The sum total of all reactions which occur in a cell
All life forms—from single-celled prokaryotes to large eukaryotes—are dependent on many hundreds of simultaneous and precisely regulated metabolic reactions.
These reactions support them from conception, through growth and maturity, to the final stages of death.
Word derivation:
Meta: change
Bolism: to throw
Metabolism: “to throw a change” … “to change”
Metabolism can be broken down into two separate processes:
The process by which complex molecules are broken down into smaller, simpler molecules
Also known as: destructive metabolism
Word derivation:
Cata: down
Bolism: to throw
Catabolism: “to throw down” … “to break down”
Two key results of catabolism:
Stored energy is released.
Complex molecules are broken into smaller molecules.
2. Anabolism
The process by which complex molecules are synthesized from simpler ones
Also known as: constructive metabolism
Word derivation:
Ana: up
Bolism: to throw
Anabolism: “to throw up” … “to build up”
Two key results of anabolism:
Energy is stored in the form of chemical bonds.
Simple molecules are linked together to form larger molecules.
Metabolism = Catabolism + Anabolism
Since metabolism represents the sum of all reactions in a living system (organism), it consists of two processes that are constantly occurring simultaneously: catabolism and anabolism
The total change in the system results from breaking down and building up.
Metabolism requires both catabolic and anabolic processes:
Catabolism: molecules are broken down and energy is released. This allows…
Anabolism: molecules are brought together to form larger structures and energy is stored.
Three possibilities result from the interaction of these two processes:
When anabolism exceeds catabolism, growth or weight gain occurs.
More energy is stored than released.
When catabolism exceeds anabolism, weight loss occurs.
More energy is released than stored.
When catabolism and anabolism occur at the same rate, a state of dynamic equilibrium occurs.
Although both breaking down and building up occurs, there is no net change.
Energy and Metabolism: An Analogy
Think of a pile of bricks or any kind of building material.
Imagine you want to build a house with these bricks: this is anabolism.
You are using simple “molecules” (bricks) to make a more complex “molecule” (building).
It takes energy to construct a building, so anabolism is an energy requiring process (but remember, the energy used to construct the building is now “stored” in the structure of the building since energy is never created nor destroyed).
Suppose someone comes along and destroys your building by pulling the bricks apart: this is catabolism.
A complex “molecule” (building) is torn apart to make simpler “molecules” (bricks).
Energy is released when a building is torn apart
Think of the energy released as bricks fall to the ground: catabolism is an energy-releasing process.
We all witnessed a dramatic catabolic process when the World Trade Center towers collapsed; as they fell to the ground enormous energy was released.
Senseless Catabolism
Catabolism in one step
All of the energy is released at once, and therefore cannot be used to do something useful.
The larger structure is disassembled so rapidly that the individual pieces cannot be recovered and used to build a new structure.
Analogy: catabolism of the World Trade Center
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Useful Catabolism
Catabolism in many steps
The energy is released bit by bit and therefore can be used to do something useful.
The larger structure is disassembled slowly, so that the individual pieces can be recovered and used to build a new structure.
Analogy:
The Coliseum of ancient Rome was partly disassembled beginning in the Middle Ages.
Since this was done stone by stone these materials were able to be incorporated in other structures—like St Peter's!
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Catabolism and Anabolism in Living Organisms
Living organisms do not do catabolism and anabolism in one big step.
Instead, they do these processes in small steps, so they can make use of the energy in the chemical bonds.
Because these are a series of chemical reactions happening in living organisms they are called “biochemical pathways” or “metabolic pathways.”
These metabolic can be linked together in an amazing web of the reactions that occur in living organisms
Metabolism Summary
Catabolism (Catabolic Pathways)
Destructive metabolism
With carbohydrates:
In plants: starch → glucose
In animals: glycogen → glucose
With lipids:
Fat → three fatty acids + one glycerol
With proteins:
Protein → amino acids (up to twenty different kinds)
With nucleic acids:
RNA or DNA → nucleotides (up to five different kinds)
Anabolism (Anabolic Pathways)
Constructive metabolism
With carbohydrates:
In plants: glucose → starch
In animals: glucose → glycogen
With lipids:
Three fatty acids + one glycerol → fat
With proteins:
Amino acids (up to twenty different kinds) → protein
With nucleic acids:
Nucleotides (up to five different kinds) → RNA or DNA
