DNA, RNA, & Protein Synthesis Discovery of DNA DNA Structure DNA Replication Protein Synthesis

Introduction Mendel - concluded that hereditary factors determine many of an organisms traits But he didn’t know what these hereditary factors were How did they share info Answers to these questions emerged during the pneumonia epidemic in London in the 1920s

Griffith’s Experiments Griffith was studying bacterium, Streptococcus pneumoniae Cause lung disease pneumonia Trying to develop a vaccine against a disease-causing agent, or virulent strain of the bacterium S strain & R strain

Nature of Hereditary Material Experiments 1 & 2 Injected either live R o live S cells into mice Only S cells killed the mice Experiment 3 Injected heat killed S bacteria into mice Mice survived Experiment 4 Injected mice w/ both heat-killed S cells and live R cells Mice died

Conclusions from Griffiths Experemint ? Heat-killed virulent bacterial cells release a hereditary factor that transfers the disease- causing ability to the live harmless cells Transfer of genetic material from one cell to another cell or from one organism to another organism = Transformation file:///Users/eastlmat/Documents/Biology%20'08- '09/Biology%20PPT/Ch10/60427.html file:///Users/eastlmat/Documents/Biology%20'08- '09/Biology%20PPT/Ch10/60427.html

Avery’s Experiments 1940s, Oswald Avery, wanted to test whether the transforming agent in Griffith’s test was protein, RNA, or DNA Used enzymes to separately destroy each of the 3 molecules in heat killed S cells Protease Enzyme Rnase DNase

What Happened in Avery’s Exp? They mixed the 3 experimental batches of heat-killed S cells w/ live R cells What Happened? Cells missing RNA & Protein were able to transform R cells into S cells = mice died Cells missing DNA did not transform R cells into S cells = mice survived DNA is transforming agent

Hershey-Chase Experiment 1952, Martha Chase & Alfred Hershey, tested whether DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium Viruses that infect a bacterium = bacteriophages

Steps of the Experiment 1: radioactive isotopes to label protein & DNA in the phage DNA labeled & protein labeled phages were separately allowed to infect E. coli 2: removed the phage coats 3: centrifuged to separate the phage from E. coli Found all viral DNA & little protein entered cells DNA is the hereditary molecule in viruses file:///Users/eastlmat/Documents/Biology%20'08- '09/Biology%20PPT/Ch10/61132.html file:///Users/eastlmat/Documents/Biology%20'08- '09/Biology%20PPT/Ch10/61132.html

DNA Structure Section 2

DNA Double Helix Watson & Crick in 1953 created a model for the structure of DNA 2 chains that wrapped around each other Double helix shape: winding spiral staircase Used X-ray diffraction and work of many scientists to determine structure

DNA Nucleotides DNA made of: 2 long chains of nucleotides, which are repeating subunits Nucleotide consists of: 5-carbon sugar = deoxyribose Phosphate group = P atom + 4 Oxygen Nitrogenous base = N atoms & C atoms, base

DNA Nucleotides

Bonds Hold DNA Together DNA Double Helix = Spiral Staircase Alternating sugar & phosphate molecules = the side “handrails” Nucleotides connected by covalent bonds Nitrogenous bases face center & connect w/ bases of opposite strand using H bonds Either 2 H bonds or 3 H bonds Form the “steps” of staircase

Visual Aid of DNA Bonds

Nitrogenous Bases Adenine = AGuanine = G Cytosine = CThymine = T 4 Kinds: Purines Pyrimidines

Complementary Bases % of Adenine = % of Thymine % of Cytosine = % of Guanine Helps understand structure Base-pairing rules in DNA Cytosine–––Guanine Adenine–––Thymine Complimentary Pairs C–G A–T Notice anything about the pairs?

Complimentary Bases Base Sequence: AAAATTTGGC on one strand, what is the opposite strand? TTTTAAACCG Important for 2 reasons: H bonds hold together Explains replication of DNA

DNA Replication Section 3

How DNA Replication Occurs DNA Replication = process by which DNA is copied in a cell before mitosis, meiosis, or binary fission 2 Nucleotide strands separate along the bases Complimentary strands serve as templates for new strands

Steps of DNA Replication 1: helicase enzyme separate DNA strands by breaking the H bonds Y-shaped region that results from the separation is a replication fork

Steps of DNA Replication 2: DNA polymerases add complimentary nucleotides to each strand Covalent bonds form b/w adjacent nucleotides, deoxyribose sugar and P groups

Steps of DNA Replication 3: DNA polymerases finish & fall off Results in 2 new DNA strands that are identical Semi-conservative replication: replication in which each new DNA molecule has kept one of the 2 original strands

