Cells - Cell Membranes

Question 2

What are the features of membranes?

Answer 2

• > regulate entry / exit of particles
• > has binding sites
• > confers antigenic properties to the cell
• > site of certain reactions
• > compartmentalises different cell reactions in organelles

Question 3

How do phospholipids affect cell membranes?

Answer 3

• > allows lipid soluble substances to enter and leave the cell by preventing water soluble substances from moving
• > makes membranes flexible and self sealing

Question 4

What molecules are present in the fluid mosaic model?

Answer 4

Phospholipids

Cholesterol

Glycolipids

Glycoproteins

Intrinsic and Extrinsic proteins

Question 5

What is the function of cholesterol in a membrane?

Answer 5

• > hydrophobic so pulls together phospholipid tails
• > adds strength and rigidity to the membrane (particularly at high temps)
• > reduces movement of other molecules

Question 6

What are the functions of glycolipids and glycoproteins in a membrane?

Answer 6

acts as recognition and binding sites

Question 7

Define a glycolipid

Answer 7

• > carbohydrate chain bound to lipids
• > lipid protein embedded in phospholipid bilayer, carbohydrate protein extends outside the cell

Question 8

Define a glycoprotein

Answer 8

• > carbohydrate chain bound to proteins
• > carbohydrate chain extends outside of the cell

Question 9

What are the 2 types of membrane proteins?

Answer 9

Intrinsic and Extrinsic

Question 10

What is the difference between intrinsic and extrinsic proteins?

Answer 10

Intrinsic proteins span throughout the membrane whereas extrinsic proteins are on the surface of the membrane

Question 11

What are the functions of intrinsic proteins?

Answer 11

To act as channel and carrier proteins

Question 12

What are the functions of extrinsic proteins?

Answer 12

to act as receptors or enzymes may have carbohydrates bound to them (eg glycoproteins)

Question 13

Define diffusion

Answer 13

The net movement of molecules with a concentration gradient

Question 14

What is the difference between diffusion and facilitated diffusion through a cell membrane?

Answer 14

• > facilitated diffusion relies on kinetic energy of molecules
• > facilitated has to happen through transmembrane channels and carriers

Question 15

What is the function of protein channels in facilitated diffusion?

Answer 15

• > water filled hydrophilic channels
• > allows specific water soluble ions to pass through
• > remains closed unless specific ions are present

Question 16

What is the function of carrier proteins in facilitated diffusion?

Answer 16

• > molecule has to be specific to the protein
• > molecule binds to protein which causes it to change shape and then is released
• > only uses kinetic energy of molecules

Question 17

Define osmosis

Answer 17

The passage of water molecules from a higher to lower water potential through a partially permeable membrane

Question 18

Define water potential

Answer 18

The quantified version of osmosis

100% pure water has a water potential of 0

anything else is negative

represented as Ψ > 0

measured in units of pressure (kPa)

Question 19

What are the 3 types of water potential in plant cells?

Answer 19

Hypotonic cells are turgid

Hypertonic cells are plasmolyzed

Isotonic cells are flaccid

Question 20

What are the 3 types of water potential in animal cells?

Answer 20

Hypotonic cells undergo lysis

Isotonic cells are isotonic

Hypertonic cells undergo crenation