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Redox Biology and
Oxidative estress
Prof. Ricardo Pinho, PhD
PPGCS
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BRIEF REVIEW
Biomolecules, enzymes and redox reactions
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Biomolecule or biological molecule, any of numerous
substances that are produced by cells and living organisms.
Biomolecules have a wide range of sizes and structures and perform
a vast array of functions.
The four major types of biomolecules are carbohydrates, lipids,
nucleic acids, and proteins.
They are made up of elements such as oxygen, hydrogen, carbon,
and nitrogen, which are called bioelements.
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Considerations
Among the 118 chemical elements, only 30 are essential for
living organisms.
The 4 most important are C, H, O, N
Most of the molecular constituents of living beings are composed
of C atoms bonded to other atoms: C, H, O, N, P and S.
Cell mass - 99% CHON
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Considerations
Most biomoleculesare derived from hydrocarbons (compounds
formed by C skeletons, covalently linked to each other, to which
they are also linked to H).
H, can be substituted by different functional groups, to form
different families of organic compounds such as: alcohols,
amines, ketone, aldehydes, carboxyl....
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Chemistry of living things is basically organized
around carbon
Corresponds to more than 50% of the dry weight of cells
Versatility in the formation of chemical bonds
Organic compounds - molecules that have covalently linked
carbon skeletons
It forms single or double bonds with itself, hydrogen, oxygen and
nitrogen.
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Functional Groups
Functional groups
determine how a molecule
will interact with other
molecules.
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Chemical Bonding
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Covalent bonds: polar or non-polar bonds (it depend on the
electronegativity of the atoms).
Polar: Molecules unequally share electrons betwen
atoms has electrons
Non-Polar: Molecules have electrons equally
shared between their atoms.
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Chemical bonds
The electrons are in the most electronegative element.
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This topic was adapted of Science Prof Online (SPO) is a free
science education website that provides fully-developed Virtual
Science Classrooms, science-related PowerPoints, articles and
images. The site is designed to be a helpful resource for students,
educators, and anyone interested in learning about science
https://www.scienceprofonline.com/
Enzymes are proteins.
Enzymes act as catalysts in cellular reactions
From the Virtual Biology Classroom on ScienceProfOnline.com
Images: Ribbon diagram of
enzyme with cofactor; Enzymatic reaction, Wiki
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How do enzymes work?
Enzymes catalyze
reactions by weakening
chemical bonds, which
lowers activation energy.
From the Virtual Biology Classroom on ScienceProfOnline.com
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Image: Activation energy graph, Wiki
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How do enzymes work?
• Each enzyme has a unique 3-D shape, including a surface groove called an
active site.
• The enzyme works by binding a specific chemical reactant (substrate)
to its active site, causing the substrate to become unstable and react.
• The resulting product(s) is then released from the active site.
Video: How Enzymes Work
From the Virtual Biology Classroom on ScienceProfOnline.com
Image: Enzymatic reaction, Jerry Crimson Manni
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Enzymes…
•
are specific for
what they will
catalyze.
•
fit with
substrate like a
key and lock.
From the Virtual Biology Classroom on ScienceProfOnline.com
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When an enzyme is interacting with
it’s substrate, during the chemical
reaction, together they are referred
to as the …
From the Virtual Biology Classroom on ScienceProfOnline.com
Image: Enzyme –substrate complex, UC Davis
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Enzymes…
…are reusable.
They are not consumed
(used up) in the
reactions they catalyze.
May perform thousands
of reactions per second.
From the Virtual Biology Classroom on ScienceProfOnline.com
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How do you sabotage an
enzyme?
• Denature it!
• Alteration of a protein shape through
some form of external stress
•
Example, by applying heat, acidic or
alkaline environment
• Denatured enzyme can’t carry out its
cellular function .
Irreversible egg protein
denaturation caused by high
temperature (while cooking it).
From the Virtual Biology Classroom on ScienceProfOnline.com
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Factors That Influence Enzyme Activity
• Temperature
• pH
• Cofactors & Coenzymes
• Inhibitors
From the Virtual Biology Classroom on ScienceProfOnline.com
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Image: Animation of Enzyme, Wiki
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Temperature & pH
• Think about what kind of cell or organism
an enzyme may work in…
• Temperatures far above the normal
range denature enzymes. (This is why
very high fevers are so dangerous. They
can cook the body’s proteins.)
• Most enzymes work best near neutral pH
(6 to 8).
