Unit 3.2 Investigating Cellular Respiration

What is cellular respiration?

Process where food is turned into useable energy for the cell

What is the chemical equation for aerobic cellular respiration?

C₆H₁₂O₆ + 6O₂ → 6H₂0 + 6CO₂ + ATP energy

What are the 4 stages of aerobic cellular respiration?

1. Glycolysis

2. Pyruvate oxidation

3. Krebs cycle

4. Electron Transport Chain/Chemiosmosis

Energy-carrying coenzymes/enzymes/specialized structures within the mitochondria do what for aerobic cellular respiration?

They incrementally extract the energy of the electrons as they move towards oxygen

Is aerobic cellular respiration anabolic or catabolic? Endothermic or exothermic?

Catabolic and exothermic

In every reaction, aerobic cellular respiration generates free energy (as ATP) along with, as always,-

the loss of energy as waste heat

Do the electrons stripped from glucose have a little energy or a lot of energy?

Have a LOT of potential energy

During the aerobic cellular respiration process, what 2 ways do electrons lose some energy?

1. To work the proton pumps

2. As heat (disorder)

What are the 2 main players involved in aerobic cellular respiration?

1. Mitochondrion

2. Enzyme/coenzymes

Where does aerobic cellular respiration start and where does it end?

Starts in the cytoplasm and ends in the mitochondrion

Label the parts of the mitochondrion from top left

Matrix, ribosome, outer membrane, DNA, crista, inner membrane

Label the part of the mitochondrion from the top

External membrane, internal membrane, matrix, cristae

What 2 places do most reactions occur in the mitochondrion?

1. Matrix

2. Internal membrane

Recall- what are enzymes?

Protein catalysts that speed up chemical reactions without themselves being used up

What is the function of a coenzyme? Are they a protein like enzymes?

Non-protein. Necessary for the proper functioning of an enzyme

What are 2 coenzymes of note here?

NADH and FADH₂

What is the main source of energy for cellular respiration?

Glucose

What 2 reasons does glucose work so fast?

1. Quickly absorbed into the bloodstream once ingested

2. Cells are permeable to glucose (by insulin)

Once glucose gets into the cytoplasm, what happens?

It’s processed for its free energy to do immediate cellular work- harvested as ATP

Where does Stage 1 Glycolysis take place?

In the cytoplasm

What is the main purpose of Stage 1 Glycolysis?

To prepare the energy-rich glucose molecule for the extraction of the energy stored in its bonds

What does it mean that the outcome of glycolysis is net 2 ATP?

Some energy, 2 ATP, needs to be used to first destabilize that glucose molecule. The outcome of glycolysis is 4 ATP and 2 NADH but because we used 2 already, we take about 2 from the end result

Does Stage 1 Glycolysis need oxygen?

No. This stage is anaerobic

What 3 products comes out of Stage 1 Glycolysis?

1. Two 3-Carbon pyruvate molecules

2. 2 NADH

3. 2 ATP (4 made but we used 2 at the beginning so net 2)

What is CoA?

Coenzyme A

Where does Stage 2 Pyruvate Oxidation occur?

In the mitochondrial matrix

Stage 2 Pyruvate Oxidation makes how many ATP?

NONE (only prepares for next steps; “transitional period”)

Before Stage 2 Pyruvate Oxidation can happen, what do the two pyruvates molecules have to do?

Stage 1 happens in the cytoplasm. Now, both pyruvates must be actively transported across the outer mitochondrial membrane, through the intermembrane space, and the inner mitochondrial membrane before finally reaching the mitochondrial matrix

What 4 products have we made during Stage 2 Pyruvate Oxidation?

1. 2 CO₂

2. 2 Acetyl-CoA

3. 2 NADH

4. 2 H⁺

What happens during the very last step of Stage 3 Krebs Cycle?

Last step resets the cycle

Where does Stage 3 Krebs Cycle occur?

In the mitochondrial matrix

Each step in Stage 3 Krebs Cycle does what for future steps?

