Ch. 12 Molecular Genetics Page 326 The discovery that DNA is the genetic code involved many experiments. Once Mendel’s work was rediscovered in the 1900s, scientists began to search for the molecule involved in inheritance. Scientists knew that genetic information was carried on the chromosomes in eukaryotic cells, and that the two main components of chromosomes are DNA and protein. For many years, scientists tried to determine which of these macromoleculesnucleic acid (DNA) or proteins-was the source of genetic information. Griffith Smooth Strain= killed or did not kill? Smooth Strain= killed Rough Strain= killed or did not kill? Smooth Strain= killed Rough Strain= did not kill Smooth Strain killed by heat= killed or did not kill? Smooth Strain= killed Rough Strain= did not kill Smooth Strain killed by heat= did not kill Smooth Strain killed by heat + Rough Strain= killed or did not kill? Smooth Strain= killed Rough Strain= did not kill Smooth Strain killed by heat= did not kill Smooth Strain killed by heat + Rough Strain= killed Suggested that a disease-causing factor was passed from the killed S bacteria to the live R bacteria. He concluded there had been a transformation from live R bacteria to live S bacteria. Avery, Macleod, and McCarty Avery discovered DNA changed R strain to S strain. Not widely accepted by the scientific community. Hershey and Chase Hershey and Chase Used a bacteriophage (virus) and bacteria. Viruses are known to inject their own DNA into a bacteria to replicate and eventually kill the bacteria cell. What were the two molecules they were experimenting with to see which one carried genetic material? Once blended and centrifuged, what was the result? Hershey and Chase Used a bacteriophage (virus) and bacteria. Viruses are known to inject their own DNA into a bacteria to replicate and eventually kill the bacteria cell. What were the two molecules they were experimenting with to see which one carried genetic material? Protein and DNA. Once blended and centrifuged, what was the result? Hershey and Chase Used a bacteriophage (virus) and bacteria. Viruses are known to inject their own DNA into a bacteria to replicate and eventually kill the bacteria cell. What were the two molecules they were experimenting with to see which one carried genetic material? Protein and DNA. Once blended and centrifuged, what was the result? The tagged (radioactive) material found was the one they had used on the DNA. DNA carries genetic material! DNA Structure Nucleotides: Made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base. DNA nucleotides contain the sugar deoxyribose, a phosphate, and one of 4 nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). RNA nucleotides contain the sugar ribose, a phosphate, and one of 4 nitrogenous bases: (A), (T), (C), and uracil (U). Chargaff Analyzed the amount of A, G, T, and C in the DNA of various species. He found the amount of G nearly equals the amount of C and the amount of A nearly equals T. Chargaff’s rule: C=G A=T Watson and Crick Known for building a model of a double helix to show the structure of DNA. First to know the structure of DNA! Went on to win the Nobel Prize. Rosalind Franklin Rosalind Franklin Used X-rays to get first picture of DNA structure. Spent her time using calculations to be able to show exactly how each bond met with the next. Very precise. By the time she had finished, Watson and Crick had guessed correctly from her picture and ideas. Unsung hero. Section 2: Replication of DNA DNA replicates by making a strand that is complementary to each original strand. Replication happens in 3 main stages: unwinding, base pairing, and joining. 1. Unwinding or Unzipping Helicase is an enzyme that “unzips” DNA. After being unzipped, where does the pairing begin? Another enzyme called RNA primase adds and RNA primer on each strand. When you paint, you start with a primer. It helps get things started the correct way. Same for RNA primase. 2. Base Pairing Chargaff’s Rule? 2. Base Pairing Chargaff’s Rule: A=T C=G DNA Polymerase adds complementary bases to open bases. Leading strand: 3` Lagging strand: 5` Leading strand, bases added continuously. 3. Joining: Okazaki Fragments Segments of DNA on the lagging strand that will be connected by ligase. Ligase=Glue Section 3: DNA, RNA, and Protein DNA codes for RNA, which guides protein synthesis. Computer programmers write their programs in a particular language, or code. The computer is designed to read the code and perform a function. Like the programming code, DNA contains a code that signals the cell to perform a function. RNA RNA is like DNA, but is usually a single strand instead of two. Uses the base Uracil (U) instead of Thymine (T). 3 Types of RNA Messenger RNA (mRNA)Formed complementary to one strand of DNA. Ribosomal RNA (rRNA)Forms ribosomes in the cytoplasm. Transfer RNA (tRNA)Transport amino acids to the ribosome. Transcription Through transcription, the DNA code is transferred to mRNA in the nucleus. “Transcribe” “Transcript” We are making a complementary RNA strand. How do we know it’s RNA? Introns and Exons Introns are parts of mRNA that do not code for a protein. They are disposed of. Exons are parts that code for a protein. They remain. The Code Scientists know that 20 amino acids were used to make proteins, so they knew that DNA must provide at least 20 different codes. Experiments during the 1960s showed that the DNA code was a 3-base code. These segments of 3-bases are called codons. Ex. ATG CAT GTA After transcription, we have translation. Translation is where the code is read and proteins are made! (Proteins are what make up our traits, along with so many other things.) After transcription, we have an RNA strand. Let’s say the strand reads like this: AUGGACUCAUGA We need to translate the code! AUGGACUCAUGA 1st step: separate into codons. We need to translate the code! AUGGACUCAUGA 1st step: separate into codons. AUG GAC UCA UGA 2nd step: see what amino acid that codon codes for. We need to translate the code! AUGGACUCAUGA 1st step: separate into codons. AUG GAC UCA UGA 2nd step: see what amino acid codes for. Start Asp Ser Stop Polypeptide Chains Codons code for/create amino acids. Amino group together forming polypeptide chains. These chains create proteins. Section 4: Gene Regulation and Mutation Gene expression is regulated by the cell, and mutations can affect this expression. When you type a sentence on a keyboard, it’s important that each letter is typed correctly. The sentence “The fat cat ate the rat” is quite different from “The fat cat ate the hat.” Though there is a difference of only one letter, the meaning is changed. This is what happens through various mutations! Operons An operon can turn genes off or on. Every cell in your body has every bit of your DNA. That means that any cell can produce any protein from any location. But we don’t want that! Imagine if your eye cells decided to code for an enzyme your stomach makes: Hydrochloric acid. An operon can turn off protein synthesis for things that particular body part doesn’t need to make! Gene regulation. Hox Genes Hox genes are differentiation is the process through which cells become specialized in structure and function. One group of genes found to control differentiation are Hox genes. They regulate the body plan of an organism. Mutations Any permanent change in a cell’s DNA. Many types of mutations. Some mutations help, hurt, or are neutral. Mutagens Anything that causes a mutation. Radiation, certain chemicals, and infections can damage DNA. Many drugs used to treat HIV mimic nucleotides, causing mutations in DNA. Cigarette smoke (dozens of mutagens), preservatives, acne treatment ingredients, etc. Vaping Our hypothesis was supported and our experiment demonstrated that all ejuices are mutagenic and possibly carcinogenic. Not only did the e-juice with nicotine turn mutagenic, but the nicotine free one also proved to be mutagenic. We have concluded that the acrolein in the Propylene Glycol made the nicotine free e-juice mutagenic, which is why our experiments tested positive. Somatic vs. Sex cell mutations When a mutation happens in a somatic (body) cell, that mutation is not passed on to offspring. When a mutation happens in a sex cell, it is passed on to the offspring.
