DNA, chromsomes& genome (2).pdf

DNA, Chromosomes & Human genome Dr/ Eman Abd El Moemen Mohammed Prof. in Medical Genetics, FOMSCU  ▪What is the Genetics branch of science ▪Genetic material (DNA) Agenda ▪Chromatin packaging ▪Chromosomes ▪Human genome organization  ▪...

DNA, Chromosomes & Human genome Dr/ Eman Abd El Moemen Mohammed Prof. in Medical Genetics, FOMSCU  ▪What is the Genetics branch of science ▪Genetic material (DNA) Agenda ▪Chromatin packaging ▪Chromosomes ▪Human genome organization  ▪ Genetics is the science concerned with nature, transmission and expression of What is genetic material Genetics? ▪ Medical Genetics: the branch of medicine concerned with inheritance, diagnosis and treatment of diseases with genetic background Genetic material DNA is the basic genetic material in the cell. Genetic information is stored in the nucleotide sequence.  DNA Deoxyribo NucleicAcid Deoxyribonucleic acid is a polymer of individual molecules called nucleotides.  DNA Nucleotide structure: - Pentose(5 Carbone sugar): deoxyribose - Nitrogenous base (A,T,C,G) - Phosphate group  DNA Nucleotide structure: 5’ Carbone Pentose (5 Carbone sugar) Deoxy ribose 3’ Carbone 5’: 5 Prime Carbone 3’: 3 Prime Carbone  DNA Nucleotide structure - Pyrimidines Nitrogenous bases: - Purines A pairing with T (two hydrogen bonds) Hydrogen bonds C pairing with G (three hydrogen bonds)  DNA Nucleotide structure - Attached to 5’ Carbone Phosphate group: - “-ve” charged ( so DNA molecule is –ve charged)  Single stranded DNA Double stranded DNA DNA Double helix Sugar- phosphate backbone (phosphodiester bonds between 3’ Carbone of sugar and an oxygen atom of 5’ Carbone of the next nucleotide ( single stranded DNA) - single stranded DNA pairing with another single stranded DNA to form double stranded DNA and double helix Double helix  DNA Double helix Anti-parallel:5’ end of the strand oppose - 3’ end of the other strand (polarity) Complementary: T-A C-G Measuring unit of DNA 3 base pair Base pair (bp) 2 base pair Kb = 1000 bp Describe this DNA molecule  ▪What is the Genetics branch of science ▪Genetic material (DNA) Agenda ▪Chromatin packaging ▪Chromosomes ▪Human genome organization  DNA packaging Packaging started with DNA wrapping around protein DNA is packaged into chromatid (chromosome). Chromosomes are stored in the nucleus  Chromatin DNA + proteins = chromatin In interphase nucleus chromatin is decondensed and can not distinguish individual chromosomes. Chromosomes are seen only during cell division (condensed)  Chromatin Chromatin basic structure is “ Nucleosome”  1- Nucleosome Chromatin 2- Solenoid packaging 3- loops levels 4- Chromatid Chromatin Packaging ▪ DNA (140 bp )wraps 1.75 times around a core of histone proteins ▪ The core consists of 2 molecules of 1- Nucleosome each of the histone proteins H2A,H2B, H3 AND H4 (8 molecules) Chromatin Packaging 1- Nucleosome ▪ DNA between nucleosomes is called linker DNA (20-60 bp) ▪ H1 interact with linker DNA ▪ Nucleosome filament 11nm “beads on a string” Chromatin Packaging 2- Solenoid ▪ Chromatin fiber (30nm): nucleosome filament is coiled into a helix with 6 nucleosome per turn Chromatin Packaging ▪ Loops domains (70nm): Loops of chromatin fibers bind to non-histone protein Scaffold 3- loops  1- Nucleosome Chromatin 2- Solenoid packaging levels 3- loops 4- Chromatid  ▪Chromatin packaging Agenda ▪Chromosomes ▪Human genome organization  Human chromosomes (p) Chromosomes (q) - In dividing cell Chromosomes are clearly seen as Rode shaped structure - Formed of two sister chromatids joined at the Centromere  Human chromosomes Chromosomes Types According to centromeric position and length of the arms, there are three types in the human cell ( metacentric, sub metacentric, acrocentric)  Human chromosome Chromosomes ❑ In Somatic cell 46 chromosome(diploid No.)= 2n number 22 pairs of autosomes + 2 sex chromosomes In Germ cell(ovum & sperm),23 chr.(haploid number= n) 22 autosomes + 1 sex chromosome  ▪Chromosomes Agenda ▪Human genome organization  DNA inside the cell present in the mitochondria beside Human the nuclear DNA genome Human genome Nuclear DNA Mitochondrial DNA ( chromosomes)  ▪ Circular ▪ 16 Kb long ▪ Encodes only 37 genes Mitochondrial ▪ Products of that genes function only in Mitochondria DNA ( ATP production mainly) ▪ Mitochondrial replication (division) is under control of the nuclear DNA  Human genome Nuclear genome organization Single copy DNA Repetitive DNA sequences sequences Genes and -Tandem repeat Non gene related -Dispersed repeats sequences sequences  ▪Single copy DNA sequences: - Present once or only a few times - Are the protein coding genes + regulatory elements of genes Nuclear genome organization ▪Repetitive DNA sequences: - Repeated hundred millions of times - Maintain chromosome structure & source of variation between individuals  ▪What is the Genetics branch of science ▪Genetic material (DNA) Agenda ▪Chromatin packaging ▪Chromosomes ▪Human genome organization  ▪ Thompson and Thompson Genetics in Medicine Suggested readings ▪ Emery’s Elements of Medical Genetics ▪ Medical Genetics (Ed. Jord,Carey, Bamshad