Microscopy, Cells, and Tonicity Notes

Microscopy

  • Compound Microscope Parts:

    • Ocular lens: Eyepiece for viewing.

    • Usually has a magnification of 10x. This lens is what the user looks through to see the magnified image of the specimen.

    • Adjustments can be made to suit individual eyesight.

    • Head: Supports the ocular lenses.

    • It can be binocular (for two eyes) or monocular (for one eye).

    • Revolving nosepiece: Holds multiple objective lenses allowing for easy switching.

    • The user can rotate the nosepiece to select different objective lenses.

    • Objective lens: Lens that is nearest to the object being viewed; usually several with different magnifications.

    • Common magnifications include 4x, 10x, 40x, and 100x. These lenses provide different levels of magnification to view the specimen in detail.

    • Has a high numerical aperture to gather more light.

    • Arm: Supports the head and connects it to the base.

    • Used to safely transport the microscope.

    • Stage: Platform that supports the slide being observed.

    • Stage clips hold the slide in place

    • Mechanical stage allows for precise movement of the slide. This allows for precise control when viewing the specimen.

    • Some stages can be rotated to adjust the orientation of the specimen.

    • Condenser: Focuses light onto the specimen. The condenser improves the clarity and sharpness of the image.

    • Can be adjusted vertically to optimize illumination.

    • Iris diaphragm lever: Adjusts the amount of light passing through the specimen. This helps to control the contrast and brightness of the image.

    • Located within the condenser.

    • Substage light: Light source located below the stage.

    • Intensity can be adjusted with the light control

    • Provides consistent and adjustable illumination.

    • Coarse adjustment knob: Used for initial focusing at lower magnifications.

    • Moves the stage up and down significantly

    • Should be used with care to avoid crashing the objective lens into the slide.

    • Fine adjustment knob: Used for precise focusing at higher magnifications.

    • Allows for subtle adjustments to focus

    • Essential for achieving a sharp image, especially at high magnifications.

    • Base: Supports the microscope.

    • Provides stability during use.

    • Light control: Adjusts the intensity of the light source.

    • Allows the user to control the brightness of the field of view.

  • Types of Microscopy

    • Brightfield Microscopy

    • Basic form of microscopy

    • Produces a dark image on a bright background. The specimen is illuminated from below with white light.

    • Commonly used for stained specimens.

    • Phase Contrast Microscopy

    • Enhances the contrast of transparent specimens

    • Useful for observing living cells

    • Converts phase shifts in light passing through the specimen to changes in brightness.

    • Fluorescence Microscopy

    • Uses fluorescent dyes to label specific cell structures

    • Allows for visualization of specific components within the cell. The fluorescent dyes emit light of specific wavelengths when excited by certain wavelengths of light.

    • Requires a specific light source and filter sets.

The Cell
Structure of the Plasma Membrane

  • Phospholipid bilayer. This forms the basic structure of the membrane, with hydrophobic tails and hydrophilic heads.

    • Arranged in such a way that the hydrophobic tails are shielded from the aqueous environment while the hydrophilic heads interact with it.

  • Proteins (integral and peripheral). Integral proteins are embedded in the lipid bilayer, while peripheral proteins are attached to the surface.

    • Integral proteins often function as channels or carriers.

  • Cholesterol. Helps to maintain the fluidity of the membrane.

    • Acts as a buffer, preventing extremes in fluidity over a range of temperatures.

Transport Across the Plasma Membrane

  • Passive Transport

    • Diffusion: Movement of molecules from an area of higher concentration to an area of lower concentration.

    • Facilitated diffusion: Diffusion with the help of membrane proteins. These proteins help specific molecules cross the membrane.

    • No energy required.

    • Osmosis: Movement of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration.

    • Water moves to equalize solute concentrations.

  • Active Transport

    • Requires energy (ATP) to move molecules against their concentration gradient.

    • Primary active transport: Directly uses ATP. For example, the sodium-potassium pump.

    • Establishes electrochemical gradients.

