Question

There is no DNA in:
A) Hair root
B) An enucleated ovum
C) Mature RBCs
D) A mature spermatozoan

Answer 1

Hint: In eukaryotic cells, the majority of DNA is found in the nucleus; however, some amount of DNA is located in the mitochondria of plants, animals and fungi and in the chloroplasts of plants.

Complete Answer:
1) Hair is composed of two distinct structures – Hair follicle and Hair shaft. Hair follicle is the living part located under the skin and Hair shaft is the non-living part that is fully keratinized and is located above the skin surface. The Hair root is present at the base of the Hair follicle and it is the active reproductive portion of the hair follicle. It consists of matrix cells which are nucleated and, thus, it has DNA.

2) An enucleated ovum means an egg cell from which the nucleus is removed, so it will not have nuclear DNA. But a number of mitochondria will remain present in the ovum and, thus, it will have mitochondrial DNA.

3) Erythrocytes or Red Blood Cells (RBCs) carry Oxygen from the lungs to other body tissues. The RBCs contain haemoglobin (an iron containing biomolecule) that can bind Oxygen. Red colour of RBCs and of blood is due to that of haemoglobin. In mammals, the mature RBCs are biconcave disc shaped cells that lack nuclei, ribosomes and other cytoplasmic organelles such as mitochondria. Thus, they neither have nuclear DNA nor mitochondrial DNA.

4) Spermatozoa or sperm cell is the male reproductive cell. It is motile. Structure of a typical mature spermatozoan consists of a head and a tail. A compact nucleus is present in the head. Thus, DNA is present in the mature spermatozoan.

Thus, the answer is C, i.e., Mature RBCs.

Note: RBCs are produced in the bone marrow by the process called erythropoiesis. During early phases of erythropoiesis they possess nuclei but during the process of development the nuclei are expelled out. Subsequently they lose all the other cellular organelles like mitochondria, Golgi apparatus and endoplasmic reticulum.