BSCI 3234 Lecture Notes - Lecture 5: Turnover Number, Dehydration Reaction, Catabolism
29 Apr 2018
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Introduction to Microbiology-Lecture 5
Microbial Metabolism I
Why study microbial metabolism?
• The biochemical reactions described in chapter 5 are fundamental to all living cells
(prokaryotic and eukaryotic).
• Understanding metabolism helps to define ways to inhibit bacterial growth yet protect the
cells of the body.
• The chapter describes how energy is obtained from our food (sugars, carbohydrates,
etc.) or from reserves of fat or protein.
• This chapter also describes how living cells capture energy from the sun and use the
simple molecules of water and carbon dioxide (CO2) to produce sugars and more
complex carbohydrates.
• These sugars can ultimately be converted to protein, fats, and nucleic acids.
Metabolism: the sum of all chemical reactions within a living organism
Catabolism: Chemical reactions in living cells that release energy
• Involve the breakdown of complex organic compounds into simpler ones
• Generally involve hydrolysis (addition of water to break a chemical bond)
• Catabolic reactions generally are exergonic reactions (produce energy).
• Example: breakdown of complex carbohydrates to simple sugars
Anabolism: (also called biosynthesis) chemical reactions within living cells that require energy
• Involve building of complex molecules from simpler ones
• Involve dehydration synthesis
• Endergonic reactions (consume energy)
• Example: building of proteins from amino acids
Which reaction is an example of catabolism?
Anabolic reactions need energy from ATP. Catabolic reactions can transfer energy to ATP
ATP ADP + Pi + Energy
ADP + Pi + Energy ATP
ENZYMES: Protein catalysts of chemical reactions
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• Without enzymes, atoms, ions, and molecules could not gain sufficient activation
energy for necessary reactions to proceed at the cool temperatures and low pressure
necessary for maintenance of life
• Activation energy is the amount of energy needed to disrupt the stable electronic
configuration of any molecule so that the electrons can be rearranged.
• Enzymes can bring two reactant molecules close together
• Enzymes can orient the molecules in the correct alignment
• Enzymes are highly specific for a single reaction
• Enzymes are highly specific for a single substrate (the molecule being changed by
enzymatic action)
• Enzymes are generally large globular proteins
• Each enzyme has a unique 3-dimensional structure (tertiary structure) that allows it
to “find” the correct substrate
• Enzymes can speed up reactions (up to 1010 times faster than reactions without
enzymes)
• Turnover number characteristic of each enzyme is the number of substrate
molecules acted upon and converted each second (~1-10,000)
Names of most enzymes end in ….”ase”
Enzyme Components
Most enzymes are part protein and part non-protein
• Protein part is called apoenzyme
• Non-protein part is called cofactor
• cofactors can be a metal such as iron, zinc, magnesium or calcium
• cofactors can be another organic molecule called a coenzyme
The apoenzyme is inactive without the cofactor. Both parts together = holoenzyme
Examples of Important Coenzymes
Coenzyme A
• Needed for preparatory step in Krebs cycle
NAD+ is nicotinamide adenine dinucleotide
NADP+ is nicotinamide adenine dinucleotide phosphate
• Both are derivatives of vitamin B (niacin)
• Both function as electron carriers (removing electrons from the substrate and
donating them to other molecules)
FMN is flavin mononucleotide
FAD is flavin adenine dinucleotide
• Both FMN and FAD are derived from riboflavin
• Both are electron carriers
Mechanisms of Enzymatic Action (Fig. 5.4A)
1) enzyme “finds” substrate and the substrate contacts the active site of the enzyme
2) an intermediate called the enzyme-substrate complex forms
3) the substrate is transformed
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Document Summary
Metabolism: the sum of all chemical reactions within a living organism. Catabolism: chemical reactions in living cells that release energy. Involve the breakdown of complex organic compounds into simpler ones: generally involve hydrolysis (addition of water to break a chemical bond, catabolic reactions generally are exergonic reactions (produce energy), example: breakdown of complex carbohydrates to simple sugars. Anabolism: (also called biosynthesis) chemical reactions within living cells that require energy. Involve building of complex molecules from simpler ones. Involve dehydration synthesis: endergonic reactions (consume energy, example: building of proteins from amino acids. Coenzyme a: needed for preparatory step in krebs cycle. Nadp+ is nicotinamide adenine dinucleotide phosphate: both are derivatives of vitamin b (niacin, both function as electron carriers (removing electrons from the substrate and donating them to other molecules) Fad is flavin adenine dinucleotide: both fmn and fad are derived from riboflavin, both are electron carriers.
