Unit 1 (General + Microscopy) - Biol 200

Plasma Membrane

Structure: Phospholipid bilayer with embedded proteins
Function: Selective barrier; regulates transport, signaling, and cell–cell interactions

Cytosol

Structure: Aqueous fluid inside the cell
Function: Site of many metabolic reactions; suspends organelles

Nucleus

Structure: Double membrane (nuclear envelope) containing chromatin
Function: Stores DNA; site of transcription and DNA replication

Nucleolus

Structure: Dense region inside nucleus
Function: rRNA synthesis and ribosome subunit assembly

Nuclear Pores

Function: Regulate transport of RNA and proteins between nucleus and cytoplasm

Rough Endoplasmic Reticulum (RER)

Structure: Flattened membranes with bound ribosomes
Function: Synthesis and initial folding of secreted and membrane proteins

Smooth Endoplasmic Reticulum (SER)

Structure: Membrane tubules lacking ribosomes
Function: Lipid synthesis, detoxification, Ca²⁺ storage

Golgi Apparatus

Function: Modifies, sorts, and packages proteins and lipids

Transport Vesicles

Structure: Small membrane-bound sacs
Function: Move proteins/lipids between organelles and to membrane

Lysosome

Structure: Acidic, enzyme-filled vesicle
Function: Intracellular digestion and recycling (autophagy)

Peroxisome

Structure: Small oxidative organelle
Function: Fatty acid breakdown; detoxification; H₂O₂ metabolism

Mitochondrion

Structure: Double membrane; inner membrane forms cristae
Function: ATP production via oxidative phosphorylation

Ribosomes

Structure: rRNA–protein complexes (free or bound)
Function: Protein synthesis

• Free: cytosolic proteins

• Bound: secreted/membrane proteins

Centrosome

Structure: Microtubule-organizing center (with centrioles)
Function: Spindle formation during cell division

Microtubules

Function: Cell shape, vesicle transport, mitotic spindle

Intermediate Filaments

Function: Tensile strength; mechanical stability

Actin Filaments (Microfilaments)

Function: Cell movement, cortex tension, muscle contraction

Extracellular Matrix (ECM)

Structure: Network of proteins (collagen, proteoglycans) outside cell
Function: Structural support, signaling, cell anchoring

What is magnification?

The apparent enlargement of an object by an optical instrument.

What is resolution?

The minimum distance between two points that can still be distinguished as separate.

Why is resolution more important than magnification?

Without sufficient resolution, increasing magnification only enlarges a blurry image.

What limits the resolution of a microscope?

The wavelength of the particle used (light vs electrons).

Resolution equation for light microscopy?

d = 0.61 × wavelength / numerical aperture

Approximate resolution limit of a light microscope?

~0.2 µm (200 nm)

Approximate resolution limit of an electron microscope?

~0.2 nm

What type of light does brightfield microscopy use?

Transmitted visible light

What kind of light is detected in fluorescence microscopy?

Emitted light from excited fluorophores

What is a fluorophore?

A molecule that absorbs light at one wavelength and emits light at another

Can fluorescence microscopy be used on live cells?

Yes

What is GFP?

Green Fluorescent Protein, a fluorescent tag that allows tracking of proteins in living cells without fixation

Why must electron microscopy be done in a vacuum?

Electrons scatter easily in air

Why are samples dead in electron microscopy?

Vacuum conditions and heavy-metal staining destroy living cells

Why are heavy metals used in TEM staining?

They increase electron density and contrast

What is immunolabeling?

Using antibodies linked to tags to detect specific proteins

Why are fluorescent antibodies often used on fixed cells?

Antibodies cannot easily cross intact membranes

What is negative staining?

Staining the background, not the specimen itself

When is negative staining useful?

Visualizing small objects like viruses or proteins

Name the four major microscopies

1. Brightfield light microscopy

2. Fluorescence light microscopy

3. Transmission electron microscopy (TEM)

4. Scanning electron microscopy (SEM)

Why do both light and electron microscopy follow similar principles?

Both photons and electrons have wave–particle properties.

What fundamentally determines how much detail a microscope can resolve?

The wavelength of the particle used to image the sample.

Why can electrons resolve much smaller structures than light?

Electrons have wavelengths ~200,000× shorter than visible light.

Name two general strategies to increase contrast in light microscopy.

1. Chemical staining

2. Optical manipulation of light

Why is antibody-based immunolabeling only used in live cells?

Antibodies cannot easily cross intact membranes to to bind to intracellular targets

What is a major advantage of GFP over immunolabeling?

No antibodies required; proteins can be tracked over time in live cells.