Transport Across Membranes

Question 1

explain the fluid-mosaic model of the cell surface membrane

Answer 1

• the cell membrane consists of proteins, glycoproteins, phospholipids, carbohydrates and cholesterol
• the phospholipid molecules form a double bilayer and the molecules that it consists of are constantly moving
• the protein molecules are unevenly distributed throughout the membrane, forming a mosaic

Question 2

explain the structure of channel proteins and its function

Answer 2

• they have a specific tertiary structure that spans the membrane and makes hydrophilic tunnels across it
• these channels are selective and will accept only one type of molecule

Question 3

explain what carrier proteins structure is and their function

Answer 3

• they have a specific tertiary structure and allow the transport of ions and polar molecules by facilitated diffusion and active transport
• carrier proteins can change their shape to move a target molecule from one side of the membrane to the other

Question 4

explain the receptors function in the cell surface membrane

Answer 4

• there is specific receptors for hormones with a complementary shape
• hormones attach to binding sites on the receptors

Question 5

explain the structure and function of glycolipids

Answer 5

• they are composed of carbohydrates attached to a phospholipid
• they are important in cell recognition

Question 6

explain the structure and function of glycoproteins

Answer 6

• they are composed of carbohydrates and protein
• they are important in cell recognition and sometimes act as antigens

Question 7

explain the role of cholesterol on the cell surface membrane

Answer 7

• cholesterol decreases permeablity and increases the stability of the membrane by restricting the movement of other molecules

Question 8

what is the equation to calculate diffusion rate

Answer 8

surface area x concentration gradient / diffusion distance

Question 9

explain simple diffusion

Answer 9

• passive process
• diffusion is the net movement of molecules from a higher concenration to a lower concentration until evenly distributed

Question 10

give 4 factors that affect the rate of diffusion

Answer 10

1. temperature
2. surface area
3. concentration gradient
4. diffusion distance

Question 11

explain how temperature affects diffusion

Answer 11

• increases kinetic energy
• faster movement of molecules

Question 12

explain how surface area affects diffusion

Answer 12

• more cell surface membrane for molecules to pass through
• therefore faster diffusion

Question 13

explain how concentraion gradient affects diffusion

Answer 13

• as concentration gradient increases the rate of diffusion becomes faster

Question 14

explain how diffusion distance affects diffusion

Answer 14

• the thinner the distance, the faster the rate of diffusion

Question 15

explain the process of facilitated diffusion

Answer 15

• polar molecules cannot pass between the hydrophobic tails of the phospholipid bilayer
• therefore, to enter or exit the cell the molcules have to move through the membrane by channel proteins or carrier proteins
• these proteins have a specific tertiary structure and only transport molecules that have complementary shapes to their binding sites
• passive process

Question 16

explain what omsosis is

Answer 16

• the net movement of water molecules from higher water potential to a solution with lower water potential through a partially permable membrane
• as water is a polar molecule, it requires a channel protein called an aquaporin to move down is water potential gradient

Question 17

what is the highest value of water potential

Answer 17

pure water
* 0

Question 18

adding a solute makes the solution ________

Answer 18

negative

Question 19

True or False

if water is seperated by a partially permeable membrane, it will diffuse from the region of higher water potential to the region of lower water potential

Answer 19

True

Question 20

what way will the water move?

-1.23kpa ——- -3.45kpa

Answer 20

to the right side (-3.45kpa)

Question 21

give the definition for hypotonic

Answer 21

the solution inside of the cell has a lower water potential than the solution outside of the cell

• water moves into the cell

Question 22

give the definition for hypertonic

Answer 22

the external solution has a lower water potential than the solution inside the cell
* the water moves out of the cell

Question 23

give the definition for isotonic

Answer 23

the external solution and internal solution has the same water potential
* no net movement

Question 24

what is active transport used for

Answer 24

used to transport molecules accross the membrane against their concentration gradient. From low concentrtion to high concentration

Question 25

what protein does active transport use

Answer 25

carrier proteins

Question 26

explain how carrier proteins work

Answer 26

1. the molecule for transport binds to the binding site of the specific carrier protein
2. the hydrolysis of atp provides a small amount of energy
3. this causes the protein to change shape which “pushes” the molecule through the membrane

Question 27

co-transport are a type of ______ proteins

Answer 27

carrier

Question 28

whats the difference between a normal carrier protein and a co-transporter protein

Answer 28

• co-transporter proteins bind two molecules at a time

Question 29

explain the equation
C1 x V1 = C2 x V2

Answer 29

• C1 = concentration of the stock solution (the original solution)
• V1 = volume of the stock solution
• C2 = concentration of the desired solution
• V2 = volume of the desired solution