 Today, we are going to talk about the heredity material, the chromosomes, DNA and genes. In this lecture, we are going to cover certain goals, goals of this lecture are structure of the chromosomes, structure and functions of genes, structure and functions of DNA and the heredity information flow, transcription and translation. We start from what is a heredity information flow? Heredity, something that is transferred from one generation to the next generation that is from parents to the offsprings, reproducing itself is a property of life and is the essential property of life. This is the characteristic of all the living organisms that they reproduce themselves and they transfer their characteristics from one generation to the next generation that is from parents to the offsprings. Heredity information flow in living organisms is carried out by the structures or we can say structure or units called the genes. Genes are present in the form of DNA molecules and the DNA molecules are organized in the structures called chromosomes or the chromatin material. We describe it as the chromosomal theory of inheritance that is there is a theory that is proved by various scientists by so many experiments that chromosomes are ultimately responsible for transferring the characteristics of the parent to the offsprings. By conducting many experiments various scientists at different locations in the world proved that without the DNA genes, chromosomes, the heredity information could not be transferred. So the DNA molecule which have genes is responsible for the heredity information flow. Here we look at a diagram which show that as we know that all the cells do have a nucleus if they are eukaryotic cells, if they are prokaryotic cells then they do not have a nucleus that is a region separated by a nuclear membrane from the cytoplasm but they do have a small region inside the center of the cell which is called the nucleotide region. The chromatin material is present inside the nucleus or the nucleotide region. As this diagram shows to you that chromatin material is present in just like entangled threads inside the nucleus if we try to elongate that chromatin material then you can see if you go towards the right side of the diagram you will see that this will be just opened like a thread and we will see more complicated threads which are wound around different sets of proteins. If we open it even more then we will see that there are small sets of proteins. These proteins are called histones. These proteins are the set of those proteins around which DNA molecule is wrapped. Around each histone set as you can see in the diagram there are the DNA fiber is wrapped around twice, two times then if we open it further and separate it from the proteins then we can see the DNA helix separately from the proteins. If we look this is this phase or this structure is actually found when the cell is not dividing that is these are not condensed but when the cell is dividing this chromatin material is present in a condensed form you can see on the extreme right in the form of the structures called chromosomes which are actually highly condensed form of these molecules we call them chromosomes. You can see the various parts of a chromosome inside the center the constricted region is called the centromere around which on the sides are the arms and the very corner of the arms are called the telomere. So this is about a generalized rough idea of that how chromatin material is present inside the chromosome sorry inside the nucleus in the non dividing phase and in the dividing phase. So chromatin is the genetic material chromatin material when we call it chromatin it is actually mainly in the non dividing phase of the cell when we call it a chromosome when this is present in the dividing phase of the cell as we looked in the previous diagram chromatin material actually in non dividing phase is so thin so spreaded so thin that it is not visible under the light microscope when the cell comes in the phase of division then what happen that these chromosomes this these DNA molecules start condensing in the pro phase the first phase of the mitosis the cell or the nuclear division these chromosomes condense and then we must say in more correct terms that the chromatin material condense and they make the condense structures called chromosomes. So chromatin material is a term for more thinner material which is not very visible the chromosome is the more right term for the chromatin material in the dividing phase when it is highly condensed and it is clearly visible under a light microscope if we stained there are certain specific characteristics of the genetic material which actually make it a genetic material because you know that genetic material means that this particular molecule should be able to transmit the heredity information from the parents to the offspring to the next generation it should have certain important functions number one is that it replicates itself number one that the genetic material should replicate itself replica means copy it should be able to copy itself if it is able to copy itself then it could go to the next generation when the cell divides second property is this that it should regulate the growth and development of the organism this particular molecule should have the capability to regulate or control the growth and development of the organism in which it is present for example if we look at the human beings we have so many characteristics we have our eye colors we have our hair colors we in our inside our body we make so many enzymes our skin is made up of cells proteins our hair are made up of different types of proteins every characteristic should be made and all of these things are regulated by the genetic material the third property is this that it allows