Module 2-Bio membranes

Question 1

What is the fluid mosaic model?

Answer 1

-describes the structure of the plasma membrane as a mosaic of phospholipids, cholesterol, proteins and carbohydrates
-the phospholipid bilayer forms the fluid part
-the mosaic part is made of proteins, carbs, lipids that punctuate the membrane

Question 2

Definition of the plasma membrane

Answer 2

-defines the border of cells
-is partially permeable as some materials can move freely whereas others can not.

Question 3

Describe the structure of the phospholipid

Answer 3

-molecule consisting of glycerol, 2 fatty acid tails and a phosphate linked head group
-these molecules arrange themselves in a bilayer which range from 5-10 nm in thickness
-the hydrophilic head faces outwards and hydrophobic tails face inwards.

Question 4

Structure of cholesterol

Answer 4

lipid that is found in the core of the membrane and makes it more rigid

Question 5

Structure and function of membrane bound proteins

Answer 5

large molecules embedded in the bilayer that can form open pores that allow the diffusion of large molecules across the bilayer.

Question 6

Function of transport proteins

Answer 6

bind to specific molecules and carry them across the membrane

Question 7

Function of ATP synthase

Answer 7

membrane bound protein that catalyses the production of ATP

Question 8

Functions of glycolipids and glycoproteins

Answer 8

-some are able to form hydrogen bonds with water molecules surrounding the cell which helps to stabilise the membrane
-other glycolipids and glycoproteins act as cell signalling receptors and have active binding sites for communication molecules e.g hormones

Question 9

How does temperature affect the permeability of membranes?

Answer 9

High temperatures increase the fluidity of the membrane therefore increasing its permeability. Phospholipids in a cell membrane are constantly moving so whenm the temperature is increased the phospholipids will have more kinetic energy and will move more causing the membrane to lose its structure becoming more fluid. This makes it easier for particles to cross it.

Question 10

How can you keep the temperature constant in an experiment?

Answer 10

by using a water bath

Question 11

How do solvents affect the permeability of membranes?

Answer 11

solvents that are less polar than water dissolve membranes making it more fluid and permeable

Question 12

Method for investigating cell membrane permeability

Answer 12

-beetroot is often used as a model as the release of the coloured pigment is easy to quantify using colorimetry
1)use a cork borer to collect samples of a uniform diameter
2)cut discs of uniform depth using a sharp knife on a white tile and rinse in cold water. this removes excess pigment that has leaked through physically broken cell membranes
3)prepare at least 5 concentrations of ethanol(e.g 0%, 20%, 40%, 60% 80%)
4)place the discs in the corresponding solution for 10 mins and mix frequently
5)remove the discs from the solutions and calibrate the colorimeter
6)measure absorbance of each concentrations and plot the data on a graph

Question 13

How can solvent concentration be controlled?

Answer 13

by using the same solvent at the same concentration for each trial.

Question 14

What is simple diffusion?

Answer 14

the net movement of particles from an area of high concentration to an area of low concentration
-passive movement of particles in fluids
-molecules move randomly but tend to move to any space available until its evenly distributed
-movement is down a concentration gradient

Question 15

What is facilitated diffusion?

Answer 15

-molecules diffuse through carrier proteins or channel proteins across a membrane
-channel proteins allow polar compounds to avoid the non polar central layer of the plasma membrane
-when a substance binds to carrier proteins there is a change in the shape of carrier proteins which moves the substance from outside the cell to inside the cell.
-because these materials are too large to move through the membrane or they are polar molecules that are repelled by the hydrophobic part of the membrane
-describes the net movement of particles from an area of high to lower concentration.
-is passive so doesn’t require energy

Question 16

What are aquaporins?

Answer 16

channel proteins that allow water to pass through the membrane

Question 17

How does concentration gradient affect the rate of diffusion?

Answer 17

the bigger the difference in concentration between 2 areas, the greater the concentration gradient and the faster the rate of diffusion because the overall movement from the higher to the lower concentration will be larger

Question 18

How does temperature affect the rate of diffusion?

Answer 18

the higher the temp the faster the rate of diffusion as the particles have more kinetic energy and therefore can move at higher speeds.

Question 19

How does membrane surface area affect the rate of diffusion?

Answer 19

the larger the SA the faster the rate of diffusion as there is more space for particles to move through at one time.

Question 20

How does the thickness of the exchange surface affect the rate of diffusion?

Answer 20

the thicker the exchange surface the slower the rate of diffusion.

Question 21

How does the concentration of channel or carrier proteins affect the rate of diffusion?

Answer 21

the higher the concentration the faster the rate of facilitated diffusion until an equilibrium is reached and the rate will level off

Question 22

What is active transport?

Answer 22

-uses energy from respiration
-dissolved molecules move from a less concentrated solution to a more concentrated solution
-in charge of moving ions and molecules across a partially permeable membrane against the concentration gradient

Question 23

What are 2 examples of active transport?

Answer 23

1)active transport allows glucose to be absorbed into the blood from the gut even when the glucose concentration of the blood is higher
2)active transport in the root hairs of plants allows plants to absorb mineral ions even though the concentration is lower in the soil than the hair.

Question 24

What factors affect the rate of active transport?

Answer 24

-SA or cell membranes
-number of carrier proteins in cell membranes

Question 25

What is exocytosis?

Answer 25

-when membrane bound vesicles fuse with plasma membranes before releasing the substances within them into their surroundings
-process used by cells when they have produced a substance that needs to be exported and when there are toxins that need to be removed from the cell
active process so needs ATP

Question 26

What is endocytosis?

Answer 26

-is when a cell engulfs a substance from its surroundings
-achieved by the fluid cell membrane folding around the substance
-at this point the substance will separate from the membrane and enter into the cytoplasm in a membrane bound vesicle
-active process so needs ATP

Question 27

Describe the process of active transport

Answer 27

1)the molecule/ion to be transported binds in receptors in the channel or carrier protein and is hydrolysed into ADP and phosphate
2)binding of the phosphate molecule to the carrier protein causes the carrier protein to change shape opening up the inside of the cell
3)the molecule or ion is released inside the cell
4)the phosphate molecule is released from the carrier protein and recombines with ADP to form ATP
5)the carrier protein returns to its original shape