Chapter 4. Prokaryotic Cells. Prokaryotic cells. Prokaryotic vs. Eukaryotic Cells. Comparing Prokaryotic and. Eukaryotic cells.

Transcription

1 Chapter 4 Comparing Prokaryotic and Eukaryotic Cells Prokaryotic vs. Eukaryotic Cells Prokaryotic cells No nucleus No organelles Cell walls composed of peptidoglycan Reproduce asexually via binary fission One circular chromosome DNA not associated with histones Eukaryotic cells Nucleus Membrane-boundbound organelles Simple cell walls composed of cellulose or chitin Cell division via mitosis Linear chromosomes DNA associated with histone proteins at times Prokaryotic Cells Size: Length= 2 to 8 um Diameter=.2 to 2 um Morphology: Cocci Bacilli Spiral 1

2 Arrangements Common bacterial arrangements Diplo Strepto Staphylo Tetrads Sarcinae Note: some bacteria are pleomorphic ( have many different shapes) Bacterial Arrangements Structures External to the Prokaryotic Cell Wall 1) Glycocalyx-sticky, gelatinous substance that surrounds bacterial cells Made of polysaccharide or polypeptide or both Mainly produced inside cell and excreted to cell surface Three forms: a) Capsule b) Slime layer c) EPS (extracellular( polysaccharide) * Example-Streptococcus mutans (teeth) 2

3 More structures outside bacterial cell wall 2) Flagella-long, filamentous appendage used for locomotion Four flagella arrangements: a) Monotrichous-1 flagella b) Amphitrichous-1 flagella at each end of the cell c) Lophotrichous-2 or more flagella at one end of the cell d) Peritrichous-many flagella surround entire cell Motility Most spiral bacteria are motile About ½ of bacilli are motile Most cocci are non-motile Advantages of motility: 1) Taxis-movement towards or away from stimulus a) chemotaxis b) phototaxis c) aerotaxis More structures outside bacterial cell wall 3) Axial filaments: provide means of motility in spirochetes a) movement resembles corkscrew 3

4 More structures outside bacterial cell wall 4) Fimbriae and Pili a) Fimbriae-short, numerous hairlike appendages used for attachment, not motility *found mainly in Gram ( )( ) microbes b) Pili-long, long, thin appendage *usually 1 or 2 per cell *function-join cells to allow transfer of DNA from cell to cell Cell Wall Complex, semi-rigid structure composed primarily of peptidoglycan Functions: cell shape attachment point for flagella prevent cell lysis due to greater water pressure inside cell vs outside cell used to differentiate bacterial cell types site of action for some antibiotics Cell Wall Structure Peptidoglycan-backbone made of repeating dissacharide units linked with polypeptide crossbridges a) Disaccharide portion made of NAG and NAM (both monosaccharides) NAG=N-acetylglucosamine NAM=N-acetylmuramic acid b) Crossbridge-made of numerous amino acid molecules(peptides) 4

5 Bacterial Cell Wall Structure Gram (+) Cell Walls Contain thick layer of peptidoglycan Techoic acids-roh & P a) cell growth, prevent cell lysis,, antigenic specificity b) Two types: *lipoteichoic-links links peptidoglycan layer to cell membrane *wall-links links peptidoglycan layer only NAG & NAM Tetrapeptide side chains Amino acid crossbridges Gram + Cell Wall 5

6 Gram (-)( ) Cell Walls Thin peptidoglycan layer-more susceptible to damage NAG & NAM Tetrapeptide side chains Amino acid crossbridges NO TECHOIC ACIDS 2 nd Outermembrane Gram Cell Walls Outermembrane of Gram (-)) Cell Wall Made of lipopolysaccharides (LPS), lipoproteins, and phospholipids Contains porins 2 nd outermembrane-characteristics: Lipid A-endotoxin A (causes fever/shock) O polysaccharide-antigen Function: Evade phagocytosis Barrier to antibiotics, dyes, digestive enzymes 6

7 Bacterial Cell Wall Damage Chemically unique from any other animal cell structure Target for drugs that attack and kill bacteria with harming host cell Selective Toxicity= kills microbe but doesn t harm host Many antibiotics directed at cell wall synthesis Damage to Cell Wall Continued Lysozyme Digestive enzyme that damages bacterial cell walls Found in tears and saliva Attacks bond between NAM & NAG Works best on Gram (+) cells If cell wall not complete, water rushes in and LYSIS occurs Structures Internal to Cell Wall 1) Plasma (Cell) Membrane a) thin membrane enclosing cytoplasm b) Composed of double layer of phospholipid and proteins c) Fluid Mosaic Model * substances move freely within membrane 7

