Microbiology Exam 2 UTA/211 Solved
Questions with Answers
Uniporters - -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 - -a phosphorylated poly alcohol found in G+ cell wall
- Lipoteichoic Acid - -Teichoic acid covalently bound to membrane lipids in
G+ cell walls
- Capsule - --Made of polysaccharide (Exopolysaccharide/ EPS) and
glycoprotein
-Protects cells from phagocytosis
-Found in G+ and G- cell walls but the structure is different
Questions with Answers
Uniporters - -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 - -a phosphorylated poly alcohol found in G+ cell wall
- Lipoteichoic Acid - -Teichoic acid covalently bound to membrane lipids in
G+ cell walls
- Capsule - --Made of polysaccharide (Exopolysaccharide/ EPS) and
glycoprotein
-Protects cells from phagocytosis
-Found in G+ and G- cell walls but the structure is different
