Intro to Prokaryotic Cells

Question 1

describe the cell wall and cell envelope structure of bacteria

Answer 1

cell envelope:
1. lipid bilayer: contains proteins and lipoproteins (outer and inner leaflet), uptake systems for nutrients, minerals, ions, and amino acids, export systems for minerals, ions, and antibiotics, allows electron transport, and functions as a permeability barrier

2. periplasm: a viscous oxidizing environment between the inner membrane and the cell wall that contains enzymes that catalyze the formation of disulfide bonds, contains proteins participating in small molecule transport or breakdown of polymers to bite-size compounds, and contains protein-folding and trafficking factors that build and maintain the cell envelope
3. cell wall: made of peptidoglycan which is unique to bacteria and not found in eukaryotes!! that gives the cell shape and structural strength (as a mesh like layer) that counteracts the osmotic pressure from cytoplasm and prevents the cell from blowing up, as well as playing a role in cell division

Question 2

describe the structure of peptidoglycan

Answer 2

alternating molecule of two sugars: N-acetyl glucosamine (NAG), and N-acetyl muramic acid (NAM) that are linked to each other through beta (1,4) glycosidic bonds with a pentapeptide linked to NAM linking NAG-NAM strands

Question 3

describe the shapes (4) and arrangements (3) of bacterial cells

Answer 3

shapes
1. coccus: spherical
2. bacillus: rod-shaped
3. spirochete: spiral-shaped
4. pleomorphic: coccobacillus (elongated coccus), curved rod, club-shaped rod, filamentous

arrangements:
1. pair:
2. chain:
3. cluster:

Question 4

explain the differences between the cell wall and cell envelope of gram-negative and gram-positive bacteria

Answer 4

gram negative: has a thin cell wall and an outer membrane that is a second lipid membrane which contains proteins and lipoproteins, uptake systems and export systems, and functions as a permeability barrier; the outer leaflet of this outer membrane contains LPS!!

gram positive: thick cell wall and no outer membrane

Question 5

describe LPS

Answer 5

found in the outer leaflet of the outer membrane of gram negative bacterial cells; is the most abundant molecule on the surface of gram (-) bacteria, and is essential for outer membrane structure; has 3 parts

1. O-antigen: series of branched sugars that vary in length and composition between species, is negatively charged, and is exposed to the surface to interact with divalent cations
2. core: contains KDO; embedded in the outer membrane and is therefore hydrophobic
3. Lipid A: the toxic part! hydrophobic and embedded in the outer membrane; triggers inflammatory reactions when interacts with immune cells and can cause septic shock (is an endotoxin)

Question 6

explain how differences in cell wall and cell envelope structure affect gram staining and acid-fast staining characteristics

Answer 6

gram staining technique:
1. fixation
2. stain with crystal violet
3. treat with iodine to form purple iodine-dye complexes in cytoplasm
4. decolorization: gram (-) bacteria are permeable to the mixture of ethanol-acetone because of their thin cell wall so they will decolorize, but gram (+) have a thick cell wall, so they are not permeable and will not decolorize!
5. counter stain with safranin: the decolorized gram (-) bacteria will take up the red dye stain and appear pink, but the gram (+) bacteria will remain purple

acid fast staining technique:
used for mycobacterium, which contain arabinogalactan polysaccharide in their cells walls, which makes them waxy and must be broken down using acid in order to stain

Question 7

recognize whether a bacterium is gram-positive or gram-negative

Answer 7

gram (-): appears pink after gram staining
gram (+): appears purple after gram staining

Question 8

describe 3 common surface-associated bacterial structures

Answer 8

1. capsule: made of polysaccharides, functions in protection and immune invasion
2. flagellum: function is motility, can have a single flagella at one pole, multiple flagella clustered at one pole (polar), or peritrichous (multiple flagella all over)
3. pilus: similar to flagella but thinner and shorter and function for adherence instead of motility

Question 9

describe 3 common growth requirements of bacteria

Answer 9

1. temperature:
   -thermophile: 45-80 degrees celsius
   -hyperthermophile: greater than 80
   -mesophile: 20-40
   -psycrophile: 0-20
2. nutrient requirements: minimal, fastidious, acidophile (<5pH), halophile (>2M salt)
3. atmosphere:
   -aerobe: requires O2
   -anaerobe: O2 is toxic
   -microaerophile: requires reduced O2
   -facultative: O2 status does not matter