北京大学：《微生物学》课程PPT教学课件（英文版）Peptidoglycan Synthesis

Peptidoglycan Synthesis Transport of peptidoglycan precursors across the cytoplasmic. membrane to the growing point of the cell wall Outside Peptidoglycan Growing point of ell wall M一G-M-G-M-G—M-G-M-G—M-G—M一G+M-G-M-G M-G-M-G-M-G-M-G-M-G-M-G M--G-M-G G Cytoplasmic membrane Bactoprenol Inside

Peptidoglycan Synthesis Transport of peptidoglycan precursors across the cytoplasmic membrane to the growing point of the cell wall

The transpeptidation reaction that lead to the final cross-linking of two peptidoglycan chains N Penicillin inhibits this reaction HAWAN D-Alanyl-D-alanine peptide bond D-Ala D-Ala HI L-Ala-o-Glu- DAP-N C-COOH Transpeptidation Peptidoglycan (penicillin inhibits) NH2 DAP-0-Glu-L-Aia-M D-Ala cH、o L-Ala D-Glu- DAP-N-C-C N—DAP→D-Glu--Ala D-Ala G CH D-Ala C-COOH

The transpeptidation reaction that lead to the final cross-linking of two peptidoglycan chains Penicillin inhibits this reaction

The majority of motile prokaryotes love by means of flage lla NNoRAW

The majority of motile prokaryotes move by means of flagella

Flagellar Arrangements Peritrichous P olar Lophotrichous

Flagellar Arrangements Peritrichous Polar Lophotrichous

14n of rotation Hook E cal of reg Oute L Ring (LPS) P Ring The e co S-M Rin gellar Structure Cytoplasmic Mot Fl pr (motor switch)

The E. coli Flagellar Structure

Bacterial Behavior S Prokaryotes encounter gradients of physica/V Chemotaxis, Phototaxis, and other axes and chemical agents in nature, and the motility machinery in the cell is designed to respond in a positive or negative way to these gradients by directing the movement of the cell either toward or away from the signal molecule respectively Such directed movements are called TAXis Chemotaxis: a response to chemicals Phototaxis: a response to light

Bacterial Behavior Chemotaxis, Phototaxis, and Other Taxes • Prokaryotes encounter gradients of physical and chemical agents in nature, and the motility machinery in the cell is designed to respond in a positive or negative way to these gradients by directing the movement of the cell either toward or away from the signal molecule, respectively. • Such directed movements are called TAXiS. • Chemotaxis: a response to chemicals. • Phototaxis: a response to light

Chemotaxis in Bacteria Chemotaxis is the Attractant movement of an Cells per tube organism toward(an attractant) or away from Repellent (a repellent)a chemical

Chemotaxis in Bacteria • Chemotaxis is the movement of an organism toward (an attractant) or away from (a repellent) a chemical

The chemotaxis P rocess (a) In the absence of a chemical attractant the cell swims randomly In runs, changing direction during Attractant tumbles (b) In the presence of an attractant runs become biased. and the cell moves up the gradient of the attractant

The Chemotaxis Process (a) In the absence of a chemical attractant the cell swims randomly in runs, changing direction during tumbles. (b) In the presence of an attractant runs become biased, and the cell moves up the gradient of the attractant

Mechanism of Chemotaxis CheB CheA CheY Chew CheY Trnsducer CheA CheR Cytoplasmic Cell wall MCPs: methyl-accepting chemotaxis proteins

Mechanism of Chemotaxis MCPs: methyl-accepting chemotaxis proteins

Phototaxis 小NM CANOHAWIGSAN ,,的 500 Accumulation of the phototrophic bacterium at light wavelengths at which its pigments absorb Phototaxis of an entire colony toward the light source on the right

Phototaxis • Accumulation of the phototrophic bacterium at light wavelengths at which its pigments absorb. • Phototaxis of an entire colony toward the light source on the right