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Nucleic Acids: DNA and RNA
Principles of Biochemistry (BCH 3000) Nucleic Acids: DNA and RNA Dr. Syahida Ahmad Department of Biochemistry Faculty of Biotechnology & Biomolecular Sciences UPM
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Introduction Nucleic acids play main roles in the storage, transfer and expression of genetic information 2 types Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA Primarily found in chromosome in the cell’s nucleus, some in mitochondria and chloroplast Repository of genetic information RNA 3 types: ribosomal, messenger and transfer Flow of biological information DNA RNA Proteins Cell structure and function
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Components of Nucleotides
Nucleic acids are linear polymers built from four different monomers called nucleotides Nucleotides has three chemical parts Heterocyclic compound containing C, H, N and some O (Nitrogenous bases) 5-C carbohydrate (aldopentose) One, two or three phosphate groups
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Nitrogenous bases of DNA and RNA
Purine and pyrimidine Purine DNA: Adenine (A) and Guanine (G) RNA: Adenine (A) and Guanine (G) Pyrimidine DNA: Thymine (T) and Cytosine (C) RNA: Cytosine (C) and Uracil (U)
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Aldopentoses of Nucleic Acids
Two types of aldopentoses are found in the nucleic acids D-Ribose in RNA 2-D-deoxyribose in DNA The difference are 2'-OH (RNA) and 2'-H (DNA) affects secondary structure and stability Sugars make nucleosides more water-soluble
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Nucleosides The linking of a nitrogenous base to an aldopentose through N-glycosidic linkages results in a nucleoside Named bases by adding -idine to the root name of a pyrimidine or osine to the root name of a purine Pyrimidine - Cytidine and Uridine Purine – Adenosine and Guanosine Synthetic nucleosides used for treatment of certain diseases E.g. 3’-azidodeoxythymidine (AZT) and 2’,3’-dideoxyinosine (DDI) for treating AIDS patients
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Drugs for treating AIDS
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Nucleotides Forms when a phosphoryl group (-PO2-3) is linked to a carbohydrate -OH group on the nucleoside Common ester linkage is the –OH group on C-5’ of the pentoses Adenosine 5’-monophosphate (5’-AMP) – one phosphate Adenosine 5’-diphosphate (5’-ADP) – two phosphate Adenosine 5’-triphosphate (5’-ATP) – three phosphate Central to energy metabolism Other nucleoside triphosphates Guanosine triphosphate (GTP) – drives protein synthesis Uridine triphosphate (UTP) – drives carbohydrates metabolism Cytosine triphosphate (CTP) – drives lipid synthesis
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Nucleic Acids DNA and RNA
Forms when nucleotides are linked together through their phosphate groups 5’-phosphate group of one nucleotide is linked to the 3’-OH group of the next nucleotide 3’,5’-phosphodiester bond Sequence is always read 5' to 3' Backbone of DNA (and RNA) consists deoxyriboses (or riboses) and phosphate groups
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DNA Consists of two polynucleotides strands folded into a double helix (double stranded) Stabilized by H bonds - Base pairs arise from H bonds Nucleotides contain a phosphate, a 2-Deoxyribose sugar, and one nitrogen base (A,T,C, or G) The secondary structure (3D) was elucidated by Watson and Crick in 1953 Complementary base pairing Guanine with Cytosine (G-C) Adenine with Thymine (A-T) Contain sugar 2-deoxyribose Make up chromosomes in the nucleus DNA, lacking 2'-OH is more stable than RNA This makes sense - the genetic material must be more stable RNA is designed to be used and then broken down
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RNA Single stranded (a template copy) Complementary base pairing
Guanine with Cytosine (G-C) Adenine with Uracil (A-U) Contain sugar Ribose Three types of RNA Ribosomal RNA (rRNA) - the basis of structure and function of ribosomes Messenger RNA (mRNA) - carries the message Transfer RNA (tRNA) - carries the amino acids
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DNA & RNA Differences? Nucleotides strands
DNA: double stranded (double helix) RNA: single stranded Complementary base pairing DNA: A-T, G-C RNA: A-U, G-C Sugar DNA: 2-D-deoxyribose RNA: D-Ribose Classes of Nucleic Acids DNA - one type RNA – rRNA, mRNA and tRNA
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Amino Acids 20 amino acids are exist in nature
Linked together in a process called protein synthesis in the cytoplasm to make polypeptides (subunits of proteins) DNA contains the instructions for making proteins but is too large to leave the nucleus mRNA codon table tells what 3 bases on mRNA code for each amino acid (64 combinations of 3 bases) Methionine (AUG) on mRNA is called the start codon because it triggers the linking of amino acids UAA, UGA, & UAG on mRNA signal ribosomes to stop linking amino acids together
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Genetic Code (RNA) Amino Acid 3 Letter Abbreviation Codons Alanine Ala
GCA GCC GCG GCU Arginine Arg AGA AGG CGA CGC CGG CGU Aspartic Acid Asp GAC GAU Asparagine Asn AAC AAU Cysteine Cys UGC UGU Glutamic Acid Glu GAA GAG Glutamine Gln CAA CAG Glycine Gly GGA GGC GGG GGU Histidine His CAC CAU Isoleucine Ile AUA AUC AUU Leucine Leu UUA UUG CUA CUC CUG CUU Lysine Lys AAA AAG Methionine Met AUG Phenylalanine Phe UUC UUU Proline Pro CCA CCC CCG CCU Serine Ser AGC AGU UCA UCC UCG UCU Threonine Thr ACA ACC ACG ACU Tryptophan Trp UGG Tyrosine Tyr UAC UAU Valine Val GUA GUC GUG GUU Start Stop UAA UAG UGA
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