2.1.5 Biological Membranes

Question 1

Biological membranes

Answer 1

All cells + organelle membranes composed of phospholipid bilayer
Provide a partially permeable membrane, the site of chemical reactions + have a role in cell communication.

Question 2

Explain the fluid-mosaic model

Answer 2

Movement of the phospholipids, proteins, glycoproteins and glycolipids + pattern of these proteins.
Phospholipids align as a bilayer due to the hydrophilic heads and the hydrophobic tails.

Question 3

Proteins in the bilayer

Answer 3

Extrinsic: provide mechanical support, cell recognition as receptors - glycoproteins, glycolipids.
Intrinsic: protein carriers or channel proteins - involved in transport of molecules across the membrane.

Question 4

Role of cholesterol in bilayer

Answer 4

Restricts the lateral movement of other molecules in the membrane
Makes membrane less fluid at high temp + prevents water + dissolved ions leaking out the cell.

Question 5

Temperature affecting membrane structure + permeability

Answer 5

High temp increase kinetic energy of phospholipids - move even more.
Increases fluidity of the membrane + permeability - structure starts to break.
Also denature carrier + channel proteins in membrane.

Question 6

Solvents in factors affecting membrane structure + permeability

Answer 6

Organic solvents (alcohol) dissolve the phospholipid bilayer in membranes.
Damage causes fluidity of membrane to increase + more permeable.

Question 7

Simple diffusion

Answer 7

Net movement of molecules from an area of higher conc to an area of lower conc until equilibrium is reached.
Must be lipid soluble + small to go across membrane

Question 8

Facilitated diffusion

Answer 8

Passive process, down the conc gradient using protein channels + carrier proteins.

Question 9

Osmosis

Answer 9

Movement of water from an area of high water potential to an area of low water potential, across a partially permeable membrane

Question 10

Types of solution

Answer 10

Isotonic - water potential of solution is the same in the solution and the cell within
Hypotonic - water potential of a solution is more positive than the cell - swelling
Hypertonic - water potential of a solution is more negative than the cell - crenation

Question 11

Active Transport

Answer 11

Movement of molecules + ions from an area of low conc to area of high conc (against the conc gradient) using ATP + carrier proteins.
ATP bids to the carrier protein - causes it to change shape = open towards the inside of the membrane.
Causes the molecule to be released on the other side of the membrane.
The Pi molecule is then released from the protein reverting to its original shape.

Question 12

Endocytosis

Answer 12

Type of active transport - bulk transport of molecules into a cell.
Cell surface membrane bends inwards around the molecule, surrounding it to form a vesicle.
Vesicle pinches off + moves within the cytoplasm.
Requires energy from ATP for the cell to engulf + change shape.

Question 13

Exocytosis

Answer 13

Bulk transport of molecules out of the cell.
Vesicles move toward the cell surface membrane + fuse with the membrane + the content of the vesicles released outside of the cell.
Requires energy from ATP - needed to more the vesicle along the cytoskeleton.