The Endomembrane System

Question 1

Cell Homeostasis

Answer 1

The membrane maintains the internal equilibrium of the cell by controlling entry to and exit from the cell.

Question 2

Functions Of The Cell Membrane

Answer 2

Transport processes
Protective barrier/boundary
Cell-cell communication
Cellular signalling
Signal conduction
Cell to cell recognition
Cell Shape

Question 3

cell to cell recognition

Answer 3

some glycoproteins in the plasma membrane act as identification tags that are specifically recognised by membrane proteins to other cells.

Question 4

Fluid-Mosaic Model

Answer 4

FLUID = individual phospholipids and proteins can move side-to-side within the layer, like its a liquid.

MOSAIC = the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Question 5

Lipid Bilayer

Answer 5

2 layers of phospholipids

Question 6

Hydrophobic

Answer 6

molecules pass through easily

Question 7

Hydrophilic

Answer 7

molecules do not pass through easily

Question 8

Structural Components

Answer 8

Lipids:
1. Phospholipids
2. Cholesterol
3. Glycolipids

Proteins:
1. Integral (involved in cell transport)
2. Peripheral

Question 9

Cholesterol

Answer 9

Cholesterol is an amphiphatic molecule with a polar head which attaches to the polar part of phospholipids and its function is to stiffen the plasma membrane.

Made up of four rings of hydrogen and carbon atoms.

They strengthen the membrane by preventing some small molecules from crossing it.

Cholesterol molecules also prevent the phospholipid tails from coming into contact and solidifying.

This ensures that the cell membrane stays fluid and flexible.

Question 10

Glycolipids

Answer 10

are molecules which have a fatty acid tail and a carbohydrate head (chains of sugars) and their function is in cell to cell recognition and communication.

play in humans is their contribution to blood type.
There are 4 main blood types: A, B AB and O, and this variation stems from the different glycolipids present on the surface of red blood cells (erythrocytes)

Question 11

Integral Proteins

Answer 11

these proteins have one or more hydrophobic regions with an affinity for the hydrophobic interior of the lipid bilayer.

these proteins are embedded in the membrane and cannot be easily removed.

generally transport proteins:
Channel proteins
Carrier proteins

Question 12

Peripheral Proteins

Answer 12

these proteins lack hydrophobic sequences and therefore do not penetrate the lipid bilayer.

instead they associate with the membrane surfaces and through weak electrostatic forces.

they bind either to the polar heads of the membrane lipids or the hydrophilic portions of the integral proteins that extend out of the membrane.

Question 13

Carrier Proteins

Answer 13

bind solute on one side of membrane, deliver it to other side by conformational change in protein (turnstile)

Question 14

Channel Proteins (Ion Channels)

Answer 14

form hydrophilic pores in membrane through which solutes (mainly ions) can diffuse (trapdoor)

Question 15

Passive transport

Answer 15

does not require energy

It occurs because of the tendency for dissolved molecules to move or diffuse from higher to lower concentrations.

passive transport can be divided into two types:
Simple diffusion
Facilitated diffusion

Question 16

Simple Diffusion

Answer 16

whereby molecules move from a region of higher concentration to a region of lower concentration.

Question 17

Facilitated Diffusion

Answer 17

whereby molecules depend on specialised membrane proteins to aid the passage of ions or polar molecules across the hydrophobic interior of the membrane.

Question 18

Active transport

Answer 18

Does require the input of energy.

Active transport moves solutes against their concentration gradient which require work.

because of the energy input , active transport can result in the generation of a concentration gradient across the membrane.

Question 19

pumps

Answer 19

special membrane proteins

Question 20

Coupled transport

Answer 20

ATP-powered pump that transports a specific solute can indirectly drive the active transport of several other solutes across the membrane.

Question 21

two types of co-transport

Answer 21

Symport
Antiport

Question 22

Symport coupled transport

Answer 22

molecules move in the same direction across the membrane.

Question 23

Antiport coupled transport

Answer 23

molecules move in opposite directions across the membrane.

Question 24

example of Symport

Answer 24

Glucose and sodium from outside to inside the cell.

Question 25

example of antiport

Answer 25

Sodium potassium pump to pump sodium outside the cell and pump potassium into the cell.

Question 26

Endomembrane system

Answer 26

the organelles that are ‘connected’ (tangibly or via transport) together by phospholipid membranes.

Question 27

compartmentalisation

Answer 27

allows different places in the cell to have different environments.