The structure of DNA and RNA Genetic material of living organisms is either DNA or RNA. DNA – Deoxyribonucleic acid RNA – Ribonucleic acid Genes are lengths of DNA that code for particular proteins.
DNA and RNA are polynucleotides Both DNA and RNA are polynucleotides. They are made up of smaller molecules called nucleotides. Nucleotide DNA is made of two polynucleotide strands:Nucleotide Nucleotide Nucleotide Nucleotide NucleotideNucleotide Nucleotide Nucleotide Nucleotide Nucleotide RNA is made of a single polynucleotide strand: Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide
Structure of a nucleotideA nucleotide is made of 3 components: A Pentose sugar This is a 5 carbon sugar The sugar in DNA is deoxyribose. The sugar in RNA is ribose.
Structure of a nucleotide A Phosphate group Phosphate groups are important because they link the sugar on one nucleotide onto the phosphate of the next nucleotide to make a polynucleotide.
Structure of a nucleotide A Nitrogenous base In DNA the four bases are: – Thymine – Adenine – Cytosine – Guanine In RNA the four bases are: – Uracil – Adenine – Cytosine – Guanine
Nitrogenous bases – Two types Pyrimidines Purines Thymine - T Adenine -A Cytosine - C Guanine -G Uracil - U
Base pairing The Nitrogenous Bases pair up with other bases. For example the bases of one strand of DNA base pair with the bases on the opposite strand of the DNA.
The Rule: Adenine always base pairs with Thymine (or Uracil if RNA) Cytosine always base pairs with Guanine. Basesare held together by weak hydrogen bonds (bonds between hydrogen and F, N, or O)
Complementary base pairingPurines PyrimidinesAdenine ThymineAdenine UracilGuanine Cytosine THE DNA Sequence Game - Wanna Play?
The 5’ to 3’ – 3’ to 5’ Rule As far a 5-3 and 3 to 5: – If one strand goes from 5’ to 3’, the other goes from 3’ to 5’ 5’- ATGCAACTCGAC – 3’ 3’- TACGTTGAGCTG – 5’ Always observe the Base Pair Rule!
DNA REPLICATION OVERVIEW Involves 20 different enzymes and other proteins. IN THREE MAJOR STEPS: (S PHASE)1. Enzymes attach to existing DNA – Break Hydrogen Bonds between base pairs – Double Helix unwinds(TEMPLATE for new bases) – Enzyme - Helicase2. NEW AND MATCHING strand is SYNTHESIZED for each existing strand. DNA POLYMERASE – enzymes that carries out replication of strand. Work in ONE direction Work from opposite ends of strands.3. New strands are sealed by - LIGASE
Simplified illustration of replication The two strands of DNA separate from one another Each strand serves as a template (model) for a new strand Each new DNA molecule consists of one old strand and one new strand
Replication Forks Areas where DNA double strands have been “unzipped” for replication to occur.