Cell respiration 2.8, 8.2

Question 1

What is cell respiration?

Answer 1

controlled release of energy from organic compounds to form ATP (process of converting food energy into ATP energy

Question 2

Molecules storing energy

Answer 2

NADH (3 ATP) and FADH2 (2 ATP)

Question 3

Redox reactions

Answer 3

• oxidation = loss of electrons.
• reduction = gain of electrons.
  
  • at the same time
• main electron carrier in respiration is NAD

Question 4

How is energy stored during cell respiration?

Answer 4

The ions (NAD+ and FAD2+) take part in redox reaction (reduced have energy)
NAD+ + H+ + 2e- → NADH

Question 5

ATP structure

Answer 5

• Adenosine Triphosphate
• adenine, ribose and 3 phosphate groups (tri-)
• one of the groups detaches (hydrolysis) → becomes ADP
  
  • releases energy

Question 6

Usage of ATP

Answer 6

• ATP → ADP and Pi
  
  • releases usable energy and non-usable (heat)
• transport work (active transport, endo- and exocytosis)
• mechanical work (muscles)
• chemical work (synthesising molecules)

Question 7

Cell respiration and photosynthesis

Answer 7

• both need light
• chemical cycles with energy flowing
• opposite reactions

Question 8

Why is ATP used instead of glucose?

Answer 8

• efficiency
• 1 ATP molecule less energy → released slowly in a controlled way
• 38% of energy from glucose yields ATP (rest is heat)

Question 9

Phosphorylation

Answer 9

• addition of PO4(3-) molecule to a substance
• molecule becomes less stable = more active
• ATP → ADP releasing P molecule
  
  • attaches to amino acid

Question 10

Anaerobic respiration

Answer 10

• produces energy without oxygen (converts glucose).
• quick rapid burst of energy
  
  • no oxygen in respiring cell
  • an environment with lack of oxygen
• in animals: lactic acid (later lactate)
• in plants ethanol and carbon dioxide
  
  • ethanol and lactic acid are toxic.

Question 11

Aerobic respiration

Answer 11

• yields more ATP than anaerobic respiration (circa 30)
• glucose + oxygen → carbon dioxide + water
• in mitochondrion and CO2 is excreted from the organism

Question 12

Glycolysis

Answer 12

• small net gain of ATP without oxygen
  
  • sugar into pyruvate
• ATP phosphorylates sugar → activation energy decreases

glucose → glucose-6-phosphate → fructose-6-phosphate → fructose-1,6-bisphosphate 

• fructose-1,6-bisphosphate → 2 triose phosphates (G3P or TP)
• hydrogen atom removed (oxidation)
  
  • NAD+ —> NADH + H+
  • creates glycerate-3-phosphate (GP or 3-PGA).
• later, phosphate group to ADP → ATP and pyruvate

Net gain:
glucose —> 2 pyruvate + 2 H2O
2 ADP + 2 Pi —> 2 ATP
2 NAD+ —> 2 NADH + 2H+

Question 13

Pyruvate after glycolysis

In presence of oxygen

Answer 13

• if oxygen is available
  
  • pyruvated moved into mitochondrion and oxidised

2 CH3COCOOH + 5 O2 —> 6CO2 +4H2O 

• carbon, oxygen removed (CO2) —> decarboxylation
• oxidation = removing H atoms
  
  • accepted by NAD+ and FAD

Question 14

The link reaction

Answer 14

• pyruvate to mitochondrial matrix
  
  • inside of mitochondrion
• decarboxylised and oxidised
  
  • 2 e- attach to NAD+
• coenzyme A group attached → acetyl coenzyme A

Net gain (for 2 pyruvates):
2 CO2 and 2 reduced NAD

Question 15

The Krebs cycle

Answer 15

• acetyl CoA into CoA (released and later reused) and 2 C which attach to 4 C molecule

1. 6 C molecule decarboxylised and 2 H are removed (NAD+ —> NADH + H+) → 5 C molecule
2. 5 C molecule decarboxylised and 2 H removed → 4 C molecule
3. 4 C molecule → 4 H removed (reduction of NAD and FAD2) + ADP phosphorylation
4. 4 C molecule is used again (binds to acetyl)

Net gain (for 2 acetyl CoA):
4 CO2 ; 2 ATP ; 2 FADH2 ; 6 NADH ; 6 H+

Question 16

Oxidative phosphorylation

Answer 16

• mitochondrial cristae
• energy from oxidation of NADH (from glycolysis, link reaction and Krebs cycle) and FADH2 (from Krebs cycle)
  
  • passed to electron transport chain (e- carriers)
  • H+ gradient formed
• H+ move down concentration gradient → mitochondrial matrix
  
  • through ATP synthase → ATP made
• terminal electron acceptor (at the end of chain) = oxygen
  
  • binds to 2H+ → H2O

Net gain:
32 ATP 
6 O2 → 6 H2O

Question 17

The electron transport chain and chemiosmosis

In cell respiration

Answer 17

• inner mitochondrion membrane
• H+ transported down the concentration gradient
• the energy released activates ATP synthase → ATP

1. NADH and FAD2 give e- and H atoms (which is split) to complex I → NAD+ and FAD back to matrix
2. e- move from complex to complex → releases energy → H+ move to intermembrane space
   
   • electron transport chain
3. electrochemical gradient created
4. H+ ions go through ATP synthase to matrix (down the gradient)
   
   • energy → ADP phosphorylised into ATP
5. e- binds to terminal electron acceptor (oxygen) → H2O formed

Question 18

Yeast and bacteria in food production

Answer 18

Lactic acid —> soy sauce, cheese, yogurt
Ethanol + CO2 —> beer
Ethanol —> wine
CO2 —> fluffy bread (by bubbles)

Question 19

Anaerobic respiration in humans

Answer 19

• pyruvate → lactate (lactic acid)
• during exercises low O2 levels → lactic acid accumulates
• when resting lactic acid → pyruvate

Question 20

What is the structure of mitochondrion?

Answer 20

• outer membrane – separates aerobic respiration (compartmentalisation)
• inner membrane – oxidative phosphorylation
  
  • electron transport chain and ATP synthase
  • cristae increase surface area of inner membrane
• intermembrane space → H+ concentration builds up
  
  • small = quicker gradient.
• matrix — link reaction and Krebs cycle
  
  • special enzymes helping reactions

Question 21

Respirometer

Answer 21

• organism breaths → O2 used and CO2 released
  
  • CO2 absorbed
• fluid in the tube moves towards the animal