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MICROBIOLOGY EXAM 2 UTA
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MICROBIOLOGY EXAM 2 UTA
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MICROBIOLOGY EXAM 2 UTAUniporters
Transport in one direction across the membrane
Symporters
Functions as co-transporters; the two molecules travel in the same direction; 1. Energy
is released as one substituent moves down its concentration gradient 2. This energy
moves a second substrate against its gradient into the cell
Anitporters
Transport a molecule across the membrane while simultaneously transporting another
molecule in the opposite direction; the actively transported molecule moves in the
direction opposite to the driving ion; 1. Antiporter binds substrate A on the cytoplasmic
side of the membrane 2.Antiporter opens to the outside, where the concentration of A is
less 3. Substrate A leaves its binding site, and substrate B then binds to its site 4.
Antiporter opens to the inside of the cell. Substrate B is released in exchange for
substrate A
The Phosphotransferase System in E.coli
-Type of group translocation
-Best studied system
-Moves glucose, fructose, and mannose
-Five proteins required
-Energy derived from phosphoenolpyruvate (PEP)
-The product Glucose 6-P is used in glycolysis
,Group Translocation
Substance transported is chemically modified during transport across the membrane,
usually phosphorylated
ABC Systems
-ATP-Binding Cassette systems
- >200 different systems identified in prokaryotes
-Often involved in uptake of organic compounds (e.g. sugars, amino acids), inorganic
nutrients (e.g sulfate, phosphate), and trace metals
-Typically display high substrate specificity
-Contain periplasmic binding proteins
3 components: Periplasmic binding proteins, Membrane- spanning transporter, and
ATP-hydrolyzing protein (i.e ATPase); also requires ATP energy
Shown in diagram at C
Cell Wall
How prokaryotes protect the cell membrane? For most species, the cell envelope
includes at least one structural supporting layer and the most common structural
support is _______?
This confers shape and rigidity to the cell and helps it withstand turgor pressure, can
see it for example in E.coli
Mycoplasmas
An example of a few prokaryotes who have a cell membrane with no outer layers
It's difficult to Gram stain
Sacculus
The bacterial cell wall, or this, consists of a single- interlinked molecule; for example
disaccharide or peptidoglycan
,Needed to maintain high pressure and solubility in order to maintain its shape
Gram- Negative
Has thin peptidoglycan (PG)
Gram- Positive
Has thick peptidoglycan (PG)
Peptidoglycan or Murein
Most bacterial cell walls are made up of this [only in bacteria]
The molecule consists of:
-Long polymers of two disaccharides called: N-acetylglucosamine (NAG or G) and N-
actelymuramic acid (NAM or M)
-The peptides can form cross-bridges connecting the parallel glycan strands
-Can have Lysine (Gram -) or Diaminopimetic acids (Gram +) amino acids
-Cross-linked differently in G+ and G- bacteria
-5 more Glycine in G+
-Peptide bonds are covalent; more peptide bonds in G+
-No inter bridge between G and G
Beta (1,4) Glycosidic Bonds
The bonds within peptidoglycan between NAG and NAM
Peptidoglycan Is Unique to Bacteria
-Thus the enzymes responsible to its biosynthesis make excellent targets for antibiotic
-Penicillin inhibits the transpeptidase that cross-links the peptides
-Vancomycin prevents cross-bridge formation by binding to the terminal Ala-Ala
, dipeptide
-Unfortunately, the widespread use of such antibiotics selects for evolution of resistant
strains
Dispersed Zonal Peptidoglycan Growth
Wall synthesis direction in bacilli ex: E.coli (pulse label, 5% doubling time)
Usually growth from the center
Septal Zonal Peptidoglycan Growth
Ex. cocci (staphylococcus, streptococcus)
Usually growth from the center
Polar Peptidoglycan Growth
Growth in one direction
Ex. actinomycetes, rhizobiales
Cell Envelope of Bacteria
Most bacteria have additional envelope layers that provide structural support and
protection
Envelope composition defines:
1) Gram positive bacteria (thick PG)- Example: the phylum Firmicutes
2) Gram negative bacteria (thin PG)- Example: the phylum Proteobacteria
3) Mycobacteria- complex, multilayered cell wall; Example: the phylum Actinomycetes
S-Layer
Found in some G+ and most archaea
1st found in archaea- An additional protective layer commonly found in free-living
bacteria (usually G+) and archaea.
-Crystalline layer of thick subunits consisting of protein or glycoprotein
-May contribute to cell shape and help protect the cell from osmotic stress
-Ex. Lysinibacillus
-Ex. in Archaea shows hexagonal symmetry
Gram Positive Cell Walls
-Can contain up to 90% peptidoglycan
-Common to have teichoic acid (acidic substances) embedded in the cell wall
Teichoic Acid
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