Biology lecture 11 (Chapter 5)

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Questions and Answers

What characterizes redox reactions?

They are always spontaneous.

They occur independently of each other.

They only involve the transfer of electrons.

The oxidation and reduction reactions occur simultaneously. (correct)

What does the acronym LEO in the context of redox reactions stand for?

Loss of Electrons = Oxidation (correct)

Low Electron Output = Oxidation

Limited Electrons = Oxidation

Loss of Energy = Oxidation

What is the role of NAD+ in redox reactions?

It increases the energy yield of glycolysis.

It is the reduced form of the electron carrier.

It acts as an oxidized form of the electron carrier. (correct)

It is produced during the cellular respiration process.

In a redox reaction, what happens to the substance that is oxidized?

It loses electrons. Signup and view all the answers

Which of the following describes the process of glycolysis?

It involves a series of 10 chemical reactions. Signup and view all the answers

During cellular respiration, glucose is converted into what products?

CO2, H2O, and energy. Signup and view all the answers

Which of the following best describes what happens to carbon during the burning of methane?

Carbon loses a relative share of electrons. Signup and view all the answers

How can reduction be characterized in a redox reaction?

As the gain of electrons. Signup and view all the answers

What phase of glycolysis consumes ATP?

Energy investment phase. Signup and view all the answers

Which statement accurately represents a key element of electron sharing in covalent bonds?

Degree of electron sharing can change. Signup and view all the answers

Where does glycolysis occur within the cell?

In the cytosol. Signup and view all the answers

What role does oxygen play in the reduction of water?

Oxygen gains electrons. Signup and view all the answers

Which statement best describes the overall process of cellular respiration?

It is controlled combustion that yields energy. Signup and view all the answers

Which statement is true regarding the products of the oxidation phase of NADH?

NAD+ is produced along with electrons and protons. Signup and view all the answers

Which best describes the term 'electron acceptor' in the context of redox reactions?

It is the substance that gains electrons. Signup and view all the answers

In a redox reaction, what is the significance of protons (H+)?

Protons accompany the transfer of electrons. Signup and view all the answers

What is the main purpose of substrate-level phosphorylation in glycolysis?

To produce ATP directly from ADP Signup and view all the answers

Which enzyme is specifically mentioned as catalyzing an ATP-consuming step in glycolysis?

Phosphofructokinase Signup and view all the answers

Where does pyruvate oxidation occur within the cell?

In the mitochondria Signup and view all the answers

What is one of the key outputs of pyruvate oxidation?

Acetyl-CoA Signup and view all the answers

Which statement about ATP production in cellular respiration is true?

Oxidative phosphorylation generates most of the ATP produced in cellular respiration. Signup and view all the answers

What happens to NAD+ during pyruvate oxidation?

It is reduced to form NADH. Signup and view all the answers

Which type of reactions primarily occur during glycolysis?

Catabolic reactions only Signup and view all the answers

What is produced as a byproduct during pyruvate oxidation?

Carbon dioxide Signup and view all the answers

Which complex in the electron transport chain directly receives electrons from NADH?

Complex I Signup and view all the answers

What is the role of cytochrome c in the electron transport chain?

It transports electrons between complexes. Signup and view all the answers

How many molecules of water are produced as a result of the entire electron transport chain process?

2 Signup and view all the answers

What is the final electron acceptor in the electron transport chain?

O2 Signup and view all the answers

Which process is primarily driven by the proton gradient established in the electron transport chain?

Oxidative phosphorylation Signup and view all the answers

What is the primary energy yield from fermentation?

2 molecules of ATP Signup and view all the answers

What is produced alongside NAD+ during lactic acid fermentation?

Lactic acid Signup and view all the answers

Which type of fermentation occurs in plants and fungi?

Ethanol fermentation Signup and view all the answers

What happens to pyruvate when oxygen is not present?

It is metabolized through fermentation Signup and view all the answers

What is the major function of NAD+ in the fermentation process?

To serve as an electron acceptor Signup and view all the answers

What is produced during pyruvate oxidation?

