Cell Structure and Function

Cellular Components and Their Functions

Cells are the basic units of life, and their structure is closely related to their function. Both prokaryotic and eukaryotic cells share certain features, but also have distinct differences.

• Nucleus: The membrane-bound organelle that contains genetic material (DNA) in eukaryotic cells.

• Microvilli: Finger-like projections on the apical surface of epithelial cells that increase surface area for absorption.

• Basolateral membrane: The side of the cell facing away from the lumen, involved in transport and cell signaling.

• Tight junctions: Specialized connections between adjacent cells that prevent leakage of materials.

• Na+-K+ ATPase: An enzyme that pumps sodium out of cells and potassium into cells, maintaining electrochemical gradients.

Example: Intestinal epithelial cells have microvilli on their apical membrane to maximize nutrient absorption.

Macromolecules and Chemical Bonds

Types of Biological Molecules

Biological macromolecules are essential for life and include carbohydrates, lipids, proteins, and nucleic acids. Their structure is determined by the types of chemical bonds that hold their monomers together.

• Covalent bond: A strong chemical bond formed by the sharing of electron pairs between atoms.

• Ester linkage: The bond formed between a fatty acid and glycerol in lipids.

• Peptide bond: The covalent bond between amino acids in proteins.

• Phosphodiester bond: The bond between nucleotides in nucleic acids (DNA and RNA).

Example: The peptide bond is formed during protein synthesis between the amino group of one amino acid and the carboxyl group of another.

Classification of Macromolecules

• Fatty acids: Building blocks of lipids, characterized by long hydrocarbon chains.

• Steroids: Lipids with a characteristic four-ring structure.

• Nucleotides: Monomers of nucleic acids, consisting of a sugar, phosphate group, and nitrogenous base.

Example: Cholesterol is a steroid, while DNA is composed of nucleotide monomers.

Digestion and Absorption

Digestive Processes and Enzymes

The digestive system breaks down food into absorbable units using mechanical and chemical processes. Enzymes play a critical role in catalyzing the breakdown of macromolecules.

• Pepsin: An enzyme in the stomach that digests proteins.

• Peristalsis: Wave-like muscle contractions that move food through the digestive tract.

• Pancreas: Secretes digestive enzymes that break down carbohydrates, proteins, and fats in the small intestine.

• Villi: Small, finger-like projections in the small intestine that increase surface area for absorption.

Example: After eating broccoli, enzymes from the pancreas help digest the carbohydrates and proteins present in the vegetable.

Absorption Mechanisms

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

• Facilitated diffusion: Movement of molecules across membranes via specific carrier proteins.

• Co-transport: Simultaneous transport of two substances across a membrane by a single protein.

Example: Glucose absorption in the intestine often occurs via co-transport with sodium ions.

Membrane Structure and Transport

Phospholipids and Membrane Proteins

Cell membranes are composed of a phospholipid bilayer with embedded proteins that regulate transport and communication.

• Phospholipid: A molecule with a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.

• Channel protein: Provides a passageway for specific molecules to cross the membrane.

• Carrier protein: Binds and transports substances across the membrane.

Example: Aquaporins are channel proteins that facilitate water movement across cell membranes.

Osmosis and Tonicity

Osmosis is the movement of water across a semipermeable membrane. Tonicity describes the relative concentration of solutes in solutions separated by a membrane.

• Hyperosmotic: Solution with higher solute concentration compared to another.

• Hypoosmotic: Solution with lower solute concentration compared to another.

Example: Red blood cells placed in a hypoosmotic solution will swell as water enters the cell.

Genetics and Cell Division

Chromosomes and Cell Cycle

Genetic material is organized into chromosomes, which are duplicated and distributed during cell division.

• Chromosome: A structure composed of DNA and proteins that carries genetic information.

• Microtubules: Cytoskeletal structures involved in chromosome movement during cell division.

• Microfilaments: Cytoskeletal elements that support cell shape and movement.

Example: During mitosis, microtubules form the spindle apparatus that separates chromosomes.

Experimental Design and Data Interpretation

Scientific Method and Hypothesis Testing

Biologists use controlled experiments to test hypotheses and interpret data. Understanding how to read tables and graphs is essential for analyzing results.

• Control group: The group in an experiment that does not receive the experimental treatment.

• Experimental group: The group that receives the treatment or variable being tested.

• Inference: A logical conclusion drawn from data and observations.

Example: In a study comparing forest and prairie mice, differences in tail length and foot size may be due to genetic adaptation to their environments.

Sample Data Table: Mouse Trait Comparison

The following table compares tail length and hind foot length in forest and prairie mice after three generations of cross-breeding.

Additional info: The table demonstrates that forest mice have longer tails and feet than prairie mice, suggesting genetic differences due to habitat.

Key Terms and Definitions

Selected Terms

• Duodenum: The first section of the small intestine, where most chemical digestion occurs.

• Ileum: The final section of the small intestine, involved in nutrient absorption.

• Phagocytosis: The process by which cells engulf large particles or other cells.

Sample Equations and Formulas

Osmolarity Calculation

Osmolarity is a measure of solute concentration, calculated as follows:

where is the molar concentration of each solute and is the number of particles the solute dissociates into.

Na+-K+ ATPase Reaction

The sodium-potassium pump operates according to the following reaction:

Diagrams and Structural Identification

Macromolecule Identification

Students should be able to identify fatty acids, steroids, nucleotides, and amino acids from structural diagrams.

• Fatty acid: Long hydrocarbon chain with a carboxyl group.

• Steroid: Four fused carbon rings.

• Nucleotide: Contains a phosphate group, pentose sugar, and nitrogenous base.

Example: In a diagram, molecules with a phosphate group and nitrogenous base are nucleotides.

Amino Acid Structure

General structure of an amino acid:

where R is the side chain, which determines the properties of the amino acid.

Summary Table: Cell Structure Terms

Additional info:

• Some definitions and diagrams were inferred from context and standard biology curriculum.

• All content is relevant to introductory college-level General Biology.