Unit 1: Membranes

Question 1

Name some functions of membranes

Answer 1

provide selectively permeable barriers
compartmentalisation
localising reactions in the cell
transport of solutes
signal transduction

Question 2

what is a membrane?

Answer 2

fluid bilayer of phospholipids with an interspersed mosaic of proteins

Question 3

what is the purpose of the hydrophobic centre of the phospholipid bilayer?

Answer 3

forms a barrier to the passage of polar molecules and ions

Question 4

How does cholesterol alter membrane fluidity?

Answer 4

the structure of cholesterol - OH is hydrophilic and four rings are hydrophobic - reduces fluidity at warmer temperature but it prevents crystallisation at low temperature
cholesterol breaks up van der waals and the close packing of phospholipid tails

Question 5

what is a peripheral (extrinsic) protein?

Answer 5

those that are easily removed from the membrane on the lab using ionic washes

Question 6

how are peripheral proteins held in membrane?

Answer 6

on the surface held by charged or polar amino R groups

Question 7

what are Integral (intrinsic) proteins?

Answer 7

cannot be washed from the membrane in the lab as they are firmly in place in the membrane by strong hydrophobic interactions with lipids tails

Question 8

give the two types of integral proteins

Answer 8

transmembrane or embedded in one side of the bilayer only

Question 9

what are glycoproteins?

Answer 9

proteins with a carbohydrate chain

Question 10

what are glycolipids?

Answer 10

phospholipids with a carbohydrate chain

Question 11

name functions of membrane proteins

Answer 11

passive transport proteins
active transport proteins
enzymes
receptor proteins
attachment proteins
cell recognition proteins
structural proteins

Question 12

what does the term crenated mean?

Answer 12

when an animal cell is placed in hypertonic solutions and it shrinks

Question 13

what does plasmolysis mean?

Answer 13

when a plant cell is placed in hypertonic solutions and the cell contents pulls away form cell wall

Question 14

What are passive transport proteins?

Answer 14

They are transmembrane (integral) proteins that transport molecules across the membrane down a concentration gradient

Question 15

why do channel proteins have a pore?

Answer 15

to facilitate or speed up diffusion

Question 16

what is a passive carrier protein?

Answer 16

bind to specific molecules to allow the passage of molecules across the membrane

Question 17

what are active transport proteins?

Answer 17

they pump ions and molecules against a concentration gradient and requires energy (ATP)

Question 18

what provides the energy for active transport proteins?

Answer 18

hydrolysis of ATP for the phosphorylation and conformational change of protein pump

Question 19

what is the function of a receptor protein?

Answer 19

they are in the plasma membrane, hydrophilic signalling molecules cannot cross hydrophobic regions in membrane, when there is a signal, the receptor proteins respond within the cell -

Question 20

what are attachment proteins?

Answer 20

provide cytoskeleton attachment points within the membrane for the structural support of the cell

Question 21

what is cell to cell recognition?

Answer 21

distinguishing between own cells and the cells of another organism by its ability to recognise glycoproteins (antigenic markers). to do with the different carbohydrate chains on the glycoprotein

Question 22

what are the three main types of cell junction in animal cells?

Answer 22

spot desmosome, tight junction and gap junction

Question 23

plants have one type of cell junction, what is it?

Answer 23

plasmodesmata

Question 24

what is a spot desmosome?

Answer 24

dense deposits of protein holding adjacent cells together

Question 25

what is a tight junction?

Answer 25

adjacent membrane proteins bonded together preventing passage of materials in spaces between cells

Question 26

what is a gap junction?

Answer 26

doughnut shaped proteins from each cell join together to form tiny channels allowing passage of small molecules

Question 27

what is plasmodesmata?

Answer 27

channels lined by cell membrane bridging the gap between cells

Question 28

what does the rate of diffusion depend on?

Answer 28

the size of the molecule and its solubility. the more hydrophobic and the smaller, the faster the rate of diffusion

Question 29

what is passive diffusion?

Answer 29

molecules are lipid soluble and pass straight through the phospholipid bilayer

Question 30

what is facilitated diffusion?

Answer 30

molecules are dependent on a carrier protein to allow its passage through a membrane