General Biology Study Notes: Cell Structure, Membrane Function, and Metabolism

A Tour of the Cell (Ch 6)

Prokaryotic vs. Eukaryotic Cells

Cells are the fundamental units of life, and they are classified as either prokaryotic or eukaryotic based on their structural features.

• Prokaryotic cells lack a membrane-bound nucleus and organelles. Their DNA is located in a region called the nucleoid.

• Eukaryotic cells have a true nucleus enclosed by a nuclear envelope and possess membrane-bound organelles.

• Common features of all cells:

  • Plasma membrane

  • Cytoplasm

  • Ribosomes

  • Genetic material (DNA)

Cell Theory

The cell theory is a foundational concept in biology that describes the properties of cells.

• All living organisms are composed of one or more cells.

• The cell is the basic unit of structure and function in living things.

• All cells arise from pre-existing cells.

Cell Organelles and Their Functions

Eukaryotic cells contain specialized structures called organelles, each with distinct functions.

• Nucleus: Contains genetic material and controls cellular activities.

• Mitochondria: Site of cellular respiration and ATP production.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes to break down waste.

• Chloroplasts: (in plants) Site of photosynthesis.

• Vacuoles: Storage of substances; large central vacuole in plant cells.

Unique Organelles in Plant/Animal Cells

• Plant cells: Have cell walls, chloroplasts, and a large central vacuole.

• Animal cells: Have centrioles and lysosomes (rare in plants).

Cell Wall, Cytoskeleton, and Extracellular Matrix

• Cell wall: Rigid structure outside the plasma membrane in plants, fungi, and some prokaryotes; provides support and protection.

• Cytoskeleton: Network of protein filaments (microtubules, microfilaments, intermediate filaments) that maintain cell shape and assist in movement.

• Extracellular matrix (ECM): Complex network of proteins and carbohydrates outside animal cells; provides structural support and mediates cell signaling.

Membrane Structure and Function (Ch 7)

Structure and Function of the Plasma Membrane

The plasma membrane is a selectively permeable barrier that surrounds the cell, controlling the movement of substances in and out.

• Composed mainly of a phospholipid bilayer with embedded proteins.

• Functions include protection, communication, and transport of materials.

The Fluid Mosaic Model

The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components that gives the membrane a fluid character.

• Phospholipids move laterally within the layer, allowing flexibility.

• Proteins are interspersed throughout, serving as channels, receptors, or enzymes.

• Cholesterol molecules help regulate membrane fluidity.

Major Components of the Plasma Membrane

• Phospholipids: Form the basic structure (bilayer).

• Proteins: Integral (span the membrane) and peripheral (attached to surface).

• Carbohydrates: Attached to proteins/lipids on the extracellular surface; involved in cell recognition.

• Cholesterol: Maintains fluidity and stability.

Cell Wall, Cytoskeleton, and Extracellular Matrix (in context of membranes)

• Plant cell walls provide additional support outside the plasma membrane.

• The cytoskeleton anchors membrane proteins and maintains cell shape.

• The extracellular matrix connects cells and transmits signals.

An Introduction to Metabolism (Ch 8)

Metabolism and Chemical Reactions

Metabolism encompasses all chemical reactions in a cell, divided into metabolic pathways.

• Metabolic pathway: A series of chemical reactions that build up or break down molecules.

• Chemical reaction: Process that changes one set of chemicals into another.

Types of Energy

• Kinetic energy: Energy of motion.

• Potential energy: Stored energy due to position or structure.

• Chemical energy: Potential energy stored in chemical bonds.

Anabolic vs. Catabolic Pathways

• Anabolic pathways: Build complex molecules from simpler ones; require energy (e.g., photosynthesis).

• Catabolic pathways: Break down complex molecules into simpler ones; release energy (e.g., cellular respiration).

• ATP (Adenosine Triphosphate): The main energy currency of the cell.

The Two Laws of Thermodynamics

• First Law: Energy cannot be created or destroyed, only transformed (law of conservation of energy).

• Second Law: Every energy transfer increases the entropy (disorder) of the universe.

Equations:

• First Law: $\Delta E = q + w$ (change in internal energy equals heat plus work)

• Second Law: $\Delta S_{universe} > 0$ (entropy of the universe increases in spontaneous processes)

ATP/ADP Cycle and ATP's Role

• ATP stores energy in its high-energy phosphate bonds.

• When ATP is hydrolyzed to ADP (adenosine diphosphate), energy is released to power cellular work.

Equation:

• $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Structure and Function of Enzymes

• Enzymes: Biological catalysts that speed up chemical reactions by lowering activation energy.

• Enzymes are specific to their substrates and are not consumed in the reaction.

• Most enzymes are proteins with a unique three-dimensional structure.

Example: Amylase is an enzyme that catalyzes the breakdown of starch into sugars.