Biology Chapter on Acids and Bases

Cellular Respiration

• Cellular respiration is a metabolic pathway that breaks down glucose and produces ATP.
• Glucose is the primary fuel for cellular respiration.
• If glucose breakdown happens all at once, energy is wasted as heat. If it occurs in steps, energy is produced.
• The process has four stages: Glycolysis, Oxidative decarboxylation, Krebs cycle, Oxidative phosphorylation (ETC).

Learning Outcomes

• Understand the concept of cellular respiration.
• Differentiate between aerobic and anaerobic glycolysis.
• Identify the source of ATP in the body.

Case Study

• A young woman (approximately age 35) was found unconscious near a doorway in a house that was filled with smoke after a fire.
• Her blood pressure was 70/50 mmHg, pulse 120/min, and respiration rate 30/min.
• She had no response to pain, was unconscious and flaccid.
• The woman was being administered 100% oxygen via face mask and improved but was lethargic and disoriented.

Photosynthesis

• Energy from sunlight drives the synthesis of glucose from CO2 and H2O.
• Oxygen is released as a byproduct.

Respiration & Cellular Respiration

• Respiration is the process of exchanging gases, while cellular respiration breaks down glucose for energy at the cellular level.
• Diagrams show components of the respiratory and cellular systems.

Cycles

• Glucose, in the presence of oxygen, produces ATP through several steps.
• Glycolysis occurs in the cytoplasm. It breaks down glucose into pyruvate.
• Oxidative decarboxylation converts pyruvate into acetyl CoA, entering the mitochondria.
• The Krebs cycle further oxidizes acetyl CoA to carbon dioxide, generating energy carriers (NADH, FADH2).
• Oxidative phosphorylation (ETC) utilizes energy carriers to create a proton gradient across the inner mitochondrial membrane to generate ATP.

Aerobic Glycolysis

• This is glucose oxidation in the presence of oxygen.
• Cells transfer energy in organic compounds to ATP.
• Carbon dioxide and water are released as byproducts (waste products of respiration).

Glycolysis

• Glycolysis is the breakdown of glucose into pyruvate in the cytoplasm.
• This process produces ATP (2 molecules).
• NAD+ is converted to NADH during this step (2 molecules).

Oxidative Decarboxylation

• Pyruvate molecules produced from glycolysis enter the mitochondria.
• Within the mitochondria, they are converted to acetyl CoA and 2 NADH are generated.

Krebs Cycle

• A series of chemical reactions that release stored energy by oxidizing acetyl CoA derived from CHO, lipids, and proteins.
• The acetyl group of acetyl-CoA is oxidized, forming CO2 and energy.
• Energy production happens by coupling to the compounds 3 NAD+ and 1 FAD+ and 1 ATP molecule for each pyruvate.
• Results in reduced 3 NADH molecules, and reduced to 1 FADH2 molecule.

Oxidative Phosphorylation (ETC)

• A group of protein complexes act in the last stage of cellular respiration and is found in the inner mitochondrial membrane.
• These complexes shuttle electrons from NADH and FADH2 to molecular oxygen, converting them to NAD+ and FAD.
• This process creates a proton gradient, providing energy for oxidative phosphorylation that synthesizes ATP.
• Oxygen is the final electron acceptor and combines with protons to form water.

Importance of ETC

• Transferring electrons regenerates empty NAD+ and FAD+ to be used again.
• Transfer of protons across the membrane establishes a gradient.
• This gradient provides energy for oxidative phosphorylation to synthesize ATP.
• Oxygen accepts electrons at the end of the electron transport chain and combines with protons to form water. This is the final electron acceptor for the system.

Total ATP Production (Aerobic)

• The complete aerobic oxidation of one glucose molecule generates approximately 38 ATP molecules through glycolysis, intermediate stage, Krebs cycle, and the electron transport chain.

Anaerobic Glycolysis

• Glucose oxidation happens in the absence of oxygen.
• A source of energy for red blood cells and contracting muscles.

Aerobic vs. Anaerobic Respiration

• Aerobic respiration requires oxygen and yields 38 ATP molecules.
• Anaerobic respiration does not require oxygen and produces only 2 ATP molecules.

Cellular Pathway

• Diagram depicts the pathway from glucose to pyruvate (via aerobic or anaerobic pathways).
• Outcomes (CO2, H2O, or lactate) are different.

Inhibition of Cellular Respiration

• Inhibition can occur through blocking the flow of glycolysis or oxidative phosphorylation.
• Pyruvate kinase deficiency is an autosomal recessive disease affecting red blood cells, which depend on glycolysis for ATP production.

