Unit 1.4 (2) - Detecting & amplifying

Question 1

What do organisms use light energy for?

Answer 1

Generating ATP

Detect changes in their enviroment

Question 2

What prosthetic group is present in rhodopsin?

Answer 2

Retinal

Question 3

Where does retinal absorb energy from?

Answer 3

Photons

Question 4

Where do the hydrogen ions diffuse back through?

Answer 4

ATP Synthase

Question 5

What is retinal?

Answer 5

Prosthetic group covalently bonded to polypeptide called opsin

Question 6

What are the two classes of photoreceptor cells found in the retina of vertebrates?

Answer 6

Cone and Rod cells

Question 7

What do cone cells contain?

Answer 7

Photopsins

Question 8

Which class of photoreceptor cells is responsible for colour vision?

Answer 8

Cone cells

Question 9

Why are cone cells less sensitive than rod cells?

Answer 9

They have about 1000x less photoreceptor molecules

Question 10

How many types of photopsins are found in human cells?

Answer 10

3

Question 11

What are the colours each type of photopsin have maximal sensitivity to?

Answer 11

Red, blue and green

Question 12

How are different photopsins formed?

Answer 12

Combining retinal with different forms of opsins

Question 13

What do Rod cells produce when no light has been absorbed?

Answer 13

Cyclic GMP (cGMP)

Question 14

Where does cGMP bind to?

Answer 14

Ligand gated Na+ channels

Question 15

What happens when a photon of light is absorbed by a retinal molecule?

Answer 15

Conformational change in rhodopsin

Activates hundreds of G proteins which activates hundred of enzymes (PDE)

Question 16

What do the enzymes do when activated by G proteins?

Answer 16

Catalyse breakdown of cGMP (PDE hydRoylses cGMP and breaks down to GMP)

Question 17

What does the breakdown of cGMP cause?

Answer 17

Na channels close
Membrane will become hyperpolarized
Nerve impulse is generated

Question 18

What provides a high degree of amplification?

Answer 18

Protein cascade

Question 19

What are the steps in the protein cascade?

Answer 19

Rhodopsin
G proteins
Enzymes
Channels

Question 20

What is a photoreceptor?

Answer 20

Name given to proteins which are capable of sensing and responding to light