ch18 - aerobic respiration

What is respiration?

The release of energy from the breakdown of complex organic molecules such as glucose, into small inorganic molecules such as CO2

> the energy released is used to synthesize ATP in all living cells 

Name the two types of cellular respiration and the key difference between them?

Aerobic respiration = requires oxygen

Anaerobic respiration = does not require oxygen

What are the three reasons why cells need energy?

-synthesis of molecules e.g. proteins

-movement (physical or mechanical) e.g. muscle contraction, movement of vesicles inside a cell along microtubules, cilia/ flagella

-active transport

What is the site of aerobic cellular respiration?

The mitochondria 

What are the 7 features of the mitochondria?

What are adaptations of these 7 features?

Outer mitochondrial membrane = compartmentalisation, separate contents from the rest of the cell - has ideal conditions for enzymes and reactions 

Intermembrane space = space between outer and inner membranes - where protons are pumped in by ETC allowing the proton concentration gradient to build up quickly 

Inner mitochondrial membrane = contains different proteins (ETC and enzymes like ATP synthase)

Cristae = folds of the inner membrane - which increases its SA so it can hold more proteins 

Matrix = contains enzymes needed for link reaction and krebs cycle as well as ribosomes and DNA

Mitochondrial DNA = codes for proteins needed by mitochondria 

Mitochondrial ribosomes (70s) = used for protein synthesis e.g. enzymes

What are the two ways in which ATP is regenerated from ADP and Pi during respiration? 

Substrate level phosphorylation = the transfer of a phosphate group, from a donor molecule, to ADP to synthesize ATP

Chemiosmosis = uses the energy released from the movement of protons (H+ ions) across the inner mitochondrial membrane to synthesize ATP

What are the four stages of aerobic cellular respiration?

1. Glycolysis 

2. Link reaction/ Oxidative Decarboxylation

3. Krebs cycle 

4. Oxidative Phosphorylation 

What is oxidation?

OIL (oxidation is loss e-) = oxidation is loss of electrons/ could also be loss of hydrogen 

What is reduction?

RIG (reduction is gain e-) = reduction is gain of electrons/ could also be gain of hydrogen 

What is dehydrogenation?

The loss/ removal of hydrogen 

What is decarboxylation?

The loss/removal of carbon dioxide

What is phosphorylation?

addition of a phosphate group to a molecule

What is the difference between an organic and inorganic phosphate?

organic phosphate is bound to a carbon containing molecule whereas inorganic phosphate is not - free flowing

What is NAD and what is its name when it is reduced?

-It's a coenzyme 

-When its reduced it forms NADH

What is FAD and what is its name when it is reduced?

-It's a coenzyme 

-When its reduced it forms FADH2​

Why are NAD and FAD important?

coenzymes that act as electron carriers - they accept electrons and protons, in the process becoming reduced

Later they become oxidised, donate the electrons to the ETC

What is the difference between NAD and FAD with how many electrons and protons are accepted?

NAD accepts 2electrons 1proton

FAD accepts 2electrons 2protons

What stages are these coenzymes present in?

NAD - all 4 

FAD - only krebs cycle

Where does glycolysis occur?

In the cytoplasm of cells

What are the four stages of glycolysis?

1. Phosphorylation = 2x ATP molecules donate a phosphate group, through ATP hydrolysis, to glucose forming hexose bisphosphate (which has 6carbons and two phosphates)

2. Lysis = Hexose bisphosphate splits in two to form 2x TP molecules (triose phosphate)

3. Phosphorylation = A free inorganic phosphate group is added to each TP molecule forming triose bisphosphate 

4. Oxidation/ Dehydrogenation & synthesis of ATP = From each TB molecule: a hydrogen is removed which forms 2x reduced NAD & both phosphate groups are removed forming 4x ATP through substrate-level phosphorylation to produce end product pyruvate 

What are the reactants required for glycolysis?

1x glucose molecule (6C)

2x ATP molecules 

2x NAD

What is the net yield of products of glycolysis?

2x ATP molecules (because 2 are used at the start and 4 are produced at the end 4-2 = 2ATP)

2x reduced NAD molecules

2x pyruvate molecules

Why are pyruvate and reduced NAD important products?

They are used in later stages of cellular respiration to generate greater yield of energy 

Is glycolysis an aerobic or anaerobic process?

Anaerobic because it does not require oxygen 

Where does the link reaction occur?

In the mitochondrial matrix 

What are the 5 stages of the link reaction?

1. Active transport of pyruvate = pyruvate from glycolysis enters mitochondrial matrix by active transport using specific carrier proteins 

2. Decarboxylation = each pyruvate molecule is decarboxylated, losing 1X CO2 molecule which diffuses out mitochondria as a waste product 

3. Oxidation = 1x hydrogen atoms are removed from pyruvate to form 2C acetyl group

4. Reduction of NAD = the hydrogen atom are used to reduce NAD forming reduced NAD 

5. Formation of acetyl CoA = acetate binds to coenzyme A to form acetyl coenzyme A (acetyl CoA)

For each glucose that enters respiration how many times does link reaction occur?

