5.4. ACTIVE TRANSPORT

Question 1

Why is diffusion no good for cellular life?

Answer 1

it leads to equilibrium however biological processes rely on concentration gradients -eg.compartmentalisation

Question 2

How is a concentration gradient maintained?

Answer 2

molecules or ions must move up the concentration gradient faster than they diffuse down

Question 3

What is active transport?

Answer 3

Movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration
-UP or AGAINST the gradient
-selective (specific to the ion)

Question 4

What do molecules/ions move through in the membrane in active transport?

Answer 4

Carrier proteins

Question 5

How do carrier proteins work in active transport?

Answer 5

Have a receptor site that bind to specific molecules and transport them across the cell membrane

Question 6

Where does active transport often take place?

Answer 6

Internal lining of the small intestine (eg. glucose into the blood)

Question 7

What type of energy is required for active transport?

Answer 7

Immediate source - ATP

Question 8

What are some examples of active transport?

Answer 8

-transportation of sodium out of the cell
-transportation of potassium into the cell
(sodium-potassium pump)

Question 9

How do plants absorb mineral ions from the soil?

Answer 9

active transport enables these cells to take up salts (from the dilute solution in the soil water) against the direction of the concentration gradient

Question 10

What are the three types of carrier protein used in active transport?

Answer 10

-Uniporter
-Synporter
-Antiporter

Question 11

What does the uniporter carrier protein transport ?

Answer 11

one molecule/ion in one direction

Question 12

What does the Synporter carrier protein transport ?

Answer 12

2 molecules/ions in one direction

Question 13

What does the Antiporter carrier protein transport ?

Answer 13

Two molecules/ions in two different directions

Question 14

What are the steps in the Possible Mechanism for Active Transport?

Answer 14

1) molecule bonds to receptor site on inner wall of the carrier protein pore
2) ATP binds to the carrier protein on the cytoplasm side -it is then hydrolysed into ADP + Pi
3) energy is transferred to the carrier protein and Pi is bound to it
4) carrier protein changes shape to open the pore on the other side of the membrane and the molecule is released
5) Pi is released from the carrier protein and it changes shape again to adopt the original conformation

Question 15

What are the two types of bulk transport?

Answer 15

Endocytosis (into the cell)
Exocytosis (out of the cell)

Question 16

What are the three types of endocytosis?

Answer 16

Phagocytosis
Pinocytosis
Receptor Mediated

Question 17

What is Phagocytosis (in terms of endocytosis)?

Answer 17

Where the membrane engulfs solid particles (ie. bacteria) with ATP via pseudopodium into a phagosome (food vacuole)

Question 18

What is pinocytosis (in terms of endocytosis)?

Answer 18

Molecules/ions are absorbed by the membrane into a vescicle in the cytoplasm (i.e. drinks a molecule/ion)

Question 19

What is receptor-mediated endocytosis?

Answer 19

A membrane with a coated pit and receptors collect molecules/ions into a coated vesicle inside the cytoplasm

Question 20

What does a coated pit do?

Answer 20

acts as a cage on the inside of a membrane - pinched off the membrane to form a coated vesicle

Question 21

What is exocytosis?

Answer 21

a mechanism by which cells are able to insert membrane proteins, lipids and other components into the cell membrane
-vesicles containing these membrane components fully fuse with and become part of the cell surface membrane

Question 22

What are the main stages of exocytosis?

Answer 22

-membrane bound secretory vesicles are carried to the plasma membrane
-vesicle contents are secreted into the extracellular environment

Question 23

Why is the secretion in the vesicles possible in exocytosis?

Answer 23

because the vesicles transiently fuse with the plasma membrane