Nucleic Acids DNA RNA 1 Nucleic acids A

Nucleic Acids • DNA • RNA 1

Nucleic acids • A Nucleic acid is a polymer of 4 nucleotides • Linked by alternating sugar-phosphate bonds. 2

Structure of Nucleic Acids base P sugar nucleotide base P sugar nucleotide 3

General characteristics of Nucleic Acids 1 - They (all) have 2 distinctive ends: a- the 5’ (5 prime) & b- the 3’ (3 prime). These refer to the carbons on the sugar. 2 - For both DNA & RNA, the 5’ end bears a phosphate & the 3’ end a hydroxyl group. 4

General characteristics of Nucleic Acids cont. • 3 - Nucleic acids are synthesized in a 5’ to 3’ direction i. e. from 5 to 3. (base sequence). • 4 - In a nucleic acid chain, 2 nucleotides are linked by a phosphodiester bond. • 5 - The precursor of the whole nucleic acid chain is either RNA Polymerase or DNA Polymerase. 5

General characteristics of Nucleic Acids cont. • 6 - A nucleic acid chain is called a strand. • 7 - DNA molecule contains 2 strands, whereas RNA contains 1 strand. • 8 - The number of bases in a nucleic acid, determine the length of the nucleic acid. 6

Deoxyribonucleic acid (DNA) • DNA contains two strands of nucleotides, arranged in a double helix form. • A helix structure is like a spiral stair case. • The 2 helices are held together by hydrogen bonds. • Bases are always paired as A–T and G-C • Thus the bases along one strand complement the bases along the other. 7

DNA Structure • • (A) with (T) (G) with(C). • (A) and (T) are connected by two H bonds • A ==== T • (G) and (C) are connected by three. • G C 8

DNA Replication • DNA in the chromosomes replicates itself every cell division • Maintains correct genetic information • Two strands of DNA unwind • Each strand acts like a template • New bases, pair with their complementary base. • Two double helices form, that are copies of original DNA 9

DNA Unwinds G-C A-T C-G T-A GACT- -C -T -G -A 10

DNA Copied with Base Pairs Two copies of original DNA strand G-C A-T C-G T-A G-C A-T 11

Ribonucleic acid RNA Is a chemical found in the nucleus and cytoplasm of cells. It plays an important role in protein synthesis and other chemical activities in the cell. There are several classes of RNA: A- Messenger RNA (m RNA) b- Transfer RNA (t RNA) C- Ribosomal RNA ( r RNA) Other small RNAs. 12

Ribonucleic acid RNA Cont. • Other classes of RNAs include: • - Ribozymes. - 85 – 90% of RNA are r RNA. - They are the major components of ribosomes together with proteins. - All classes of RNA cooperate in protein synthesis. 13

Structure of RNA • RNA are single stranded. • RNA contains ribose as sugar & and uracil as a base (instead of thymine in DNA). • They may form secondary structures such as a stem loop, a bulge or a hairpin. 14

A- hairpin B- bulge C- loop 15

Comparison between DNA & RNA Similarities: 1 - Both DNA & RNA have a sugar – phosphate backbone. 2 - Both contain the bases adenine (A), cytosine (C) & guanine (G). 16

Comparison between DNA & RNA Cont. Differences: • 1 - The sugar of DNA is deoxyribose & that of RNA is ribose. • 2 - Instead of the base Thymine, RNA has Uracil. • 3 - DNA strands form double helix, while RNA strand is single forming stem loop, bulging or hair pin shape. • DNA is found in nucleus, RNA is found in various parts of the cell including nucleus & cytoplasm 17

General properties DNA & RNA • 4 - RNA serves as a genetic messenger relaying the information stored in DNA out of the nucleous to help in protein synthesis. • 5 - In viruses RNA is the main genetic material. • 6 - DNA (high molecular weight) is found in the nuclei of complex cells known as eukaryotes, or in the nucloids of prokaryotes such as bacteria. 18

General properties DNA & RNA Cont. • 7 - RNA (lower molecular weight), is more aboundant and distributed throughout the cell, most commonly in ribosomes. 8 - RNA = Plays a vital role in transfer of information (transcription) from DNA, to the ribosomes (protein factory)& in Interpretation of that information (translation) for specific protein synthesis. 19

Denaturation & annealing of DNA. • If a solution of DNA is heated, the strands separate or denature (Denaturation). • Upon cooling, these strands rejoin i. e. renature (Annealing). 20