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Chapter 8



1. Properties of enzymes (catalytic power and its specificity)
a. Enzymes are mainly proteins that usually catalyze a single chemical reaction or a set of closely related reactions. b. it has active site so that it can bind to specific reactant, substrate. C. they enhance reaction rates. D. they require cofactors for catalysis. E. enzyme can transfer one form of energy into another form. During the photosynthesis, enzyme will capture the sun light; the light energy is converted into chemical bond energy or in the mitochondria energy from small molecules is converted into chemical energy in the form of ATP.

To give you more details about enzyme properties...

There is another important enzymatic function which is enzymes may also transform energy from on form into another. it is common case that energy of the reaction is converted with high efficiency into a different form. as an example in biochemistry, the energy from the sun light can be converted to free energy saved in the mitochondria. in this step, enzymes may be needed; enzyme myosin converts the energy of ATP into the mechanical energy of contracting muscles. pumps in the meberanes of cells and organelles, which can be thought of as enzymes that move substrates rather than chemically altering them, creat chemical and electrical gradients by using the energy of ATP to transport molecules and ions.

Examples of enzymes,
a.	Proteases: it catalyze the cleavage of the peptide bond (hydrolysis of peptide bond)  it is importnat to remember that there is protein turnover in system. in order to server this, protein must be degratded so that their constituent amino acids can be recycled for the synthesis of new proteins. likewise, protein you had this morning must be ingested, which means it should be broken down into small peptides and amino acids so that it can be absorbed in your body. here is where the proteases needed. enzyme proteases cleave protiens by a hydrolysis reaction, which means there is a addition of a molecule of water to a peptide bond even though the reaction of peptide bond breaking mechanism is thermodynamically favored, such hydrolysis reaction are extremly slow, which is why we need an enzyme to make the reaction goes faster. There are three residue in this enzyme but the serine residue is the most highly reactive site in this enzyme. b.	Carbonic anhydrase can hydrate a million molecules of carbon dioxide in one second. Even hydration of carbon dioxide is catalyzed by an enzyme called carbonic anhydrase

Classification of enzymes
1.	Oxidoreductases: transfer of electrons (hydride ions or H atoms) 2.	Transferases: group transfer reactions 3.	Hydrolases: hydrolysis reactions (transfer of functional groups to water) 4.	Lyases: addition of groups to double bonds, or formation of double bonds by removal of groups 5.	Lsomerases: transfer of groups within molecules to yield isomeric forms 6.	Ligases: formation of c-c, c-s, c-o, and c-n bonds by condensation reactions coupled to ATP cleavage.

Cofactors (not protein)


Many enzymes require cofactors for activity, it helps reaction carry out a.	metal ion b.	small organic molecules (called coenzyme, many times derived from vitamins) enzyme with out cofactor called apoenzyme; enzyme with cofactor is called holoenzyme coenzyme with tightly bond to enzyme called prosthetic group; coenzyme loosely bond to enzyme called cosubstrates.

Enzymes are highly specific catalysts. the catalysits in biological systems are enzymes, and nearly all enzymes are proteins. enzymes are highly specific and have great catalytic power. they can enhance reaction rates. Like i stated earlier, cofactors can be metal ions or small, vitamin-derived organic molecules, which is called coenzyme.

based on what they catalyze, enzymes can be classified and many enzymes have common names that provide little information about reactions that they catalyze. for example. a proteolytic enzyme secreted by the pancreas is called trypsin. most other enzymes are named for their substrates and for the reactions that they catalyze, with the suffix "ase" added. thus, an ATPase is an enzyme that breaks down ATP, whereas APT synthesis is an enzyems that synthesizes ATP. reactions are divided into six major groups numbered from 1 to 6. these groups were subdivided and further subdivided, so that four-digit number preceded by the letters EC for enzymes commission could precisely identifiy all enzymes.

Free energy in enzymatic reactions
a.	Free energy(delta G) provides information about the spontaneity of a reaction but it doesn’t explain the rate of reaction. b.	It is independent of path ways. 1st. delta G is negative =rxn spontaneous. (exergonic) 2nd. Delta G is zero =rxn is at equilibrium (no overall movement) 3rd. delta G is positive =rxn is non-spontaneous (endorgonic)



Transition state
It is defined as the state corresponding to the highest energy of the reaction. And it can be lower as the enzyme catalyzes the reaction. It is a way of determining the rate of reaction. -interaction of the enzyme and substrate at the active site promotes the formation of the transition state. In fact, the active site lower the transition stat and it makes the reaction goes faster. catalytic antibodies demonstrate the importance of selective binding of the transition state to enzymatic activity. antibodies that recognized transtion state should function as catalysts as long as the state that the transition state is the place where where the catalysis happens is correct. the preparation of an antibody that catalyzes the insertion of a metal ion into porphyrin incely illustrates the validity of this explanation. catalytic antibodies can indeed be produced by using transition-state analogs as antigens.

Enzyme-substrate complex
there are 3 hypothetical models for describing enzyme-substrate complex a.	lock-key model: one substrate binds to one active site of an enzyme. b.	induced-fit model: active site forms a shape complementray to the subrat only after substrate bond. Enzyme may have more than one substrate as the substrate comes and it induces the enzyme. c.	transition-state model:

Regulatory strategies
Let’s study Regulatory Strategies: Enzymes and Hemoglobin

In order for proteins and enzymes to work properly, they must be regulated by some factors. There are 4 ways that the enzymatic reaction is regulated by. 1.	Allosteric control. Allosteric protein has the regulatory of many proteins. It is not the same as the substrate bind to active site of an enzyme instead it binds to s site and it changes the conformational form of the enzyme. Thus the further reaction will not be preceded. With a help of small signal molecule, we can control the activity of the many proteins, which is significant.

2.	Multiple forms of enzymes As an example, there is a homologs enzyme called isozymes and it provides an avenue for varying regulation of the same reaction distinct locations or times. 3.	Reversible covalent modification Covalent attachment of modifying group often time alter many enzymes. ATP In this case, the ATp serves as the phosphoryl donor in the reaction, which is catalyzed by protein kinases. The protein kinases are enzymes that add a phosphate group to a protein. And it is called phosphorylation. The removal of phosphoryl groups by hydrolysis is catalyzed by protein phosphatases. 4.	Proteolytic activation. There is an enzyme controlled in a cycle between active and inactive states. Many enzymes are activated by the hydrolysis of a few or even one peptide bond by zymogenes or proenzymes. How does the Aspartate transcarbomoylase is inhibited by the end product of its pathway? In the first step of biosynthesis of pyrimidines, there is a aspartate transcarbamoylase catalyzation. It is mainly the condensation of aspartate and carbamoyl phosphate to form N-carbamoylaspartate and orthophosphate. ATCase catalyzes in the pathway that will ultimately yield pyrimidine nucleotides such as CTP.