quiz 2 advanced micro

61 flashcards · Biology · by Baher Nazar Gul

1. fimbriae (s., fimbria)

   short, thin, hairlike, proteinaceous appendages •up to 1,000/cell mediate attachment to surfaces –some (type IV fimbriae) required for twitching motility or gliding motility that occurs in some bacteria

2. sex pili (s., pilus)

   similar to fimbriae except longer, thicker, and less numerous (1-10/cell) –required for mating encoded by the fertility F sex factor

3. Flagella

   hreadlike, locomotor appendages extending outward from plasma membrane and cell wall

4. Patterns

   monotrichous – one flagellum • polar flagellum – flagellum at end of cell • amphitrichous – one flagellum at each end of cell • lophotrichous – cluster of flagella at one or both ends • peritrichous – spread over entire surface of cell

5. functions

   -motility and swarming behavior –attachment to surfaces –may be virulence factors

6. Flagella Structure

   1. Flagellar filament: extends from the cell surface to the tip 2. Basal body: embedded in the cell membrane 3. Flagellar hook: Links the filament to the basal body, acts as a flexible coupling

7. The filament

   •extends from cell surface to the tip •Largest, most visible part of the flagella •Hollow, rigid cylinder •composed of the protein flagellin, capping protein.

8. filament structure

9. hook

   –links filament to basal body –Protein sheath around the filament –Made of several proteins

10. basal body

    Smallest, most complex part –series of rings that drive flagellar motor –Gram negative: four rings connected to a central rod (L,P,MS,C rings) –Gram positive: Two basal body rings (C, MS)

11. basal and hook

12. Flagellar Synthesis

    •complex process involving many genes ( at least 20) for synthesis of filament, hook, and basal body. •new molecules of flagellin are transported through the hollow filament. •Growth is from tip, not base, cap protein helps assembly •an example of self-assembly: No chaperone proteins

13. Archaeal Flagella

    •flagella thinner •more than one type of flagellin protein •flagellum are not hollow •hook and basal body difficult to distinguish •growth occurs at the base, not the end

14. Motility

    •Flagellar movement •Spirochete motility (creeping/crawling motility) •Twitching motility •Gliding motility

15. The Mechanism of Flagellar Movement

    •Filament is a rigid helix. •flagellum rotates like a propeller on a boat, rings rotate, convey motion to the filament. •very rapid rotation up to 1100 revolutions/sec •in general, counterclockwise rotation causes forward motion ( run), clockwise rotation disrupts run causing a tumble (twiddle). •Alternation between clockwise and counterclockwise rotation gives bacteria their characteristic pattern of random motility. •Electrical motor powered by ion gradients.

17. Molecular basis for flagellar movement

    •A Flagellum is an electrical motor producing torque •Electricity is changed to mechanical movement •Electricity comes from guarded and regulated movement of protons across the plasma membrane from the outside to the inside (Proton motive force or PMF) •Rotor •C (FliG protein) ring and MS ring turn and interact with stator •Stator - Mot A and Mot B proteins •form channel through plasma membrane •protons move through Mot A and Mot B channels using energy of proton motive force •torque powers rot…

18. movement pic

19. Creeping motility/crawling motility in Spirochetes

    • Highly coiled and cork-screw shaped bacteria • multiple flagella form axial fibril which winds around the cell • flagella remain in periplasmic space inside outer sheath • Rotates similar to a normal, outer flagella • corkscrew shape exhibits flexing and spinning movements • Creeping motility/crawling motility

20. Creeping motility/crawling motility

21. Twitching Motility

    Involves Type IV pili at ends of cell – On moist surfaces – short, intermittent, jerky motions – cells are in contact with each other and surface

22. Gliding motility

    – Smooth movements – Nature of the movement differs: • Parallel to the longitudinal axis of the cell • Perpendicular to the longitudinal axis of the cell. • Some rotate while gliding – Suggestive of the occurrence of multiple mechanisms for gliding motility. – Not well understood

23. Myxococcus xanthus

    Movement •social –Movement by twitching motility. – Type IV-mediated pili movements, with cells moving together in large groups. •Adventurous –Movement by gliding motility. –slime released moves cell forward. –adhesion complexes move in track provided by cytoskeleton.

