Biol 211 Midterm 2

Aerobic Respiration

Combustion reaction, also a series of coupled and connected reactions that release and transfer free energy of glucose.

Non polar colvalent (c-c, c-h, o=o) bonds in the reactants lose electrons which means that they are…

Oxidized

Polar covalent (c=o, o-h) bonds in the products gain electrons which means that they are…

Reduced

In co2 the bonding electrons share equally between the carbon atoms in glucose…

move farther away from the carbon nuclei

In h2o the bonding electrons share equally between the oxygen atoms in o2…

move closer to the o nuclei

Glycolysis occurs in the?

Cytsol

Electron Carrier (redox) Coenzymes

Biological redox reactions generate reduction potential that is stored in electron carriers.

Chemoorganotrophy Steps that Do not Require oxygen

Glycolysis, Pyruvate oxidation, krebs cycle, pyruvate reduction (Fermentation), Oxidative Phosphorylation(anaerobic Respiration)

Chemoorganotrophy Steps that Require oxygen

Oxidative Phosphorylation (aerobic respiration)

What happens to non-polar covalent bonds (C-C, C-H, O=O) in the reactants of aerobic respiration?

They lose electrons (are oxidized)

What happens to polar covalent bonds (C=O, O-H) in the products of aerobic respiration?

They gain electrons (are reduced)

During respiration, where do bonding electrons shared between carbon atoms in glucose move?

They move farther away from the carbon nuclei and end up in CO2

During respiration, where do bonding electrons shared between oxygen atoms in O2 move?

They move closer to the oxygen nuclei and end up in H2O.

What is generated by biological redox reactions, and where is it stored?

They generate reduction potential, which is stored in electron carriers.

What are the reduced forms of the electron carriers NAD+, NADP+, and FAD?

NADH + H+, NADPH+H+, FADH2

How should we conceptually think of reduced electron carriers?

As high-energy electron transport molecules.

Where does glycolysis occur in the cell, and in what domains of life is this true?

It occurs in the cytosol. This is true in both prokaryotes and eukaryotes.

True or False: The Krebs Cycle requires oxygen (O2).

False. Your notes highlight that the Krebs Cycle is "entering in while it does not require O2

Which type of respiration requires oxygen (O2) and is used exclusively by prokaryotes, bacteria, and archaea?

Oxidative Phosphorylation (Anaerobic Respiration).

What are the three main takeaways to DO know about the Glycolysis overview?

1. It is a partial glucose oxidation pathway.
2. It consists of 10 connected and coupled reactions.

3. Each step requires a unique enzyme.

What are the inputs ("what goes in") and outputs ("what comes out") of Glycolysis?

Inputs: 1 Glucose (6C), 2ATP, 2NAD+

Outputs: 2 Pyruvate (3C}), 4ATP (2 net), 2NADH

What would happen if NADH was not recycled back into NAD+ during glycolysis?

It would build up and create an equilibrium, stalling the pathway.

How are electron carriers reduced during Glycolysis?

Glyceraldehyde-3-P + Pi is converted to 1,3-bisphosphoglycerate, while NAD+ is reduced to NADH + H+

What are the 3 components required for Substrate-Level Phosphorylation?

1. Enzyme

2. Phosphorylated substrate

3. ADP

What is the net ATP yield per glucose molecule during Glycolysis?

Net 2 molecules of ATP per glucose (4 produced minus 2 used).

Why is glycolysis considered only a partial oxidation of glucose?

Because not much ATP has been made, the cell still needs to remove the product (pyruvate), and it needs to restore NAD+ by oxidizing NADH.

What is the metabolic checkpoint for pyruvate if oxygen is LIMITING?

Pyruvate is reduced via fermentation into lactate or ethanol.

What is the metabolic checkpoint for pyruvate if oxygen is PRESENT?

Pyruvate is oxidized and moves into the Citric acid cycle and oxidative phosphorylation.

What is the definition of fermentation

The anaerobic reduction of pyruvate (pyruvate gains electrons from NADH -^ NAD+)

Is glycolysis considered part of fermentation?

No

What is the unique first step in alcoholic fermentation that does not happen in lactate fermentation?

