What are the 5 elements essential for life?
Hydrogen, Carbon, Sulfur, Nitrogen & Oxygen
Why can’t obligate anaerobes survive in an oxygenated environment?
Obligate anaerobes can’t survive in an oxygenated environment because they do not express the gene that produces the enzyme SUPEROXIDE DISMUTASE.
- Superoxide dismutase eliminates oxygen radicals (a byproduct of aerobic respiration) by breaking down oxygen radicals into peroxides, which are then in turn broken down by catalase enzyme (seen before) into H2O and O2.
- Macrophages often use oxygen radicals to kill bacterial pathogens.
In the oral cavity there are no autotrophic bacteria but there are some bacteria that utilize CO2. Through what process do they do this?
CO2 heterotrophic fixation. Require CO2 AND O2 for optimal growth.
What are the optimal growth temperatures for thermophiles, mesophiles and psychrophiles?
Thermophiles = 50-60 C Mesophiles = 20-40 C Psychrophiles = 10-20 C
For the 3 transport systems tell whether they’re active or passive transport systems and what their main substrates are.
- Facilitated Diffusion
- Proton symport
- Phosphotransferase system (PTS)
- Facilitated Diffusion = passive transport of small sugars such as glycerol through Permease (pore) along concentration gradients.
- Proton symport = active diffusion of Disaccharides
- Phosphotransferase System (PTS) = Active diffusion of large sugars such as glucose, fructose, and sucrose. Most complicated and important.
Once the active transport system has transported the sugar into the cell, using a conformational change permease, how does the bacteria ensure that the sugar will remain in the cell?
By phosphorylating the sugar upon entering using an ATP molecule or a PEP molecule(PTS).
-Gives sugar a negative charge.
Briefly describe the mechanisms by which the PTS system transfers glucose and sucrose across the bacterial cytoplasmic membrane.
Glucose: Enzyme IIGlc (transmembrane permease) actively transports Glucose across cytoplasmic membrane. A phosphorylation cascade, starting with PEP –> Enzyme IGlc –> HPr –> EnzymeIIIGlc (a membrane associated enzyme), which phosphorylates glucose to G-6-P.
Sucrose: Same as glucose except there is no Enzyme III (HPr directly phosphorylates P –> P-6-P and Enzymes I & II are sucrose specific.
Compare the # of ATP used and the # of ATP produced in the normal EMP pathway and when the PPP pathway is being utilized?
-Is this ATP made via Oxidative or Substrate level phosphorylation?
EMP only: 2 ATP used - 4 ATP produced = Total gain of 2 ATP
EMP + PPP: 1 ATP used - 2 ATP produced = Total gain of 1 ATP (+ nucleic acid intermediate)
-Substrate level phosphorylation
When is the PPP utilized?
When bacteria in need of nucleic acids.
-Note not 100% of glucose directed to this pathway. When turned on usually about 30%
What is the major goal of fermentation pathways carried out by anaerobic bacteria?
-Name two forms of fermentation. Which is the most important in the formation of dental carries?
Major goal of fermentation pathways is to Reduce NADH back to NAD so it can be recycled back to the EMP pathway for continued ATP production via substrate level phosphorylation.
- Lactic acid fermentation. Major cause of dental caries.
- Alcoholic fermentation (yeast produce ethanol)
Streptococcus species and some Lactobacillus species of bacteria in the oral cavity are homolactic and heterolactic fermentors. What does this mean?
Homolactic fermentors convert Pyruvic acid (pyruvate) to lactic acid only.
Heterolactic fermentors convert Pyruvic acid to lactic acid, acetic acid, succinic acid, formic acid and ethanol.
Cariogenic bacteria such as S. mutans CAN ferment sucrose but CAN NOT ferment sucrose’s 5 ‘smart sugars’ (positive).
But, another oral bacterium L. buccalis can ferment four of the five ‘smart’ sugars.
-What may be a consequence of switching to a diet higher in ‘smart’ sugars with L. buccallis’ ability to ferment these sugars?
Could cause a change in the composition of bacterial flora. What this would mean is not known but could have unintended negative effects.
What are the two major products of the bacterial TCA cycle used in anabolic nucleic acid production?
What was the product of the PPP used in nucleic acid synthesis?
a-ketogluterate and Oxaloacetate.
-Remember erythrose-4-phosphate is the intermediate in PPP also utilized to create nucleic acids in bacteria.
E. coli, facultative bacteria, do not utilize entire TCA cycle. What is the branch run under aerobic conditions? Anaerobic?
- What is the enzyme that is not functional under anaerobic conditions that requires the switch to anaerobic pathway?
- B/c the TCA isn’t a complete cycle in E. coli PEP plays an important role in both the aerobic and anaerobic branches. What is PEP’s role?
Aerobic = Oxidative branch
Anaerobic = Reductive branch
-a-ketogluterate oxidase is the essential enzyme for aerobic growth that is inactivated in the absence of O2.
-PEP, with the addition of HCO3- from a biotin carrier, produces oxaloacetate. Oxaloacetate combines w/ acetyl CoA to form citrate in aerobic branch and is the first intermediate in the reductive branch.
What is the source of H+ in the elctron transport chain?
What is the enzyme associated with the proton channel that produces the ATP?
- NADH and FADH form TCA cycle = source of protons
- ATP synthase = enzyme associated w/ proton channel that produces ATP
The Pasteur Effect says facultative bacteria will always act in what way in the presence of oxygen?
Pasteur Effect says that facultative bacteria will always carry out respiration rather than fermentation when O2 is available b/c respiration results in max 38 ATP produced/mol substrate while fermentation results in max 2 ATP produced/mol substrate.
Some heterotrophic CO2 fixing bacteria require CO2 for optimal growth. What role does the CO2 play in anaerobic metabolism? What is the advantage?
CO2 replaces biotin carrier in providing carbon to PEP in oxaloacetate production.
-Results in additional ATP (2) made in this pathway.