Unit  Nucleic acids CHEM 203 Biochemistry 9/15/20141Ola Fouad Talkhan

Nucleoproteins : are conjugated proteins formed of: a) basic protein (histone or protamine) and b) nucleic acid as prothetic group. They are very complex high molecular weight proteins present in every cell. Functions of nucleic acids 1-In cell nuclei they form the chromosomes which are responsible for cell division and carries of hereditary factors known as (genes). 2-In cytoplasm are associated with ribosome, the center of protein biosynthesis in every cell. 9/15/20142Ola Fouad Talkhan

Nucleoprotein hydrolysis Protein Histone or protamin (one or more molecules) Nucleic acids  Nucleic acids is composed of large number of nucleotides, which considered as basal structural component of nucleic acids.  There are two types of nucleic acid Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) Nucleic acid can be easily separated from nucleoprotein by addition of acids or alkalis. 9/15/20143Ola Fouad Talkhan

Nucleoproteins Protein Histone or protamin Nucleic acid (Polynucleotide) Large number of mononucleotides Phosphoric acid Sugar Ribose Deoxyribose Nitrogenous base Nucleoside Purin base Pyrimidine base 9/15/20144Ola Fouad Talkhan

Nucleotides Nucleic acids consist of nucleotides that have a nitrogen base, Pentose sugar, and phosphate 5 NUCLEIC ACID STRUCTURE Nucleic acids are polynucleotides Their building blocks are nucleotides 9/15/2014Ola Fouad Talkhan

6 Nitrogenous Bases The nitrogen bases in nucleic acids are: Pyrimidine bases: Cytosine Thymine Uracil purine bases: Adenine Guanine 9/15/2014Ola Fouad Talkhan

7 Pentose Sugars The pentose (five-carbon) sugar: In RNA is ribose. In DNA is deoxyribose. Has carbon atoms numbered with primes to distinguish them from the nitrogen bases. 9/15/2014Ola Fouad Talkhan

8 HO A nucleoside: Has a nitrogen base linked by a glycosidic bond to C1’ of a ribose or deoxyribose. Is named by changing the the nitrogen base ending to -osine for purines and –idine for pyrimidines  Nucleosides 9/15/2014Ola Fouad Talkhan

9 A nucleotide: Is a nucleoside that forms a phosphate ester with the C5’ OH group of ribose or deoxyribose. Is named using the name of the nucleoside followed by 5’-monophosphate.  In a nucleoside,the glycosidic C-1 atom of the pentose bonded to N-1 of the pyrimidine or N-9 of the purine base Nucleotides 9/15/2014Ola Fouad Talkhan

Nitrogenous bases + ribose = Nucleosides Nucleoside + Phosphate group = Nuclotides 9/15/201410Ola Fouad Talkhan

11 Names of Nucleosides and Nucleotides 9/15/2014Ola Fouad Talkhan

12 Primary Structure of Nucleic Acids In the primary structure of nucleic acids: Nucleotides are joined by phosphodiester bonds. The 3’-OH group of the sugar in one nucleotide forms an ester bond to the phosphate group on the 5’-carbon of the sugar of the next nucleotide. 9/15/2014Ola Fouad Talkhan

13 Primary Structure of Nucleic Acids 9/15/2014Ola Fouad Talkhan

14 A nucleic acid polymer: Has a free 5’-phosphate group at one end and a free 3’-OH group at the other end. Is read from the free 5’-end using the letters of the bases. This example reads 5’—A—C—G—T—3’. Structure of Nucleic Acids 9/15/2014Ola Fouad Talkhan

15 RNA In RNA, A, C, G, and U are linked by 3’-5’ ester bonds between ribose and phosphate. 9/15/2014Ola Fouad Talkhan

Types of RNA 9/15/201416Ola Fouad Talkhan

17 DNA In DNA, A, C, G, and T are linked by 3’-5’ ester bonds between deoxyribose and phosphate. 9/15/2014Ola Fouad Talkhan

18 DNA Double Helix: A Secondary Structure In DNA: There are two strands of nucleotides that wind together in a double helix. Two hydrogen bonds form between the complementary base pairs A-T. Three hydrogen bonds form between the complementary base pairs G-C. 9/15/2014Ola Fouad Talkhan

The negatively charged phosphate group and the sugar units expose themselves to the outside of the chain. 9/15/201419Ola Fouad Talkhan

20 DNA Double Helix Structure 9/15/2014Ola Fouad Talkhan

The antiparallel nature of the DNA double helix. 9/15/201421Ola Fouad Talkhan

The DNA Double Helix The double helix is stabilized by hydrogen bonds and hydrophobic interactions Watson and Crick were Proposed a structure of DNA double helix 9/15/201422Ola Fouad Talkhan

