1.3 - membrane structure tushar

Question 1

what is cell membrane made of

Answer 1

• phospholipid bilayer as phospholipids have amphipathic properties (hydrophobic and hydrophilic)

Question 2

Different parts of phospholipds

Answer 2

Phosphate head (phosphate and glycerol) - polar and hydrophilic, makes contact with cytosol and extracellular fluids

fatty acid tail (2 fatty acids)) - non-polar and hydrophobic, faces inward

Bilayer is held by weak hydrophobic interactions

Question 3

Cell membrane is

Answer 3

• Fluid
• flexible (for endocytosis and exocytosis)
• semi-permeable
• bends in phospholipid tails prevent close packing

Question 4

3 types of membrane proteins and its descriptions

Answer 4

Integral proteins: permanent+ transmembrane, amphipathic

Peripheral proteins: mostly hydrophilic, some attached to surface of integral proteins

Glycoprotein: hydrophilic, for cell-to-cell recognition/hormone binding site+ help immune responses

Question 5

Functions of membrane proteins

Answer 5

JETRAT
junction (join 2 cells)
enzymes
transport
recognition
anchorage (attachment point for cytoskeleton/extracellular matrix)
transduction (receptor for hormones)

Question 6

Cholesterol

Answer 6

Lets membrane maintain fluidity in different temperatures

• only in animal cells
• lipid - steroid + amphipathic (mostly hydrophobic but has hydroxyl -OH group that is hydrophilic

Cholesterol disrupts regular packaging of the membrane to:

• make membrane more rigid (high temp)
• prevent crystallisation of membrane (low temp)
• makes membrane less permeable
• helps membrane curve into concave shape (helps vesicle formation in endocytosis)
• anchor peripheral proteins

Question 7

Fluid mosaic model

Answer 7

fluid: phospholipids can move
mosaic: embedded with proteins all around

Question 8

Davson-Danielli model

Answer 8

• Proved wrong model of cell membrane

- lipid-protein sandwich, proteins forming uniform layer on the extracellular and intracellular surface of the membrane

Question 9

Things that falsified the model

Answer 9

• freeze-etched electron micrographs: rapid freezing of cell to split it open, revealed transmembrane proteins
• structure of membrane proteins : proteins were found to vary in size and have at least one hydrophobic surface (so cant for uniform continous layer on outside surfaces)
• fluorescent antibody tagging: proved that membrane proteins are mobile. Membrane proteins of 2 cells marked with colours. when cells fused, markers were mixed throughout the membrane of the fused cell