    • Secondary active transport: Uses the electrochemical gradient created by primary active transport. This gradient drives the movement of other molecules.

    • Can be symport or antiport.

Cytoplasmic Organelles

  • Nucleus

    • Contains the cell's DNA

    • Control center of the cell

    • Surrounded by a nuclear envelope.

    • The nuclear envelope consists of two membranes: an inner and an outer membrane.

    • Nuclear pores in the envelope allow for the transport of molecules into and out of the nucleus.

  • Endoplasmic Reticulum (ER)

    • Rough ER: Contains ribosomes for protein synthesis.

    • The ribosomes give it a rough appearance.

    • Proteins synthesized on the rough ER are often destined for secretion or for use in the cell membrane.

    • Smooth ER: Involved in lipid synthesis and detoxification.

    • Also involved in carbohydrate metabolism.

    • Plays a role in calcium storage in some cell types.

  • Golgi Apparatus

    • Modifies, sorts, and packages proteins and lipids.

    • Proteins are further processed and sorted for distribution.

    • The Golgi apparatus has a distinct polarity, with a cis face (receiving side) and a trans face (shipping side).

  • Mitochondria

    • Powerhouse of the cell; produces ATP through cellular respiration.

    • Has a double membrane structure.

    • The inner membrane is highly folded into cristae, which increases the surface area for ATP production.

  • Lysosomes

    • Contains enzymes for breaking down cellular waste and debris.

    • Important for autophagy and programmed cell death.

  • Peroxisomes

    • Involved in detoxification and lipid metabolism.

    • Contains enzymes that catalyze oxidation reactions.

    • Catalase is an enzyme found in peroxisomes that breaks down hydrogen peroxide into water and oxygen.

The Cytoskeleton

  • Provides structural support and facilitates movement within the cell.

  • Microfilaments

    • Made of actin proteins

    • Involved in cell movement and muscle contraction

    • Dynamic and versatile.

    • Important for cell shape, cell crawling, and cytokinesis.

  • Intermediate Filaments

    • Provide structural support and stability

    • Various types of proteins. These proteins vary depending on the cell type.

    • More stable than microfilaments or microtubules.

    • Examples include keratin filaments in epithelial cells and neurofilaments in neurons.

  • Microtubules

    • Made of tubulin proteins

    • Involved in cell division, movement, and transport of materials within the cell.

    • Form the spindle apparatus during cell division.

    • Also involved in intracellular transport, such as moving vesicles and organelles.

    • Centrosome

    • Microtubules extend out from the centrosome

    • Pair of centrioles is critical for cellular division (mitosis)

    • Centrosome

    • Tubulin proteins

    • Centrioles

The Cell Cycle
Metaphase

  • Metaphase

    • Spindle fibers from opposite poles of cell arrange sister chromatids into line along middle (equator) of cell

    • Sister chromatids

    • Attached to each other at the centromere.

    • Each sister chromatid contains an identical DNA molecule.

    • Centriole pairs

    • Located at opposite poles of the cell.

    • Serve as microtubule organizing centers (MTOCs).

    • Spindle fibers

    • Made of microtubules.

    • Attach to the kinetochore of each sister chromatid.

Anaphase

  • Anaphase

    • Sister chromatids pulled toward opposite poles; individual chromosomes then called daughter chromosomes

    • Each new daughter cell will have 46 chromosomes (23 pairs).

    • Ensures each daughter cell receives the correct number of chromosomes.

    • Daughter chromosomes

    • Now separate and moving to opposite poles.

    • Each is a complete chromosome.

Interphase

  • Period of the cell cycle between cell divisions.

  • Chromosomes are not visible

  • Cell performs its normal functions

  • Cell prepares for division

    • DNA replication

    • Protein synthesis

Telophase

  • Telophase

    • Chromosomes arrive at opposite poles

    • Daughter nuclei form

    • Nucleoli reappear

    • Chromosomes unwind into chromatin

Cytokinesis

  • Cytokinesis

    • Division of the cytoplasm

    • Results in two identical daughter cells