visible light passes though a specimen and then through glass lenses, which magnify the image. 

• Magnify to 1,000 x actual size 
• Resolution 200nm 
• Can enhance contrast by stain or label 
• Most subcellular structures too small for LM 

Pass beam of electrons through a specimen to magnify image 

• Magnification 250,000 x actual size 
• Resolution 2nm

• Dark objects visible agains a bright background
• Light objects are visible against a dark background 

• Uses UV light 
• Fluorescent substances absorb UV light and emit visible light 
• Cells may be stained with fluorescent dyes (fluorochromes)

• Uses fluorochromes and a laser light 
• The laser illuminates each plane in a specimen to produce a 3-D image

Focus electron beam through thin section, study internal structures.

 Beam passes differentially (density), bend transmitted electrons with electromagnets to magnify image. 

Take cells apart and separate major organelles 

• Use ultracentrifuge 
• Can determine organelle functions 

• Cell Wall
• Lysosomes 
• Centrosomes with centrioles 
• Chloroplasts 
• Central vacuole 
• Plasmodesmata 
• Flagella*

Contains most of cell's genes, usually most cospicuous organelle 

Encloses nucleus, separates it from cytoplasm 

• a double membrane; each membrane is a lipid bilayer
• pores regulate entry/exit of molecules  

• Composed of protein 
• Maintains shape of nucleus 

genetic material in the nucleus, formed by DNA and proteins 

• condenses to from discrete chromosomes 

structures made of ribosomal RNA and protein 

Protein synthesis in two locations

• In cytosol (free ribosomes): Funtion within cytosol 
• Outside of ER or Nuclear Envelope (bound ribosomes): Function in membranes, packaged in lysosomes, or for export from cell. 

Used for the synthesis of proteins that: 

• Remain in cytoplasm 
• Go to Nucleus 
• Mitochondria/ Chloroplast 
• Peroxisomes 

Enter ER: stay ther or go on to Golgi

From Golgi: 

• Go to lysosomes 
• Go to the plasma membrane 
• Secreted out of the cell 
• Go bak to the ER 

components either continuous or connected (by vesicle transfer) 

• Nuclear envelope 
• Endoplasmic reticulum 
• Golgi apparatus 
• Lysosomes 
• Vacuoles 
• Plasma membrane 

• Protein synthesis 
• Transport 
• Metabolism 
• Detoxification 

More than half total membrane in many eukaryotic cells 

Continuous with nuclear envelope 

Two Regions:

• Smooth ER: Lacks ribosomes 
• Rough ER: Ribosome stud surface 

• Synthesizes lipids (oils, phospholipids, steroids)
• Metabolizes carbohydrates
• Detoxifies poison (sedatives)
• Stores calcium 

Functions vary by cell type

• Bound ribosomes secrete gycloproteins (proteins covalently bonded to carbohydrates)
• Distributes transport vesicles (proteins surrounded by membranes) 
• Membrane factory 

Flattened membranous sacs called cisternae

Functions 

• Modifies ER products (carbohydrates, glycoproteins, proteins)
• Manufactures certain macromolecules 
• Sorts and packages materials (like proteins) into transport vesicles 

• Modification occurs during transit 
• Different cisternae contain different enzymes 
• cis face: "receiving" side of golgi apparatus 
• trans face: "shipping" side of golgi apparatus 

• Proteins shipped to an organelle 
• Secreted out of cell 
• Incorporation into membranes 
• Ship back to ER 

a membranous sac of hydrolytic enzymes that can digest macromolecules 

• Can function by fusing with food vacuoles (formed whena cell engulfs another cell by phagocytosis)
• Function best in acidic internal enviroment 

• hydolyze proteins, fats, polysaccharides, and nucleic acids, products pass to cytosol
• recycle cell's own organelles and macromolecules (autophagy) 

• Hold organic compounds, inorganic ions, water 
• Site for disposal of metabolic by-products 
• Contain pigments that color cells 
• Protection- may contain poisonous compounds 
• Growth- by water absorption 

Site of cellular respiration (metabolic process that generates ATP)

