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AP Biology Test, Chapter 7

front 1

Which macromolecules make up membranes?

back 1

  • lipids and proteins
  • carbohydrates also important

front 2

most abundant lipid in most membranes

back 2

  • phospholipids

front 3

amphipathic

back 3

  • has both a hydrophilic ("water loving") and hydrophobic ("water fearing) region

front 4

how can a phospholipid bilayer exist as a stable boundary between two aqueous compartments?

back 4

  • the molecular arrangement shelters the hydrophobic tails of the phospholipids from water while exposing the hydrophilic heads to water

front 5

fluid mosaic model

back 5

  • describes membrane as fluid, with proteins embedded in or associated with the phospholipid bilayer

front 6

plasma membrane

back 6

  • selectively permeable
  • it allows some substances to cross more easily than it does others

front 7

membranes are predominantly made of...

back 7

  • phospholipids and proteins held together by weak interactions
  • cause the membrane to be fluid

front 8

phospholipids

back 8

  • provide a hydrophobic barrier that separates the cell from its liquid environment

hydrophilic molecules cannot easily enter the cell, but hydrophobic molecules can

front 9

cholesterol

back 9

  • hydrophobic steroid
  • found embedded in animal membranes
  • helps membranes resist changes in fluidity when the temperature changes
  • at high temp - makes membrane less fluid
  • at low temp - helps membrane retain fluidity

front 10

proteins

back 10

  • embedded in the membrane
  • can serve as transport channels to move materials across hydrophobic interior of the phospholipid bilayer
  • can act as molecular receptors to bind to signaling molecules (ligands)

front 11

peripheral proteins

back 11

  • loosely bound to membrane's surface
  • not embedded in the lipid bilayer

front 12

membrane carbohydrates

back 12

  • crucial in cell-cell recognition
  • important in the sorting of cells into tissues in an animal embryo
  • basis for rejection of foreign cells by the immune system
  • short, branched chains
  • fewer than 15 sugar units

front 13

intergral proteins

back 13

  • penetrate the hydrophobic interior of the lipid bilayer

front 14

glycolipids

back 14

  • membrane carbohydrate chains covalently bonded to lipids
  • short, branched

front 15

glycoproteins

back 15

  • membrane carbohydrate chains covalently bonded to proteins

front 16

integrins

back 16

  • cell-surface receptor proteins

front 17

non-polar molecules (hydrophobic)...

back 17

  • can dissolve in the hydrophobic interior of the phospholipid bilayer
  • cross the membrane easily
  • examples: hydrocarbons, oxygen, carbon dioxide

front 18

hydrophobic core of the membrane...

back 18

  • impedes the passage of ions and polar molecules (hydrophilic)

front 19

transport proteins

back 19

  • enable hydrophilic substances to avoid the lipid bilayer and pass through
  • span the membrane
  • are specific, like enzymes, for the substances they transport

front 20

aquaporins

back 20

  • transport (channel) proteins
  • accelerate the speed at which water can cross membranes (three billion water molecules per second)

front 21

passive diffusion

back 21

  • substance travels from where it is more concentrated to where it is less concentrated
  • diffuses down its concentration gradient
  • does not require energy
  • relies only on the thermal motion energy intrinsic to the molecule in question

front 22

concentration gradient

back 22

  • process in which particles move from an area of high concentration to low concentration
  • region along which the density of a chemical substance increases or decreases

front 23

osmosis

back 23

  • the diffusion of water across a selectively permeable membrane
  • water diffuses from the solution with the less concentrated solute to that of the more concentrated solute

front 24

isotonic solution

back 24

  • no net movement of water across the plasma membrane
  • water crosses the membrane at the same rate in both directions

front 25

hypertonic solution

back 25

  • cell loses water to surroundings (shrivels, may die)
  • more solutes in the water around the cell

front 26

hypotonic solution

back 26

  • water will enter the cell faster than it leaves (will swell and may burst)
  • fewer solutes around the cell

front 27

water moves from...

back 27

Hypo-> Hyper

front 28

ions and polar molecules...

back 28

  • cannot move easily across the membrane

front 29

facilitated diffusion

back 29

  • process by which ions and polar molecules diffuse across the membrane with the help of transport proteins

front 30

how do transport proteins work?

back 30

  • provide a hydrophilic channel through which the molecules in question can pass
  • bind loosely to molecules in question and carry them through the membrane

front 31

active transport

back 31

  • substances are moved against their concentration gradient
  • low concentration -> high concentration
  • requires energy, usually in the form of ATP

front 32

sodium-potassium pump

back 32

  • good example of active transport
  • transmembrane protein
  • pumps sodium out of the cell and potassium ions into the cell
  • necessary for proper nerve transmission and is a major energy consumer in the body

front 33

membrane potential

back 33

  • difference in electrical charge across a membrane
  • expressed in voltage
  • inside of the cell is negatively charged compared with outside the cell

front 34

why are positively charged ions on the outside of the cell attracted to the inside of the cell?

back 34

  • inside of cell is negatively charged

front 35

what two forces drive the diffusion of ions across a membrane?

back 35

  • chemical force - ion's concentration gradient
  • voltage gradient across the membrane - attracts positively charged ions and repels negatively charged ions

front 36

chemical force

back 36

  • ion's concentration gradient

front 37

voltage gradient

back 37

  • across the membrane
  • attracts positively charged ions and repels negatively charged ions

front 38

combination of forces acting on ion forms...

