Chapter 7

Question 1

Plasma Membrane

Answer 1

• selectively permeable
• bilayer of phospholipids
• colder temperatures (depending on lipids) = fluid membrane becomes more solid
• more unsaturated fatty acids = more fluid membrane
• must be fluid to properly function
• have distinct inside and outside faces determined when formed by ER and Golgi
• hydrophobic (nonpolar) molecules can pass easy, like oxygen
• hydrophillic (polar) molecules need transport proteins to pass through, like sugar

Question 2

Phospholipids

Answer 2

• amphipathic, means they have hydrophillic heads and hydrophobic tails; needed for membrane to be selectively permeable
• most abundant lipid in membrane
• are able to move within the bilayer, creating fluidity
• usually shift laterally, rarely flipper to other side of membrane
• unsaturated makes tails bent (which creates distance between phospholipids which creates fluidity), saturated makes tails extremely straight

Question 3

Integral proteins

Answer 3

• imbedded in cell membrane
• has hydrophillic region - part that sticks out of the membrane, and hydrophobic region - part that is within the bilayer
• if they span the membrane, they are called transmembrane proteins

Question 4

Fluid mosaic model

Answer 4

• theory for cell membrane structure proposed by Singer and Nicolson
• where proteins are imbedded within the bilayer
• free fracture procedure (splitting membrane bilayer apart) proved this correct

Question 5

Cholesterol

Answer 5

• amongst the phospholipids in a membrane
• when temperatures get hot, cholesterol restricts fluidity, holding membrane together
• when temperatures get cold, cholesterol maintains fluidity, preventing tight packing of phospholipids

Question 6

Membrane proteins

Answer 6

• drift in bilayer, more slowly than lipids because bigger
  include: peripheral proteins - not embedded and on either surface of membrane and integral proteins

Question 7

Six major membrane protein functions

Answer 7

• transport
• enzymatic activity
• signal transduction
• cell-cell recognition
• intercellular joining
• attachment to the cytoskeleton and extracellular matrix (ECM)

Question 8

Membrane carbohydrates

Answer 8

• is the main molecule on the plasma membrane that helps with cell to cell recognition
  includes: glycolipids - carbohydrates covalently bonded to lipids, or glycoproteins - carbohydrates covalently bonded to proteins
• vary among species / individuals

Question 9

Transport proteins

Answer 9

• helps hydrophillic substances get through membrane
  includes: channel proteins - hydrophilic channel that molecules or ions can use as a tunnel, carrier proteins - bind to molecules and change shape to transport across membrane
• aquaporins: channel proteins that transport water
• specific for the substances they move

Question 10

Passive transport

Answer 10

• diffusion of substance across membrane without using energy
• includes when substances move down their concentration gradient (not against it)

Question 11

Diffusion

Answer 11

• tendency for molecules to spread out evenly into available space
• molecules can move randomly as individuals, but as a population they can have a general, all-together direction
• dynamic equilibrium: the same # of molecules that cross one way also cross in the other direction
• substances diffuse down their concentration gradient, like sliding down a hill

Question 12

Osmosis

Answer 12

• diffusion of water across a selectively permeable membrane
• direction of process is determined by difference in total solute concentration
• water diffuses from lower to higher solute concentration

Question 13

What are the three types of solute concentration solutions?

Answer 13

1) hypertonic: outside solute concentration is greater than concentration inside the cell; cell loses water (because it goes from low to high solute concentration)
2) isotonic: outside solute concentration is the same as concentration inside the cell; no water movement
3) hypotonic: solute concentration is less than concentration inside the cell; cell gains water

Question 14

Why do some cells have osmolarity problems?

