Structure and function of the cell membrane. Transport of substances through the cell membrane basic characteristics of the transport processes

Question 1

intro

Answer 1

cell membrane is also known as plasma-membrane

cell membrane is composed of phospholipid bilayer, proteins, cholesterol and carbohydrates

Question 2

phospholipid bilayer

Answer 2

1) hydrophilic head - water attracting
hydrophobic tail - water repelling
- amphipathic = form bilayer in aqueous solution

2) bilayer forms semi-permeable membrane allowing selective entry in/out of cell
- large polar ions not allowed e.g. ions/ proteins/ polysaccharides
- small uncharged ions ions (e.g. water)

Question 3

proteins

Answer 3

integral proteins - span the whole membrane, involved in receptor, channel, carrier formation

peripheral proteins - span only one side of membrane, involved in signal transduction

Question 4

cholesterol (3)

Answer 4

located inbetween the phospholipid bilayer components

hydrophobic tail interacts with fatty acid tail of bilayer

hydroxyl head interacts with hydrophilic head of bilayer forming hydrogen bonds

Question 5

cholesterol function 1

Answer 5

1 - membrane fluidity during temperature change

• high temperatures - cholesterol increases MP of bilayer to prevent leakage
• low temperature - cholesterol decreases MP of bilayer to prevent crystallisation

Question 6

cholesterol function 2

Answer 6

2 - membrane stability during hyper-movements

• structural support of bilayer

Question 7

carbohydrates

Answer 7

GLYCOLIPID = carbohydrate with lipid chain attatched = covalent bond
example = sphingomylein
function cell communication
- immune cells can ID foreign cells vs own body cells
- blood group type recognition

GLYCOPROTEIN = carbohydrate with protein chain attatched = covalent bond
exampe = collagen
function = cell adhesion

Question 8

list functions of cell membrane

Answer 8

selective permeability
protection
communication by receptors
cell adhesion

Question 9

function - selective permeability

Answer 9

• controlling what enters/ exit cell -> enters = O2 / exits = CO2
• aiding transport of substances in/ out of cell
• maintain cell internal environment - homeostasis

Question 10

function - protection

Answer 10

chemical barrier = prevents chemical imbalance of ICM-ECM

physical barrier = prevents damages to ICM-ECM

Question 11

function - communication by receptors

Answer 11

receives + responds to signals from ECM e.g. hormones, neurotransmitters

signal transduction by initiating intracellular cascade events which allows cell to adjust to changes in environment

Question 12

function - cell adhesion

Answer 12

to cells
- proteins adhere to other cells to form tissues/ organs

to ECM
- cells bind to structures in ECM for structural support

Question 13

list type of transport

Answer 13

passive
active
bulk

Question 14

types of passive transport

Answer 14

simple diffusion
facilitated diffusion
osmosis

Question 15

passive transport facts (2)

Answer 15

• does not rely on energy from cell
• relies on concentration gradient of substance to move them

Question 16

simple diffusion

Answer 16

high to low conc

• direct
• constant
• e.g. small/ nonpolar molecules - o2/co2

Question 17

facilitated diffusion

Answer 17

high conc. to low conc.
- carrier proteins
- channel proteins

example - glucose via GLUT transporers

Question 18

osmosis

Answer 18

low to high conc
- partially permeable membrane
- e.g. water entering cells