back 38

  • electrochemical gradient

front 39

cotransport

back 39

  • ATP pump that transports a specific solute indirectly drives the transport of other substances
  • substance that was initially pumped across the membrane can do work as it moves back across the membrane by diffusion
  • brings with it a second compound against gradient

front 40

carrier protein

back 40

  • change shape in a way that shuttles their "passengers" across the membrane

front 41

channel proteins

back 41

  • function by having a hydrophilic channel that certain molecules or ions use as a tunnel through the membrane

front 42

large molecules are moved across the cell membrane through...

back 42

  • exocytosis and endocytosis

both processes require energy

front 43

exocytosis

back 43

  • vesicles from the cell's interior fuse with the cell membrane
  • expelling contents

front 44

endocytosis

back 44

  • cell forms new vesicles from the plasma membrane
  • allows the cell to take in macromolecules
  • examples: engulfing of foreign particles by white blood cells or amoebas
  • reverse of exocytosis

front 45

examples of molecules that pass through phospholipid bilayer using simple diffusion

back 45

  • CO2
  • O2

front 46

examples of molecules that pass through phospholipid bilayer using carrier proteins

back 46

  • glucose

front 47

examples of molecules that pass through phospholipid bilayer using channel proteins

back 47

  • H+ ions (protein pump)

front 48

bulk transport

back 48

  • moves large molecules
  • exocytosis and endocytosis
  • requires energy

front 49

what is meant by membrane fluidity?

back 49

  • membranes are not static sheets of molecules locked rigidly in place
  • they move and shift sideways, hence the "fluid" classification

front 50

how can decrease in temperature affect membrane fluidity?

back 50

  • membrane becomes more solid
  • phospholipids settle into closely packed arrangement

front 51

how do phospholipids with unsaturated hydrocarbon chains affect membrane fluidity?

back 51

  • with temperature decrease, membrane still remains fluid
  • kinks in tails don't allow the phospholipids to pack tightly together

front 52

how does cholesterol affect membrane fluidity?

back 52

  • acts as a "fluidity buffer"
  • resists changes in membrane fluidity that can be caused by changes in temperature
  • at low temperatures - hinders solidification by disrupting the regular packing of phospholipids
  • at moderate temperatures - reduces phospholipid movement, reducing membrane fluidity

front 53

how do phospholipids with saturated hydrocarbon chains affect membrane fluidity?

back 53

  • saturated carbon tails pack together, increasing membrane viscosity

front 54

major functions of membrane proteins

back 54

  • transport
  • enzymatic activity
  • signal transduction
  • cell-cell recognition
  • intercellular joining
  • attachment to cytoskeleton and ECM

front 55

transport

back 55

  • proteins guide and pump substances across the membrane using energy

front 56

enzymatic activity

back 56

  • enzymes in membrane organized into teams to carry out sequential steps of metabolic pathway

front 57

signal transduction

back 57

  • signaling molecule binds to receptor
  • may cause receptor to change shape
  • allows message to be relayed

front 58

cell-cell recognition

back 58

  • glycoproteins act as identification tags
  • recognized by membrane proteins of other cells

front 59

intercellular joining

back 59

  • membrane proteins hook together to those of the adjacent cell

front 60

attachment to cytoskeleton and ECM

back 60

  • cytoskeleton elements bind to membrane proteins
  • maintains cell shape
  • stabilizes protein location
  • proteins bind to ECM
  • coordinate cellular changes outside or inside cell

front 61

integrins

back 61

  • cell surface receptor proteins

front 62

cytoskeleton microfilaments

back 62

  • thin, solid rods
  • form structural networks when certain proteins bind along the side of other filaments

front 63

ECM fibers

back 63

  • made up of glycoproteins
  • embedded in a network woven out of proteoglycans

front 64

example of transport proteins being specific

back 64

  • doesn't allow fructose to pass, a structural isomer of glucose

front 65

diffusion

back 65

  • the movement of particles of any substance so that they spread out into the available space

front 66

turgid

back 66

  • healthy state for most plant cells
  • very firm

front 67

flaccid

back 67

  • no net tendency for water to enter
  • plant wilts
  • limp

front 68

plasmolysis

back 68

  • plasma membrane pulls away from the cell wall at multiple places as plant cell shrivels
  • causes plant to wilt and can lead to plant death

front 69

why does the plant cell not burst like the red blood cell when placed in a hypotonic solution?

back 69

  • the plant cell has a cell wall
  • uptake of water is eventually balanced by the wall pushing back on the cell

front 70

summary: sodium-potassium pump

back 70

  1. cytoplasmic Na+ binds to sodium-potassium pump
  2. binding of 3 Na+ stimulates phosphorylation by ATP
  3. phosphorylation leads to change in protein shape - Na+ is released
  4. new shape attracts K+ - K+ binds to extracellular side, triggers release of the phosphate group
  5. phosphate group restores protein's OG shape
  6. 2 K+ released, cycle repeats with affinity for Na+ once again

front 71

receptor-mediated endocytosis

back 71

  • enables the cell to acquire bulk quantities of specific substances
  • specialized type of pinocytosis
  • key feature: receptor sites that bind with specific solutes

front 72

phagocytosis

back 72

  • a cell engulfs a particle by extending a pseudopodia fluid around it, and packaging it within food vesicle

front 73

pinocytosis

back 73

  • cell continually gulps droplets of extracellular fluid into tiny vesicles formed by infolding of plasma membrane