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Questions and Answers
What is the non-protein part in a complex enzyme called?
What is the non-protein part in a complex enzyme called?
- Proenzyme
- Cofactor (correct)
- Coenzyme
- Zymogen
Which of the following is an example of a metal ion cofactor found in enzymes?
Which of the following is an example of a metal ion cofactor found in enzymes?
- NAD+
- Heme
- Zn2+ (correct)
- NADP+
Why are zymogens stored in their inactive forms?
Why are zymogens stored in their inactive forms?
- To prevent autodigestion of secretory cells (correct)
- To enhance their binding to substrates
- To speed up their reaction rates
- To increase their catalytic efficiency
What is the mechanism by which pepsinogen is activated to pepsin?
What is the mechanism by which pepsinogen is activated to pepsin?
What is the role of catalase in living organisms?
What is the role of catalase in living organisms?
What happens when fresh, living material is exposed to hydrogen peroxide?
What happens when fresh, living material is exposed to hydrogen peroxide?
Which condition is associated with extremely low catalase activity?
Which condition is associated with extremely low catalase activity?
What is the primary function of a catalyst in a chemical reaction?
What is the primary function of a catalyst in a chemical reaction?
Under what conditions do enzymes typically function in biological systems?
Under what conditions do enzymes typically function in biological systems?
Who was the first to isolate and crystallize an enzyme in pure form?
Who was the first to isolate and crystallize an enzyme in pure form?
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Study Notes
Nobel Prize in Enzyme Research
- John H. Northrop and Wendell M. Stanley of the Rockefeller Institute for Medical Research shared the 1947 Nobel Prize with Sumner.
- They discovered a complex procedure for isolating pepsin, which has been used to crystallize several enzymes.
Types of Enzymes
- Simple enzymes: containing only a protein part (e.g. hydrolases like pepsin, trypsin, or ribonuclease).
- Complex enzymes: consisting of a protein part (apoenzyme) and a non-protein part (cofactor), which forms a biologically active molecule of enzyme (holoenzyme).
Cofactors
- Metal ions: Zn2+, Mn2+, Fe2+, Cu2+, Mg2+
- Organic molecules: often derivatives of vitamins
- Coenzymes: non-protein organic molecules that bind to apoenzyme freely (e.g. NAD+, NADP+)
- Prosthetic group: non-protein organic molecules that bind to apoenzyme tightly (e.g. heme, FAD)
Zymogens
- Proenzymes produced and stored in their inactive forms to protect secretory cells from autodigestion.
- Activated at the desired location, often through partial proteolysis.
- Examples: pepsinogen (activated by HCl in gastric juice) and trypsinogen
Mechanism of Enzyme Action
- Enzymes are catalysts, increasing the speed of a chemical reaction without undergoing permanent change.
- Steps: formation of enzyme-substrate complex, conversion of substrate to product, and release of product.
- Enzymes are not used up in the reaction and do not appear as reaction products.
Catalase
- Breaks down hydrogen peroxide (H2O2) to water and oxygen.
- Fresh, living material has enough catalase to produce bubbles of gas (oxygen) upon exposure to hydrogen peroxide.
- Persons with acatalasemia have extremely low catalase activity.
Catalysts and Enzymes
- Catalysts: substances that increase the rate of a chemical reaction without altering chemical equilibrium.
- Enzymes: specific organic molecules (biocatalysts) that speed up reactions in biological systems, enabling reactions to occur under relatively low temperatures, neutral pH, and atmospheric pressure.
Early Enzyme Discoveries
- Jon Jakob Berzelius: Swedish chemist who coined the term "catalytic" in 1835.
- James B. Sumner: isolated and crystallized the enzyme urease from the jack bean in 1926.
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