5 Energy transfers- Respiration

Question 1

What is the structure of the mitochondria?

Answer 1

-Two phospholipid membranes
-Outer membrane= smooth, permeable to several molecules
-Inner membrane= folded (cristae), less permeable, site of ETC, location of ATP synthase
-Intermembrane space= low PH due to high concentration of protons
-Matrix= aqueous solution within inner membranes, has ribosomes, enzymes and circular DNA

Question 2

What is the function of the mitochondria?

Answer 2

-Site of aerobic respiration in eukaryotes
-Synthesises ATP

Question 3

How is the structure of the mitochondria related to its function?

Answer 3

Makes them well adapted to their function because;
-Have large surface area due to cristae (folds), membrane can hold ETC proteins + ATP synthase enzymes
-More active cell types have bigger mitochondria, longer cristae- more ATP synthesised (larger SA)
-Number of mitochondria varies in cells; muscle cells have more as are more active

Question 4

Where does aerobic respiration occur?

Answer 4

-Glucose= main respiratory substrate used by cells
-Aerobic respiration breaks down a respiratory substrate to make ATP using oxygen
Each stage is split in 4 and occurs in different locations;
Glycolysis- cytoplasm
Link reaction- mitochondrial matrix
Krebs cycle- mitochondrial matrix
Oxidative phosphorylation- inner membrane of mitochondria

Question 5

What is the first stage of aerobic respiration, + what it involves & produces?

Answer 5

Glycolysis
Involves- trapping glucose in cell, by phosphorylating molecule and splitting it into 2
Produces- 2 pyruvate (3C) molecules, net gain 2 ATP and 2 reduced NAD

Question 6

What are the steps of glycolysis?

Answer 6

-Phosphorylation; glucose (6C) phosphorylated by 2 ATP, making fructose biphosphate (6C)

-Lysis; Fructose biphosphate splits into 2 molecules of Triose phosphate (TP) (3C)

-Oxidation; hydrogen removed from each TP, transferred to co-enzyme NAD, making 2 reduced NAD
4H+ 2NAD—> 2NADH + 2H+

-Dephosphorylation; phosphates transferred from intermediate substrate molecules, making 4 ATP by substrate-linked phosphorylation
4Pi+ 4ADP—> 4ATP

-Pyruvate made; used in next stage
2 TP—> 2 pyruvate

Question 7

How does the product of glycolysis enter the link reaction?

Answer 7

Pyruvate (glycolysis product) has a lot of chemical energy, which is further used to make more ATP. When oxygen is available, pyruvate enters the mitochondrial matrix, across the double membrane via active transport. (Requires transport protein + small # of ATP) Once in the mitochondrial matrix, pyruvate takes place in the link reaction.

Question 8

What is the second stage of aerobic respiration and what occurs?

Answer 8

Link reaction- in mitochondrial matrix, links glycolysis and Krebs cycle; hence name. dehydrogenates & decarboxylates the three-carbon pyruvate to = two-carbon acetyl CoA that can enter the Krebs Cycle.

-Pyruvate oxidised by enzymes, makes acetate, CH3CO(O) and carbon dioxide, requiring reduction of NAD to NADH
-Combines with coenzyme A, making acetyl coenzyme A (acetyl CoA)
It produces: Acetyl CoA, carbon dioxide and reduced NAD

Pyruvate + NAD + CoA—> Acetyl CoA + carbon dioxide + reduced NAD

Question 9

What is the reaction of the coenzyme A?

Answer 9

Coenzyme= molecule that helps enzyme carry out its function, but isn’t used in the reaction itself
Coenzyme A consists of a nucleotide (ribose, adenine) and a vitamin. In link reaction, it binds to remainder of Pyruvate molecule (acetyl group 2C), forming acetyl CoA.
Then it supplies the acetyl group to the Krebs cycle, used to continue aerobic respiration. This stage brings part of the carbohydrate/lipid/amino acids further stages of respiration and links initial stage in cytoplasm to later stages in mitochondria

Question 10

What is the third stage of aerobic respiration and what occurs?

Answer 10

Krebs cycle/citric acid cycle, consists of series of enzyme-controlled reactions
2C acetyl CoA enters circular pathway from link reaction in glucose metabolism
(Acetyl CoA formed from fatty acids, after breakdown of lipids, and amino acids enters directly into the Krebs Cycle from other metabolic pathways)
4C oxaloacetate accepts 2C acetyl fragment from acetyl CoA, making 6C citrate (coenzyme A released)

Citrate converted back to oxaloacetate through series of oxidation-reduction reactions:
-Oxaloacetate is regenerated through redox reactions;
-Decarboxylation of citrate, releasing 2CO (2) as waste gas;
-Oxidation (dehydrogenation) of citrate, releasing H atoms which reduce coenzymes NAD and FAD
3 NAD + FAD —> 3NADH + H+ + 1FADH (2);
-Substrate-linked phosphorylation; phosphate transferred from one of intermediates to ADP, forming 1 ATP

Question 11

What is the role of Nad and FAD in aerobic respiration?

Answer 11

These coenzymes play a critical role
When hydrogen atoms (H ion and electron) become available at different points, FAD and NAD accept them
When this happens, they become reduced (OILRIG). They transfer the hydrogen atoms from different respiration stages to the ETC on inner mitochondria membrane, where hydrogens are released from coenzymes; they’re then oxidised
H ions & electrons are important in ETC at end of respiration since they play role in ATP synthesis
-Electrons from r NAD and r FAD given to ETC
-H ions from