Physiology: What is a Membrane

Question 1

what are the functions of a cell membrane (5)

Answer 1

• forms outer boundary of cell
• controls entry of nutrients, exit of waste and secretory products
• maintains ion conc. in and out cell
• enables cell to respond to signals
• part of joining cells to form tissues/organs

Question 2

what is a membrane made of

Answer 2

• phospholipids
  
  • -ve polar hydrophilic head
  • +ve non-polar hydrophobic tail

Question 3

what is the lipid bilayer impermeable to

Answer 3

water-soluble molecules

Question 4

what is allowed to cross the membrane (without transport)

Answer 4

small uncharged molecules

Question 5

what are the 3 important functions of the lipid bilayer

Answer 5

• basic structure of the membrane
• hydrophobic interior acts as a barrier
• membrane fluidity and selective permeability

Question 6

describe a peripheral protein

Answer 6

not embedded in the membrane but adhered to the cytoplasmic or extracellular membrane surfaces

Question 7

describe the 3 ways an integral protein is associated with the bilayer

Answer 7

• span membrane (1+ times) - transmembrane
• embeddedbut doesnt cross bilayer
• linked to a lipid component to fatty-acid derivative

Question 8

what are the 7 functions of integral proteins

Answer 8

• ligand-binding receptors
• adhesion molecules
• pores and channels
• carriers
• pumps
• enzymes
• participate in intracellular signalling

Question 9

how do intgeral proteins act as adhesion molecules and why is this important

Answer 9

• forms contact with extracellular matrix or cellular neighbours
• important in regulating cell shape, growth and differentiation

Question 10

what is the function of pores and channels

Answer 10

passive movement of watwr/specific ions

Question 11

what is the function of carrier proteins

Answer 11

facilitate transport of a specific molecule or couple transport of a molecule to other solutes

Question 12

what is the function of protein pumps

Answer 12

use energy from ATP to drive transport in/out against a gradient

Question 13

where are dicking-marker receptors and what is their function

Answer 13

• on inner membrane surface

- interact with secrtory besicles leading to exocytosis of the vesicles contents

Question 14

where do membrane carbohydrates reside

Answer 14

on outer surface of cells often bound to membrane proteins and sometimes lipids

Question 15

when a membrane carbohydrate is bound to a protein/lipid what is it called

Answer 15

glycoprotein/glycolipid

Question 16

glycoproteins and glycolipids together form a layer called what

Answer 16

glycocalyx

Question 17

what is the function of glycolipids

Answer 17

act as self identity markers

- important in cell to cell interactions and play a role in tissue growth

Question 18

what is the role of glycolipids in tissue growth and what is the exception to this

Answer 18

• ensures cells dont overgrow their territory

- cancer cells are the exception as they have abnormal markers

Question 19

what are the 3 types of specialised cell junctions

Answer 19

• tight junctions
• desmosomes
• gap junctions

Question 20

function of tight junctions and what are the 2 types

Answer 20

join lateral edges of epithelial cells near apical membranes
- tight or leaky

Question 21

function of desmosomes

Answer 21

adhering junctions that anchor cells together especially in tissues subject to stretch

Question 22

function of gap junctions

Answer 22

communicating junctions - allow movement of charge carrying ions and small molecules between adjacent cells