Download Microbial Metabolism Overview

Microbial Metabolism Overview
A. Energy flows through the cell as a flow of electrons
Compound that loses electrons → oxidized
Compound that gains electrons → reduced
-energy is released by an electron during its transfer from one compound to another
-this energy is captured → converted into high energy bonds on ATP
B. Energy storage molecules
ATP, NADH, NADPH, FADH
ex. NADH – reduced, NAD+ - oxidized
these molecules carry energy from cell respiration to the electron transport chain
C. Cell Respiration
1. Glycolysis – glucose is partially digested into 2 smaller molecules (pyruvate)
and the released energy is captured as NADH
2. Krebs Cycle (also called the TCA cycle or the Citric Acid cycle)
-oxidation of these smaller molecules is completed
-produces more energy-carrying molecules such as NADH
Both of the above pathways combined → make only a small amount of ATP
3. Electron Transport Chain
-energy-carrying molecules made in first 2 pathways (NADH, FADH) are oxidized
- molecules like O2 (aerobes) or N, S, etc. (anaerobes) are reduced
-released energy is captured as ATP
-most of the cell’s ATP is made here
D. Bacteria/Archaea have 3 pathways to catabolize (digest) glucose → pyruvate
1. Glycolysis (EMP) pathway (prokaryotes and eukaryotes)
2. Enter-Doudoroff (ED) pathway (only prokaryotes)
3. Pentose Phosphate Shunt (PPS) (prokaryotes and eukaryotes)
E. Electron Transport System (ETS or ETC - electron transport chain)
-Series of electron carriers that transfer electrons to electron acceptors
-Results in a flow of electrons through the ETS
-ETS generates Proton Motive Force (PMF), which pushes H+ into the cell
-As electrons are passed through the electron transport chain → energy released is
used to pump protons (H+) across the membrane, which is called the PMF.
PMF drives: ATP synthase – enzyme complex to produce ATP
Ion transport – to move compounds across the cell membrane
Flagella motion - makes flagella move or spin
ATP production – more variable in anaerobic respiration because fewer carriers in ETC
Proton Gradient
- low H+ inside the cell – high outside the cell (lots of H+)
- causes proton gradient across the cell membrane
1. H+ cannot easily diffuse back inside the cell
2. H+ can only flow back in through an enzyme complex called ATP synthase, which
has a channel to pump H+ back into the cell:
a. also binds ADP + P (ADP + P = ATP)
b. as H+ flow back into the cell through the channel they release energy → ATP
c. enzyme complex spins making ATP
Fermentation
If a cell runs out of electron acceptor (O2 or N or S), respiration can only proceed
through glycolysis.
Prokaryotes – some only go this far to make energy, they only do fermentation and do
not have the capability to do respiration.
6C molecule (glucose) → two 3 carbon molecules (pyruvate)
this makes ATP and NADH
if NADH forms → recycle NAD+ so cell regenerates NAD+ by oxidizing NADH and
reducing pyruvate (waste products from this reaction are valuable, such as ethanol,
lactic acid, propionic acid, etc.)
Molecules besides glucose can be used for energy:
lipids → lipases are enzymes that breakdown lipids
proteins → proteases and peptidases are enzymes that breakdown proteins
many other compounds (such as aromatic biological compounds) can also be used
bacteria - insecticides etc. are metabolized - biodegradation
- petroleum can be metabolized - bioremediation
-often look for microorganisms that can do these reactions – commercial value
General Types of Microorganisms
Heterotrophs - energy from biological molecules, must absorb (eat) biological molecules
Autotrophs - can make their own biological molecules from N2, CO2, etc
Photoautotrophs – convert light energy → ATP
Chemoautotrophs – convert chemical energy → ATP
Instead of light they can use ammonia, methane, hydrogen sulfide, etc.
Photosynthesis – opposite of aerobic cell respiration
(respiration starts with sugars while photosynthesis produces sugars)
1. Light reactions, light energy → ATP
e- → ETS → chlorophylls → H+ gradient → ATP synthase → ATP
2. Carbon cycle, ATP + NADPH + CO2 → sugars
- also called Carbon Fixation