Chapter 5, Problem 1TY

Summary Introduction

Introduction: The biological membrane helps to separate the contents of the cell from the outside environment. Besides protecting the cell and maintaining its shape, the membranes play several vital roles. They help in cell signal and transport of molecules in and out of the cell.

Answer to Problem 1TY

Correct answer: The chemical composition of biological membranes can be best described by the statement, “Biological membranes are bilayers of phospholipids with associated proteins and carbohydrates”. Hence, the correct answer is option c.

Explanation of Solution

Reason for correct answer:

The membrane is made up of a bilayer of phospholipids. It can be confirmed by taking a look at the nature of the membrane which is both fluid and rigid. It consists of polar heads of phospholipids on the outside and is made up of hydrophobic tails from the inside. Thus, the membrane is polar from the exterior of the layer and hydrophobic from the interior.

The presence of proteins can be easily detected by the presence of various peripheral proteins and protruded fragments of integral proteins. Also, the receptors and associated structures confirm the presence of glycolipids and glycoprotein (made up of carbohydrate) in the membrane.

Option c. is given as “Biological membranes are bilayers of phospholipids with associated proteins and carbohydrates”.

Biological membranes are composed of bilayer of phospholipids along with the proteins and carbohydrate molecules. Hence, the correct answer is option c.

Reasons for the incorrect answer:

Option a. is given as, “Biological membranes are bilayers of proteins with associated lipids and carbohydrates”.

Biological membranes are composed of bilayer of phospholipids not proteins. The membrane is associated with proteins and carbohydrate molecules. Hence, option a. is incorrect.

Option b. is given as, “Biological membranes are composed of two layers-one layer of phospholipids and one layer of proteins”.

Biological membranes are not made up of a layer of proteins and a layer of phospholipids. Hence, option b. is incorrect.

Option d. is given as, “Biological membranes are composed of equal numbers of phospholipids, proteins, and carbohydrates”.

The protein and carbohydrate content in the biological membrane is very small compared to the phospholipids. Hence, option d. is incorrect.

Option e. is given as, “Biological membranes are composed of lipids with proteins attached to the outer surface”.

The polar ends of the phospholipids make the polar head on either side of the membrane. This is possible due to the presence of polar side chains of phosphate. The lipids lack polar ends and hence it cannot form a membrane. Hence, option e. is incorrect.

Hence, the options a., b., d., and e. are incorrect.

Conclusion

The biological membranes is made up with phospholipids bilayers along with proteins and carbohydrates.