1.1.5 Energy and Metabolism

Question 1

Where does the body undergo respiration?

Answer 1

The mitochondria

Question 2

Recall the aerobic respiration equation

Answer 2

oxygen + glucose –> carbon dioxide + water + ATP

6O2 + C6H12O6 –> 6CO2 + 6H2O + 38ATP

Question 3

Why is ATP considered a universal energy currency?

Answer 3

It is a high-energy molecules which can be used by all organisms at any time to release energy for almost all reactions

Question 4

Recall the process of Glycolysis

Answer 4

1. Glucose (6 Carbon) undergoes phosphorylation, where 2 x ATP are hydrolysed and the energy released is used to attach Pi to the Glucose, making hexose phosphate. This destabilizes glucose, preventing it from leaving the cell. In this stage 2x ATP are used up.
2. The molecule of hexose phosphate is split into two molecules of triose phosphate (3 Carbon)
3. The two triose phosphate molecules get oxidized into two molecules of pyruvate. Hydrogen is removed from each of the two triose phosphate molecules and transfers to a coenzyme called NAD to form NADH. Four ATP molecules are formed from the energy released during this oxidation (because 2 each triose phosphate)

Question 5

What are the final products of glycolysis for each glucose molecule entering the reaction?

Answer 5

• 2 molecules of ATP are used
• 4 molecules of ATP are produced
• so there is a net gain of 2 ATP molecules
• 2 molecules of reduced NAD are produced
• Glucose is converted to 2 molecules of pyruvate

Question 6

Recall the process of the link reaction:

Answer 6

1. One carbon atom is removed from pyruvate in the form of CO2.
2. Another oxidation reaction occurs when NAD+ collects more hydrogen ions. This forms NADH
3. This produces acetate
4. Acetate combines with coenzyme A to produce Acetyl Coenzyme A (acetyl CoA)
5. No ATP is produced in this reaction

Question 7

What are the final products of the Link Reaction for each glucose molecule entering the reaction?

Answer 7

• 2 Acetyl Coenzyme A: go into Krebs cycle
• 2 Carbon dioxide: released as a waste product
• 2 NADH: go to the electron transport chain

Question 8

Recall the process of the Krebs Cycle:

Answer 8

1. the 2C Acetyl CoA combines with 4C oxaloacetate to form 6C citrate.
2. The citrate is decarboxylated (CO2 goes out as waste) and dehydrogenated (NAD –> NADH), forming a 5C compound.
3. This happens again to the now 5C compound, forming a 4C compound
4. The 4C compound is changed into another 4C compound and ATP is produced.
5. The 4C compound is changed into another 4C compound and FADH is produced
6. The 4C compound is changed into oxaloacetate and NADH is produced

Question 9

Recall the CONA CONA A FA NA song

Answer 9

• Remember that Acetyl CoA enters the cycle
  1. CONA: production of CO2 and NADH
  2. CONA: production of CO2 and NADH
  3. A: Production of ATP
  4. FA: Production of FADH
  5. NA: Production of NADH
• Remember that Oxaloacetate finishes the cycle

Question 10

What are the final products of the Krebs Cycle for each glucose molecule entering the reaction?

Answer 10

• 1 x oxaloacetate
• 2 x CO2
• 3 x NADH
• 1 x FADH

Question 11

Recall the process of the ETC:

Answer 11

1. NADH and FADH donate H atoms to the electron carriers. H is split into protons and electrons
2. Electrons are accepted from NADH by first electron carrier. FADH binds to Complex II to release its hydrogen. Protons go into solution in the matrix.
3. The electrons are passed along a chain of electron carriers. This is the electron transport chain
4. As electrons flow along the ETC, energy is released. This energy is used to pump protons across the intermembrane space.
5. This produces a proton gradient. Potential energy therefore builds up in the intermembrane space.
6. The protons cannot escape through the lipid part of the inner membrane. They have to diffuse through the the ATP synthase. The flow of protons is chemiosmosis.
7. Protons flowing through ATP synthase cause the rotation of part of the enzyme, causing ADP and Pi to join, forming ATP.
8. The electrons that has been passing along the ETC are passed from the last carrier to molecular oxygen. This is the final electron acceptor.
9. Hydrogen ions also join the oxygen, causing it to be reduced to water.

Question 12

What is the final electron acceptor?

Answer 12

oxygen; where it combines with protons and electrons to form water

Question 13

ETC Summary:

Answer 13

1. Hydrogen atoms released from reduced NAD and FAD as they are oxidized
2. Hydrogen atoms split into protons and electrons
3. Electrons move along the ETC, releasing energy at each carrier
4. This energy is used to pull the protons through the pumps, into the intermembrane space
5. This forms a proton gradient.
6. Protons must move back to matrix via ATP synthase
7. This movement drives the synthesis of ATP from ADP and inorganic phosphate
8. The final electron acceptor, oxygen, combines with protons and electrons to form water.

Question 14

How many ATP will FAD generate?

Answer 14

2, due to two proton pumps

Question 15

How many ATP will NAD generate?

Answer 15

3, due to three proton pumps

Question 16

Summary: How many ATP is made from Glycolysis, Link reaction, Krebs Cycle, ETC from NADH and ETC from FADH?

Answer 16

Glycolysis: 2

Link Reaction: 0

Krebs Cycle: 2

ETC from NADH: 30 (10 NADH made in previous stages and 3 ATP produced per NADH molecule)

ETC from FADH: 4 (2 FADH made in previous stages and 2 ATP is produced per FADH molecule)

Question 17

Where does photosynthesis occur?

