METABOLISM
Enzymes
Functionality of Enzymes
Enzyme function can be affected by various factors, including:
pH
Temperature
Presence of inhibitors
Presence of coenzymes and cofactors
Concentration of reactants and products
Definition and Structure of Enzymes
Definition: Enzymes are proteins that catalyse specific chemical reactions without being altered in the process.
Example: Pyruvate dehydrogenase (PDA) – a model of an enzyme.
Main Features of Enzymes
Protein Nature: All enzymes are proteins.
Speed of Reactions: All enzymes speed up chemical reactions.
Reaction Specificity: Enzymes are not used up in the reaction and are specific to particular reactions.
Working Conditions: Each enzyme works under specific conditions, such as pH and temperature.
Energy Reduction: Enzymes work by lowering the energy required for reactions (activation energy).
Lock-Key Principle: Enzymes function based on the lock-key model, where specific substrates fit into specific enzymes.
Coenzyme and Cofactor Interaction: Enzymes often work with coenzymes and cofactors to facilitate reactions.
Denaturation: Enzymes can be denatured by excessive heating, altering their function.
Activation Energy
Definition: Activation energy is the minimum energy required to initiate a chemical reaction.
Role of Enzymes: Enzymes function by lowering the activation energy needed for a reaction to occur.
Visualization
Diagram representation:
Without enzyme: Higher activation energy represented by stairs.
With enzyme: Reduced activation energy shown by lower stairs.
Enzyme-Substrate Complex
Definition: The molecules that enzymes act on are called substrates.
Specificity: Enzymes are specific, meaning each enzyme only binds to particular substrate molecules.
Structural Fit: The enzyme and substrate must have compatible shapes to bind efficiently.
Shape Alteration Impact: Changes in shape or structure (due to temperature or pH changes) prevent binding, inhibiting enzyme activity.
Lock-Key Model
Analogy: This model explains the specific interaction between an enzyme and a single substrate, analogous to a key fitting into a lock.
Active site mechanism:
The active site on the enzyme binds to the substrate to form an enzyme-substrate complex.
The enzyme facilitates breakdown of the substrate into smaller product molecules without altering itself.
Denaturation of Enzymes
Active site importance: The active site is critical for substrate attachment.
Shape Maintenance: The specific shape of the active site must remain unchanged for proper enzyme function.
Causes of Denaturation: Changes due to heating or toxic substances can alter the active site shape, leading to loss of function.
Enzyme Activity Affected by pH
Optimal pH: Enzymes generally function optimally at neutral pH.
Digestive Enzymes: Some enzymes, like rennin in gastric juice, require acidic conditions.
Example**:
Rennin: Found in the stomach, starts denaturation as food moves to the alkaline region of the intestines.
Factors Influencing Enzyme Function
Concentration:
Enzyme concentration:
Too little = slow reaction.
Too much = constant reaction rate.
Just right = fast reaction.
Substrate concentration:
Too little = slow reaction.
Too much = constant reaction rate.
Just right = fast reaction.
Temperature:
Optimal body temperature is approximately 37°C.
Higher temperatures lead to enzyme denaturation.
Lower temperatures decrease collision rates, resulting in decreased activity.
Coenzymes and Cofactors:
These compounds bind to the active site along with the substrate and may carry electrons or other atoms needed for reactions.
Presence of Inhibitors:
Inhibitors typically bind to the active site, blocking substrate bonding and reducing enzyme activity.
Macronutrients
SCSA Dot Point: Cells require oxygen and nutrients for efficient metabolism:
Nutrients include:
Carbohydrates
Proteins
Lipids
Vitamins
Minerals
Nutrients Defined
Definition: Nutrients are chemical compounds in foods essential for life.
Categories of Nutrients:
Carbohydrates
Lipids
Proteins
Vitamins
Minerals
Carbohydrates
Examples: Include sugars and starches.
Composition: All contain elements C, H, O in a ratio of approximately 1C:2H:1O.
Building Blocks: Monosaccharides (simple sugars such as glucose).
Main Uses of Carbohydrates
Energy Source: Main energy source for cellular respiration.
Combination with Other Substances: Forms structures such as glycoproteins in cell membranes.
Storage: Can be stored as glycogen in liver and muscle cells.
Sugars
Definition: Small carbohydrate molecules, can be monosaccharides or disaccharides.
Characteristics: Water soluble and typically sweet.