1.Two helical polynucleotide chains are coiled around a common axis. The chains run in opposite directions, (anti parallel). 2. The two antiparallel polynucleotide chains are not identical, but they are complimentary. 3. The purine, pyrimidine bases are on the inside of the helix, the phosphate and deoxyribose groups are on the outside. 4. The two chains are held together by hydrogen bonds between pairs of bases. Adenine is two hydrogen bonds (A= T), Guanine is bonded to cytosine by three hydrogen bonds (G=C) 9/15/201423Ola Fouad Talkhan

Comparison between DNA and RNA DNARNA Nitrogen bases a-Purines b- Pyrimidines Adenine &Guanine Cytosine& Thymine Adenine &Guanine Cytosine& Uracil Sugar2-Deoxy riboseRibose Shape of strandDouble helixSingle strand SiteNucleus and Mitochondria Mainly in cytosol, less commonly in nucleus and mitochondria Functions Genetic information and synthesis of mRNA Protein synthesis Reaction with dil. acidsdepurinated by dilute acid.resistant to dilute acid Reaction with dil. basenot susceptible to basehydrolyzed by dilute base. DNA - one type, one purpose. RNA - Several types, several purposes: ribosomal RNA - the basis of structure and function of ribosomes (largest amount). messenger RNA - carries the message for protein synthesis (fewest and unique). transfer RNA - carries the amino acids for protein synthesis (smallest molecules). 9/15/201424Ola Fouad Talkhan

25 DNA replication involves: Unwinding the DNA Pairing the bases in each strand with new bases to form new complementary strands. Producing two new DNA strands that exactly duplicate the original DNA. DNA Replication The duplication of DNA to give two DNA molecules identical to the original one. DNA in the chromosomes replicates itself every cell division Maintains correct genetic information 9/15/2014Ola Fouad Talkhan

Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides. Primase is the enzyme that synthesizes the RNA Primer. DNA polymerase can then add the new nucleotides 26 DNA polymerase can only add nucleotides to the 3’ end of the DNA. This causes the NEW strand to be built in a 5’ to 3’ direction 9/15/2014Ola Fouad Talkhan

DNA Replication - General considerations A. Function of replication. 1.Proteins must have the correct shape. 2.The shape is determined by the primary structure (amino acid sequence. 3.The amino acid sequence is determined by the gene (the sequence of bases in the DNA). Base Pairing & Double Helix Replicating DNA 9/15/201427Ola Fouad Talkhan

Information Transfer in Cells Figure 10.1 The fundamental process of information transfer in cells. 9/15/201428Ola Fouad Talkhan

Transcription Process of copying DNA to mRNA Differs from DNA synthesis in that only one strand of DNA, the template strand, is used to make mRNA Does not need a primer to start as RNA polymerases have ability to initiate synthesis de novo Can involve multiple RNA polymerases Divided into 3 stages Initiation Elongation Termination 299/15/2014Ola Fouad Talkhan

30 In transcription: A section of DNA containing the gene unwinds. One strand of DNA is copied starting at the initiation point, which has the sequence TATAAA. An mRNA is synthesized using complementary base pairing with uracil (U) replacing thymine (T). The newly formed mRNA moves out of the nucleus to ribosomes in the cytoplasm. Transcription: Synthesis of mRNA 9/15/2014Ola Fouad Talkhan

31 RNA Polymerase During transcription, RNA polymerase moves along the DNA template in the 3’-5’direction to synthesize the corresponding mRNA. The mRNA is released at the termination point. 9/15/2014Ola Fouad Talkhan

Interpreting the information coded in the mRNA into proteins The nucleotides are read in triplets (set of three) called codons Each triplet code for a specific amino acid, and sometimes more than one codon exist for an amino acid mRNA are read by the translational machinery including ribosomes, tRNAs and rRNAs Like transcription, it also includes initiation, elongation and termination 32 Translation 9/15/2014Ola Fouad Talkhan

Translation 339/15/2014Ola Fouad Talkhan

DNA Replication - General considerations A. Function of replication. 1.Proteins must have the correct shape. 2.The shape is determined by the primary structure (amino acid sequence. 3.The amino acid sequence is determined by the gene (the sequence of bases in the DNA). The flow of genetic information in the cell. DNA  RNA  protein 9/15/201434Ola Fouad Talkhan

Mutation A change or alteration that occurs in the DNA. Mutations can be caused by the environment (sun, radiation, or chemicals), aging, or chance. Some mutations do not affect the information contained in the DNA. Other mutations have serious consequences on how that gene functions. 9/15/201435Ola Fouad Talkhan