Cell Structure, Function, and Study Strategies in General Biology

Course Structure and Study Strategies

Course Evaluation and Grading

This course uses a combination of unit exams, assignments, and a cumulative final to assess student understanding. The grading breakdown is as follows:

Assessment	Percentage of Total Grade
Unit Exams (4 total, best 3 count)	60%
Pre-read Assignments	10%
Case Studies	10%
Cumulative Final Exam	20%
Quizzes (Extra Credit)	+2%
Total	102%

Note: One unit exam score may be replaced by the final exam score if it is higher.

Effective Study Techniques

Success in biology requires active engagement with the material. The following strategies are recommended:

• The Study Cycle: A structured approach to learning that includes pre-reading, attending lectures, reviewing notes, and self-testing.

• Focused Study Sessions: Plan, study with focus, take breaks, recap, and decide on next steps. Each session should last 30-50 minutes with short breaks.

• Pomodoro Technique: Work in focused intervals (typically 25-30 minutes) followed by short breaks to maximize concentration and retention.

• Active Learning: Teaching others, practicing by doing, and participating in discussions are among the most effective ways to retain information.

Cell Structure and Function

Cell Theory

The cell theory is a fundamental 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 Size and Microscopy

Most cells are small due to limitations in surface area to volume ratio, which affects the ability to exchange materials with the environment.

• Surface Area to Volume Ratio: As a cell increases in size, its volume grows faster than its surface area, limiting efficient nutrient uptake and waste removal.

• Microscopy: Light microscopes can visualize most cells and some organelles, while electron microscopes are required to see smaller structures such as proteins and lipids.

Example: Enterocytes in the small intestine have a high surface area to volume ratio to maximize nutrient absorption.

Types of Cells: Prokaryotic vs. Eukaryotic

Cells are classified into two main types based on their structural characteristics:

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present (true nucleus)
Organelles	Few, non-membrane bound	Many, membrane-bound
Size	Typically smaller	Typically larger
Complexity	Simple	Complex
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Common Features of All Cells

• Genetic Material: DNA is centrally located (nucleoid in prokaryotes, nucleus in eukaryotes).

• Ribosomes: Sites of protein synthesis.

• Cytosol: The fluid component inside the cell where metabolic processes occur.

• Plasma Membrane: Encloses the cell and regulates the movement of substances in and out.

Cytosol and Its Functions

The cytosol is the aqueous component of the cytoplasm, where many metabolic reactions take place.

• Composed mostly of water, dissolved ions, small molecules, and large macromolecules.

• Site of important processes such as glycolysis and signal transduction.

The Cytoskeleton

The cytoskeleton is a network of protein fibers that provides structural support, organization, and movement within cells.

• Functions:

  • Maintains cell shape

  • Anchors organelles

  • Facilitates intracellular transport

  • Enables cell motility and division

Components of the Cytoskeleton

Component	Diameter	Structure	Protein Subunits	Characteristics	Primary Roles
Microfilaments (Actin Filaments)	7 nm	Thin, entwined strands	Actin	Very dynamic	Cell shape, muscle contraction, cell division, cytoplasmic streaming
Intermediate Filaments	8-12 nm	Stretchy, rope-like	Various (e.g., keratin, laminin)	Very stable	Cell shape, anchor organelles, nuclear lamina
Microtubules	25 nm	Hollow tubes	α- and β-tubulin	Very dynamic	Cell shape, motility (cilia/flagella), chromosome movement, intracellular transport

Motor Proteins and Cytoskeletal Interactions

• Motor Proteins: Use ATP to move along cytoskeletal filaments, transporting vesicles and organelles.

• Examples:

  • Myosin (moves along actin filaments)

  • Kinesin and Dynein (move along microtubules)

Flagella and Cilia

• Both are composed of microtubules arranged in a characteristic "9+2" pattern (axoneme).

• Flagella: Longer, usually one or a few per cell, used for locomotion.

• Cilia: Shorter, often numerous, used for movement or moving substances along the cell surface.

Clinical Connections: Cytoskeletal Defects

• Alzheimer's Disease: Abnormal tau protein disrupts microtubule stability in neurons, impairing transport of neurotransmitters and leading to cell death.

• Hypertrophic Cardiomyopathy: Mutations in cytoskeletal or associated proteins (e.g., actin, myosin) can impair heart muscle contraction, leading to thickened heart walls and risk of heart failure.

• Progeria (Hutchinson-Gilford Progeria Syndrome): Mutations in the LMNA gene affect the nuclear lamina (intermediate filaments), causing nuclear instability and premature aging.

Additional info: The LMNA gene encodes lamin A, a key intermediate filament protein in the nuclear envelope.