exam tmr

Studying Cells

• Cytology – The study of the structure and function of cells.

• Light Microscopy (LM) – Uses visible light to magnify cell structures. Can observe live or stained cells but has limited resolution.

• Electron Microscopy (EM) – Uses electron beams for high-resolution imaging of cells.

• Scanning Electron Microscopy (SEM) – Provides a 3D view of the cell’s surface.

• Transmission Electron Microscopy (TEM) – Provides detailed images of internal cell structures.

Cell Theory

• Basic Concepts of Cell Theory:

• All living things are made of cells.

• Cells are the basic units of life.

• All cells arise from pre-existing cells.

• Cells are the fundamental units of homeostasis.

Overview of Cell Anatomy

• Extracellular Fluid (Interstitial Fluid) – Fluid surrounding cells that provides nutrients and removes waste.

• Cell Membrane (Plasma Membrane) – A lipid bilayer that separates the cell from the external environment.

• Cytoplasm – The fluid inside the cell that contains cytosol and organelles.

• Cytosol – The intracellular fluid containing ions, proteins, and dissolved nutrients.

• Organelles – Specialized structures within the cytoplasm that perform specific functions.

The Cell Membrane

• Functions of the Plasma Membrane:

• Physical Isolation – Separates the cell from the external environment.

• Regulation of Exchange – Controls what enters and exits the cell.

• Sensitivity – Responds to environmental changes.

• Structural Support – Provides shape and strength.

• Membrane Structure:

• Phospholipid Bilayer – Two layers of phospholipids with hydrophilic heads and hydrophobic tails.

• Membrane Proteins:

• Receptors – Detect signals from the environment.

• Channels – Allow specific molecules to pass through.

• Carriers – Transport substances across the membrane.

• Enzymes – Catalyze reactions on the membrane.

• Anchors – Attach the membrane to the cytoskeleton.

• Identifiers – Help the immune system recognize self vs. foreign cells.

Membrane Transport

• Selective Permeability – The ability of the membrane to control which substances enter or exit the cell.

• Factors Affecting Permeability:

• Molecular Size – Smaller molecules pass through more easily.

• Electrical Charge – Charged molecules may require transport proteins.

• Molecular Shape – Only molecules of the correct shape fit through transport proteins.

• Lipid Solubility – Lipid-soluble molecules pass more easily.

• Types of Membrane Transport:

• Passive Transport (no ATP required):

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

• Osmosis – Movement of water across a membrane to balance solute concentrations.

• Filtration – Movement due to hydrostatic pressure (e.g., in kidneys).

• Carrier-Mediated Transport:

• Facilitated Diffusion – Transport proteins help molecules move down a concentration gradient.

• Active Transport – Moves molecules against a concentration gradient using ATP (e.g., Sodium-Potassium Pump).

• Vesicular Transport:

• Endocytosis – Bringing substances into the cell.

• Receptor-Mediated Endocytosis – Specific molecules bind to receptors before being engulfed.

• Pinocytosis – “Cell drinking”; ingestion of fluids.

• Phagocytosis – “Cell eating”; engulfing large particles.

• Exocytosis – Expelling materials from the cell.

• Osmotic Effects on Cells:

• Isotonic Solution – No net movement of water; cell remains stable.

• Hypertonic Solution – Water moves out of the cell, causing it to shrink (crenation).

• Hypotonic Solution – Water moves into the cell, causing it to swell and possibly burst (lysis).

The Cytoplasm and Organelles

• Types of Organelles:

• Nonmembranous Organelles:

• Cytoskeleton – Provides cell shape and movement.

• Microfilaments – Actin fibers for movement and structure.

• Intermediate Filaments – Strength and support.

• Microtubules – Tubulin structures for intracellular transport.

• Centrioles – Organize chromosomes during mitosis.

• Microvilli – Increase surface area for absorption.

• Cilia – Move fluids across the cell surface.

• Flagella – Propel the cell (e.g., sperm cells).

• Ribosomes – Produce proteins.

• Proteasomes – Degrade damaged proteins.

• Membranous Organelles:

• Endoplasmic Reticulum (ER):

• Rough ER (RER) – Studded with ribosomes; produces proteins.

• Smooth ER (SER) – No ribosomes; synthesizes lipids and detoxifies substances.

• Golgi Apparatus – Modifies, packages, and distributes proteins.

• Lysosomes – Contain digestive enzymes; break down waste.

• Peroxisomes – Detoxify harmful substances like hydrogen peroxide.

• Mitochondria – Generate ATP through aerobic respiration.

The Nucleus

• Structure of the Nucleus:

• Nuclear Envelope – Double membrane surrounding the nucleus.

• Nuclear Pores – Allow exchange of materials between the nucleus and cytoplasm.

• Chromatin – Uncoiled DNA and proteins.

• Chromosomes – Condensed DNA during cell division.

• Genetic Code and Protein Synthesis:

• Transcription – DNA is copied into mRNA in the nucleus.

• Translation – Ribosomes use mRNA to assemble proteins in the cytoplasm.

Cell Division

• Mitosis – The division of somatic (body) cells.

• Phases of Mitosis:

• Prophase – Chromosomes condense; spindle fibers form.

• Metaphase – Chromosomes align at the cell’s equator.

• Anaphase – Chromosomes separate to opposite poles.

• Telophase – Nuclear envelopes reform.

• Cytokinesis – Cytoplasm divides, forming two identical daughter cells.

• Meiosis – Division of sex cells, resulting in four genetically unique haploid cells.

• Apoptosis – Programmed cell death, crucial for development and maintaining homeostasis.

Cell Division and Cancer

• Tumors (Neoplasms):

• Benign Tumor – Non-cancerous, remains localized.

• Malignant Tumor – Cancerous, invades tissues and may metastasize.

• Causes of Cancer:

• Genetic mutations affecting cell cycle regulation.

• Uncontrolled cell division leads to tumor formation.

Cell Differentiation

• Differentiation – The process where cells become specialized in structure and function.

• Stem Cells – Undifferentiated cells with the potential to become different cell types.