Cellular Metabolism

Chemical Reactions and Metabolism

• Metabolism are the chemical processes enabling cells to survive
• Key chemical reactions in cells center around obtaining energy from food and making it available for bodily functions
• Two main types of metabolism are anabolism (synthesis) and catabolism (breakdown)

Carbohydrate Metabolism and ATP Formation Chapter 69

• After absorption, fructose and galactose are quickly converted to glucose in the liver
• Glucose (C6H12O6) is the final pathway used by the body to transport carbohydrates into cells

Transport of Glucose Through Cell Membrane

• Glucose cannot passively enter cells, requiring active or facilitated transport with a carrier protein.
• Insulin plays a vital role in this process

Phosphorylation

• Glucose, upon entering a cell, combines with a phosphate radical forming glucose-6-phosphate.
• This glucose can be immediately used for energy or stored as glycogen in the liver and muscles

Glycogenesis

• The formation of glycogen, a storage form of glucose.

Glycogenolysis

• Breakdown of glycogen into glucose within the liver.
• It is a crucial process for maintaining glucose levels in the blood.
• Hormones like epinephrine and glucagon stimulate the process

Release of Energy from Glucose

• Glucose's breakdown occurs through several stages including glycolysis, the citric acid cycle, and the electron transport chain
• Each stage yields ATP, a source of energy for cellular functions

Glycolytic Pathway

• One molecule of glucose can release a large amount of energy (686,000 calories), but only 12,000 calories are needed to form ATP.
• Enzymes facilitate the gradual oxidation of glucose, optimizing the capture of energy as ATP.
• 38 moles of ATP are generated per mole of glucose

Glycolysis

• Glycolysis is the primary process for extracting energy from glucose
• Involves ten steps and occurs in the cytoplasm
• Glucose is broken down into two pyruvic acid molecules (3 carbons each)
• This process also produces ATP, a form of usable chemical energy.

Glycolysis (Continued)

• Net gain of ATP from one glucose molecule: 2 pyruvic acid molecules, 2 ATP molecules, and 4 hydrogen atoms.
• Efficiency of ATP formation is 43%.
• Pyruvic acid combines with Coenzyme A to form Acetyl-CoA, which produces 6 more ATP molecules later in the process

Citric Acid Cycle (Krebs Cycle)

• Occurs within the mitochondria
• Acetyl CoA combines with oxaloacetic acid forming citric acid (first product of the cycle).
• The cycle results in the continual production of oxaloacetic acid
• 24 hydrogen atoms are released for each glucose molecule

Citric Acid Cycle (Krebs Cycle) (Continued)

• 20 hydrogen atoms combine with NAD+ via dehydrogenase.
• During further stages, water is added and carbon dioxide and hydrogen atoms are released.
• 2 molecules of ATP are produced

Net Reaction per Molecule of Glucose in the Citric Acid Cycle

• The overall reaction involves Acetyl CoA, water, ADP, and CO2, resulting in the formation of CoA and ATP

Oxidative Phosphorylation

• Oxygen is essential to the process
• NADH within mitochondria is converted to NAD+ , H+, and electrons.
• The electrons initiate the Electron Transport Chain where energy is generated, captured as a proton gradient
• The resulting process is called chemiosmosis.

Energy production through oxidative phosphorylation

• A series of steps in the electron transport chain within the mitochondria produce considerable amounts of ATP
• The process captures energy from the reactions

Summary of ATP Formation

• Glycolysis produces 4 ATP (2 consumed), Citric Acid Cycle produces 2 ATP.
• The Electron Transport Chain produces 34 ATP, resulting in a total of 38 ATP.
• The efficiency of ATP production during glucose is roughly 66%.
• Feedback mechanisms regulate ATP production

Anaerobic Glycolysis

• This process yields a diminished amount of energy from glucose.
• Pyruvic acid combines with NADH and hydrogen to form lactic acid.
• Used as a measure of cellular oxygen usage and overall body efficiency

Storage of Glucose

• Glycogen stores are filled up first
• Excess is stored as fat

Gluconeogenesis

• The synthesis of glucose from non-carbohydrate sources (fatty acids and protein) when blood sugar is low.
• Low blood glucose triggers the release of cortisol, which initiates protein breakdown into amino acids for glucose formation

Lipid Metabolism Chapter 69

• Lipids are concentrated cellular energy sources.
• The most efficient way cells store energy
• Lipids include triglycerides (neutral fats), phospholipids, and cholesterol along with other lipids

Fatty Acids

• Fatty acids are long-chain hydrocarbon molecules containing a carboxylic acid group.
• Common types like palmitic acid have a particular structure

Triglycerides

• Triglycerides are structures with glycerol (a three-carbon alcohol) bonded to three fatty acids.
• A major storage form of lipids in animals.

Absorption of Fats

• Dietary triglycerides break down into monoglycerides and fatty acids within the intestines.
• The broken-down fats are reassembled into triglycerides, creating chylomicrons.
• Absorption into the lymphatic system occurs, and plasma appears cloudy one hour after high-fat consumption.

Uptake Into Cells

• Lipoprotein lipase in capillary cells breaks down triglycerides into fatty acids and glycerol.
• Fatty acids diffuse into cells
• Inside the cells, fatty acid resynthesizes into triglycerides and are then stored.

Transport Through Body

• When needed, fat cells liberate triglycerides into fatty acids and glycerol.
• These components combine with albumin, forming free fatty acids to be transported around the body

Fat Deposits

• Fat deposits are accumulations of adipose tissue in the body and liver
• Adipose tissue cells, or fat cells, are largely made of triglycerides, the body's primary form of lipid storage.

