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Chapter 12: DNA and RNA Biology- Kirby 12-1: DNA • 1928- Frederick Griffith- studied the bacteria that caused pneumonia. He found 2 strains of bacteria: diseasecausing and harmless. • Griffith’s experiment: page 288 • Transformation- one strain of bacteria is changed by a gene from another strain of bacteria. 12-1: DNA • 1944- Oswald Avery- repeated Griffith’s work- discovered that DNA stores and transmits the genetic information from one generation to the next. • 1952- Hershey-Chase Experiment– Bacteriophage- virus that infects bacteria. – Concluded that the genetic material of the bacteriophage was DNA, not protein. 12-1: DNA • DNA is made of nucleotides. • 4 nitrogenous bases in DNA: – – – – – Adenine Guanine Cytosine Thymine Adenine and guanine are purines (2 ring structure). Cytosine and thymine are pyrimidines (1 ring structure). 12-1: DNA • The backbone of DNA is made from sugar and phosphate groups. • Chargaff’s Rules– A=T, and G=C • 1950’s- Rosalind Franklin- used x-ray diffraction to get information about the structure of DNA. 12-1: DNA • 1950’s- Francis Crick and James Watson- began making 3-D models of DNA. After viewing Franklin’s x-rays Watson and Crick developed the double helix model for DNA. • Double helix- 2 twisted strands held together by base pairs. Base pairing explains Chargaff’s rules; A bonds to T, and G bonds to C. 12-2: Chromosomes and DNA Replication • DNA is very long and has to be folded tightly to fit inside cells. • The nucleus of a human cell has more than 1 meter of DNA!! • The composition of the chromosomes allows for these long stands of DNA to exist. 12-2: Chromosomes and DNA Replication • Chromosome Structure– Made of DNA and proteins – Chromatin- consists of DNA coiled tightly around proteins. – Histone- proteins DNA is coiled around. – Nucleosome- DNA and histones in a beadlike structure. Nucleosomes fold DNA into tiny spaces in the nucleus. 12-2: Chromosomes and DNA Replication • The double helix structure of DNA explains how it can be replicated, or copied. • Each side, or strand, can make another copy. • DNA begins replication at one point and proceeds in both directions until replication is complete. 12-2: Chromosomes and DNA Replication • Replication- process in which the cell copies its DNA. – The DNA molecule separates into 2 strands. – Base pairs are made to complement the original nitrogenous bases on the strand. – Example: TACGTT (original) – ATGCAA (copy) 12-2: Chromosomes and DNA Replication – Each strand of the double helix of DNA serves as a template, or model, for the new strand. – Results in 2 identical DNA strands. – Replication is carried out by enzymes. These enzymes “unzip” DNA by breaking the hydrogen bonds between the base pairs. 12-2: Chromosomes and DNA Replication – DNA polymerase- enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule. 12-3: RNA & Protein Synthesis • RNA consists of: – Nucleotides – Ribose (sugar) – Single-strand – Contains uracil instead of thymine. 12-3: RNA & Protein Synthesis • Types of RNA: – Messenger RNA (mRNA)- carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell. – Ribosomal RNA (rRNA)- makes up ribosomes. – Transfer RNA (tRNA)- transfers amino acids to ribosomes during protein synthesis. 12-3: RNA & Protein Synthesis • Transcription- the nucleotide sequence of DNA is copied into a complementary sequence of RNA. – RNA polymerase- enzyme that binds to DNA and separates the DNA strands. It uses one strand of DNA as a template to assemble a strand of RNA. 12-3: RNA & Protein Synthesis • RNA polymerase will only bind to regions of DNA called promoters. These specific base sequences signal DNA to start and stop making RNA. • Codon- 3 nucleotide sequence on mRNA that codes for amino acids. – AUG is the “start” codon. 12-3: RNA & Protein Synthesis • Translation- decoding of mRNA message into a polypeptide chain. – Anticodon- complementary to a codon. – How it works: 12-4: Mutations • Mutation- changes in the genetic material. • Gene mutations- change in the DNA sequence. • Chromosomal mutations- change in the chromosome structure. • Most mutations are neutral, but dramatic changes are harmful.