1 DNA RNA structure 2 DNA replication 3

1. DNA, RNA structure 2. DNA replication 3. Transcription, translation

DNA and RNA are polymers of nucleotides • DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Sugar Phosphate group Nitrogenous base (A, G, C, or T) Nucleotide Thymine (T) Sugar (deoxyribose) DNA nucleotide Polynucleotide Sugar-phosphate backbone Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10. 2 A

• DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Pyrimidines Adenine (A) Guanine (G) Purines Figure 10. 2 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• RNA is also a nucleic acid – different sugar – U instead of T Nitrogenous base (A, G, C, or U) Phosphate group Uracil (U) Sugar (ribose) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10. 2 C, D

DNA is a double-stranded helix • James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10. 3 A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Hydrogen bonds between bases hold the strands together: A and T, C and G Hydrogen bond Ribbon model Partial chemical structure Computer model Figure 10. 3 D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Untwisting and replication of DNA • each strand is a template for a new strand helicase DNA polymerase Figure 10. 4 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

How can entire chromosomes be replicated during S phase? • DNA replication begins at many specific sites Origin of replication Parental strand Daughter strand Bubble Two daughter DNA molecules Figure 10. 5 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Each strand of the double helix is oriented in the opposite direction 5 end 3 end P P P P Figure 10. 5 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 3 end 5 end

• DNA polymerase works in only one direction • Telomere sequences are lost with each replication. DNA polymerase molecule 5 end Daughter strand synthesized continuously Parental DNA 5 3 Daughter strand synthesized in pieces 3 5 P 5 3 • Cancer, aging Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 3 5 P telomeres DNA ligase Overall direction of replication Figure 10. 5 C

• The information constituting an organism’s genotype is carried in its sequence of bases – The DNA is transcribed into RNA, which is translated into the polypeptide DNA TRANSCRIPTION RNA TRANSLATION Protein Figure 10. 6 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Transcription produces genetic messages in the form of m. RNA polymerase RNA nucleotide Direction of transcription Template strand of DNA Figure 10. 9 A Newly made RNA Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

RNA polymerase • In transcription, DNA helix unzips DNA of gene Promoter DNA – RNA nucleotides line up along one strand of DNA, following the base-pairing rules – single-stranded messenger RNA peels away and DNA strands rejoin Initiation Elongation Terminator DNA Area shown in Figure 10. 9 A Termination Growing RNA Completed RNA Figure 10. 9 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA polymerase

Eukaryotic RNA is processed before leaving the nucleus • Noncoding segments, introns, are spliced out Exon Intron Exon DNA Cap RNA transcript with cap and tail • A cap and a tail are added to the ends Transcription Addition of cap and tail Introns removed Tail Exons spliced together m. RNA Coding sequence NUCLEUS CYTOPLASM Figure 10. 10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Translation of nucleic acids into amino acids • The “words” of the DNA “language” are triplets of bases called codons – The codons in a gene specify the amino acid sequence of a polypeptide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Figure 10. 7 Amino acid Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Virtually all organisms share the same genetic code “unity of life” Second Base C U UUC UUA UUG C CUU CUC CUA CUG A AUU AUC ile AUA AUG met (start) ACU ACC ACA ACG G GUU GUC GUA GUG GCU GCC GCA GCG phe leu val UCU UCC UCA UCG CCU CCC CCA CCG A ser UAU UAC UAA UAG pro CAU CAC CAA CAG thr AAU AAC AAA AAG ala GAU GAC GAA GAG G tyr stop his gln asn lys asp glu UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG cys stop trp arg ser arg gly U C A G Third Base First Base U

• An exercise in translating the genetic code Transcribed strand DNA Transcription RNA Start codon Polypeptide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Translation Stop codon Figure 10. 8 B

Transfer RNA molecules serve as interpreters during translation • In the cytoplasm, a ribosome attaches to the m. RNA and translates its message into a polypeptide • The process is aided by transfer RNAs Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Figure 10. 11 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Each t. RNA molecule has a triplet anticodon on one end an amino acid attachment site on the other Amino acid attachment site Anticodon Figure 10. 11 B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Ribosomes build polypeptides Next amino acid to be added to polypeptide Growing polypeptide t. RNA molecules P site A site Growing polypeptide Large subunit t. RNA P m. RNA binding site A m. RNA Codons m. RNA Small subunit Figure 10. 12 A-C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

An initiation codon marks the start of an m. RNA message Start of genetic message End Figure 10. 13 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• m. RNA, a specific t. RNA, and the ribosome subunits assemble during initiation Large ribosomal subunit Initiator t. RNA P site A site Start codon m. RNA Small ribosomal subunit 1 Figure 10. 13 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2

Elongation • The m. RNA moves a codon at a time relative to the ribosome – A t. RNA pairs with each codon, adding an amino acid to the growing polypeptide – A STOP codon causes the m. RNA-ribosome complex to fall apart Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Amino acid Polypeptide A site P site Anticodon m. RNA 1 Codon recognition m. RNA movement Stop codon New peptide bond 3 Translocation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 Peptide bond formation Figure 10. 14

b a Red object = ribosome What molecules are present in this photo?

Table 14. 2 Types of RNA Type of RNA Functions in Messenger RNA (m. RNA) Nucleus, migrates to ribosomes in cytoplasm Transfer RNA (t. RNA) Cytoplasm Provides linkage between m. RNA and amino acids; transfers amino acids to ribosomes Ribosomal RNA (r. RNA) Cytoplasm Structural component of ribosomes Function Carries DNA sequence information to ribosomes

Review: The flow of genetic information in the cell is DNA RNA protein • The sequence of codons in DNA spells out the primary structure of a polypeptide – Polypeptides form proteins that cells and organisms use Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence – caused by errors in DNA replication or by mutagens – change of a single DNA nucleotide causes sicklecell disease Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Normal hemoglobin DNA m. RNA Mutant hemoglobin DNA m. RNA Normal hemoglobin Glu Figure 10. 16 A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sickle-cell hemoglobin Val

• Types of mutations NORMAL GENE m. RNA Protein Met Lys Phe Gly Ala Lys Phe Ser Ala BASE SUBSTITUTION Met Missing BASE DELETION Met Lys Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Leu Ala His Figure 10. 16 B

• Summary of transcription and translation TRANSCRIPTION DNA m. RNA polymerase Stage 1 m. RNA is transcribed from a DNA template. Amino acid TRANSLATION Enzyme Stage 2 Each amino acid attaches to its proper t. RNA with the help of a specific enzyme and ATP. t. RNA Initiator t. RNA m. RNA Figure 10. 15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Anticodon Large ribosomal subunit Start Codon Small ribosomal subunit Stage 3 Initiation of polypeptide synthesis The m. RNA, the first t. RNA, and the ribosomal subunits come together.

New peptide bond forming Growing polypeptide Codons Stage 4 Elongation A succession of t. RNAs add their amino acids to the polypeptide chain as the m. RNA is moved through the ribosome, one codon at a time. m. RNA Polypeptide Stop Codon Figure 10. 15 (continued) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Stage 5 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released.