Zoology 100 Notes 2

ZOOLOGY 100 NOTES (2) Continuation The Human Cell • bounded by a plasma membrane that encloses a central nucleus surrounded by cytoplasm. – Cytoplasm contains organelles, membranous structures, and a cytoskeleton • Human cells differ in size, shape and function

CELL SIZE

• • •

most cells are microscopic length of nerve cell largest single cell

Junctional complexes of the Cell membrane 1. Zonula adherens 2. Macula adherens 3. Spot desmosomes

5-100 microns 1 meter (m) ostrich egg

Lysosomal activity 1. AUTOPHAGY – digestion of damaged organelles by the lysosomes of the cells 2. AUTOLYSIS – digestion of the its own damaged cells. - related to aging PEROXISOMES • Membranous sacs containing powerful oxidase • For detoxification of toxins such as alcohol, formaldehyde • Disarm dangerous free radicals (highly reactive chemicals w/ unpaired e- which can scramble CHON & nucleic acid structures) • Ex. H2O2- à H2O + O Differences of organelles and inclusions ORGANELLES • Permanent living components of the cell • Machinery of the cell engineered to carry out their own function • examples: Nucleus, G.A., mitochondria, ER, lysosomes, peroxisome, proteasomes INCLUSIONS • temporary, non-living accumulation of metabolites • Stored nutrients and cellular products • examples: Fat droplets,granules,pigment,crystals and secretory products

Types of Organelles 1. Membranous Organelles - membrane-bounded structures of the cell - Nucleus, G.A., mitochondria, ER, lysosomes, peroxisome, proteasomes 2. Non-membranous Organelles - not bounded by membrane ex. cytoskeleton, centrioles Enzymes - Large protein molecules that act as a catalyst in chemical reactions • a. enzymes have an active site where they hold reacting molecules in the correct position for a bond to form or to break a bond - specific to one reaction - affected by temperature and pH - The process of inactivating it is called denaturing Coenzymes - Non-protein molecules that aid in the function of enzymes

Step 1: Glycolysis • Takes place in the cytoplasm • Glucose is split into two molecules of pyruvate Step 2: Krebs Cycle • Takes place in the matrix of the mitochondria • Requires oxygen Step 3: Electron transport chain • Occurs across the membranes (christae) of the mitochondrion of the Eukaryotes, and plasma membrane of the Prokaryotes • Produces ATP Step 1: Synthesising ACETYL COENZYME A:

Step 2: Oxidising Acetyl CoA:

THE ELECTRON TRANSPORT CHAIN (ETC) • Most ATP is manufactured by oxidative phosphorylation. • A series of redox reactions using electron acceptor/donor molecules coupled to glycolysis and the Kreb's cycle. • The electron acceptors/donors reduce (when receiving electrons) and oxidise (when losing electrons) one another along an electrochemical gradient. Each molecule in the series has a lower redox potential than the one before. • Each redox reaction results in a release of energy. • If this energy release is > 30.5 kJ mol-1 a mole of ATP can be synthesised from ADP by a coupled reaction. The first molecule in the series is NAD (or FAD), a coenzyme of various dehydrogenase enzymes.

NAD (oxidised) NADH + H+ (reduced) • Next come a series of iron containing proteins called cytochromes The last electron acceptor in the series is oxygen. Electrons are produced by splitting hydrogen atoms taken from the food molecules (H H+ + e-) by dehydrogenases. Thus at the end of the ETC:

2H+ + 2e- + ½O2 H2O