Category: Biology Second Paper

If three nitrogen bases form a code, the arrangement or assembly of four nitrogen bases will be 4×4×4=64. That is, the triplet codon number is 64. 64 codes can code for 20 amino acids. The number of functional codons is 61 and termination codons are 3. In 1964, Nirenberg and Matthaei discovered 64 triplet codes for 20 amino acids.

There are 3 types of genetic codon.
1. Sense codon: All the codons that provide the signal for the creation of amino acids are called sense codons. There are 61 sense codons for 20 amino acids.
2. Start codon: All the codons that initiate protein synthesis are called start codons or initial codons. The start codon is AUG. Amino acids that initiate protein synthesis are methionine (true cells) and formyl methionine (primitive cells).
3. Stop codon: Those codons that terminate protein synthesis are called termination or stop codons. The stop codons are UAA, UAG and UGA. They do not provide any signal for the formation of amino acids. Hence they are called non sense codons.

The code that carries the hereditary characteristics of an organism is called genetic code. The code formed by the combination of three adjacent nitrogen bases in the DNA molecule is called the genetic code. It is also called mRNA code. The genetic code is the biochemical basis of heredity. Scientist Francis Crick proved that the genetic code is a triplet or 3-letter code. Nirenberg was able to synthesize artificial mRNA using poly U (polyuridylic acid) in a cell-free or in vitro system. Indian scientist Hargobind Khorana synthetically synthesized the 5-GUGUGUGUGU-3 nucleotide chain and used it to create the valine-cysteine valine-cysteine polypeptide chain. Nirenberg and Hargobind Khorana won the Nobel Prize in 1969 for this discovery.

Gene action in actual cells is accomplished in three steps.
1. Replication: The process in which another DNA is created from DNA is called replication. DNA replication occurs in the S phase of the cell cycle.
2. Transcription: The process by which mRNA is produced from DNA is called transcription. Transcription occurs inside the cell nucleus.
3. Translation: The process by which protein is produced from mRNA is called translation. Translation occurs in the cytoplasm of the cell.

The unit of gene expression is called an operon. Jacob and Mond (1961) proposed the operon model. According to them, an operon is formed by the combination of several genes and their interaction in primitive cells results in the expression of functional genes. They discovered the lactose operon. The operon consists of four segments.
1. Structural genes: It synthesizes enzymes.
2. Driver Gene: It controls the production of protein.
3. Regulatory Gene: A gene that controls the functions of an operon is called a regulatory gene. An increase in the transcription of a gene in a cell is called induction and a decrease is called repression.
4. Promoter or stimulator gene: RNA polymerase enzyme binds to it.
Send feedback
Side panels
History
Saved

The word Vertebrata is derived from the Latin word vertebratus meaning having a backbone. Animals in which the embryonic notochord is fully replaced by bony or cartilaginous vertebrae are called Vertebrata. Vertebrata or vertebrates are known as higher order animals. Because their brain is located in the cranium, their other name is craniata. Their species number is 66,178 (IUCN, 2014).
Vertebrates (fish) have been in the ocean for over 150 million years. Hands and feet evolved in a group of vertebrates about 365 million years ago. As a result, they qualify as amphibians to live in water and on land. Over time, the descendants of amphibians adapted and evolved into reptiles, birds and mammals.

Characteristics of Vertebrata
1. Their notochord is replaced by a spinal cord.
2. The anterior part of the hollow nerve forms the brain and the posterior part the spinal cord.
3. They have 5-15 pairs of pharyngeal florets.
4. Lateral pairs of fins or feet act as their locomotion organs.
5. Blood circulatory system is closed type. It is composed of a muscular heart, blood vessels and red blood (containing hemoglobin).
6. Body skin consists of the epidermis (derived from the ectoderm) and the dermis (derived from the mesoderm).
7. 2-4 chambered heart and blood vessels.
8. The brain is protected by the cortex. Brain contains 10-12 pairs of carotid nerves.
9. There is an endoskeleton made of bone or cartilage. Arises from the intraskeletal neural crest.
10. Skin glands, feathers, scales, nails, claws, hairs, horns, hooves etc. exist in the body.
11. There are different types of endocrine glands in the body.
12. Nutrition is complete; Consists of muscular alimentary canal, liver and pancreas.
13. There are well-developed kidneys for excretion and osmoregulation.
[Key words to remember features: spinal cord, brain, mesentery, pharynx, feet, fins, closed circulatory system, carotid nerve, endoskeleton, excretion, osmoregulation]

1. Their notochord is replaced by a spinal cord.
2. The anterior part of the hollow nerve forms the brain and the posterior part the spinal cord.
3. They have 5-15 pairs of pharyngeal florets.
4. Lateral pairs of fins or feet act as their locomotion organs.
5. Blood circulatory system is closed type. It is composed of a muscular heart, blood vessels and red blood (containing hemoglobin).
6. Body skin consists of the epidermis (derived from the ectoderm) and the dermis (derived from the mesoderm).
7. 2-4 chambered heart and blood vessels.
8. The brain is protected by the cortex. Brain contains 10-12 pairs of carotid nerves.
9. There is an endoskeleton made of bone or cartilage. Arises from the intraskeletal neural crest.
10. Skin glands, feathers, scales, nails, claws, hairs, horns, hooves etc. exist in the body.
11. There are different types of endocrine glands in the body.
12. Nutrition is complete; Consists of muscular alimentary canal, liver and pancreas.
13. There are well-developed kidneys for excretion and osmoregulation.
[Key words to remember features: spinal cord, brain, mesentery, pharynx, feet, fins, closed circulatory system, carotid nerve, endoskeleton, excretion, osmoregulation]

The word Vertebrata is derived from the Latin word vertebratus meaning having a backbone. Animals in which the embryonic notochord is fully replaced by bony or cartilaginous vertebrae are called Vertebrata. Vertebrata or vertebrates are known as higher order animals. Because their brain is located in the cranium, their other name is craniata. Their species number is 66,178 (IUCN, 2014).
Vertebrates (fish) have been in the ocean for over 150 million years. Hands and feet evolved in a group of vertebrates about 365 million years ago. As a result, they qualify as amphibians to live in water and on land. Over time, the descendants of amphibians adapted and evolved into reptiles, birds and mammals.

A pair of mucus-secreting folds in the pharynx of urochordate and cephalochordate animals is called the endostyle. Endostyle is a parallel longitudinal fold. It is located at the base of the pharynx. In vertebrates, the endostyle transforms into a thyroid gland. For example – Branchiostoma.

The oral hood of cephalochordate animals has narrow thread-like structures called oral cirri. Oral cirri hang around the mouth. It is a sensory organ. It acts as a filter. Such as Branchiostoma