Prepares for the harvesting of energy in successive steps.

Enzymes in Stage 3 Krebs Cycle turn 2 Acetyl-CoA molecules into what 8 things?

Citrate → isocitrate → alpha-ketoglutarate → succinyl-CoA → succinate → fumarate → malate → oxaloacetate

What is important about oxaloacetate?

It begins the cycle as a reactant and is regenerated as a product during the last reactions in the cycle to reset it

During Stage 3 Krebs Cycle, energy is removed from the transformed Acetyl-CoA molecules as what 3 things?

1. ATP

2. NADH

3. FADH₂

Where does Stage 4 Electron Transport Chain (ETC) and Chemiosmosis occur?

In the cristae of the mitochondrial matrix, the inner membrane, and the intermembrane space

In simplest terms, what happens during Stage 4 ETC and Chemiosmosis?

Electrons harvested from the oxidation of glucose move from electron donors (NADH, FADH₂) to an electron acceptor (oxygen) via ETC. ETC is made up of molecules (cytochrome complexes) that release some energy from the electrons at each step in the chain. Energy powers 3 proton pumps that push H⁺ ions out across the mitochondrial matrix membrane into the intermembrane space. Resulting transmembrane proton gradient is used to make ATP by chemiosmosis

What is a simple way to describe all 4 stages of cellular respiration?

Energy in C-H bonds of glucose → energy carriers → transported/harvested along the ETC → pump protons into the matrix → generate PMF → form ATP

ATP generation depends on the constant maintenance of what?

H⁺ reservoir in the intermembrane space

Why is it called aerobic cellular respiration?

Electrons will only keep moving through the ETC if oxygen is present to accept them at the end of the process

What is the main goal of the ETC and Chemiosmosis?

To harvest energy from the carrier molecules produced in the first three stages of cellular respiration

At the end of all stages of cellular respiration, what is the net ATP yield?

32 ATP

Are there alternative metabolic pathways? For who? Why?

Yes. Fats and other lipids get used up for energy when glucose isn’t available

What is beta-oxidation?

Aerobic breakdown (catabolism) of fats

How do proteins provide energy for cellular respiration?

Proteins are broken down into amino acids which are “deaminated” to produce energy-rich molecules. Amino groups are removed during deamination. Because of their unique functional groups, once deaminated they form products that can feed into Glycolysis or the Krebs Cycle

Deamination can create what toxic substance? How is it removed?

Urea; filtered by the kidneys and excreted via urine

What happens is anaerobic cellular respiration?

First set of electrons oxidized from glucose reduce NAD⁺ to NADH. Cells do not have limitless supplies of NAD⁺ available to undergo reduction reactions to gain electrons. Until NADH can offload their electrons to an acceptor they become unavailable for further electron removal

What happens in anaerobic cellular respiration when oxygen isn’t available? What have organisms learned to do to cope?

Another electron acceptor must be used; or organisms have had to evolve different mechanisms

What is lactic acid fermentation in muscle cells after strenuous exercise?

O₂ will be used faster than glucose can be metabolized. Will shift temporarily to produce lactic acid. Protons and electrons that were removed from glucose during glycolysis attach back onto pyruvate thus creating lactic acid

How do muscle cramps form? How can they be reduced?

From lactic acid; increasing oxygen will reduce cramps and restart aerobic cellular respiration

Is cellular respiration efficient?

No

If 1 Glucose has 3012kJ of energy, 1 ATP has 30kJ, and cellular respiration makes 32 ATP, how much energy is lost as heat? What is the percentage?

Lose 2052kJ of energy lost as heat; use only 32% of Glucose’s available energy

Is the efficiency of aerobic cellular respiration better than anaerobic?

Yes! 32% vs only 2%

Where are two places where we lose efficiency?

1. Some H⁺ leaks out of the proton reservoir and makes it’s way back into the matrix thus avoiding making ATP

2. Some energy from the proton pumps does other things not ATP related