Nucleic Acids Ch 12

Macromolecules n Macromolecules –“giant molecules” –Formed when monomers join together to form polymers Monomer = molecules, sm. Unit that can join to form polymers Polymer = multiple monomers (large molecules) –There are 4 types of macromolecules Carbohydrates, lipids, nucleic acids (we will be talking about these today), and proteins

Monomers vs. Polymers n Think of monomers like blocks. Each monomer is one block. –How many monomers are in this picture? n A polymer is what you build from those monomers. They are linked together by bonds.

Nucleic Acids  Contain H, O, N, C, and P  Polymers made from monomers known as nucleotides  Consist of: a nitrogenous base ( there are 4), a phosphate group, and a 5-carbon sugar (ribose and deoxyribose)  Nucleotides join by covalent bonds (sharing of e-) to form a nucleic acid  These nucleotides form to create DNA or RNA

Nucleic Acids are complex macromolecules composed of nucleotides that store and transmit genetic information.

Searching for Genetic Material n Mendel: modes of heredity in pea plants n Morgan: genes located on chromosomes n Griffith: bacterial work; transformation: change in genotype and phenotype due to assimilation of external substance (DNA) by a cell n Avery: transformation agent was DNA

Searching for Genetic Material n Hershey and Chase √ bacteriophages (phages) √ DNA, not protein, is the hereditary material √ Expt: sulfur(S) is in protein, phosphorus (P) is in DNA; only P was found in host cell

DNA Structure n Chargaff ratio of nucleotide bases (A=T; C=G) n Watson & Crick (Wilkins, Franklin) n The Double Helix (sometimes called a twisted ladder) n nucleotides: nitrogenous base (thymine, adenine, cytosine, guanine); sugar deoxyribose; phosphate group

Nucleotides are composed of: 1.A sugar 2.A phosphate group 3.A nitrogenous base

Types of Nucleic Acids n DNA (Deoxyribose Nucleic Acid) n RNA (Ribose Nucleic Acid)

DNA Structure

DNA Bonding n Purines: ‘A’ & ‘G’ n Pyrimidines: ‘C’ & ‘T’ (Chargaff rules) n ‘A’ H+ bonds (2) with ‘T’ n ‘C’ H+ bonds (3) with ‘G’ n Notice the number of H-bonds between G-C and A-T. What do you think this means?

DNA Replication n Watson & Crick strands are complementary; nucleotides line up on template according to base pair rules (Watson) n Meselson & Stahl replication is semiconservative; Expt: varying densities of radioactive nitrogen

DNA Replication: a closer look n Origin of replication (“bubbles”): beginning of replication n Replication fork: ‘Y’-shaped region where new strands of DNA are elongating n Helicase:catalyzes the untwisting of the DNA at the replication fork n DNA polymerase:catalyzes the elongation of new DNA

DNA Replication n Antiparallel nature: sugar/phosphate backbone runs in opposite directions (Crick); one strand runs 5’ to 3’, while the other runs 3’ to 5’; DNA polymerase only adds nucleotides at the free 3’ end, forming new DNA strands in the 5’ to 3’ direction only

DNA Replication n Leading strand: synthesis toward the replication fork (only in a 5’ to 3’ direction from the 3’ to 5’ master strand) n Lagging strand: synthesis away from the replication fork (Okazaki fragments); joined by DNA ligase (must wait for 3’ end to open; again in a 5’ to 3’ direction) n Initiation: Primer (short RNA sequence~w/primase enzyme), begins the replication process

DNA Replication: the leading and lagging strands

DNA Repair n Mismatch repair: DNA polymerase n Excision repair: Nuclease n Telomere ends: telomerase

RNA n A messenger between DNA and ribosomes n “Decodes” the genetic message contained in the DNA molecule

3 Types of RNA: n Messenger RNA (mRNA) - copies information from DNA and carries it to the ribosomes in the cytoplasm n Ribosomal RNA (rRNA) - makes up the major part of the ribosomes n Transfer RNA (tRNA) - carries amino acids to the ribosomes where the amino acids are joined to form a polypeptide

Transcription n Information in a DNA molecule is transferred to an mRNA molecule (DNA  RNA). n Guanine pairs with Cytosine n Adenine pairs with Uracil n Thymine pairs with Adenine

Practice Transcribing DNA CUAGGA

Translation n Decoding mRNA into a chain of amino acids (RNA  proteins) n Groups of 3 RNA nucleotides, called codons are “decoded” into amino acids

Translation Section 12-3

Translation Section 12-3

DNA RNA n Deoxyribose (sugar) n Double stranded n Nitrogenous bases: –Guanine –Cytosine –Adenine –Thymine n Ribose (sugar) n Single stranded n Nitrogenous bases: –Guanine –Cytosine –Adenine –Uracil

Codon n Three-nucleotide sequence on mRNA that codes for a single amino acid

The Genetic Code

Mutation n Change in a DNA sequence that affects genetic information

Genetic Mutations n Point Mutations – change involving one or a few nucleotides –Substitution of one base for another –Insertion or deletion of a base Frameshift Mutations – shifts the reading of the genetic message by inserting or deleting a mucleotide

SubstitutionInsertion Deletion Genetic Mutations: Substitutions, Insertions, Deletions Section 12-4

Chromosomal Mutations involve a change in the number or structure n Deletion – loss of chromosome n Duplication – produce extra copies of parts n Inversions – reverse direction of parts n Translocations – part breaks off and attaches to another part

Deletion Duplication Inversion Translocation Chromosomal Mutations Section 12-4