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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 10 Molecular Biology of the Gene Modules 10.6 – 10.16 From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN • DNA is our genetic material: it contains the information coded by our genotypes • RNA contains the instructions for making proteins • Proteins are necessary for all life functions • DNA RNA Protein is the central dogma of molecular biology • Transcription is the process of making RNA from DNA • Translation is the process of making proteins from RNA Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • DNA is transcribed (goes through transcription) to become RNA which is then translated (goes through translation) to become protein. DNA TRANSCRIPTION RNA TRANSLATION Protein Figure 10.6A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10.7 Codons • A codon is a 3 nucleotide sequence that specifies a specific amino acid (building block of protein). • For example, in DNA you might have: ACG • After transcription, the RNA codon would be: UGC • After translation, the amino acid that matches that codon is cysteine. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10.8 The genetic code • There are 64 possible triplet combinations that match up with specific amino acids (there are 20 different amino acids) • AUG codes for the start of a polypeptide chain • UAA, UAG, and UGA code for stop Figure 10.8A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Bacteria, plants and animals all have DNA and go through the same process to make protein Transcribed strand DNA Transcription RNA Start codon Polypeptide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation Stop codon Figure 10.8B • Transcription occurs in the nucleus • 1. DNA unzips • 2. RNA nucleotides match up in triplets called mRNA (messenger RNA) *remember, C with G and A with U (not T)* • 3. RNA polymerase links up these nucleotides • 4. A promoter tells the RNA polymerase where to copy the nucleotides, and a terminator tells it when to stop • 5. The new RNA strand elongates and then peels away from the DNA Figure 10.9B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10.10 Eukaryotic RNA is processed before leaving the nucleus • Before the mRNA leaves the nucleus, a cap (made of one G) and a tail (made of lots of As) is added. • Introns (non-coding regions) are removed and exons (coding regions) are joined. • This process is called RNA splicing. • mRNA now goes into the cytoplasm Figure 10.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Exon Intron Exon Intron Exon DNA Cap RNA transcript with cap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM 10.11 Translation • Translation (RNA to protein) occurs in the cytoplasm and in ribosomes • Transfer RNA (tRNA) matches up the mRNA codons with amino acids • 1. Each mRNA codon matches up with one end of a tRNA (called the anti-codon). • 2. The other end of the tRNA then attaches to the amino acid that the anti-codon tells it to. • 3. The tRNA then line up the amino acids in order to form a protein. *this occurs in a RIBOSOME* Figure 10.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • tRNA Amino acid attachment site Anticodon Figure 10.11B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Proteins are assembled in ribosomes. • Ribosomes are made of 2 subunits. • They are made of rRNA (ribosomal RNA, the most abundant kind of RNA) Large ribosomal subunit Initiator tRNA P site A site Start codon mRNA Small ribosomal subunit 1 Figure 10.13B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 10.16 Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence – These are caused by errors in DNA replication or by mutagens (a physical or chemical agent such as UV light, x-rays, chemicals) – Mutagenesis is the creation of mutations Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings