Respiration

Question 1

What does aerobic respiration need and produce?

Answer 1

needs oxygen and produces CO2, water and lots of ATP

Question 2

What are the 4 stages of aerobic respiration?

Answer 2

1. GLYCOLYSIS- the splitting of the 6- carbon glucose molecule into 3 carbon pyruvate molecules.
2. LINK REACTION- the conversion of the 3-carbon pyruvate molecule into carbon dioxide and a 2-carbon molecule called acetylcoenzyme A.
3. KREBS CYCLE- the introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large number of electrons.
4. ELECTRON TRANSPORT CHAIN- the use of the electrons produced in the Krebs cycle to synthesise ATP with water produced as a by-product.

Question 3

Where does glycolysis occur?

Answer 3

In the cytoplasm of all living cells

Question 4

Describe the first stage of glycolysis- phosphorylation of glucose.

Answer 4

1. activation of glucose by phosphorylation- Before it can be split into two, glucose must first be made more reactive by the addition of two phosphate molecules (PHOSPHORYLATION). The phosphate molecules come from the hydrolysis of two ATP molecules to ADP. Provides energy to activate glucose (lowers activation energy for enzyme controlled reactions that follow.

Question 5

Describe the second stage of glycolysis- splitting of phosphorylated glucose.

Answer 5

Each glucose molecule is split into two 3-carbon molecules known as triose phosphate.

Question 6

Describe the third stage of glycolysis- oxidation of triose phosphate.

Answer 6

Hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen carrier molecule known as NAD to form reduced NAD (NADH)

Question 7

Describe the fourth stage of glycolysis- production of ATP.

Answer 7

Enzyme controlled reactions convert each triose phosphate into another 3- carbon molecule called pyruvate. In the process, two molecules of ATP are regenerated from ADP.

Question 8

What is the overall yield from one glucose molecule undergoing glycolysis?

Answer 8

• 2 molecules of ATP (4 produced, two used)
• 2 molecules of NADH
• 2 molecules of pyruvate.

Question 9

Where are the enzymes for the glycolytic pathway found and why is this important?

Answer 9

In the cytoplasm so glycolysis does not require a specific organelle or membrane to take place.

Question 10

Where does the link reaction and the Krebs cycle take place?

Answer 10

Mitochondria.

Question 11

How do pyruvate molecules enter the mitochondria?

Answer 11

active transport into matrix.

Question 12

Describe the Link reaction.

Answer 12

• pyruvate is oxidised by removing hydrogen. This hydrogen is accepted by NAD to form reduced NAD.
• The 2-carbon molecule, called an acetyl group, that is thereby formed combines with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.
• A carbon dioxide molecule is formed from each pyruvate.

pyruvate + NAD + CoA = acetyl CoA + reduced NAD + CO2

Question 13

What are the products of the link reaction and what happens to them?

Answer 13

• Two molecules of acetyl coenzyme A go into the Krebs cycle.
• Two CO2 molecules are released as a waste product of respiration.
• Two molecules of reduced NAD are formed and go to the last stage (oxidative phosphorylation)

Question 14

Describe the Krebs cycle.

Answer 14

-The 2- carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule (oxaloacetate) to produce a 6-carbon molecule (citrate). CoA goes back to link reaction.
- Citrate (6-C) loses CO2 and hydrogens to give a 5- carbon molecule.
-Decarboxylation occurs, where CO2 is removed.
-Dehydrogenation also occurs, where hydrogen is remove.
-Hydrogen used to make NADH.
-The 5C molecule is then turned into a 4C molecule
-Decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced NAD.
-ATP is produced by the direct transfer of a phosphate molecule group from an intermediate compound to ADP.
CITRATE (6C) NOW CONVERTED TO OXALOACETATE(4C)

Question 15

What is substrate-level phosphorylation?

Answer 15

The formation of ATP by the direct transfer of a phosphate group from a reactive intermediate to ADP.

Question 16

What does the link reaction and Krebs cycle produce for each molecule of pyruvate?

Answer 16

• reduced coenzymes - FAD and NAd - have potential to produce ATP molecules.
• one molecule of ATP
• 3 molecules of CO2

X2

Question 17

What are coenzymes?

Answer 17

Molecules that some enzymes require in order to function.

In photosynthesis and respiration they carry hydrogen atoms from one molecule to another.

Question 18

Give 3 examples of coenzymes.

