Study Guide for BSC1010 Chapter 4
Chapter 4: THE ENERGY OF LIFE
1. Definition of ENERGY
Energy: The capacity to do work or to produce change. It exists in various forms, including kinetic and potential.
2. Distinction between Kinetic and Potential Energy
a. Kinetic Energy
Definition: The energy of motion.
Examples in the cell:
Movement of molecules across a membrane during diffusion.
The motion of motor proteins moving along cytoskeletal filaments.
b. Potential Energy
Definition: Stored energy that has the potential to do work.
Examples in the cell:
Chemical energy stored in the bonds of glucose molecules.
Energy stored in a concentration gradient, such as ions across a membrane.
3. Laws of Thermodynamics
a. 1st Law of Thermodynamics
Definition: Energy cannot be created or destroyed, only transformed from one form to another.
b. 2nd Law of Thermodynamics
Definition: In any energy transfer, the universe tends to increase in disorder or entropy; energy transformations are not 100% efficient.
4. Application to Biological Systems
Biological systems adhere to these laws, constantly transforming energy and increasing entropy through metabolic processes.
5. Definition of Entropy
Entropy: A measure of the disorder or randomness in a system; it reflects the amount of energy in a physical system that is unavailable for doing work.
6. Organisms as Open Systems
An organism is considered an open system because it exchanges both energy and matter with its environment, helping it maintain order and organization against entropy.
7. Definition of Metabolism
Metabolism: The totality of an organism's chemical reactions, encompassing both the energy-producing and energy-consuming processes within a cell.
8. Catabolism vs. Anabolism
a. Catabolism
Definition: The set of metabolic pathways that break down molecules into smaller units to release energy.
Examples:
Glycolysis: the breakdown of glucose into pyruvate.
Lipolysis: the breakdown of fats into fatty acids and glycerol.
b. Anabolism
Definition: The set of metabolic pathways that construct molecules from smaller units, consuming energy in the process.
Examples:
Protein synthesis: the creation of proteins from amino acids.
Gluconeogenesis: the synthesis of glucose from non-carbohydrate substrates.
9. Free Energy
Definition: The amount of energy in a system that is available to do work at constant temperature and pressure. It is represented by the symbol G (Gibbs free energy).
10. Exergonic and Endergonic Reactions
a. Exergonic Reaction
Definition: A reaction that releases energy.
Example: Cellular respiration, where glucose is broken down to CO2 and water and releases energy.
b. Endergonic Reaction
Definition: A reaction that requires energy input.
Example: Photosynthesis, which converts carbon dioxide and water into glucose while absorbing sunlight energy.
11. Oxidation-Reduction Reactions
Definition: Reactions that involve the transfer of electrons between two species; oxidation involves loss of electrons while reduction involves gain of electrons.
a. Oxidation
Definition: The process where a molecule loses electrons and increases its oxidation state.
b. Reduction
Definition: The process where a molecule gains electrons and decreases its oxidation state.
12. Electron-Transport Chain
Definition: A series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions and couples this electron transfer with the transfer of protons ( ext{H}^+ ions) across a membrane.
13. Main Kinds of Cellular Work
Types of Cellular Work:
Chemical Work: Biosynthesis of macromolecules.
Transport Work: Moving substances across membranes against concentration gradients.
Mechanical Work: Movement such as muscle contractions.
14. Energy Obtaining by Cells
Cells obtain energy by coupling exergonic reactions (which release energy) to endergonic reactions (which require energy), primarily through the use of ATP.
15. Structure of ATP
Structure: ATP consists of adenosine (adenine base + ribose sugar) bonded to three phosphate groups. The bond between the second and third phosphate group is more likely to break, releasing energy for cellular processes.
16. Biological Macromolecule Class of ATP
ATP belongs to the class of biological macromolecules known as nucleotides, aiding in energy transfer in cells.
ENZYMES
1. Definition of Enzymes
Definition: Enzymes are biological catalysts that speed up reactions by lowering activation energy. They are specific to their substrates and play crucial roles in metabolic pathways.
2. Key Terms Related to Enzymes
Enzyme: A protein that catalyzes biochemical reactions.
Substrate: The reactant molecule upon which an enzyme acts.
Products: The molecules generated by an enzyme-catalyzed reaction.
Induced Fit: A model that describes how an enzyme changes shape to better fit the substrate upon binding.
Active Site: The region of the enzyme where substrate molecules bind and undergo a chemical reaction.
3. Factors Affecting Enzyme Activity
a. Temperature
Effect: Increased temperature can increase activity up to a point but can lead to denaturation beyond optimal ranges.
Example: Enzyme activity of pepsin is optimal around pH 2.
b. pH
Effect: Each enzyme has an optimal pH range; deviations can result in decreased activity or denaturation.
Example: Salivary amylase is active at neutral pH.
c. Salt Concentration
Effect: High salt concentrations can disrupt ionic bonds and lead to denaturation.
d. Concentration of Substrate
Effect: Increasing substrate concentration increases reaction rate until the maximum velocity (Vmax) is reached.
e. Concentration of Enzyme
Effect: Increasing enzyme concentration increases reaction rates proportionally, assuming substrate is sufficient.
4. Cofactors and Coenzymes
Cofactors: Non-protein chemical compounds that assist enzymes; they can be metal ions or organic molecules.
