Category: Biology Second Paper

Cell death occurs in two ways. Necrosis and apoptosis. Cell death due to lack of nutrients or toxic substances is called necrosis. Apoptosis is the process of death of unnecessary cells or organs in the body. Apoptosis is the destruction or death of tissue between human fingers. Apoptosis causes red blood cells, white blood cells and platelets to die after a certain period of time.

The spread of cancer cells to different parts of the body is called metastasis. Malignant tumor cells that cause cancer spread through the blood and lymph to different parts of the body and form new tumors. Cancer formation is accelerated due to metastasis.

All substances or agents that cause cancer in the body are called carcinogenic agents. Carcinogenic agents like UV rays, cigarette tar, X-rays etc. These substances cause mutations or changes in genes. Mutagenic genes cause cancer.

Tumor suppressor genes are negative cell cycle regulatory genes. It prevents the uncontrolled growth of cells. Stops the formation of tumors and cancer in the body.

Different types of papilloma virus help to cause cancer. Papillomaviruses contain B6 and B7 genes. This gene displaces two proteins that regulate cell division. It destroys the normal cell division ability. The result is the formation of tumors that can later turn into cancer.

Genes that create positive cell cycle regulators in the body are called proto-oncogenes. Proto-oncogenes become oncogenes due to mutations. Oncogenes cause cell cycle disruption and cancer. CDK is a proto-oncogene.

Ribosome is derived from the Greek word ribo meaning ribonucleic acid and soma meaning body. Ribosome means a substance containing nucleic acid. An uncoated protein-synthesizing particle composed of proteins and RNA is called a ribosome. It is called protein factory or protein making machine. Ribosomes in cytoplasm are called cytoribosomes and ribosomes in mitochondria are called mitoribosomes.

 

Discovery and naming of ribosome

In 1953 scientists Robinson & Brown observed the presence of ribosomes in plant cells. In 1954 Albert Clode discovered it from liver cells and named it microsome. It is also called Claude’s grain. In 1955, the Romanian scientist Palade discovered the ribosome as the heavy substance of the cell. In 1958, Richard B. Robert named microsome as ribosome.

 

Origin of the ribosome

Ribosomes are produced from DNA in primitive cells. Ribosomes are synthesized during transcription of the operon in the cytoplasm of the primitive cell. In real cells, two subunits are made separately inside the nucleus. Later the two subunits move to the cytoplasm and combine to form ribosomes.

 

Number and distribution of ribosomes

25% of bacterial cells are ribosomes. The number of ribosomes in a cell of E. coli is 10,000. The size of the ribosome in a normal cell is twice that of a protocell. Mammals can have up to 10 million ribosomes per cell.

 

Type of ribosome

There are two types of ribosomes.

1. 70S ribosomes: 70S ribosomes are present in primitive cells. It is small, with a diameter of 150Å and a molecular weight of 2.7×106 Daltons. Its two sub units are 50S and 30S. During protein synthesis, the 50S and 30S subunits combine to form the 70S unit in progenitor cells. Bacteria, mitochondria and chloroplasts contain 70S ribosomes.
2. 80S ribosomes: 80S ribosomes are present in real cells. Its molecular weight is 40×106 daltons. The two subunits of the 80S ribosome are 60S and 40S. During protein synthesis, the 60S and 40S subunits combine to form the 80S unit in normal cells.

In addition, 77S ribosomes are known to exist in fungi and 55S ribosomes in mammalian mitochondria.

 

Physical structure of Ribosome

Ribosomes are spherical, ovoid, granular and bulky organelles. It can be triangular or pentagonal. Its diameter is 150-200Å. It is 22nm in width and 20nm in height. Each ribosome has two subunits. The smaller subunit is at the top and the larger subunit is at the bottom. The small subunit consists of three parts. Head, Foot and Stage. The large subunit consists of three parts. Apex, peduncle and swollen center.

In real cells, there is a groove where the two subunits of the ribosome meet. Proteins are synthesized in this cavity. A narrow tunnel runs through the large subunit from the shaft. Endoplasmic reticulum moves through these tunnels. When two subunits of a ribosome are joined, four sites appear. Aaminoacyl site, peptidyl site, exit site and mRNA attachment site. Many ribosomes join together to form polyribosomes. Ribosomes associated with chloroplasts, mitochondria and nuclear membranes are called ribonucleo-protein particles. E. coli bacteria contain 1300-20,000 ribosomes. That is, about 22 percent of the dry weight of E. coli bacteria is ribosomes.

