Enzymes as biological catalysts

What is the role of an enzyme in a chemical reaction?

It speeds up the rate at which the reaction reaches equilibrium without changing the equilibrium position

How much faster does carbonic anhydrase catalyse CO2 +H2O = H2CO2 compared to the uncatalysed reaction?

From 220 molecules/hour to 600,000 molecules/second

What specific reaction does carbonic anhydrase catalyse?

The conversion of CO2 and H2O into carbonic acid

What are the most biological catalysts made of and what is the major exception?

Most are proteins, bust some RNA molecules also act as catalyst

Under what condition do enzymes typically function efficiently?

Body temp, aqueous solution, and near neutral pH

How specific are enzymes for their substrates?

very specific

How potent can enzymes be in catalysing reaction?

They can increase reaction rates by up to 10(20) and convert many substrate molecules per second

What do enzymes specifically bind and stabilise during a reaction?

The transition state

What is special about the transition state in terms of energy?

It has the highest free energy of all reaction intermediates

How do enzymes reduce activation energy?

By providing alternative reaction pathways that stabilise the transition state

What is a glycogen storage disorder in biochemical terms?

An enzyme deficiency that prevents glycogen from entering its required phospohorylated transition state

How does failure to reach the phosphorylated transition state affect glycogen?

It blocks normal glycogen metabolism, leading to accumulation or improper breakdown

What are the two main types of molecule enzymes require for catalytic activity?

Metal ion cofactors and organic coenzymes

What is a metalloprotein?

An enzyme that uses a metal cofactors as a metal coordination centre

How do coenzymes behave during reactions?

they bind transiently, change charge/structure during the reaction, and are then regenerated

What is a prosthetic group?

A tightly bound coenzyme

What is the difference between an app enzyme and a holoenzyme?

Apoenzyme - Enzyme without cofactor

Holoenzyme - enzyme with its cofactor

Which coenzymes are involved in group transfer reactions?

Coa transfer acetyl groups; ATP transfer phosphate groups

What are many coenzymes derived from?

often vitamin-derived

What does the lock and key model propose?

The active site is already complementary in shape to the substrate before binding

What does the induced fit model propose?

Substrate binding induces a conformational change, creating a complementary fit

What feature do pancreatic protease share?

A reactive serine residue in the active site that catalyses peptide bond hydrolysis

Why does elastase only binds small amino acids?

It’s active site is partially blocked

What are isozymes?

Isoforms of the same enzyme that catalyse the same reaction but differ in structure and properties

Why are isozymes useful in clinical diagnosis?

Different tissues express different isozymes, so their appearance in blood can indicate which tissue is damaged

What does detection of CK-BB or Ck-MB in blood suggest?

CK-BB = Stroke or brain tumour

CK-MB = heart attack

What are zymogens?

Inactive precursors of an enzyme

What are 5 universal characteristics of enzymes?

Catalytic

Specific

Efficient

Regulated

Reusable