Enlist the role of following in protein synthesis :
(i) mRNA (ii) rRNA (iii) tRNA
(iv) ribosomes (v) Amino Acids (vi) ATP
Answers
Answer:
tores the information for protein synthesis and RNA carries out the instructions encoded in DNA, most biological activities are carried out by proteins. The accurate synthesis of proteins thus is critical to the proper functioning of cells and organisms. We saw in Chapter 3 that the linear order of amino acids in each protein determines its three-dimensional structure and activity. For this reason, assembly of amino acids in their correct order, as encoded in DNA, is the key to production of functional proteins.
Three kinds of RNA molecules perform different but cooperative functions in protein synthesis (Figure 4-20):
Figure 4-20. The three roles of RNA in protein synthesis.
Figure 4-20
The three roles of RNA in protein synthesis. Messenger RNA (mRNA) is translated into protein by the joint action of transfer RNA (tRNA) and the ribosome, which is composed of numerous proteins and two major ribosomal RNA (rRNA) molecules. [Adapted from (more...)
1.
Messenger RNA (mRNA) carries the genetic information copied from DNA in the form of a series of three-base code “words,” each of which specifies a particular amino acid.
2.
Transfer RNA (tRNA) is the key to deciphering the code words in mRNA. Each type of amino acid has its own type of tRNA, which binds it and carries it to the growing end of a polypeptide chain if the next code word on mRNA calls for it. The correct tRNA with its attached amino acid is selected at each step because each specific tRNA molecule contains a three-base sequence that can base-pair with its complementary code word in the mRNA.
3.
Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains. They also bind tRNAs and various accessory molecules necessary for protein synthesis. Ribosomes are composed of a large and small subunit, each of which contains its own rRNA molecule or molecules.
Translation is the whole process by which the base sequence of an mRNA is used to order and to join the amino acids in a protein. The three types of RNA participate in this essential protein-synthesizing pathway in all cells; in fact, the development of the three distinct functions of RNA was probably the molecular key to the origin of life. How each RNA carries out its specific task is discussed in this section, while the biochemical events in protein synthesis and the required protein factors are described in the final section of the chapter.
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Messenger RNA Carries Information from DNA in a Three-Letter Genetic Code
RNA contains ribonucleotides of adenine, cytidine, guanine, and uracil; DNA contains deoxyribonucleotides of adenine, cytidine, guanine, and thymine. Because 4 nucleotides, taken individually, could represent only 4 of the 20 possible amino acids in coding the linear arrangement in proteins, a group of nucleotides is required to represent each amino acid. The code employed must be capable of specifying at least 20 words (i.e., amino acids).
If two nucleotides were used to code for one amino acid, then only 16 (or 42) different code words could be formed, which would be an insufficient number. However, if a group of three nucleotides is used for each code word, then 64 (or 43) code words can be formed. Any code using groups of three or more nucleotides will have more than enough units to encode 20 amino acids. Many such coding systems are mathematically possible. However, the actual genetic code used by cells is a triplet code, with every three nucleotides being “read” from a specified starting point in the mRNA. Each triplet is called a codon. Of the 64 possible codons in the genetic code, 61 specify individual amino acids and three are stop codons. Table 4-2 shows that most amino acids are encoded by more than one codon. Only two — methionine and tryptophan — have a single codon; at the other extreme, leucine, serine, and arginine are each specified by six different codons. The different codons for a given amino acid are said to be synonymous. The code itself is termed degenerate, which means that it contains redundancies.
Table 4-2. The Genetic Code (RNA to Amino Acids)*.
Table 4-2
The Genetic Code (eflection of the common evolutionary origin of the most basic constituen
mRNA
mRNA is the molecule that carries the message contained within DNA to the ribosome. Ribosomes are where proteins are produced. mRNA is important because ribosomes can't reach the DNA inside our cell nucleus, which is the location inside the cell where DNA is housed. DNA is made from molecules called bases.
rRNA
the rRNA molecules direct the catalytic steps of protein synthesis — the stitching together of amino acids to make a protein molecule. In fact, rRNA is sometimes called a ribozyme or catalytic RNA to reflect this function.
tRAN
The overall role of tRNA in protein synthesis is to decode a specific codon of mRNA, using its anticodon, in order to transfer a specific amino acid to the end of a chain in the ribosome. Many tRNAs together build upon the amino acid chain, eventually creating a protein for the original mRNA strand.
Ribosomes
Ribosomes are the sites in a cell in which protein synthesis takes place. ... Within the ribosome, the rRNA molecules direct the catalytic steps of protein synthesis — the stitching together of amino acids to make a protein molecule. In fact, rRNA is sometimes called a ribozyme or catalytic RNA to reflect this function.
Amino Acids
A long chain of amino acids emerges as the ribosome decodes the mRNA sequence into a polypeptide, or a new protein. Molecules of tRNA are responsible for matching amino acids with the appropriate codons in mRNA. ... During translation, these tRNAs carry amino acids to the ribosome and join with their complementary codons.
ATP
ATP powers the synthesis of proteins, nucleic acids and all other building blocks that make up organisms. In addition, ATP fuels transport of molecules across the membrane, cell movement and cell division