Chapter 1 The structure and function of prokaryotes EUKARYOTES EUKARYOTES PROKARYOTES BACTERIAARCHAEA
1.Differences between prokaryotes/eukaryotes 2.Shape and arrangement 3.Procaryoic cell organization
Prokaryotes (Bacteria) Eubacter "True" bacteriaEubacter "True" bacteria – human pathogens – clinical or environmental – one kingdom Archaea Archaea – Environmental organisms – second kingdom
Eukaryotes Other cell-based life e.g.Other cell-based life e.g. –plants –animals –fungi
1. The prokaryotic cell, in contrast to the eukaryotic cell, is not compartmentalized. Nuclear membranes, mitochondria, endoplasmic reticulum, Golgi body, phagosomes and lysosomes are not present. 2. Prokaryotes generally possess only a single circular chromosome. Since there is no nuclear membrane, the chromosome is bound to a specific site on the cell membrane - the mesosome. 3. Prokaryotic ribosomes are 70S (S stands for Svedberg unit, a measure of size), whereas eukaryotic ribosomes are larger (80S). Prokaryotic ribosomal subunits are 30S and 50S (eukaryotic are larger). The 30S ribosome has 16S RNA, whilst the 50S ribosome contains 23S and 5S RNA. Ribosomal RNA is larger in eukaryotes (e.g. 18S versus 16S rRNA). 4. Bacterial membranes generally do not contain sterols ( 甾醇 )(e.g. cholesterol). Differences between prokaryotes/eukaryotes
Prokaryotic Cell (versus Eukaryotic Cell) Not compartmentalizedNot compartmentalized Cell membranes lack sterols (e.g. cholesterol)Cell membranes lack sterols (e.g. cholesterol) Single circular chromosomeSingle circular chromosome Ribosomal are 70S withRibosomal are 70S with –subunits 30S (16S rRNA) –50S (5S & 23S rRNA)
Structure of the cytoplasmic membrane Prokaryotes Membrane Stabilizers: hydrogen bonds hydrophobic interactions Mg 2+, Ca 2+, hopanoids Phospholipids bilayer+protein, 5-10nm thick
Many bacterial membrane Strengthening Agents: Hopanoids 类何帕烷 (a) General structure of a sterol; (b) The structure of cholesterol; (c) The structure of the hopanoid diploptene. Eukaryotes membrane stabilizer: Sterol
Functions of the Cytoplasmic Membrane The cytoplasmic membrane is selectively permeable and contains specific carrier proteins that participate in the transport process Selectively Permeability: nonpolar and fat-soluble such as fatty acids, alcohols and benzene (permeable); charged molecules such as organic acids, amino acids and inorganic salts (impermeable, must be specifically transported) Carrier Proteins: or Membrane Transport Proteins: Uniporters, Symporters and Antiporters 1. Permeability barrier - prevents leakage and function as gate way for transport of nutrients into and out of the cell. 2. Protein anchor- site of many proteins involved in transport, bioenergetics, and chemotaxis. 3. Energy conservation- site of generation and use of the proton motive force.
Mesosome: invaginationa of the plasma membrane in the shape of vesicles, tubules, or lamellae. Functions: 1.cell wall formation during division. 2.play a role in chromosome replicaton and distribution to daughter cells.
The cytoplasmic matrix: substance lying between the plasma membrane and the nucleoid. Protoplast: the plasma membrane and everything within.
Making Wall-less forms Result from action of:Result from action of: –enzymes lytic for cell wall –antibiotics inhibiting peptidoglycan biosynthesis Wall-less bacteria that don’t replicate:Wall-less bacteria that don’t replicate: –spheroplasts (with outer membrane)? –protoplasts (no outer membrane). ? Wall-less bacteria that replicateWall-less bacteria that replicate –L forms Naturally Wall-less Genus Mycloplasma
Within the cytoplasm of procaryotic (and eucaryotic) cells are several kinds of reserve deposits, known as inclusions. Some inclusions are common to a wide variety of bacteria, whereas others are limited to a small number of species and therefore serve as a basis for identification. Among the more prominent bacterial inclusions are the following: Carbon storage polymers – PHB and glycogen Phosphate polymers Sulfur Granules Gas Vacuoles INCLUSIONS
Polyhydroxybutyric acid (PHB) PHB is a lipidlike compound - one of the most common inclusion bodies in prokaryotic organisms. PHB is commonly found as a storage material and unique to bacteria Glycogen is a starchlike polymer of glucose subunits. Glycogen granules are usually smaller than PHB granules. A Vibrio species
Many microorganisms accumulate granules of polyphosphate, which are large reserves of inorganic phosphates that can be used in the synthesis of ATP Polyphosphate granule in a bacterial cell A Pseudomonas species
The sulfur globules inside the cells of purple sulfur bacterium Chromatium buderi Some bacteria, including many photosynthetic bacteria, accumulate elemental sulfur granules as a result of their metabolism.
Gas vacuoles (blue) and storage granules (red) in the cyanobacterium Microcystis The formation of gas vacuoles by aquatic bacteria provides a mechanism for adjusting the buoyancy of the cell.Many aquatic cyanobacteria use their gas vacuoles to move up and down in the water column.
Magnetosomes Magnetic particles of Fe 3 O 4 Isolated from Aquaspirillum magnetotacticum
Ribosomes: protein synthesis Procaryotic: 70S (50S 30S) Eucaryotic: 80S ( 60S 40S) What is S: Svedberg unit. This is the unit of the sedimentation coefficient, a measure of the sedimentation velocity in a centrifuge; the faster a particle travels when centrifuged, the greater its Svedberg value or sedimentation coefficient. The sedimentation coefficient is a function of a particle’s molecular weigh, volume, and shape.
The Nucleoid Usually procaryotics contain a single circle of double-stranded DNA. But some: a linear DNA chromosome Recently: Vibrio cholerae: >one chromosome. Nucleoid: 60% DNA, 30% RNA, 10% protein (by weight) Exceptions: 1. Pirellula: a single membrane 2. Gemmata obscuriglobus: two membrane
DNA Supercoiling To package the DNA into the cell requires that the DNA be supercoiled. There are over 50 supercoiled domains in the E. coli chromosome, they are stabilized by association with the structural proteins.
Plasmids: ds, circular or linear DNA, exist and replicate independently of the chromosome or may be integrated with it, not required for host growth and reproduction.Plasmids: ds, circular or linear DNA, exist and replicate independently of the chromosome or may be integrated with it, not required for host growth and reproduction. extrachromosomal DNA multiple copy number coding pathogenesis and antibiotic resistance factors bacterial replication
What have we learned so far? Major difference between prokaryotes and Archaebacteria? Major difference between prokaryotes and eukaryotics? Morphology of prokaryotes? Components of prokaryotic cells? Structure of cytoplasmic membrane? Differences between archeal and prokaryotic membranes? Functions of cytoplasmic membrane? Actions of carrier proteins? What types of cytoplasmic inclusions are formed by prokaryotes? What is mesosome? Its function? Wall-less form? What is protoplast? Prokaryotic ribosome, nucleiod and plasmids?