General Biology Study Guide: Cell Structure, Cytoskeleton, and Study Strategies

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Course Structure and Study Strategies

Course Evaluation and Grading

The course uses a combination of exams, assignments, and participation to assess student learning. Understanding the grading breakdown helps students prioritize their efforts.

Unit Exams: Four exams, each worth 15%, with the lowest exam score eligible for replacement. Total unit exams: 60% of final grade.
Pre-read Assignments: 10% of final grade.
Case Studies: 10% of final grade.
Cumulative Final Exam: 20% of final grade.
Quizzes (Extra Credit): Up to +2% added to course total.
Course Total: 102% (including extra credit).

Assessment	Percentage
Unit Exams (4)	60%
Pre-read Assignments	10%
Case Studies	10%
Cumulative Final	20%
Quizzes Extra Credit	+2%

Effective Study Techniques

Active learning strategies and structured study sessions are essential for mastering biology concepts.

The Study Cycle: Involves pre-reading, attending lectures, annotating slides, reviewing notes, and filling gaps in understanding.
Focused Study Sessions: Plan, study, take breaks, recap, and choose next steps. Recommended session: 30-50 minutes of focused study, followed by a short break and review.
Pomodoro Technique: Work in intervals (e.g., 25 minutes study, 5 minutes break) to maintain focus and productivity.
Bloom's Taxonomy: Progress from understanding and summarizing to applying, analyzing, evaluating, and creating knowledge.
Active Recall: Practice by teaching others, discussing, and self-testing to reinforce learning.

Cell Structure and Function

Cell Theory

The cell theory is a foundational concept in biology, describing the properties and functions of cells.

Principle 1: Cells are the smallest units of life.
Principle 2: All organisms are composed of one or more cells.
Principle 3: Cells arise only by division from pre-existing cells.

Limitations on Cell Size

Cell size is constrained by the relationship between surface area and volume, which affects nutrient supply and demand.

Surface Area: Determines the rate at which nutrients and waste products can enter or leave the cell.
Volume: Represents the cell's metabolic demand.
Surface Area to Volume Ratio: As cells grow, volume increases faster than surface area, limiting efficient exchange.

Example Calculation:

For a spherical cell of radius :
Surface area:
Volume:
Surface area to volume ratio:

Types of Cells: Prokaryotic vs. Eukaryotic

Cells are classified into two main types based on their structure and organization.

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No true nucleus	True nucleus present
Size	Smaller	Larger
Organelles	Few, not compartmentalized	Many, compartmentalized
Specialization	Generalists	Specialists

Prokaryotes: Include bacteria and archaea; lack membrane-bound organelles.
Eukaryotes: Include plants, animals, fungi, and protists; possess membrane-bound organelles.

Common Features of All Cells

Despite differences, all cells share several key features:

Genetic Material: Centrally located (nucleoid in prokaryotes, nucleus in eukaryotes).
Ribosomes: Sites of protein synthesis.
Cytosol: Fluid matrix where metabolic processes occur.
Internal Structures: Organize and support cellular functions.
Plasma Membrane: Encloses the cell and regulates exchange with the environment.

Cytosol

The cytosol is the aqueous component of the cytoplasm, where many cellular processes take place.

Composition: Mostly water, dissolved ions, small molecules, and large macromolecules.
Functions: Site of metabolic pathways such as glycolysis, signal transduction, and protein synthesis.
Location: Found in both prokaryotic and eukaryotic cells.

The Cytoskeleton

Functions of the Cytoskeleton

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

Maintains cell shape
Anchors organelles to specific locations
Facilitates intracellular transport of materials
Enables cell motility and division

Components of the Cytoskeleton

The cytoskeleton consists of three main types of protein filaments, each with distinct structure and function.

Component	Diameter	Structure	Protein Subunits	Primary Roles
Microfilaments (Actin Filaments)	7 nm	Thin, entwined strands	Actin	Cell shape, motility, contraction, division
Intermediate Filaments	8-12 nm	Stretchy, rope-like proteins	Keratin, vimentin, laminin, neurofilaments	Cell shape, organelle anchoring, nuclear lamina
Microtubules	25 nm	Hollow tubes	α- and β-tubulin	Cell shape, motility (cilia/flagella), transport, chromosome movement

Motor Proteins

Motor proteins use ATP to move along cytoskeletal filaments, transporting cellular cargo.

Myosin: Moves along actin filaments; involved in muscle contraction and cell movement.
Kinesin and Dynein: Move along microtubules; transport organelles and vesicles.

Flagella and Cilia

Flagella and cilia are cellular appendages composed of microtubules, enabling movement.

Flagella: Longer, usually singular or few per cell; provide propulsion (e.g., sperm cells).
Cilia: Shorter, numerous; move fluid or particles across cell surfaces (e.g., respiratory tract).
Axoneme: The core structure of flagella and cilia, consisting of microtubule pairs arranged in a characteristic pattern.

Clinical Connections: Cytoskeletal Disorders

Mutations in cytoskeletal proteins can lead to human diseases.

Alzheimer's Disease: Abnormal tau protein disrupts microtubule stability in neurons, impairing transport of neurotransmitters.
Hypertrophic Cardiomyopathy: Mutations in actin or myosin affect heart muscle contraction, leading to thickened heart walls and reduced efficiency.
Progeria (Hutchinson-Gilford Progeria Syndrome): Mutations in the LMNA gene (coding for lamin A, an intermediate filament protein) destabilize the nuclear lamina, causing premature aging.

Additional info: The nuclear lamina is a meshwork of intermediate filaments that supports the nuclear envelope and regulates gene expression.