Microscopy

Light Microscopy (LM)

  • Brightfield + Stained - Cells must be fixed (and killed).
  • Phase-contrast - Enhance contrast to examine living and unpigmented cells.
  • Defferential-interference-contrast - appears almost 3-D
  • Fluorescence - Labeling molecules with dyes or antiboidies.
  • Confocal - optical sectioning to 3-D reconstruction
  • Deconvolution - sharper 3-D image
  • Super-resolution

About 1000x of specimen, organelles are too samll for LM.

Electron Microscopy(EM)

Scanning Electron Microscopy (SEM) - 3-D image of the surface Transmission Election Microscopy (TEM) - reveals internal structure

Cell Fractionation

Homogenization - Homogenate - Centrifugation - Differential Centrifugation - Pallet

Prokaryotic Cell

Nucleoid, Plasma Membrane, Cell Wall, Capsule, Fimbriae, Flagella (locomotion)

Plasma Membrane

Hydrophilic - Phospholipid - Hydrophilic; Carbonhydrated side chains + proteins.

Eukaryotic Cell

Animal

  • Centrosome (where microtubules initiated, contains a pair of centrioles);
  • Flagellum (motility structure, cluster of microtubules);
  • Cytoskeleton (Microfilaments, Intermediate Filaments and Microtubules.);
  • Microvili (increase surface area);
  • Endoplasmic Reticulum (Rough ER and Smooth ER);
  • Plasma Membrane;
  • Golgi Apparatus;
  • Lysosome (hydrolyze macromolecules);
  • Mitochondrion;
  • Peroxisome (produces hydrogen peroxide and converts to water);
  • Ribosomes;
  • Nucleus (Nuclear Envelope, Nucleulus and Chromatin);

Plant

PLUS

  • Chloroplast (photosynthesis);
  • Plasmodesmata (cytoplasmic channels);
  • Central Vacuole (breakdown of waste, hydrolysis 水解, plant growth);
  • Cell Wall (made of cellulose, polysaccharides and protein);

Nucleus

Nuclear Envelope

Double membrane, seperated by space of 20-40nm, with pores about 100nm in diameter.

Pore Complex

Regulating the entry and exit of proteins and RNAs.

Nuclear Lamina

Netlike array of protein filaments to maintain the shape of Nuclear Envelope.

Nuclear Matrix

Chromatin

Complex of DNA and proteins making up chromosomes.

Nucleulus (Nucleoli)

Granules and fibers adjoining part of the chromatin. Sythesizes ribosomal RNA (rRNA) and proteins imported from cytoplasm are assembled into large and small subunits of ribosomes.

Ribosomes

Free ribosomes (suspended in the cytosol) and bound ribosomes (attaced to the RER, produce proteins for secretion, etc.).

Endoplasmic Reticulum (Rough ER and Smooth ER)

endomembrane system - ER, lysosomes, Golgi apparatus, vesicles (transfer), vacuoles, nuclear envelope, plasma membrane.

  • Cisternae: network of tubules and sacs.
  • ER lumen (cavity, cisternal space)

Smooth ER

  • Sythesis of lipids (oil, steroids, new membrane phospholipids).
  • Detoxification of drugs and poisons (especially in liver cells), adding hydroxl groups. e.g. sedative phenobarbital and barbiturates (巴比妥, 中樞神經抑制劑), alchohol. Note: Barbiturate abuse can decrease effectiveness of certain antibiotics and drugs because the proliferation of smooth ER.
  • Stores Calcium Ions (muscle cells, trigger responses)

Rough ER

  • Secrte glycoproteins (with bound ribosomes)
  • New polypetide folds into functional shape when entering the ER lumen.
  • Transport Vesicles
  • Membrane Factory

Golgi Apparatus

Modify, Store, Transport proteins, e.g. glycoproteins. Cisternae: flattened sacs. Cis face (receiving) - Trans face (shipping) * Produce pectins, noncellulose polysaccharides, etc. Cisternal Maturation Model

Lysosome

  • Pagocytosis: food vacule fuse with lysosome. e.g. macrophages.
  • Autophagy: recycle orgnaic material.

Vacuoles

Food vacuoles, Contractile vacuoles (pump excess water), Central vacule (repository of inorganic ions. e.g. potassium ions and chloride).

Mitochondrion

  • Cristae: convoluted inner membrane
  • Mitochondrial Matrix: cell respiration, DNA and ribosomes.
  • Dynamic tubular network of mitochondria

Chloroplasts

Thylakoids (flattened, connected sacs) - Granum (thylakoid stacks) Stroma: DNA, ribosomes and enzymes. Plastids: amyloplasts (starch, amylose in roots and tubers), chromoplasts (pigments in fruits and flowers).

Peroxisome

Remove hydrogen and transfer to \(O_2\), \(H_2O_2\) to \(H_2\); break fatty accids; detoxify alcohol, etc. glyoxysomes: in fat-storing tissues of plant seeds, initiate the conversion of fatty acids to sugar.

Cytoskeleton

Motor Protein Molecular Motors: Kinesin, Dynein and Myosin

Microtubules

  • Proteins: alpha and beta Tubulin + Dynein
  • Diameter: 25nm, 15nm lumen
  • Function: Compression-Resisting, Cilia and Flagella, Chromosome Movements in Cell Division, Organell Movements.

Centrosome: a pair of centrioles (animal cells)

Cilia and Flagella: 9 (microtubule doublets) + 2 (single microtubule) pattern + Basal Body 9 + 0 pattern

Dynein: movement of dynein feet cause microtubles to bend.

Microfilaments

  • Proteins: Actin + Myosin
  • Diameter: 7nm
  • Function: Tension-Bearing, Muscle Contraction, Cytoplasmic Streaming, Amoeboid Movement, Divion of Animal Cells

Actin: Globular protein, microfilament is twisted double chain of actin.

Cortical Microfilaments: gives cortex the semisolid consistency of a gel; make up the core of microvilli.

Myosin: Contraction of muscel cells.

Amoeboid Movement: Cell crawls along cellular extension Pseudopodia (localized contractions).

Cytoplasmic Streaming: actin-myosin interaction, speeds distribution of materials.

Intermediate Filaments

  • Proteins: Keratins and others
  • Diameter: 8-12nm
  • Function: Tension-Bearing, Nuclear Lamina, Anchorage (e.g. Nucleus, Desmosomes)

Only found in the cells of some animals, e.g. vertebrates. More permanent than microfilaments and microtubules. e.g. dead skill cells full of keratin.

Inner Life of a Cell (Video) Cell Structure (Video)

Cell Walls

primary - middle lamella (pectins) - secondary

Extracellular Matrix (ECM)

Collagen: 40% of total protein in human body, embedded in a web of proteoglycan complexes.

Proteoglycans: Core protein + Polysaccharide / Carbohydrate chains

Fibronectin: Glycoprotein, attach cell to ECM.

Integrins: Cell-Surface Receptor, built into plasma membrane, attached to microfilaments.

Cell Junctions

In animals (common in epithelial tissues)

  • Plasmodesmata: certain protein and RNAs can pass as well.
  • Tight Junctions: Continuous seal, prevents leakage of fluid across epithelial cells.
  • Desmosomes (Anchoring Junction): Intermediate filaments made of sturdy keratin anchor desmosomes to cytoplasm.
  • Gap Junctions: cytoplasmic channels

References

N. Campbell, J. Reece, L. Urry M. Cain, S Wasserman, P. Minorsky and R. Jackson. Biology: A Global Approach. Pearson Education 2014