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Biochemistry- Enzymes Notes
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An organized pre-laboratory discussion notes regarding the basics of Enzymes, along with pictures and notes from books.
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ACTIVITY 3 PRELAB DISCUSSION NOTES: ENZYMESENZYMES: - They may be tightly bound to the
enzyme itself, and if that is the case,
Biological Catalysts the enzyme is known as the prosthetic
Almost all enzymes are proteins. Enzymes follow group.
the physical and chemical reactions of proteins.
Heat labile CO-ENZYMES
Water-soluble i. Enzymes may be simple proteins, or complex
They can be precipitated by protein precipitating enzymes, containing a non-protein part, called
reagents (ammonium sulfate or trichloroacetic acid) the prosthetic group. The prosthetic group is
They contain 16% weight as nitrogen called the co-enzyme. It is heat stable.
Hastens chemical reactions without being ii. The protein part of the enzyme is then named
exhausted in the process the apo-enzyme. It is heat labile.
Only act upon specific substrates iii. These two portions combined together is called
the holo-enzyme.
*Enzyme production: follows the central dogma iv. Co-enzymes may be divided into two groups
a. Those taking part in reactions catalyzed by
How do enzymes hasten chemical reactions?
oxidoreductases by donating or accepting
- They lower activation energy
hydrogen atoms or electrons.
b. Those co-enzymes taking part in reactions
transferring groups other than hydrogen.
ENZYME SUBSTRATE INTERACTIONS
I. ENZYME SITE:
a. Active Sites:
- There are cavities on the surface of the enzyme
- Specific part where the substrate interacts with
the enzyme
- Often a water- free cavity
- Has a particular charged amino acid residues
that interact with substrate
- The active site occupies only a small portion of
the whole enzyme.
b. Allosteric site:
- Cavities other than the active site
- Does not interact with the substrate
- May bind to regulator molecules
- Activation energy is defined as the energy
required to convert all molecules of a reacting
substance from the ground state to the transition
state.
- During enzyme substrate binding, weak
interactions between enzyme and substrate are
optimized. This weak binding interaction
between enzyme and substrate provides the
major driving force for the enzymatic catalysis.
OTHER TERMS RELATED TO ENZYMES
Substrates Substances that enzymes act upon
Isoenzymes Different forms of the same enzymes
that can be distinguished from each
other via physical properties such as
electrophoretic mobility, solubility and
resistance to inactiviation
Isoforms Enzymes after post-translational
modification
Cofactor Non-protein molecules that are
essential to enzyme function
a. Inorganic Known as an activator
b. Organic - Known as co-enzymes
BANAS | STUDYING SUCKS LESS THAN FAILING ☻
, ACTIVITY 3 PRELAB DISCUSSION NOTES: ENZYMES
MODELS OF ENZYMES SUBSTRATE INTERACTION ENZYME INHIBITION
1. LOCK & KEY MODEL 1. COMPETITIVE INHIBTION
- The enzyme and substrate poses a specific - Physically bind to the active site of the enzyme
geometric conformation that fit exactly into one - It competes with the substrate for the active site
another. - Reversible effects
- Enzyme and substrate interaction is highly Substrate concentration higher than the
specific inhibitor concentration= substrate more
likely to bind to the active site. Provided
that the enzyme is not destroyed.
- In competitive inhibition, the Km is increased in presence
of competitive inhibitor. Thus competitive inhibitor
apparently increases the Km. In other words, the affinity of
the enzyme towards substrate is apparently decreased in
presence of the inhibitor. But Vmax is not changed.
2. NONCOMPETITIVE INHIBITOR
- Binds an enzyme at a place other than the active
2. INDUCED- FIT MODEL site, leading to a change in conformation/ shape.
- In the presence of the correct/ proper substrate, - May be reversible. Some naturally present in
the enzyme will mold itself to the shape of the metabolic substances combine reversibly with
substrate. certain enzymes because you can easily detach
the substrates.
- Majority are irreversible. Inhibitors destroys a
part of the enzyme involved in the catalytic
activity. In other words, the active site was
destroyed
- Inhibitors binds the enzyme independently from
the substrate. Increasing susbstrate
concentration does not reverse the inhibition.
- Enzyme–Substrate complex theory. Accordingly,
the enzyme (E) combines with the substrate (S),
to form an enzyme-substrate (ES) complex,
which immediately breaks down to the enzyme
and the product (P) (Fig. 5.7). E + S ↔ E–S
Complex → E + P
- The inhibitor combines with the enzymes by forming a
covalent bond and then the reaction becomes irreversible.
The velocity (Vmax) is reduced. But Km value is not
changed, because the remaining enzyme molecules have
the same affinity for the substrate.
- Increasing the substrate concentration will abolish the
competitive inhibition, but will not abolish non-competitive
inhibition.
BANAS | STUDYING SUCKS LESS THAN FAILING ☻
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