From the Virtual Biology Classroom on ScienceProfOnline.com
Images: pH scale, Edward Stevens, Wiki
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Factors That Influence Enzyme Activity
• Temperature
• pH
• Cofactors & Coenzymes
• Inhibitors
From the Virtual Biology Classroom on ScienceProfOnline.com
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Image: Animation of Enzyme, Wiki
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Coenzyme: Vitamin B12
• Most vitamins are coenzymes essential in
helping move atoms between molecules in
the formation of carbohydrates, fats, and
proteins.
• Exclusively synthesized by bacteria.
• Dietary sources include meat, eggs, dairy
products and supplements.
Images: Streptomyces spores, Wiki; Vitamin B12 chemical structure, Wiki
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From the Virtual Biology Classroom on ScienceProfOnline.com
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Factors That Influence Enzyme Activity
• Temperature
• pH
• Cofactors & Coenzymes
• Inhibitors
From the Virtual Biology Classroom on ScienceProfOnline.com
Image: Animation of Enzyme, Wiki
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Enzyme Inhibitors
Blocking an enzyme's activity can kill a pathogen or correct a
metabolic imbalance.
Many medications are enzyme inhibitors.
Enzyme inhibitors are also used as herbicides and pesticides.
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Two Types of Enzyme Inhibitors
1. Competitive
inhibitor
Chemicals that resemble an enzyme’s normal
substrate and compete with it for the active
site.
Reversible depending on concentration of
inhibitor and substrate.
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EXAMPLE1 : The drug Antabuse is
used to help alcoholics quit
drinking. Antabuse inhibits
aldehyde oxidase, resulting in the
accumulation of acetaldehyde (say
a-si-’tell-de-hide) during the
metabolism of alcohol. Elevated
acetaldehyde levels cause
symptoms of nausea and vomiting.
EXAMPLE 2:
•Another example of competitive
inhibition is protease inhibitors.
•They are a class of anti-retroviral
drugs used to treat HIV.
•The structure of the drug
ritonavir (say ri-TAHN-a-veer)
resembles the substrate of HIV
protease, an enzyme required for
HIV to be made.
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Two Types of Enzyme Inhibitors
2. Non-competitive inhibitor
Do not enter active site, but bind to another part of the enzyme, causing
the enzyme & active site to change shape.
Usually reversible, depending on concentration of inhibitor & substrate.
EXAMPLE: You may know that compounds containing heavy
metals such as lead, mercury, copper or silver are
poisonous. This is because ions of these metals are noncompetitive inhibitors for several enzymes.
From the Virtual Biology Classroom on ScienceProfOnline.com
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Oxidation-Reduction Reactions
(Redox System)
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Redox System
Chemical reactions in which
the oxidation states of atoms
are changed, and it is
characterized by the transfer
of electrons between chemical
elements
These reactions are called “redox”.
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Redox System
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Clinical Science, 2017; 131(14):1669-1688 ·
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Oxidation is…
Reduction is…
– the loss of electrons
– the gain of electrons
– an increase in oxidation state
– a decrease in oxidation state
– the addition of oxygen
– the loss of oxygen
– the loss of hydrogen
– the addition of hydrogen
Oxidation and reduction always occur together.
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Redox system
whole reaction
half-reactions
half-reactions
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Redox Transfer
Depends on REDOX PONTENTIAL (electron affinity): RP of a system is the electron
transfer potential (Eo’)
Low RP signifies LOW ELECTRON AFFINITY
More negative (or low) RP
Greater tendency to lose electrons
High RP signifies HIGH ELECTRON ASSINITY
More positive (or high) RP
Greater tendency to accept electrons
i.e Electron Transport Chain: it is a chain of protein complexes and coenzymes of
increasing redox potential
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Redox Potential
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Oxidation States

Oxidation states (or oxidation number) are numbers (value) assigned to
atoms that reflect the charge of an atom.
Oxidation Number = ON

They are assigned according to the following set of rules:
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#1
The ON of a simple ion is equal to its ionic charge.
+1
Na +
+2
Cu 2+
-3
N3-
#2 The ON of hydrogen is always +1.
+1
HCl
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#3 The ON of oxygen is always –2.
-2
H2 O
#4 The ON of an uncombined element or diatomic
molecule is always zero.
0
Na
0
Cu
0
N2
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#5 For any neutral (zero charge) compound, the sum of
the ON’s is always zero.
+4-2
CO2
+4 + (-4) = 0
#6 For a complex ion, the sum of the ON’s equals the
charge of the complex ion.
+7 -2
MnO41-
+7 + (-8) = - 1
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Oxidation Number Changes
 an increase in oxidation number of an atom signifies
oxidation
(loss e-)
+2 to +4
 a decrease in oxidation number of an atom signifies
reduction
(gain e-)
0 to -1
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The end
Have a nice weekend!
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