membrane structure and function

Question 1

how are all eukaryotic cells bounded by

Answer 1

plasma membrane

Question 2

what is the plasma membrane made of and what does this result in

Answer 2

it is a lipid bilayer therefore acts as a barrier allowing selective molecules into and out of the cell

Question 3

how many layers is the membrane and how is it arranged

Answer 3

two layers of phospholipids, hydrophilic phosphate groups facing outwards and hydrophobic tails inwards

Question 4

what is hydrophobic

Answer 4

molecule that is water hating

Question 5

what is hydrophilic

Answer 5

molecule water loving

Question 6

what is found between the lipids

Answer 6

proteins, glycoproteins, cholesterol

Question 7

what is a glycoprotein

Answer 7

protein joined to a carbohydrate

Question 8

what is the purpose of the membrane

Answer 8

membrane forms the external barrier and encapsulates sub cellular organelles
create a barrier for movement of molecules creating osmotic gradients and electrostatic gradients

Question 9

what is the composition of a phospholipid

Answer 9

• phosphate group
• 2 fatty acids
• glycerol

Question 10

why is there more than one type of phospholipid in the membrane

Answer 10

• have different structural and cellular roles eg signalling roles

Question 11

what is the role of cholesterol

Answer 11

• structural role and helps cluster membrane proteins together in cholesterol rich regions of the membrane called lipid rafts which help regulate function of membrane protein
• increases fluidity of membrane

Question 12

what do liquid rafts help with

Answer 12

help regulate function of membrane protein

Question 13

how can lipid rafts be disrupted and what can this result in

Answer 13

• rafts can be disrupted through diet high in cholesterol and alcohol
• this can alter protein function - implicated in Alzheimer disease

Question 14

what role do membrane proteins play and how are they classed

Answer 14

• play a role in structure and function of the membrane
• can be classed as extrinsic (just on surface)
• or intrinsic (spanning the membrane)
• or receptors - signalling molecule
• or membrane bound enzymes

Question 15

name the three phospholipids

Answer 15

• phosphatidylcholine (most common)
• phosphatidylethanolamine
• phosphatidylserine

Question 16

five functions and properties of phosphatidylcholine

Answer 16

• makes up most of the membrane
• mainly a structural component
• naturally form a bilayer
• kinked fatty acid tail therefore resulting in fluidity of membrane
• may have a role in signalling

Question 17

five functions and properties of phosphatidylethanolamine

Answer 17

• second most common membrane lipid
• mainly in inner leaflet
• does not form bilayer alone
• stabilises membrane structure
• hydrogen bonds form with proteins due to amine group

Question 18

what four mechanisms are used to regulate transport of molecules

Answer 18

• facilitated diffusion
• gated channels
• active transport
• diffusion

Question 19

how do diffusion and facilitated diffusion differ

Answer 19

• facilitated diffusion requires the presence of a protein

Question 20

what is diffusion and what two factors affect the rate of diffusion

Answer 20

• diffusion is the movement from a high to low concentration
• size and charge affect diffusion rate
  small uncharged polar molecules

Question 21

examples of molecules that can pass through the membrane

Answer 21

oxygen, water, lipids

Question 22

describe facilitative diffusion

Answer 22

• solute binds to protein
• protein changes shape allowing solute to move into the cell
• moving solute into cell
• no energy required

Question 23

how do gated channels work

Answer 23

• open and close by ligand binding
• proteins in membrane form a pore
• open and close in response to a stimuli
• move down a conc gradient

Question 24

what does active transport require and what are the two types of active transport

Answer 24

• requires atp

- primary and secondary active transport

Question 25

what is primary active transport

Answer 25

involves the pumping of a single solute against its concentration gradient

Question 26

what is secondary active transport

Answer 26

uses the electrochemical gradient by actively transporting one substrate to provide and electrochemical gradient to transport a different solute

Question 27

what is membrane anchors and what are they called

Answer 27

• many membrane proteins anchor a cell to its surrounding
• cells are surrounded by a mixture of proteins - ECM
• most anchors are called integrins

Question 28

what are membrane receptors and what do they do

Answer 28

• receptors are another class of membrane proteins
• membrane receptors binds specific molecules outside of the cell termed LIGANDS and translate this event via interactions with other proteins into signals within the cell, allowing cells to adapt and respond to changes in the environment

Question 29

name the most common receptors

Answer 29

• ion channel receptors
• heptahelical receptors
• kinase associated receptors

Question 30

where do the external signals come from

Answer 30

• autocrine (same cell)
• juxtacrine (neighbouring cell)
• paracrine (cell nearby)
• endocrine (distant cell elsewhere in body)

Question 31

ion channel receptors

Answer 31

• often bind neuropeptides

- binding causes conformational changes in associated ion channel

Question 32

hepthahelical receptors

Answer 32

• binding of signal to receptor causes intracellular changes
• often involves non protein ‘second messenger’
• this triggers signals to nucleus

Question 33

kinase associated receptors

Answer 33

• binding of single molecule causes phosphorylation of intracellular region
• triggers changes in other proteins - signal cascade

Question 34

what is major function of membrane bound enzymes

Answer 34

• catalyse reactions

- modifying function of other proteins