Chapter 11 DNA and Protein Synthesis Mrs. Svencer

11.1 Genes are made of DNA Frederick and Griffith Transformation –bacteria with mice Strain A – pneumonia, fatal Strain B – harmless Heated strain A – harmless Mix heated strain A and strain B - death Harmless bacteria - “transformed” Descendents were too - trait was passed on Heritable change

                                                                                                                                                                            Figure 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."

Oswald Avery – focused on protein and DNA Heat strain A + strain B + protein-destroying enzymes Offspring still transformed Protein not accountable for transformation Heat strain A + strain B + DNA-destroying enzymes Colonies did not transform Therefore, DNA = genetic material

Hershey and Chase – used viruses Virus = nucleic acid in a protein coat Bacteriophage = virus that infects bacteria Batch 1 Labeled protein coats with radioactive sulfur Radioactivity detected outside of the cells Batch 2 Labeled DNA with radioactive phosphorus Radioactivity inside cells Therefore, phage’s DNA entered bacteria Therefore, DNA is the hereditary material

                                                                                                                                                                            Figure 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.

11.2 Nucleic Acids store information DNA (deoxyribonucleic acid) Stores genetic information Built from nucleotides – 3 parts 1. Sugar – ring shape, “deoxyribose” 2. Phosphate group 3. Nitrogenous base – single or double ring of C and N atoms

                                                                  Figure 11-5 A nucleotide has three components: a sugar, a phosphate group, and a nitrogenous base.

4 bases in DNA Pyrimidines: single rings Purines: double rings Thymine (T) Cytosine (C) Purines: double rings Adenine (A) Guanine (G)

                                                                                                                                   Figure 11-6 DNA contains four different nitrogenous bases. Thymine and cytosine have single-ring structures. Adenine and guanine have double-ring

DNA Strands Covalent bonds connect sugar to phosphate between nucleotides Sugar-phosphate “backbone” Nucleotides arrange in different 1. Numbers 2. Sequences (combinations are unlimited)

Rosalind Franklin and Maurice Wilkins X-ray crystallography DNA = helix shape Watson and Crick Made model of double helix using Franklin’s pictures Twisted ladder

Complementary Base Pairs Purine + Pyrimidine A-T (2 hydrogen bonds) G-C (3 hydrogen bonds)

11.3 DNA Replication – mechanism of inheritance (DNA – copying) Template Mechanism 2 strands of double helix separate at origins of replication Copying goes outward from origin in both directions, making a “bubble” Each strand is a “template” for a new, complementary strand Bases line up according to base-pairing rules

                                                                                                   Figure 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.

                                                                                                           Figure 11-10 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.

New strands = daughter strands Fast and accurate DNA polymerase (enzyme) links nucleotides together using covalent bonds DNA opens further as nucleotides added Eukaryotic DNA – many origins - speedy New strands = daughter strands Fast and accurate 1 error / billion nucleotides

Review: DNA Replication occurs before a cell divides during the S phase of interphase of the cell cycle

11.4 Genes Provide Information for Making Proteins Beadle and Tatum – orange bread mold Mutant strains unable to grow on nutrient medium Lacked single enzyme needed to produce a needed molecule Each mutant defective in a single gene “one gene-one enzyme” hypothesis – one gene produces one specific enzyme NOW, “one gene – one polypeptide”

RNA is needed to make a protein Nucleic Acid RNA – ribonucleic acid DNA – deoxyribonucleic acid Sugar Ribose Deoxyribose Nitrogenous bases AUCG ATCG Shape Single helix Double helix

Gene to Protein 1. Transcription - DNA to RNA Transcribed message (RNA) leaves nucleus to cytoplasm 2. Translation – RNA to amino acid Codon = on RNA - 3 bases that code for amino acid

Table of Codons RNA Figure 11-13 61/64 code for amino acids – some amino acids coded for by more than 1 codon Ex: UUU UUC – both code for phenylalanine 3/64 – stop codons – end of each gene sequence

                                                                                                           Figure 11-13 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.

11.5 Two steps from Gene to Protein Transcription: DNA to RNA Messenger RNA (mRNA) transcribed from DNA template – only 1 strand of DNA RNA nucleotides pair to complementary bases – AUCG RNA polymerase - RNA nucleotides together RNA splicing – introns are removed and exons are joined together Therefore, mRNA has a continuous coding sequence mRNA leaves nucleus

                                                                                                                                       Figure 11-12 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.

                                                                                                   Figure 11-15 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.

Intron = noncoding region of mRNA Exon = coding region of mRNA that is “expressed” or translated

Translation: RNA to protein 1. Start codon: AUG –translation begins 2. Amino acids added one-by-one to a chain of amino acids A. tRNA (transfer RNA) translates codons of mRNA to amino acids 1. tRNA molecule binds to appropriate amino acid

2. tRNA recognizes, using base-pairing rules, codons in mRNA by its own complementary anticodon Anticodon = 3 bases at one end of tRNA 3. Other end of tRNA = where amino acid attaches 4. An enzyme links tRNA to its amino acid, using ATP

                                                                      Figure 11-16 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.

C. ribosome connects new amino acid to the growing polypeptide chain B. occurs at ribosome 2 subunits – made of protein and rRNA (ribosomal RNA) Small subunit – binding site for mRNA Large subunit – 2 binding sites for tRNA 1. “P” site (polypeptide) – holds tRNA carrying the growing polypeptide chain 2. “A” site (amino acid) – holds tRNA carrying next amino acid to be added to the chain 2 subunits hold mRNA and tRNA close together C. ribosome connects new amino acid to the growing polypeptide chain

                                                                          Figure 11-17 Ribosomes bring mRNA and tRNAs together during translation. Each ribosome has an attachment site for an mRNA transcript, and two sites for tRNAs.

4. Completed polypeptide set free from tRNA by hydrolysis 3. Reaches stop codon UAA, UAG, UGA No amino acid at “A” site Translation stops 4. Completed polypeptide set free from tRNA by hydrolysis

11.6 Mutations Mutation – any change in the nucleotide sequence of DNA Can be Large regions of chromosomes Single nucleotide pairs

Base substitutions Replacement of 1 base or nucleotide with another Sometimes no effect – “silent mutation” Sometimes large effect Why? Several amino acids have more than 1 codon

More disastrous mutations Insertion Putting in an additional nucleotide Deletion Taking away 1 nucleotide Both insertion and deletion alter the triplet groupings Now they code for new amino acids

Cause of mutations Error during DNA replication Error during crossing over in meiosis Mutagens – physical / chemical agents that cause mutations Ex: high-energy radiation, x-rays, UV light Usually harmful, sometimes helpful Ex: dark color in female tiger swallowtails

Mutations may be passed to offspring, if they occur in gametes Ultimate source of genetic diversity