 

Chemical structure of ribosome

The main chemical components of ribosomes are protein and RNA. The ratio of protein and RNA is 1:1. It contains small amount of metal ions Mg++, Ca++, Mn++ etc. The 70S ribosome contains 3 rRNAs (5S, 16S and 23S) and 52 types of proteins. The 80S ribosome contains 4 rRNAs (5S, 5.8S, 18S and 28S) and 80 types of proteins.

 

Svedberg unit of Ribosome

The rate of sedimentation of objects of various masses during rapid rotation in a centrifuge is called Vedberg unit. It is denoted by S. It stands for the first letter S of Swedish biochemist Theodor Svedberg’s name. S=1×10-13 cm/sec/dyne/gm. He was awarded the Nobel Prize in Chemistry in 1926 for his invention of the ultracentrifuge technique for colloidal materials.

 

Ribosome called universal organelle

All plant and animal cells contain ribosomes. Ribosomes are found in both protozoan and protozoan cells. Protocells contain 70S ribosomes and true cells contain 80S ribosomes. All organisms, from viruses and bacteria to humans, have ribosomes in their cells. Hence ribosomes are called universal organelles.

All plant and animal cells contain ribosomes. Ribosomes are found in both protozoan and protozoan cells. Protocells contain 70S ribosomes and true cells contain 80S ribosomes. All organisms, from viruses and bacteria to humans, have ribosomes in their cells. Hence ribosomes are called universal organelles.

 

Functions of Ribosome

1. Protein Factory: The main function of ribosomes is protein synthesis. It produces proteins in the process of translation. Associated ribosomes produce proteins for use in the endoplasmic reticulum, Golgibodies, lysosomes, and the plasma membrane. Free ribosomes produce proteins for use in the cytoplasm, mitochondria and chloroplasts. Hence it is called protein making factory.
2. Cytochrome production: Ribosomes help in cytochrome production. Cytochrome transports electrons in the cell.
3. Metabolism of lipids: Metabolism of lipids takes place in ribosomes.
4. Phosphorylation: Phosphorylation of glucose occurs in ribosomes.
5. Effects of damaging enzymes: Ribosomes protect polypeptides from the damaging action of proteolytic enzymes and mRNA from the damaging effects of nuclease enzymes.
6. Contains enzymes: It contains protein synthesizing enzymes. This enzyme makes proteins in the process of translation.
7. rRNA Storage: Ribosomes store rRNA.
8. Genetic Code: It determines the meaning of the genetic code. Hence hereditary traits are revealed.

[The ribosomes of primitive cells are chemically different. So when tetracycline or streptomycin drugs are applied to the patient’s body, the protein synthesis of the bacteria is stopped and the bacteria is destroyed. but no harm to the patient]

If cytokinesis does not occur, multiple nuclei are formed in the same cell by karyokinesis. It is called Free nuclear division. The water (liquid endosperm) of the tubers is the product of free nuclear division. Multinucleated cells of algae and fungi are called sinocytic, multinucleated cells of slime molds are called plasmodium and multinucleated cells of animals are called syncytium.

The process by which the cytoplasm of a cell divides is called cytokinesis. Cytokinesis occurs at the end of the telophase phase. Differences in cytokinesis can be observed in plant cells and animal cells.
1. Cytokinesis in plant cells: Towards the end of the telophase phase, the equatorial region of the cell spindle apparatus gradually widens and touches the cell wall. Then the spindle machines disappeared. Lysosome-like phragosomes accumulate in the equatorial region of the cell. Later phragosomes fuse to form plasmalemma or cell membrane. A variety of substances accumulate on the plasmalemma and form the cell plate. Cellulose, hemicellulose, pectin and other substances accumulate on the cell plate to form the cell wall. When the cell wall is formed, the cytoplasm divides into two parts. As a result, two new cells are formed.
2. Cytokinesis in animal cells: Towards the end of telophase, the cell membrane intrudes from both sides along the equator and forms a cleavage furrow. Actin proteins and myosin proteins help form grooves in the cell membrane. The cytoplasm of the cell begins to contract from the periphery along the transverse midline. This constriction gradually expands and divides the cytoplasm into two parts. As a result, two new cells are formed.