Examples of Sugars
Monosaccharides:
Glucose (dextrose)
Fructose
Galactose
Ribose
Disaccharides:
Sucrose
Maltose
Lactose
Polysaccharides
Examples:
Starch: Common polysaccharide, a major component of carbohydrate intake.
Glycogen: Found in animals.
Properties:
Long chains of simple sugars (polymers).
Not sweet and do not dissolve in water.
Carbohydrate-Rich Foods
Foods Rich in Starch:
Cereal-based foods (bread, pastry, pasta, noodles, rice)
Vegetables (potatoes, beans, corn)
Nuts
Foods Rich in Sugars:
Cakes, biscuits, candies
Many processed foods
Fruits (dried fruit, stone fruits, bananas, and citrus)
Sweetened drinks (fruit juices, flavored milk, sodas)
Lipids
Examples: Fats and oils composed of the elements C, H, and O, but with a lower proportion of oxygen than carbohydrates.
Building Blocks: Fatty acids and glycerol.
Essential Fatty Acids: Such as omega-3 and omega-6.
Triglycerides
Most lipids are triglycerides, composed of one glycerol molecule attached to three fatty acids.
Bonds between C and H in fatty acids determine whether a fat is 'saturated' or 'unsaturated'.
Lipid Classification
Low-Density Lipoproteins (LDL): Transport cholesterol from liver to tissues, often termed 'bad' cholesterol as high levels can lead to plaque formation and cardiovascular diseases.
High-Density Lipoproteins (HDL): Transport cholesterol from tissues back to the liver, referred to as 'good' cholesterol.
Main Uses of Lipids
Energy Source: Lipids have double the energy content of carbohydrates.
Energy Storage: Store excess energy.
Insulation: Helps maintain body temperature.
Organ Protection: Surrounds and protects organs.
Structural Functions: Integral to cell membranes and myelin sheaths.
Metabolic Functions: Includes cholesterol and steroid production.
Chemical Messengers: Acts as hormones and prostaglandins.
Foods Rich in Lipids
Dairy products (cream, butter, cheese)
Fried foods and pastries
Meat (fatty cuts) and poultry (with skin)
Oily fish
Avocados, olives, and nuts
Proteins
Composition: Contain C, H, O, and N. Some proteins also contain iron, sulfur, and phosphorus.
Building Blocks: Made up of amino acids.
Main Uses of Proteins
Structural Functions: Essential components of muscle (actin and myosin) and connective tissues (collagen).
Metabolic Functions: Enzymes and other metabolic proteins.
Oxygen Transport: Hemoglobin’s role in carrying oxygen.
Protection: Antibodies and factors in blood clotting.
Energy Source: Can provide energy during shortages.
Essential Amino Acids
Definition: The eight (or possibly nine) amino acids that cannot be synthesized by the body and must be ingested through diet.
Complete vs Incomplete Proteins:
Complete proteins (animal sources such as meat, eggs, and milk) contain all essential amino acids.
Incomplete proteins (plant sources such as grains and legumes) may lack one or more essential amino acids.
Protein-Rich Foods
Dairy products (milk, cheese, yogurt)
Eggs
Lean meats, fish, and chicken
Soy products, beans, and lentils
Grains (bread and pasta)
Nuts and seeds
Nucleic Acids
Composition: Contains C, H, N, and P.
Building Blocks: Nucleotides, which join to form DNA or RNA strands.
Vitamins
Definition: Organic compounds needed in small amounts for normal health.
Function: Many act as coenzymes or regulate metabolic processes.
Categories: 13 known vitamins, most sourced from foods, some synthesized in the body.
Solubility of Vitamins
Classifications:
Water-soluble: Vitamins B and C; easily excreted from the body.
Fat-soluble: Vitamins A, D, E, K; absorbed in the gut with lipids.
Vitamin Deficiency Diseases
Night Blindness (Vitamin A deficiency)
Beriberi (Vitamin B1 deficiency)
Pellagra (Vitamin B3 deficiency)
Anemia (B6 and B12 deficiencies)
Miscarriage and neural tube defects (Folic acid deficiency)
Scurvy (Vitamin C deficiency)
Rickets (Vitamin D deficiency)
Dietary Minerals
Definition: Chemical elements necessary for life, in addition to C, H, N, and O.
Natural Occurrence: Found in all natural foods.
Macrominerals and Trace Minerals
Macrominerals: Required in relatively large amounts (e.g., Na, Mg, K, Ca, Fe, P, S, Cl).
Trace Minerals: Needed in small amounts.
Functions of Dietary Minerals
Calcium: Crucial for bone and muscle function.
Sodium & Potassium: Essential electrolytes.