the organism to adapt to the environmental changes now we know that environment is always changing environment is like a temperature around us is changing always with the seasons wind blowing around us is always changing something sometimes it is too much of wind if sometimes there is a breeze low one sometimes in if it is very it may be very hot sometimes it may be very cold and even there are certain environmental disasters which can change the environment altogether the genetic material should have the property that it can change adapt or we can say mutate itself to give the living organism a room for adapting or dealing with or coping with the changes in the environment so there are three properties which makes a material a molecule a hereditary molecule number one it replicates itself number two it regulates the growth and development of the organism and number three that it allows to adapt allows the organism to adapt to environmental changes in the situation now the chromosomes DNA and the genes chromosomes consist of DNA molecules and proteins when we call it call a genetic material or a DNA molecule a chromosome when this molecule is wrapped around or we can say wound around different types of proteins so chromosome is a complex of DNA wrapped around different types of protein DNA plus proteins in chromosomes DNA is wrapped around proteins few of these proteins are called histones these are a specific type of proteins and they are named as histones as we have seen in the previous diagram that around which there are two full circles of DNA which are wrapped but there are certain other proteins which are also associated with the DNA molecules in the chromosome but these are not histones we can call them non-histone protein so we divide the proteins associated with DNA into histone stones and the non-histone protein so we are talking about the chromosomes the genetic material DNA what is DNA? DNA is deoxyribonucleic acid DNA stands for deoxyribonucleic acid DNA is large molecule we call it a macromolecule and this is present in all types of organisms except for a few in which the genetic material is RNA in most of the organisms DNA is the genetic material DNA is different as it is present structurally in different types of cells we know that there are cells which are called the prokaryotic cells which don't have a true nucleus there are other cells which are called eukaryotic cells which includes animals and plants these cells have a true nucleus in the prokaryotic cells DNA exist as a circular molecule though this is a chromosome because this is associated with the proteins different types of proteins these proteins are sometimes different from the proteins present in the eukaryotic chromosome but some proteins are similar to that of eukaryotic chromosomes and eukaryotic chromosomes their DNA molecule their chromosome is actually a linear DNA molecule in prokaryotes it was circular DNA molecule in eukaryotes it is a long linear DNA molecule in the form of a chromosome that is associated with different types of proteins histone and non histone proteins the prokaryotes also have another form of DNA present outside their nucleotide region inside their cytoplasm which are small circular DNA molecules these are called plasmids the bacterial chromosome or the prokaryotic chromosome as we know that bacteria are the prokaryotes the prokaryotic chromosomes they have the genes for the regulation of growth for control for development and everything the plasmids which are the we can call them extra nucleotide DNA circular DNA molecules do not have essential genes but these have certain genes for resistance to for example antibiotics resistance to salinity or resistant to extreme environmental conditions so the plasmids give an extra advantage to the prokaryotes particularly the bacteria to cope with the extreme environment in eukaryotes as we talked about that DNA is a linear molecule it is a straight linear molecule there are two more organelles which have their DNA molecule of their own these are the mitochondria and chloroplast mitochondria also have a circular DNA molecule of its own and the chloroplasts which are we know that present in the plant cells and these conduct the photosynthesis these also have their own DNA molecule that is why we assume that mitochondria and chloroplast they may be originated from some bacteria because they matches in their chromosome in their DNA material and in their division of the organelle with the binary fission in the bacteria so DNA molecule in prokaryotes is a circular molecule it may be in the form of a chromosome or a plasmid in eukaryotes DNA molecule is linear and is present in the form of a linearly arranged chromosome and in mitochondria and chloroplast DNA is a circular molecule present inside their matrix next is gene what is a gene gene is a length of DNA that codes for a peptide or a protein so gene is a part of DNA or a piece of DNA that codes for a peptide or a protein gene is nothing but a piece of DNA length of DNA so the chromosomes are the genetic or the chromatin material is the genetic material which is during the mitosis or division phase highly condensed and we call them chromatin material is during the mitosis or division phase highly condensed and we call them chromosomes organisms have different number of chromosomes for example humans have 46 chromosomes present inside each cell the nucleus of each cell these 46 chromosomes are present in 23 pairs onion have 16 chromosomes which are present in 8 pairs while drosophila the fruit fly have 4 chromosomes are present in 2 pairs there are different types of organisms which have different number of chromosomes chromosomes also somehow determines the complexity of life mostly more complex the organism more complex a more number of chromosomes