Module 1

Question 1

describe diffusion in the presence of a membrane, in relation to the membrane’s permeability.

Answer 1

if membrane is permeable to the substance, there will be net diffusion of substance passively down its concentration gradient across the membrane until equilibrium has been achieved

If membrane is not permeable to substance then no diffusion will occur and concentration gradient will remain in place

Question 2

What is osmosis?

Answer 2

diffusion of water across the plasma membrane

Question 3

What are aquaporins?

Answer 3

specific membrane proteins that move water

Question 4

When does osmosis occur?

Answer 4

When membrane separates unequal solutions (different concentrations of water)
- can occur simultaneously with diffusion of a penetrating solute

Question 5

What is the name of the underlying force that moves water down its concentration gradient?

Answer 5

osmotic pressure

Question 6

what is hydrostatic pressure?

Answer 6

Force created by given volume of water

- Increased volume means increased hydrostatic pressure

Question 7

what is facilitated diffusion?

Answer 7

uses carriers to assist transport a substance down concentration gradient
- no energy needed

Question 8

Describe the mechanism used by facilitated diffusion.

Answer 8

• carrier protein takes conformation in which solute binding site is exposed to a region of higher solute concentration
• solute protein binds to carrier protein
• carrier protein changes shape so binding site exposed to a region of low solute concentration
• transported solute is released and carrier protein returns to conformation from beginning

Question 9

what is active transport?

Answer 9

Moves substances against their concentration gradient using a carrier protein and ATP or energy

Question 10

What are the three characteristics of carrier mediated transport?

Answer 10

specificity, saturation, competition

Question 11

What is vesicular transport?

Answer 11

Transport via a membrane enclosed vesicle and as it uses energy, it is a form of active transport

Question 12

Describe endocytosis.

Answer 12

Vesicular transport that moves substances from outside to inside of the cell

Question 13

List the three types of endocytosis.

Answer 13

pinocytosis, receptor mediated endocytosis, phagocytosis

Question 14

what is pinocytosis?

Answer 14

Cell membrane engulfs and internalizes a small drop of extracellular fluid

• membrane deforming coat proteins on inner side of plasma membrane cause formation of an endocytic pouch pinched off by dynamin, an enzyme that aids in formation of endocytic vesicle
• non selective transport, as vesicle will contain whatever substances were close to membrane at time
• steps: first solute molecules and water molecules are outside plasma membrane, then membrane pockets inward enclosing solute molecules and water molecules, finally pocket pictures off as an endocytic vesicle containing sample of extracellular fluid

Question 15

What is receptor mediated endocytosis?

Answer 15

Like pinocytosis except trigger to create a vesicle depends on binding of substance to specific receptor on cell surface

• Substances first attach to membrane receptors and then the membrane pockets inward
• finally pinching off as an endocytic vesicle containing the target molecule

Question 16

What is phagocytosis?

Answer 16

The internalization of large multi molecular particles that only occurs in a few specialized cell types

• first pseudopods begin to surround prey, then they close around prey
• prey is enclosed in endocytic vesicle that sinks into cytoplasm
• lysosome fuses with the vesicle and releases enzymes that attack material inside the vesicle

Question 17

What is exocytosis?

Answer 17

A membrane enclosed vesicle formed within the cell fuses with the plasma membrane and releases its contents into extracellular environment

• essentially the opposite of endocytosis
• Materials produced by the endoplasmic reticulum and Golgi apparatus use this process for two purposes: to provide mechanism of releasing large polar molecules that can’t cross plasma membrane and it enables cell to move proteins
• release of vesicles is often dependent on the cell receiving a particular signal to release substance

Question 18

What does it mean for a membrane to be depolarizing?

Answer 18

if magnitude of polarization decreases, moving towards 0 mV

Question 19

What does it mean when a membrane is repolarizing?

Answer 19

After either a depolarization or a hyperpolarization once the polarizing begins to return towards the RMP or resting membrane potential

Question 20

Describe a membrane that is hyperpolarizing.

Answer 20

If the magnitude of polarization increases, moving even more negative than the resting membrane potential

Question 21

What are graded potentials?

Answer 21

Changes in member and polarization used for short distance communication that diminish in strength

Question 22

what are action potentials?

Answer 22

cause localized depolarization in response to a triggering event or stimulus and can conduct or propagate throughout the entire membrane, not diminishing in strength, which is why they can be used for long distance signalling

Question 23

What is temporal summation?

Answer 23

summing of several excitatory postsynaptic potentials occurring close together in time due to the repetitive firing of a single presynaptic neuron

Question 24

What is spatial summation?

Answer 24

summation of excitatory postsynaptic potentials and inhibitory postsynaptic potentials originating from several different person attic inputs having simultaneous effects on membrane potential