8 Cell Membrane Components 1) Phospholipid bilayer Polar heads (made of phosphate and glycerol) *hydrophilic (loves water) Nonpolar tails (made of fatty acids) *hydrophobic (water hating) Cell Membrane Components Continued 2) Proteins: Two types: a) Peripheral-located located only on the edge of inner or outer surface of membrane *Easily removed *Function-support, act as enzymes b) Integral-extends extends all the way through bilayer *Difficult to remove *Function-act as channels that allow substances to move in/out of cell Cell membrane structure 8

9 Functions of Cell Membrane 1) Barrier-selectively permeability determines what molecules pass through membrane a) large(protein, starch, etc.) don t pass through easily b) small (H2O, O2, CO2) pass through easily Movement of Materials Across Cell Membranes Two types of processes: 1) Passive-high to low concentration (no energy used) a) Examples-osmosis, simple diffusion, facilitated diffusion 2) Active-low to high concentration (uses energy) a) Examples-active active transport Passive Processes 1) Simple diffusion-molecules/ions move from area of high to low concentration until they are evenly distributed (equilibrium) Examples-O2 and CO2 2) Osmosis-water molecules move from high to low concentration 3) Facilitated diffusion-substance substance being transported needs assistance from a plasma membrane protein (transporter protein) - Example-glucose 9

10 Principles of Osmosis Active Processes 1) Active Transport-transporter transporter proteins move substances across cell membrane while using energy (ATP) Cell Membrane Functions Continued 2) Secrete exoenzymes that breakdown nutrients to provide energy a) Examples-amylase amylase & lipase 3) ETS found here 4) Cell wall synthesis enzymes located here 10

11 Antimicrobial Agents Antiseptics and Disinfectants Often disrupt cell membrane and cause cell death (membrane lysis) Cytoplasm Substance located within cell membrane 80% water (other-protein, carbs, lipids, inorganic ions) Thick, elastic, semitransparent Contains DNA and ribosomes Nuclear Area (nucleoid( nucleoid) Contains 1 single, long, circular ds DNA (called ccdna) *Function-carries carries all info required for cell structure & function *plasmids also in nucleoid 11

12 Prokaryote structure Plasmids Small, circular, extra-chromosomal DNA genes Carry genes for antibiotic resistance, synthesis of enzymes, and production of toxins Transferred from 1 bacteria to another Replicate independently from ccdna Ribosomes Site of protein synthesis Two subunits-each made of protein and ribosomal RNA Prokaryotic: 70 S (50 S & 30 S) Eukaryotic: : 80 S (60 S & 40 S) *S (Svedberg( unit)-function of size, weight, and shape 12

13 Prokaryotic ribosome Selective Toxicity Some antibiotics aimed at 70S ribosome of bacterial cells *Streptomycin-attach to 30S subunit and disrupt protein synthesis *Erythromycin-attach of 50 S subunit and interferes with protein synthesis Inclusions Reserve deposits found in prokaryotic cytoplasm Examples: a) lipid-fat b) gas vacuoles-buoyancy c) polysaccharide-starch starch d) metachromatic-inorganic inorganic phosphate (create ATP) 13

14 Endospores Formed by some bacteria to survive harsh environmental conditions (dry, extreme temp, ph, salinity, chemicals)-viable for up to 7500 yrs! Cryptobiotic-no metabolic activity Survive boiling up to 20 hours Vegetative cells-killed above 70C Found in Gram + only -Bacillus and Clostridium genera Eukaryotic Cell Organelles Nucleus-contains contains genetic material (DNA) Nucleolus-inside nucleus- produces ribosomal RNA (ribosome component) Golgi body-modify, sort, package, and transport proteins (shipping/receiving area of cell) Eukaryotic cell organelles (continued) Endoplasmic reticulum (E.R.) Membraneous network connecting cell and nuclear membrane Function= surface for chemical reactions, transportation network, stores chemical molecules Two types: ser-smooth smooth-no ribosomes (lipid synthesis) rer-rough rough-ribosomes ribosomes (protein synthesis) 14

15 Eukaryotic cell organelles (continued) Ribosomes-protein synthesis 80 S Lysosomes-store store degradative enzymes Mitochondria-site of ATP production Contain 70 S ribosomes Circular chromosome Replicate on its own (binary fission) Eukaryotic cell organelles (continued) Chloroplasts-house house chlorophyll and enzymes needed for photosynthesis 70 S ribosome Circular chromosome Replicate on its own (binary fission) Evolution of Eukaryotes Endosymbiotic Theory States that mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by amoeba-like eukaryotic cells Evidence *same size/shape as bacteria *70 S ribosome *circular chromosome *reproduce independently (binary fission) 15