Membrane, Cytoskeleton & Endocytosis

Question 1

How are new membranes synthesized?

Answer 1

Can add phospholipids to inside and then flipase enzymes move polar heads through membrane (cannot happen spontaneously) - highly selective process with specific ratio to each half of membrane
OR
Vesicles bud off from Golgi or ER - what was on inside membrane ends up outside cell
Esp. important for glycolipid distribution - large carb chains synthesized in golgi can go to cell surface, used for protection and cell recognition

Question 2

Why cholesterol in membrane?

Answer 2

Provides greater stiffness/structure

Help maintain structure of lipid rafts

Question 3

Functions of proteins in Cell membrane

Answer 3

Transporters
Anchors
Receptors
Enzymes
Stay in place
Move nutrients
Communicate
Receive environmental signals

Question 4

What do transporters in the membrane transport? what types of transporters are there? What can freely pass?

Answer 4

Transporters are needed for ions, very polar molecules and large molecules

Ion channels allow ions to move across, others change conformation to move larger molecules

Small hydrophobic and uncharged polar molecules can freely pass.

Question 5

CAMs

Answer 5

Cell adhesion molecules, cross membrane binding to something outside and cytoskeleton inside, some can also pass signals

Question 6

Two types of receptors responding to binding of external ligand…?
Describe other type

Answer 6

1) Change permeability of the cell
2) Changes intracellular processes (enzymes or signal transducers) via second messengers eg GPCRs

Other type often in nerve cells and responds to neurotransmitters to open ion channels

Question 7

Types of channels and their structure

Answer 7

Composed of transmembrane alpha helixes or beta barrels
Leak channels always open
Gated channels controlled

Question 8

Glycocalyx

Answer 8

External membrane surface composed of many carbohydrates synthesized in the golgi, provides cell protection and recognition

Question 9

Glycoproteins and proteoglycans

Answer 9

Glycoproteins - proteins in membrane linked to oligosaccharides
Proteoglycans- proteins in membrane linked to long polysaccharides

Carbs compose glycocalyx

Question 10

Membrane dynamics and protein movement

Answer 10

Protein movement restricted by internal or external attachments, or cell attachments
Such unequal distributions are called membrane polarization’s
Proteins clustered into lipid rafts based on complimentary function, supported by cholesterol and certain phospholipids