Transcript Document
Chapter 12 Remember! Chargaff’s rules • The relative amounts of adenine and thymine are the same in DNA • The relative amounts of cytosine and guanine are the same. • Named after Erwin Chargaff Review of the double-helix • A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands. How long is the DNA molecule? Male vs Female • MALE • Usually the Y • FEMALE • Usually the X chromosome. • Y is usually smaller • Male genotype = XY chromosome. • Larger than the Y • Female genotype XX Except Birds Male = XX Female = XY Chromosome structure: DNA replication • Replication must occur before a cell divides. • Each new cell needs a copy of the information in order to grow. DNA replication. Why needed? • Before DNA strand can be replicated or copied it must be “unzipped” • DNA polymerase (enzyme that unzips) • Starts at many different points. Why? Completing the replication • After the DNA molecule comes apart, bases of free nucleotides in the nucleus join their complimentary bases. RNA • Ribonucleic Acid • It is a DISPOSABLE copy of DNA • Its job? To make PROTEINS!!! • Very similar to DNA w/ 3 Exceptions: 1) Ribose is the 5-carbon sugar 2) Uracil replaces thymine 3) Single-stranded Types of RNA • A. mRNA (messenger) • Copies genetic code of DNA by matching bases. • Occurs in the nucleus. • Carries copies of information TRANSCRIPTION • The process of turning DNA into mRNA • Requires the enzyme RNA polymerase. 1. RNA polymerase binds to the DNA and unwinds it. 2. Separates the DNA strands 3. Uses one strand as a template to make mRNA • Where does this take place? NUCLEUS! Transcription continued: Confusing genetic terms: • Amino acids = building blocks of a polypetide • Polypeptide = building blocks of a protein. • Protein = a bunch of polypeptides Reading the genetic code • The genetic code is responsible for building all the proteins in the body using 20 different amino acids. • Extra credit: How many 3 letter words can you make from the letters A,T,G and C? • Answer: 64 Codons • A three letter “word” that specifies an amino acid. Genetic code: tRNA (transfer) • approx. 80 nucleotides • • • • in length. Cross-like shape At one end an amino acid is attached At the other end there is an anticodon Acts like a truck Polypeptide assembly • Translation = reading or “translating” the RNA code to form a chain of amino acids. • Known as protein synthesis • Occurs in the cytoplasm. (p.304) Mutations • The source of variation in a genetic sequence. • Can be either gene or chromosomal mutations. • Point mutations = a change in a single nucleotide in a sequence of DNA. Frameshift Mutation • Inserting an extra nucleotide which, in turn, shifts the entire sequence one way or the other. Chromosomal mutations • Involves a change in the number or structure of the chromosomes. • Deletion : when a piece of a chromosome breaks off and is lost. • Duplication : when a segment of a chromosome is repeated • Inversion : when a segment of a chromosome is reversed. More chromosomal mutations • Translocation : when part of a chromosome breaks off and is attached to a nonhomologous chromosome. Advanced Honors: Control of gene expression • Genes are often like light switches that can be turned off and on. • Operon = occur in prokaryotes. (bacteria) different genes that work together to activate gene functions Eukaryotic gene expression • Controlled by complex sequences of DNA. • Example: “TATA box” Factors: • Overall gene control is more difficult for eukaryotes because functional genes may be on different chromosomes. • Environmental such as chemicals and temperature. Hox and Oncogenes • Hox genes • Genes that actively control embryonic development. • Oncogenes • Genes known to cause cancer. • Usually these are switched “off”, but can be switched “on” by a number of factors.