1.3: Membrane Structure

Question 1

Chemical Composition of Membranes

Answer 1

Lipids
Proteins

Question 2

Three types of lipids found in cell membranes:

Answer 2

Phospholipids
Glycolipids
Cholesterol

Question 3

Phospholipids

Answer 3

Have 2 fatty acid chains bound to the glycerol
Have a phosphate group covalently bound to the third hydroxyl of the glycerol

Question 4

Phosphate group

Answer 4

The head
Hydrophilic
Polar

Question 5

Fatty Acid

Answer 5

The tail
Hydrophobic
Non-polar

Question 6

Glycolipid

Answer 6

lipid molecules with short chains of carboydrates attached to it

Question 7

Cholesterol

Answer 7

a steroid made up of a non-polar part comprising of a 4 ring structure and a hydrocarbon tail and a polar hydroxyl group

Question 8

The Fluid Mosaic Model

Answer 8

plasma membranes consist of phospholipid bilayers with proteins inside of it(bilayer) which makes it look like a mosaic

the hydrophilic (phosphate) heads face the water(cytoplasm)
the hydrophobic tails (fatty acids) are sandwiched in between

Question 9

Membrane proteins

Answer 9

2 types:
Integral(intrinsic)
Peripheral(extrinsic)

Question 10

Integral proteins

Answer 10

are amphipathic (they have hydrophobic and hydrophilic properties) and are embedded in the plasma membrane

Question 11

Peripheral proteins

Answer 11

Peripheral proteins are polar (hydrophilic) and are attached to the outside of the plasma membrane.

Question 12

Functions of membrane proteins

Answer 12

• channel proteins
  -carrier proteins
  -enzymes

Question 13

channel proteins

Answer 13

have a pore that allow polar molecules and ions to pass through the plasma membrane passively

Question 14

carrier proteins

Answer 14

bind to substances on one side of the membrane and then change shape to transport them to the other side

Question 15

enzymes

Answer 15

they catalyse various reactions
eg.
ATP synthase
digestive enzymes

Question 16

enzymes

Answer 16

they catalyse various reactions
eg.
ATP synthase
digestive enzymes

Question 17

recognition

Answer 17

certain proteins help the cell in differentiating between self and non-self cells

Question 18

recognition

Answer 18

certain proteins help the cell in differentiating between self and non-self cells

Question 19

receptors

Answer 19

allow cell signalling:
allow cells to relay information inside and outside the cell

Question 20

Functions of phospholipids

Answer 20

-hydrophobic tails act as a barrier to water-soluble molecules
-allow lipid-soluble substances to pass through easily by diffusion
-can be modified to act as signalling molecules to activate enzymes

Question 21

Functions of cholesterol

Answer 21

-restricts movement of phospholipids and other molecules which reduces membrane fluidity at high temperatures
-at low temperatures, it disrupts the regular packing of the hydrocarbon tails
-prevent ions/ polar molecules from passing through the membrane
-cholestero(mammalian membranes) reduces membrane fluidity and permeability of some solutes

Question 22

Functions of cholesterol

Answer 22

-restricts movement of phospholipids and other molecules which reduces membrane fluidity at high temperatures

-at low temperatures, it disrupts the regular packing of the hydrocarbon tails

-prevent ions/ polar molecules from passing through the membrane

-cholesterol(mammalian membranes) reduces membrane fluidity and permeability of some solutes

Question 23

Role of glycolipids

Answer 23

-the carbohydrate chains project like antennae into the watery fluid surrounding the cell and from hydrogen bonds with the water molecules to stabilize the membrane
-the chains help gltyolipids to act as receptor molecules
-act as cell markers/antigens=cell to cell recognition

Question 24

Role of glycolipids

Answer 24

-the carbohydrate chains project like antennae into the watery fluid surrounding the cell and from hydrogen bonds with the water molecules to stabilize the membrane

-the chains help glycolipids to act as receptor molecules

-act as cell markers/antigens=cell to cell recognition

Question 25

Davson Danielli Model

Answer 25

-The model was described as a ‘lipo-protein sandwich’, as the lipid layer was sandwiched between two protein layers

-The dark segments seen under electron microscope were identified (wrongly) as representing the two protein layers

Question 26

Falsification of the Davson Danielle Model

Answer 26

Freeze-etched micrographs

Structure of membrane proteins

Fluoroscent antibody tagging