Nucleic Acids

Nucleic acids DNA and RNA are chemical carriers of a cell’s genetic information Coded in a cell’s DNA is the information that determines the nature of the cell, controls cell growth, division Nucleic acid derivatives are involved as phosphorylating agents in biochemical pathways

Ribose is a sugar, like glucose, but with only five Ribose & deoxyribose 4 Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule Deoxyribose is almost the same but lacks one oxygen atom Both molecules may be represented by the symbol

5 The bases The most common organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Combine to form a nucleotide Nucleotides 6 The ribose, the phosphate and one of the bases Combine to form a nucleotide bases ribose PO4 It is the phosphate group which gives DNA its acidic properties

Heterocycles in DNA and RNA Adenine, guanine, cytosine and thymine are in DNA RNA contains uracil rather than thymine

Nucleotides and Nucleic Acids Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are the chemical carriers of genetic information Nucleic acids are biopolymers made of nucleotides, aldopentoses linked to a purine or pyrimidine and a phosphate RNA is derived from ribose DNA is from 2-deoxyribose (the ' is used to refer to positions on the sugar portion of a nucleotide)

Nucleosides in DNA Base Sugar Nucleoside Adenine (A) Deoxyribose Adenosine Guanine (G) Deoxyribose Guanosine Cytosine (C) Deoxyribose Cytidine Thymine (T) Deoxyribose Thymidine

Nucleosides in RNA Base Sugar Nucleoside Adenine (A) ribose Adenosine Guanine (G) ribose Guanosine Cytosine (C) ribose Cytidine Uracil (U) ribose Uridine

Nucleotides Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate nucleoside Base PO4 Sugar

Example of a Nucleoside

Nucleotides In DNA and RNA the heterocycle is bonded to C1 of the sugar and the phosphate is bonded to C5 (and connected to 3’ of the next unit)

Nucleotides join together in DNA and RNA by as phosphate between the 5’-on one nucleotide and the 3 on another One end of the nucleic acid polymer has a free hydroxyl at C3 (the 3 end), and the other end has a phosphate at C5 (the 5 end).

Nucleotides in DNA and RNA dAMP Deoxyadenosine monophosphate dGMP Deoxyguanosine monophosphate dCMP Deoxycytidine monophosphate dTMP Deoxythymidine monophosphate RNA AMP adenosine monophosphate GMP guanosine monophosphate CMP cytidine monophosphate UMP uridine monophosphate

Structure of Nucleic Acids Polymers of four nucleotides Linked by alternating sugar-phosphate bonds RNA: ribose and A, G, C, U DNA: deoxyribose and A,G,C,T nucleotide nucleotide nucleotide nucleotide base base base base sugar sugar P sugar P sugar P P

Nucleic Acid Structure 3,5-phosphodiester bond 3 5

Base Pairing in DNA: The Watson–Crick Model In 1953 Watson and Crick noted that DNA consists of two polynucleotide strands, running in opposite directions and coiled around each other in a double helix Strands are held together by hydrogen bonds between specific pairs of bases Adenine (A) and thymine (T) form strong hydrogen bonds to each other but not to C or G Guanine (G) and cytosine (C) form strong hydrogen bonds to each other but not to A or T

DNA stands for deoxyribose nucleic acid 2 DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA controls all the chemical changes which take place in cells The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA

3 DNA molecule DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of a sugar called deoxyribose a phosphate group -PO4 and an organic base

or adenine deoxyribose 6 Nucleotides PO4 Thymine (T) Cytosine (C) It is the phosphate group which gives DNA its acidic properties Guanine (G)

Joined nucleotides 7 sugar-phosphate + bases backbone PO4 A molecule of DNA is formed by millions of nucleotides joined together in a long chain

8 In fact, the DNA usually consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases

Hydrogen Bonds in DNA The G-C base pair involves three H-bonds The A-T base pair involves two H-bonds

Complementary Base Pairs Two H bonds for A-T Three H bonds for G-C

Replication of DNA Begins with a partial unwinding of the double helix, exposing the recognition site on the bases Activated forms of the complementary nucleotides (A with T and G with C) associate two new strands begin to grow

The Replication Process Addition takes place 5  3, catalyzed by DNA polymerase Each nucleotide is joined as a 5-nucleoside triphosphate that adds a nucleotide to the free 3-hydroxyl group of the growing chain

Transcription of DNA RNA contains ribose rather than deoxyribose and uracil rather than thymine There are three major kinds of RNA - each of which serves a specific function They are much smaller molecules than DNA and are usually single-stranded

Messenger RNA (mRNA) Its sequence is copied from genetic DNA It travels to ribsosomes, small granular particles in the cytoplasm of a cell where protein synthesis takes place

Ribosomal RNA (rRNA) Ribosomes are a complex of proteins and rRNA The synthesis of proteins from amino acids and ATP occurs in the ribosome The rRNA provides both structure and catalysis

Transfer RNA (tRNA) Transports amino acids to the ribosomes where they are joined together to make proteins There is a specific tRNA for each amino acid Recognition of the tRNA at the anti-codon communicates which amino acid is attached

The Structure of tRNA

Transcription Process Several turns of the DNA double helix unwind, exposing the bases of the two strands Ribonucleotides line up in the proper order by hydrogen bonding to their complementary bases on DNA Bonds form in the 5  3 direction,

Transcription of RNA from DNA Only one of the two DNA strands is transcribed into mRNA The strand that contains the gene is the coding or sense strand The strand that gets transcribed is the template or antisense strand The RNA molecule produced during transcription is a copy of the coding strand (with U in place of T)

Mechanism of Transcription DNA contains promoter sites that are 10 to 35 base pairs upstream from the beginning of the coding region and signal the beginning of a gene There are other base sequences near the end of the gene that signal a stop Genes are not necessarily continuous, beginning gene in a section of DNA (an exon) and then resume farther down the chain in another exon, with an intron between that is removed from the mRNA