chapter 5: enzymes

Question 1

what are catalysts?

Answer 1

• it is a substance which can alter or speed up a chemical reaction, without itself being chemically changed at the end of the reaction

Question 2

describe how a catalyst helps the breakdown of potassium chlorate (VII).

Answer 2

• eg. potassium chlorate (VII) naturally breaks down into potassium chloride and oxygen gas
  > very slowly and at a high temperature
• when potassium chlorate (VII) is heated strongly in a test tube, oxygen in given off
  > gentle heating only melts the potassium chlorate (VII) and no oxygen is produced
• if a little Manganese(IV) oxide is added to the melted substance, reaction is speeded up and oxygen is rapidly given off
• Manganese(IV) oxide
  > allows the reaction to be carried out at a lower temperature
  > speeds up reaction

-at the end of the reaction, the same mass of Manganese(IV) oxide remains, not changing in the reaction
> it is an inorganic catalyst
> inorganic catalyst - are not destroyed by boiling or by changes in the pH of the solution

Question 3

what are enzymes?

Answer 3

• proteins that function as biological catalysts
• they can alter or speed up chemical reactions
  > they remain chemically unchanged at the end of the reaction

Question 4

how does enzymes lower the activation energy? and its function in our bodies.

Answer 4

• enzymes provide an alternative pathway with lower activation energy required to start a chemical reaction
  > lower the ‘height’ of the ‘hill’ (page73)
• in our bodies, enzymes speed up the breakdown of glucose and fats to carbon dioxide and water at body temperature
  > 37°C
• no strong heat is required to start the reaction

Question 5

what is an example of an enzyme catalyst process?

Answer 5

Digestion is an enzyme catalyst process
- some food molecules are large and insoluble in water
> these food molecules cannot diffuse through cell surface membrane
- large molecules must first be converted into simpler and smaller substances which are
> soluble in water and
> small enough to diffuse through cell surface membrane
- process is known as the digestion of food
> food digested by enzymes
eg.
-amylase: digests starch to maltose
- maltase: digests maltose to glucose
- protease: digests protein to amino acids
- lipase: digests fats to fatty acids and glycerol

Question 6

What is activation energy?

Answer 6

It is the minimum amount of energy needed to start a chemical reaction

Question 7

What can enzymes-catalyst reactions classified into?

Answer 7

• reactions that build up complex substances
  >(Anabolic reactions)
• reactions the break down complex substances substances
  > catabolic reactions

Question 8

What are anabolic reactions?

Answer 8

• the build up or synthesis of complex substances from simpler ones.
  > eg. Amino acids taken into cells may be used to build up proteins
  > cytoplasm contains special enzymes o catalyse such reactions

Question 9

What are catabolic reactions?

Answer 9

• the breakdown of complex substances into simpler substances
• eg: pg 75
  1. large molecule in food converted to smaller molecules by digestive enzymes
  2. In cell respiration, glucose broken down
  > release energy and form carbon dioxide and water > enzymes act together to completely break down glucose
  3. Hydrogen peroxide is sometimes produced during chemical reaction in the cells
  > substance toxic to cells
  > plants and animals produce the enzyme catalase to break down hydrogen peroxide to water and oxygen
  > removing the toxic effect

Question 10

How are enzymes classified?

Answer 10

• classified according to the chemical reactions they catalyse
  -enzymes that catalyse hydrolytic reactions are known as hydrolytic reactions
  > hydrolases
  Types of hydrolases:
• carbohydrases ( digests carbohydrates)
• proteases ( digests proteins)
• lipases ( digests fats)

Question 11

What are the characteristic of enzymes?
(Pg 77)

Answer 11

1. speeds up chemical reactions
   > alter rates of chemical reactions that occur in a cell
   > speed up chemical reaction by lowering the activation energy needed to start the reaction
2. required in minute amounts
   > enzymes are very efficient molecules
   > remained unchanged in reactions so enzyme molecules can be used over and over again
   > small amount of enzyme can catalyse a large number for chemical reactions
3. specific in action
   > enzyme specificity: each chemical reaction inside a cell is catalyse by a unique enzyme
   > is specific due to its 3-D shape

Question 12

what are substrates?

Answer 12

the substances which enzymes act on

Question 13

what are active sites?

Answer 13

• depressions or ‘pockets’ on the surface of an enzyme molecule which complimentary substrate molecules can fit

Question 14

how is an enzyme substrate complex formed?

Answer 14

1.enzymes have as specific 3D shape
> have depressions called active sites
> substances that enzymes act on are substrates

2. only the substrates with a 3D shape complementary to the active site can fit into the enzyme
   > formation of: enzyme substrate complex
3. while the substrate is attached to the enzyme, a chemical reaction occurs
   > substrate is converted into products
4. products leave the active site
   & remains unchanged

Question 15

what is the specificity of an enzyme due to?

Answer 15

• 3D shapes of the substrate and the enzyme being complimentary to each other

Question 16

what is optimum temperature? and what is the optimum temperature of enzymes?

Answer 16

• every enzyme has an optimum temperature at which it is most active
• for most enzymes, 40-50°C or around 37°C

Question 17

how are enzymes affected when the temperature is increased from low to high?

Answer 17

• enzymes have optimum temperature which it is most active
  > 40-50°C
• enzymes are inactive at low temps
  > kinetic energy is low & chances of the substrate colliding with enzymes is low
  
  • increasing temp from low to optimum
    > increases rate of enzyme reaction & higher temperature increases the kinetic energy of molecules
    > higher chance of substrates fitting into active sites
• increases the rate of formation of enzyme-substrate complex
• for every 10°C increase, the rate of enzyme reaction is doubled until the optimum temperature is reached

Question 18

what happens to an enzyme when the temperature is increased above the optimum temperature?

Answer 18

• causes a rapid decrease in the rate of reaction
• enzymes are made of proteins
  > high temps breaks the bonds that keep enzyme in shape
• active site of the enzyme loses its original shape
  > substrate molecule can no longer fit into the active site
  ( enzyme is denatured)
• the higher the temp, the faster the rate of denaturation
• most enzymes completely denatured by 60°C
  > enzyme lost its ability to catalyse

Question 19

what is denaturation?

Answer 19

definition: its the change in the three-dimensional structure of an enzyme or any other soluble protein, caused by heat or chemicals such as acids and alkalis

-3D structure plays an impt role in its function
- denaturation results in the loss or alteration of the enzyme’s active site
> substrate can no longer fit into the enzyme’s active site
> no reaction will occur
> no longer act as a catalyst

Question 20

how are enzymes affected by pH?

Answer 20

• affected by the acidity or alkalinity of the solutions in which they act
• some works best in acidic solutions and some works best in alkaline solutions
  -extreme changes in the acidity or alkalinity of the solutions denature the enzyme