AP Biology Test, Chapter 7 Flashcards


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1

Which macromolecules make up membranes?

  • lipids and proteins
  • carbohydrates also important

2

most abundant lipid in most membranes

  • phospholipids

3

amphipathic

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

4

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

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

5

fluid mosaic model

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

6

plasma membrane

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

7

membranes are predominantly made of...

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

8

phospholipids

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

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

9

cholesterol

  • 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

10

proteins

  • 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)

11

peripheral proteins

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

12

membrane carbohydrates

  • 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

13

intergral proteins

  • penetrate the hydrophobic interior of the lipid bilayer

14

glycolipids

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

15

glycoproteins

  • membrane carbohydrate chains covalently bonded to proteins

16

integrins

  • cell-surface receptor proteins

17

non-polar molecules (hydrophobic)...

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

18

hydrophobic core of the membrane...

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

19

transport proteins

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

20

aquaporins

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

21

passive diffusion

  • 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

22

concentration gradient

  • 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

23

osmosis

  • 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

24

isotonic solution

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

25

hypertonic solution

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

26

hypotonic solution

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

27

water moves from...

Hypo-> Hyper

28

ions and polar molecules...

  • cannot move easily across the membrane

29

facilitated diffusion

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

30

how do transport proteins work?

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

31

active transport

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

32

sodium-potassium pump

  • 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

33

membrane potential

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

34

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

  • inside of cell is negatively charged

35

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

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

36

chemical force

  • ion's concentration gradient

37

voltage gradient

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

38

combination of forces acting on ion forms...

  • electrochemical gradient

39

cotransport

  • 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

40

carrier protein

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

41

channel proteins

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

42

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

  • exocytosis and endocytosis

both processes require energy

43

exocytosis

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

44

endocytosis

  • 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

45

examples of molecules that pass through phospholipid bilayer using simple diffusion

  • CO2
  • O2

46

examples of molecules that pass through phospholipid bilayer using carrier proteins

  • glucose

47

examples of molecules that pass through phospholipid bilayer using channel proteins

  • H+ ions (protein pump)

48

bulk transport

  • moves large molecules
  • exocytosis and endocytosis
  • requires energy

49

what is meant by membrane fluidity?

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

50

how can decrease in temperature affect membrane fluidity?

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

51

how do phospholipids with unsaturated hydrocarbon chains affect membrane fluidity?

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

52

how does cholesterol affect membrane fluidity?

  • 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

53

how do phospholipids with saturated hydrocarbon chains affect membrane fluidity?

  • saturated carbon tails pack together, increasing membrane viscosity

54

major functions of membrane proteins

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

55

transport

  • proteins guide and pump substances across the membrane using energy

56

enzymatic activity

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

57

signal transduction

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

58

cell-cell recognition

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

59

intercellular joining

  • membrane proteins hook together to those of the adjacent cell

60

attachment to cytoskeleton and ECM

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

61

integrins

  • cell surface receptor proteins

62

cytoskeleton microfilaments

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

63

ECM fibers

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

64

example of transport proteins being specific

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

65

diffusion

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

66

turgid

  • healthy state for most plant cells
  • very firm

67

flaccid

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

68

plasmolysis

  • 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

69

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

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

70

summary: sodium-potassium pump

  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

71

receptor-mediated endocytosis

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

72

phagocytosis

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

73

pinocytosis

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