Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 2 Ribose & deoxyribose 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 4 5 The bases The most common organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G) 6 Nucleotides The ribose, the phosphate and one of the bases Combine to form a nucleotide PO4 bases ribose Heterocycles in DNA and RNA Adenine, guanine, cytosine and thymine are in DNA RNA contains uracil rather than thymine 6 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) 7 Nucleosides in DNA Base Adenine (A) Guanine (G) Cytosine (C) Thymine (T) Sugar Deoxyribose Deoxyribose Deoxyribose Deoxyribose Nucleoside Adenosine Guanosine Cytidine Thymidine 8 Nucleosides in RNA Base Adenine (A) Guanine (G) Cytosine (C) Uracil (U) Sugar ribose ribose ribose ribose Nucleoside Adenosine Guanosine Cytidine Uridine 9 Nucleotides Nucleic acids consist of nucleotides that have a sugar, nitrogen base, and phosphate Base PO4 Sugar nucleoside 10 Example of a Nucleoside NH2 N O O- O P O CH2 - N O O OH deoxyctyidine monophosphate (dCMP) 11 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) 12 13 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). 14 Nucleotides in DNA and RNA DNA dAMP dGMP dCMP dTMP RNA AMP GMP CMP UMP Deoxyadenosine monophosphate Deoxyguanosine monophosphate Deoxycytidine monophosphate Deoxythymidine monophosphate adenosine monophosphate guanosine monophosphate cytidine monophosphate uridine monophosphate 15 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 base P sugar base P nucleotide sugar base P sugar base P sugar nucleotide nucleotide nucleotide 16 Nucleic Acid Structure NH2 N CMP O O O- P O CH2 - O N O 3 NH2 3,5-phosphodiester bond OH O 5 O P O CH2 - N N N O N AMP O OH 17 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 18 2 DNA 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 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 3 6 Nucleotides PO4 adenine or deoxyribose Thymine (T) Cytosine (C) Guanine (G) Joined nucleotides 7 PO4 PO4 PO4 PO4 sugar-phosphate + bases backbone 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 24 Complementary Base Pairs •Two H bonds for A-T •Three H bonds for G-C 25 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 26 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 27 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 28 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 29 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 30 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 31 The Structure of tRNA 32 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, 33 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) 34 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 35