Use of Triglycerides for Energy

• Triglycerides provide a considerable portion of the energy in many diets
• Fatty acids and glycerol are products of triglycerides breakdown.
• Glycerol is converted for glucose breakdown, while fatty acids are oxidized in mitochondria

Beta-Oxidation

• Fatty acids are gradually converted into Acetyl-CoA via a process called beta-oxidation within the cell.
• This Acetyl-CoA then enters the Citric Acid (Krebs) cycle
• A substantial quantity of ATP is generated through this process, effectively exploiting fatty acids for cellular energy production.

Ketosis

• When the body lacks carbohydrates, fats are used for energy.
• This results in the production of ketone bodies, including B-hydroxybutyric acid, acetoacetic acid, and acetone.
• Possible causes include starvation, diabetes, and high-fat, low-carbohydrate diets.

Regulation of Fat Utilization

• Epinephrine and norepinephrine boost triglyceride lipase activity, significantly increasing FFA levels.
• Rate of fatty acid usage is influenced by: corticotropin release from the anterior pituitary, glucocorticoid release from the adrenal cortex, and less insulin secretion.

Phospholipids

• Phospholipids consist of a fatty acid, phosphoric acid, and a nitrogenous base.
• Types include lecithins, cephalins, and sphingomyelins.
• Essential components of cell membranes and lipoproteins.

Uses of Phospholipids

• Phospholipids are crucial components of cell membranes.
• They are constituents of lipoproteins and are involved in clotting (thromboplastin).
• Sphingomyelin forms myelin sheaths around nerve cells.

Uses of Cholesterol

• Cholesterol is involved in bile formation in the liver.
• It is a precursor to essential hormones such as estrogen, progesterone, and testosterone.
• Cholesterol is critical in forming the skin's protective outer layer.

Atherosclerosis

• A buildup of fatty deposits (plaques) in the arteries where fat and cholesterol are deposited.
• This leads to thickened and hard arteries, a condition also known as arteriosclerosis.
• Arterial blockages and potential ruptures may occur if this deposit persists

Factors Leading to Atherosclerosis

• Risk factors include physical inactivity, obesity, diabetes, hypertension, high lipids, and smoking.

Prevention of Atherosclerosis

• Key preventative measures include low-fat diets, smoking cessation, exercise, blood pressure and glucose control, and consumption of high-fiber options (e.g., oat bran).
• Prescription drugs, such as statins, inhibit cholesterol production.

Protein Metabolism Chapter 70

• Proteins comprise a substantial part of the body's structure.
• Proteins are made up of different amino acids linked together by peptide bonds and hydrogen bonds.

Protein Functions

• Proteins have various functions including structural roles, enzymatic action, oxygen transport, roles in nucleoproteins and in muscle contraction and cellular function.

Regulatory Proteins

• Regulatory proteins carry messages from chemical signals throughout the cell.
• These signaling molecules involve G protein-coupled receptors.
• Ligand binding is the initiating step, leading to downstream effects and impacting other body parts.

Transport of Amino Acids

• Digested proteins become free and separate amino acids in the gastrointestinal tract.
• The process of absorbing proteins into their constituent amino acids typically takes 2-3 hours.
• Amino acids enter the cells using active transport or facilitated diffusion.
• Excess amino acids are expelled via urine if their concentrations exceed renal reabsorption capacity.

Storage of Amino Acids

• Amino acids are quickly integrated into new proteins after entering body cells.
• When necessary, these amino acids are released and transported to the blood to resupply depleted resources.

Major Plasma Proteins

• Albumin regulates colloid osmotic pressure in the blood.
• Globulins are associated with metabolic processes and immune responses
• Fibrinogen is a crucial component in blood clotting

Dietary Amino Acids

• Ten amino acids are deemed essential, as the body cannot produce them.
• Ten others are deemed non-essential, as the body can synthesize them

Use of Proteins for Energy

• Protein breakdown to get energy happens in the liver.
• Deamination removes amino groups (-NH2) from amino acids.
• Enzymes called aminotransferases facilitate the deamination process

Urea

• The liver converts ammonia produced during deamination into urea.
• Ammonia is hazardous to neurons, making its removal essential.
• Urea is eliminated from the body through the kidneys.

Oxidation of Deaminated Amino Acids

• Following deamination, resulting keto acids are converted into substances that can enter the citric acid cycle.
• These substances can then be oxidized to generate ATP.
• The process of forming keto acids or fatty acids from amino acids is called ketogenesis

Obligatory Degradation of Proteins

• The body processes 20-30 grams of protein for degradation into amino acids for use and disposal.
• Protein deficiency will impact the functioning of the various organs.
• Carbohydrates save protein for functional purposes when adequate levels are present.

Hormonal Regulation of Protein Metabolism

• Growth hormone accelerates amino acid transport into cells for protein synthesis.
• Insulin aids amino acid cellular uptake, promoting protein generation.
• Glucocorticoids increase extrahepatic protein breakdown to increase amino acid availability.
• Testosterone supports protein deposition in muscles.
• Thyroxine helps accelerate metabolism, facilitating either catabolism or anabolism, depending on need.

This quiz covers key concepts in cellular metabolism, including glycogenolysis, glycolysis, the Krebs cycle, oxidative phosphorylation, and triglyceride uptake. Questions focus on enzyme functions, energy yields, and the roles of essential molecules like oxygen. Understanding these processes is important for comprehending how cells generate and utilize energy.