DNA Structure & Organization PDF

DNA Structure & Organization SBI 4U – Lesson 1 Deoxyribonucleic Acid  Made up of repeating subunits called nucleotides  Each nucleotide is made of 3 parts  Deoxyribose sugar (5 C )  Phosphate group  Nitrogen base Nucleotide structure  Deoxyribose sugar...

DNA Structure & Organization SBI 4U – Lesson 1 Deoxyribonucleic Acid  Made up of repeating subunits called nucleotides  Each nucleotide is made of 3 parts  Deoxyribose sugar (5 C )  Phosphate group  Nitrogen base Nucleotide structure  Deoxyribose sugar Phosphate attached to carbon 5 (5’) Nitrogen base attached to carbon 1 (1’) Next nucleotide attaches to carbon 3 (3’) 2 types N-bases: PYRIMIDINES PURINES Single rings Two rings 1. Uracil (U,RNA only) 1. Adenine (A) 2. Thymine (T,DNA only) 2. Guanine (G) 3. Cytosine (C)  Complementary base pairing G and C pair Both pairs together with 3 have the H bonds holding same them together diameter H bond is weak but A and T pair collectively together with 2 strong bonds holding them together  Double helix Two strands Phosphate and sugar support on outside Strands run antiparallel Clockwise direction 1 turn. 10 nucleotides Nucleotides spaced out 0.34nm apart Complementary Base Pairing  The two strands are complementary due to complementary base pairing of A -T and C-G via Hydrogen bonds  Each strand has a 5′ end and a 3′ end, from the numbering of the carbons in the deoxyribose sugar.  The two strands are antiparallel (5′ end from one strand is across from the 3′ end of the complementary strand)  Usually only write the 5’ to 3’ strand (other one can be deduced)  E.g. 5’ A T C T T G A G T 3’ 3’ T A G A A C T C A 5’ Organization of DNA  Genome: the total genetic material of an organism  Gene: a functional unit of DNA  The majority of DNA in an organism’s genome does not contain genes and, instead, has non-coding regions. Prokaryotes - Circular, double stranded DNA molecule - No nuclear membrane, packed in region called ‘nucleoid’ - Tightly packed by coiling, compacting and supercoiling Prokaryotes  DNA supercoiling is the formation of additional coils in the structure of DNA due to twisting forces. It is controlled by the enzymes topoisomerase I and topoisomerase II.  Antibacterial drugs have been developed to specifically block these enzymes and inhibit bacterial survival. Prokaryotes  Plasmids: small, circular or linear DNA molecules that often carry non-essential genes.  Not part of the nucleoid  Can be transferred from cell to cell  Prokaryotes are haploid  One copy of each gene  genomes are composed of regions that contain either genes or regulatory sequences (determine when certain genes are activated) Eukaryotes  Double stranded & linear  More DNA than prokaryotes ∴ more compact  Histones: a family of proteins that associates with DNA to help compact it  Nucleosome: the condensed structure formed when double-stranded DNA wraps around an octamer of histone proteins DNA Packaging Size & Number of Genes Vary  The eukaryote genome can vary greatly between species.  (A) Lungfish have 40 times more DNA per cell than a human cell.  (B) Rice has 30 000 more protein-coding genes than a human.  (C) C. elegans has the same number of genes as humans but less DNA