Cellular Respiration and Electron Carriers

Cellular Respiration

• Cellular respiration is the breakdown of glucose to produce ATP, a crucial energy source for cells.
• The process occurs in four main stages: Glycolysis, Pyruvate processing, Citric Acid Cycle, and Electron Transport Chain.
• It involves the oxidation of glucose, releasing energy.
• The breakdown of glucose is a series of chemical reactions.
• These reactions are controlled by enzymes.
• By the end of a lecture students should be able to describe the process of cellular respiration, explain glycolysis and Krebs cycle, and understand the differences between aerobic and anaerobic respiration.

Metabolism

• Metabolism refers to all the chemical processes occurring within an organism.
• Understanding metabolism is important clinically for diagnosis and treatment of various diseases.
• It allows for study of human biochemistry.
• Many diseases impact metabolism
• Nutritional deficiencies can impact metabolism.
• Age-related changes affect cellular metabolism.
• Enzyme deficiencies can lead to metabolic disorders.
• Inherited metabolic disorders stem from genetics
• Cancer can affect cell metabolism.
• Hormone imbalances impact cellular metabolism, such as in diabetes.
• Metabolic disorders affect organ function and need to be controlled by the right therapeutic targets.
• Unwanted by-products are also produced during metabolism, which can affect blood pH levels.

Nutrition and Digestive System

• Food is digested into basic components (fats, carbohydrates, amino acids, vitamins, and minerals).
• These are converted to biomolecules, including proteins, lipids/fats, complex sugars, and DNA.
• Biomolecules undergo Metabolism (chemical processes for life).
• The gastrointestinal system is crucial for food breakdown and absorption, detailed in later stages.
• The digestive system digests, absorbs and processes food.
• The digestive enzymes break down biomolecules for energy.

Glucose as a Fuel Source

• Glucose is the primary fuel source for the brain and red blood cells.
• Starch and a smaller amount of glycogen in diets are broken down to glucose.
• Glucose is absorbed from the intestine and transported to the blood.
• Glucose is metabolized for energy by cells, which is important to maintain living systems.

Biomolecules

• Glucose is a simple carbohydrate with the formula C₆H₁₂O₆.
• Sucrose (table sugar) is composed of glucose and fructose.
• Lactose (milk sugar) is composed of glucose and galactose.
• Maltose is composed of two glucose molecules.

Glucose: Provider of Cellular Energy

• Glucose is the primary source of energy, used to produce ATP.
• Glucose can be stored as glycogen or starch for later use.
• Glucose is broken down.
• Glucose breaks down to release energy so smaller building blocks can be produced..

Cellular Respiration: Oxidation of Glucose

• Glucose is broken down in cells in multiple small steps to make ATP (adenosine triphosphate)
• The process of electrons moving through chemical reactions releases energy..
• This energy is used to create ATP, the cell's main energy currency.
• The overall chemical reaction is: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP).

Oxidation and Reduction

• Oxidation is the removal of electrons, releasing energy.
• Reduction is the addition of electrons, storing energy.
• These reactions are central to how energy is used within the cell.
• Cells use oxidation and reduction to transfer energy.
• Key processes in cellular respiration are oxidation and reduction.

Redox Reaction

• The process of Oxidation and reduction occurs as part of cellular respiration.
• The reaction of glucose and oxygen is a redox reaction.
• Electrons are moved from one molecule to the next.

Movement of Electrons in Biology

• Electrons are not usually transported in isolation.
• Hydrogen atoms act as electron carriers.
• Electrons are moved in hydrogen atoms.

Electron Carriers

• Electron carriers (e.g., NAD+ and FAD) facilitate the transportation of high-energy electrons during cellular respiration.
• NAD+ accepts two electrons to reduced NADH.
• FAD accepts two hydrogens and two electrons to become FADH2.

Example of NADH Production

• NADH produced in reactions in the citric acid cycle.
• This NADH is used to make ATP in the electron transfer transport chain (ETC).

Electron Carriers: FAD

• FAD is a coenzyme derived from vitamin B2.
• FAD is an electron carrier useful in cellular respiration.
• Like NAD+, FAD accepts electrons.

Example of FADH2 Production

• FADH2 is produced during reactions in the citric acid cycle.
• FADH2 is used in the electron transfer transport chain (ETC).

ATP as an Energy Currency

• ATP (adenosine triphosphate) is the main energy currency in cells.
• It provides energy for muscle contraction, nerve impulses, and many other cellular processes.
• Hydrolysis (breaking down) of ATP releases energy for work to be done.

Hydrolysis of ATP

• ATP is unstable due to the repulsion among oxygen atoms.
• Hydrolysis of the terminal phosphate group of ATP stabilizes the molecule and releases energy.
• Breaking the phosphate bond in ATP releases stored energy.
• This energy is then used by the cells to perform work.

ATP → ADP → AMP

• ATP is the most common form of energy.
• ATP is hydrolyzed to form ADP (adenosine diphosphate) then AMP (adenosine monophosphate).
• This continuous breakdown releases energy used by cells

###Metabolism of Glucose Diagram

• Glucose is metabolized through Glycolysis and other pathways to produce energy in the form of ATP.

Overview of Respiration

• Glycolysis, Pyruvate processing, Citric acid cycle, and Electron transport are part of the process.
• The stages take place within different structures of the cell.

Glycolysis as the First Stage of Energy Production

• Glycolysis uses glucose from the diet as a starting material.
• Glucose is converted to pyruvate.
• The process involves 10 chemical reactions, controlled by enzymes.

