Cellular Structure, Energy, and Membrane Function in General Biology

Harnessing Cellular Structures

Cells: Monocellular Functions

Cells are the basic units of life, responsible for energy processing and the production of various products. They utilize specialized structures to control their chemical environment.

• Energy Processing: Cells convert energy from one form to another to sustain life processes.

• Production of Products: Cells synthesize and secrete molecules necessary for growth and maintenance.

Cellular Control of Chemical Environment

• Energy: Cells manage energy flow for metabolic activities.

• Enzymes: Biological catalysts that speed up chemical reactions.

• The Plasma Membrane: Regulates the movement of substances in and out of the cell.

Cell-based nanotechnology may be used to power microscopic robots. Additional info: This is an emerging field in biotechnology.

Conservation of Energy

Definition and Types of Energy

Energy is defined as the capacity to cause change. It exists in various forms and is essential for cellular function.

• Kinetic Energy: The energy of motion. Example: Movement of molecules.

• Potential Energy: Stored energy due to an object's position or structure. Example: Energy stored in chemical bonds.

Life depends on the conversion of energy from one form to another. The conservation of energy principle states that energy cannot be created or destroyed, only transformed.

Heat and Entropy

• Heat: A type of kinetic energy resulting from the random motion of atoms and molecules.

• All energy conversions generate some heat.

• Entropy: A measure of disorder or randomness in a system. Every energy transfer increases entropy.

Chemical Energy

Chemical energy is stored in the bonds of molecules such as food, gasoline, and other fuels. This energy can be released by chemical reactions.

• Chemical reactions: Rearrangement of atoms releases energy.

• Living cells: Use chemical energy to fuel metabolic processes.

Cellular Energy

• Cellular respiration: The process by which cells break down food molecules to release energy.

• Storage: Energy stored in a form that cells can use for work.

Humans convert about 34% of food energy to useful work.

Food Calories

• Calorie (cal): The amount of energy needed to raise the temperature of 1 gram of water by 1°C.

• Food calories: Kilocalories (kcal), equal to 1,000 calories.

• The energy in food is used to fuel cellular activities.

ATP and Cellular Respiration

ATP: Adenosine Triphosphate

ATP is the primary energy carrier in cells, generated during cellular respiration.

• Acts like an energy shuttle.

• Stores energy obtained from food.

• Releases energy as needed.

ATP Structure: Consists of adenosine and three phosphate groups.

Phosphate Transfer

• ATP energizes other molecules by transferring phosphate groups.

• This transfer enables shape changes and transport of ions and molecules.

• Drives production of large molecules.

The ATP Cycle

• Cells spend ATP continuously.

• ATP is recycled when ADP and phosphate are combined during cellular respiration.

• Up to 10 million ATP molecules are consumed and recycled per second in a working muscle cell.

Enzymes and Metabolism

Enzyme Function

Enzymes are proteins that act as biological catalysts, speeding up chemical reactions without being consumed.

• Metabolism: The sum of all chemical reactions in an organism.

• Most metabolic reactions require enzymes.

Activation Energy

• Activation energy: The energy required to start a reaction.

• Enzymes lower activation energy, enabling reactions to occur more easily.

Structure and Function: Enzyme Activity

• Enzymes are highly selective for the reactions they catalyze.

• Each enzyme recognizes a substrate (the reactant molecule).

• The active site binds the substrate, often changing shape to fit (induced fit).

• After the reaction, the enzyme releases the product and can catalyze another reaction.

• Enzyme names often end with -ase.

Enzyme Inhibitors

• Certain molecules inhibit enzyme activity by binding to the enzyme or blocking the active site.

• Some inhibitors resemble substrates and act as imposters.

• Inhibitors can disrupt enzyme function by altering its shape.

Membrane Function

Plasma Membrane Structure

The plasma membrane regulates the flow of materials into and out of the cell. It consists of a double layer of phospholipids with embedded proteins.

• Controls chemical exchanges with the environment.

• Essential for maintaining cellular homeostasis.

Movement of Molecules

• Diffusion: Movement of molecules from high to low concentration.

• Passive Transport: Diffusion across a membrane without energy input.

• Facilitated Diffusion: Passive transport aided by proteins.

Osmosis and Water Balance

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Solute: Substance dissolved in a solution.

• Hypertonic solution: Higher concentration of solute.

• Hypotonic solution: Lower concentration of solute.

• Isotonic solution: Equal concentration of solute.

• Osmoregulation: Control of water balance.

Water Balance in Plant Cells

• Plant cells have rigid cell walls.

• Plant cells in hypotonic environments do not burst due to cell walls.

Active Transport

• Requires cellular energy (usually ATP) to move molecules against a concentration gradient.

• Drives the movement of ions and other substances across membranes.

Exocytosis and Endocytosis

• Exocytosis: Movement of material out of the cell via vesicles.

• Endocytosis: Movement of material into the cell via vesicles. Example: Phagocytosis (cellular eating).

Evolution Connection: The Origin of Membranes

• A membrane can enclose a solution different from its surroundings.

• Regulation of chemical exchanges is essential for life.

Key Equations and Concepts

• Conservation of Energy: $\text{Energy}_{\text{initial}} = \text{Energy}_{\text{final}}$

• ATP Hydrolysis: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

• Calorie Definition: $1 \text{calorie} = \text{energy required to raise 1g water by 1^\circ C}$

Comparison Table: Types of Transport Across Membranes

Type	Energy Required?	Direction	Example
Diffusion	No	High to Low	Oxygen entering cells
Facilitated Diffusion	No	High to Low	Glucose transport via protein channels
Active Transport	Yes (ATP)	Low to High	Sodium-potassium pump
Osmosis	No	Water: High to Low	Water movement in plant cells

Example: Enzyme Activity

• Lactase: An enzyme that catalyzes the breakdown of lactose into glucose and galactose.

• Enzyme Inhibitors: Penicillin inhibits bacterial enzymes, blocking cell wall synthesis.

Additional info: Expanded explanations and examples were added for clarity and completeness.