Mebrane Transport and Cell Signaling (Chapter 5)

Question 1

ingredients of membranes

Answer 1

lipids and proteins

phospholipids are most abundant

Question 2

amphipathic

Answer 2

quality of having both hyrdophilic and hydrophobic regions

membrane phospholipidss and proteins are amphipathic

Question 3

fluid mosaic model

Answer 3

membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

Question 4

sensitivitivity of membranes to temperature

Answer 4

at lower temperatures phospholipids become closely packed

phospholipids with unsaturated hyrdocarbon tails stay fluid

kinks in the tail where double bonds are located keep them from being closely packed

cholesterol wedged between phospholipids changes fluidity at different temperatures:

high temperatures cause membrane to be less fluid

lowers the temperature at which membrane will solidify

Question 5

reason for variations in lipid composition

Answer 5

maintains fluidity in extreme environments

fishes in cold water have lots of unsaturated hyrdocarbon

bacteria in geysers have unusual lipids that prevent fluidity

lipid composition can change over time (e.g. winter wheat)

Question 6

integral proteins

Answer 6

penetrate the hyrdophopic interior of the lipid bilayer

most are transmembrane proteins and span the membrane

hydrophobic region consisting of non-polar amino acids

some have hydrophilic channels allowing passage

Question 7

peripheral proteins

Answer 7

not embedded in lipid billayer

appendages are loosely bound to the surface of the membrane

some are held in place by the cytoskeleton

Question 8

functions of proteins in plasma membrane

Answer 8

transport: hydrophilic channel across the membrane

enzymatic activity: active site exposed to adjacent solution

attachment to cytoskeleton and extracellular matric: microfilaments non-covalently bound

cell-cell recognition: allow recognition by membrane proteins on other side of membrane

intercellular joining: hook together various kinds of junctions

signal transduction: one side of protein receieves message from hormone and transmits by changing shape on other side

Question 9

role of carbohydrates in cell-cell recognition

Answer 9

cells recognize other cells by binding molecules

membrane carbohydrates are commonly the bound molecule

short (<15) chains of sugar units

glycolipids: carbohydrates covalently bonded to lipid
glycoprotein: carbohydrate covalently bonded to protein

great variation in membrane carbohydrates: species to species and among cell types

Question 10

selective permeability

Answer 10

nonpolar molecules (hydrocarbons, carbon dioxide, oxygen) are hydrophobic, can dissolve in lipid bilayer, and can cross it easily without membrane protein

polar molecules and ions (glucose, sugars) are hydrophilic and cnanot pass from the inside of the hydrophobic membrane

Question 11

transport proteins

Answer 11

span lipid bilayer and allow passage of polar molecules and ions

specific to the substance it translocates

Question 12

channel proteins

Answer 12

hyrdophilic channel that molecules use as a tunnel

Question 13

aquaporins

Answer 13

type of channel protein

allows passage of water through the plasma membrane

consists of four identical subunits

polypeptide forms channel for single file passage

Question 14

carrier proteins

Answer 14

hold onto passengers and change shape to shuttle across

Question 15

diffusion

Answer 15

movement of particles as a result of constant motion due to thermal energy

Question 16

rule of diffusion

Answer 16

substance will diffuse to be less concentrated

Question 17

concentration gradient

Answer 17

region along which concentration increases or decreases

substances diffuse down their concentration gradient

no work must be done; diffusion is spontaneous

each substance diffuses down its own gradient unaffected by other substances

Question 18

passive transport

Answer 18

diffusion of substance across a biological membrane

cell does not expend energy to make it happen

concentration gradient represents potential energy

membranes have different effects on rates of diffusion

Question 19

osmosis

Answer 19

diffusion of free water across selectively permeable membrane

tight clustering of water molecules around the hydrophilic solute molecules make some water unavailable

remaining free water diffues across membrane from highest free water concentration to lower

Question 20

tonicity

Answer 20

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

factors affecting tonicity:

solute concentration

membrane permeability

Question 21

isotonic environment

Answer 21

results in no net movement of water

water diffuses across the membrane but at same rate

example: seawater is isotonic to many marine invertebrates

Question 22

hypertonic environment

Answer 22

high concentration of non-penetrating solutes in surrounding solution

will case water to leave cell

cell will loose water, shrivel and possibly die

Question 23

hypotonic environment

Answer 23

low concentration of non-penetrating solutes in surrounding solution will cause water to enter cell

cell will gain water, swell, and burst

Question 24

osmoregulation

Answer 24

mechanism by which cells in hypotonic and hypertonic environments control water balance

example: contractile vacuole organelle functions as bilge pump

Question 25

turgor pressure

Answer 25

cell walls exert back pressure prevents futher uptake of water walls help maintain the cell's water balance without turgor pressure plant cells become flaccid

Question 26

plasmolysis

Answer 26

plant cell in hypertonic enviornment plant cell loses water to environment and wilts

Question 27

facilitated diffusion

Answer 27

transport proteins help diffuse polar molecules and ions most transport proteins are specific

Question 28

active transport

Answer 28

mechanism to pump solute against the concentration gradient allows cell to maintain internal concentration of small solutes animal cells have high concentrations of potassium ions (K⁺) animal cells have low concentrations of sodium ions (Na^-) plasma membrane pumps Na⁺ out and K⁺ inot the cell ATP supplies the energy for most active transport

