bioenergetics

Question 1

First law of thermodynamics?

Answer 1

Total energy of a system remains constant. Energy neither lost nor gained, but may be transferred from one state to another.

Question 2

Second law of thermodynamics?

Answer 2

Total entropy must increase for simultaneous reactions.
Gibbs free energy = change in heat - absolute temperature x change in entropy

Question 3

If G is +?

Answer 3

Endergonic reaction, Non simultaneous, needs energy for reaction to occur, anabolism
example: phosphorylation of glucose to glucose-6-phosphate

Question 4

If G is negative?

Answer 4

Exergonic reaction, releases energy, spontaneous, catabolism

Question 5

Which enzyme helps oxidation without the presence of Oxygen molecule?

Answer 5

Dehydrogenase enzymes.
In anaerobic conditions, the use coenzymes as acceptors of H atom
Example: lactate dehydrogenase

Question 6

Many drugs, pollutants and chemical carcinogens (xenobiotics) are metabolized by oxygenases known as?

Answer 6

Cytochrome p450 system

Question 7

What is the role of oxygenases?

Answer 7

The mediate the hydroxylation of steroids and hormones.

Question 8

Oxidases

Answer 8

• They remove hydrogen using oxygen as a H acceptor.
• Product is H2O2 or H2O
• Examples: Cytochrome oxidase, Tyrosinase, Monoamine oxidase
• CN, H2S, CO act as inhibitors of this enzyme, cause poisoning due to inhibition of cellular respiration.

Question 9

What is cytochrome oxidase

Answer 9

It is an oxidase enzyme which is a heme protein. It is the terminal component in respiratory carrier chain present in mitochondria. It transfers electrons to their acceptor oxygens from their substrate molecules after oxidation.

Question 10

Dehydrogenase

Answer 10

1. Aerobic: - Removes H and O acts as acceptor but product is H2O2
   - Amino acid oxidase, xanthine oxidase.
2. Anaerobic: - Removes H and COENZYMES (NAD+, NADP+, FAD, FMN) act as acceptor.
   - Lactate dehydrogenase (reversible, during anaerobic phase of glycolysis)

Question 11

Hydroperoxidases

Answer 11

1. Peroxidases
   
   • found in milk, leukocytes, platelets
   • need a reducing donor
2. Catalases
   
   • found in bone marrow, blood, kidney, mucous, liver
   • it’s a heme protein containing FOUR heme groups
   • destroys millions of H2O2/second

Question 12

Oxygenases

Answer 12

Add oxygen to substrate
1. Monooxygenase
- One substrate O is added, other reduced to H2O
- Tyrosine hydroxylase, Phenylalanine hydroxylase, cytochrome p450

2. Dioxygenase
   
   • Tryptophane pyrrolase, homogentistic acid oxidase

Question 13

Which specific enzyme protects tissues from oxygen toxicity caused by superoxide free radical

Answer 13

Superoxide dismutase

Question 14

Coenzymes
NAD+ and NADP+ are derived from?

Answer 14

Niacin

Question 15

Coenzymes
FAD & FMN are derived from?

Answer 15

Riboflavin

Question 16

Which oxidoreductase requires a reducing donor to reduce H2O2

Answer 16

Hydroperoxidase
PEROXIDASES NOT CATALASES

Question 17

Which oxidoreductases are heme proteins

Answer 17

Cytochrome oxidase (present in respiratory chain)
Catalase (4 heme groups)