Ans.
Protein synthesis involves formation of proteins, during which information present in DNA is used to make polypeptide chains. Hence, amino acid sequence of a polypeptide chain is determined by the sequence that may differ in different species having proteins with same amino acid sequence.
Thus, the molecules that are used to compare different species with proteins having exact same amino acid sequences are DNA molecules.
Protein synthesis includes two steps, transcription and translation. During transcription, DNA gets converted into RNA by RNA polymerase enzyme, while during translation, RNA provides information to make proteins.
In RNA information is present as triplets of nucleotides, known as codon. Each code codes for a specific amino acid. There are a total of 64 codons, while number of protein-forming amino acids is 20. Hence, one amino acid can be coded by more than one codon and this property of codons is known as degeneracy of codons.
Thus, two species may have the same protein even if their DNA molecules are different because of degeneracy of codons.
The sequence of amino acids in a protein is determined by DNA. In a protein that is present in all species, the amino acid sequence will be different. Once a protein has been chosen, the amino acid sequence of that protein in different species are compared. More similarities, or fewer differences, indicate that two species are closely related. (sorry if im wrong!)
Option A
DNA is always synthesized in the 5' to 3' direction, meaning that nucleotides are added only to the 3' end of the growing strand.
Answer:
Option-B
Explanation:
The brain is an organ composed of neurons which controls all the voluntary and involuntary of animals. In humans, the brain is located in the skull where the brain is suspended in a fluid called cerebrospinal fluid.
As humans ages and becomes old aged, the neurons in the brain losing their ability to perform their function, if they are lost they cannot be regenerated.
The lesions appear on the white matter of the brain and the brain shrink. Due to these known and other unknown features, the process controlled by these neurons become inadequate and shows slower brain processing and weak memory.
Thus, Option-B is the correct answer.
