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Flashcards in Enzymes 1 Deck (21)
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1
Q

Definition of Enzymes:

A

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.
2
Q

What are Ser-proteases?

A

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.

3
Q

What are co-factors?

A

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.
4
Q

Example of a enzyme that containes a metal cofactor:

A

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

5
Q

What is a Holoenzyme?

A

Coenzyme + Apoenzyme

6
Q

What are Coenzymes?

A

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.
7
Q

Most water soluble vitamins are components of?

A

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

8
Q

What is a Apoenzyme?

A

The enzyme minus its Coenzyme

9
Q

What are Prosthetic groups?

A

Tighty-bound organic cofactors.

Such as FAD

10
Q

What is the Active site?

A

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.

11
Q

Serine Proteases:

A

Hydrolyze the petide bonds of proteins.

- Chymotrypsin, trypsin and elastase (from the mammalian pancreas)

12
Q

Substrate binding sites of Chymotrypsin:

Ser-proteases

A

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.

13
Q

Substrate binding sites of Trypsin:

Ser-proteases

A

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

14
Q

What is the “lock and key model”?

A
  • 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.
15
Q

What is the Induced fit model?

A
  • 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.
16
Q

What is the Fluctation theory?

A
  • the conformation of the enzymes active site always changes and the substrate will be bound only if the substrate binding site has just complementarity.
17
Q

What is activation energy?

A

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

18
Q

Mechanism of enzyme action:

A
  • Enzymes speed up the rate of reactions

- Enzymes lower activation energy

19
Q

What happens when a reaction rearranges the atoms of molecules?

A

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

20
Q

What if the reaction is exergonic?

A

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

21
Q

Specificity of enzymes:

A
  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