Tag: cell-the basic unit of life

Cyanobacteria are prokaryotes so, they lack a membrane-bound well-defined nucleus. Cell membrane and ribosomes are the cell structures, common to both prokaryotes and eukaryotes.

DNA is stored in the nucleus, while proteins are assembled from free amino acids in the cytoplasm in structures called ribosomes.

Nucleus and mitochondria are double membrane-bound organelles while ribosome is not membrane bound. Prokaryotes are the organisms that lack any membrane-bound organelles which means that out of given options, only ribosomes are present in them. 

The nucleus is the largest and most significant living organelle of the cell. All the cellular activities of the cell are regulated by the nucleus. Hence it is called brain or control centre of the cell. The nucleus is surrounded by a double unit membrane from all sites. The chromosomes and genes which have genetical characters and transmit from one generation to another are found in the nucleus. Thus option D is the correct answer. 

The nucleus is an important cell organelle. It is the repository of genetic material. Inside nucleus, there is a synthesis of mRNA which is subsequently transported to the cytoplasm for protein synthesis. Thus, nucleus controls proteins synthesized in a cell and also is a repository of genetic material. Hence, the nucleus is controlling centre of the cell.

'Karyon' refers to the nucleus and 'logy' stands for systematic study. Hence, Karyology is the study of the nucleus. It can be defined as a cytological study of the cell nucleus, especially regarding the chromosomes.

Bacteria and cyanobacteria are prokaryotes, i.e., having pro or primitive karyon. These cells have primitive nucleus, not having a distinct nuclear membrane. These cells have a single circular molecule of DNA as genetic material but it is not present inside membrane bound nucleus.

Nucleo-lemma is a term used in parallel with plasma-lemma. The nucleo-lemma is a part of the nuclear membrane. The outer membrane may have ribosomes and interconnections with ER. Nuclear membrane has a large number of pores for the nucleo-cytoplasmic exchange of materials.

Prokaryotic cells like bacteria have a single circular DNA molecule as their genetic material which is also called as a bacterial chromosome. The eukaryotic cells have a prominent nucleus with species-specific number of linear chromosomes having well-defined centromere and telomeres.

• The nucleus controls protein synthesis and is the genetic repository of a cell. 
• Hence, the nucleus can be called as the mastermind of cell.
• Thus, option C is correct.