• Smooth outer membrane 
• Inner membrane folded into cristae (large surface area for enzymes that synthesize ATP)
• In nearly all eukaryotic cells

intermembrane space 

mitocondial matrix - contains DNA 

• In leaves and other green organs of plants, in algae; type of plastid 
• Thylakoids: membranous sacs, stacked to form a granum, light capturing pigment chlorophyll
• Stroma: the internal fluid, contains DNA, enzymes, ribosomes

• Are not part of the endomembrane system 
• Have a double membrane 
• Have proteins made by free ribosomes 
• Contain their own circular DNA 
• Can grow and reproduce in the cell 

1. An early ancestor of eukaryotic cells engulfed and oxygen-using nonphotosynthetic prokaryotic cell
2. They formed a relationship 
3. They became one organism 

Metabolic compartments bound by a single membrane 

• produce hydrogen peroxide, convert to water 
• oxygen breaks down molecules 
• In liver, produce bile salts, cholesterol, break down fats 

• Specialized peroxisomes 
• fat storing tissues in plant seeds 
• contain enzymes to convert fatty acids to sugars, can use as a source of energy and carbon until it is able to make its own sugar 

Dynamic network of fibers throughtout the cytoplasm that organizes structure and activity; anchors many organelles 

• Microtubules (thickest) 
• Microfilaments (thinnest; actin fibers)
• Intermediate filaments 

• Support the cell and maintain its shape 
• Provides anchorage for organelles and molecules 
• Interacts with motor proteins (ATP powered walkig proteins) for mobility (moving just parts of cells and entire cells)
• May help regulate biochemical activities 

Structure: Hollow tubes; wall consist of tubulin molecules 

Diameter: 200 nm to 25 microns long 

Protein subunits: Tubulin (alpha and beta tubulin)

Main Funtions: 

• Maintance of cell shape
• Cell mobility 
• Chromosome movements in cell division 
• Organelle movements 

Structure: Fibrous proteins supercoiled into thicker cables  

Diameter: 8-12 nm

Protein Subunits: One of several different proteins of the keratin family 

Main Functions: 

• Maintenance of cell shape 
• Anchorage of nucleus and certain other organelles 
• Formation of nuclear lamina 

"microtubule-organizing center"

• near nucleus 
• microtubules grow from there 

Locomotor appendages of some cells 

• Microtubules control beating 
• Cilia and flagella differ in beating patters 

• Dynein (large motor proteins) arms alternately grab, move, and release the outer microtubules
• Protein cross-linked limit sliding 
• Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum 

solid rods, twisted double chain of actin subunits 

• Form 3-D network (cortex, semisolid gel, while interior cytoplasm is more fluid (sol)) inside plasma membrane to support cell shape 
• Bundles are core of microvilli for intestinal cells 
• Also key in muscle cells. 

used for motility 

• muscle cells: actin filaments arranged in parallel 
• Thicker filaments have myosin between actin fibers 

(cellular extensions; false foot) extend and contract 

A reversible assembly of actin subunits into microfilaments 

circular flow of cytoplasm within cells 

• speeds distribution of materials 
• In plant cells, driven by actin-myosin interactions and sol-gel transfromations 

more permanent fixtures than other classes 

• Stabilize cell structure 
• Fix organelles in place 
• Diverse class 
• Constructed from a variety of a family of proteins including keratins 
• In some cells radiate from nuclear envelope-maintain position of nucleus and other organelles
• Example:  Lamins of nuclear lamina 

• Protects cells, maintans shape, prevents excessice water uptake 
• Made of cellulose fibers embedded in other polysaccharides and protein 

Extracellular Matrix (ECM;animal cells)

collagen, proteoglycans and fibronectin 

ECM proteins bind to receptor proteins in plasma membrane (integrins, transmit signals from ECM to cytoskeleton).

facilitate contact between neighboring cells through direct physical contact 

several types: 

