NUCLEIC ACIDS (DNA and RNA) They are large, complex molecules of high molecular weight. They contain C, H, O, N and P. Their monomers are nucleotides.

The Structure of a Nucleotide PO 4 5C Sugar (ribose or deoxyribose) Nitrogenous bases (adenine, guanine, thymine,cytosine, uracil) Nucleic acids are polymers of nucleotides. Phosphoester bond Glycoside bond

Nitrogenous base + 5C Sugar + Phosphate group Nucleotides Nucleic acids Nucleotide Adenine = CytosineGuanine Thymine Number of H bonds between bases Adenine Guanine Cytosine Thymine Purine bases Pyrimidine bases A T =1 G C =1 T+C A+G =1 Purines Pyrimidines =1 Nucleoside

A+G T+C == Number of nucleotide in DNA 1/2 A+G == T+C 1 Number of nucleotide in one strand Number of H bonds = ( A X 2 ) + ( G X 3 ) Number of H bonds = ( T X 2 ) + ( CX 3 ) Number of phosphodiester bonds = Number of nucleotide in DNA- 2 Number of phosphodiester bonds = Number of nucleotide in one strand - 1 X 2

ratio is specific for species. If the ratio is smaller and it is resist to heating. In prokaryotes, DNA is found in cytoplasm and naked. In eukaryotes, histones are found in the structure of DNA. DNA is located in nucleus, mitochondrion, chloroplast. All kind of biological process are directed by DNA. DNA is replicated during interphase. DNA undergoes mutations. If a mutation occurs within the sex cell, it is inherited to next generation. A+T G+C

Nucleic Acids DNA (Deoxyribonucleic acid)RNA (Ribonucleic acid) DNA: Found in nucleus, mitochondria and chloroplast in eukaryotes Is the hereditary material that is transmitted from one generation to the next, during reproduction Contains 5 C sugar(deoxyribose), phosphate group (PO 4 ), nitrogenous bases adenine (A) guanine (G) cytosine (C) thymine (T) DNA is double stranded (double helix)

Crick and Watson walking along the Backs. 1953

RNA: Found in nucleus and cytoplasm Works with DNA, involved in protein synthesis Contains 5 C sugar (ribose), phosphate group (PO 4 ) and nitrogenous bases adenine (A) guanine (G) cytosine (C) uracil (U) RNA is single stranded.

DNARNA It is double stranded ( in some viruses, it is single) It is single stranded ( but in some RNA viruses, it is double helix) 5C sugar is deoxyribose5C sugar is ribose Nitrogenous bases are A, G, C, T Nitrogenous bases are A, G, C, U Location: prokaryotes: in cytoplasm eukaryotes: nucleus, mitochondrion, chloroplast Location: prokaryotes: in cytoplasm eukaryotes: nucleus, cytoplasm mitochondrion, chloroplast, ribosome

DNARNA Function: is the primary hereditary material, controls the structure of proteins synthesized and this way controls all cellular activities Function: vital for protein synthesis can replicate itself is transcribed by DNA

DNARNA Enzymes for replication: DNA polymerase DNA ligase DNA nucleotide sentetase Enzyme for production: RNA polymerase RNA nucleotide sentetase Enzymes for depolymerization: DNAse ( deoxyribonuclease) Enzymes for depolymerization: RNAse ( ribonuclease)

GRIFFITH’S EXPERIMENT

Griffith was trying to find out a vaccine against pneumonia transformation Blood analysis showed the presence of some live S- type bacteria

THE CHEMICAL BASES OF HEREDITY HERSEY AND CHASE EXPERIMENT

Hersey and Chase worked with bacteriophage because it is analog of chromosome

The Hershey-Chase Experiment – Bacteriophage 1. Hershey and Chase forced one population of phages to synthesize DNA using radioactive phosphorous. 2. The radioactive phosphorous "labeled" the DNA. 3. They forced another group of phages to synthesize protein using radioactive sulfur. 4. The radioactive sulfur "labeled" the protein. 5. Bacteria infected by phages containing radioactive protein did not show any radioactivity. 6. Bacteria infected by phages containing radioactive DNA became radioactive. 7. This showed that it was the DNA, not the protein, that was the molecule of heredity.

DNA REPLICATION Three possible mechanisms of DNA replication

a)Semiconservative replication: The two parental strands seperate, each forms a template for new strand. b)Conservative replication: Each of the two strands of parent DNA is replicated, without strand seperation. c) Dispersive replication: During replication, parent chains break at intervals, and replicated segments are combined into strands with segments from parent chains. All daughter helixes are part old, part new.

DNA REPLICATION DNA is labelled with 15 N isotope Normal or 14 N compound medium F1 generation 100% hybrid DNA 15 Normal or 14 N compound medium % hybrid DNA 15 N - 14 N 50% normal DNA 14 N - 14 N F2 generation

If normal DNA is given; 2 n 2 hybrid and 2 pure heavy DNA are formed If hybrid DNA is given; 2 n one of the DNA is always hybrid the others are pure DNA REPLICATION Replication number

DNA REPLICATION MECHANISM

DNA REPLICATION Replication occurs in three stages: 1. UNWINDING: Helicase enzymes seperate the parental double helix by breaking down the H bonds, forming the replication fork. Replication fork

2. CONTINUOUS SYNTHESIS: The “leading strand” is assembled continuously in the 5' to 3' direction by DNA polymerase, using the single parental strand as a template, it adds nucleotides to the growing 3' end DNA REPLICATION

C A T G 5'5' 5'5' 5'5' 3'3' 3'3' Replication is continuous DNA polymerase can work only in the 5' - 3' direction 3'3' 5'5' 5'5' 5'5' 3'3' 3'3' 3'3' With okazaki fragments replication is discontinuous DNA ligase links the okazaki fragments which are nucleotide long fragments in prokaryotes and nucleotide long in eukaryotes

3. DISCONTINUOUS SYNTHESIS: The “lagging strand” is assembled discontinuously. It is produced as a series of short segments ( Okazaki fragments), each of which is synthesized in the 5' to 3' direction by DNA polymerase, using the single parental strand as a template DNA REPLICATION

OKAZAKI FRAGMENTS In bacteria, the Okazaki fragments are each nucleotides long In eukaryotes, they are 100 to 300 nucleotides length Finally, the fragments are joined to the 5' end of the growing chain by a DNA ligase enzyme