chapter 3 biological molecules (nutrients & enzyme)

Question 1

what elements are carbohydrates made up of and what is the general formula for it?

Answer 1

carbohydrates are made up of
1. hydrogen
2. oxygen
3. carbon

and its general formula is C6H12O6.

Question 2

how is each disaccharide combined from monosaccharides?

give the 3 examples

Answer 2

1. glucose + glucose -> maltose + water
2. glucose + fructose -> sucrose + water
3. glucose + galactose -> lactose + water

Question 3

name the non-reducing sugars (4).

Answer 3

1. sucrose
2. starch
3. glycogen
4. cellulose

Question 4

how are disaccharides formed?

Answer 4

a condensation reaction — during which small molecules join to form a large molecule, with the RELEASE of WATER.

Question 5

how are polysaccharides formed?

Answer 5

polymerisation — joining many small molecules to form a large molecule.

Question 6

what elements are proteins made up of?

Answer 6

proteins are made up of
1. hydrogen
2. oxygen
3. carbon
4. NITROGEN
(+ sometimes sulfur)

Question 7

explain the structure of proteins.

Answer 7

3 or more amino acids (basic units) are linked up by peptide bonds to form a polypeptide. 2 or more polypeptide chains coiled together forms a protein molecule.

Question 8

what are the functions of proteins? (5)

Answer 8

1. growth & repair of cells (when new protoplasm is made)
2. form physical structures in body
3. synthesis of enzymes
4. formation of antibodies
5. source of energy

Question 9

what elements are fats made up of?

Answer 9

1. hydrogen
2. oxygen
3. carbon

there is no fixed ratio, thus no general formula, BUT there is much MORE HYDROGEN than oxygen.

Question 10

explain the process of hydrolysis of fats.

Answer 10

fats + water —(hydrolysis)—> glycerol + fatty acids

Question 11

explain the process of condensation of fats.

Answer 11

glycerol + fatty acids —(condensation)—> fats & water

Question 12

what are the functions of fats? (3)

Answer 12

1. insulation to prevent excessive heat loss
2. long-term storage of energy
3. protect internal organs (such as heart, liver) from shock & injury

Question 13

What are the 2 things that enzymes can do?

Answer 13

1. Break down large, complex, insoluble substances into smaller, simpler, soluble substances.
2. Build up large, complex, insoluble substances from smaller, simpler, soluble substances.

Question 14

What are the characteristics of enzymes? (6)

Answer 14

1. An enzyme is a biological catalyst that is usually made of proteins.
2. Enzymes increases the rate of chemical reactions by LOWERING ACTIVATION ENERGY of chemical reaction
3. Enzymes remain CHEMICALLY UNCHANGED at the end of the reaction.
4. Enzymes have a UNIQUE 3D SHAPE
5. Enzymes are SPECIFIC in nature. The active site of the enzyme has a shape that is COMPLEMENTARY only to the shape of the SPECIFIC SUBSTRATE.
6. Enzymes are affected by temperature and pH, and can be denatured..

Question 15

Explain the process of lock and key hypothesis.

Answer 15

1. The lock represents the enzyme, and the substrates represents the key.
2. The substrates bind to the ACTIVE SITE of the enzyme, forming an ENZYME-SUBSTRATE COMPLEX, which LOWERS the activation energy.
3. A new product is formed and the new product leaves the active site.

Question 16

As the temperature rises, the enzyme activity increases. Explain why.

Answer 16

• Enzyme and substrate molecules move and collide with one another at random (Brownian motion).
• At low temperature, the molecules have low kinetic energy and the enzymes are inactive.
• Raising the temperature INCREASES the kinetic energy of enzyme and substrate molecules.
• These molecules move faster and collide with each other more often.
• This increases chances of substrates colliding into enzymes and fitting perfectly into active sites. i.e. This increases the rate of effective collision between substrate and enzyme molecules.
• The rate of enzyme-substrate complexes formation increases.
• The rate of formation of product molecules formed increases.

Question 17

When the temperature continues to rise beyond the optimum temperature, the enzyme activity decreases. Explain why.

Answer 17

• An increase in temperature increases vibrations of the enzyme.
• The vibrations become so violent that it breaks the weak hydrogen bonds within the
  enzyme.
• The enzyme loses its 3-dimensional shape, and the shape of the active site is altered. The shape of the active site is no longer complementary to its substrate. The enzyme is denatured.
• As more and more enzymes are denatured, fewer substrates can bind to the active site to form enzyme-substrate complexes, resulting in decline in the rate of product formation.
• Such denaturation by extreme temperature is irreversible.

Question 18

What happens to the enzyme when there are extreme changes to the pH level?

Answer 18

• At pH values slightly above or below optimum pH, rate of reaction starts to fall drastically.
• A pH change will cause weak bonds to break, altering the 3D shape of the enzyme.
• The shape of the enzyme active site is altered, and the active site will no longer by complementary to the substrate
• Substrate cannot fit into active site to form enzyme-substrate complex, and rate of product formation declines
• This explains the decrease in rate of enzyme reaction when there are extreme changes to pH.

Question 19

What are the factors that affect the rate of enzyme reactions?

Answer 19

1. temperature
2. pH
3. substrate concentration
4. enzyme concentration

Question 20

Explain the effect of substrate on the rate of enzyme reaction.

Answer 20

▪ At low substrate concentration, increase in substrate concentration increases the number of effective collisions between enzyme and substrate molecules. Because not all the active sites of the enzyme molecules present have been occupied at any point in time.
▪ More enzyme-substrate complexes are formed per unit time. Hence, there is a proportional increase in the rate of formation of products.
▪ When all active sites of enzymes are already occupied by the substrates at any one time (saturation of active sites), the rate of formation of products has reached the maximum.

Question 21

Explain the effect of enzyme concentration on the rate of enzyme reactions.

Answer 21

▪ At low enzyme concentration, increase in enzyme concentration increases the number of effective collisions between enzyme and substrate molecules. (Thus the enzyme concentration is LIMITING.)
▪ There is an increase in the number of enzyme-substrate complex formed per unit time as enzyme concentration increases.
▪ A further increase in enzyme concentration does not lead to further increase in the rate of reaction, because there are limited substrate molecules to bind with the enzymes. (Thus, the enzyme concentration is no longer the limiting factor.)