DNA Deoxyribonucleic Acid PDF

DNA (Deoxyribonucleic Acid) Def: poly deoxyribonucleotide linked by 3'→5'-phosphodiester bonds found in a-Eukaryotic cells: in nucleus and mitochondria and chloroplast of plants b-Prokaryotic cells: single chromosomal DNA and nonchromosomal DNA "plasmid" It May be 1- Double Strand Linear as in Nucle...

DNA (Deoxyribonucleic Acid) Def: poly deoxyribonucleotide linked by 3'→5'-phosphodiester bonds found in a-Eukaryotic cells: in nucleus and mitochondria and chloroplast of plants b-Prokaryotic cells: single chromosomal DNA and nonchromosomal DNA "plasmid" It May be 1- Double Strand Linear as in Nuclear DNA 2- Double Strand Circular as Bacterial chromosomal DNA, Plasmids and Some Viruses 3- Single strand Circular or linear in some small viruses Primary DNA Structure - linear polymer of nucleotides. Each nucleotide consists of (deoxyribose + phosphate+ nitrogen base - - nucleotides bound together by hydrogen bonds. - sugar-phosphate are on outside of the helix, and bases are on inside - Polarity (one end has 5' phosphate group while other end has 3' OH group Secondary DNA structure - two chains ( Double Helix ) are held together by hydrogen bonding between the bases. - polynucleotide chains are antiparallel, which run in opposite directions to each other. NB: base stacking: hydrophobic interactions between adjacent base pairs which add stability to helix DNA conformation (At least 6 different conformation of DNA is known A, B, C, D, E and Z) B-DNA - Each turn of DNA is made up of 10.4 nucleotide pairs -distance between adjacent nucleotide pairs is 3.4nm. - coiling of two strands creates two groves : major groove, minor grove. - physiological conformation of DNA A-DNA - similar to B-DNA as it is right handed but more compact (11 bp per turn of the helix). - Z-DNA -produced experimentally 12 base pairs per turn of the helix and left handed ,less stable Nucleotide Bases (Chargaff's rules) -Adenine (A) bonds with Thymine (T) (two hydrogen bonds) -Cytosine (C) bonds only with Guanine (G) (three hydrogen bonds). Denaturation (Melting) -Is separation of 2 strands of DNA and can done by 1- Enzymes (helicase) 2-↑ temperature 3-Addition of alkalis ( break down of hydrogen bonds). Melting temperature (TM): -temperatures that can denaturate 50% of the DNA molecule. Annealing (renaturation): reforming of the DNA double helix again if thermally melted DNA is cooled Hybridization: -rejoin between DNA strand and other DNA, RNA or prob. Arrangement of DNA gene: segment of DNA. functional and physical unit of heredity passed from parent to offspring Genome: all the DNA contained in an organism or a cell. Chromatid: During mitosis, the chromosomes become more condensed and become visible Chromosomes: pieces of linear DNA and contain many genes Chromatin:In non-dividing cells, chromosomes are too fine and tangled to be seen clearly. Genes in eukaryotes consist of: a- Coding regions→ exons b- Non-coding regions→ introns C- Regulatory sequences Genetic Information -Human genome consists of 23 pairs of chromosomes, this includes 22 pairs of autosomes and a pair of sex chromosomes (X/Y). Females- XX; Males-XY Chromatin/Chromatids -Complex of DNA and protein.(Histones and non-histone proteins) Non-histone proteins : -in transcription, replication and DNA repair. - Histones : -responsible for the structure of chromatin and regulation of gene expression. -contains positively charged amino acids. interacts with negatively charged phosphate - Five types of histones →Linker histone(H1 or H5).core histone (H2A, H2B, H3, H4) -H1 or H5 contain: 220 amino acid linker histones. -H2A, H2B, H3 and H4: contain about 100-150 amino acid.are called core histones. Nucleosomes -Fundamental packing unit of chromatin. - nucleosome consists of 146 base pair DNA and 8 histone molecules. Two copies(H2A,H2B,H3 ,H4) - DNA is wrapped around the histone core, making nearly 2 turns per nucleosomes. - DNA extends as a thread from nucleosome to nucleosome -A 50 base pair DNA connects the two nucleosome (linker DNA) NB: Without histones DNA in chromosomes would be very long. For example,. Each human cell has about 1.8 meters of DNA, but when coiled on histones it is about 0.09 mm. -Histones Bind to DNA when Not Acetylated as histones contain a few lysine (+ve charge) which can interact with the negatively charged phosphates in DNA. Which neutralized by acetylation, reducing binding force between histones and DNA. This play role in regulation of gene transcription. Histone Acetylation→ decrease binding for regulation of gene transcription. Histone deacetylases→ increase binding when no transcription RNA (Ribonucleic acid) RNA : polymer of nucleotides. Each nucleotide ( ribose , a phosphate, and a nitrogen base.) Types of RNA tRNA (Transfer RNA) mRNA (Messenger RNA -10-15% of total cell RNA - forms 1-5% of cellular RNA - > 20 different tRNA molecules. -Eukaryotic mRNA is more stable than prokaryotic mRNA. - 75-95 nucleotides. -Eukaryotic mRNA molecules are - contain 4 arms and 3 loops a- capped at 5’ end to protect mRNA from nuclease attack. NB: - carrier of a.a to site of protein cap is methylated GTP. synthesis. b- At 3' end it contains poly A tail to protects mRNA from - at least one t-RNA molecule to each nucleaes attack. of 20 amino acids required for protein Functions synthesis. 1. mRNA carry of genetic information from nucleus to cytoplasm. 3.Eukaryotic tRNAs are less stable 2. Genetic information in mRNA in form of genetic code. than prokaryotic tRNAs 3. single mRNA can form of more than one protein rRNA (Ribosomal RNA) 4- snRNA: - component of the ribosomes (the protein Small nuclear RNA. synthetic factories in the cell). - Small molecules. Present in nucleus. - at least 80% of RNA molecules found in the cell. - Associated to SNRNP (snurps). - ribosome contains three RNA binding sites that Important for: are: The A site The P site The E site - Removal of introns (splicing). - consists of 2 subunits, large and small one - Maintenance of telomeres or chromosomal ends.