Lec 4 (membrane 1)

Question 1

Membranes

Answer 1

are barriers/define boundaries

Question 2

Pros have what type of membranes

Answer 2

Single membrane (no membrane bound organelles)

Question 3

Eus have what type of membranes?

Answer 3

plasma membrane (outside) 
- membrane bound organelles (intracellular)

Question 4

Barrier function (4)

Answer 4

1) Prevents loss of required metabolites
2) Protects against unwanted outside molecules (disease)
3) Capacitor function: stores electrical chemical energy (enables a ion gradient)
4) Important for energy production and electrical signalling

Question 5

Importation and exportation?

Answer 5

Cells need import and export molecules

Question 6

Importation and exportation tends to be carried about by?

Answer 6

Intergral membrane proteins

Question 7

Intergral membrane proteins definition?

Answer 7

Set of proteins which give the membrane is properties

Question 8

Example of exportation in mammalian cells?

Answer 8

Insulin in order to control glucose conc

Question 9

Receptors function?

Answer 9

receiving information (cell signalling)

Question 10

Functions of membrane proteins? (8)

Answer 10

Selective permeability
Maintaining ionic composition on either side
Maintaining cytoplasmic pH
Controlling cytoplasmic osmotic pressure
Sensing the environment: receptors
Anchoring cytoskeletal structures
Mediating cell/cell and cell extracellular matrix interactions
Carrying out membrane requiring enzymatic reactions

Question 11

Usual pH inside cells?

Answer 11

7.2

Question 12

Membrane surrounding outside?

Answer 12

Plasma membrane

Question 13

Which cell has the lowest amount of plasma membrane?

Answer 13

Liver cell, 2% 
internal membrane (rest)

Question 14

Lysosome contains

Answer 14

hydrolytic enzymes/hydrolases

Question 15

Lysosome pH

Answer 15

pH 5

Question 16

How thick is the lipid bilayer ?

Answer 16

5nm

Question 17

Amphipathic

Answer 17

have both hydrophobic and hydrophilic components

Question 18

Lipids when added to water

Answer 18

will spontaneously arrange themselves

Question 19

The bilayer is

Answer 19

thermodynamically favourable

Question 20

how many nm is 1mm

Answer 20

1 000 000

Question 21

Bilayer is what shape?

Answer 21

Plannar

Question 22

How do liposomes form?

Answer 22

It is energetically favourable for lipids to form sealed compartments. With a sealed compartment there are no hydrophobic ‘edges’ in contact with water. (circular)

Question 23

Glycerophospholipids other name?

Answer 23

Phosphoglycerides

Question 24

3 Carbon backbone

Answer 24

glycerol

Question 25

3rd chain in glycerophospholipids?

Answer 25

phosphate and x group which can vary between each. Giving different properties

Question 26

R (fatty acid hydrocarbon chain) number

Answer 26

Varys which each usually r1 and r2 are different

Question 27

When x= serine

Answer 27

phosphatidyl serine ^ " for each acidic due to positively charged serine

Question 28

Sphingoldlipids

Answer 28

sugars attached to lipids>> phospholipid Also have variable c (classed as phospholipids)

Question 29

Sterols example in membranes

Answer 29

cholesterol

Question 30

Lipid bilayers are

Answer 30

fluid

Question 31

Lipids within the bilayer can

Answer 31

rotate freely

Question 32

flip flop mechanism?- when and if it occurs, limitations

Answer 32

Hydrophilic head through a hydrophilic environment (not energetically favourable, but does occur sometimes eg protein mediated)

Question 33

Why is membrane fluidity important?

Answer 33

- allows for interactions to take place | - E.G groups of membrane assembling at particular sites within the membrane

Question 34

Why is the fluidity of the membrane perfect for its function?

Answer 34

provides the perfect compromise between ridged and ordered, and fluid and non viscous

Question 35

Experiment which demonstrated membrane fluidity?

Answer 35

cell fusion between two cells. One of which contained a rhodamine labelled membrane protein and the other containing a flouresein labelled membrane protein. The two cells were fused, to form a hybrid. after 40 minutes, incubated at 37 degrees>>>>> equally distributed within a cell

Question 36

Factors influencing membrane fluidity (no reasons)

Answer 36

- Temperature (in exotherms) - Saturation of acyl chains - Length of acyl chains - Cholesterol

Question 37

Temperature factor (increasing membrane fluidity)

Answer 37

only applies to exotherms (don't control their body temperature, relies on its environment)

Question 38

How does saturation of acyl chain effect membrane fluidity?

Answer 38

if unsaturated= kink in chain (double c=c) increases the fluidity of the membrane as the lipids are further apart, and therefore experience less van Der Waals interactions Vice versa for saturated.

Question 39

Cholesterol?

Answer 39

decreases membrane fluidity, therefore mobility. Increases the rigidness of it

Question 40

Lipid asymmetry is described by?

Answer 40

Lipid distribution not being random.

Question 41

Leaflet

Answer 41

One layer of the bilayer

Question 42

Usually negative phospholipids are restricted to the cytoplasmic leaflet unless?

Answer 42

Apoptosis, lipid asymmetry begins to breakdown and we start to see negatively charged phospholipids on the extracellular leaflet.

Question 43

Orientation is maintained?

Answer 43

During budding and fusion (planar)

Question 44

Lipid compositions are ??

Answer 44

Different on different membranes >>>. functional consequences

Question 45

Why are there so many different lipids?+ examples

Answer 45

Due to their many different functions - biological effects: curvature, fusion, fluidity - Can act as signalling molecules - Cell interactions (exportation/importation) - Effect the activity of membrane proteins

Question 46

Lipid bilayers are permeable and impermeable to? examples of each

Answer 46

``` permeable to:Small hydrophobic molecules (02, n2), Small uncharged Polar molecules (h20, glycerol) ``` Impermeable to: Larger uncharged (amino acids, glucose nucleotides) Polar molecules, and ions (H+ Na+ etc)

Question 47

Types of membrane protein

Answer 47

Integral membrane proteins Peripheral membrane proteins Lipid anchored membrane proteins

Question 48

Intergral membrane proteins cover?

Answer 48

Entire length of the bilayer (domains on either side of the membrane)

Question 49

Peripheral

Answer 49

Lipid associated

Question 50

Lipid anchored membrane proteins

Answer 50

Lipid linked

Question 51

If you wash cells in high salt?

Answer 51

Peripheral aren't removed due to non covalent interactions in which are occurring.

Question 52

What percentage of ORF's (Protein coding genes) in genomes are predicted to encode membrane proteins

Answer 52

20-30 larger genomes contain a larger fraction than smaller ones

Question 53

How many structures of membrane protein are known at high resolution? By which method Is this information derived?

Answer 53

300 via x-ray crystallography