Glycolysis Overview

• Glycolysis contains 2 main stages.
• Stage 1 (preparation stage): The initial stage requires energy input to proceed.
• Stage 2: The second stage converts cyclic rings to smaller 3-carbon products.

Stage 1 of Glycolysis

• This stage uses ATP to prime the reactions.
• The process needs energy input to begin. Glucose turns into its 6-phosphate form.

Second Phase of Glycolysis

• This is when ATP is produced from substrate-level phosphorylation, and two NADH are made.

ATP Generation from Stage 2 of Glycolysis

• PEP is converted to Pyruvate through phosphate group transfer to ADP.
• This step is part of the production of ATP in the process of Glycolysis

Glycolysis Summary

• Glucose conversion to pyruvate by a 10-step process in the cell's cytoplasm
• 2 ATP molecules are produced
• 2 NADH molecules are generated through redox reactions

Sugars as Bonded Molecules

• Glycogen and Starch are formed through the formation of a 1,6 bond, and 1,4 bonds between glucose monor units.

Feeder pathway for Glycolysis

• Sugars (e.g., lactose, sucrose, glucose) feed into glycolysis pathways in different ways, entering different steps of glycolysis to provide energy for cellular function.

Metabolism and Lactose Intolerance

• Lactose found in milk can't be digested by those lacking the lactase enzyme
• Lack of lactase causes digestive issues like gas, bloating, and diarrhea after consuming milk.

NAD+ Regeneration

• NAD+ needs to be regenerated to keep glycolysis operating.
• Regeneration can happen through aerobic respiration (with oxygen) or anaerobic respiration (without oxygen).

Exercise and Physical Demand Can Increase the Glycolysis Rate

• Increased physical activity causes a shift in the metabolic pathway towards greater glycolysis.

In The Absence of Oxygen - Anaerobic Respiration Occurs

• Pyruvate is converted to lactate.
• Production of lactate occurs in the absence of oxygen.

Lactic Acid Fermentation

• The process of making lactate from pyruvate in the absence of oxygen.
• Lactate fermentation generates 2 ATP.

Cori Cycle (aka Lactic Acid Cycle)

• The cycle involving lactate transport to the liver to be converted into glucose, then transported to the muscles.
• It allows for the continuous cycling of glucose and lactate between muscle and liver.

When the Body Lacks Fuel It Can Make Its Own Glucose Supply

• Pyruvate can be converted back into glucose via Gluconeogenesis, for cells to use. This process takes place in the liver when glucose levels drop

Active Metabolic Pathways

• Glycolysis, gluconeogenesis, lactic acid fermentation, citric acid cycle, oxidative phosphorylation, glycogen breakdown, fatty acid oxidation, and amino acid catabolism are different metabolic processes occurring in cells.

Glycolysis Recap

• The process of glycolysis, containing 2 major stages.
• Key concepts on glycolysis:
• Stage 1 (preparation stage): ATP required.
• Stage 2 (energy payoff phase): ATP generated and cyclic rings converted to smaller molecules.

What Next? Oxidation Of Pyruvate

• In the presence of oxygen, pyruvate is oxidized to acetyl CoA inside the mitochondria.
• Pyruvate is transported into the mitochondria and converted into Acetyl-CoA.

Now The Molecules Start to Get Larger

• Acetyl CoA is formed from pyruvate entering the Citric Acid Cycle..
• The molecules have now grown bigger, ready to be used for energy

Acetyl CoA Then Enters- The Citric Acid Cycle

• CoA from the previous stages of cellular respiration converts into Acetyl-CoA, which enters the Citric Acid Cycle..
• Acetyl CoA moves into the citric acid cycle inside the mitochondria.

The Citric Acid Cycle Harvests High-energy Electrons

• Molecules are oxidized to generate high-energy electrons for NADH and FADH₂.
• NAD+ and FAD are reduced and carry high energy electrons to other stages of cells respiration.
• ATP and Co2 are produced.

Citric Acid Cycle

• A cycle that produces molecules from Acetyl-CoA. (citric acid/TCA/Krebs).
• High-energy molecules are created in these reactions.

Breakdown Of One Glucose: So Far..

• A summary of ATP and other molecules produced at each stage of cellular respiration.

So WHY Have We Been Collecting All This NADH And FADH2??

• These molecules carry high-energy electrons to the electron transport chain (ETC).
• Electrons provide energy needed for further ATP production.

The Enzyme ‘ATP Synthase’ Uses These Electrons To Make LOTS More ATP

• ATP synthase uses the energy from the electron transport chain (ETC) to make ATP, the primary energy currency of cells

Metabolism of Glucose

• A summary of the different stages of glucose metabolism and the ATP yields of each stage.

Aerobic Respiration

• Cellular respiration using oxygen.
• Glucose is completely broken down for maximum ATP production.
• Oxygen acts as the final electron acceptor in the electron transport chain.

Anaerobic Respiration

• Cellular respiration without oxygen.
• Glucose is incompletely broken down to yield less ATP.
• An organic molecule is the final electron acceptor in fermentation, producing lactate instead.

Biochemistry (Additional Information)

• Metabolism of different types of biomolecules, including carbohydrates, lipids, and proteins.
• Metabolic pathways are interconnected and regulated, to support homeostasis and cellular functions
• The text mentions biochemistry textbooks for further learning.

This quiz explores the role of electron carriers in cellular respiration, including molecules like NAD+ and FAD. It covers key processes such as glycolysis and the Electron Transfer Chain, as well as distinctions between aerobic and anaerobic respiration. Test your understanding of ATP production and the breakdown of glucose in energy metabolism.