General Biology A Tour of the Cell

I. What is a Cell? A. The cell theory 1. The fundamental units of both structure and function in all living things. 2. That all forms of life are composed of cells and their structures. 3. That cells arise only from pre-existing cells. 4. Each cell having a life of its own in addition to its integrated role in multi-cellular organisms.

B. Types of Cells and Other Things 1. Prokaryotes – Bacteria and Some Blue Green Algae 2. Eukaryotes – Plants and Animals 3. Viruses – Are not cells, but have either DNA or RNA 4. Prions – Are not cells, no DNA or RNA (protein particle) 5. Viroids – Are not cells, naked RNA 6. Archaea – A microbe – The third form of life?

II. Cell Size A. Limits to Sizes 1. Range of cell size is limited by metabolic requirements. 2. As a cell increases in size, its volume grows proportionately more than its surface area. (Think of it like a balloon) 3. Surface area of plasma membrane must be large enough for the cell volume to provide adequate exchange with the surroundings.

B. Cell sizes vary with their function.

IV. Prokaryotic Cells

V. Organells A. The Nucleus 1. Contains most of the genes that control the entire cell. 2. Nuclear envelope – A double membrane which encloses the nucleus. 3. Chromatin – A complex of proteins and DNA 4. Chromosome – Long threadlike association of genes. 5. Nucleolus – Where ribosomes are made.

B. Ribosomes 1. A cytoplasmic organelle that is the site for protein sysnthesis. 2. Are complexes of RNA and protein. 3. Two types: a. Free ribosomes – suspended in the cytosol. b. Bound ribosomes – attached to the ER

C. Endomembrane System 1. A system which makes up many of the organelles in eukaryotes. 2. Membranes may be interrelated directly through physical contact. 3. Include; a. Nuclear envelope b. Endoplasmic reticulums c. Golgi apparatus (body) d. Vacuoles e. Plasma membrane

D. Endoplasmic Reticulum 1. Manufactures membranes 2. Most extensive portion of endomembrane system. 3. Two distinct regions a. Smooth ER b. Rough ER

a.Smooth ER 1. Participates in the synthesis of lipids – fatty acids, phospholipids and steroids. 2. Participates in carbohydrate metabolism. 3. Detoxifies drugs and poisons. 4. Stores Calcium Ions (Ca +2 ) 5. Found in abundance in the liver and in muscle cells.

b. Rough ER 1. Studded with ribosomes 2. Continues with outer membrane of the nuclear envelope 3. Manufactures secretory proteins and membranes 4. Vessicle – membrane enclosed sacs that are pinched off portions of membranes moving form the site of one membrane to another.

E. Golgi Apparatus 1. Finishes, Sorts, and Ships cell products 2. Many vesicles leave the ER and travel to the Golgi body. 3. Enzymes in the Golgi body modify products of the ER in stages as they move through.

F. Lysosomes 1. Digestive compartments 2. Keeps hydrolytic enzymes from free floating in the cytosol. 3. Recycles cell’s own organic material. 4. Programmed cell destruction 5. causes some human diseases a. Pompe’s disease (glycogen accumulation in liver) b. Tay-Sachs disease (lipid accumulation in the brain)

G. Vacuoles 1. Membrane – enclosed sac that is larger than a vesicle. 2. Food vacuole – site of intracellular digestion in some 3. Contractile vacuole – vacuole that pumps excess water form the cell. 4. Central vacuole – mature plant cells, performs many functions.

H. Peroxisomes 1. Contain specialized enzymes for specific metabolic functions. 2. Breakdown fatty acids into smaller molecules. 3. Detoxification of alcohol and other harmful components. 4. Biogenesis occurs by pinching off from preexisting peroxisomes.

I.Mitochondria 1. Site cellular respiration 2. Are very dynamic structures – can move, change their shape, and divide on their own. 3. Contain their own DNA

J. Chloroplasts 1. Plastids – a group of plant and algae membrane-bound organelles. 2. Where photosynthesis takes place.

VI. The Cytoskeleton A. Functions 1. Gives mechanical support to the cell – maintains shape. 2. Enables a cell to change shape in an adaptive manner. 3. Associated with motility. 4. Helps in transmitting signals from cell’s surface to its interior. 5. Organizes structures and activities of the cell.

B. Structures 1. Microtubules a. Found in cytoplasm in all eukaryotes. b. Provide cellular support – reinforce cell shape. c. Tracks for organelle movement. d. Separation of chromosomes during cell division.

2. Centrosomes and Centrioles a. Organizes microtubules assembly during cell division. 3. Cilia and Flagella a. Locomotor organelles in eukaryotes that are formed from a specialized arrangement of microtubules. b. Basal body – A cellular structure identical to a centriole that anchors the microtubular assembly of cilia and flagella.

4. Microfiliaments (actin filaments) a. Provides cellular support. i. Bears tension ii. Make up microvilli b. Participates in muscle contraction c. Responsible for localized contraction of cells. i. Elongation and contraction of pseudopodia. ii. Involved in cyclosis in plant cells.

5. Intermediate filaments a. Anchor some organelles in fixed positions b. Reinforces cell shape.