Steps of DNA Replication

Action at the Replication Fork DNA synthesis: Occurs in different directions on each strands Synthesis of one strand follows the movement of the replication fork Replication occurs from 5’ to 3’ h?v=nIwu5MevZyg&feature= related h?v=nIwu5MevZyg&feature= related

Prokaryotic & Eukaryotic Replication Prokaryotic 1 circular chromos. Repl. begins at one place 2 repl. forks moving in opposite directions at the origin Repl. continues until entire molecule is copied Eukaryotic Long chromos. DNA polymerase adds nucleotides at 50/sec, if there were only one DNA polym. it would take 53 days to finish Multiple points of origin for replication 2 repl forks moving in opposite directions at each origin Fruit fly has 3500 origin sites

DNA Errors in Replication Usually has great accuracy 1:1,000,000,000 error chances in paired nucleotides added Proofreading functions in DNA polymerases When a mistake does happen a mutation occurs Mutation = a change in the nucleotide sequence of a DNA molecule Can have serious effects on fxns of genes Chemicals & UV light damage DNA & lead to Cancer

DNA Replication & Cancer DNA replication is an amazing process that passes genetic info from cell to cell It also explains how mutations arise & lead to altered cells May allow for better survival and repro, & these variations increase in populations over time May cause diseases, like cancer

Protein Synthesis Section 4

Flow of Genetic Information Gene: Hair Color Directs making of protein, called Melanin, in the hair follicle, through an intermediate Ribonucleic acid: RNA

Flow of Genetic Information Transcription: In Nucleus, DNA is template for RNA Translation: In Cytoplasm, RNA directs assembly of proteins Protein Synthesis: Forming proteins based on information in DNA & carried out by RNA

RNA Structure & Function Contains sugar ribose Contains nitrogenous base, uracil, instead of thymine Usually, single stranded Usually, much shorter than DNA

Types of RNA messenger RNA: mRNA Single-stranded Carries instructions from gene to make protein

Types of RNA ribosomal RNA: rRNA Part of a ribosome Where protein synthesis occurs

Types of RNA transfer RNA: tRNA Transfers amino acids to the ribosome to make the protein

Transcription Genetic instructions in a specific gene are transcribed or “rewritten” into an RNA molecule Takes place in Nucleus in eukaryotes Cytoplasm in prokaryotes

Steps of Transcription 1: RNA polymerase binds to a promoter RNA polymerase = enzyme that catalyzes the formation of RNA on DNA template Promoter = specific nucleotide sequence of DNA where RNA polymerase binds and initiates transcriptions

Steps of Transcription 2: RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one of the DNA strands Results in an RNA molecule DNA strand = ATCGAC RNA strand = UAGCUG Only uses a gene, not the whole DNA strand

Steps of Transcription 3: RNA polymerase reaches a termination signal, or stop signal Termination signal = specific sequence of nucleotides that marks the end of a gene Newly formed RNA can now perform its job in the cell

The Genetic Code Def: rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid 3 adjacent nucleotides in mRNA specify an amino acid in a polypeptide Codon: 3-nucleotide sequence in mRNA that encodes an amino acid, or signifies a start or stop signal

Translation Protein Structure Made of one or more polypeptides, chains of amino acids linked by peptide bonds 20 different amino acids in living things Each polypeptide chain may consist of hundreds or thousands of the 20 a.a., arranged in a specific sequence Sequence determines how the polypeptides will twist and fold into the 3-D structure of the protein. Shape is critical to its function

Steps of Translation Step 1: Initiation 2 Ribosomal subunits, mRNA, and the tRNA carrying methionine bind together One end of tRNA contains a specific a.a. Other end contains anticodon = 3 nucleotides on the RNA that are complementary to the sequence of a codon in mRNA

Steps of Translation Step 2: Elongation tRNA carrying the appropriate a.a., pairs its anticodon with the second codon in the mRNA Ribosome detaches methionine from the first tRNA Peptide bond forms b/w methionine & 2nd a.a. Ribosome moves a distance of 1 codon along mRNA

Steps of Translation Step 3: Elongation, cont’d 1st tRNA detaches and leaves it’s a.a. behind Polypeptide chain continues to grow one a.a. at a time

Steps of Translation Step 4: Termination Ribosome reaches the stop codon, tRNA has no complementary anticodon Newly made polypeptide falls off

Steps of Translation Step 5: Disassembly Ribosome complex falls apart Newly made polypeptide is released related related

The Human Genome Def: entire gene sequence of the complete genetic content of humans Now known: 3.2 billion base pairs/10 yrs. Learn what info the DNA sequences encode Info is important b/c help diagnose, treat, and prevent genetic disorders, cancer, and infectious diseases