?

Trp and Tyr (polar and NP)

Parts of glycoproteins? (3)

1) N-linked carbohydrate chain
2) O-linked carbohydrate chain
3) Sugar groups

Components of N-linked carbohydrate chains?

-Asn side chain (-CO-NH2)
-N-acetylglucosamine (GlcNAc)

Components of O-linked carbohydrate chains?

-Ser of The side chain (-OH)
-N-acetylgalactosamine (GalNAc)

What do sugar groups of glycoproteins and glycolipids do? (2)

1) contribute to cell surface recognition
2) function as receptors

Ways fluid mosaic model shows movement? (2)

1) lateral movement (fast - within plane of membrane, 2D)
2) flipping/flopping/scrambling (slow - needs enzymes)

Membranes change shape without loss of _____ or becoming ______

integrity, leaky

Membrane dynamics states? (2)

1) Gel Phase
2) "Liquid" states

What is the gel phase?

motion of bilayer is constrained in a paracrystalline state

What are the liquid states? (2)

1) Liquid-ordered state
2) Liquid-disordered state (fluid state)

What is the liquid-ordered state?

-intermediate thermal motion of acyl chains and atoms
-lateral movement in the plane of the bilayer is allowed

What is the liquid-disordered state?

hydrocarbon chains are in constant motion

__________

paracrystalline state (gel) to fluid state transition

Difference between paracrystalline and fluid states?

saturated FA can align linearly with one another vs unsaturated C=C are cis/kinked/disordered

At physiological temperatures, long chain FA (C16:0 or 18:0) _________________

pack well into liquid-ordered state (semi solid)

At physiological temperatures, unsaturated and shorter chain FA favour ________________

liquid-disordered state, cis (kinked

At physiological temperatures, sterols _________

(ie cholesterol) reduce fluidity

Cells regulate lipid composition in order to _________. For example, bacteria _________.

achieve a constant membrane fluidity

Maintain membrane fluidity with ______

temperature

What is required for the slow trans-bilayer "flip-flop" to occur?

requires that the polar or charged head group leaves its aqueous environment and moves into the hydrophobic interior of the bilayer

Types of "flipping/flopping/scrambling" translation movements + times? (3)

1) Uncatalyzed transbilayer ("flip-flop") diffusion
------very slow (t1/2=days)
2) Uncatalyzed lateral diffusion
------very fast (t1/2=1 µm/s)
3) Catalyzed transbilayer translocations
------unfavorable, needs enzyme

Family of enzymes that facilitates catalyzed transbilayer translocations? (3)

1) Flippase
2) Floppase
3) Scramblase
(Flip it In, Flop it Out)

What is single particle tracking?

follow a single lipid molecule on a short time scale (sec)

What does single particle tracking show?

-that lipids generally stay within one region and do not leave that region
-some proteins are floating around unrestricted in a seas of lipid, others aggregate in patches

Importance of lipid rafts?

~500A across, up to 50% of membranes, more solid like than regular membrane, can sequester important signalling complexes

Intracellular membrane traffic points (3)

-reorganization of membrane-bound compartments at synapse
-exchange of membrane and "cargo" between compartments (neurotransmitter release)
-internalization/recycling/degradation of material from plasma membrane (Glut4 transporters, endocytosis in digestion, antigen recognition)

The complex, multi-stage process of intracellular membrane traffic? (5)

1) budding (fission of vesicles)
2) transport
3) tethering/docking at target membrane
4) priming
5) fusion (of vesicle and target membranes)

What do caveolae do?

(mini-caves) put curvature into membranes and SNARE proteins help pinch off caveolae

What are SNARES?

-Soluble N-ethylmaleimide-sensitive factor Attachment protein Receptor
-membrane associated proteins
-contain 1 or 2 coiled-coil domain(s) (helical domains--approx 60AA-- that interact to form coiled-coil structures)

SNARES regulate membrane fusion during ...? (5)

1) transport between ER and Golgi
2) insulin secretion
3) up-regulation of glucose transporters
4) phagocytosis
5) neurotransmitter release

What is exocytosis?

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane

Why does membrane have hydrophobic core?

-prevent charged, polar compounds from entering cells
-NP compounds can cross membrane

Why can aspirin be absorbed into the stomach?

enters at low pH, enters as neutral, becomes negative at high pH

Why would we want cocaine in the free-base form?

it'll be neutral, normally it is charged, but then can't get across membrane

What molecules can readily cross membranes? Which cannot?

-ions and polar molecules are essentially impermeable (Na+, Cl-, sugars, AA)
-small, uncharged, somewhat polar molecules can (EtOH, glycerol)
-hydrophobic molecules, gases can cross quickly (steroid hormones, O2, CO2, N2)

Cytosol has ___ K+, ___ Na+, and ___ Ca2+

more, less, less

__________ composition of cytosol is different from extracellular environment

ionic composition

Where are there ion concentration gradients?

across plasma and organelle membranes

How much percentage of the total energy is needed to maintain the Na+/K+ ATPase?

25%

Membrane transport types (6)

1) Simple diffusion
2) facilitated diffusion
3) Primary active transporter
4) Secondary active transport
5) ion channel
6) ionophore-mediated ion transport

Simple diffusion

NP only, down conc gradient

Facilitated diffusion

down electrochemical gradient

Primary active transporter

against electrochemical gradient

Secondary active transporter

against electrochemical gradient, driven by ion moving down its gradient

ion channel

down electrochemical gradient, may be gated

ionophore-mediated ion transport

down electrochemical gradient

Examples:
1) Simple diffusion =
2) facilitated diffusion=
3) Primary active transporter =
4) Secondary active transport =
5) ion channel =

1) drugs
2) glucose RBS and liver
3) Ca pumps
4) Pi pump into mito
5) K+ valinomycin

Solute transport types across membranes? (2)

1) simple diffusion
2) transport of hydrophilic solutes

Logic behind simple diffusion

-free energy of solution (ΔG= ΔGo+RTln[c])
- ΔG when molecule moves from c1 (high) to c2 (low)-- ΔG=RTln[c2]-RTln[c1]=RTln[c2/c1]
-if c1>c2, ln(c2/c1) is negative and ΔG is negative
-diffusion occurs spontaneously from high to low concentration
-c1=c2 at equilibrium
-this energy is needed to maintain chemical gradient

Why is transport of hydrophilic solutes slow without transporter? What must be broken?

very few solutes have enough energy to get over the activation barrier

must break solvent-solute bonds

Ways of transporting hydrophilic solutes? (3)

1) membrane channels
2) Passive transporters
3) Active transporters

What are membrane channels?

-donut-like pore spans bilayer
-compared to transporters, solutes flow through rapidly (diffusion)
-rate of transport alpha [substrate] = not saturable
-gated (open and close to stimuli)
-highly selective

Membrane channel examples? (4)

Na+, K+, Cl-, H2O

What are aquaporins?

-water channels
-water transport=very fast
-H20 across, not H+ (makes sense bc mito pumps them out, and you can't have passive diffusion of protons)