The Genetic Material: DNA PDF

THE GENETIC MATERIAL  Organization (Complex – simple) Country - Genome Regions – Chromatin/Chromosome Provincials - Nucleosome Cities/Municipalities– DNA Deaprtments/Institutions/Offices – Gene Employees/People - Nucleotide  Organization (Complex to simple)...

THE GENETIC MATERIAL  Organization (Complex – simple) Country - Genome Regions – Chromatin/Chromosome Provincials - Nucleosome Cities/Municipalities– DNA Deaprtments/Institutions/Offices – Gene Employees/People - Nucleotide  Organization (Complex to simple) Nucleotide (made-up of) Nitrogenous bases Pentose sugar Phosphate group Is this a male or a female?  Inheriting Traits We inherit many of our physical characteristics or traits from our parents. This is known as heredity – the passing of traits from one generation to the next. In addition to our physical characteristics we also inherit many other traits that may not be as evident, but may be of particular importance. In scientific terminology, a trait is a particular characteristic or feature of an organism.  Why are traits inherited? Chromosomes contain the hereditary (genetic) information in living cells. All living cells and viruses contain genetic information in chromosomes. Each unique sequence of DNA (gene) carries a particular instruction for a cell. Genes vary in size from about 100 to 2.5million base pairs. The length of the sequence of DNA and the precise order of the base pairs in a gene are the critical factors that determine what the gene product (usually a protein) will be like and what it will do in a cell.  Eukaryotes Prokaryotes Viruses Location of In the nucleus In the cytoplasm Core Chromosomes Structure of Double stranded Single, circular Contain either DNA Chromosomes molecules of DNA, chromosome or RNA (not both), with attached composed of DNA, with no attached protein molecules. with very few or no proteins (naked attached proteins. nucleic acids). Number of Varies from species One. One to many. Chromosomes to species. Humans have 46. Reproduction Nuclear DNA is Single circular Reproduce only in replicated prior to chromosome is host cells. They cell division and the replicated prior to force host cells to chromosomes cell division. Each make copies of distributed evenly daughter cell their DNA or RNA. to daughter cells. receives one copy of this chromosome. Extra-chromosomal Mitochondria Small circular DNA Not applicable. DNA contain DNA. molecules known as plasmids.  Packaging DNA into Chromosomes In humans the average DNA molecule is about 6.5x107 base pairs in length. The nucleus of a human cells is just 6mm in diameter, yet it contains 1.8m of DNA. This can only be achieved because DNA in eukaryotes is tightly packaged into chromosomes. DNA is coiled around small proteins (histones). Where the DNA is wrapped around a core of histone proteins it forms a particle about 10nm in diameter called a nucleosome. The nucleosomes give the DNA strand the appearance of a string of beads, and this arrangement of DNA wrapped around histones serves to package the DNA efficiently and protected from enzymatic degradation. When a eukaryotic cell is preparing to divide, chromosomes become very condensed and are visible under a light microscope. Packaging of DNA into Chromosomes  Genes and Chromosomes Each DNA molecule contains many genes. Each gene has a particular position, called a locus, on a specific chromosome. Different forms of the same gene found in members of the same species are called alleles and will have the same locus on the same chromosome. Alleles are the basis of heritable variation. The genes on each DNA molecule are separated by regions called spacer DNA. Spacer regions include DNA that does not encode a protein product, and may function in spacing genes apart so that enzymes or other molecules can interact easily with them.  Chromosomes Chromosomes in dividing cells consist of two chromatids. Each chromatid contains an identical copy of the DNA molecule. Chromosomes in non-dividing cells chromosomes exist as a single-armed structures (each is the equivalent of one of the chromatids in a metaphase chromosome prepared for cell division).  Homologous chromosomes The same genes are found at the same locations (loci) on the two chromosomes in a pair. This is why they are referred to as homologous chromosomes or homologues. The two chromatids of a chromosome in a somatic cell contain identical DNA molecules. While there can only be a maximum of two alleles (one from each parent), there may be two copies of each.  Karyotypes The karyotype of an organism is the full set of chromosomes of a cell or individual. Karyotyping involves formally arranging the chromosomes in relation to their length and the position of the centromere. Karyotyping allows us to identify changes in chromosome number and structure. Changes of this nature may be associated with genetic abnormalities.  Classifying chromosomes Chromosomes are identified by length, banding and position of the centromere. Chromosomes that the centromere centrally positioned, giving arms of equal length, are metacentric. Submetacentric chromosomes have the centromere towards one end, resulting in arms of unequal length. When the centromere is very close to one end, the chromosome is acrocentric. Human chromosomes have been assigned to seven groups (A-G) according to their length and the position of the centromere. The groups of autosomes in humans Group Autosome Position of Autosome length Number centromere A 1-5 metacentric long B 4-5 submetacentric long C 6-12 metacentric, medium submetacentric D 13-15 acrocentric medium E 16-18 metacentric short F 19-20 metacentric shorter G 21-22 acrocentric shortest  Human Karyotype In humans (and some other organisms), sex chromosomes are distinguished from the remaining chromosomes (autosomes). Human somatic cells have a diploid chromosome number of 2N=46 consisting of 22 pairs of autosomes and one set of sex chromosomes. Human gametes have only one set of chromosomes and are referred to as being haploid. Is this a male or a female?  Karyotype Organism Haploid no. of Diploid no. of chromosomes chromosomes Amoeba 25 Chimpanzee 24 Hamster 22 Human 46 Dog 32 Horse 64 Ant 1 Ascaris 2 Mosquito 3 Onion 16 Corn 20 Fern 1010 THE GENETIC MATERIAL: DNA James Dewey Watson & Francis Harry Compton Crick  Differences of DNA and RNA DNA RNA Genetic material Protein synthesis Deoxyribose sugar Ribose sugar Adenine, Guanine, Cytosine, Adenine, Guanine, and Thymine Cytosine, and Uracil Double-stranded Single-stranded Helical form Linear form  5’ 3’ Guanine Cytosine Thymine Adenine 3’ 5’  The Central Dogma of Molecular Biology First proposed by Francis Crick (1958) He said that the sequence involved in the expression of hereditary characteristics is: DNA to RNA to Protein The Central Dogma of Molecular Biology  The Central Dogma of Molecular Biology The Central Dogma involves three major players, namely DNA, RNA, and proteins. It also involves three processes, namely DNA replication, transcription, and translation through protein synthesis. It forms the basis of storage, transmission, and expression of hereditary information.  The Genetic Code Specifically, the code defines a mapping between tri-nucleotide sequences called codons and amino acids. Every triplet of nucleotides in a nucleic acid sequence specifies a single amino acid. END