24. The Bacterial Endospore

    •Formed by some bacteria. •Dormant. •Resistant to numerous environmental conditions e.g. heat, radiation, chemicals, desiccation. •Sporogenesis endospore formation or sporulation is a complex process that commences when growth ceases because of lack of nutrients. •Germination: transformation of endospore into vegetative cell

25. Endospore structure

    •Spore surrounded by thin covering called exosporium •Thick layers of protein form the spore coat •Cortex, beneath the coat, thick peptidoglycan •Core has nucleoid and ribosomes

26. What makes an endospore so resistant?

    Core – Dehydrated core: cortex can remove water from the core protect it from heat and radiation damage – Dipicolinic acid (15% of dry weight of the spore, complexed with Ca ions), located in the core: thought to be involved in heat resistance. – Calcium: help increase resistance to wet heat, dry heat, and oxidizing agents. – small acid-soluble, DNA-binding proteins (SASPs): saturate spore DNA and protect it from heat, radiation, desiccation, and chemicals. – DNA repair enzymes: repairs DNA onc…

27. Chemotaxis

    •movement towards a chemical attractant or away from a chemical repellent. •concentrations of chemical attractants and chemical repellents detected by chemoreceptors on surfaces of cells.

28. Chemotaxis Towards Attractant

    in presence of attractant (figure b), tumbling frequency is reduced and runs in direction of attractant are longer.

29. Molecular mechanism of chemotaxis

    •Two component signal transduction system: •Sensor kinase a membrane-bound histidine kinase senses a specific environmental stimuli and autophosphorylates a specific histidine residue (also called histidine autokinase). •Phosphorylation of sensor kinase relays the signal to a response regulation, causing its activation through phosphorylation. •Activation of response regulator mediates the required cellular response, mostly through differential expression of target genes. •Sensor Kinase in E. C…

31. Phototaxis:light-regulated movement of motile organisms

    Within bacteria most phototactic Bacteria are phototrophic. Generally similar to chemotaxis: Two component signal transduction Within Archaea Phototaxis occurs within halophilic Archaea

32. Protein Secretion in Prokaryotes

    •Plasma membranes, cell walls function as barriers for the movements of molecules in or out of the cell. •Many important structures (like what?) are located outside the cell membrane (In the periplasm), others outside the cell wall. •Protein translocation versus protein secretion. •Elaborate protein secretion mechanisms are needed.

33. Overview of Bacterial Protein Secretion

    • gram+ and gram - bacteria have different problems secreting proteins based on the differences between the structure of their walls . Why? • for both types of cells, the major pathways for transporting proteins across the plasma membrane (i.e. translocation) are the Sec- dependent pathway , and the Twin arginine translocase (TAT) system. • All protein secretion systems require energy.

34. Sec-Dependent Pathway

    • also called general secretion pathway. • translocates proteins from cytoplasm across or into plasma membrane. • secreted proteins synthesized as preproteins having amino- terminal signal recognition peptide (SRP). • signal peptide delays protein folding • chaperone proteins (secB) keep preproteins unfolded. • Certain proteins (e.g. Sec Y, Sec E, and SecG) form a channel through the membrane through which a preprotein passes. • Another protein (secA) Binds to SecY, E, and G, and acts as a moto…

35. Twin arginine translocase (TAT) system.

    • Similar to the Sec system, moves proteins through plasma membrane. • Differs from the sec system by the nature of translocated protein. TAT translocates folded proteins, while SEC translocates unfolded proteins. • TAT-translocated proteins feature two (Twin) arginine residues as their signal sequence.

36. Protein Secretion in Gram-ve bacteria

    • Translocation of proteins across the plasma membrane is often only a first step in the protein secretion pathways of gram negatives. • 5 secretion pathways have been identified in gram- bacteria. • Some proteins cross in a two-step process (Sec-dependent) – The first step is translocation to the periplasm by the Sec or Tat system. – The second step is secretion across the outer membrane. • Some proteins cross in a one-step processes – Involve structures composed of multiple polypeptides that…

37. Sec-dependant pathways: Type II Protein Secretion Pathway

    • Present in a number of plant and animal pathogens. • transports proteins from periplasmic across outer membrane. • complex systems consisting of up to 12-14 proteins, most are integral membrane proteins. • In addition to unfolded proteins translocated across plasma membrane using the sec pathways, folded protein translocated using the Tat (Twin arginine translocation) pathway are secreted in gram -ve bacteria using Type II secretion pathways .

38. TAT

39. Sec independent protein secretion pathways: Type I secretion pathway (ABC Protein Secretion Pathway) •

    • Ubiquitous in prokaryotes. • transports proteins from cytoplasm across both plasma membrane and outer membrane. • secreted proteins have C-terminal secretion signals, helps direct the protein to the type I secretion machinery. • ABC: ATP binding cassette. • No chaperone, just a signal peptide.

