Transcript prokaryotes
Diversity of livinng Organisms Read pages 18-30 Department of biology Cell Structure is Evidence for Relatedness • There are two main types of cells, prokaryotes and eukaryotes. • Prokaryotes are bacteria. (Monera) Prokaryotes are much simpler and usually much smaller than Eukaryotes. • Eukaryotes are represented by the remaining four kingdoms: Animalia, Plantae, Fungi, and Protista. • Monera (Prokaryota) : • Prokaryotes are simple cells. • The DNA is loose in the cytoplasm—there is no separate • • • • • nucleus. The ribosomes are also in the cytoplasm. In prokaryotes, transcription (synthesis of RNA) and translation (synthesis of proteins) occurs simultaneously. The cell is surrounded by a membrane, but there are no internal membranes. Outside the membrane is a cell wall, and sometimes an outer capsule which can have structures projecting form it. Bacteria move using flagella: whip-like hairs similar to the flagellum of a sperm cell. http://fig.cox.miami.edu/Faculty/Dana/monera.html http://community.webshots.com/photo/95521344/95541019zbQjjB Bacterial Reproduction • • Bacteria reproduce by the process of binary fission. The circular chromosome replicates its DNA. Then, the cell splits into 2 halves, each containing a single chromosome No spindle apparatus (as exists in eukaryotic mitosis and meiosis). Shape: coccus (spheres) and bacillus (rods). Spirillum (spiral) is less common. Aggregation of cells: single cells, pairs (diplo), chains (strepto), clusters (staphylo). Thus we have types such as diplococcus (pair of spheres) and streptobacillus (chain of rods). Exercise one Eukaryotic cell components • • • • Cell wall (optional) Plasma membrane Cytosol containing organelles: * Nucleus – DNA in chromosomes * Other membrane-bound organelles • Mitochondria • Chloroplasts (optional) * Ribosomes * Membrane system Flagella (optional) Eukaryotic vs. prokaryotic cells • • • • Size * Prokaryotes ≤ 10 µm * Eukaryotes ≥ 10 µm Bacteria & Archea protists, Fungi, Plants, Animals Complexity * Prokaryotes – simple * Eukaryotes – complex Location of chromosomes * Prokaryotes – free in cytosol * Eukaryotes – within a nucleus Flagellar mechanisms differ Figures 7.4, 7.7, 7.8 Bacterium (prokaryote) (Actual size relative to eukaryotes below) Animal (eukaryote) Plant (eukaryote) • Protista – single celled with a nucleus http://www.mcwdn.org/Animals/Paramecium.html • Euglena sp. * Members of the Euglenid group of the clade Euglenozoa * Characterized by an anterior pocket from which one or two flagella emerge, and the storage polysaccharide paramylon - The eyespot functions as a light shield allowing only certain light rays to strike the light detector - The pellicle is constructed of protein bands beneath the plasma membrane and provides strength and flexibility . Nutrition Euglena are mixotrophic – Perform photosynthesis in the light Lose chlorophyll in the dark & absorb organic molecules via the plasma membrane Locomotion Locomotion is either swimming (flagellar motion), gliding, or euglenoid movement1 Euglena exhibit positive phototaxis – the light detector senses light, the flagellum propels the Euglena toward it Osmoregulation Euglena are hypertonic to their freshwater environment Water enters by osmosis and needs to be removed The contractile vacuole fills with water and then fuses with the gullet to release it II. Protista A. General Info B. Groups 1. Protozoa (“Animal-like”)- heterotrophs Amoeba use “pseudopodia” to move Paramecium-uses cilia to move Undulating membrane in groove (ciliary) Food vacuoles Oral groove on surface Macronucleus w/ micronuclei behind Cilia Contractile vacuoles Paramecium, a ciliated protozoan Food Site of cell “anus” particles