Answer 17

In the chloroplasts

Question 18

Where does Glycolysis occur?

Answer 18

cytoplasm

Question 19

Where does the Link Reaction occur?

Answer 19

mitochondrial matrix

Question 20

Where does the Krebs Cycle occur?

Answer 20

In the mitochondrial matrix

Question 21

Where does the ETC occur?

Answer 21

In the mitochondrial inner membrane: from matrix across cristae into inter-membrane space and back to matrix

Question 22

What is the photosynthesis equation?

Answer 22

Carbon dioxide + water –> glucose + oxygen

6CO2 + 6H2O –> C6H12O6 + 6O2

Question 23

Where does the light-dependent stage of photosynthesis occur?

Answer 23

• Takes place on the thylakoid membranes

Question 24

Does the light-dependent stage use PSI and PSII?

Answer 24

yes

Question 25

What happens in the light-dependent stage?

Answer 25

• light energy converted to ATP, called photophosphorylation
• two types of photophosphorylation:
• cyclic and non-cyclic

Question 26

Recall the process of Cyclic Photophosphorylation

Answer 26

Light will hit PSI, exciting electrons and causing them to pass to an electron acceptor then back to the chlorophyll molecule, and producing small amounts of ATP. This process will continue to cycle through, recycling electrons as long as light is present.
NOTE:
- no photolysis of water (splitting of water molecule into H ions, oxygen, electrons in presence of light)
- no production of reduced NADP (NADPH)

Question 27

Recall the process of Non-cyclic photophosphorylation

Answer 27

1. Light energy excites electrons in chlorophyll.
   - light energy absorbed by PSII, exciting electrons in chlorophyll
   - electrons move to a higher energy level
   - high energy electrons move along the electron transport chain, producing ATP
   - electrons eventually replace those lost by PSI
2. Energy from the excited electrons make ATP
   - excited electrons lose energy as they move along the ETC, energy which is used to transport protons into the thylakoid. The thylakoid has a higher concentration of protons than the stroma, forming a proton gradient across the membrane.
   - protons move down the concentration gradient, into the stroma, via ATP synthase
   - this movement synthesizes ATP from ADP and inorganic phosphate
   NOTE:
   - same as what happens in respiration, just in the stroma rather than matrix
3. Photolysis of water
   - as the excited electrons from chlorophyll leave PSII, they must be replaced
   - this can be done via photolysis, where light energy split water into protons (H ions), electrons and oxygen (2H2O –> 4H + 3e + O2)
4. Generation of NADPH
   - light energy has also been absorbed by PSI, which has again excited electrons to a higher energy level
   - these electrons and a proton made from photolysis of water join NADP, producing NADPH

Question 28

which photosystem/s does non-cyclic photophosphorylation use?

Answer 28

• uses PSI and PSII
• produces ATP, NADPH and oxygen
• PSI and PSII are linked by electron carriers, which are proteins that transfer electrons.

Question 29

summary: explain the light dependent stage of photosynthesis

Answer 29

Takes place on the thylakoid membranes
Needs light energy

Cyclic photophosphorylation:

• PSI
• Photons cause..
• ..electron to be excited
• Captured by electron acceptor and is passed back to chlorophyll.
• Energy is released to make ATP from ADP + Pi

Non-cyclic photophosphorylation:
- Excited electrons emitted from the primary pigments of both reaction centers of PSI and PSII
- The electrons lost from PSI are replaced by electrons transferred from PSII by electron carriers
- PS II receives replacement electrons from the photolysis of water
(2H2O  4H+ + 4e- + O2)
- ATP is synthesized as electrons lose energy whilst passing along the electron carrier chain from PS II to PS I
- Hydrogen ions (photolysis) combine with electrons from PS I and NADP to form reduced NADP.

Question 30

Where does the light independent stage take place?

Answer 30

In the stroma of chloroplasts

Question 31

What are the products of the light independent stage?

Answer 31

• triose phosphate from carbon dioxide and ribulose bisphosphate
• the reactions are linked in a cycle which means the starting compound, ribulose bisphosphate is regenerated

Question 32

what does the light-independent stage require to keep going?

Answer 32

ATP and H ions

Question 33

Recall the Light independent stage (Calvin cycle):

Answer 33

1. CO2 combines with Ribulose Bisphosphate (RuBP) to form an unstable compound that breaks into two molecules of Glyerate-3-phosphate (GP)
2. ATP from the light-dependent reaction turns GP (3C) into TP. This also requires H from NADP. 1 x TP is then converted into useful compounds such as hexose sugars.
3. RuBP is regenerated by the 5 x TP molecules. This regeneration also requires the rest of the ATP made in the light dependent reaction.

Question 34

Is oxygen produced in the light-dependent or light-independent reaction:

Answer 34

light-dependent

Question 35

Is carbon dioxide fixed in the light-dependent or light-independent reaction?

Answer 35

light-independent

Question 36

Is ATP produced in the light-dependent or light-independent reaction?

Answer 36

light-dependent

Question 37

does the light-dependent or light-independent reaction use NADPH?

Answer 37

light-independent

Question 38

does the light-dependent or light-independent reaction occur in the stroma?

Answer 38

light-independent

Question 39

What will happen to the body when there’s no oxygen?

Answer 39

undergo anaerobic respiration - ineffective:
Glucose –> lactic acid + 2ATP
- NADH must be deoxidized to NAD
- Pyruvate is the hydrogen acceptor, making lactate
NAD is now oxidized and so able to accept more H atoms from glucose
- Allows glycolysis to continue, providing 2ATP