Lecture 15: Membranes

Question 1

Functions of the biological membranes are? (6)

Answer 1

1. Define cell boundary - PM specific
2. Define enclose compartments
3. Control movement of material into and out of cell/organelles - PM specific
4. Allow response to external stimuli. - PM specific
5. Enable interactions between cells - PM specific
6. Provide scaffold for biochemical activities

Question 2

Biological membranes are _______ structures

Answer 2

Semi-permeable
(Control what goes in and out)

Question 3

Energy production is done by which two organelles?

Answer 3

Mitochondria and chloroplast (photosynthesis)

Question 4

Biological membranes are ________ structures

Answer 4

Trilaminar (3 layers)

Question 5

Membranes are _____

Answer 5

Lipid bilayers

Question 6

The lipid bilayer is made up of?

Answer 6

Phospholipids

Question 7

In the phospholipid bilayer, there are many ____ embedded

Answer 7

Proteins

Question 8

Fluid mosaic model is?

Answer 8

Fluid - components are mobile
Mosaic - diverse proteins, carbs, cholesterol, components can interact

Question 9

Outer leaflet faces?

Answer 9

Exterior of the cell

Question 10

Inner leaflet faces?

Answer 10

Cytosol, or inside of the structure

Question 11

Biological membranes consist of ?

Answer 11

Outer leaflet and Inner leaflet

Question 12

Phospholipid structure consists of?

Answer 12

Glycerol backbone bound by two non-polar fatty acrylic molecules (FA chains) and a polar head group linked by phosphate residue

Question 13

Phospholipids are amphipathic..?

Answer 13

Hydrophilic - attracted to water
Hydrophobic - repelled by water

Question 14

Hydrophilic part of phospholipid is?

Answer 14

Polar head

Question 15

Hydrophobic part of phospholipid is?

Answer 15

FA tails

Question 16

Types of phospholipids with different heads (4)

Answer 16

Ethanolamine
Choline
Serine
Inositol

Question 17

If thrown in water, phospholipids will…?

Answer 17

Spontaneously aggregate to bury their hydrophobic tails in the interior and expose their hydrophilic heads to the water

Question 18

Where do phospholipids come from?

Answer 18

Synthesis occurs in multistep process at cytosol and outer endoplasmic reticulum membrane - ER membrane contains all enzymes for synthesis and distribution

Question 19

What are the three classes of membrane proteins?

Answer 19

1. Integral
2. Peripheral
3. Lipid-anchored

Question 20

Membrane protein - Integral

Answer 20

Span the lipid bilayer, parts of proteins exposed to one side of membrane and another part that is also on the other side, (sticks out of both side), can be transport proteins

Question 21

Membrane proteins - Peripheral

Answer 21

Associate with surfaces of the lipid bilayer, do not interact with the membrane itself but interact with other proteins or other objects integrated in the membrane itself

Question 22

Membrane proteins - Lipid anchored

Answer 22

Attach to a lipid in the lipid bilayer, integrate into one of the leaflets

Question 23

Functions of membrane proteins (3)

Answer 23

1. Transport of nutrients and ions
2. Cell-cell communication (gap junction) (pores)
3. Attachment

Question 24

Dynamic of plasma membrane

Answer 24

(Lateral shift) Lipids move laterally, easily, within leaflet
(Transverse diffusion) Lipids movement between leaflets is difficult and slow

Question 25

Dynamics of proteins in the biological membranes

Answer 25

Diffuse within the bilayers, movement is restricted, diffusion is slow, rapid movement is spatially limited Modifications to allow proteins to move

Question 26

Structure of biological membranes (4)

Answer 26

- 6nm thick - Stable - Flexibke - Capable of self assembly

Question 27

Biological membrane - mitochondria

Answer 27

- inner membrane of mitochondria have very high concentration of proteins to make ETC and ATP synthesis

Question 28

Biological membrane - neuronal cells

Answer 28

- myelin sheath - consists of layers of plasma membrane wrapped around neurons axon, provides insulation and increases speed - myelin sheaths have ow amounts of protein

Question 29

Symmetry of biological membranes is _______

Answer 29

Asymmetrical

Question 30

The two leaflets of a membrane are _____

Answer 30

Distinct

Question 31

Leaflet distinction

Answer 31

- Distinct lipid composition - Outer leaflet contains glycolipids and glycoproteins (sugar molecules)- attach to proteins and phospholipids - Glycolipids and glycoproteins - tells cell where to move to, glycosylation event, allows proteins to binds and perform certain functions

Question 32

How does temperature affect the fluidity of biological membranes? (2)

Answer 32

- warming increases fluidity - fluid like - cooling decreases fluidity - gel

Question 33

Membrane fluidity is determined by nature of _____ in membrane

Answer 33

Lipids

Question 34

(Double bonds - Kinks) Unsaturated lipids ____ _____

Answer 34

Increase fluidity

Question 35

(Single bonds) Saturated lipids _____ ______

Answer 35

Reduce fluidity

Question 36

Balance between rigid and disordered structure allows (3)

Answer 36

- mechanical support and flexibility - membrane assembly and modification - dynamic interactions between membrane components

Question 37

What modulate membrane fluidity?

Answer 37

Cholesterol

Question 38

How does cholesterol regulate membrane fluidity?

Answer 38

- bidirectional - at high temp, stabilizes membrane and raises melting point - at low temp, intercalates between phospholipids and prevents from clustering together and stiffening

Question 39

Cholesterol impacts (3)

Answer 39

- alter packing and flexibility of lipids - if added to a liquid crystal membrane, fluidity will decrease - if added to crystalline gel membrane, fluidity will increase