Chapter 5 notes.pdf

work CHAPTER 5: Bacterial Cell: An overview Cells are the fundamental unit of life: more Prokaryotic cells cells without a “true” nucleus (no nuclear membrane) Bacteria and archa...

work CHAPTER 5: Bacterial Cell: An overview Cells are the fundamental unit of life: more Prokaryotic cells cells without a “true” nucleus (no nuclear membrane) Bacteria and archaea Eukaryotic cells cells with a true nucleus and other organelles All other organelles (animals, plants, fungi, and protists) Bacteria small cell size (usually 0.2 - 10 micrometer) DNA organized in nucleotide throughout the cytoplasm Small genome (0.5-15 million base pairs) Circular chromosomes (usually) although may have multiple circular and linear chromosomes ◦ allows transcription and translation to occur simultaneously Few intracellular membrane (such as thylakoid of photosynthetic bacterial) No intracellular endosymbiosis organelles Cell wall composed of peptidoglycan Rotary flagella for motility, driven by proton motive force Eukaryotes wide range of cell size, from very small to very large DNA contained in the nucleus, enclosed by the nuclear membrane Wide range of genome size Linear chromosomes (in nucleus) ; mitochondria (derived from bacteria) have one circular chromosome, Many types of organelles Mitochondria and chloroplasts have evolved from endosymbiotic bacteria. Cell walls composed of carbohydrates and nor peptidoglycan Whiplike flagella for motility, with microtubule contraction driven by ATP. Model of Bacterial Cell anpia I.in Cytoplasm of the bacterial cell is a gel-like network of proteins and other p macromolecules. It is contained by a cell membrane. ◦ cell membrane keeps cytoplasmic proteins from leaking out ◦ Allows nutrients to enter ◦ Maintain concentration gradient of ions and nutrients. ◦ Process where oxidative phosphorylation occurs. Outside of the membrane the cell body is enclosed by a cell wall. ◦ the cell wall is made up of peptidoglycan - amino acids and sugars, f ◦ Gram negative bacteria have an outer membrane outside the cell wall. The cell membrane, cell wall, and outer membrane (for gram negative bacteria) constitutes the cell envelope. The chromosome is organized within the chtoplasm as a system of looped coils called the nucleois Peptidoglycanmurein Cell Wall The cell wall consists of glucose chains (parallel rings) linked by peptides (arrows). The crosslinked spaces between links are open, porous to large molecules. ◦ protecting the bacteria from outside and osmotic change ◦ Acts as a molecular cage ◦ Most bacteria; cell walls consists of peptidoglycan (also called murein) that consists of parallel polymers of disaccharides called glycan chains - parallel polymers of disaccharides. ‣ the glycan chains are cross-linked with short peptides. ◦ This is unique to bacteria never found in human cells to ◦ For this reason, antibiotics that target peptidoglycan synthesis typically have minimal side effects for a patient. openporous largemolecules Long glycan chains of peptidoglycan consists of repeating units of 2 amino sugars: NAG & NAM The parallel glycan strands are linked by short peptide cross bridge containing 4-6 amino acid residues disaccharide  itsD alaninggaugem diaminopimeliacidthatformsthe A disaccharides unit of glycan had an attached peptide of four to six amino acids attached to the NAM terminal. On the peptide, the extra amino group of m-diaminopimelic acid can cross-link to the carbonyl terminus of a neighbouring peptide. 0 The addition of D - alanine to the peptide is blocked by 0 vancomycin, and the cross-bridge formation by transpeptidase is blocked by penicillin. M-diaminopimelic acid attaches to D-alanine from a neighbouring peptide on a parallel glycan chain. -> always attached to NAM. if we don'twantthe bridgetoformwewanttoblock theiradditiontothepeptidechain Peptide = shorter amino acid compared to proteins. D alanine vancomycin Gram positive and Gram negative Outer Layers: whenpeptidecross bridgeforms theDalanine isreleased Bacterial cell wall types penicillin formationisblocked Peptide cross bridge by Gram-positive (purple) thick cell wall, multiple layers of peptidoglycan ◦ Bacillus anthracis, Streptococcus pyogenes 0 Consists of multiple layers of peptidoglycan (up to 40 in some species) The peptidoglycan is reinforced by teichoic acids (threaded to its multiple layers) ◦ Teichoic acids are chains of phosphodiester-linked sugar alcohols (glycerol or ribitol) ◦ The phosphodiester links are deprotinated (ionized) and thus have a negative charge ◦ The negative,y charged property of teichoic acid and the multiple layers of the gram positive cell wall helps retain the crystal violet. ◦ Acts as bacterial signature molecules that alert the immune system of an impending infection. Gram-negative (pink) thin cell wall, single layer of peptidoglycan, enclosed by an outer membrane innermembrane cellmembrane ◦ Escherichia coli, pseudomonas aeruginosa siderophore-iron complex then attaches to specific receptors in the bacterial outer membrane. The siderophore-fe complex may then be transported across the cell membrane by an ABC transporter. Proton Motive Force PMF is generated when chemical energy is used to pump protons outside the cell, so that the proton concentration is greater outside the cell than inside. Because proton are positively charged, proton movement across the cell membrane produces an electrical gradient, making the inside of the cell more negatively charged than the outside. The energy stored in the PMF can be used to move nutrients into the cell, to drive motors that rotate flagella, and drive the synthesis of ATP. The proton-powered ATP synthase is a target for antibiotics.