Coenzymes: Organic cofactors, such as vitamins that assist with enzyme function and help in transferring chemical groups.
5. Competitive vs. Non-Competitive Inhibitors
a. Competitive Inhibitors
Definition: Molecules that compete with the substrate for the active site of the enzyme.
b. Non-Competitive Inhibitors
Definition: Molecules that bind to an enzyme at a site other than the active site, causing a conformational change and preventing enzyme activity without competing with the substrate.
6. Feedback in Enzymatic Reactions
a. Positive Feedback
An increase in the output of a pathway enhances the process that leads to that output.
Example: In childbirth, oxytocin increases contractions during delivery.
b. Negative Feedback
A process in which an increase in the output of a pathway inhibits that process altogether.
Example: High levels of ATP inhibit a key enzyme in the pathway of its synthesis.
Membrane Transport
1. Concentration Gradient
Definition: A difference in the concentration of a substance across a biological membrane, serving as a driving force for movement.
2. Passive Transport
Definition: Movement of molecules across a membrane without energy expenditure, following their concentration gradient.
3. Active Transport
Definition: Movement of molecules against their concentration gradient, requiring energy (ATP).
4. Types of Transport Mechanisms
a. Simple Diffusion
Definition: Movement of solutes through a membrane without assistance from proteins, from areas of higher to lower concentration.
b. Facilitated Diffusion
Definition: Movement of polar or charged substances across a membrane via a membrane protein, down their concentration gradient.
c. Osmosis
Definition: The diffusion of water through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
d. Active Transport
Definition: Utilizes ATP to move substances against their gradient through specific transport proteins.
5. Differences Between Facilitated Diffusion and Passive Diffusion
Facilitated Diffusion: Involves specific proteins and occurs more efficiently for molecules that cannot easily pass through the lipid bilayer.
Passive Diffusion: Simple movement without protein assistance, relying solely on concentration gradients.
6. Differences Between Facilitated and Active Transport
Facilitated Transport: Does not require ATP and relies on concentration gradients.
Active Transport: Requires energy input to move molecules against their concentration gradients.
7. Drug Effects on Membrane Proteins
A drug that binds tightly to a membrane protein may block the function of transport proteins involved in facilitated diffusion or active transport, inhibiting substance movement across the membrane.
8. Important Ion Gradients in Human Cells
Typical Ion Concentrations:
Calcium ions (Ca2+), sodium ions (Na+), potassium ions (K+), and chloride ions (Cl-) are kept at different concentrations by the cell.
Higher concentration outside the cell: Na+ and Ca2+
Higher concentration inside the cell: K+ and proteins.
9. Concentration Definitions Related to Solute and Water Movement
a. Isotonic
Definition: Solutions with equal solute concentrations, leading to no net movement of water.
b. Hypertonic
Definition: Solutions with a higher solute concentration compared to another, causing cells to lose water.
c. Hypotonic
Definition: Solutions with a lower solute concentration, leading to the intake of water by cells.
d. Lysis
Definition: The rupture of a cell due to excess water intake; often occurs in hypotonic solutions.
e. Plasmolysis
Definition: The shrinkage of a cell away from its cell wall due to loss of water in a hypertonic solution (only relevant for cells with a wall).
f. Osmosis
Definition: Movement of water through a semi-permeable membrane in response to solute concentration differences.
10. Salt Concentration Equivalent of a Human Cell
Typical Salt Concentration: Isotonic saline solutions are approximately 0.9% sodium chloride.
Distilled Water IV Impact: If a person received distilled water in an IV, their cells would swell and potentially burst due to a hypotonic environment.
11. Effect on Lettuce Leaves
a. Wilted Lettuce Leaf in Fresh Water
Effect: The leaf will become turgid as water moves into the cells, causing them to swell.
Relevant Terms: It involves osmosis and terms of hypotonic solutions.
b. Lettuce Leaf in Salt Water
Effect: The leaf will wilt as water moves out of the cells, leading to plasmolysis.
Relevant Terms: Hypertonic solutions involve loss of water.
12. Molecule Transport Across Membrane
a. Endocytosis
Definition: The process through which cells internalize substances by engulfing them in membranes.
i. Phagocytosis
Definition: Cell engulfs large particles or microorganisms.
ii. Pinocytosis
Definition: Cell takes in small particles dissolved in liquid.
iii. Receptor-mediated Endocytosis
Definition: A process where cells internalize molecules based on their receptor recognition on the cell surface.
b. Exocytosis
Definition: The process through which cells expel materials in membrane-bound vesicles that fuse with the plasma membrane.
13. Molecules Crossing Plasma Membrane
a. Molecules Transported Without Protein Carriers
Examples: Water, small nonpolar molecules (e.g., ethanol).
b. Molecules Requiring Specific Carriers
Examples: Glucose, ions such as sodium and potassium, and large biomolecules like amino acids or proteins.
c. Review of Transport Mechanisms
Transport methods: Molecules that are small and nonpolar may diffuse across the membrane, while larger or charged molecules require specific carriers and may engage in facilitated diffusion or active transport depending on their gradients and energy requirements.
d. Cystic Fibrosis and Membrane Transport
Cystic Fibrosis results from a mutation in a gene that codes for a protein that transports chloride ions across cell membranes, leading to thick mucus buildup in various organs. This condition clearly illustrates how a defect in membrane transport can have widespread physiological effects.