Chapter 12 & 13 DNA and RNA

Timeline of the Discovery of DNA DO NOT COPY 1928 Griffith Transformation of one type of bacteria into another 1944 Avery DNA is the molecule responsible for transformation and makes up genetic material of cells. 1952 Hersey and Chase Confirmed DNA is the molecule that makes up genetic material of cells. Chargaff’s Rule In DNA from all species, adenine = thymine and cytosine = guanine. 1950’s Franklin X-ray diffraction photograph of DNA 1953 Watson and Crick build a 3D model of structure of DNA

1952 Hershey and Chase Studied viruses called bacteriophages. Bacteriophage: virus that infects bacteria Marked viruses with radioactive P and S, mixed with bacteria and tested for radioactivity. (Sulfur is part of protein and Phosphorus is part of DNA) WHY?? DNA doesn’t contain sulfur and proteins doesn’t contain phosphorus Marked with radioactive Phosphorus isotopes and sulfur isotopes

The Role of DNA Store: Information: DNA stores information for genes that control patterns of development. Copy: Before a cell divides, it must make a complete copy of every one of its genes Transmit: the genetic information in a cell.

Nucleic Acids and Nucleotides (Review chapter 2.3) Nucleic acids are long molecules found in the cell nucleus. Subunit: Nucleotides Nucleotides are made of: Nitrogen base Deoxyribose sugar Phosphate group

Nitrogenous Bases and Covalent Bonds DNA has four kinds of nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Chargaff’s Rules: The percentages of adenine [A] = thymine [T] and The percentage of guanine [G] = cytosine [C].

Franklin’s X-Rays – Photo 51 British scientist Rosalind Franklin used saw DNA with x-ray

The Work of Watson and Crick Watson and Crick built a model that explained the structure and properties of DNA.

Strands of DNA are held together by Hydrogen bonds Hydrogen Bonding Strands of DNA are held together by Hydrogen bonds

Base Pairing Watson and Crick realized that base pairing explained Chargaff’s rule. It gave a reason why [A] = [T] and [G] = [C].

The Replication Process Before a cell divides, it duplicates its DNA in a copying process called replication. Each strand of the double helix of DNA serves as a template, or model, for the new strand.

The Replication Process The two strands of the double helix separate, or “unzip,” allowing two replication forks to form. As each new strand forms, new bases are added following the rules of base pairing. (A T and C G)

The Replication Process Each DNA molecule resulting from replication has one original strand and one new strand.

The Role of Enzymes -“proofreads” new DNA strand. DNA polymerase: joins nucleotides to produce a new strand of DNA -“proofreads” new DNA strand.

Telomeres The tips of chromosomes are known as telomeres. The ends of DNA molecules, located at the telomeres, are particularly difficult to copy. Over time, DNA may be lost from telomeres each time a chromosome is replicated. Telomerase: 1. adds short, repeated DNA sequences to telomeres 2. lengthens the chromosomes 3. Reduces likelihood that gene sequences will be lost during replication.

Replication in Living Cells **Replication always occurs before cell division Prokaryotes: have a single, circular DNA molecule in the cytoplasm. Replication starts from a single point and proceeds in two directions until the entire chromosome is copied. Eukaryotes: have up to 1000 times more DNA and nearly all of the DNA is found in the nucleus. Replication starts in hundreds of places.

RNA & Protein Synthesis Chapter 13

DNA = book of instructions that tells which proteins to make 13.1 DNA = book of instructions that tells which proteins to make The path from genes to proteins has two steps: Transcription—copying the DNA codes to make RNA Translation—using the codes to make proteins

Ribonucleic Acid (RNA) Long chains of nucleotides made by transcription Most RNA is used for protein synthesis Nucleotide Structure

DNA v. RNA DNA RNA 5 Carbon Sugar Deoxyribose (one less oxygen) Ribose Nitrogen Bases Adenine Thymine Guanine Cytosine Uracil Phosphate Same in both Number of strands Double strand (base pairs) Single strand (single bases) Size 100s of million base pairs 100s - 1000s of bases

Three Forms of RNA Messenger RNA (mRNA) carries copies of the instructions for protein synthesis from the nucleus to the cytoplasm Transfer RNA (tRNA) transfers the amino acids to the ribosomes in the order specified by the mRNA Ribosomal RNA (rRNA) is part of the structure of ribosomes (where proteins are made)

Transcription DNA is read and a strand of RNA is created from it. Segments of DNA are templates to produce complementary RNA molecules DNA RNA A U T G C

Transcription RNA Polymerase: reads DNA during transcription, builds RNA Promoters: sequences of DNA that show RNA polymerase where to attach (BINDING SITE).

RNA Editing Introns: part of first draft of RNA that is cut out and discarded. Exons: all other parts spliced together to form the final mRNA

Translation = Protein Synthesis 13.2 Translation = Protein Synthesis mRNA (from transcription) is then translated by the ribosome. tRNA brings the appropriate amino acids that are sequenced to create the protein.

Proteins (review Ch 2 pages 48-49) Amino Acids (AA): about 20 different types; each with identical amino group and a carboxyl group and a unique side group Polypeptide: long chains of amino acids formed when the amine of one AA binds with the carboxyl of next AA; order of AA determined by the mRNA code

The Genetic Code 4 letters: A, U, G, and C 64 possible 3 letter combinations from 4 letters (4 x 4 x 4 = 64) Codon: 3 letter code found in mRNA; one AA per codon (and some AA have multiple codons) Anticodon: 3 letter code found in tRNA that carries AA and is the complement of a codon

Reading codons (version 1)

Reading Codons version 2 Protein Synthesis Animation: http://www.biostudio.com/demo_freeman_protein_synthesis.htm

The Big Picture

Mutations Inheritable changes in genetic information Causes: 13.3 Mutations Inheritable changes in genetic information Causes: Random Errors in replication Stress Physical Mutagens (x – ray, UV light) Chemical Mutagens (pesticides, tobacco)

Types of Mutations 2 types of mutations: 13.3 Types of Mutations 2 types of mutations: 1. Gene Mutations (point and frameshift) 2. Chromosomal Mutations

Point Mutations Change in a single nucleotide in DNA Substitutions Insertions Deletions

Chromosomal Mutations Change in number or structure of chromosomes Deletion Duplication Inversion Translocation

Effects of Mutations None Harmful Beneficial Change has no effect on the AA inserted Harmful Disrupts normal cell function Sickle Cell Anemia Hemophilia Cancer Beneficial Change increases variation in the species and improves chance of survival in changing environmental conditions Pesticide resistant mosquitoes Polyploidy plants

Prokaryote Gene Regulation 13.4 Prokaryote Gene Regulation Proteins bind to parts of DNA to turn on/off transcription

Eukaryotic Gene Regulation Much more complex than in prokaryotes Important to cell differentiation in multi-cellular organisms Influenced by the physical and chemical environment of the cell (example frog metamorphosis)