Question 29

sodium-potassium pump

Answer 29

exchanges Na⁺ for K⁺ across the plasma membrane

Question 30

membrane potential

Answer 30

voltage across a membrane voltage is electrical potential energy and comes from seperation of opposite charges cytoplasmic side is negative in charge relative to extracellular side ranges from -50 to -200 millivolts (mV) acts like a battery energy source

Question 31

electrochemical gradient

Answer 31

combination of forces acting on an ion ion diffuses down its electrochemical gradient important to nerve impulses

Question 32

electrogenic pump

Answer 32

transport proteins actively contribute to membrane potential sodium-potassium pum pumps 3 Na⁺ out for 2 K⁺ in each pup there is net transfer of one positive charge out

Question 33

proton pump

Answer 33

main electogenic pump of plants, fungi actively transports protons out of the cell transfers positive charge from the cytoplasm to the extracellular proton gradients useful for: ATP synthesis during cellular respiration co-transport

Question 34

cotransport

Answer 34

special transport mechanism single ATP-powered pump transports a specific solute indrectly drives the active transport of other solutes substance pumped across a membrane can do work diffusing back example: proton pump in plants H⁺ pumped into cell with proton pump H⁺ diffuses out and provides energy to pump sucrose in from photosynthesis

Question 35

exocytosis

Answer 35

molecule secretion by fusion of vesicles with membrane transport vesicle budded from Golgi apparatus moves along microtubules of the cytoskeleton to the plasma membrane plasma membranes fuse when vesicle membrane and plasma membrane come into contac contes of vesicle spill to the outside of the cell vesicle membrane becomes part of the plasma membrane examples: pancreas cells secrete insulin into extracellular fluid, nerve cells release neutrotransmitters, plant cells build walls by delivering protein

Question 36

endocytosis

Answer 36

cell takes in molecules and particulate matter forming new vesicle events of endocytosis look like reverse of exocytosis three types: phagocytosis, pinocytosis, receptor-mediated endocytosis

Question 37

phagocytosis

Answer 37

cell engulfs a particle by wrapping speudopodia around it packages it within a mebranous sac called food vacuole particle digested after food vacuole fuses with lysosome lysosome contains hydrolytic enzymes

Question 38

pinocytosis

Answer 38

cell continually "gulps" droplets of extracellular fluid cell otains molecules dissolved in the droplets any and all substances are taken into the cell parts of plasma that form vesicles are lined with protein

Question 39

receptor-mediated endocytosis

Answer 39

specialized type of pinocytosis that acquires bulk quantities embedded in plasma membrane are proteins with receptors after ingested material is liberated from vesicle, emptied receptrs are recycled to plasma membrane by the same vesicle

Question 40

local cell to cell communication types

Answer 40

direct contact between eukaryotic cells cell to cell recognition paracine signaling: signaling cell secrete messenger molecules synaptic signaling: electrical signal moving along nerve cell triggers secretion of neurotransmitter molecules

Question 41

paracine signaling

Answer 41

requires local regulators signaling cell secretes messenger molecules growth factors are one class and stimulate cells to grow

Question 42

synaptic signaling

Answer 42

occurs in the animal nervous system electrical signal moving along nerve cell triggers secretion of neurotransmitter molecules molecules diffuse across the synapse

Question 43

endocrine or hormonal signaling

Answer 43

type of long distance cell to cell communication specialized cells secrete hormones which travel via blood target cells can recognize and react to the hormone

Question 44

Earl W. Sutherland

Answer 44

made discovers about cell signaling

Question 45

stages at receiving end of cell to cell communication

Answer 45

reception transduction response

Question 46

receptor protein

Answer 46

detects the signal on or in the target cell

Question 47

signaling molecule

Answer 47

provides signal to receptor protein complementary in shape behaves as a ligand (type of molecule that specifically binds to another molecule) ligand binding causes receptor protein to undergo change

Question 48

ligand

Answer 48

signaling molecule that specifically binds to another molecule

Question 49

G protein-coupled receptors (GPCR)

Answer 49

cell surface transmembrane receptor works with the help of a G protein binds the energy rich molecule GTP GPCR pathways are extremely diverse in their functions: embryonic development, senses of smell and taste, involved in many diseases

Question 50

ligand-gated ion channels

Answer 50

membrane receptor that has a region that can act as a gate signaling molecule binds as a ligand to the receptor protein gate opens and closes allowing or blocking diffusion very important in nervous system

Question 51

intracellular receptors

Answer 51

found in either the cytoplasm or nucleus of target cells chemcial messenger passes through the target cells membrane messenger binds to receptor protein protein then enters nucleus

Question 52

signal transduction pathway

Answer 52

multistep pathway binding of specific signaling molecule to receptor in membrane triggers first step in the chain of interactions activates another molecule which activates another molecule

Question 53

protein kinase

Answer 53

enzyme that transfers phosphate groups from ATP to a protein widely involved in signaling pathways signal is transmitted by casade of protein phosphorylations

Question 54

protein phosphatases

Answer 54

enzyme that can rapidly remove phosphate groups from protein process is called phophorylation provides mechanism for turning off transduction pathway make the protein kinase available for reuse

Question 55

second messengers

Answer 55

small, non-protein, water-soluable molecules involved in transduction can rapidly spread by diffusion because they are small

Question 56

cyclid AMP (cAMP)

Answer 56

second messenger important to many biological processes binding of epinehrine to a specific receptor protein leads to activation of adenylyl cyclase, an enzyme embedded in the plasma membrane that converts ATP to cAMP cAMP activates protein kinase A

Question 57

Response

Answer 57

occur in nucleus or cytoplasm can include: protein synthesis activity of protein