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DNA and RNA Structure of DNA Chromosomes and Replication Transcription and Translation Mutation and Gene Regulation Experiments leading to DNA structure • Griffith – genetic information can be transferred from one organism to another • Avery – discovered that DNA is the transforming factor for genetic information • Hershey-Chase – concluded that DNA is the genetic material, not proteins • Watson, Crick, Franklin – used X-ray diffraction to show the structure of DNA Components of DNA • Nucleotide – made of a 5 carbon sugar, a phosphate group, and a nitrogenous base • Purines – nucleotides containing two rings in their base (adenine and guanine) • Pyrimidines – nucleotides containing one ring in their base (cytosine, uracil and thymine) Components of DNA Chargaff’s Rules of base pairing • Adenine always pairs with thymine (A-T) • Guanine always pairs with cytosine (G-C) Chromosomes and DNA • Prokaryotes have a circular DNA molecule that is located in the cytoplasm. • Eukaryotes have a huge DNA molecule located on the chromosomes within the nucleus. Chromosomes and DNA • Chromosomes are the structures containing genetic information (humans have 23 pairs) • Chromatin – DNA and protein tightly packed together • Histones – spherical protein in which DNA is wrapped around. • Nucleosome – DNA and histone complex Chromosomes and DNA Chromosomes and DNA Replication • Replication – the process of DNA copying itself • During DNA replication, the DNA molecules separates into two strands, then produces two new complementary strands following the base pairing rules. • Each strand of the double helix of DNA serves as a template, or model for the new strand. Replication • Enzymes unzip the DNA molecule by breaking the hydrogen bonds. • DNA polymerase joins nucleotides to template strand. It also “proofreads” to ensure accuracy. RNA • Ribonucleic acid – single stranded nucleotide molecule, contains ribose instead of deoxyribose and uracil instead of thymine. • Messanger RNA (mRNA) – carries copies of instructions for assembling amino acids • Ribosomal RNA (rRNA) – contained on the ribosomes • Transfer RNA (tRNA) – transfers each amino acid to the ribosome as coded by mRNA Transcription • The process of constructing mRNA from a DNA molecule. • RNA polymerase binds to DNA and separates the strands. • RNA polymerase uses one strand of DNA as a template to assemble nucleotides of the mRNA • Promoters – specific base sequences in DNA that indicate to the enzyme where to make RNA. Transcription • Introns – segments of nucleotides not involved in coding for proteins • Exons – segments of nucleotides that are expressed in protein synthesis • Codon – three consecutive nucelotides that specify a single amino acid Transcription • DNA: ATCGGCACTGGC mRNA: UAGCCGUGACCG DNA: CGATCTACGCCGTAC mRNA: GCUAGAUGCGGCAUG DNA: AATCTGCAGCCATTC mRNA: UUAGACGUCGGUAAG Translation • The process of decoding a mRNA into a polypeptide chain • Translation begins when mRNA attaches to a ribosome. • mRNA contains a “start” codon to begin protein assembly. • Each codon matches with an anticodon on a tRNA that contains amino acid. • Enzymes join amino acids until reaching a “stop” codon and ribosome detaches. Translation Translation mRNA: AUGCGUACCUUA protein: met-arg-thr-leu mRNA: UUCCAAGGCAAC protein: ala-glu-gly-asp mRNA: ACAUACCCCGCG protein: thr-tyr-pro-ala Mutations • Changes in the genetic material • Point mutation – gene mutations involving changes in one or a few nucleotides • Frameshift mutation – insertions or deletions that can shift the reading of the codons • Polyploidy – condition in which an organism has an extra set of chromosomes Gene regulation • Operon – a group of genes that operate together • The lac genes are turned off by repressors and turned on by the presence of lactose. (Occurs in bacterium). • In eukaryotes, “TATA” box, series of adenines and thymines, that help position RNA polymerase. • Enhancer sequences will also bind to proteins to begin the process of transcription • Hox genes – series of genes that control the differential of cells in the embryo