1 acetyl-CoA, 1 NADH, 1 CO2 Signup and view all the answers

How many ATP molecules are produced from the oxidation of one acetyl-CoA in the citric acid cycle?

1 ATP Signup and view all the answers

Which of the following correctly describes the outputs of the citric acid cycle for one acetyl-CoA?

2 CO2, 3 NADH, 1 ATP, 1 FADH2 Signup and view all the answers

What role does coenzyme A play in the oxidation of pyruvate?

It is involved in the formation of acetyl-CoA from pyruvate. Signup and view all the answers

What is the primary function of the electron transport chain?

To convert potential energy in NADH and FADH2 into ATP. Signup and view all the answers

How many total NADH are generated from the complete oxidation of 2 acetyl-CoA in the citric acid cycle?

6 NADH Signup and view all the answers

Which statement accurately describes the relationship between glycolysis and the citric acid cycle?

Glycolysis converts glucose into pyruvate, which is then oxidized to enter the citric acid cycle. Signup and view all the answers

What is the outcome of oxidative phosphorylation?

Production of a significant amount of ATP from the electron transport chain. Signup and view all the answers

Which of the following is NOT an output of the citric acid cycle?

2 acetyl-CoA Signup and view all the answers

What happens to the electrons removed during the citric acid cycle?

They are transferred to electron carriers NAD+ and FAD. Signup and view all the answers

Study Notes

BI110 Lecture 11 - October 23

Lecture date: Wednesday, October 23
Instructor: Dr. Leonard
Reminders: SI sessions on Sunday, Monday and Wednesday

Reminders

Today's lecture: Review of Chapter 4 (Cell Membranes and Signalling) and introduction to Chapter 5
Chapter 4 Mindtap Assignment due: Sunday, October 27th, at 11:59 PM
Midterm #2: Wednesday, November 20th, during class

Signal Transduction Pathways

Binding a signal molecule to a plasma membrane receptor triggers a signalling cascade.
The signal molecule does not enter the cell.
Molecules similar to the signal molecule can either trigger or block a cellular response if able to bind to the receptor's recognition site.
Drug treatments often target signal transduction pathways, sometimes at the receptor level.

Signal Transduction Pathways (continued)

Cells often use protein kinases to relay signals.
Protein kinases transfer phosphate groups from ATP to target proteins.
Added phosphate groups can stimulate or inhibit target protein activity.
Protein phosphatases reverse the effects of kinases by removing phosphate groups from target proteins, keeping them continuously active.
Some signal cascades include second messengers like cAMP.

Phosphorylation

Protein kinases often act in a chain, creating a phosphorylation cascade.
Each kinase in the cascade phosphorylates the next, culminating in a target protein.
Target protein phosphorylation affects activity, thus impacting the cellular response.

Phosphorylation Cascade (Figure 4.24)

Process starts with the signal binding to a receptor.
Receptor activates protein kinase 1.
Protein kinase 1 activates protein kinase 2.
Protein kinase 2, in turn, activates a target protein, creating a cellular response

Amplification (Figure 4.25)

Amplification increases the magnitude of each stage during a signal transduction pathway.
Each activated enzyme can activate hundreds of other proteins (enzymes) in the next stage of the pathway.
More enzyme steps in a pathway correlate to a greater degree of amplification of the response.
A few external signal molecules binding to receptors can result in a full internal response.

Example: Stimulation of Glycogen Breakdown (Epinephrine Pathway)

The Nobel Prize-winning researcher Sutherland discovered the role of epinephrine in blood glucose increase.
Epinephrine is a hormone secreted from the adrenal gland
It's the first messenger.
It initiates the process of glycogen breakdown, raising blood glucose levels.
Hormone binding triggers secondary messenger production.
Kinases phosphorylate, activating enzymes to stimulate glycogen breakdown.

Adrenaline Responses

The "fight or flight" response (caused by adrenaline) causes various physiological changes.
These changes include a burst of glucose energy release into the bloodstream, increased heart rate, and dilated pupils.
Longer-term responses may involve the expression of specific genes in different cell types.

