The structure and function of membrane 5.1

Question 1

what is compartmentalisation and why is it important

Answer 1

the formation of seperate membrane-bound areas in a cell is called compartmentalisation

Compartmentalisation is vital to a cell as metabolism includes many different and often incompatible reactions. Containing reactions in separate parts of the cell allows the specific conditions required for cellular reactions, such as chemical gradients, to be maintained and protects vital cell components

Question 2

what is the plasma membrane

Answer 2

All the membranes in a cell have the same basic structure. The cell surface membrane which separates the cell from its external environment is known as the plasma membrane

Question 3

what is the structure of the plasma membrane

Answer 3

Membranes are formed from a phosphoplipid bilayer.
The hydrophilic phosphate heads of the phospholipids form both the inner and outer surface of a membrane, sandwiching the fatty acid tails of the phospholipids to from a hydrophobic core inside the membrane

Question 4

explain the fluic-mosaic model

Answer 4

the phospholipids are free to move within the layer relative to each other (they are fluid), giving the membrane flexibility and because the proteins embedded in the bilayer vary in shape, size and position (in the same way as the tiles of a mosaic)

the movement of the phospholipids in a membrane causes the movement of the other components

Question 5

what are the 2 types of membrane protein

Answer 5

intrinsic and extrinsic proteins

Question 6

what are the 2 different types of intrinsic proteins and what are their main difference

Answer 6

channel protein (passive), carrier protein (active or passive)

Question 7

where would you find intrinsic proteins

Answer 7

intrinsic proteins , or integral proteins are transmembrane proteins that are embedded through both layers of a membrane.

Question 8

what is the structure of intrinsic proteins

Answer 8

• intrinsic meaning within the cell membrane
• contain amino acids with hydrophobic R-groups on their external surfaces,
• ^these interact with the hydrophobic core of the membrane, keeping them in place

Question 9

what is the structure of a channel protein molecule and how does it help it carry out its function

Answer 9

Channel proteins provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes.
They are held in position by interactions between the hydrophobic core of the membrane and they hydrophobic R-groups on the outside of the proteins

Question 10

what type of cell-surface protein is a glycoprotein and what gives them the name ‘glyco’ proteins

Answer 10

Glycoproteins are intrinsic proteins
they are proteins with carbohydrates groups attached

Question 11

what is the function of glycoproteins

Answer 11

cell adhesion (cells join together) and as receptors for chemical signals

Question 12

what is the process of cell signalling

Answer 12

• a chemical binds to a receptor,
• ^this elicits a response from the cell.
• This may cause a direct response or set off a cascade of events inside the cell.

Question 13

give some examples of cell signalling within the body

Answer 13

hormonal and nerve vommunication

Question 14

what are glycolipids and what are the function

Answer 14

lipids with carbohydrates (sugar) chains.
function as cell markers or antigens to help the immune system with self recongintion

Question 15

what are extrinsic proteins and where can they be found

Answer 15

Extrinsic proteins or peripheral proteins are present in one side of the bilayer.
They normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins.
They can be present in either layer and some move between layers

Question 16

what is the structure of cholesterol and what is its function

Answer 16

cholesterol is a lipid with a hydrophilic end and a hydrophobic end, like a phospholipid. It regulates the fluidity of membranes

Question 17

where do you find cholesterol molecules and explain the biology of how they complete their function

Answer 17

cholesterol molecules are positioned between phospholipids in a membrane bilayer, with the hydrophilic end interacting with the heads and the hydrophobic end interacting with the tails, pulling them together.
In this way cholesterol adds stability to membranes without making them too rigid.
The cholesterol molecules prevent the membranes becoming too solid by stopping the phospholipid molecules from grouping too closely and crystallising

Question 18

GIve an example of a chemical reaction that involves cell-surface membrane proteins

Answer 18

The electron carriers and the enzyme ATP synthase have to be in the correct positions within the Cristae (inner membrane of mitochondrion) for the production of ATP in respiration.
The enzymes of photosynthesis are found on the membrane stacks within the chloroplasts