Unit 2 - Plasma membranes

Question 1

State 4 functions of plasma membranes

Answer 1

Options:
-recognition of other cells
-separates cell contents from the outside (barrier between cells and its environment)
-controls the passage of materials in and out
-allow cell communication
-phagocytosis
-cell to cell attachment

Question 2

State 4 functions of membranes inside cells

Answer 2

Options:
-isolates DNA
-acts as an intracellular transport system
-compartmentalises reactions
-can be the site of chemical reactions
-ribosomes attach
-protection from lysosomes
-forms vesicles

Question 3

Define semi-permeable

Answer 3

A membrane that allows some substances to cross but not others

Question 4

Define cell signalling

Answer 4

A complex system of intercellular communication

Question 5

Define phospholipid bilayer

Answer 5

-arrangement of phospholipids found in cell membranes
-the hydrophilic phosphate heads form the inner and outer surface of a membrane ,
-sandwhiching the fatty acid tails to form a hydrophobic core

Question 6

Why are membranes referred to as having a ‘fluid-mosaic structure’ ?

Answer 6

-the phospholipids are able to move freely relative to each other (fluid)
-the proteins embedded in the bilayer vary in shape, size, and position (mosaic)

Question 7

Define glycoprotein

Answer 7

Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes

Question 8

Define glycolipid

Answer 8

Cell-surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes

Question 9

Define phospholipid

Answer 9

Modified triglycerides, where one fatty acid has been replaced with a phosphate group

Question 10

What are channel proteins?

Answer 10

Membrane proteins that provide a hydrophilic channel through a membrane

Question 11

What are receptor proteins?

Answer 11

Extrinstic glycopoteins that bind chemical signals, triggering a response by the cell

Question 12

What are carrier proteins?

Answer 12

Membrane proteins that play a part in the transport of substances through a membrane

Question 13

What are the functions of cholesterol in cell surface membranes?

Answer 13

-regulates fluidity and adds stability to membranes
-prevents phospholipids from crystallising

Question 14

What are the functions of phospholipids in cell surface membranes?

Answer 14

-forms basic structure
-acts as partially permeable barrier
-allows the passage of lipid soluble molecules
-prevents water soluble molecules from moving across

Question 15

What are the functions of glycoproteins in cell surface membranes?

Answer 15

-receptors for chemical signals
-cell adhesion
-when chemical binds to the receptor, events inside the cell are set off
-binding sites for chemical e.g hormones
-Hydrogen bonds to water to stabilise membrane

Question 16

What are the functions of glycolipids in cell surface membranes?

Answer 16

-act as antigens that can be recognised by the immune system
-form hydrogen bond with water molecules to stabilise membrane

Question 17

What are the functions of carrier proteins in cell surface membranes?

Answer 17

-have an important role in both passive movement of polar molecules and ions down a concentration gradient
-this involves the shape of the protein changing

Question 18

What are the functions of channel proteins in cell surface membranes?

Answer 18

-provide a hydrophillic channel that allows passive movement of polar molecules and ions down a concentration gradient

Question 19

Define cell adhesion

Answer 19

The process by which cells make contacts with each other

Question 20

Describe 2 ways in which cholesterol regulates membrane fluidity

Answer 20

-hydrophillic end of cholesterol interact with phosphate heads
-hydrophobic end of cholesterol interacts with fatty acid tails
-pulling the phospholipids together
-prevents membranes from becoming too solid and crystallising by preventing the phospholipids from getting too close together

Question 21

What 3 factors affect membrane structure?

Answer 21

Temperature
Solvents
Cholesterol

Question 22

How does an increase in temperature affect cell membranes?

Answer 22

-increases membrane fluidity
-increases membrane permeability
-carrier and channel proteins are denatured at higher temperatures
-membrane loses its structure

Question 23

Why does an increase in temperature increase membrane permeability?

Answer 23

-more temperature means phospholipids move more
-because they have a higher kinetic energy
-makes it easier for things to pass through