Chapter 5

Introduces topics relating to oxidation-reduction reactions.

Oxidation-Reduction (Redox) Reactions

Electron transfer reactions between atoms or molecules.
Oxidation: loss of electrons
Reduction: gain of electrons
LEO the lion says GER (Loss of Electrons is Oxidation)

Redox reactions can involve partial electron sharing changes in covalent bonds.
For example, methane (CH4) burning demonstrates relative electron sharing shifts.
Oxygen gains a larger share of electrons relative to carbon.

Oxidation

Partial or complete electron loss.
The electron donor is oxidized.
Example: Glucose oxidation to carbon dioxide.

Reduction

Partial or complete electron gain.
The electron acceptor is reduced.
Example: Oxygen reduction to water.

A Redox Reaction

Oxidation and reduction occur concurrently, or as coupled reactions.

Combustion and Cellular Respiration (Figure 5.4)

Cellular respiration is a controlled combustion process.
Energy released is transferred to carrier molecules, preventing excessive heat gain.
Energy is released from glucose through a stepwise process to maintain a manageable degree of temperature increase.

Electron Carrier NAD+ (Figure 5.5)

NAD+ is the oxidized form of an electron carrier involved in redox reactions
Two electrons and a hydrogen ion bind to NAD+ to produce NADH.

Oxidation-Reduction Reactions (Continued)

Reduction of NAD+, to NADH and FAD to FADH2.
Reverse to oxidize NADH to NAD+ and the FADH2 to FAD.

Cellular Respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
Glucose + Oxygen → Carbon dioxide + Water + Energy

Cellular Respiration: Three Stages (Figure 5.6)

Glycolosis (cytosol): Glucose is broken down into pyruvate.
Pyruvate oxidation and the citric acid cycle (mitochondria): Pyruvate is oxidized to acetyl CoA and enters the citric acid cycle.
Oxidative phosphorylation (mitochondria): Electrons are transferred through the electron transport chain to produce ATP.

Mitochondria

Major site of cellular respiration.
Reactions carried out in mitochondria´s: Inner mitochondrial membrane and matrix.

Reactions of Glycolysis (Figure 5.9)

Glycolysis is a universal and ancient process in all cells.
It takes place in the cytosol of the cell.
The process involves a series of steps catalyzed by enzymes, and can be separated into two phases; the energy investment phase and the energy payoff phase.
Glucose is converted into two molecules of pyruvate.

Glycolysis Summary

Glycolysis does not require oxygen.
Ten chemical reactions produce pyruvate from glucose.
Two different phases: energy investment and energy payoff phases.

ATP molecules

Produced in glycolysis
Result of substrate-level phosphorylation.

Substrate-level Phosphorylation (Figure 5.10)

Phosphate from high-energy donor to ADP.
Forming ATP via enzyme-catalyzed reaction.

Cellular Respiration: Catabolism

Carbohydrates are broken down into simpler molecules like CO2.
ATP and electron carriers like NADH and FADH2 are generated.

Pyruvate Oxidation (Figure 5.11)

Pyruvate is converted to acetyl-CoA.
Takes place in the mitochondrial matrix.
Produces 2 CO2.
Generates one NADH for each pyruvate.
Links glycolysis to the citric acid cycle.

Pyruvate Oxidation (continued)

Each pyruvate yields one acetyl CoA, one NADH, and one CO₂.

Citric Acid Cycle (Figure 5.12)

Acetyl-CoA is completely oxidized to CO₂.
Electrons are removed and passed to NAD+ and FAD.
Producing NADH and FADH₂.
ATP is also produced via substrate-level phosphorylation.

Citric Acid Cycle Summary

Each acetyl-CoA cycle yields 2 CO2, 1 ATP, 3 NADH, and 1 FADH₂.

Electron Transfer System and Oxidative Phosphorylation (Figure 5.14)

NADH and FADH₂ donate electrons to the electron transport chain (ETC)
Electrons move through a series of proteins, releasing energy used to actively transport H+ across the mitochondrial membrane, generating a H+ gradient.
The electrochemical gradient (proton motive force) drives ATP synthesis by ATP synthase.