Decarboxylation (the release of CO2 from pyruvate to form acetaldehyde).

What are the boundaries pyruvate must cross to enter the mitochondrial matrix in eukaryotes?

It must cross the OM (Outer Membrane), the IMS (Intermembrane Space), and the IM (Inner Membrane).

By what mechanism does pyruvate cross the outer mitochondrial membrane (OM)?

Facilitated diffusion.

By what mechanism does pyruvate cross the inner mitochondrial membrane (IM) into the matrix?

Secondary active transport (a symport mechanism moving pyruvate against its gradient using energy from H+ moving down its gradient).

What happens during Pyruvate Oxidation (The Bridge Reaction)?

Pyruvate (3C) is oxidized to Acetyl-CoA (2C) in the matrix, releasing CO2 and reducing NAD+ to NADH.

What are the products of the Citric Acid (Krebs) Cycle per turn?

2 CO2, 3 NADH, 1 FADH2, 1 ATP(via substrate-level phosphorylation)

What starting molecule does Acetyl-CoA combine with to begin the Krebs Cycle, and what does it form?

It combines with Oxaloacetate (4C) to form Citrate (6C).

What is the main biological purpose of the Citric Acid (Krebs) Cycle?

To finish the oxidation of glucose across 8 connected and coupled reactions.

True or False: The Citric Acid Cycle only processes sugars/glucose.

False. It is NOT just glucose; it processes amino acids (proteins), monosaccharides (carbs), and glycerol/fatty acids (fats).

How many protein complexes make up the Electron Transport Chain (ETC), and what are they?

4 complexes (composed of groups of proteins tightly working together).

Where are the ETC complexes located, and how are they structurally categorized?

Complexes I, III, and IV: Transmembrane proteins embedded in the inner membrane.

Complex II: Peripheral protein located on the matrix side.

Is ATP Synthase considered part of the Electron Transport Chain?

No.

What drives the flow of electrons down the Electron Transport Chain?

REDOX reactions. Electrons move from complex to complex, from the least electronegative component to the most electronegative component.

What happens to the complexes as electrons flow down the ETC?

The complexes cycle between a reduced state (as they accept electrons) and an oxidized state (as electrons leave).

Which of the following is NOT a product of Glycolysis?

NAD+. is consumed as a reactant to made NADH

Which of the following is required for Substrate level Phosphorylation?

A Phosphorylated reactant molecule

What is the primary purpose of fermentation?

To oxidize NADH back into NAD+, and to allow glycolysis to continue without oxygen

What is the fundamental purpose of electron flow down the ETC?

For the system to release free energy via sequential redox reactions.

Which molecule in the matrix donates electrons only to Complex I?

NADH, the active site of Complex I specifically recognizes it

What occurs as electrons flow through Complex I?

Free energy is released and used to pump protons H+ from the matrix into the intermembrane space (IMS).

Which molecule in the matrix donates electrons only to Complex II?

FADH2, the active site of Complex II specifically recognizes it

Why does Complex II not contribute directly to the proton gradient across the inner membrane?

It is a peripheral protein and cannot pump protons across the membrane.

What is Ubiquinone (UQ) and what is its specific function?

A hydrophobic mobile electron carrier ("taxi") that resides within the lipid bilayer. It shuttles electrons from Complex I to Complex III and from Complex II to Complex III.

What unique action does Ubiquinone (UQ) perform while being reduced and oxidized?

While being reduced, it takes $\text{H}^+$ from the matrix, and it releases them into the IMS when oxidized (pumping them across).

What is Cytochrome c (Cyt c) and what is its specific function?

A hydrophilic mobile electron carrier ("taxi") that shuttles electrons from Complex III to Complex IV.

What is the ultimate role of Complex IV in the Electron Transport Chain?

It uses the energy from flowing electrons to pump $\text{H}^+$ from the matrix to the IMS, and it reduces O2 to form H2O in the matrix.

What two actions lower the concentration of protons (H}+) inside the matrix?

Protons are pumed and taxied from the matrix into the IMS, Protons are consumed to reduce O2 into H2O

What is the resulting electrochemical gradient created by the ETC called?

