Lecture #1 Chapter 6~ A Tour of the Cell

Nucleus Genetic material... •chromatin •chromosomes •nucleolus: rRNA; ribosome synthesis Protein synthesis (mRNA) Double membrane envelope with pores Pores designed to allow RNA to exit the nucleus

Ribosomes Manufacture Protein – complete the protein structure not finished in the nucleus; addition of amino acids Free •cytosol; •protein function in cell Bound •endoplasmic reticulum; •membranes, organelles, and export

Endomembrane system, I Endoplasmic reticulum (ER) Continuous with nuclear envelope Rough ER •with ribosomes; •synthesis of secretory proteins (glycoproteins), membrane production Smooth ER •no ribosomes; •synthesis of lipids, •metabolism of carbohydrates; •detoxification of drugs and poisons

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

Endomembrane system, III Lysosomes •sac of hydrolytic enzymes; digestion of macromolecules Phagocytosis – the intake of particulate matter into the cell Autophagy: recycle cell’s own organic material Tay-Sachs disease lipid-digestion disorder which causes the brain to become congested with lipids; lipids are not broken down

Endomembrane system, IV Vacuoles membrane-bound sacs (larger than vesicles) Found in plant cells Used for Storage Food (phagocytosis) Contractile (pump excess water) Central (storage in plants) tonoplast membrane separates the cytosol from cell sap

Other membranous organelles, I Mitochondria quantity in cell correlated with metabolic activity cellular respiration double membranous (phospholipid) cristae/matrix intermembrane space contain own DNA believed to originate through symbiosis

Endosymbiosis Theory

Other membranous organelles, II Chloroplast •type of plastid; •double membranous; •thylakoids (flattened disks); •grana (stacked thylakoids); •stroma; •own DNA

Peroxisomes Single membrane Produce hydrogen peroxide in cells Metabolism of fatty acids; detoxification of alcohol (liver) Hydrogen peroxide then converted to water

The Cytoskeleton I 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

Actin and Keratin Filaments

The Cytoskeleton II Cell motility: Changes in the cell location Limited movements of parts of the cell All membrane bound organelles are bound to the cytoskeleton. Movement of vesicles, peroxisomes, lysosomes, etc. all occurs through the cytoskeleton

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

Cytology: science/study of cells Light microscopy •resolving 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

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

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

Cell Signaling I Cells use the intracellular junctions to communicate with each other Signal Transduction Stimulus used to send signals Mechanical: physical touch of one cell to another Chemical: use of ions such as Ca2+ Electrical: used in nerve cell communications

Signal Hypothesis

Cell Signaling II Three stages: Reception: the cell’s detection of a signal from outside the cell, usually binding of protein to a receptor on the membrane surface Transduction: converts the initial signal to a form than can bring about a specific cellular response Often relay molecules and second messengers are used Response: the specific desired result Many possibilities including rearrangement of the cytoskeleton Amplification can occur to make the signal stronger within the cell