Protein-Enzyme

Question 1

What are Enzymes?

Answer 1

Are biological catalysts - they speed up the rate of chemical reactions without being used up →lower the activation energy required

Question 2

What is the active site?

Answer 2

-A specific shape to fit a specific substrate - they are complementary

Question 3

Why do enzymes have complementary shape?

Answer 3

Is determined by the tertiary structure of protein that makes up the enzyme

Question 4

What is an enzyme-substrate complex?

Answer 4

• forms when an enzyme and its substrate join together
  -The enzyme-substrate complex is only formed temporarily, before the enzyme catalyses the reaction and the product(s) are released

Question 5

What is a Catabolic reactions?

Answer 5

Involve the breakdown of complex molecules into simpler products

Question 6

What is a Anabolic reactions?

Answer 6

Involve the building of complex molecules from simpler ones

Question 7

How do enzymes lower the activation energy?

Answer 7

Enzymes speed up this process by making bond-breaking & bond-forming occur more readily → lowers the activation energy

Question 8

What is the The lock-and-key hypothesis?

Answer 8

Based on the idea that the shape of enzymes are highly specific & fixed structures

Question 9

The induced-fit hypothesis

Answer 9

The enzyme and its active site (and sometimes the substrate) can change shape slightly as the substrate molecule enters the enzyme - these are called conformational changes

Question 10

Limiting Factors Affecting Enzymes: Temperature

Answer 10

Bonds (e.g., hydrogen bonds) holding the enzyme molecules together start to break

Tertiary structure of the protein (enzyme) changes

Active site becomes damaged → substrate cannot bind → enzyme becomes denatured

Question 11

Limiting Factors Affecting Enzymes: pH

Answer 11

Too acidic solutions (H+ ions) or alkaline solutions (OH- ions) can cause hydrogen & ionic bonds to break

Shape of the active site changes → enzyme-substrate complexes form less easily - enzyme denatures

Question 12

Limiting Factors Affecting Enzymes: Enzyme concentration

Answer 12

Higher the enzyme conc. → greater number of active sites available → greater likelihood of enzyme-substrate complex formation

This relationship is linear until the amount of substrate becomes limited …

… any further increase in enzyme concentration will not increase the rate of reaction - substrate becomes the limiting factor

Question 13

Limiting Factors Affecting Enzymes: Substrate concentration

Answer 13

Greater the substrate concentration → greater likelihood of enzyme-substrate complex formation → higher the rate of reaction

When all active sites are saturated (full), no more enzyme-substrate complexes can form → rate of reaction plateaus

Question 14

Competitive inhibitors

Answer 14

Have a similar shape to substrate molecules → compete with the substrate for the active site

Question 15

Non-competitive inhibitors

Answer 15

Bind to the enzyme at an alternative site → alters the shape of the active site → prevents the substrate from binding to it

Question 16

Inhibitors in metabolism

Answer 16

-Metabolic reactions must be tightly controlled and balanced → presents the excess formation of products
-End-product can then detach from the enzyme → allows the active site to reform and the enzyme to return to an active state → occurs in a continuous feedback loop