Cell Biology - Membranes

Front 1

What are the functions of membranes?

Back 1

1. Define Boundaries and serve as permeability barriers

2. sits of specific function: glucose phosphatase and ER membrane

3. Regulate transport of solutes (simple, facilitated diffusion; active transport, endo/exo cytosis)

4. Detect and transmit electrical and chemical signals (signal transduction)

5. Mediate cell-to-cell communication (gap junctions)

Front 2

What is the Fluid Mosaic Model?

Back 2

Singer and Nicolson: membrane consists of a mosaic of proteins in a fluid lipid layer

Davson and Danielli: membranes also contain proteins (protein-lipid sandwich model

Overton and Langmuir: Lipids are important components of membranes

Gorter and Grendel: The basis of a membrane structure is a lipid bilayer

Robertson: all membranes share a common underlying structure

Unwin and Henderson: some membrane proteins contain transmembrane segments

updated verson postulates that regions of membranes have proteins and lipids athat are ordered into domains (rafts)

Front 3

What are the classes of lipids found in membranes?

Back 3

Phospholipids:
-glycerol based: phosphoglycerides
-sphingolipids
-4 important ones: Phosphatidylcholine, Phosphatidylethanolamine, Phosphatidylserine, Phosphatidylthreonine

Glycolipids: NO phosphate have sugar
-cerebrosides (neutral single uncharged sugar)
-gangliosides (Tay Sachs)

Sterols:
-cholesterol (series of rings)

Front 4

What is Cardiolipin?

Back 4

component of inner membrane of mitochondria - 20 %

important in ETC

patients with anticardiolipin Ab (Antiphospholipid syndrome) can have thrombotic events in mid teens (also called Hughes Syndrome)

Front 5

What is a difference between E coli and a human membrane in variations in phospholipid composition?

Back 5

E. Coli has a lot of ethanol amine and very little of everything else

Front 6

What are Hopanoids?

Back 6

They are in the bacteria plasma membrane

do the same thing for prokaryotes as cholesterol does for us

they are sterol like molecules because prokaryotes do not have sterols

Front 7

What happens in Thin-layer chromatography for Lipid Analysis?

Back 7

sample spotted onto a hydrophilic stationary phase

placed into mixture of organic solvents (mobile phase)

solvent moves up late via capillary action, nonpolar lipids (cholesterol) do not adhere to silicic acid and move further up plate, more polar (phospholipids) move slower

Front 8

What are some basic features of FA?

Back 8

between 12-20 Cs:
-thickness is dictated by chain length of FA required for bilayer stability

saturated FA

unsaturated FA:
-found in Cis
-do not pack tightly due to structural "kinks"

Front 9

What is Membrane Asymmetry?

Back 9

Phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine more abundant in inner-monolayer (Some Enter Innermembrane)
-involved in signal transduction

Glycolipids and glycoproteins found in outermembrane - charged

asymmetry caused by phospholipid translocators or flippases

Front 10

What are the 3 types of movement in the Lipid Bilayer?

Back 10

Transverse diffusion (rare) - flip flop

Lateral diffusion (rapid)

Rotation

Front 11

What is evidence for the lipid bilayer's fluid property?

Back 11

Fluorescence recovery after photobleaching (FRAP)

Front 12

What is characteristic of Transition temperatures in FA?

Back 12

long chain FA have higher Tm than shorter chain

unsaturated FA have lower Tm and more fluid

Front 13

What is Cholesterol's effect on Membrane fluidity?

Back 13

Cholesterol makes the membranes less fluid at higher temperatures and increases fluidity at lower temperatures (prevent FA chains from getting closer)

Sterols decrease permeability of a lipid billayer to ions and small molecules (better barrier and insulator)

Front 14

What is Homeoviscous adaptation?

Back 14

way for organism to regulate membrane fluidity:

-increase amount of shorter chain FA
-increase % of unsaturated FA
-increase amount of cholesterol

Front 15

How does cholesterol bind to the phospholipid?

Back 15

through a hydrogen bond

Front 16

What is a Caveolae?

Back 16

a type of lipid raft (sequester proteins involved in cell signaling)

small flask-shaped invaginations of plasma membrane that are coated with caveolin (cholesterol-binding protein)

Front 17

How is freeze-fracture microscopy used for membrane protein analysis?

Back 17

frozen sample is given a sharp blow and the resultant fracture follows the plane between the two layers, giving rise to the E (exterior) face and the P (protoplasmic) face

E = inside of outer leaf
P = inside of inner leaf

Front 18

What are the 3 types of proteins in membranes?

Back 18

Integral membrane proteins:
-single pass or multipass proteins
-hydrophobic transmembrane segments
-can predict by hydropathy plot ( hydrophillic = -G exergonic, hydrophobic = +G endergonic)
ex. glycophorin (single pass in RBC), bacteriordhopsin (multipass), Band 3 protein

Peripheral Membrane Proteins:
-weak electrostatic forces and hydrogen bonding
-lack discrete hydrophobic segments
ex. Spectrin, Ankyrin, and Band 4.1 (RBC)

Lipid-Anchored Proteins:
-covalently linked to lipids in membrane
-linked to either FA or isoprene derivative in inner surface
-attached to outer surface are linked to Glycosylphosphatidylinositol (GPI)
-GPI anchored proteins are made in ER as single-pass proteins, cleaved, then linked to GPI
-GPI proteins relased by Phospholipase C

Front 19

What is SDS PAGE?

Back 19

polypeptides move down the gel at a rate that is inversely related to size

neutralizes charge to separate by size not charge

Front 20

What is western blot?

Back 20

transferring protein from the SDS page gel

ex. CFTR patient, most applicable would be western blot

Front 21

What are restriction enzymes what is its process?

Back 21

cut DNA into fragments

highly specific, developed for protection against viral infection

cut the viral DNA

bacterial DNA is protected so not cut by own restrictive enzymes

EcoR1 is a popular restrictive enzyme

1st step: RE recognizes enzyme site on DNA, then cut with each strand
2nd step: cut is palindromic, read same in 5-->3 and 3-->5 direction
3rd step: recognize
4th step: bind
5th step: cut and hydrolyze

To digest RE you used gel electrophoresis

1 RE has 2 cutting sites, 2 RE has 3 cutting sites

Front 22

What is sense and antisense RNA?

Back 22

mRNA is sense:
-single stranded
-read in 5-->3

Antisense:
-complementary 3-->5
-blocks translation

Front 23

How are membranes glycosylated?

Back 23

N-linked glycosylation (Asparagine)

O-linked glycosylation (Serine, Threonine, Hydroxylysine, Hydroxyproline)

Most common sugars (carbs): galactose, mannose, N-acetylglucosamine, and sialic acid

Lectins: proteins that bind specific sugar groups very tightly - useful for sugar determination

Front 24

What is the Glycocalyx?

Back 24

the surface coat of carbohydrates extending from glycoproteins and glycolipids

fuction to protein microvilli of intestine

Front 25

What are examples to prove that membrane proteins vary in their mobility?

Back 25

expermental evidence of protein mobility:
-cell fusion experiments
-freeze fracture experiments of membrane exposed to an electric field

experimental evidence of restricted mobility:
-photobleaching

mechanisms of restricting protein mobility:
-tight junctions
-anchoring proteins
-polarized cells: membrane proteins are restricted to a specific part of the cell membrane

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