Chapter 7

Question 1

what is the plasma membrane?

Answer 1

it is the boundary that separates the living cell from its surroundings (8mm)
- it is selectively permeable

Question 2

what is selective permeability?

Answer 2

allowing some substances to cross it more easily than others

Question 3

what lipid is the most abundant in the plasma membrane?

Answer 3

the phospholipids are the most abundant lipid in the plasma membrane

• phospholipids are also amphipathic molecules
• phospholipids can move within the bilayer

Question 4

what are amphipathic molecules?

Answer 4

molecules that contain a hydrophobic and a hydrophilic region(s)

Question 5

what is the fluid mosaic model?

Answer 5

it states that the membrane is a fluid structure with a “mosaic” of various proteins embedded in it or attached.

Question 6

hydrophobic interactions are what?

Answer 6

they are weaker than covalent bonds

and membranes are held together by these types of bonds

Question 7

what rarely happens across a membrane?

Answer 7

rarely does a molecule flip-flop transversely across the membrane

Question 8

How are the membrane of a cell and temperature related?

Answer 8

• As temperatures cool, membranes switch from a fluid state to a solid state
• the temperature at which a membrane solidifies depends on the type of lipids
• membranes must be fluid to work properly

Question 9

membranes rich in…?

Answer 9

membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids

Question 10

At warm temperatures of about 37 degrees celsius?

Answer 10

cholesterol restricts the movement of phospholipids

- at cool temperatures it maintains fluidity by preventing tight packing

Question 11

proteins do what?

Answer 11

• proteins determine most of the membranes specific functions
• proteins can be peripheral( attached outside the membrane) or integral (within the membrane)

Question 12

what are peripheral proteins?

Answer 12

they are like appendages bound loosely to the surface of the membrane

Question 13

what are integral proteins?

Answer 13

they penetrate the hydrophobic core

- integral proteins that span the membrane are called TRANSMEMBRANE PROTEINS

Question 14

Integral proteins contain how many regions?

Answer 14

2 regions
hydrophobic region: consists of one or more stretches of nonpolar amino acids, often coiled into alpha helices
hydrophilic region: is in contact with the aqueous solution

Question 15

what are the 6 major functions of membrane proteins?

Answer 15

1. transport
2. enzymatic activity
3. signal transduction
4. cell - cell recognition
5. intercellular joining
6. attachement to the cytoskeleton and extracellular matrix (ECM)

Question 16

what is the role of carbohydrates in cell- cell recognition?

Answer 16

• cells recognize each other by binding to surface molecules, often carbohydrates (there are 15 sugars), on the plasma membrane
• Carbohydrates act as makers to distinguish one cell from another
• Membrane carbohydrates maybe covalently bonded to lipids (glycolipids) or more commonly proteins (glycoproteins)

Question 17

The asymmetrical distribution of lipids, proteins and carbohydrates in the membrane is determined when?

Answer 17

This is determined when the membrane is built by the golgi apparatus and the ER

Question 18

what is the Asymmetry of membrane lipids?

Answer 18

• Inner and outer membrane leaflets have different lipid compositions
• Provides different physicochemical properties appropriate for different interactions
• membrane lipids move easily within a leaflet but only rarely flip-flop

Question 19

Hydrophobic (non-polar) molecules can?

Answer 19

can dissolve in the phospholipid bilayer and pass through the membrane rapidly
(hydrocarbons, oxygen, and carbon dioxide)

Question 20

Hydrophilic (polar) molecules?

Answer 20

do not cross the membrane as easily (sugars, ions and water)

Question 21

what are transport proteins?

Answer 21

allow passage of of hydrophilic substances across the membrane without coming in touch with the hydrophobic part

Question 22

what are channel proteins?

Answer 22

A type of transport protein that has a hydrophilic that certain ions or molecules can use as a tunnel

Question 23

what is an aquaproin?

Answer 23

a channel protein that facilitate the passage of water

Question 24

what are carrier proteins?

Answer 24

bind to molecules and change the shape to shuttle them across the membrane

Question 25

transport proteins are an example of what?

Answer 25

active transport, which means they require energy to go through with reactions

Question 26

what is passive transport?