Twice 

What are the reactants required for 2 link reactions?

2x pyruvate 

2x NAD

2x coenzyme A

What is the net yield of products of 2 link reactions?

2x CO2 

2x reduced NAD 

2x acetyl CoA

What is the function of acetyl coenzyme A?

To deliver the acetyl group to another part of matrix for the next stage, Krebs cycle 

Why is link reaction also called oxidative decarboxylation?

Because both oxidation and decarboxylation reactions occur

Where does the Krebs cycle occur?

In the mitochondrial matrix 

What are the 6 stages of the Krebs cycle?

1. Formation of citrate = Acetyl CoA (which contains 2C acetate) reacts with 4C molecule oxaloacetate OAA, to form 6C citrate 

2. Decarboxylation and Dehydrogenation = Citrate is decarboxylated, releasing 1x CO2 & dehydrogenated, releasing a hydrogen which produces 1x reduced NAD to form a 5C molecule 

3. Decarboxylation and Dehydrogenation = Another decarboxylation reaction take place releasing 1x CO2 & another dehydrogenation reaction occurs to produce 1x reduced NAD 

4. Synthesis of ATP = 1x ATP molecule is produced by substrate level phosphorylation

5. Dehydrogenation = Dehydrogenation occurs twice producing 1x reduced FAD and 1x reduced NAD

6. Regeneration of 4C OAA = allows krebs cycle to continue 

For each glucose that enters respiration how many times does the Krebs cycle occur?

Twice 

What is the net yield of products of 2 Krebs cycles?

2x CoA

6x reduced NAD 

2x reduced FAD

2x ATP 

4x CO2

Where does the CO2 go?

diffuses out of mitochondria and is removed as a waste product

When citrate is formed the coenzyme A is released, where does it go?

Back to the link reaction to be reused 

Are Links and Krebs aerobic or anaerobic process?

Aerobic - although they doesn’t use oxygen, oxygen is required indirectly for these reactions to operate

Why are links and krebs aerobic

-they both depend on NAD and FAD being available

-in the ETC oxygen is the final electron acceptor which allows NADH and FADH₂ to be oxidised back to NAD and FAD

» if there is no oxygen the ETC stops meaning NADH and FADH₂ are no longer oxidised back so NAD and FAD are not produced - none available to enter links or krebs

What is the ETC?

A series of 4 protein complexes that carry molecules and release energy

Where does oxidative phosphorylation occur?

At the inner mitochondrial membrane, where the cristae is 

Why is oxidative phosphorylation important?

It produces the majority of ATP during aerobic respiration

How many ATP molecules does each coenzyme synthesize?

NAD - 3ATP

FAD - 2ATP

So far across all 3 stages how many of each coenzyme has been produced?

10X NADH

2X FADH2

When NADH and FADH2 are oxidised what happens to the electrons?

The high energy electrons are released - they are already high energy, the coeznymes just transported them to the ETC

What happens to the reduced coenzymes after they donate their electrons?

After donating their electrons they become oxidised allowing them to be reused in earlier stages 

What is a redox reaction?

When something is reduced and something else is oxidised at the same time 

How many protein complexes are there in the ETC?

4

What are the 4 stages of the ETC?

1. Coenzymes are becomes oxidised, releasing their protons and electrons into the matrix 

2. The 2 high energy electrons pass into ETC 

3. Redox reactions = As the electrons are transferred along the ETC, the previous complex is oxidised, next one is reduced - electrons loose energy as they travel across ETC

4. Once the electrons have passed along all 4 complexes and released all their energy they will bind with ½ oxygen 

What is the final electron acceptor and what's its function?

½ Oxygen will bind to the 2 electrons and combine with 2 protons to produce H2O water 

(O₂ oxygen is naturally diatomic so to get only 1x oxygen you need half = ½ O2)

As electrons move down ETC they lose energy, what is this energy used for?

Used by the ETC to actively pump protons from matrix to intermembrane space creating a proton gradient

What is the only stage that actually uses oxygen throughout aerobic respiration?

Oxidative phosphorylation

What is the difference between the coenzymes in where the electrons enter the ETC?

Electrons from FADH2 enter at the middle rather than the start 

Why do protons build up in the intermediate space?

Because the inner mitochondrial membrane is impermeable to them

Once a steep concentration gradient of protons is established what process does this lead to

Chemiosmosis 

What does diffusion down the electrochemical gradient mean? 

movement of ions and other substances from an area of high to low concentration

Describe chemiosmosis 

1. Protons diffuse across down their electrochemical gradient from the intermembrane space back into the matrix through the ion channel center in ATP synthase 

2. This movement of protons releases energy 

3. This energy released is used by enzyme ATP synthase to regenerate ADP and Pi into ATP

In theory how much ATP is made in oxidative phosphorylation per glucose molecule?

34

In theory how much total ATP is made during the whole aerobic cellular respiration process per glucose molecule?

38

Why may this theoretical yield of ATP not occur?

- not all reduced coenzymes will reach ETC 

- protons may leak hence not all will diffuse across ATP synthase