What DNA Does - DNA's Role | HowStuffWorks
Relationship Between DNA Bases Genes, Proteins and Traits Your DNA carries information in the sequence of base pairs of its nucleotides. And how did they link chromosomes — and the specific genes within them — to the As it turns out, the connections between genes, chromosomes, DNA, and that carried the information about these traits from one generation to the next. All organisms inherit the genetic information specifying their structure and function in a characteristic manner such that the ratio between F2 plants with yellow of genes, leading to the conclusion that genes are carried on chromosomes.
The combination TTT, for example, codes for the amino acid phenylalanine. Regulatory regions of the gene also contribute to protein synthesis by determining when the gene will be switched on or off. Sciencing Video Vault Proteins In active genes, genetic information determines which proteins are synthesized and when synthesis is turned on or off. These proteins fold into complicated three-dimensional structures, somewhat like molecular origami.
Heredity, Genes, and DNA - The Cell - NCBI Bookshelf
Because each amino acid has specific chemical characteristics, the sequence of amino acids determine the structure and shape of a protein. For example, some amino acids attract water, and others are repelled by it. Some amino acids can form weak bonds to each other, but others cannot. Proteins that catalyze accelerate chemical reactions, for example, have "pockets," which can bind specific chemicals and make it easier for a particular reaction to occur.
Genes, Traits, and Proteins
Variations in the DNA code of a gene can change either the structure of a protein or when and where it is produced. If these variations change the protein structure, they could also change its function. Chromosomes contain proteins as well as DNAand it was initially thought that genes were proteins. The first evidence leading to the identification of DNA as the genetic material came from studies in bacteria. These experiments represent a prototype for current approaches to defining the function of genes by introducing new DNA sequences into cells, as discussed later in this chapter.
The experiments that defined the role of DNA were derived from studies of the bacterium that causes pneumonia Pneumococcus.
Virulent strains of Pneumococcus are surrounded by a polysaccharide capsule that protects the bacteria from attack by the immune system of the host. Because the capsule gives bacterial colonies a smooth appearance in culture, encapsulated strains are denoted S. Mutant strains that have lost the ability to make a capsule denoted R form rough-edged colonies in culture and are no longer lethal when inoculated into mice.
In it was observed that mice inoculated with nonencapsulated R bacteria plus heat-killed encapsulated S bacteria developed pneumonia and died. Importantly, the bacteria that were then isolated from these mice were of the S type.
Subsequent experiments showed that a cell-free extract of S bacteria was similarly capable of converting or transforming R bacteria to the S state. Thus, a substance in the S extract called the transforming principle was responsible for inducing the genetic transformation of R to S bacteria. In Oswald Avery, Colin MacLeod, and Maclyn McCarty established that the transforming principle was DNAboth by purifying it from bacterial extracts and by demonstrating that the activity of the transforming principle is abolished by enzymatic digestion of DNA but not by digestion of proteins Figure 3.
Although these studies did not immediately lead to the acceptance of DNA as the genetic material, they were extended within a few years by experiments with bacterial viruses.
In particular, it was shown that, when a bacterial virus infects a cell, the viral DNA rather than the viral protein must enter the cell in order for the virus to replicate. Moreover, the parental viral DNA but not the protein is transmitted to progeny virus particles.
How DNA Works
The concurrence of these results with continuing studies of the activity of DNA in bacterial transformation led to acceptance of the idea that DNA is the genetic material. DNA is extracted from a pathogenic strain of Pneumococcus, which is surrounded by a capsule and forms smooth colonies S.
At the time of Watson and Crick's work, DNA was known to be a polymer composed of four nucleic acid bases—two purines adenine [A] and guanine [G] and two pyrimidines cytosine [C] and thymine [T] —linked to phosphorylated sugars.
Given the central role of DNA as the genetic material, elucidation of its three-dimensional structure appeared critical to understanding its function. Analysis of these data revealed that the DNA molecule is a helix that turns every 3. In addition, the data showed that the distance between adjacent bases is 0.
An important finding was that the diameter of the helix is approximately 2 nm, suggesting that it is composed of not one but two DNA chains. The central features of the model are that DNA is a double helix with the sugar-phosphate backbones on the outside of the molecule.
The bases are on the inside, oriented such that hydrogen bonds are formed between purines and pyrimidines on opposite chains. The base pairing is very specific: A always pairs with T and G with C.
This specificity accounts for the earlier results of Erwin Chargaff, who had analyzed the base composition of various DNAs and found that the amount of adenine was always equal to that of thymineand the amount of guanine to that of cytosine. Because of this specific base pairing, the two strands of a DNA molecule are complementary:DNA, Chromosomes, Genes, and Traits: An Intro to Heredity