Biology Unit 3 Lecture 1

Chemical Reactions in Living Organisms

Chemical reactions are fundamental processes that build molecules essential for life.
Digestion is the term used when breaking down molecules.
Synthesis involves starting with multiple components that react chemically, either with or without energy input, to yield a final product.
The product can be viewed as a substrate, which is subsequently broken apart in catabolism.

Insulin is crucial to metabolic processes; it requires enzymes for every chemical reaction occurring in living organisms.
Enzymes mediate critical signaling processes such as blood flow and vesicle transport in cells.
Each step of metabolic processes is enzyme-mediated, highlighting their role in both building and digesting molecules.
Digestive enzymes accelerate reactions, but the term "speed up" should be understood beyond physical velocity; it can involve eliminating steps in reactions to streamline processes.
Enzymes function as catalysts, which are molecules that facilitate reactions without being consumed in the process.

Enzymes are complex proteins that alter the pathway of a reaction.
Understanding enzymatic functions is critical for exams, and various representations may be used.
A reaction graph illustrates the energy dynamics throughout the reaction.

Activation energy is the minimum energy required for a reaction to start.
Without an enzyme, the activation energy is notably higher, whereas enzymes lower this energy requirement, facilitating quicker reactions.
Graph interpretation: The graph plots reaction progress over time, with energy peaks representing activation energy and corresponding energy levels throughout the reaction.

Enzymes are composed of long chains of amino acids, folding into distinct structures:
- Primary structure: sequence of amino acids.
- Secondary structure: localized folding patterns such as alpha helices or beta sheets, stabilized by hydrogen bonds.
- Tertiary structure: overall 3D shape resulting from interactions between R groups (side chains), involving sulfur bonds among cysteines.
- Quaternary structure: assembly of multiple tertiary structures.

Each enzyme's specificity is dictated by its unique shape, emphasizing that "shape dictates function" is a principle applicable throughout biology.
Enzymes generally adopt names ending with "-ase" which often hints at their substrate; for example:
- Sucrase: breaks down sucrose.
- Proteases: break down proteins.
- Lipases: degrade lipids.
- DNA polymerase: synthesizes DNA.

Enzymes remain unchanged post-reaction and are reusable, serving as aids to facilitate chemical reactions.
Interaction between a substrate and enzyme leads to the formation of an enzyme-substrate complex, facilitating the conversion of substrates to products.

Lock and Key Model: The enzyme's active site is a specific shape that corresponds precisely to a substrate, similar to a key in a lock. If the key (substrate) is incorrect, the reaction cannot proceed.
Induced Fit Model: The enzyme's active site can slightly adjust its shape to fit the substrate more snugly upon binding, akin to a handshake adapting to different hand shapes, showcasing a more dynamic interaction than the lock and key model.

Temperature: Enzymes function optimally at specific temperatures (e.g., 37°C for human enzymes) and can denature (unravel) at higher temperatures, losing their function.
pH levels: Varying pH conditions affect enzyme activity; for example:
- Gastric enzymes in the stomach operate optimally in highly acidic environments.
- Salivary amylase functions at neutral pH in the mouth.
Salinity: Changes in salt concentrations can also influence enzyme function.

Metabolism consists of reactions that enable organisms to sustain life, divisible into two categories:
- Catabolism (breaking down molecules, releasing energy).
- Anabolism (building up molecules, consuming energy).
Example of Catabolic Reaction: Glycolysis, Krebs cycle, and electron transport chains convert glucose into ATP, yielding energy.
Example of Anabolism: Protein synthesis from linked amino acids consumes energy.

Bioenergetics: Study of energy flow through living systems, emphasizing the transformation and conservation of energy (e.g., from sunlight to plant storage and ultimately to various consumers in the food web).
Nutrients from food (proteins, carbohydrates, fats) enter metabolic pathways to contribute to ATP production differently:
- Proteins: broken into amino acids or small chains, entering respiration pathways.
- Carbohydrates: directly enter respiration pathways.
- Fats: undergo lipase action to yield glycerol and fatty acids before participating in energy production or storage.

Each metabolic pathway begins and ends with specific molecules, facilitated by respective enzymes that convert substrates into products, continuing down the pathway until a final product is reached.
Understanding the flow of energy and how substrates are converted through enzymatic processes is crucial for grasping metabolic functions in living organisms.