Answer 26

is diffusion of a substance across a membrane with no energy investment

Question 27

what is diffusion?

Answer 27

is the tendency for molecules to spread out evenly into the available space - goes from high to low concentration

Question 28

what is a concentration gradient?

Answer 28

the difference in concentration of a substance from one area to another - no work must be done to move substances down their concentration gradient

Question 29

a concentration gradient represents what?

Answer 29

potential energy

Question 30

what is osmosis?

Answer 30

is the diffusion of water across a selectively permeable membrane - goes from lower solute concentration to higher solute concentration

Question 31

what is tonicity?

Answer 31

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

Question 32

what is an isotonic solution?

Answer 32

solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

Question 33

what is a hypertonic solution?

Answer 33

solute concentration is greater than that inside the cell, cell loses water

Question 34

what is a hypotonic solution?

Answer 34

solute concentration is less than that inside the cell, cell gains water

Question 35

what is facilitated diffusion?

Answer 35

transport proteins speed the passive movement of molecules across the plasma membrane - channel proteins provide corridors that allow a specific molecule or ion to cross the membrane

Question 36

channel proteins include?

Answer 36

- aqauporins for facilitated diffusion of water | - ion channels that open and close in response to a stimulus (Gated Channels)

Question 37

what is active transport?

Answer 37

active transport moves ions against their concentration gradients and they require energy to do this - allows cells to maintain concentration gradients that differ fro their surroundings

Question 38

what is the sodium-potassium pump?

Answer 38

is one type of active transport system - found in animal cells - the pump is an integral membrane glycoprotein ( an antiporter) - for every 3 Na+ that goes in 2 K+ go out

Question 39

what is primary active transport?

Answer 39

requires direct hydrolysis of ATP

Question 40

what s secondary active transport?

Answer 40

energy comes from an ion concentration gradient that is established by primary active transport

Question 41

what is membrane potential?

Answer 41

is the voltage difference across a membrane - all membrane have a potential of -50mV to -200mV because the inside of the cell is more negative than the outside of the cell

Question 42

what is voltage?

Answer 42

voltage is created by differences in the distribution of positive and negative ions

Question 43

what is an electrochemical gradient?

Answer 43

DRIVE THE DIFFUSION OF IONS ACROSS A MEMBRANE - A chemical force (the ion's concentration gradient) - An electrical force ( the effect of the membrane potential on the ion's movement) - Ions will diffuse down the concentration gradient and down the electrochemical gradient

Question 44

what is an electrogenic pump?

Answer 44

is a transport protein that generates voltage across a membrane - the sodium-potassium pump is the major electrogenic pump of animals

Question 45

what is a proton pump?

Answer 45

The main electrogenic pump of plants, fungi, and bacteria

Question 46

what is co-transport ?

Answer 46

Occurs when active transport of a solute indirectly drives transport of another solute

Question 47

what is the Glucose Transporter?

Answer 47

an example of facilitated diffusion - the gradient for glucose entry into the cell is maintained by phosphorylation of glucose in the cytoplasm - insulin stimulates glucose uptake by causing the insertion into cell membrane vesicles containing preformed glucose transporters

Question 48

what is exocytosis?

Answer 48

transport vesicles migrate to the membrane, fuse with it, and release their contents

Question 49

bulk transport across the plasma membrane occurs by?

Answer 49

exocytosis and endocytosis

Question 50

what is endocytosis?

Answer 50

the cell takes in macromolecules by forming vesicles from the plasma membrane - there are three types of endocytosis

Question 51

what are the 3 types of endocytosis?

Answer 51

1. phagocytosis ( cellular eating) 2. pinocytosis ( cellular drinking) 3. Receptor-mediated endocytosis

Question 52

what is phagocytosis?

Answer 52

A cell engulfs a particle in a vacuole, the vacuole fuses with the lysosome to digest the particle

Question 53

what is pinocytosis?

Answer 53

molecules are taken up when extracellular fluid is "gulped" into tiny vesicles

Question 54

what is receptor-mediated endocytosis?

Answer 54

binding of ligands to receptors triggers vesicle formation

Question 55

what are ligands?

Answer 55

any molecule that binds specifically to a receptor site of another molecule