Presentation on theme: "Chapter 11 DNA and Protein Synthesis"— Presentation transcript:
1Chapter 11 DNA and Protein Synthesis Mrs. Svencer
211.1 Genes are made of DNA Frederick and Griffith Transformation –bacteria with miceStrain A – pneumonia, fatalStrain B – harmlessHeated strain A – harmlessMix heated strain A and strain B - deathHarmless bacteria - “transformed”Descendents were too - trait was passed onHeritable change
3Figure 11-1 Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor."
4Oswald Avery – focused on protein and DNA Heat strain A + strain B + protein-destroying enzymesOffspring still transformedProtein not accountable for transformationHeat strain A + strain B + DNA-destroying enzymesColonies did not transformTherefore, DNA = genetic material
5Hershey and Chase – used viruses Virus = nucleic acid in a protein coatBacteriophage = virus that infects bacteriaBatch 1Labeled protein coats with radioactive sulfurRadioactivity detected outside of the cellsBatch 2Labeled DNA with radioactive phosphorusRadioactivity inside cellsTherefore, phage’s DNA entered bacteriaTherefore, DNA is the hereditary material
6Figure 11-4 Hershey and Chase offered further evidence that DNA, not proteins, is the genetic material. Only the DNA of the old generation of viruses is incorporated into the new generation.
711.2 Nucleic Acids store information DNA (deoxyribonucleic acid)Stores genetic informationBuilt from nucleotides – 3 parts1. Sugar – ring shape, “deoxyribose”2. Phosphate group3. Nitrogenous base – single or double ring of C and N atoms
8Figure 11-5 A nucleotide has three components: a sugar, a phosphate group, and a nitrogenous base.
94 bases in DNA Pyrimidines: single rings Purines: double rings Thymine (T)Cytosine (C)Purines: double ringsAdenine (A)Guanine (G)
10Figure 11-6 DNA contains four different nitrogenous bases. Thymine and cytosine have single-ring structures. Adenine and guanine have double-ring
11DNA StrandsCovalent bonds connect sugar to phosphate between nucleotidesSugar-phosphate “backbone”Nucleotides arrange in different1. Numbers2. Sequences(combinations are unlimited)
12Rosalind Franklin and Maurice Wilkins X-ray crystallographyDNA = helix shapeWatson and CrickMade model of double helix using Franklin’s picturesTwisted ladder
1411.3 DNA Replication – mechanism of inheritance (DNA – copying) Template Mechanism2 strands of double helix separate at origins of replicationCopying goes outward from origin in both directions, making a “bubble”Each strand is a “template” for a new, complementary strandBases line up according to base-pairing rules
15Figure 11-9 During DNA replication, the two strands of the original parent DNA molecule, shown in blue, each serve as a template for making a new strand, shown in yellow. Replication results in two daughter DNA molecules, each consisting of one original strand and one new strand.
16Figure DNA replication begins at origins of replication and proceeds in both directions, producing "bubbles." Eventually, all the bubbles merge, resulting in two separate daughter DNA molecules.
17New strands = daughter strands Fast and accurate DNA polymerase (enzyme) links nucleotides together using covalent bondsDNA opens further as nucleotides addedEukaryotic DNA – many origins - speedyNew strands = daughter strandsFast and accurate1 error / billion nucleotides
18Review: DNA Replication occurs before a cell divides during the S phase of interphase of the cell cycle
1911.4 Genes Provide Information for Making Proteins Beadle and Tatum – orange bread moldMutant strains unable to grow on nutrient mediumLacked single enzyme needed to produce a needed moleculeEach mutant defective in a single gene“one gene-one enzyme” hypothesis – one gene produces one specific enzymeNOW, “one gene – one polypeptide”
20RNA is needed to make a protein Nucleic AcidRNA – ribonucleic acidDNA – deoxyribonucleic acidSugarRiboseDeoxyriboseNitrogenous basesAUCGATCGShapeSingle helixDouble helix
21Gene to Protein 1. Transcription - DNA to RNA Transcribed message (RNA) leaves nucleus to cytoplasm2. Translation – RNA to amino acidCodon = on RNA - 3 bases that code for amino acid
22Table of Codons RNA Figure 11-13 61/64 code for amino acids – some amino acids coded for by more than 1 codonEx: UUU UUC – both code for phenylalanine3/64 – stop codons – end of each gene sequence
23Figure Each codon stands for a particular amino acid. (The table uses abbreviations for the amino acids, such as Ser for serine.) The codon AUG not only stands for methionine (Met), but also functions as a signal to "start" translating an RNA transcript. There are also three "stop" codons that do not code for amino acids, but signal the end of each genetic message.
