Question

Of the following molecules, which pair are amphipathic?

a) triglyceride; phospholipid

b) eicosanoid; transmembrane protein

c) steroid;  triglyceride

d) phospholipid; transmembrane protein

e) peripheral protein, eicosanoid.

2) All of the following are example of the external environment Except:

a) surroundings external to the skin

b) food in the gastrointestinal (Gl; digestive) tract

c) the plasma of the blood stream

d) air in the lungs

e) urine in the urinary bladder

Answer 1

1. Amphipathic molecules are those which contain both hydrophilic ( water attracting) and hydrophobic ( water repelling) regions. Phospholipids are amphipathic as they contain both hydrophilic region (Head) and hydrophobic region ( tail). Triglycerides are type of fat molecules found in the blood and contain only hydrophobic regions. Hence triglycerides are not amphipathic. Transmembrane proteins are type of integral proteins present in the cell membranes. Their central body is hydrophobic and the ends are hydrophilic. Hence transmembrane proteins are amphipathic. Peripheral proteins are only hydrophilic in nature.

Steroids are mainly hydrophobic but are considered amphipathic, as they contain hydrophilic regions also. Eicosanoids are bioactive molecules which are lipid soluble. Hence option (d. Phospholipid; transmembrane proteins) is correct.

2. Sorroundings external to the skin constitute the external environment with which our body interacts. The food present in the digestive tract is also present outside the body cells and thus constitute external environment. The urine in the urinary bladder and air in the lungs are also present outside of the body cells and tissues and thus constitute external environment. The plasma of the blood stream, is part of the intracellular fluid present inside the blood cells ( erythrocytes). Thus plasma constitute the internal environment. Hence option ( c. Plasma of the blood stream) is correct.