Answer 18

• NAD- important throughout resp.
• FAD- important in kerbs cycle
• NADP- photosynthesis

Question 19

What is the significance of the Krebs cycle?

Answer 19

• Breaks down macromolecules into smaller ones; pyruvate is broken down into CO2
• It produces hydrogen atoms that are carried by NAD to the electron transport chain for oxidative phosphorylation. Leads to the production of ATP that provides metabolic energy for the cell.
• Regenerates 4-C molecule(oxaloacetate) that combines with acetylcoenzyme A, which would otherwise accumulate.
• Source of intermediate compounds use by cells in the manufacture of other important substances such as fatty acids and chlorophyll.

Question 20

What is oxidative phosphorylation?

Answer 20

The process where energy carried by electrons, from reduced coenzymes, is used to make ATP.

Question 21

Describe oxidative phosphorylation.

Answer 21

1: Hydrogen atoms are released from reduced NADH and FADH as they’re oxidised to NAD and FAD. The H atoms split into protons (H+) and electrons (e-). Donate electrons to first molecule of electron transport chain, releasing protons.
2: The electrons move along the electron transport chain (made up of three electron carriers), losing energy at each carrier.
3: Energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space (between inner and out membrane).
4: The conc. of protons is now higher in the intermembrane space than in the matrix- forms electrochemical gradient (conc. gradient of ions).
5: Protons move down the electrochemical gradient, back into the matrix, via ATP synthase. This movement drives the synthesis of ATP from ADP and inorganic phosphate.
6: The movement of H+ ions across the membrane, generating ATP, is called CHEMIOSMOSIS.
7: In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and O2 (from blood) combine to form water. OXYGEN IS THE FINAL ELECTRON ACCEPTOR.

Question 22

Why is oxygen important in the electron transport chain?

Answer 22

Final electron acceptor.

With out oxygen removing the hydrogen ions at the end, they would build up and respiration would stop.

Question 23

What is cyanide and how does it work?

Answer 23

Respiratory inhibitor.
non-competitive inhibitor of the last enzyme in the chain. This enzyme catalyses the addition of hydrogen ions and electrons to oxygen to form water.

Question 24

How many molecules of ATP can be made from one molecule of glucose?

Answer 24

Oxidative phosphorylation makes ATP using energy from the reduced coenzymes- 2.5 ATP from NADH and 1.5 ATP from FADH. 
Glycolysis: 
2 ATP
2 NADH = 5 ATP
Link reaction:
2 NADH = 5 ATP
Krebs cycle:
2 ATP 
6 NADH = 15 ATP
2 FADH = 3 ATP

TOTAL = 32 ATP

Question 25

What cannot happen if oxygen is not present?

Answer 25

Krebs cycle and electron transport chain.

Question 26

Describe anaerobic respiration in plants and microorganisms such as yeast.

Answer 26

Pyruvate converted to ethanol and CO2.
The pyruvate cells formed at the end of glycolysis loses a molecule of CO2 and accepts hydrogen from NADH to produce ethanol.

pyruvate + NADH = ethanol + CO2 + NAD

Lactate needs to be oxidised back into pyruvate. Can be further oxidised to release energy or converted into glycogen in liver.— When O2 available again.

Question 27

Describe anaerobic respiration in animals.

Answer 27

Pyruvate converted to lactate.
For glycolysis to continue and release energy , NADH must be removed.
Each pyruvate molecule produced takes up two hydrogen atoms from NADH to form lactate.

pyruvate + NADH = lactate + NAD

Question 28

What is anaerobic respiration of yeast used for?

Answer 28

Brewing- yeast grown in anaerobic conditions in which it ferments natural carbohydrates in plant products, such as grapes (wine) or barley seeds (beer) into ethanol.

Question 29

Why do animals respire anaerobically?

Answer 29

to overcome a temporary oxygen shortage.

Question 30

When is anaerobic especially useful in animals?

Answer 30

Baby mammals in period immediately after birth, and animal living in water where O2 might be very low.
Exercise- muscles. Oxygen used more rapidly than can be supplied so oxygen debt.

Question 31

In what two ways is energy derived from cellular respiration?

Answer 31

• Substrate level phosphorylation in glycolysis and the Krebs cycle. Direct linking of inorganic phosphate and ADP to produce ATP.
• Oxidative phosphorylation in the electron transfer chain. this is the indirect linking of inorganic phosphate to ADP to produce ADP using the hydrogen atoms from glycolysis and Krebs cycle that are carried on NAD and FAD. Most of ATP comes from this.