Respiratory Electron Transport Chain (Figure 5.15)

Three (3) major protein complexes are involved
Hydrogen ions (H+) are pumped from the matrix to the intermembrane space.
Prosthetic groups cycle between reduced and oxidized states.
Oxygen is the electron acceptor.

Electron Transport Chain

Electrons pass from NADH and FADH₂ to oxygen.
The chain includes four protein complexes and two smaller shuttle carriers.

Electron Transport Chain (continued 2)

Oxidations in the ETC generate energy utilized to pump protons (H+) from the matrix to the inner membrane space.
Creates a proton-motive force.
Drives ATP synthesis by ATP synthase.

Oxidative Phosphorylation and Chemiosmosis (Figure 5.16)

ATP synthase uses energy from the proton gradient across the membrane (chemiosmosis).
ATP synthase is a molecular motor embedded in the inner mitochondrial membrane.

Oxidative Phosphorylation

Understanding the differentiation between the ETC, proton-motive force, chemiosmosis, ATP synthase, and oxidative phosphorylation is crucial for this section.

ATP Yield from the Oxidation of Glucose (Figure 5.18)

Glycolysis: 2 ATP, 2 NADH
Pyruvate oxidation: 2 NADH, 2 CO2
Citric acid cycle: 2 ATP, 6 NADH, 2 FADH₂
Oxidative phosphorylation: ~ 25 ATP from 10 NADH, ~ 3 ATP from 2 FADH₂
Total energy yield from glucose oxidation: 30-32 ATP

Major Pathways Oxidizing Carbohydrates, Fats, and Proteins (Figure 5.19)

Diverse molecules (proteins, fats, carbohydrates) contribute to energy pathways.
They enter at various points in the respiratory chain.

Respiratory Intermediates

Glycolysis and citric acid cycle intermediates are often diverted for other biosynthetic processes.
Provide carbon backbones for making hormones, growth factors, prosthetic groups, and other essential cofactors.

Control of Cellular Respiration (Figure 5.20)

Various molecules regulate key steps in cellular respiration.
Control is based on supply and demand via these regulatory molecules.

Dependence upon Presence of Oxygen

Aerobic Respiration requires oxygen.
Anaerobic Respiration does not use oxygen.
Fermentation happens in the absence of oxygen.

Fermentation

Oxidizes fuel molecules without oxygen.
Two types exist: lactate and alcoholic fermentation.

Fermentation (continued)

Produces ATP without the use of the ETC in anaerobic conditions.
Pyruvate is used to produce either lactic acid or ethanol.

Lactate Fermentation (Figure 5.22a)

Pyruvate converted to lactate.
Electrons are transferred from NADH to pyruvate.
Occurs in animals and bacteria
Generates limited ATP without oxygen.

Alcoholic Fermentation (Figure 5.22b)

Pyruvate converted to ethanol and CO2.
Electrons are transferred from NADH to acetaldehyde.
Occurs in plants and fungi
Generates limited ATP without oxygen.

Anaerobic Respiration

Some bacteria and archaea lack mitochondria but have internal membrane systems.
Electron acceptors can be sulfate, nitrate, or ferric ion instead of oxygen for respiration.

Lifestyles Dictated by Oxygen

Strict anaerobes cannot grow in the presence of oxygen.
Strict aerobes require oxygen.
Facultative aerobes can use either fermentation or respiration depending on oxygen availability.

Paradox of Aerobic Life

While oxygen is crucial for respiration, it also creates harmful reactive oxygen species (ROS).
ROS are strong oxidizing agents.

Reduction of Oxygen to Water (Figure 5.24)

Oxygen reduction to water involves ROS intermediates.
ROS are potentially harmful; need protective measures.

Defense against Reactive Oxygen Species (ROS)

Cellular defense systems (enzymes like superoxide dismutase and catalase and non-enzymes like vitamin C and vitamin E) combat ROS.

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