2411.5 Two steps from Gene to Protein Transcription: DNA to RNAMessenger RNA (mRNA) transcribed from DNA template – only 1 strand of DNARNA nucleotides pair to complementary bases – AUCGRNA polymerase - RNA nucleotides togetherRNA splicing – introns are removed and exons are joined togetherTherefore, mRNA has a continuous coding sequencemRNA leaves nucleus
25Figure Information flows from gene to polypeptide. First, a sequence of nucleotides in DNA (a gene) is transcribed into RNA in the cell's nucleus. Then the RNA travels to the cytoplasm where it is translated into the specific amino acid sequence of a polypeptide.
26Figure In eukaryotes, the RNA transcript is edited before it leaves the nucleus. Introns are removed and the exons are spliced together before the "final draft" transcript moves into the cytoplasm where it gets translated.
27Intron = noncoding region of mRNA Exon = coding region of mRNA that is “expressed” or translated
28Translation: RNA to protein 1. Start codon: AUG –translation begins2. Amino acids added one-by-one to a chain of amino acidsA. tRNA (transfer RNA) translates codons of mRNA to amino acids1. tRNA molecule binds to appropriate amino acid
292. tRNA recognizes, using base-pairing rules, codons in mRNA by its own complementary anticodon Anticodon = 3 bases at one end of tRNA3. Other end of tRNA = where amino acid attaches4. An enzyme links tRNA to its amino acid, using ATP
30Figure During translation, tRNAs transport and match amino acids to their appropriate codons on the mRNA transcript. One end of the tRNA attaches to an amino acid. At the other end, a triplet of bases called the anticodon matches to the complementary mRNA codon.
31C. ribosome connects new amino acid to the growing polypeptide chain B. occurs at ribosome2 subunits – made of protein and rRNA (ribosomal RNA)Small subunit – binding site for mRNALarge subunit – 2 binding sites for tRNA1. “P” site (polypeptide) – holds tRNA carrying the growing polypeptide chain2. “A” site (amino acid) – holds tRNA carrying next amino acid to be added to the chain2 subunits hold mRNA and tRNA close togetherC. ribosome connects new amino acid to the growing polypeptide chain
32Figure Ribosomes bring mRNA and tRNAs together during translation. Each ribosome has an attachment site for an mRNA transcript, and two sites for tRNAs.
334. Completed polypeptide set free from tRNA by hydrolysis 3. Reaches stop codonUAA, UAG, UGANo amino acid at “A” siteTranslation stops4. Completed polypeptide set free from tRNA by hydrolysis
3411.6 Mutations Mutation – any change in the nucleotide sequence of DNA Can beLarge regions of chromosomesSingle nucleotide pairs
35Base substitutions Replacement of 1 base or nucleotide with another Sometimes no effect – “silent mutation”Sometimes large effectWhy?Several amino acids have more than 1 codon
36More disastrous mutations InsertionPutting in an additional nucleotideDeletionTaking away 1 nucleotideBoth insertion and deletion alter the triplet groupingsNow they code for new amino acids
37Cause of mutations Error during DNA replication Error during crossing over in meiosisMutagens – physical / chemical agents that cause mutationsEx: high-energy radiation, x-rays, UV lightUsually harmful, sometimes helpfulEx: dark color in female tiger swallowtails
38Mutations may be passed to offspring, if they occur in gametes Ultimate source of genetic diversity