Answer 14

• cells without cell walls cannot regulate water intake as well as cells with them
• causes osmolarity problems for these cells in hypotonic and hypertonic solutions
• cells must have adaptations to compensate, like contractile vacuoles

Question 15

Cell walls (osmolarity and water wise)

Answer 15

• help maintain water balance
• in a hypotonic solution, cell wall it swells until it opposes uptake; the cell is now turgid
• in isotonic solutions, the cell becomes flaccid (limp) and the plant may wilt
• in hypertonic solution, cell loses water; membrane eventually pulls away from the wall, usually killing it the cell - called plasmolysis

Question 16

Facilitated diffusion

Answer 16

• passive transport (moves down gradient) with the help of transport, channel, or carrier proteins
• transport proteins: speed molecular movement across membrane
• channel proteins: provide corridors that allow a specific molecule or ion to cross the membrane
• carrier proteins: undergo a subtle change in shape that moves the solute-binding site across the membrane

Question 17

Active transport

Answer 17

• uses energy (ATP) to move solutes AGAINST concentration gradient
• done through some transport proteins or specific proteins embedded in membrane
• sodium-potassium pump is an example; when NA is expelled it changes the proteins shape, then allowing for K to enter (which returns the shape back to NA usable)

Question 18

Membrane potential

Answer 18

• voltage difference across a membrane

Question 19

Electrochemical gradient

Answer 19

• two forces that drives ion diffusion across membrane
• chemical force: ion’s concentration gradient
• electrical force: membrane potential effect on ion’s movement

Question 20

Electrogenic pump

Answer 20

• a transport protein that hydrolyzes ATP and uses the energy released from ATP hydrolysis to transport ions across membranes, which also moves net charge across membrane
• main pump of plants, fungi, and bacteria is a proton pump
• plant cells use hydrogen ion gradient to use active transport to get nutrients inside

Question 21

Cotransport

Answer 21

• occurs when active transport of one solute indirectly drives transport of another solute

Question 22

Exocytosis

Answer 22

• handles bulk transport across membrane
• where transport vesicles migrate to the membrane, fuse with it, and release their contents
• secretory cells use this to export their products

Question 23

How do small and large molecules enter and leave the cell?

Answer 23

• small: through bilayer or by transport proteins
• big (polysaccharides or proteins): by vesicles

Question 24

Endocytosis

Answer 24

• handles bulk transport across membrane
• where the cell takes in macromolecules by forming vesicles from the plasma membrane
• reversal of exocytosis with different proteins
• 3 types: Phagocytosis (“cellular eating”) - cell engulfs particle in a vacuole, Pinocytosis (“cellular drinking”)- cell creates vesicle around fluid, and Receptor-mediated endocytosis - binding of ligands to receptors triggers vesicle formation

Question 25

Ligand

Answer 25

• an ion or molecule attached to a metal atom by coordinate bonding.
• bind on outside of the cell?

Question 26

amphipathic

Answer 26

A molecule that has a hydrophilic region and a hydrophobic region is

Question 27

receptor mediated endocytosis

Answer 27

A type of endocytosis in which the cell takes in specific substance after the substances bind to ligands in a coated pit on the cell membrane.

Question 28

phagocytosis

Answer 28

A type of endocytosis in which the cell takes in a particle by wrapping pseudopodia around it and packaging it into what will become a food vacuole.

Question 29

In what way do the membranes of eukaryotic cells vary?

Answer 29

certain proteins are unique to each membrane

Question 30

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

Answer 30

they can move laterally among the membrane

Question 31

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

Answer 31

it exhibit a specificity for a particular molecule

Question 32

glycoprotein

Answer 32

a protein with a short, usually branched chain of carbohydrates attached to it.

Question 33

glycolipid

Answer 33

a short, usually branched carbohydrate attached to a phospholipid in the membrane

Question 34

sodium potassium pump

Answer 34

An important transport system in animal cells which exchanges sodium and potassium ions across a membrane.

Question 35

proton pump

Answer 35

A pump in the membrane of cells that pumps hydrogen ions (H+) out of a cell or into an intermembrane space.

Question 36

electrogenic pump

Answer 36

A transport protein that generates voltage across a membrane, such as the sodium potassium pump.

Question 37

In a hypotonic solution an animal cell will?

Answer 37

lyse

Question 38

The sodium-potassium pump is called an electrogenic pump because it?

Answer 38

contributes to the membrane potential

Question 39

carrier molecules are passive or active transport?

Answer 39

active