Cell Membrane Structure

Question 1

what are the roles of plasma membrane

Answer 1

• respond to stimuli
• export/import molecules (endo-, exo-cytosis)
• allow for movement during cell growth since it grows itself

Question 2

describe the plasma membrane’s lipid bilayer

Answer 2

• semi-permeable
• embedded proteins which provide uniqueness
• phospholipids: hydrophilic heads align outside and hydrophobic tails on inside

Question 3

define amphipathic molecule

Answer 3

those that contain both hydrophilic and hydrophobic groups (EX cholesterol)

Question 4

phospholipids and glycolipids are distributed ___________ in the membrane

Answer 4

asymmetrically

Question 5

how is the cell membrane formed

Answer 5

hydrophobic molecules force water molecules to make cage-like arrangement which forces formation of lipid bilayer

Question 6

the cell membrane is energetically ______________

Answer 6

favourable

Question 7

why do the properties of phospholipids cause membranes to be spherical

Answer 7

any tear in plasma membrane will expose an edge of tails to water which makes it energetically unfavourable. this is why edges merge and form spherical shape

Question 8

define fluidity

Answer 8

dynamic cell barrier is able to respond to changing environment

Question 9

what factors affect fluidity of plasma membrane

Answer 9

• length of hydrocarbon tail
• degree of unsaturation (double bonds)
• dissimilar structures in between (EX cholesterol in between)

Question 10

what are transporters

Answer 10

membrane proteins that transport nutrients and ions

Question 11

what are anchor proteins

Answer 11

anchor macromolecules

Question 12

what are receptor proteins

Answer 12

those that receive information

Question 13

what do enzymes do

Answer 13

catalyze reactions

Question 14

how do membrane proteins associate with the membrane in various ways

Answer 14

• transmembrane proteins
• membrane-associated proteins
• lipid-linked proteins
• protein attached proteins

Question 15

describe transmembrane proteins

Answer 15

hydrophobic regions interact with phospholipid tails, whilst hydrophilic portions interact with cytosol and extracellular environment

Question 16

describe membrane-associated proteins

Answer 16

protein is entirely cytosolic with alpha-helix associated with inner leaflet of membrane

Question 17

describe lipid-linked proteins

Answer 17

linked to membrane by covalent bond

Question 18

describe protein-attached proteins

Answer 18

one protein is held in place with another protein that’s associated with plasma membrane

Question 19

how can a peptide chain cross the membrane

Answer 19

as alpha-helix, where hydrophobic side chains interact with hydrophobic portion of membrane

Question 20

how can beta sheets cross the membrane

Answer 20

as beta-barrels, an aqueous channel lining is formed by the hydrophilic portion of beta-sheets and hydrophobic portion interacts with plasma membrane

Question 21

what is a cortex; what can it do

Answer 21

• protein framework attached by transmembrane proteins
• strengthens cell/plasma membrane

Question 22

what protein is the human red blood cell cortex made of; what does it do

Answer 22

spectrin; forms meshwork that provides shape

Question 23

what is the cell surface coated with

Answer 23

carbohydrates

Question 24

why is cell surface coating beneficial

Answer 24

• prevents cells from sticking together
• cell-cell recognition
• some cells (white-blood) can squeeze between others since it is slimy
• protection from mechanical and chemical damage
• recognize sites of infection (neutrophils)

Question 25

what are glycolipids

Answer 25

lipids with carbohydrates

Question 26

what are glycoproteins

Answer 26

membrane proteins with sugars attached (oligosaccharides)

Question 27

how are carbohydrates on surface of neutrophils beneficial

Answer 27

- oligosaccharides on neutrophils bind to lectin proteins on endothelial cells at infection site - neutrophils migrate through blood vessel at correct location to site of infection