UNIT 2

Question 1

what does the cell membrane do

Answer 1

encloses the cell and organelles- provides a Barrier to prevent the contents of the cell from escaping and mixing with the surrounding medium

Question 2

what does the plasma membrane do

Answer 2

separates the cell from the outside enabling its composition to differ from that of the environment

Question 3

what are the inner membranes and what do they do

Answer 3

the inner membranes are the mitochondrial membrane, the nuclear membrane ect and are made of the same componenets and allow substances to pass through them

Question 4

is the membrane a solid barrier?

Answer 4

no many mlecules must pass inward and many must pass out, the membrane acts as a selective barrier

Question 5

how many membranes are eurkaryotic cells surrounded by

Answer 5

the organelles in eukaryotic cells are surrounded by one membrane with the exception of the nucleus, mitochondria and chloroplasts which have two

Question 6

what needs to get into the cell

Answer 6

oxygen, water, nutrients

Question 7

what needs to get out of the cell

Answer 7

CO2, water, wastes and other molecules

Question 8

composition of cell membrane

Answer 8

lipids, proteins and carbs make up all membranes and all membranes share a common general structure

Question 9

Fluid Mosaic model

Answer 9

the plasma membrane is a mosaic of components- lipids and proteins that move freely in the plane of the membrane, the membranes are fluid and not rigid they can bend and flex in 3D while still maintaining their integrity

Question 10

what is fundamental structure of membranes

Answer 10

phospholipids but proteins are then inserted in a lipid bilayer and carry out the specific functions of the membrane

Question 11

what are phospholipids

Answer 11

provide most of structure of the membrane, they are amphipathic molecules meaning they have a hydrophobic and hydrophilic region and are arranged in a phospholipid bilayer to form a stable barrier between two aqueous compartments

head is polar hydrophilic, tail is non polar hydrophobic

Question 12

glycerophospholipid

Answer 12

glycerol + 2 fatty acids + phosphorous + x

polar head group w fatty acid tail

Question 13

sphingo phospholipids

Answer 13

sphingosine +fatty acid + phosphorous +X

Question 14

unsaturated Fatty acids in phospholipids

Answer 14

phospholipids can not pack as closely together, membrane is more fluid, lowered temperature of thawing

Question 15

types of glycerophospholipids

Answer 15

there are 5 different types of X moieties- Serine, choline, ethanolamine, inositol and glycerol, that can bind to the P head so you have 5 different types of glycerophospholipids

Question 16

what is the most common type of phospholipid in most cell membranes

Answer 16

lectin- phosphatidyl choline, a choline attached to the P group

Question 17

Role of PC (phosphatidylcholine)

Answer 17

it is a major constituent of cell membranes, its primary role is to provide a structural framework for the membrane and maintain the permeability barrier, plays role in membrane mediated cell signaling

Question 18

sphingo- phospholipids

Answer 18

sphingosine backbone instead of glycerol backbone, one FA, phosphate and alcohol group

Question 19

relevance of spingophospholipids

Answer 19

abundant in membrane of cells in nervous tissue, important is sphingomyelin which are found in membranes of cells that form myelin sheaths around axon

Question 20

Cholesterol

Answer 20

important lipid component of membranes is cholesterol, its a steroid built from 4 linked hydrocarbons, amphipathic so makes up the lipid bilayer, oriented parallel to the fatty acid chains of phospholipids

Question 21

presence of cholesterol

Answer 21

absent from prokaryotes, makes up about 25% of membrane lipids of animal cells- not in plant cells

Question 22

insertion of cholesterol in a membrane

Answer 22

inserts into the membrane with its polar hydroxyl group close to the polar head groups of the phospholipids

Question 23

how does cholesterol interact with membrane fluidity

Answer 23

the rigid hydrocarbon portion makes the membrane more rigid stabilizing the membrane at high temperatures but also interferes with interactions of fatty acids at low temps to maintain fluidity at low temperatures

Question 24

cholesterol at low and high temps

Answer 24

at low temps it increases fluidity as it separates phospholipids, at high temps the phospholipids are more separated and the cholesterol draws them closer together to decrease the fluidity of the membrane

Question 25

membrane proteins

Answer 25

carries out membrane functions- 50% of membrane mass is protein

Question 26

integral membrane proteins

Answer 26

embedded into the membrane

Question 27

peripheral proteins

Answer 27

associated to the membrane

Question 28

transmembrane proteins

Answer 28

type of integral proteins: extend though the bilayer with part of mass on either side hydrophobic regions in interior hydrophilic layer on either side

