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Definition of Enzymes:

Proteins with catalytic power.
- catalyse thousands of chemical reactions in the intermediary metabolism of the cells.
- accelerate the chemical reactions
- the larges and most highly specialized class of proteins
- Enzymes acts as catalyst for specific chemical reactions, converting a specific set of reactants (substrates) into specific products.


What are Ser-proteases?

Some enzymes do not need any additional components (consists of only proteins) to show full activity, such as Ser-proteases:
- Tyrpsine, chymotrypsine, eastase and also acetylcholinesterase, where one amino acid, Ser, is responsible for catalytic activity.


What are co-factors?

some types of Enzyme require non-protein molecules (co factors) to be bound for activity. Co factors can be:
- Metal ions (iron sulfur clsters, Zn)
- Water-soluble vitamin derivates (NAD+, PALP, TPP) called as coenzymes.


Example of a enzyme that containes a metal cofactor:

Carbonic anhydrase (4 zinc cofactors bound in its active sites).


What is a Holoenzyme?

Coenzyme + Apoenzyme


What are Coenzymes?

Organic cofactors, derivates of water-soluble vitamins.

- Coenzymes are intermediary carriers of electrons, specific atoms or function groups in biochemical reactions.

- they act as carriers of a variety of chemical groups.


Most water soluble vitamins are components of?

Coenzymes, such as Thiamine, Riboflavin, Nicotinic acid, Folic acid, Pantothenic acid, Pyridoxal, Biotin


What is a Apoenzyme?

The enzyme minus its Coenzyme


What are Prosthetic groups?

Tighty-bound organic cofactors.
Such as FAD


What is the Active site?

Substrate binding site + catalytic site.

The region that contains these catalytic residues, binds the substrate and then carries out the reactions is known as active site.


Serine Proteases:

Hydrolyze the petide bonds of proteins.
- Chymotrypsin, trypsin and elastase (from the mammalian pancreas)


Substrate binding sites of Chymotrypsin:

Substrate binding sites: Ser-189, Gly-216, has a large pocket which accommadates the large side chains of Phenylalanine, Tyrosine and Trypophan, and so catalyses the cleavage of peptides and esters of these amino acids.


Substrate binding sites of Trypsin:

Subsrate binding sites: Asp-189, Gly-216.


What is the "lock and key model"?

- it describes the binding pocket as a rigid "lock" that is ccomplementary to the substrate (the key).
- proposed by Emil Fischer.
- In this hypothesis there are no conformational changes upon substrate binding.
- the protein enzyme is viewed as rigid.


What is the Induced fit model?

- it views the binding of substrate as a structurally-interactive process.
- proposed by Daniel Koshland.
- the protein structure is not viewed as rigid.
- the binding site not exactly complementary to the substrate.


What is the Fluctation theory?

- the conformation of the enzymes active site always changes and the substrate will be bound only if the substrate binding site has just complementarity.


What is activation energy?

Free energy between initial and transitional state. (Reactions need actication energy!)


Mechanism of enzyme action:

- Enzymes speed up the rate of reactions
- Enzymes lower activation energy


What happens when a reaction rearranges the atoms of molecules?

Hydrate hull is removed, existing bonds in the reactants must be broken and the new bonds of the products formed.


What if the reaction is exergonic?

more energy is released than was invested in the breaking of bonds.


Specificity of enzymes:

1. Bond (reaction) scpecitfity (broad): alpha-amylase, aplha-1-4 bonds are broken in glucogen and startch.

2. Group (reaction) specifity (medium) peptide bonds are broken.
- endopeptidase
- exopeptidases

3. Substrate specifity (strick) : glucose-6-phosphate.

4. Sterospecificity (very strick): L-glutamate dehydro-genase, D-amino acid oxidase