Heredity, Genes, and DNA - The Cell - NCBI Bookshelf
Get an answer for 'Describe the relationship between cells, chromosomes, genes , and DNA.' and find homework help for other Science questions at eNotes. Let us start with DNA, and, to keep things more relatable, let us use human DNA. Human DNA contains about 3 billion base pairs. That is a really long code. Find information, videos, and activities about DNA, genes, chromosomes, the Like a recipe book it holds the instructions for making all the proteins in our bodies. Experiment with the forces involved and measure the relationship between.
It consists of a specific sequence of nucleotides at a given position on a given chromosome that codes for a specific protein or, in some cases, an RNA molecule. Genes consist of three types of nucleotide sequence: These genes are known, collectively, as the human genome.
Chromosomes Eukaryotic chromosomes The label eukaryote is taken from the Greek for 'true nucleus', and eukaryotes all organisms except viruses, Eubacteria and Archaea are defined by the possession of a nucleus and other membrane-bound cell organelles. The nucleus of each cell in our bodies contains approximately 1. This DNA is tightly packed into structures called chromosomes, which consist of long chains of DNA and associated proteins. In eukaryotes, DNA molecules are tightly wound around proteins - called histone proteins - which provide structural support and play a role in controlling the activities of the genes.
A strand to nucleotides long is wrapped twice around a core of eight histone proteins to form a structure called a nucleosome. The chains of histones are coiled in turn to form a solenoid, which is stabilised by the histone H1.
Further coiling of the solenoids forms the structure of the chromosome proper. Each chromosome has a p arm and a q arm. The p arm from the French word 'petit', meaning small is the short arm, and the q arm the next letter in the alphabet is the long arm. In their replicated form, each chromosome consists of two chromatids. Chromosome unraveling to show the base pairings of the DNA The chromosomes - and the DNA they contain - are copied as part of the cell cycle, and passed to daughter cells through the processes of mitosis and meiosis.
Read more about the cell cycle, mitosis and meiosis Human beings have 46 chromosomes, consisting of 22 pairs of autosomes and a pair of sex chromosomes: One member of each pair of chromosomes comes from the mother through the egg cell ; one member of each pair comes from the father through the sperm cell. A photograph of the chromosomes in a cell is known as a karyotype.
The autosomes are numbered in decreasing size order. Karyotype of a human male Prokaryotic chromosomes The prokaryotes Greek for 'before nucleus' - including Eubacteria and Archaea lack a discrete nucleus, and the chromosomes of prokaryotic cells are not enclosed by a separate membrane.
Most bacteria contain a single, circular chromosome. The chromosome - together with ribosomes and proteins associated with gene expression - is located in a region of the cell cytoplasm known as the nucleoid. The genomes of prokaryotes are compact compared with those of eukaryotes, as they lack introns, and the genes tend to be expressed in groups known as operons.
DNA, Genes and Chromosomes
The circular chromosome of the bacterium Escherichia coli consists of a DNA molecule approximately 4. Each mutant was found to require a specific nutritional supplement, such as a particular amino acidfor growth.
Furthermore, the requirement for a specific nutritional supplement correlated with the failure of the mutant to synthesize that particular compound. Thus, each mutation resulted in a deficiency in a specific metabolic pathway.
BBC - GCSE Bitesize: DNA, genes and chromosomes
Since such metabolic pathways were known to be governed by enzymes, the conclusion from these experiments was that each gene specified the structure of a single enzyme—the one gene-one enzyme hypothesis. Many en-zymes are now known to consist of multiple polypeptides, so the currently accepted statement of this hypothesis is that each gene specifies the structure of a single polypeptide chain.
Identification of DNA as the Genetic Material Understanding the chromosomal basis of heredity and the relationship between genes and enzymes did not in itself provide a molecular explanation of the gene. 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.What is DNA and Genes?
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.
Gene - Wikipedia
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. 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.
What is the relationship between chromosomes and DNA?
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.