Question

Prokaryotes contains
A) 50 S ribosomes
B) 70 S ribosomes
C) 80 S ribosomes
D) No ribosomes

Answer 1

Hint: When we talk about prokaryotes we mean bacteria, blue-green- algae, mycoplasma and Pleuropneumonia-like organisms. In prokaryotes, ribosomes are associated with the plasma membrane of the cell and are made up of 2 subunits. We know that ribosomes assemble amino acid into a protein which is controlled by the mRNA sequence which is usually required by all the cells that are living.

Complete answer:
The purpose of the ribosomes is to translate mRNA into proteins with the help of the tRNA. Ribosomes play a key role in the catalysis of 2 major biological processes that take place in the body which are peptidyl hydrolysis and peptidyl transfer. They are tiny spherical organelles that join together with the protein and make up a protein. They are found in the endoplasmic reticulum or are found free in the cytosol.

Let us see the structure of prokaryotes firstly:
The organisation of the prokaryotes is similar through wide varieties of them. All of them have cell walls surrounding the cell membrane. There is no well-defined nucleus fluid-filled in the matrix. The genetic material is naked and their plasma membrane does not have well-defined envelopes. No organelles except the ribosomes are common in them with eukaryotes. All these ribosomes are the site for protein synthesis. There are several other ribosomes that may attach to a single mRNA and form a chain called polyribosomes or polysomes. The ribosomes of a polysome translate these mRNA into proteins.

The ribosomes in the prokaryotes are associated with the membrane of the cell. They are about 15 nm by 20 nm in size and are made up of 2 subunits - 50 S and 30S unit. That is, they are present together as 70S ribosomes. The 50S subunit contains 23S and 5S rRNA while the 30S subunit contains the 16S rRNA. They are composed of two subunits, one large and the other small as they bind together during protein synthesis. The major purpose of this ribosome is to take the actual messages and the charge aminoacyl tRNA complex so that it can generate the protein. There are three binding sites, one is mRNA and the other two are tRNA. 80S ribosome is present in the eukaryotic cell. It comprised of subunits 60S and 40S.

Thus the correct answer is option ‘B’.

Note: Ribosomes are the granular structure first observed by the scientist George Palade in 1953 under the microscope as a dense particle. They are composed of ribonucleic acid and proteins and are not surrounded by the membrane. The eukaryotic ribosomes are the 80S while that of prokaryotes is 70S. Here "s" is the Svedberg's Unit that stands for the sedimentation coefficient that indirectly measures the density and size. Both 70S and 80S are composed of 2 subunits.