Membranes

Question 1

• Total solute concentration of a solution

- One osmol is equal to 1 mol of solute particles

Answer 1

Osmolarity

Question 2

Process in which membrane folds into the cell, forming small pockets that pinch off to produce vesicles

Answer 2

Endocytosis

Question 3

• Endocytic vesicle encloses small volume of extracellular fluid
• Nonspecific

Answer 3

Pinocytosis

Question 4

Phagocytosis

Answer 4

• Cells engulf bacteria or cell debris from damaged tissues
• Pseudopodia fold around surface of particle, engulfing it entirely
• Pseudopodia fuse with phagosomes
• Phagosomes migrate and fuse with lysosomes

Question 5

• Certain molecules in extracellular fluid bind to receptors
• Each receptor recognises one ligand with high affinity
• Receptor undergoes conformational change
• Clathrin is recruited to plasma membrane
• Adaptor proteins link ligand-receptor complex to clathrin
• Forms cagelike structure that leads to aggregation of ligand-bound into a localised membrane forming a clathrin-coated put, which then pinches off to form a clathrin-coated vesicle
• Leads to a selective concentration in the endocytic vesicle of a specific ligand-bound to one type of receptor

Answer 5

Receptor-Mediated Endocytosis

Question 6

Functions of exocytosis

Answer 6

• To replace membrane

- Provide a route for membrane-impermeable molecules to pass out of cell

Question 7

• Proteins travel from Golgi apparatus to membrane in vesicles
• Triggered by stimuli that lead to increase in cytosolic Ca2+ concentration
• Increase in Ca2+ concentration activates protein required for the vesicle to fuse with the membrane
• Used in neurotransmitters and hormones

Answer 7

Exocytosis

Question 8

Epithelial transport

Answer 8

• Regulate absorption
• Membranes have different ion channels
• Osmosis can occur as a result of the active transport of solutes
• Net movement of solute across an epithelium is accompanied by flow of water in same direction
• Large net movements of water can occur with very small differences in osmolarity

Question 9

Surface that faces hollow chamber

Answer 9

Apical membrane

Question 10

Surface adjacent to blood vessels

Answer 10

Basolateral membrane

Question 11

• Diffusion between adjacent cells

- Limited by tight junctions

Answer 11

Paracellular pathway

Question 12

Substance diffuses across both membranes

Answer 12

Transcellular pathway

Question 13

How to resist water movement

Answer 13

Movement of water can be prevented by applying pressure to compartment with higher solute concentration

Question 14

Pressure required to prevent net flow of water

Answer 14

Osmotic pressure

Question 15

Functions of membranes

Answer 15

• Selective barrier
• Detect chemical signals
• Anchoring cells to adjacent cells

Question 16

Structure of membrane

Answer 16

• Phospholipid bilayer
• Embedded proteins
• No chemical bonds, allowing moderate changes in shape
• Cholesterol form clusters to form vesicles that deliver contents to organelles

Question 17

• Associated with membrane lipids
• Cannot be extracted without disrupting rest of membrane
• Amphipathic

Answer 17

Integral membrane proteins

Question 18

• Located at membrane surface
• Bound to polar regions of integral membrane proteins
• Not amphipathic

Answer 18

Peripheral membrane proteins

Question 19

Tight junctions

Answer 19

• Form when extracellular surfaces of 2 adjacent membranes join close
• Only ions and water flow freely
• Occurs in a band around the entire circumference of the cell

Question 20

Gap junctions

Answer 20

• Connexins form 2 membranes join
• Form protein-lined channels
• Only allows small molecules and ions to pass through

Question 21

Magnitude of flux

Answer 21

• Temperature
• Mass of molecule
• Surface area
• Medium through which molecules are moving

Question 22

Specificity of ion channels

Answer 22

• Pore size
• Charge
• Binding sites

Question 23

• Hold adjacent cells firmly together
• Accumulations of protein along cytoplasmic surface
• Serve as anchoring points for cadherins
• Cadherins link with cadherins from other cells
• Other proteins anchor cytoplasmic surface to internal structures

Answer 23

Desmosomes

Question 24

Mediated Transport Systems

Answer 24

• Facilitated diffusion

- Active transport

Question 25

Magnitude of solute flux

Answer 25

• Saturation of transport binding sites
• Number of transporters
• Rate of conformational change

Question 26

Specific molecule bind causing allosteric change

Answer 26

Ligand gated channel

Question 27

Change in membrane potential

Answer 27

Voltage gated channel

Question 28

Physically deform

Answer 28

Mechanically gated channel

Question 29

Primary Active Transport (Na+/K+ Pump)

Answer 29

1 - Transporter binds 3 Na+ ions on intracellular surface
2 - Binding of Na+ results in activation of ATPase activity, causing phosphorylation of the cytosolic surface of transporter
3 - Phosphorylation results in conformational change, exposing Na+ ions to extracellular fluid, reducing affinity for Na+ ions
4 - New conformation increases affinity for 2 K+ ions
5 - Binding of K+ ions causes dephosphorylation of transporter, returning original conformation

Question 30

• Uses electrochemical gradient to transport solutes against concentration gradient
• The movement of an ion down its electrochemical gradient is usually coupled to transport of another molecule
• Transporters have 2 binding sites

Answer 30

Secondary active transport