Biochemistry Part 3 Flashcards
Define enzyme
Catalyse chemical reactions which together make up metabolism
Describe the specificity of enzymes?
Limited range of substrates
Some can identify stereoisomers
Why are enzymes so potent?
They can convert many substrate molecules into product per second
What is the transition state?
Reaction intermediate species which has the greatest free energy
How do enzymes reduce activation energy?
Providing alternative reaction pathways
What is the cause of glycogen storage disease?
Defective glycogen synthesis/breakdown in muscle, liver and kidney
What does catalytic activity of many enzyme depend upon?
Presence of small molecules, called cofactors or coenzymes
Describe cofactors
Metal ions, inorganic (form a neat co-ordination centre in the enzyme)
How do coenzymes mostly associate with the enzyme?
Transiently
What happens to coenzymes during the course of reaction?
Change charge or structure during the course, but are regenerated
What are tightly bound coenzymes called?
Prosthetic groups
What is an enzyme without a cofactor called?
Apoenzyme
What is an enzyme with a cofactor called?
Holoenzyme
Give some examples of metal ions and their functions?
Zinc, Iron, Copper
Involved in redox reactions
Stabilise transition states
Describe the origin of coenzymes?
Many are derived from vitamins
What are coenzymes involved in (give examples)?
Involved in redox reactions
- NAD+, FAD
Involved in transfer processes
- CoA transfers acetyl groups
- ATP transfers phosphate groups
What does a substrate bind to?
Active site on an enzyme
-cleft or crevice
What does an active site contain?
- amino acids essential for catalytic activity
- amino acids for highly specific interactions
What is the induced fit model?
Binding of substrate induces a conformational change in enzyme, results in complementary fit
Describe chymotrypsin?
pancreatic serine proteases
Contain reactive serine residue
hydrophobic pocket binds aromatic amino acids
Describe trypsin?
pancreatic serine proteases
Contain reactive serine residue
negatively charged Asp interacts with positively charged Lys or Arg
Describe elastase?
pancreatic serine proteases
Contain reactive serine residue
active site partially blocked, only amino acids with small or no side chains can bind
What affects enzyme activity?
Temperature and pH
What is an isozyme?
isoforms of enzymes, they catalyse the same reaction but have different properties and structure (and sequence)
