General Biology Exam 2 Study Notes: Enzymes, Cell Structure, Membrane Transport, and Cytoskeleton

Enzymes and Chemical Reactions

How Enzymes Aid Chemical Reactions

Enzymes are biological catalysts, typically proteins, that accelerate chemical reactions by lowering the activation energy required. They achieve this by physically interacting with reactants (substrates) and altering their orientation or strain to facilitate the reaction.

• Enzyme: A protein that speeds up chemical reactions without being consumed.

• Activation Energy: The minimum energy required to start a chemical reaction.

• Mechanism: Enzymes physically manipulate the substrate, making the reaction more likely to occur.

• Example: The enzyme sucrase catalyzes the breakdown of sucrose into glucose and fructose.

Enzyme Regulation

Enzymes can be regulated by molecules that either inhibit or activate their activity. Inhibitors can bind covalently (irreversible inhibition) or non-covalently (reversible, competitive inhibition).

• Competitive Inhibition: Inhibitor binds to the active site, blocking substrate binding.

• Non-competitive Inhibition: Inhibitor binds elsewhere, changing enzyme shape so it cannot bind substrate.

• Regulation: Enzymes can be turned on or off by regulatory molecules.

Cell Theory and Cell Types

Cell Theory

Cell theory is a fundamental concept in biology stating:

• All living organisms are made up of one or more cells.

• All cells arise from other pre-existing cells.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles (e.g., animal and plant cells).

Venn Diagram Comparison:

• Animal Cells: Centrioles, lysosomes

• Plant Cells: Chloroplasts, cell wall, central vacuole

• Both: Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, plasma membrane

Endosymbiosis Theory

Endosymbiosis is the evolutionary theory that eukaryotic cells originated when a prokaryotic cell engulfed another, leading to beneficial relationships. The engulfed cells became organelles such as mitochondria and chloroplasts.

• Mitochondria and Chloroplasts: Organelles with their own DNA, evidence of endosymbiotic origin.

Membrane Transport

Types of Membrane Transport

Cells transport substances across their plasma membrane using various mechanisms:

• Simple Diffusion: Small, non-polar molecules (gases, small lipids) move directly through the membrane without channel proteins.

• Facilitated Diffusion: Proteins help move larger or charged molecules across the membrane via channel proteins.

• Active Transport: Moves substances from low to high concentration against the gradient, requiring energy (ATP).

Active Transport Details

• Primary Active Transport: Uses pump proteins and ATP to move molecules (low to high concentration).

• Secondary Active Transport: Uses concentration gradients created by pumps to facilitate transport of other molecules.

• Endocytosis: Cell engulfs materials via vesicles (e.g., phagocytosis).

Osmosis and Tonicity

Osmosis is the movement of water across a membrane. Tonicity describes the effect of solute concentration on cell volume.

• Hypotonic Solution: Lower solute concentration outside; water enters cell, cell swells.

• Hypertonic Solution: Higher solute concentration outside; water leaves cell, cell shrinks.

• Isotonic Solution: Equal solute concentration; water movement is balanced.

The Nucleus

Structure and Function

The nucleus is the control center of eukaryotic cells, containing genetic material and coordinating cellular activities.

• Chromatin: Thin fibers of DNA carrying hereditary information, associated with proteins.

• Nucleolus: Site where ribosomal subunits are assembled.

• Nuclear Membrane: Double membrane with nuclear pores for transport of molecules.

The Cytoskeleton

Components and Functions

The cytoskeleton is a network of protein fibers that provides structural support, facilitates cell movement, and enables intra-cellular transport.

• Microtubules: Thick, hollow tubes that transport materials and help in cell division. Also form cilia and flagella for movement.

• Intermediate Filaments: Durable, rope-like systems of overlapping proteins that support cell shape and provide strength.

• Microfilaments: Long, solid, rope-like fibers involved in cell movement and contraction.

Example: Muscle contraction is driven by microfilaments (actin and myosin).

Fiber Type	Main Function	Structure
Microtubules	Transport, cell division, movement	Thick, hollow tubes
Intermediate Filaments	Support cell shape, strength	Durable, rope-like
Microfilaments	Cell movement, contraction	Long, solid fibers

Additional info: These notes cover foundational topics in cell biology, including enzyme function, cell structure, membrane transport, and cytoskeletal organization, suitable for General Biology college students.