Bio307 Lecture 3 (introduction To Enzymes).ppt

Primary Structure - Proteins Example: A change in the amino acid sequence leads to Sickle Cell Anemia

Secondary structure – Protein example for error: Mad cow/Creutzfeld-Jacobs Disease

Tertiary structure: Water-soluble proteins fold into compact structures with non-polar cores Myoglobin

Yellow: hydrophobic amino acids Blue: charged amino acids White: white: others

Some proteins fold into domains quarternary structure

Extracellular part of CD4, cell surface protein on immuno cells that is essential for HIV-infection – four similar domains of 100 aa

What are enzymes?

Enzymes are powerful and highly specific catalysts of cellular reactions l Enzymes accelerate reactions by factors of as much as a million or more Carbonic anhydrase Enzyme (E)

Substrates (S)

Products (P)

Hydration of CO2 by carbonic anhydrase: 106 molecules per second 107 times faster than uncatalyzed

Enzymes are highly specific l Enzymes are highly specific in catalysing a single chemical reaction or a set of closely related reactions in transforming substrates

Trypsin l Specificity is due to precise interaction of substrate with enzyme at active site Precision is a result of 3dimensional structure of the enzyme

Thrombin

Models of Enzyme/Substrate binding sites: lock-and-key

This model presumes that there is a perfect fit between the substrate and the active site – the two molecules are complementary in shape. Lock-and-key is the model such that active site of enzyme is good fit for substrate that does not require change of structure of enzyme after enzyme binds substrate

Models of Enzyme/Substrate binding sites: Induced-fit

Enzymes accelerate reactions by facilitating the formation of a transition state Enzyme/Substrate complex

S+E

ES

P+E

Formation of product or decrease of substrate can be measured

Model of enzyme active site - Trypsin

Many enzymes need co-factors – Example: Succinate dehydrogenase

Co-factors are non-protein molecules Without co-factors the active site of an enzyme is not active FADH2

Iron/sulphur centers for e-transfer Heme

Enzymes are classified on the basis of the types of reactions they catalyse Table 8.3. Six major classes of enzymes Class

Type of reaction

1. Oxidation-reduction Oxidoreductases 2. Transferases Group transfer 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases

Example Lactate dehydrogenase

Nucleoside monophosphate kinase (NMP kinase) Hydrolysis reactions (transfer of Chymotrypsin functional groups to water) Addition or removal of groups to Fumarase form double bonds Isomerization (intramolecular Triose phosphate isomerase group transfer) Ligation of two substrates at the Aminoacyl-tRNA synthetase expense of ATP hydrolysis

Cha