Chapter 12 Nucleic Acids. A. Nucleic Acids Macromolecules composed of subunits called nucleotides ...

of 28 /28
Chapter 12 Nucleic Acids

Embed Size (px)

Transcript of Chapter 12 Nucleic Acids. A. Nucleic Acids Macromolecules composed of subunits called nucleotides ...

Slide 1

Chapter 12Nucleic AcidsA. Nucleic AcidsMacromolecules composed of subunits called nucleotidespolymers made of monomersNucleotides:building blocks for DNA (deoxyribonucleic acid) & RNA (ribonucleic acid)

Cont. NucleotidesBased on sugar (2 general types of nucleotides)a. Ribotides ribose nucleotidesb. Deoxyribotides deoxyribose nucleotides

Cont. NucleotidesNucleotides composed of 3 subunits: a. Pentose sugar (C5) RNA: ribose (R) DNA: deoxyribose (D)

Cont. Nucleotidesb. Phosphate group (H2PO3)Derived from phosphoric acid (H2PO3 - inorganic compound)c. Nitrogen baseDNA: adenine (A) , cytosine (C), guanine (G), thymine (T)RNA: adenine, cytosine, guanine, uracil (U)

c. Nitrogen bases are 1 of 2 types: Pyrimidine- C, T, U (consist of single-ring) Purines- A, G (consist of double-ring)

CytosineAdenineThymineUracilGuanineB. Ribose and DNA Nucleotides

*** NOTE: Uracil only in ribose series; thymine only in deoxyribose series!!!

RNA NucleotidesDNA NucleotidesAdenine ribose O PAdenine deoxyribose O PCytosine ribose O PCytosine deoxyribose O PGuanine ribose O PGuanine deoxyribose O PUracil ribose O -- PThymine deoyxyribose O -- PC. Nucleotides can be synthesized into:1. Energy carriers ATP, CTP, GTP, TTP, UTP2. Coenzymes (carry H2)FMN (Flavin Mononucleotide)FAD (Flavin Adenine Dinucleotide)NAD (Nicotinamide Adenine Diphosphate) NADP (Nicotinamide Adenine Dinucleotide Phosphate)3. Genetic Systems polymers called DNA & RNA

DNA Nucleotides

A-T or A-U(2 H-bonds)G-C(3 H-bonds)D. DNA (Watson-Crick Model); proposed 19531. Genetic material composed of 2 long chains of nucleotides2. A=T ; C=G (*base pairs rule pyrimidine always pairs with purine3. 2 chains run in opposite directions, connected by nitrogen bases to form double helix. 4. Hydrogen bonds between bases

Cont. DNA (Watson-Crick Model)5. DNA forms genes genetic information that passes from parent to offspring

E. RNA (essential to protein synthesis)1. Contains ribose instead of deoxyribose2. Contains uracil instead of thymine3. Nucleotides in long chains, in single strands unless RNA is the only nucleic present in the organism4. THREE types of RNA:a. messenger RNA (mRNA)b. transfer RNA(tRNA) Essential in protein synthesis!c. ribosomal RNA (rRNA)

RNA vs DNA

Chapter 12: DNA Replication***RECAP: DNA replication occurs in S phase of cell cycle

A. DNA Structure1. Double-stranded polymer composed of paired nucleotides2. Because A combines with T, C with G, SEQUENCE of bases varies to produce different genes3. Once nucleotide sequence is fixed, sequence in other strand is also determinedB. DNA Replication (S phase)1. Requires a team of enzymes (DNA polymerase)2. Steps in replication:a. One enzyme unwinds portion of DNAb. Another enzyme breaks H-bonds between paired nucleotides and separates strandsc. New nucleotides are added to each original strand in proper direction according to original strandd. Phospates of new nucleotides bond to sugarse. New strand attached to original

DNA Replication

Cont. DNA Replication3. Semiconservative Replication (validated!) each new DNA molecule contains of original

Cont. DNA Replication4. Conservative Replication (negated) one DNA molecule = 2 old strands one DNA molecule = 2 new strands5. Each new cell formed after M phase (mitosis) in cell cycle contains same set of chromosomes & genes as parent cell (each DNA old, new)

C. Replication Forks1. DNA is a giant molecule!2. If replication began at one end, process would take TOO LONG!3. Replication forks multiple sites of DNA replicationCont. Replication Fork4. Replication different along each strand (done by DNA POLYMERASE!)a. Leading strand synthesis continues in ONE direction Nucleotides added one at a time- in orderb. Lagging strand short, discontinuous segments of DNA synthesizedSegments then joined by DNA ligases5. Result: Synthesis of 2 new DNA molecules behind the replication fork as it moves along original DNA molecule

Chemical Evidence for Watson-Crick Model

CELL TYPEA (%)G (%)C (%)T (%)Human30.419.619.930.1Ox29.021.221.228.7Salmon sperm29.720.820.429.1Wheat germ28.121.822.727.4E coli26.024.925.225.9Sea urchin32.817.717.332.1Erwin Chargaff- analyzed nuclei of different cell types

*** SIGNIFICANCE: The concentration of specific bases (A & T)/ (C & G) approached a 1:1 ratio (A=T) and (C=G)

Upon analysis of many tissues from many different species, Chargaff concluded that the amounts of A & T and C & G were ALMOST EXACTLY EQUAL!Cont. Watson-Crick Model2. Watson and Crick reasoned that these the 1:1 ratio was due to PAIR BONDING between the 2 bases that were equal (A-T) and (C-G)3. Watson and Crick reasoned that these specific bases would bond according to SIZE always 1 pyrimidine paired with 1 purineSize of these base pairings was proven experimentally by the x-ray diffraction work of Wilkins and Franklin

4. Watson and Crick used the 1:1 ratio of A-T and C-G to propose a mechanism of replication or making an exact copy of itselfProposed in 1953 that the method of replication of DNA would be SEMI-CONSERVATIVEEach new strand molecule retains of the original DNA molecule

Cont. Watson-Crick Model5. Watson-Crick Model for the structure of DNA in 1953 revolutionized Biology a. Nature of the geneb. Explanation of mutationsc. Variations w/in species sequence of nucleotides make specific types of genesd. Cell division and reproductione. Abnormal cell division cancer

Meselson- Stahl confirmed semi-conservative replication

1928- Griffiths Transformation

Avery, MacLeod, McCarty 1944- DNA was transforming agent

1952- Chase & Hersheys Experiment