© 2010 Pearson Education, Inc. Lectures by Chris C. Romero, updated by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Chapter 10 The Structure and Function of DNA

© 2010 Pearson Education, Inc. DNA: STRUCTURE AND REPLICATION DNA: –Was known to be a chemical in cells by the end of the nineteenth century –Has the capacity to store genetic information –Can be copied and passed from generation to generation DNA and RNA are nucleic acids. –They consist of chemical units called nucleotides. –The nucleotides are joined by a sugar-phosphate backbone.

Sugar-phosphate backbone Phosphate group Nitrogenous base DNA nucleotide Nucleotide Thymine (T) Sugar Polynucleotide DNA double helix Sugar (deoxyribose) Phosphate group Nitrogenous base (can be A, G, C, or T) Figure 10.1

© 2010 Pearson Education, Inc. The four nucleotides found in DNA differ in their nitrogenous bases. These bases are: –Thymine (T) –Cytosine (C) –Adenine (A) –Guanine (G) RNA has uracil (U) in place of thymine. James Watson and Francis Crick determined that DNA is a double helix.

James Watson (left) and Francis Crick Figure 10.3a

X-ray image of DNA Rosalind Franklin Figure 10.3b

© 2010 Pearson Education, Inc. The model of DNA is like a rope ladder twisted into a spiral. –The ropes at the sides represent the sugar-phosphate backbones. –Each wooden rung represents a pair of bases connected by hydrogen bonds.

© 2010 Pearson Education, Inc. DNA bases pair in a complementary fashion: –Adenine (A) pairs with thymine (T) –Cytosine (C) pairs with guanine (G)

(a) Ribbon model Figure 10.5a

© 2010 Pearson Education, Inc. DNA Replication When a cell reproduces, a complete copy of the DNA must pass from one generation to the next. Watson and Crick’s model for DNA suggested that DNA replicates by a template mechanism.

Parental (old) DNA molecule Daughter (new) strand Daughter DNA molecules (double helices) Figure 10.6

© 2010 Pearson Education, Inc. DNA can be damaged by ultraviolet light. DNA polymerases: –Are enzymes –Make the covalent bonds between the nucleotides of a new DNA strand –Are involved in repairing damaged DNA

© 2010 Pearson Education, Inc. DNA specifies the synthesis of proteins in two stages: –Transcription, the transfer of genetic information from DNA into an RNA molecule –Translation, the transfer of information from RNA into a protein

TRANSLATION Protein RNA TRANSCRIPTION DNA Cytoplasm Nucleus Figure

© 2010 Pearson Education, Inc. When DNA is transcribed, the result is an RNA molecule. RNA is then translated into a sequence of amino acids in a polypeptide (protein).

© 2010 Pearson Education, Inc. What are the rules for translating the RNA message into a polypeptide? A codon is a triplet of bases, which codes for one amino acid.

Second base of RNA codon First base of RNA codon Phenylalanine (Phe) Leucine (Leu) Cysteine (Cys) Leucine (Leu) Isoleucine (Ile) Valine (Val) Met or start Serine (Ser) Proline (Pro) Threonine (Thr) Tyrosine (Tyr) Histidine (His) Glutamine (Gln) Asparagine (Asn) Alanine (Ala) Stop Glutamic acid (Glu) Aspartic acid (Asp) Lysine (Lys) Arginine (Arg) Tryptophan (Trp) Arginine (Arg) Serine (Ser) Glycine (Gly) Third base of RNA codon Figure 10.11

© 2010 Pearson Education, Inc. Transcription: From DNA to RNA Transcription: –Makes RNA from a DNA template –Uses a process that resembles DNA replication –Substitutes uracil (U) for thymine (T) RNA nucleotides are linked by RNA polymerase. The “start transcribing” signal is a nucleotide sequence called a promoter.

© 2010 Pearson Education, Inc. Initiation of Transcription The first phase of transcription is initiation, in which: –RNA polymerase attaches to the promoter –RNA synthesis begins During the second phase of transcription, called elongation: –The RNA grows longer –The RNA strand peels away from the DNA template During the third phase of transcription, called termination: –RNA polymerase reaches a sequence of DNA bases called a terminator –Polymerase detaches from the RNA –The DNA strands rejoin

Newly made RNA RNA nucleotides RNA polymerase Template strand of DNA Direction of transcription (a) A close-up view of transcription Figure 10.13a

© 2010 Pearson Education, Inc. Translation: The Players Translation is the conversion from the nucleic acid language to the protein language. Transfer RNA (tRNA): –Acts as a molecular interpreter –Carries amino acids –Matches amino acids with codons in mRNA using anticodons Ribosomes are organelles that: –Coordinate the functions of mRNA and tRNA –Are made of two protein subunits –Contain ribosomal RNA (rRNA)

tRNA polynucleotide (ribbon model) RNA polynucleotide chain Anticodon Hydrogen bond Amino acid attachment site tRNA (simplified representation) Figure 10.15

Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA Codons (b) The “players” of translation Figure 10.16b

© 2010 Pearson Education, Inc. Translation: The Process Translation is divided into three phases: –Initiation –Elongation –Termination

© 2010 Pearson Education, Inc. Initiation Initiation brings together: –mRNA –The first amino acid, Met, with its attached tRNA –Two subunits of the ribosome The mRNA molecule has a cap and tail that help it bind to the ribosome. Initiation occurs in two steps: –First, an mRNA molecule binds to a small ribosomal subunit, then an initiator tRNA binds to the start codon. –Second, a large ribosomal subunit binds, creating a functional ribosome.

© 2010 Pearson Education, Inc. Elongation Elongation occurs in three steps. –Step 1, codon recognition: –the anticodon of an incoming tRNA pairs with the mRNA codon at the A site of the ribosome. –Step 2, peptide bond formation: –The polypeptide leaves the tRNA in the P site and attaches to the amino acid on the tRNA in the A site –The ribosome catalyzes the bond formation between the two amino acids

© 2010 Pearson Education, Inc. –Step 3, translocation: –The P site tRNA leaves the ribosome –The tRNA carrying the polypeptide moves from the A to the P site Elongation continues until: –The ribosome reaches a stop codon –The completed polypeptide is freed –The ribosome splits into its subunits

New peptide bond Stop codon mRNA movement mRNA P site Translocation Peptide bond formation Polypeptide ELONGATION Codon recognition A site Codons Anticodon Amino acid Figure

© 2010 Pearson Education, Inc. Review: DNA  RNA  Protein In a cell, genetic information flows from DNA to RNA in the nucleus and RNA to protein in the cytoplasm.

Transcription RNA polymerase mRNA DNA Intron Nucleus mRNA Intron Tail Cap RNA processing tRNA Amino acid attachment Enzyme ATP Initiation of translation Ribosomal subunits Elongation Anticodon Codon Termination Polypeptide Stop codon Figure

© 2010 Pearson Education, Inc. Mutations A mutation is any change in the nucleotide sequence of DNA. Mutations can change the amino acids in a protein. Mutations can involve: –Large regions of a chromosome –Just a single nucleotide pair, as occurs in sickle cell anemia Mutations may result from: –Errors in DNA replication –Physical or chemical agents called mutagens

© 2010 Pearson Education, Inc. Types of Mutations Mutations within a gene can occur as a result of: –Base substitution, the replacement of one base by another –Nucleotide deletion, the loss of a nucleotide –Nucleotide insertion, the addition of a nucleotide

Normal hemoglobin DNA mRNA Normal hemoglobin Mutant hemoglobin DNA mRNA Sickle-cell hemoglobin Figure 10.21