The Proton Motive Force (PMF).

What are the approximate pH values and proton concentrations in the IMS vs. the matrix?

IMS High H+ concentration, (100x ratio) pH of 5

Matris low H+ concentration (1x ratio) pH of 7

What are the specific functions of the F0 and F1 portions of ATP Synthase?

F0 portion: Acts as the physical H+ channel across the membrane.

F1 portion: Catalyzes actual ATP synthesis in the matrix.

What is the approximate total ATP yield from the aerobic respiration of exactly one glucose molecule?

~32 ATP (though it can theoretically scale as high as 38 ATP).

What does your professor state about memorizing the reasons for variations in total ATP yields?

Don't memorize them (reasons like "hard to measure" and "some done in lab/organisms" are non-essential details).

What should you memorize regarding the ATP yield slide?

Memorize the ATP yields of individual processes (e.g., Glycolysis, Krebs Cycle) rather than trying to reconcile the varying grand totals.

If a cell does not immediately need ATP, how is excess glucose stored?

It is stored as a polymer: Glycogen in animals (short-term storage) and Starch in plants.

Besides glucose polymerization, how are excess resources saved for even longer-term storage?

Cells generate Triglycerides (fats); specifically, Acetyl-CoA from metabolism can be redirected to build fatty acids.

If a cell requires ATP after a period of storage, what happens to the polymer storage forms?

The storage processes are reversed to break down glycogen, starch, or lipids back into active metabolic pathways.

What macromolecules do heterotrophic organisms specifically require Carbon to synthesize?

Amino acids, nucleic acids, and phospholipids.

How can Acetyl-CoA be utilized in heterotrophic pathways outside of generating ATP?

It can be siphoned out to generate essential macromolecules directly instead of traveling through the remainder of the Krebs Cycle.

Where does aerobic respiration occur in prokaryotes since they do not possess mitochondria?

All metabolism occurs in the cytosol and along the cell membrane.

How does the metabolic efficiency of prokaryotes compare to eukaryotes during aerobic respiration?

It is less efficient.

In which domain of life is Anaerobic Respiration uniquely known to occur?

Prokaryotes.

When did Anaerobic Respiration likely evolve in Earth's history?

Early in evolutionary history, at a time when oxygen was not abundant in the atmosphere (likely evolving before aerobic respiration).

What defines Anaerobic Respiration structurally compared to Aerobic Respiration?

It uses final electron acceptors other than $\text{O}_2$ (such as sulfate or nitrate); otherwise, the processes (glycolysis, bridge, Krebs, ox-phos) are "the same."

What are two common examples of final electron acceptor conversions during anaerobic respiration?

Nitrate to Nitrite ($\text{NO}_3 \rightarrow \text{NO}_2$)

* Sulfate to Sulfite ($\text{SO}_4 \rightarrow \text{SO}_3$)

What environments drove the evolution of Chemolithotrophy?

Environments where organic molecules were not abundant.

What defines Chemolithotrophy regarding its choice of initial resource inputs?

It uses inorganic primary electron donors other than $\text{NADH}$ or $\text{FADH}_2$ (such as $\text{H}_2\text{S}$, $\text{Fe}^{2+}$, or $\text{H}_2$) to power its Electron Transport Chain.

Which pathways are NOT required by chemolithotrophic organisms?

Glycolysis, the Bridge reaction, and the Krebs cycle.

Which pathways ARE required by chemolithotrophic organisms?

The Electron Transport Chain (ETC) and chemiosmosis.

How does the strength of the Proton Motive Force (PMF) vary across distinct respiration pathways?

* Aerobic Respiration ($\text{NADH} + \text{O}_2$): Strong PMF

* Chemolithotrophy ($\text{H}_2\text{S} + \text{O}_2$): Medium PMF

* Anaerobic Respiration ($\text{NADH} + \text{SO}_4$): Weak PMF

Why do organic electron donors generate a stronger PMF than inorganic electron donors?

Organic electron donors store more free energy than inorganic electron donors.

Why does oxygen ($\text{O}_2$) generate a stronger PMF than other final electron acceptors?

Oxygen is a stronger final electron acceptor than any other acceptor in nature.