Question 29

monolayer

Answer 29

located in cytosol associated with the inner leaflet of the bilayer by an amphipathic alpha helix

Question 30

lipid linked integral membrane protein

Answer 30

located on the surface facing inside or outside of the cell, covalently attached to lipid groups

Question 31

protein linked peripheral proteins

Answer 31

associated with other membrane proteins

Question 32

atoms forming the protein backbone are driven to form what

Answer 32

alpha helicies, the majority of the membrane spanning segments of polypeptide chains traverse the bilayer as alpha helices

Question 33

pores

Answer 33

some transmembrane proteins form pores that allow passage of water soluble molecules though them

Question 34

beta barrel pores

Answer 34

form wide channels

Question 35

Charbohydrates and the membrane

Answer 35

sugar groups (oligosaccharides) are only present on the outer surface of the plasma membrane and are attached to protiens or lipids

Question 36

n linked oligosaccharides

Answer 36

attached via asparagine

Question 37

o linked oligiosacchardies

Answer 37

through serine or threonine

Question 38

O and N linked oligosaccharides

Answer 38

o linked sugars are added only in the golgi while N linked sugars are attached starting in the ER and compleated in the golgi

Question 39

glycero-glycolipids

Answer 39

glycerol backbone, two fatty acids and carbohydrate head

Question 40

sphingo-glycolipids

Answer 40

sphingosine backbone one fatty acid and carbohydrate head

Question 41

function of the carbohydrate layer

Answer 41

protects cells from mechanical and chemical damage, adsorbs water which helps white blood cells to squeeze through

Question 42

sialic acid

Answer 42

sugar residues on cell surface important for cell recognition

Question 43

immune cells and sialic acid

Answer 43

sialic acid is linked to glycoprotiens and gangliosides, they are seen by immune cells as self markers and used by many viruses as a receptor to invade cells

Question 44

sialic acid blood cell recognition of cancer cells

Answer 44

sialic acid in the surface of normal cells inhibit the immune systems from recognizing and attacking them, cancer cells produce less sialic acid so the immune system can see them and attack them however many tumors now produce many sialic acids that hide them from immune system so they look normal and are not destroyed

Question 45

energetically unfavorable vs favorable bilayer

Answer 45

unfavorable is planer structure where edges of bilayer are exposed to water, favorable is when the phospholipid is a sealed compartment

Question 46

fluidity of a lipid bilayer

Answer 46

depends on the lipid composition, the closer and more regular the packing of the fatty acid tails the more viscous and less fluid the bilayer will be

Question 47

what is packing of the lipid bilayer affected by

Answer 47

length of fatty acids, number of double bonds (unsaturated)

Question 48

more fluid bilayer

Answer 48

shorter fatty acids, unsaturated fatty acids

Question 49

less fluidity bilayer

Answer 49

longer fatty acids, saturated fatty acids

Question 50

at high temperatures how does the bilayer adjust to stay less fluid

Answer 50

increases length and saturation

Question 51

at low temperatures how does bilayer stay more fluid

Answer 51

stay shorter and unsaturated

Question 52

what is role of cholesterol in membrane fluidity

Answer 52

cholesterol helps to maintain membrane fluidity

Question 53

how are carbohydrates aquired

Answer 53

after the proteins are synthesized in the RER and they travel through the golgi, aquire sugar inside golgi

Question 54

how to separate membrane proteins

Answer 54

use detergents

Question 55

detergents

Answer 55

small lipidic amphipathic molecules they substitute and intercalate the phospholipid and ultimately destroy the lipid bilayer by disrupting the hydrophobic associations

Question 56

cell cortext

Answer 56

framework of support made of actin that are attached to the cytosolic surface of the membrane via transmembrane proteins. Help keep shape of a cell and give mechanical properties and strength to the membrane

Question 57

what is the cell cortex made of

Answer 57

spectrin and actin,

Question 58

cell cortext and red blood cells

Answer 58

a cortex made of largly spectrin gives human red blood cells their shape

Question 59

spherocytosis

Answer 59

mutation of spectrin, the RBC are spherical instead of flat and abnormally fragile, people generally become anemic

Question 60

protein movement in lipid bilayer

Answer 60

most proteins like the lipids can move freely within the plane of the lipid bilayer

Question 61

FRAP experiments

Answer 61

how movement of membrane proteins, FRAP allowed the property that many membrane embedded proteins can move laterally in the plane of the bilayer to be discovered

Question 62

how does FRAP work

Answer 62

proteins are labeled with anti-protein antibodies with fluorescent markers, bleached with laser and then you can observe cells