40. Type VI secretion system

    Contractile weapons.....Injecting toxins to neighboring cells. Two concentric cylindrical structures docking in the inner membrane. Inner tube is ejected in response to a contact signal, puncturing target cell and delivering toxins (effector). Related bacteria has immunity proteins. Example Vibrio cholera Type VI system attacking amoeba in aquatic environment and gut microbiome (post injection).

41. type 4

42. All Organisms Require Carbon, energy, and Electron Source

    •carbon is backbone of all organic components present in cell •Hydrogen and oxygen are often supplied with the carbon source •electrons play a role in energy production and reduction of CO2 to form organic molecules

43. Requirements for Carbon, energy, and electrons

    often satisfied together – carbon source often provides H, O, and in some cases energy and electrons

44. Based on carbon sources, microorganisms could be classified as:

    heterotrophs –use organic molecules as carbon sources which often also serve as energy, electron sources •autotrophs –use carbon dioxide as their sole or principal carbon source –must obtain energy, electrons, from other sources

45. Nutritional Types of Organisms

    •based on energy source –phototrophs use light –chemotrophs obtain energy from oxidation of chemical compounds •based on electron source –lithotrophs use reduced inorganic substances –organotrophs obtain electrons from organic compounds

46. source

47. Nutritional Types of Microorganisms

48. The Common Nutrient Requirements

    macroelements (macronutrients) –C, O, H, N, S, P, K, Ca, Mg, and Fe –required in relatively large amounts •micronutrients (trace elements) –Mn, Zn, Co, Mo, Ni, and Cu –required in trace amounts –often supplied in water or in media components

49. Requirements for Nitrogen, Phosphorus, and Sulfur

    nitrogen is needed for synthesis of important molecules nitrogen supplied in numerous ways (amino acids, NH4+, nitrate, N2). •phosphorus usually supplied as inorganic phosphate, some (e.g. E. Coli can use organophosphates). •sulfur usually supplied as sulfate via assimilatory sulfate reduction, few require reduced sulfur compounds

50. Uptake of Nutrients by the Cell

    •Some nutrients enter by passive diffusion •Most nutrients enter by: –facilitated diffusion –active transport

51. Passive Diffusion

    • molecules move from region of higher concentration to one of lower concentration because of random thermal agitation •H2O, O2 and CO2 often move across membranes this way

52. Facilitated Diffusion

    •similar to passive diffusion: –movement of molecules is not energy dependent. –direction of movement is from high concentration to low concentration. –size of concentration gradient impacts rate of uptake.

53. Facilitated diffusion..

    •differs from passive diffusion: uses carrier molecules (permeases).  smaller concentration gradient is required for significant uptake of molecules.  rate of facilitated diffusion increases more rapidly and at a lower concentration. diffusion rate reaches a plateau when carrier becomes saturated (carrier saturation effect).

54. Mechanism

    Concentration gradient in passive versus facilitated diffusion

55. Active Transport

    •Differs from various diffusion processes in: –energy-dependent process –ATP or proton motive force used •moves molecules against the gradient •concentrates molecules inside cell •Similar to facilitated diffusion in: –involves carrier proteins (permeases) –carrier saturation effect is observed at high solute concentrations.

56. Primary active transport by ABC transporters

    •Use energy generated by ATP hydrolysis to directly transport molecular across the membrane. •ABC: ATP-binding cassette transporters. •observed in bacteria, archaea, and eucaryotes. •Could transport a variety of sugars and amino acids, inorganic compounds (e.g. phosphate, and larger compounds (e.g. vitamin B12).

57. Structure, Mechanism of ATP transport

    •Two hydrophobic membrane spanning domains, associated on their cytoplasmic surfaces with two ATP-binding domains. •Special substrate binding proteins are used to bind the solute. •Solute imported to the cell, the process is coupled to ATP hydrolysis for energy production.

58. The special case of Iron Uptake

    •ferric iron is very insoluble so uptake is difficult •microorganisms use siderophores to aid uptake •siderophore complexes with ferric ion •complex is then transported into cell by an ABC transporter

59. Secondary active transport by symport and antiport

    Secondary: transport coupled to the movement of ions H+ or Na+ across the membrane. •Proton translocation across the membrane is an important way of energy generation • Specific permiases could couple proton translocation to solute (e.g. lactose) translocation across the membrane

60. Antiport

    Indirect utilization of energy generated during proton translocation. Energy generated during proton gradient drives sodium ion expulsion. Sodium couples to a permease. Delivery of solute to the inside of the cell Not entirely understood