Chapter 4 A Tour of the Cell

Cytology: science/study of cells

• Light microscopyresolving power = measure of clarity

• Electron microscopy TEM = electron beam to study cell ultrastructure SEM = electron beam to study cell surfaces

• Cell fractionation = cell separation; organelle study• Ultracentrifuges = cell fractionation; 130,000 rpm

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Cell Types: Prokaryotic

• Nucleoid: DNA concentration

• No organelles with membranes

• Ribosomes: protein synthesis

• Plasma membrane (all cells); semi-permeable

• Cytoplasm/cytosol (all cells)

Cell Size• As cell size increases, the surface area to

volume ratio decreases• Rates of chemical exchange may then be

inadequate for cell size• Cell size, therefore, remains small

Range of Cell Size

Cell Fractionation

Nucleus

• Genetic material...•chromatin•chromosomes•nucleolus: rRNA; ribosome synthesis

• Double membrane envelope with pores

• Protein synthesis (mRNA)

Ribosomes• Protein manufacture• Free - cytosol, proteins function in cell• Bound - endoplasmic reticulum, membranes,

organelles, and export

Compartmentalization• Increases internal

surface area• Sometimes enzymes

are incorporated into the membrane.

• Provide localized environmental areas.

• Sequester reactions (hydrolytic enzymes in lysosomes)

The Endomembrane System• Membranes may be

interrelated directly or indirectly via vesicles.

• Membranes are dynamic structures.

• Nuclear Envelope• Endoplasmic Reticulum• Golgi Apparatus• Lysosomes• Vacuoles• Plasma membrane (not

actually a member of the system, but related to it).

Continuous with nuclear envelope

• Smooth ER •no ribosomes •synthesis of lipids

•metabolism of carbohydrates •detoxification of drugs and

poisons

Stores Ca2+ ions

• Rough ER

•with ribosomes;

•synthesis of secretory proteins (glycoproteins), membrane production

1. Endoplasmic Reticulum (ER)

Rough ER Ribosomes1. Rough ER ribosomes

synthesize secretory proteins

2. Growing polypeptide is threaded through the ER membrane into the lumen or cisternal space

3. Protein folds into its native conformation

4. Local enzymes catalyze covalent bonding-modifications

5. Protein departs in a transport vesicle

• ER products are modified, stored, and then shipped• Cisternae: flattened membranous sacs• trans face (shipping) & cis face (receiving)• Transport vesicles

2. Golgi Apparatus

• Sac of hydrolytic enzymes; digestion of macromolecules• Phagocytosis• Autophagy: recycle cell’s own organic material• Tay-Sachs disease - lipid-digestion disorder• Apoptosis

3. Lysosomes

4.Vacuoles

• Membrane-bound sacs (larger than vesicles)

• Food vacuole

(phagocytosis)• Contractile (pump

excess water)• Central vacuole

(storage in plants) • Tonoplast (membrane)

Relationships Among Endomembranes

Other Membranous Organelles

• Not part of endomembrane system

• Peroxisomes• Mitochondria• Chloroplasts

Peroxisomes

• Single membrane• Produce hydrogen

peroxide in cells• Metabolism of fatty

acids; detoxification of alcohol (liver)

• Hydrogen peroxide produced, then converted to water – action of catalase.

Mitochondria

• quantity in cell correlated

with metabolic activity;

• cellular respiration;

• double membranous (phospholipid);

• cristae/matrix;

• intermembrane space;

• contain own DNA• bacterial origin

Chloroplasts• type of plastid; • double membranous; • thylakoids (flattened disks) • grana (stacked thylakoids);• stroma; • own DNA

The Cytoskeleton• Fibrous network in cytoplasm• Support, cell motility, biochemical

regulation

• Microtubules: thickest;

tubulin protein; shape, support, transport, chromosome separation

• Microfilaments : thinnest; actin protein filaments; motility, cell

division, shape

• Intermediate filaments: middle diameter; keratin;

shape, nucleus anchorage

Tubulin in endothelial cell

Motor Molecules and the Cytoskeleton

a. motor molecules on one microtubule ‘grab’ and slide past another microtubule.

b. motor molecules attach to receptors on organelles such as vesicles, enabling them to ‘walk’ along the microtubule

Centrosomes/centrioles• Centrosome: region near nucleus• Centrioles: 9 sets of triplet microtubules in a ring;

used in cell replication; only in animal cells

Cilia/flagella

• Locomotive appendages

• Ultrastructure: “9+2”

• 9 doublets of microtubules in a ring

• 2 single microtubules in center

• connected by radial spokes

• anchored by basal body

• dynein protein

a. ls. ciliumb. cs cilium, showing 9+2 arrangementc. cs basal body, anchors the cilium to the cell – third microtubule incorporated (centriole) central 2 lost

How Dynein ‘walking’ Moves Cilia and Flagella

The dynein arms of one doublet grip the adjacent doublet.

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Microfilaments and Motility

Cell Surfaces & Junctions

• Cell wall:

not in animal cells

protection, shape, regulation• Plant cell:

primary cell wall produced first

middle lamella of pectin (polysaccharide);

holds cells together• Some plants:

a secondary cell wall;

strong durable matrix;

wood (between plasma membrane and primary wall)

Extracellular Matrix (ECM) Glycoproteins:

proteins covalently bonded to carbohydrate

Collagen (50% of protein in human body)embedded in proteoglycan (another glycoprotein-95% carbohydrate)

Fibronectins bind to receptor proteins in

plasma membrane called integrins (cell communication?)

Intracellular Junctions• PLANTS:• Plasmodesmata: cell wall perforations; • water and solute passage in plants

• ANIMALS:• Tight junctions: fusion of neighboring cells;

prevents leakage between cells• Desmosomes: riveted, anchoring junction;

strong sheets of cells • Gap junctions: cytoplasmic channels; allows

passage of materials or current between cells

Plamodesmata in a thin plant section

Intercellular Junctions in Animals

The Lives of a CellHarvard Animation

• http://aimediaserver.com/studiodaily/videoplayer/?src=harvard/harvard.swf&width=640&height=520

http://www.bu.edu/histology/m/t_electr.htm

Assignment

Choose 4 images to draw and label

Narrated version