the critical role of membranes

Question 1

what are the two types of membrane

Answer 1

1) plasma/cell
2) intracellular membranes of organelles

Question 2

what are the functions of cell membranes

Answer 2

1) to act as a permability barrier
2) organize organelle function
3) mediate transport processes
4) mediate interaction with external environment
5) cell-cell communication

Question 3

outline the function of acting as a permeability barrier

Answer 3

• it can control substances inside and outside the cell
  -compartmentalises specific functions

Question 4

outline how the cell membrane organises and localises functions

Answer 4

1) hosts essential cellular functions such as the ETC, photosynthesis and translocation
2) the membrane has functional proteins embedded which help exploit gradients allowing specific biochemical reactions

Question 5

outline how the cell membrane regulates transportation of solutes

Answer 5

1) passive transport such as simple diffusion, faciliated or osmosis
2) active transport processes
3) endo/exocytosis

Question 6

outline how the cell detects signals

Answer 6

1) the receptor binds to a molecule
2) the binding generates a secondary messenger
3) the secondary messenger alters gene expression and function= produces a response

Question 7

outline how the cell allows communication with other cells

Answer 7

1) joins cells of similar functions together
2) the cells connected allow component exchange e.g. plasmodesmata, septa and gap junctions

Question 8

what are the two types of membrane proteins

Answer 8

1) integral
2) peripheral

Question 9

what is an integral protein

Answer 9

1) proteins which span the membrane consisting of hydrophobic aminoacids, usually arranged in alpha helices allowing them to become embedded inside the membrane with hydrophili regions on the cytoplasmic face or outside

Question 10

what are peripheral proteins

Answer 10

proteins which only have contact with the membrane temporarily and are easily removed, this allows cell signalling

Question 11

what are the main components of plasma membranes

Answer 11

1) phosopholipids
2) sphingolipids
3) glycolipids
4) membrane proteins
5) sterols

Question 12

what are the features of a phospholipids

Answer 12

1) amphipathic= both hydrophilic and phobic
2) self -assemble into bilayers in water
3) formation of micelles in water

Question 13

what is a micelle

Answer 13

occurs when lipid molecules arrange themselves into a spherical form in aqueous solutions

Question 14

what is the composition of a phospholipid

Answer 14

1) one glycerol molecule
2) 2 fatty acid non-polar tails
3) 1 phosphate group

Question 15

what are the properties of biological membranes

Answer 15

1) frequent lateral movement
2) increased phospholipid movement leads to increased fluidity
3) high levels of unsaturated acids tails prevent molecular packing
4) cholesterol reduces fluidity

Question 16

what is the fluid mosaic model

Answer 16

describes cell membranes as a tapestry of several types of molecules which are constantly moving. This movement helps the cell membrane to maintain its role as a barrier inside and outside the cell

Question 17

outline the process of phosphlipid synthesis

Answer 17

1) membrane proteins have N-terminal sequences which direct ribosomes to the ER membrane
2) attachment of the signal recognition particle
3) ribosomes dock on a protein complex
4) polypeptide synthesis starts
5) a signal peptide is cleaves
6) full synthesis
7) folding

Question 18

what are the three transmembrane proteins in the cell membrane which mediates transport

Answer 18

1) ATP powered pumps
2) ion channels
3) protein transporters

Question 19

outline an ATP powered pump

Answer 19

• uses the energy released by ATP hydrolysis to power the movement of specific ions or small molecules against a gradient
  = active transport

Question 20

outline ion channels

Answer 20

protein channels which allow the movement of specific ions or hydrophilic molecules down their electrochemical gradient via facilitated diffusion in responce to a specific chemical or electrical signal

Question 21

what are the tree types of protein transporters

Answer 21

1) uniporters
2) symporters
3) antiporters

Question 22

what is a uniporter

Answer 22

a protein transporter which transports a single molecule down a conc gradient

Question 23

outline how a uniporter works

Answer 23

1) binding of a molecule to outward facing site
2) this triggers a conformational change resulting in binding site facing inwards to cystol
3) molecule then released inside the cell
4) transporter undergoes the reverse conformational change

Question 24

what is a symporter

Answer 24

a protein transporter which transports molecules and ions in the same direction

Question 25

outline how a symporter works

Answer 25

1) simultaneous binding of molecules to the outwards facing binding site
2) causes a conformational change resulting in an inward facing site
3) dissociation of bound molecules allows it to revert back to original outward facing conformation

Question 26

what is an antiporter

Answer 26

a protein transporter which transportes molecules and ions in the opposite direction

Question 27

outline how an antiporter works

Answer 27

1) one molecule bind to the outward facing state causing it to switch to an inward facing state
2) on the inside the bound molecule is exchanged for a different one and the protein carrier reverts to outwards facing state

Question 28

what is a vesicle

Answer 28

a self-contained structure consisting of fluid or gas surrounded by an outer membrane

Question 29

what is endocytosis

Answer 29

the pinching off of the plasma membrane to form vesicles

Question 30

what is exocytosis

Answer 30

the fusion of vesicles with the plasma membrane discharging contents into the extracellular space