Post on 30-Jan-2016
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METABOLISM: OVERVIEW
METABOLISM-is the collection of enzyme catalyzed reactions that convert substrates that are external to the cell into various internal products.
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CHARACTERISTICS OF METABOLISM
1. Varies from organisms to organism
2. Many common characteristics
3. Affected by environmental conditions
» a) O2 availability: Saccharomyces cerevisiae
Aerobic growth on glucose → more yeast cells
Anaerobic growth on glucose → ethanol
» b) Control of metabolism is important in bioprocesses
TYPES OF METABOLISM
1. Catabolism
-metabolic reactions in the cell that degrade a substrate into smaller / simpler products
Glucose → CO2
-Reactions that release energy by breaking complex molecules into simpler ones
X—Y →X + Y + energy
Exergonic reaction
• Energy is captured / stored in high energy bonds of ATP & similar molecules
• Involves electron transfer (oxidation-reduction)
2. Anabolism
-metabolic reactions that require energy to synthesize larger or complex molecules from simpler ones
X + Y +energy →X—Y
endergonic reaction
• Needed for growth, reproduction, repair, movement, transport, etc.
• Where does the energy come from?
ENERGY & CARBON SOURCES
• All living things need energy
• All living things need Carbon
– Why? To synthesize all organic molecules
Microbes are extremely versatile in the ways in which they acquire energy & carbon.
OBTAINING CARBON
• Auto- (self)
– get carbon from CO2 to synthesize organic molecules
• Hetero- (other)
– get carbon from pre-made organic sources
OBTAINING ENERGY
•Photo-
-capture the energy of light
•Chemo-
-capture energy from chemicals
In metabolism, the energy carrier is often electrons, moving through redox reactions.
REDOX REACTIONS
• Oxidation & reduction reactions are always coupled so we call them RedOx
In redox reactions,
• Electrons are transferred from one atom/molecule to another
– Simultaneously 2 reactions: red/ox: electron gain/electron loss
• The electrons carry energy (so redox reactions are energy transfers)
• In a chain of reactions, the electrons must have a final resting place (a terminal electron acceptor).
- Often, this is oxygen.
Reduction:
• net charge is reduced (made more negative) because electrons are gained
• Energy is gained (reduced compound has more energy)
• Often, hydrogen is gained, oxygen is lost
For example, think: Hydrocarbons.
• Totally reduced
• Saturated with hydrogen
• No oxygen
• Lots of energy stored Propane
Oxidation:
• Electrons are lost
• Energy is lost
• Often, the electrons are transferred to oxygen
• Oxygen is NOT the only electron acceptor around
• There must always be an electron acceptor and an electron donor in redox reactions (coupled)
For example, think: Hydrocarbons burning
•The molecule gains oxygen/loses hydrogen (yielding CO2 & H2O)
•Energy is released (heat)
•Oxygen is the electron acceptor
If it has hydrogens, it likely canbe oxidized as an energy source(food) by some type of bacteria!
• Electron donor = reducing agent
-The atom or molecule that is oxidized
- It causes something else to be reduced (hence the name reducing agent)
• Electron acceptor = oxidizing agent
-The atom or molecule that is reduced
-It causes something else to be oxidized (oxidizing agent)
ELECTRON CARRIERS IN METABOLISM
• NAD (nicotinamide adenine dinucleotide)
- Derived from vitamin niacin
• FAD (flavin adenine dinucleotide)
-Derived from vitamin riboflavin
Both carriers cycle between oxidized (NAD+, FAD)and reduced states (NADH, FADH2)
ATP: Adenosine triphosphate
•is a nucleotide (yes, the same one that goes into DNA!)
•Has 3 phosphate groups attached (tri-)
•The distal, third phosphate group can be hydrolyzed to release a significant amount of energy:
ATP ↔ADP + Pi + energy
Where ADP = adenosine diphosphate
Pi = inorganic phosphate (PO43-)
•Release of the next phosphate group also releases a lot of energy (ADP AMP + Pi + energy)
•This process is not used as much by living things
One reason why so much energy is released by hydrolysis of the 2nd and 3rd phosphate groups: Electrostatic repulsion
-Each phosphate group is negatively charged; binding them together takes a lot of energy
{The “first” phosphate, attached to the adenosine, can also be cleaved off but the energy release is not impressive: no repulsion from other phosphates!}
ATP AS GLOBAL ENERGY CURRENCY
• The energy of ATP hydrolysis can be captured to perform the work of the cell
• ATP is like money that can “buy” almost any energy-requiring activity
• This reaction is reversible– i.e., an input of energy (such as the energy derived from glucose) can be used to make ATP from ADP & Pi
• Phosphorylation of ADP to make ATP is a key feature of metabolism