BIS2A MT2: Lecture 13-17

What is fermentation and its purpose?

• The process of replenishing NAD+ pools after glycolysis is complete

• Electron recycling; oxidizes NADH back to NAD+

• Does not produce more ATP, allows ATP production via glycolysis to continue

What are the two types of fermentation?

• Lactic Acid Fermentation

• Alcohol fermentation

What type of process is fermentation?

• Anaerobic process

• ETC can’t function in the absence of oxygen

What does lactic acid fermentation input/output, where does it occur, and its key function?

• Input: Pyruvate + NADH

• Output: Lactic Acid + NAD+

• Occurs in muscle cells (exercise) and bacteria (yogurt production)

• Function: Prevent NADH accumulation, allows glycolysis to continue

What does alcohol acid fermentation input/output, where does it occur, and its key function?

• First input/output: Pyruvate; Acetaldehyde + CO2

• Second input/output: Acetaldehyde + NADH; Ethanol + NAD+

• Occurs in yeast, alcohol, some bacteria

What is co-enzyme A (COA) and its purpose?

• Assists in transfer of 2 carbon units

• Stores energy in a thioester (derived from amino acid) linkage

• Aids in the production of Acetyl-CoA, which is users in the TCA cycle

What is the purpose of the TCA Cycle?

• Fully oxidizes Acetyl-CoA to Co2

• Generates e- carriers (NADH, FADH2) for ATP production via oxidative phosphorylation

Where does the TCA Cycle take place?

• In bacteria/archaea: Cytoplasm

• Eukaryotic cells: Mitochondrial matrix

What is the significance of step 3 in the TCA cycle?

• Redox reaction

• First decarboxylation step and CO2 release. One carbon is lost.

• NADH is formed for ATP synthesis

What is the significance of step 4 in the TCA cycle?

• Redox reaction

• Second decarboxylation step and another CO2 release. Another carbon is lost.

• Original glucose molecule is further oxidized

• More NADH production for ATP synthesis

What is the significance of step 5 in the TCA cycle?

• Substrate level phosphorylation

• Directly produces ATP (bacteria/plant cells) or GTP (animal cells)

• Succinyl-CoA from previous step breaks the high energy bond, releases energy and drives phosphorylation of ADP (or GDP)

• CoA is released as waste and can be recycled for other processes.

What is the significance of step 6 in the TCA cycle?

• Redox reaction

• Succinate is oxidized; two H atoms removed

• Reaction uses FAD to produce FADH2 (carries electrons to ETC)

What is the significance of step 8 in the TCA cycle?

• Final redox/oxidation step

• NAD+ produces NADH which will be used in the ETC to produce ATP

• Oxaloacetate combines with acetyl-CoA to continue the TCA cycle

What is oxidative phosphorylation?

• Process in which ATP is formed as electrons are transferred from NADH/FADH2 to O2 by electron carriers

Where does oxidative phosphorylation occur?

The mitochondria

What are the two components of oxidative phosphorylation?

• ETC

• ATP synthase

What is substrate-level phosphorylation?

• A way for cells to make ATP directly by transferring a phosphate group from a high energy molecule (substrate) to ADP, making ATP

• Process can occur without oxygen or an ETC

Where does substrate-level phosphorylation occur?

• Anaerobic conditions: Glycolysis

• Aerobic: TCA cycle when oxygen is available

• Can still happen in both conditions regardless of O2 present

What is respiration?

The transfer of electrons from electron donors (NADH; FADH2) to terminal electron acceptors (oxygen; nitrate)

What is the ETC?

• A series of redox reactions where electrons move stepwise through protein complexes, releasing energy used to pump protons across a membrane

• Electron donors pass electrons through multiple elctron carriers

What is the proton gradient?

• Established by the ETC

• Powers ATP synthase, thus generating ATP

What is the proton motive force?

• Energy released from the ETC that pumps protons across the membrane

What does ATP Synthase use to synthesize ATP from ADP and Pi?

Proton motive force

What are the key steps of the ETC (through aerobic respiration)?

1. Electrons enter the ETC via NADH or FADH₂.

2. Redox reactions occur, transferring electrons stepwise and pumping protons.

3. Proton gradient forms (high H⁺ outside, low H⁺ inside).

4. ATP synthase produces ATP as protons flow back.

5. Electrons are transferred to a terminal electron acceptor (e.g., O₂ in aerobic respiration).

What are some examples of efficient terminal electron acceptors?

Oxygen, nitrate, sulfate, iron used in anaerobic respiraiton.

What do uncoupling agents do?

• Disrupt the proton gradient, reduces ATP production, generates heat

• Ex: DNP

What is chemiosmosis?

The diffusion of protons down their gradient, driving ATP synthase

Is fermentation the same as anaerobic respiration?

No! Fermentation does not use an ETC

What are the differences between aerobic and anaerobic terminal electron acceptors?

• Aerobic: Oxygen

• Anaerobic: Nitrate, Sulfate

Is aerobic or anaerobic respiration more efficient?

• Anaerobic; alternative electron acceptors provide less energy

Where does regulation occur?

• Branch Points

• Rate-limiting steps

• Irreversible reactions

What is a rate-limiting step?

The slowest reaction in a pathway that controls overall speed

What is an irreversible reaction?

Steps with large negative delta G that are difficult to reverse and serve as commitment points

How do pathways perform regulation?

• Allosteric regulation

• Feedback Inhibition

• Activation by precusors

What is allosteric regulation?

Binding of molecules to an enzyme at sites other than the active sit to regulate function

What is feedback inhibition?

The end product of a pathway that inhibits an earlier step to prevent wasteful overproduction

What does Activation by Precursors mean?

Pathway intermediates that can enhance enzyme activity.