Transcript Bacterial Metabolism and Growth

BIO 411 - Medical Microbiology
Chapter 4
Bacterial Metabolism and Growth
Metabolic Requirements
• Bacteria’s first priority – Survive and Reproduce
• To do this they need:
– Source of Energy (for human pathogens sugars,
fats, and proteins)
– Raw materials to build all cell structures
•
•
•
•
Carbon source
Nitrogen source
Water
Ions
– Table 4-1
Metabolic Requirements
• Different O2 needs:
– Obligate anaerobes (Clostridium
perfringens, and others)
– Obligate aerobes (Mycobacterium
tuberculosis)
– Facultative anaerobes (most bacteria)
Metabolic Requirements
• Differences is metabolic requirements:
– E. coli
– Treponema pallidum
Overview of Metabolism
• Metabolism = the sum of all chemical processes within a
cell
• Consists of:
– Catabolism - breakdown of nutrients for energy and
building blocks (precursor metabolites)
– Anabolism - building of cellular components using energy
and building blocks
• These both occur through metabolic pathways
• Overview of bacterial metabolism. (extracellular
digestion, etc.)
Metabolism of Glucose (cont.)
• Bacteria can catabolize glucose by (in order of
decreasing efficiency):
– Respiration - Final electron acceptor in the
electron transport chain is an inorganic molecule
• Aerobic - O2 is the final e- acceptor
• Anaerobic - something else is (NO3-, SO42- , CO2 )
– Fermentation - final electron acceptor is an
organic molecule
Respiration
• Deals with three metabolic pathways:
– Glycolysis (Embden-Meyerhof-Parnas)
– TCA cycle (also called the Krebs Cycle and the
citric acid cycle)
– Electron Transport System
Respiration (cont.)
• Glycolysis:
– 1 glucose molecule is split into 2 molecules of
pyruvate
– 2 ATP are gained for every glucose molecule
– 2 NADH are produced for every glucose molecule
• NADH picks up high-electrons lost by glucose
– Figure 4-2
Respiration (cont.)
• Conversion of pyruvate to acetyl-CoA
– pyruvate cannot enter directly into the TCA
cycle
– 1 NADH is produced for every pyruvate
– 1 molecule of CO2 is release for every pyruvate
Respiration (cont.)
• TCA cycle:
– cyclic metabolic pathway
– produces 1 ATP for every acetyl-CoA
– produces 3 NADH for every acetyl-CoA
– produces 1 FADH2 for every acetyl-CoA
– All 6 carbons from the original glucose
molecule have been converted to CO2 by
the end of the TCA cycle
– Figure 4-4
Respiration (cont.)
• Electron Transport System
– All NADH molecules formed in the previous steps
bring the electrons they have gained to the electron
transport system
– These electrons are passed along a series of
membrane proteins
• eventually the electrons are given to the final eacceptor (O2 to form H2O, etc.)
• Figure 4-5
Respiration (cont.)
– These proteins use the energy of the electrons to
pump protons across the membrane (from the inside
of the cell to the outside)
– This pumping of protons across the membrane
generates an electrochemical gradient across the
membrane
– These protons are then brought back through the
membrane and the associated energy is used to
produce ATP
– Analogy involving a dam
Respiration (cont.)
• One molecule of glucose can produce 38 ATP
through this complete process
– Figure 4-6
Aerobic vs. Anaerobic Respiration
• If oxygen is the final electron acceptor, the
process is called aerobic respiration
• If some other molecule is the final electron
acceptor, the process is called anaerobic
respiration
– sulfate reducers, nitrate reducers, methane
bacteria
Fermentation
• Fermentation begins with glycolysis
– Fermentation usually occurs under anaerobic
conditions (no oxygen = no final electron
acceptor)
– Problem: 2 NADH don’t give off e- at the ETS
• NADH build-up would eventually shut down glycolysis
– Fermentation unloads electrons on pyruvate or a
derivative of pyruvate
• this regenerates NAD+ so glycolysis can continue
– Figures 4-1 and 4-3
Lipid Catabolism
• Lipids are broken down to glycerol and fatty
acids
• Glycerol enters glycolysis
• Fatty acids undergo beta-oxidation to form
acetyl-CoA
• Figure 4-1
Protein Catabolism
• Proteins are broken down outside the cells by
protease enzymes.
• The amino acids are brought inside the cells
and funnel into glycolysis or the Krebs cycle
• Figure 4-1
Anabolism
• What is anabolism?
• Anabolism also occurs through metabolic
pathways
– Many times it’s just the opposite of protein, lipid
and carbohydrate catabolism
• Figures 4-1 and 4-7
Disease of the Day
•
•
•
•
Dental Caries (cavities)
Etiology – Streptococcus mutans
Reservoir – Our Mouthes (normal flora)
Transmission and Development
– Transmission – NA
– Development
– Importance of sucrose (Figure 25.3)
Disease of the Day
• Prevention and Control
– Brushing/Flossing
– Fluoride
– Decrease sucrose intake