Inhibition of Oxidative Phosphorylation

• Inhibitors block the electron flow through the electron transport chain (ETC) or phosphorylation processes.
• Examples include Rotenone, Antimycin A, Cyanide (CN), and Carbon monoxide (CO).
• Oligomycin inhibits ATP synthase (complex V).

Uncouplers

• Uncouplers disrupt the proton gradient, hindering ATP synthesis.
• Examples include Ca injection, high-dose aspirin, high levels of thyroid hormones, and progesterone.

Case Study (Smoke Inhalation)

• A young woman, experiencing smoke inhalation, is presented.
• The cause of impairment is related to cyanide blocking the electron transport chain and preventing oxygen utilization.
• This leads to anaerobic metabolism and metabolic acidosis as well as contributing to the symptoms observed.

pH and Acid-Base Balance

• Students will be able to differentiate between acids and bases, define pH and its scale, list sources of acid production, and understand how the body defends against pH changes through buffers, the respiratory system, and the renal system.
• Disturbances in pH balance can lead to acidosis or alkalosis, each presenting with a range of possible symptoms.

Important Buffer Systems in the Body

• Bicarbonate, phosphate, and protein systems are important physiological buffers.

Buffer Systems (1st Line of Defense)

• They help maintain stable pH when acids or bases are added.
• Buffers are solutions resisting pH changes with small additions of acid or base.
• They comprise a "taker" and a "giver" part which respectively remove H+ or donate H+ to regulate pH.

Respiratory System (2nd Line of Defense)

• The lungs adjust acid/base balance quickly by controlling CO2 removal.
• If pH falls (acidosis), rapid respiration occurs to remove CO2.
• If pH rises (alkalosis), slow respiration minimizes CO2 loss.

Kidneys (Final Line of Defense)

• The kidneys control pH by excreting or reabsorbing hydrogen ions/bicarbonate.

Reference Range of Arterial Blood Gases (ABG)

• Table provides the normal physiological ranges of pH, PaO2, PaCO2, HCO3, and SaO2.

Acid-base Imbalance

• Acidosis/alkalosis is the result of an imbalance between the body's acid and base production/removal mechanisms.

Respiratory Acidosis

• Characterized by a low blood pH and increased carbon dioxide levels, often due to impaired lung function (e.g., asthma)
• Reduced ventilation and increased CO2 level due to breathing disorders.

Respiratory Alkalosis

• Characterized by a high blood pH and decreased carbon dioxide levels.
• Rapid breathing (hyperventilating) often due to stress or panic results in excessive CO2 loss.

Metabolic Acidosis

• Produced when the body generates excessive amounts of acids or loses the ability to neutralize or eliminate them.
• Excessive acid production or loss of buffer capacity in the body contribute to metabolic acidosis, for example, lactic acidosis or diabetic ketoacidosis.

Metabolic Alkalosis

• Characterized by a high blood pH and increased levels of bicarbonate due to an excessive loss of acid (vomiting) or gain of bicarbonate in the body.

The Respiratory Parameter of ABG

• Summarized table representing how the respiratory parameter of ABG assists in determining and identifying acid/base imbalance through the measures of pH/PCO2/HCO3-.

Pulmonary Surfactants

• Complex formed by type II alveolar cells.
• Secreted into airspaces around week 22 of gestation for lung maturity.
• It decreases surface tension in the alveoli, reducing the pressure needed to re-inflate alveoli.

Surfactant Insufficiency

• Associated with Respiratory Distress Syndrome (RDS) and neonatal death in preterm infants.
• Management involves administering glucocorticoids before delivery to accelerate lung maturation, or synthetic surfactant after birth.

Testing Lung Maturity

• Evaluation of fetal pulmonary maturation is important for risk stratification.

Measurement of L/S Ratio by Thin Layer Chromatography (TLC)

• The L/S ratio (lecithin/sphingomyelin) is a standard method for assessing lung maturity.

Phosphatidylglycerol (PG) Assay

• Detects Phosphatidylglycerol antibodies in amniotic fluid to determine lung maturity.

Types of Antioxidants

• Enzymatic and non-enzymatic antioxidants neutralize reactive oxygen species (ROS).

Oxidative Stress

• Imbalance between oxidants (ROS) and antioxidants causes oxidative stress.

Antioxidant Mechanisms

• Preventing generation of ROS/free radicals (preventive), breaking down chain reaction of ROS/free radicals (chain-breaking), and repairing the damage caused by free radicals (repair).