Respiration

Question 1

What processes require energy

Answer 1

• Movement e.g. flagella and muscle contraction
• Cell division and growth
• Anabolic processes e.g. synthesis of polysaccharides
• Catabolic processes
• Maintaining constant body temp
• Active transport
• Bioluminescence e.g. glow worms
• Secretion e.g. insulin in pancreas

Question 2

Whats the role of ATP

Answer 2

• Short term energy store of cell

Question 3

Describe the structure and full name of ATP

Answer 3

• Adenine (base)
• Ribose (pentose sugar)
• 3 phosphate groups
• Adenosine triphosphate

Question 4

How does ATP release energy

Answer 4

• 3 phosphate groups joined by 2 high energy bonds
• ATP hydrolysed to break a bond releasing a large amount of energy
• Hydrolysis of ATP to ADP (later to AMP) is catalysed by enzyme ATPase

Question 5

Outline the process of glycolysis

Answer 5

• Occurs in cytoplasm
• First stage of both aerobic and anaerobic respiration
• Glucose is phosphorylated to form Glucose-6-phosphate as ATP is hydrolysed to form ADP
• Next Glucose-6-phosphate is changed to Fructose-6-phosphate
• Then Fructose-6-phosphate is phosphorylated to form Hexose-1,6,-bisphosphate (ATP hydrolysed to ADP)
• Each molecule of hexose is split into two triose phosphates
• Two H atoms removed from each triose phosphate (dehydrogenase enzyme) - aided by coenzyme NAD which reduced to NADH and two ADP used to form two ATP
• Two intermediate compound formed and four enzyme catalysed reactions convert each into a molecule of pyruvate and two ADP phosphorylated to two ATP.

Question 6

Describe the role and structure of the outer membrane in mitochondria

Answer 6

• A barrier that stops entry of large molecules that could interfere with Krebs cycle and oxidative phosphorylation
• Pyruvate can pass freely into matrix

Question 7

Describe the role and structure of the inner membrane in mitochondria

Answer 7

• Holds both electron carriers and ATP synthase molecules.
• Prevents small molecules from cytoplasm from entering matrix
• Pyruvate passes freely

Question 8

Describe the role and structure of the inter membrane space in mitochondria

Answer 8

• Activity of electron carriers in the inner membrane causes a reservoir of H+ to build up in the space as a temporary energy store before being used to make ATP

Question 9

Describe the role and structure of the crista in mitochondria

Answer 9

• Inner membrane largely folded to create large SA to hold electron carriers and ATP synthase molecules

Question 10

Describe the role and structure of the matrix in mitochondria

Answer 10

• Where enzymes of the Krebs cycle are found

- Krebs cycle removes electrons from the intermediates of the cycle and produced reduced NAD and FAD

Question 11

Describe the role and structure of the ATP synthase in mitochondria

Answer 11

• Molecule that makes ATP from ADP and P using energy from electrons obtained from reduced NAD and FAD
• Molecules span the inner membrane and have channels that allow H+ ions to pass through

Question 12

Outline the link reaction

Answer 12

• Occurs twice per glucose and no ATP involved
• Occurs in matrix
• CO2 is released in a decarboxylation reaction catalysed by pyruvate decarboxylase to produce a molecule of acetate
• This immediately combines with coenzyme A to produce acetyl CoA and carry it to Krebs cycle
• A molecule of NAD is reduced to form NADH, by pyruvate dehydrogenase

Question 13

Outline the Krebs Cycle

Answer 13

• Acetate combines with oxaloacetate to form citrate
• Citrate is decarboxylated and dehydrogenated to form a 5C compound releasing CO2 and NADH
• 5C compound is decarboxylated and dehydrogenated to form a 4C compound releasing CO2 and NADH
• ATP is released under substrate level phosphorylation to form another 4C compound
• 4C compound is dehydrogenated releasing FADH to form another 4C compound
• The 4C compound is dehydrogenated, releasing NADH

Question 14

Describe the importance of coenzymes

Answer 14

• coenzymes to transfer protons, electrons and functional groups
• coenzymes mostly derived from vitamins hence why vitamins are essential micronutrients

Question 15

Describe the differences between NAD and FAD

Answer 15

• NAD takes part in all stages of cellular respiration but FAD only accepts hydrogens in the Krebs cycle
• NAD accepts one H whereas FAD accepts two
• reduced NAD oxidised at start of electron transport chain releasing protons and electrons whereas reduced FAD is oxidised further along the chain
• Reduced NAD results in synthesis of three ATP molecules but reduced FAD results in synthesis of only two ATP molecules

Question 16

Outline the process of oxidative phosphorylation

Answer 16

• NADH releases its H which dissociates into H+ and e- (high energy electrons)
• The e- transported between e- carriers found within four protein complexes on IMM (cristae)
• The e- transfer between e- carriers releases a small amount of energy which is used to pump the H+ from the matrix into the IMM
• The H+ build up in the IM space creating a electrochemical gradient
• H+ flow down the electrochemical gradient through ATP synthase
• The movement of H+ thru ATP synthase creating a proton motive force causing head of ATP synthase to rotate allowing it to add Pi to ADP creating ATP
• H+ and e- rejoin in matrix and combine with O2 (final e- acceptor) to produce H2O

Question 17

Outline the process of chemiosmosis

Answer 17

• The ATP produced in respiration is synthesised primary by chemiosmosis
• It involves the diffusion of protons from region of high conc to low conc through partially permeable membrane
• The movement of protons as they flow releases energy that is used in the attachment of an inorganic phosphate (Pi) to ADP forming ATP
• This depends on the creation of a proton conc gradient and this energy comes from high-energy electrons

Question 18

Why is the theoretical yield of ATP per glucose rarely ever achieved?

Answer 18

• Some of the NADH formed between glycolysis and the Krebs cycle is used in other reduction reactions in the cell rather than in oxidative phosphorylation
• Some ATP used up in actively transporting substances such as pyruvate, ADP and Pi into the mitochondria during respiration
• The inner membrane of the mitochondria is leaky - some protons leak into the matrix without passing through ATP synthase and without making ATP

Question 19

Why does anaerobic respiration produce a much lower yield of ATP than aerobic respiration

Answer 19

• Only ATP made in anaerobic respiration is in glycolysis

Question 20

Contrast anaerobic respiration in mammals and in yeast

Answer 20

MAMMALS:
- pyruvate hydrogenated to lactate (lactate dehydrogenase)
- NADH oxidised to NAD
YEAST:
- Pyruvate is decarboxylated by pyruvate decarboxylase by releasing a molecule of CO2 producing ethanal
- Ethanal hydrogenated by ethanol dehydrogenase and NADH is oxidised to NAD to produce ethanol

Question 21

State the similarities of anaerobic respiration in mammals and yeast

Answer 21

BOTH:

• start with glycolysis
• no final electron acceptor
• H+ conc in matrix increases so electrochemical gradient reduces
• Oxidative phosphorylation stops
• NADH and FADH can’t be oxidised
• Link reaction and Krebs cycle stop

Question 22

Why are glass beads needed in the container with the dry beans in an investigation of respiration

Answer 22

• Dry beans take up less room than the germinating beans

- There should be a constant volume