1. Lecture #1
Chapter 6~ A Tour of the Cell

2. 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

3. 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

4. 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

5. 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

6. 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

8. 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

9. 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

10. Endosymbiosis Theory

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

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

13. 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

14. Actin and Keratin Filaments

15. 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

17. Centrosomes/centrioles
Centrosome: region near nucleus
Centrioles: 9 sets of triplet microtubules in a ring; used in cell replication; only in animal cells

18. 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

22. 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

23. Cell Types: Prokaryotic
Nucleoid: DNA concentration
No organelles with membranes
Ribosomes: protein synthesis
Plasma membrane (all cells); semi-permeable
Cytoplasm/cytosol (all cells)

24. 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

25. 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)

26. 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?)

27. 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

28. 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

29. Signal Hypothesis

30. 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