Transcript DNA & RNA
DNA & RNA CHAPTER 12 Griffith & Transformation Discovered transformation using bacteria that causes pneumonia Transformation Process in which part of the nucleotide sequence of DNA is copied into a complementary sequence in RNA Avery & DNA Retested Griffith’s experiment to determine what caused transformation Discovered that the nucleic acid in DNA stores and transmits the genetic information from one generation of an organism to the next Hershey-Chase Experiment Studied viruses Concluded that DNA was the genetic material of bacteriophages, not protein Components & Structure of DNA • DNA is made up of Nucleotides • Each nucleotide is made up of 3 basic components: – 5 carbon sugar (deoxyribose) – A phosphate group – Nitrogenous base • 4 nitrogen bases – Adenine – Guanine – Cytosine – thymine Chargaff’s Rule The observation that [A] = [T] & [G] = [C] Found that in 4 different types of organisms the amount of A & T were nearly the same as well as the amount of G & C were nearly the same. Double Helix • Watson & Crick built a 3-D model of DNA based on the evidence found by Franklin using X-ray. • Found that DNA was a double helix, in which two strands were wound around each other resembling a spiral staircase • Hydrogen bonds hold the two strands together but only formed between A&T and G&C • This is called base pairing 12-2 Chromosomes & DNA Replication DNA Replication Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing. Replications proceeds in both directions until each chromosome is completely copied Duplicating DNA Before a cell divides it duplicates DNA During duplication, the DNA molecule separates into 2 strands, produces 2 new complementary strands based on base pairing. How Replication Works Replication is carried about by many enzymes, the principle enzyme is DNA polymerase It joins individual nucleotides to produce a DNA molecule Proofreads each new DNA strand 12-3 RNA & Protein Synthesis The Structure of RNA Consists of a long chain of nucleotides 3 main differences between RNA & DNA The 5 carbon sugar is ribose, not deoxyribose RNA is generally single stranded RNA contains uracil instead of thymine Types of RNA RNA has many functions, but in the majority of cells most RNA molecules are involved in only one thing – PROTIEN SYNTHESIS 3 main types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA) Types of RNA Genes contain instructions for assembling amino acids into proteins RNA molecules that carry copies of these instructions are known as mRNA Proteins are assembled on the ribosomes. Ribosomes are made up of several dozen proteins as well as a form of RNA called rRNA During protein construction, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA. This is known as tRNA. Transcription RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA. This is called transcription. Requires RNA polymerase RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA. RNA Editing DNA of eukaryotic genes contains sequences of nucleotides called introns that are not involved in coding for proteins. The DNA sequence that code for proteins are called exons because the are expressed in the synthesis of proteins. When RNA molecules are formed they copy both the introns and exons. The Genetic Code The language of mRNA instructions is called the genetic code. A codon consists of 3 consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide There are 64 possible the base codons During translation, the cell uses information from mRNA to produce proteins Mutations & Gene Regulation Kinds of Mutations Mutations are changes in the genetic material Point Mutations = gene mutations involving changes in one or few nucleotides Include: Substitutions Insertions Deletions Frameshift Mutations = shift the “reading frame” of the genetic message Examples Point The fat cat ate the wee rat. The fat hat ate the wee rat. Frameshift The fat cat ate the wee rat. The fat caa tet hew eer at. Chromosomal Mutations Involve changes in the number or structure of chromosomes May change locations of genes on chromosomes 4 types Deletions Duplications Inversions Translocations Examples Original ABCDEF Deletions ACDEF Duplications ABBCDEF Inversion AEDBBF Translocations ABCJKL GHIDEF