• Plasmodesmata 
• Tight junctins 
• Desmosomes 
• Gap junctions 

• phospholipids can move
• most lipids(and some proteins) drift laterally 
• rarely flip-flop across membrane 
• solidification temperature depends on lipid types 
• unsaturated fatty acids: more fluid 
• cholesterol a buffer 

• Transport 
• Enzymatic activity 
• Signal transduction 
• Cell-cell recognition 
• Intercellular joining 
• Attachment to the cytoskeleton and extracellular matrix (ECM)

• Binding to surface molecules on membrane 
• Often these molecules are carbohydrates covalently bonded to 

1. lipids (forming glycolipids)
2. proteins (forming glycoproteins)

• Hydophobic (nonpolar) molecules can pass through membrane rapidly 
• Polar molecules do not cross easily 

High to low

• small, nonpolar molecules 
• small uncharged polar molecules 
• large, uncharged polar molecules 
• ions 

transport proteins: allow passsage of hydrophillic substances, specific for the substance it moves 

allow passage of hydrophillic substances, specific for the substances it moves 

water pores allow water to pass through 

(Channel protein)

the tendency for molecules to spread out evenly into available space; can be direct or facilitated 

• spread down concentration gradient 
• no work to move substances doen concentration gradient 

diffusion of water across selectively permeable membrane 

• moves from region of lower solute concentration to region of higher solute concentration 

a solution's ability to cause cell to gain/lose water

• Hypotonic: swells until wall opposes uptake; cell now turgid 
• Isotonic: no net movement of water into cell; cell becomes flaccid (limp)
• Hypertonic: plant cells lose water; membrane pulls away from wall, usually lethal; plasmolysis 

transport proteins speed passive movement of molecules across membrane 

• Still passive (solute moves down concentratin gradient)
• Channel proteins

1. Aquaporins 
2. Ion channels 
3. gated channels 

subtle change in shape translocates solute-binding site across membrane 

moves substances agains their concentration gradient 

• requires energy, usually in the form of ATP
• performed by specific proteins embedded in the membranes 
• allows cells to maintain concentration gradients that differ from surroundings 

transport vesicles migrate to membrane, fuse, and release contents 

• important in secretory cells 

series of steps by which signal on cell's surface converts to specific cellular response

• similarities suggest ancestral signaling molecules evolved in unicellular organisms
• signaling between organisms
• adopted for signaling between cells of a multicellular organism 

• Direct contact (no secretions)
• Short distance (local)
• Long distance 

• Cell junctions 
• Cell-cell recognition 

• Paracrine signaling 
• synaptic signaling 

• Endocrine signaling 
• Nervous system signaling 

• some cell junctions directly connect cytoplasm 
• membrane-bound cells communicate through surface molecules 

• Electrical synapses: electrical current flows from one neuron to a target cell through gap junctions 
• Chemical synapses: chemical neurotransmitter signals to receptors across the synaptic cleft 

1. presynaptic neuron synthesizes neurotransmitter
2. packages neurotransmitter in synaptic vesicles at synaptic terminal 
3. action potential causes voltage-gated channels to open and allowe Ca 2+ into cell terminal 
4. Ca 2+ causes vesicles to fuse with terminal membrane, releasing neurotransmitter 
5. neurotransmitter diffuses across synaptic cleft 
6. binds to receptors on postsynpatic cell 
7. neurotransmitters bind to ligand-gated in channels in postsynaptic cell membrane 
8. causes ion channels to open 
9. generates postsynaptic potential: can be excitatory or inhibitory 
10. ion channels release neurotransmitter to synaptic cleft
11. neurotransmitters may experience diffusion, active transport, or enzyme degradation 

• cells secrete hormones that travel through circulatory system 
• only affect targe cells with correct receptors 

• neurons transmit signal through cell (electrical signal) and between cells (chemical signal) across body 

messenger molecules that travel short distances 

ex: neurotransmitters; growth factors 

messenger molecules that travel long distances through the blodd stream 

Ex: steroid hormones; peptide hormones; neurohormones 

• Hormones: long-lasting, slow, global effects in small amounts
• Neurotransmitters: fast, local effects 

• signal reception 
• signal transduction 
• cellular response