Chapter 7 - Membrane Structure and Function

Question 1

list the components of membranes

Answer 1

lipids, carbohydrates, proteins

Question 2

list the functions of membranes

Answer 2

selective permeability barrier, compartmentalization of function, energy transduction, transport (water and solutes), site of some enzymatic activity, communication, intercellular joining, anchorage

Question 3

describe the fluid mosaic model of membranes

Answer 3

membrane components and functions are asymmetric

Question 4

define membrane fluidity

Answer 4

movement of membrane components (phospholipids and proteins)

Question 5

list the 4 types of movement of phospholipids

Answer 5

lateral movement, rotation, flexing of fatty acids, flip-flop transverse diffusion

Question 6

what is the importance of membrane fluidity?

Answer 6

important for basic cell processes to occur

Question 7

what happens when membranes are too fluid?

Answer 7

loss of structural organization and mechanical support - membranes leak

Question 8

what happens when membranes are too rigid?

Answer 8

mobility is poor - membranes leak

Question 9

list the factors that affect membrane fluidity

Answer 9

temperature, lipid composition

Question 10

define selective permeability

Answer 10

allow some things to cross but not others - eg phospholipid bilayers allow water to cross but not all solutes

Question 11

how do hydrophobic molecules pass through the phospholipid bilayer?

Answer 11

simple diffusion

Question 12

how do small, uncharged, polar molecules pass through the phospholipid bilayer?

Answer 12

transport proteins help them cross

Question 13

how do large, uncharged, polar molecules pass through the phospholipid bilayer?

Answer 13

transport proteins are required to help them cross

Question 14

how do inorganic and organic ions pass through the phospholipid bilayer?

Answer 14

transport proteins are required to help them cross

Question 15

passive transport definition

Answer 15

diffusion of a substance across a membrane with no energy investment

Question 16

define diffusion

Answer 16

spontaneous movement of particles of any kind from where they are more concentrated to where they are less concentrated

Question 17

define concentration gradient

Answer 17

increase or decrease in the density of a chemical substance in an area

Question 18

define osmosis

Answer 18

simple diffusion of free water across a selectively permeable membrane; moves from areas of low concentration of solute to high concentration to even out the concentration across the membrane

Question 19

define an osmole

Answer 19

amount of substance that results in Avogadro’s number of particles when placed in solution

Question 20

define osmotic pressure

Answer 20

a measure of the tendency of a solution to take up water when separated from pure water by a selectively permeable membrane; the amount of pressure that will just stop the flow of water

Question 21

define tonicity

Answer 21

the ability of a solution to cause a cell within it to gain or lose water

Question 22

what does it mean to be isosmotic with a medium fluid?

Answer 22

the same osmotic pressure as the medium

Question 23

what does it mean to be hyperosmotic with a medium fluid?

Answer 23

osmotic concentration is higher than the medium

Question 24

what does it mean to be hyposmotic with a medium fluid?

Answer 24

osmotic concentration is lower than the medium

Question 25

what does it mean to be isotonic with a solution?

Answer 25

have the same solute concentration

Question 26

what does it mean to be hypertonic with a solution?

Answer 26

the one with a greater solute concentration

Question 27

what does it mean to be hypotonic with a solution?

Answer 27

the one with a lower solute concentration

Question 28

define facilitated diffusion

Answer 28

passive transport mediated by channel proteins or carrier proteins

Question 29

explain how channel proteins work

Answer 29

possess a hydrophilic channel through which atomic ions and some small molecules can pass; some are open all the time, others are gated

Question 30

explain how carrier proteins work

Answer 30

undergo a shape change which takes small ions or molecules across

Question 31

define active transport

Answer 31

movement of a substance across a membrane, through a transport protein, against a chemical or electrochemical gradient; requires energy input and is powered by ATP (or cotransport with a substance moving down its gradient)

Question 32

define exocytosis

Answer 32

vesicular removal of molecules to the extracellular fluid

Question 33

define constitutive exocytosis

Answer 33

ubiquitous and continuous, supplies proteins and lipids to the plasma membrane, secretes many molecules from the cell

Question 34

define regulated exocytosis

Answer 34

operates in cells specialized for secretion, membrane fusion occurs only in response to extracellular signal

Question 35

define membrane fusion

Answer 35

when membranes fuse with each other, the orientation of the leaflets remains the same

Question 36

define endocytosis

Answer 36

vesicular uptake of molecules from the extracellular fluid

Question 37

define phagocytosis

Answer 37

uptake of large, bulky material

Question 38

define pinocytosis

Answer 38

non-specific uptake of fluid from extracellular fluid; occurs almost continuously in most cells

Question 39

define receptor-mediated endocytosis

Answer 39

uptake of specific molecules from extracellular fluid

Question 40

what builds the membrane?

Answer 40

the endoplasmic reticulum and Golgi apparatus