Gene ⇒ Polypeptide | BioNinja
Although DNA stores the information for protein synthesis and RNA carries out the We saw in Chapter 3 that the linear order of amino acids in each protein These coupling enzymes link an amino acid to the free 2′ or 3′ hydroxyl of the . Jun 18, Proteins are chains of chemical building blocks called amino acids. in a gene's DNA is transferred to a similar molecule called RNA in the cell. A gene is a sequence of DNA which encodes a polypeptide sequence instructions of the mRNA transcript to link amino acids together (occurs at the ribosome).
Inhe published his observations regarding patients whose urine turned black.
This condition known as alkaptonuria happens when there is a buildup of the chemical homogentisate, which causes the darkening of urine. In most situations, excess amounts of amino acid phenylalanine are metabolised by the body.
This led Garrod to surmise that the enzyme responsible for its breakdown must be defective in these patients. In addition, since the black urine phenotype was passed from generation to generation in a regular pattern, Garrod reasoned that a gene had to be responsible for the production of the defective enzyme.
He attributed a defective enzyme to a defective gene, suggesting a direct link between genes and proteins. The Relationship Between Genes and Proteins Most genes contain the information require to make proteins. The journey from gene to protein is one that is complex and controlled within each cell and it consists of two major steps — transcription and translation.
Together, these two steps are known as gene expression. Although both DNA and RNA are made up of a chain of nucleotide bases, they have slightly different chemical properties. This is the second step in the production of proteins and it takes place in the cytoplasm. Each sequence has three bases called a codon, which codes for one particular amino acid.
A protein is made from amino acids, these form a strand. I show the protein strand as a linear line, but in reality complex interactions between amino acids lead to 3 dimensional forms that are essential for the functioning of the protein. During this translation, 1 amino acid is added to the protein strand for every 3 bases in the RNA.
So a RNA sequence of 48 bases codes for a protein strand of 16 amino acids. A certain combination of 3 bases always gives the same amino acids, so we can put the translation into a table see below. We take the first 3 bases from the figure above as example, which are AUG.
Uncovering the Relationship Between Genes and Proteins - ATA Scientific
There we see our third base and our combination. In this way we can translate the complete RNA sequence into the protein sequence. In the cell But how does this work in an actual cell?
And why make RNA first and then protein? Why not make protein from the DNA directly? After transcription the RNA is relocated to the cytoplasm of the cell, here it is translated into protein.
So the separation of nucleus and cytoplasm prevents protein from being made directly from DNA.
But there are other reasons why RNA is made. I will name a few, but not all there are so many. First, the DNA is well protected in the nucleus against everything that floats around in the cytoplasm, which prevents the DNA from getting damaged. Another reason is that we only have 1 copy of DNA in each cell, but sometimes we need a lot of the same protein.Protein Synthesis
Therefore it would be convenient if we could make more than one copy of the same protein at the same time. So protein can be made 10x as fast. So making RNA prevents DNA damage and provides flexibility in the amount and speed of protein synthesis see the figure below.