Iron: Integral to hemoglobin formation.
Phosphorus: Key component of nucleic acids (DNA & RNA).
A Balanced Diet
USDA Food Pyramid Serving Recommendations:
Fats, Oils & Sweets: Use sparingly.
Milk, Yogurt & Cheese: 2-3 servings.
Vegetable Group: 3-5 servings.
Meat, Poultry, Fish, Dry Beans, Eggs & Nuts: 2-3 servings.
Fruit Group: 2-4 servings.
Bread, Cereal, Rice & Pasta: 6-11 servings.
Metabolism
SCSA Dot Points:
Biochemical processes, including anabolic and catabolic reactions in cells, are controlled by specific enzymes.
Cellular respiration occurs in different cytosol and mitochondrial locations to catabolize organic compounds (aerobically or anaerobically) to release energy in the form of ATP.
Overview of Metabolism
Definition: Total of all chemical processes in the body which convert food into energy and materials necessary for life.
Inputs and Outputs of Metabolism
Input Components:
Oxygen (O2)
Water (H₂O)
Glucose
Nutrients
Output Components:
Metabolic wastes (e.g., carbon dioxide CO2 and urea)
Water and salts
Anabolism and Catabolism
Definitions:
Anabolism: Constructive metabolic processes that build complex substances from simpler ones, requiring energy.
Catabolism: Destructive metabolic processes that break down complex substances into simpler ones, releasing energy.
Catabolic Process
Role: Catabolic reactions, like cellular respiration, release energy as complex substances are broken down.
Cellular Respiration Equation
Reaction:
Source: Glucose, formed from the breakdown of complex carbohydrates, is the primary food material used in respiration.
Location of Cellular Respiration
Anaerobic Stage: Occurs in the cytoplasm.
Aerobic Stages: Takes place in the mitochondria.
Mitochondrial Structure
Components:
Outer membrane
Inner membrane (cristae)
Matrix
Key Definitions
Aerobic: A process that requires oxygen.
Anaerobic: A process that does not require oxygen.
Overview of Cellular Respiration
Products:
Water + 34 ATP
Carbon Dioxide + 2 ATP
Oxygen
Glucose
Pyruvate
Acetyl Coenzyme A
Krebs Cycle + 2 ATP
Electron Transfer Chain
Glycolysis
Breakdown Processes
Glycolysis:
Converts glucose (C6H12O6) into two molecules of pyruvic acid (C3H4O3)
Yields two molecules of ATP
Occurs in the cytoplasm and is anaerobic
Krebs Cycle
Definition: Also known as citric acid cycle, it involves the complete breakdown of pyruvate (via acetyl coenzyme A) to CO2.
Yields: 36 molecules of ATP
Location: Takes place in the mitochondria and requires oxygen.
ATP (Adenosine Triphosphate)
Definition: The primary energy carrier in cells.
Conversion: Energy from the Krebs cycle converts adenosine diphosphate (ADP) into ATP, storing energy.
Energy Release: When a phosphate group is removed from ATP, energy is released, reverting ATP to ADP.
ATP-ADP Cycle
Cycle Description:
ATP is formed from ADP and a phosphate group, storing energy.
Energy is released for cellular processes when ATP is converted back to ADP.
Uses of Energy in Biological Processes
Thermoregulation: 60-80% of energy from ATP breakdown is released as heat, maintaining body temperature.
Biological Functions:
Muscle contraction
Active transport across membranes
Synthesis of large molecules for growth and repair
Transmission of nerve impulses
Cellular division
Other cellular activities involving substance movement
Example of Anaerobic Respiration
Context: Occurs during extreme physical exercise when oxygen becomes limited in muscle cells.
Function: Provides additional energy, but results in lactic acid accumulation, causing pain and fatigue.
Anabolism
Description: Anabolic reactions construct complex substances from simpler ones, requiring energy for synthesis.
Example: Protein synthesis is a key anabolic process.
Protein Synthesis Process
Structure: Proteins consist of long chains of amino acids (20 common amino acids).
Information Source: Instructions for protein assembly (sequence of amino acids) are encoded in DNA.
Ribosome Role: Ribosomes serve as the sites for protein synthesis, translating genetic information into functional proteins.
Ribosome Structure
Composition: Made of RNA, consisting of large and small subunits.
Small sub-unit
Large sub-unit
Function: Assemble amino acids into proteins.
Basal Metabolic Rate (BMR)
Definition: The minimum energy needed to sustain life, representing the energy required for the body to function at rest.