Microscope, Cellular Organelles, and Mitosis: Study Notes for ANP College Students

Microscope Structure and Function

Parts of the Microscope

The microscope is an essential tool for studying cells and tissues in anatomy and physiology. Understanding its parts and their functions is crucial for proper usage and care.

• Base: The bottom support of the microscope; provides stability.

• Substage Light: Located in the base, directs light upward toward the stage; intensity can be adjusted.

• Stage: Platform where slides are placed; contains a hole for light passage.

• Condenser: Non-magnifying lens beneath the stage; focuses light onto the specimen.

• Iris Diaphragm: Part of the condenser; regulates the amount of light reaching the specimen.

• Arm: Vertical portion; used for carrying the microscope.

• Coarse Focus Knob: Moves the stage for large adjustments; used only with low power objectives.

• Fine Focus Knob: Allows precise focusing; used with all objectives.

• Nosepiece: Rotates to switch between objective lenses.

• Objective Lenses: Magnify the specimen; typically 4x (scanning), 10x (low), 40x (high), 100x (oil immersion).

• Ocular Lenses: Eyepieces; usually provide 10x magnification.

Total Magnification

The total magnification achieved is the product of the ocular lens and the objective lens magnifications.

• Formula:

$\text{Total Magnification} = \text{Ocular Lens Magnification} \times \text{Objective Lens Magnification}$

Microscope Care

• Carry with two hands: one on the arm, one under the base.

• Keep upright at all times.

• Clean lenses only with lens paper or cleaner.

• Begin focusing with the scanning (4x) lens.

• Do not use coarse focus with high power or oil immersion lenses.

• Before storage: remove power cord, set scanning lens, lower stage.

Preparing a Wet Mount

Wet mounts are used to observe living cells under low and high power. Refer to lab manual for detailed steps.

The Cell: Structure and Function

Plasma Membrane

The plasma membrane forms the cell's outer boundary and regulates the movement of substances in and out of the cell.

• Structure: Lipid bilayer composed of phospholipids and cholesterol; proteins embedded or attached.

• Functions: Controls entry/exit, intercellular communication, cell recognition via marker molecules.

Nucleus

The nucleus is the control center of the cell, housing genetic material and regulating cellular activities.

• Contains DNA: DNA exists as chromatin when not dividing; condenses into chromosomes during division.

• Nucleolus: Site for ribosome assembly; contains ribosomal RNA and proteins.

• Nuclear Envelope: Double-layered membrane surrounding the nucleus.

Ribosomes

Ribosomes are the sites of protein synthesis, composed of RNA and proteins.

• Can be free-floating in cytoplasm or attached to rough endoplasmic reticulum.

Endoplasmic Reticulum (ER)

The ER is a network of membranous tubules involved in synthesis and transport.

• Rough ER (RER): Has ribosomes; synthesizes proteins for transport to Golgi apparatus.

• Smooth ER (SER): Lacks ribosomes; synthesizes lipids/carbohydrates, detoxifies chemicals, stores calcium.

Golgi Apparatus

The Golgi apparatus modifies, packages, and distributes proteins and lipids for secretion or internal use.

• Consists of stacked, flattened sacs.

Lysosomes

Lysosomes are membrane-bound vesicles containing digestive enzymes.

• Digest worn-out organelles and foreign substances.

• Rupture can lead to cell death.

Peroxisomes

Peroxisomes are membrane-bound vesicles involved in lipid and amino acid degradation and breakdown of hydrogen peroxide.

• Protect cells from oxidative damage.

Mitochondria

Mitochondria are the cell's powerhouses, generating ATP through aerobic respiration.

• Double membrane; inner membrane forms cristae.

• Major site of ATP synthesis when oxygen is available.

Centrioles

Centrioles are paired cylindrical organelles involved in cell division and microtubule formation.

• Located in the centrosome.

• Determine cell polarity during division.

• Form basal bodies for cilia and flagella.

Cilia and Microvilli

• Cilia: Extensions containing microtubules; move materials over cell surfaces.

• Microvilli: Extensions containing microfilaments; increase surface area for absorption/secretion.

Cytoskeleton

The cytoskeleton is a network of rods supporting cellular structure and movement.

• Three types: microfilaments, intermediate filaments, microtubules.

Cell Cycle and Mitosis

Cell Cycle Overview

The cell cycle consists of interphase (growth and DNA replication) and cell division (mitosis and cytokinesis).

• Interphase: Cell grows, duplicates DNA and centrioles.

• Cell Division: Includes mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Interphase Subphases

• G1 Phase: Cell grows, centrioles begin replication.

• S Phase: DNA is replicated.

• G2 Phase: Proteins and enzymes for division are synthesized; centriole replication completes.

Mitosis

Mitosis produces two genetically identical daughter nuclei, essential for growth and repair.

• Stages: Prophase, Metaphase, Anaphase, Telophase

Prophase

• Chromatin condenses into chromosomes connected by centromeres.

• Centrioles separate, form mitotic spindle.

• Nuclear envelope and nucleolus disappear.

Metaphase

• Chromosomes align along the metaphase plate.

Anaphase

• Centromeres split; chromatids move to opposite poles.

Telophase

• Chromosomes uncoil to chromatin.

• Spindle breaks down.

• Nuclear envelope and nucleoli reappear.

Cytokinesis

Cytokinesis is the division of the cytoplasm, beginning in late anaphase and continuing through telophase.

• Cleavage furrow forms, pinching the cell into two parts.

Summary Table: Major Cellular Organelles and Functions

Organelle	Structure	Function
Plasma Membrane	Lipid bilayer with proteins	Boundary, regulates entry/exit, communication
Nucleus	Double membrane, nucleolus	Control center, houses DNA
Ribosomes	RNA and protein spheres	Protein synthesis
ER (Rough/Smooth)	Membranous tubules	Protein/lipid synthesis, detoxification
Golgi Apparatus	Stacked sacs	Modify, package, distribute proteins/lipids
Lysosomes	Membrane vesicle	Digestion of organelles/substances
Peroxisomes	Membrane vesicle	Lipid/amino acid degradation, peroxide breakdown
Mitochondria	Double membrane, cristae	ATP synthesis
Centrioles	Cylindrical microtubules	Cell division, microtubule formation
Cilia/Microvilli	Membrane extensions	Movement, increased surface area
Cytoskeleton	Network of rods	Support, movement

Example: During mitosis, the centrioles organize the mitotic spindle, ensuring accurate chromosome separation. The plasma membrane forms the cleavage furrow during cytokinesis.

Additional info: The cell cycle is tightly regulated by checkpoints to prevent uncontrolled division, which can lead to cancer. Mitochondria contain their own DNA, inherited maternally.