5.2.2 - Respiration✅

Question 1

Explain what glycolysis is, where does it occur?

Answer 1

• first stage of respiration, occurs in the cytoplasm of cell
• anaerobic process (oxygen not required)
• glucose (6 carbon) is split into 2 pyruvate molecules (3 carbon) ATP and NAD molecules are also produced

Question 2

Outline and explain the 4 main steps of glycolysis?

Answer 2

1) phosphorylation - 2 molecules of ATP required, 2 phosphates released from ATP attach to glucose to form hexose bisphopshate

2) lysis - this destabilises the molecule and it splits into 2 triose phosphate (TP) molecules

3) phosphorylation another phosphate group (from free inorganic phosphate ions present in cytoplasm) added to each triose phosphate molecule forming 2 triose bisphosphate molecules

4) dehydrogenation and formation of ATP - 2 triose bisphosphate molecules oxidised by removal of hydrogen atoms (dehydrogenation) forming 2 pyruvate molecules - 2 NAD coenzymes accept the hydrogens forming 2 reduced NAD molecules - removal of phosphates forms 4 ATP molecules

Question 3

Explain what the products of glycolysis are?

Answer 3

• 2 pyruvate molecules
• 2 reduced NAD molecules
• 4 ATP molecules produced (Overall net ATP yield is 2 - as 2 molecules of ATP used to prime process at begging)

Question 4

Explain how mitochondria are adapted for their role in respiration - give 5 ways?

Answer 4

• matrix - contains enzymes for kerbs cycle and link reaction
• inner mitochondrial membrane - contains electron transport chains + ATP synthase
• cristae - increase SA for oxidative phosphorylation
• inter membrane space - small area where proteins are pumped into (Conc builds up quickly)
• outer membrane - separates contents from rest of cells maintaining ideal conditions

Question 5

Explain what the link reaction is?

Answer 5

• first step in aerobic respiration - also called oxidative decarboxylation
• links anaerobic glycolysis (occurring in cytoplasm) with aerobic steps of respiration (occurring in mitochondria)

Question 6

Outline and explain the 3 main steps of the link reaction?

Answer 6

1) pyruvate transported (Active transport) and enters mitochondria matrix - undergoes decarboxylation (removal of carbon dioxide) and oxidation (removal of hydrogen)

2) removed hydrogen accepted by NAD forming reduced NAD (NADH)

3) resulting 2 carbon acetyl group bound by coenzyme A forming acetyl-coenzyme A - continues to next stage (Krebs cycle)

Question 7

Give the 3 products of the link reaction?

Answer 7

• acetyl-coenzyme A
• 2 molecules of carbon dioxide (diffuses out or is removed as metabolic waste)
• 2 molecules of reduced NAD

These are products for every 2 molecules of pyruvate

Question 8

What 2 processes take place during the link reaction?

Answer 8

decarboxylation - removal of carbon dioxide

dehydrogenation - removal of hydrogen

Question 9

Give the overall equation for the link reaction?

Answer 9

pyruvate + NAD + CoA → acetyl CoA + carbon dioxide + reduced NAD

Question 10

Explain what the Krebs cycle is?

Answer 10

• also called citric acid cycle - consists of enzyme-controlled reactions
• takes place in mitochondrial matrix
• involves decarboxylation, dehydrogenation and substrate-level phosphorylation

Question 11

Outline the stages of the Krebs cycle?

Answer 11

1) Acetyl CoA delivers an acetyl group (2C) which combines with oxaloacetate (4C) to form citrate (6C)

2) citrate undergoes decarboxylation and dehydrogenation - produces 1 reduced NAD, carbon dioxide and intermediate compound (5C)

3) intermediate compound undergoes decarboxylation and dehydrogenation - regenerating oxaloacetate (4C) - produces carbon dioxide, 2 reduced NADs and 1 reduced FAD + ATP (through substrate-level phosphorylation)

Question 12

Outline the products from the Krebs cycle?

Answer 12

• 2 molecules of carbon (2 carbon dioxides)
• 3 molecules of reduced NAD
• 1 module of reduced FAD
• 1 molecule of ATP

products from 1 cycle - cycle goes 2x for each pyruvate molecule

Question 13

What is phosphorylation - how does it differ to substrate-level phosphorylation?

Answer 13

The addition of a phosphorylation group to a molecule

Substrate-level phosphorylation is the production of ATP involving the transfer of a phosphate group from an intermediate compound - oxidative phosphorylation couples the flow of protons down a protein gradient through ATP synthase to produce ATP from ADP

Question 14

Outline the differences between the coenzymes NAD and FAD - give 3?

Answer 14

• NAD takes part in all stages of cellular respiration - FAD only accepts hydrogen in Krebs cycle
• NAD accepts 1 hydrogen - FAD accepts 2 hydrogens
• reduced NAD results in synthesis of 3 ATP molecules - reduced FAD results in synthesis of 2 ATP molecules

Question 15

Briefly explain what oxidative phosphorylation is?

Answer 15

• last stage of aerobic respiration - takes place in membrane of the cristae of mitochondria
• produces ATP

Question 16

Outline the process of oxidative phosphorylation?

Answer 16

• hydrogen atoms (collected by NAD and FAD) delivered to electron transport chains in crisate of mitochondria
• hydrogen atoms dissociate - forms hydrogen ions + electrons (used in synthesis of ATP by chemiosmosis) H ions creates proton gradient
• at end of electron transport chains (ETC) electrons combine with hydrogen ions and oxygen - forms water (Oxygen is final electron acceptor and required)

Question 17

Explain how ATP is produced through oxidative phosphorylation - describe process of chemiosmosis?

Answer 17

Hydrogen ions (delivered to electron transport chain [ETC] by NAD and FAD) dissociate forming hydrogen ions and electrons

• electrons move along ETC and lose energy - this energy pumps protons into intermemrbane space (creating a proton gradient)
• proteins diffuse down conc gradient through ATP synthase enzyme - energy is released which is used to convert ADP and inorganic phosphate to ATP
• electrons at end of ETC and protons which have flowed through ATP synthase combine with oxygen - forming water

Question 18

Explain why it’s oxidative phosphorylation?

Answer 18

Phosphorylation of ADP to form ATP is dependent on electrons moving along electron transport chains - requires presence of oxygen

• oxygen must be present for ETC to operate - oxygen is the final electron acceptor and combines with electrons and hydrogen ions to form water

Question 19

What is anaerobic respiration?

Answer 19

If not enough oxygen can be supplied fast enough, eukaryotic cells respire anaerobically resulting in the synthesis of smaller quantities of ATP

Question 20

anaerobic repsiration