L27: Prokaryotic Cells

• structural components of a prokaryotic (bacterial) cell

  A) fimbrae/pili

  B) nucleiod

  C) plasma membrane

  D) cell regulation

  E) ribosomes

  F) protein synethsis

  G) cell wall

  H) cell integrity

  I) glycocalyx

  J) extracellular: cell protection

  K) flagella

  L) cell movement

  
• the bacterial genome is the nucleoid. it is a circular chromosome. there is no nuclear membrane, however the chromosome is restricted to defined region of the bacterial cell, known as nucleoid.
• other small circular self-replicating DNA molecules can be found in the cytosol, known as plasmids
• the cell wall is to maintain cell shape, protects cell and prevents it from bursting in a hypotonic environment
• the cell wall of bacteria is made of peptidoglycan. its function is a rigid macromolecular layer that provides strength to the wall and protects cells from osmotic lysis and confers cell shape
• peptidoglycan is a polymer composed if modified sugars cross-linked by short polypeptide
• transpeptidase is the enzyme that cross-links the peptidogylcan chains to from rigid walls.
• gram-positive bacteria have simple walls composed of thick layer of peptidoglyan
• structure of gram-positive

  A) gram-positive bacteria

  B) cell wall

  C) peptidoglycan layer

  D) plasma membrane

  E) thick

  
• gram-negative have less peptidoglycan and are structurally more complex. the outer membrane contains lipopolysaccharides
• gram-negative label

  A) easily

  B) red safranin dye

  C) carbohydrate

  D) lipopoylysaccharide

  E) outer membrane

  F) thinner

  G) plasma

  H) outer membranes

  I) 5-10nm

  
• bacterial flagella are capable of movement in liquid medium
• motile bacteria produce flagella
• the long flexible appendage in flagella resemble tails with a 10-20nm in diameter, 5-10 in cell.
• the number of flagella and location on cell surface varies
• flagella acts like a propeller: the cell rotates them to move through a liquid medium
• chemotaxis is a tactic response. the bacteria move along a concentration gradient towards a chemical attractant (positive) or away from a chemical repellent (negative)
• bacterial adherence factors include fimbriae and pili
• fimbriae are structures with adhesive properties that cause bacteria to stick/adhere to surfaces. not all bacteria possess fimbriae, it is an inherited trait.
• fimbriae are not involved with motility and are much shorter and more numerous than flagella. they are 100-1000 in cell and 2-8nm in diameter, 1 micrometre in length
• pili is singular. they are attachment to other bacteria. they are the transfer of genetic material from one cell to another.
• the genetic transfer of pilia is called conjunction. conjunction is a form of horizontal gene transfer
• glycocalyx can be capsules and slime layers
• glycocalyx is a gelatinous polysaccharide and/or polypeptide outer covering. it forms a sticky meshwork of fibres
• capsule glycocalyx, it is a organised into a defined structure attached firmly to a cell wall.
• slime layer glycocalyx, it is disorganised without a cell shape, attached loosely to a cell wall
• capsules can serve numerous functions including: virulence factors, which protects bacteria from phagocytosis and engulfment by immune cells. it also prevents cells from drying out (desiccation)
• another way to withstand harsh conditions are bacterial endospores
• bacterial endospores are formed during unfavourable growth conditions and germinate under favourable conditions, which protect cells from stress
• stressors that trigger endospore formation are nutrient starvation and high cell density
• bacterial endospores are only present in some gram-positive bacteria