An Introduction to Metabolism

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27 Οκτ 2013 (πριν από 3 χρόνια και 11 μήνες)

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An Introduction to Metabolism



Metabolism, energy and life


Enzymes


The control of metabolism

Metabolism


Metabolism
-

totality of an organism’s
chemical reactions


Metabolism


Catabolic pathways
-

release energy by
breaking down complex molecules to simpler
compounds


Metabolism


Anabolic pathways
-

consume energy to
build complex molecules from simpler
compounds

Energy


Energy
-

capacity to do work


Kinetic energy
-

the energy of motion


Potential energy
-

the capacity to do work,
energy stored as a result of its location or
structure


Chemical energy
-

form of potential energy
-

stored in molecules as a result of the
arrangement of the atoms


Metabolism, energy, and life


Metabolism = anabolism +
catabolism


Metabolic reactions are
organized into
pathways


Energy: kinetic and
potential

Thermodynamics


Thermodynamics
-

study of energy
transformations


The First Law
-

the energy of the universe is
constant


Energy can be transferred and transformed
but it cannot be created or destroyed


“principle of conservation of energy


Thermodynamics


The Second Law
-

Every energy transfer or
transformation increases the entropy of the
universe


Entropy
-

the measure of disorder



Free Energy
-

the portion of a system that can
perform work


It is available for work


Symbol is G


Exergonic

reaction
-

“energy outward”

Proceeds with a net release of free energy

Occurs spontaneously

Endergonic

reaction
-

“energy inward”


absorbs free energy from its surroundings


nonspontaneous


Energy Coupling
-

the use of an
exergonic

process
to drive an
endergonic

one


Cells are kept alive with a flow of energy

The products of a reaction become the
reactants of the next reaction.

Rube Goldberg Machine


Cellular Work


1. Mechanical work


2. Transport work


3. Chemical work

ATP


Adenosine
Triphosphate


Adenine bonded to ribose

RNA has one phosphate group attached to ribose

ATP has three phosphate groups attached to ribose


ATP to ADP


Phosphate bonds
-

broken by hydrolysis


Without 3
rd

Phosphate Group= Adenosine
Diphosphate

(ADP) and inorganic phosphate

ATP + H
2
O → ADP + P
i





Test tube: Change in G =
-
7.3 kcal/mol

Cell: Change in G=
-
13 kcal/mol

ATP to ADP

Is this reaction
Exergonic

or
Endergonic
?



Exergonic
-

ADP is more stable than ATP,
energy is released with the loss of P
i


Negative G value

Phosphorylation


P
i

is not transferred into solution, given to
another compound


Compound receiving the P
i
is
phosphorylated
.


ATP cycle

ATP + H
2
O → ADP + P
i


Change in G =
-
7.3 kcal/mol

ADP + P
i
→ ATP + H
2
O


Change is G = 7.3 kcal/mol

Enzymes

Catalyst
-

chemical agent that changes the rate
of a reaction without being consumed by the
reaction

Enzyme
-

catalytic protein


Activation Energy
or “free energy of
activation”


the energy required to break the
bonds in the reactants


Symbol
-

E
A



Cellular issue with heat


Induced fit hypothesis


Change in the shape of
an enzyme’s active
site, which is induced
by the substrate.


Enzyme
-
substrate complex


Substrate held by weak interactions
-

hydrogen and ionic bonds


R
-
groups of amino acid chain of the protein
catalyze the substrate


Lowering the E
A

Active site


Stresses critical bonds that must be broken


Can provide a microenvironment



Ex: Acidic R groups form a pocket of
low pH


Brief bonding
-

covalent bonding between
substrate and R groups



Rate of reaction


Determined by the concentration of
substrate and enzyme


Saturation point

Temperature and pH

Optimal Temperature

Optimal pH


Cofactors


Bind to active site permanently or loosely


Inorganic


Organic
-

coenzyme



Inhibitors


Competitive inhibitors
-

block active site


Noncompetitive inhibitors
-

bind to another
part of enzyme


Types: poison, antibiotics



When is it useful to inhibit
enzymes?

Allosteric

regulation


Allosteric

site
-

specific receptor site on
enzyme away from active site



Can activate or inhibit

Feedback inhibition

Most common

Pathway switch off by its end product


Cooperativity


Substrate induces enzyme to accept more
substrates


Multienzyme

complex

Team of enzymes assembled together


Ex: Mitochondria in eukaryotic cells
-

enzymes for respiration are clustered
together