1. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Human Biology Sylvia S. Mader Michael Windelspecht Chapter 21 DNA Biology and Technology Lecture Outline Part 2

2. 2 Comparing DNA and RNA Similarities –They are nucleic acids. –They are made of ___________. –The have sugar- phosphate backbones. –They are found in the _________. Differences –DNA is _________ ________ while RNA is ______________. –DNA has T while RNA has U. –RNA is also found in the ___________ as well as the nucleus while DNA is not. 21.1 DNA and RNA Structure and Function

3. 3 Proteins: A review Proteins are composed of subunits called _______ _______ The sequence of amino acids determines the shape of the protein. They are synthesized at the ____________. Proteins are important for diverse functions in the body including hormones, enzymes, and transport. They can _________, causing a loss of function. 21.2 Gene Expression

4. 4 2 steps of gene expression 1.____________ – DNA is read to make a mRNA in the nucleus 2.____________ – mRNA is read to make a protein in the cytoplasm Figure 21.5 Summary of gene expression. 21.2 Gene Expression transcription innucleus DNA mRNA translation at ribosome polypeptide OOO ProlineAspartic acidSerine NCCNC CN CC R1R1 R2R2 R3R3 codon 3codon 2codon 1 3′ 5′ C G G CA G CC G C GTT AG CG C GCACCCAGC template strand nontemplate strand 3′ 5′ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. 5 The genetic code It is made of 4 kinds of bases. Bases act as a code for __________ used in translation. Every 3 bases of the mRNA is called a ________; a typical codon specifies a particular _________ in translation. Figure 21.6 The genetic code. 21.2 Gene Expression Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Second Base arginine CGG arginine AGU serine AGC serine arginine AGG arginine GGU glycine GGC glycine GGG glycine UGC cysteine UGG tryptophan CGU arginine CGC arginine stop CAC histidine glutamine CAG glutamine AAU asparagine AAC asparagine lysine AAG lysine GAU aspartic acid GAC GAG UUU phenylalanine UUC phenylalanine leucine UUG leucine CUU leucine CUC leucine CUG leucine AUU isoleucine AUC isoleucine GUU valine GUC valine GUG valine UCC serine UCG serine CCU proline CCC proline CCG proline ACU threonine ACC threonine ACG threonine GCU alanine GCC alanine GCG alanine UAC tyrosine CAU histidine stop UAG stop UCU serine UAU tyrosine UGU cysteine U C A G U C A G U C A G U C A G U C A G UCAG First Base Third Base AUG (start) methionine UGAUAA CGACUA UUAUCA CCACAA AUAACAAAAAGA GUAGCAGAAGGA aspartic acid glutamic acid

6. 6 1. Transcription mRNA is made from a DNA template. mRNA is _________ before leaving the nucleus. mRNA moves to the ___________ to be read. Figure 21.7 Transcription of DNA into mRNA. 21.2 Gene Expression Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G A T T G C template strand direction of polymerase movement RNA polymerase DNA template strand mRNA transcript to RNA processing U G C A A A A A A A A A A A C C C C C C C C C C C T T T T T T T T T T T G G G G G G G C3′3′ 5′ 3′3′ 3′3′

7. 7 Processing of mRNA after transcription Modifications of mRNA One end of the RNA is capped. _________ are removed. A ___________ is added. 21.2 Gene Expression

8. 8 Figure 21.8 mRNA processing. 21.2 Gene Expression Processing of mRNA after transcription Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA exon transcription intron pre-mRNA exon intron poly-A tailcap intron exon poly-A tail pre-mRNA splicing cap intron RNA mRNA poly-Atailcap nuclear pore in nuclear envelope nucleus cytoplasm spliceosome 5′ 3′

9. 9 2. Translation 3 steps 1.Initiation: mRNA binds to the small ribosomal subunit and causes the 2 ribosomal units to associate 2.___________: polypeptide lengthens tRNA picks up an amino acid. tRNA has an anticodon that is complementary to the codon on the mRNA. tRNA anticodon binds to the codon and drops off an amino acid to the growing polypeptide. 3.Termination: a ______________ on the mRNA causes the ribosome to fall off the mRNA 21.2 Gene Expression

10. 10 Visualizing the 3 steps of translation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C G UA UA U A CA UGGAC CUG U C A G U G GAC U A ACC CUG thr C U A G A U 2a. Elongation occurs in two stages. First stage of elongation. tRNA-polypeptide is at the P site and a tRNA amino acid is at the A site. The polypeptide will be transferred to the tRNA-amino acid. 2b. Second stage of elongation. The ribosome has moved to the right and the tRNA polypeptide at the P site is now longer by one amino acid. One tRNA is outgoing and another tRNA is incoming. 3. Termination. When the ribosome reaches a stop codon, all participants separate and the polypeptide is released. 1. Initiation. The small ribosomal subunit, the mRNA, the first tRNA amino acid, and the large ribosomal subunit come together. large ribosomal subunit free polypeptide polypeptide bond amino acid polypeptide small ribosomal subunit met ser ala tryp val asp thr met ser ala tryp val asp met ser ala tryp val asp A site P site Figure 21.10 Formation of the polypeptide during translation. 21.2 Gene Expression

11. 11 Overview of transcription and translation 3. mRNA moves into cytoplasm and becomes associated with ribosomes. Translation 1. DNA in nucleus serves as a template for mRNA. 2. mRNA is processed before leaving the nucleus. primary mRNA mature mRNA DNA TRANSCRIPTION introns exons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CC GG G G G C C C G U A C U A UUU U A 4. tRNAs with anticodons carry amino acids to mRNA. nuclear pore mRNA peptide amino acids 5. Anticodon–codon complementary base pairing occurs. anticodon codon ribosome AAA large and small ribosomal subunits tRNA 6. Polypeptide synthesis takes place one amino acid at a time. Figure 21.12 Summary of transcription and translation. 21.2 Gene Expression