DNA Replication When a cell or organism reproduces, a complete set of genetic instructions must pass from one generation to the next

Watson and Crick’s model for DNA suggested that DNA replicated by a template mechanism Parental (old) DNA molecule Daughter (new) strand Daughter DNA molecule (double helices) Figure 10.6

THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN DNA functions as the inherited directions for a cell or organism How are these directions carried out?

How an Organism’s DNA Genotype Produces Its Phenotype An organism’s genotype, its genetic makeup is the sequence of nucleotide bases in DNA The phenotype is the organism’s specific traits

What is the language of nucleic acids? DNA molecule Gene 1 Gene 2 In DNA, it is the linear sequence of nucleotide bases Gene 3 DNA strand Transcription RNA Translation Codon Polypeptide Amino acid Figure 10.10

DNA specifies the synthesis of proteins in two stages Nucleus DNA Transcription RNA Transcription Translation Translation Protein Cytoplasm Figure 10.9

When DNA is transcribed, the result is an RNA molecule RNA is then translated into a sequence of amino acids in a polypeptide

Transcription: From DNA to RNA In transcription Genetic information is transferred from DNA to RNA An RNA molecule is transcribed from a DNA template

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

Transcription of an entire gene RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation RNA Area shown in part (a) Elongation Termination Growing RNA Completed RNA RNA polymerase (b) Transcription of a gene Figure 10.13b

RNA processing includes Intron Exon Exon Intron Exon DNA Transcription Addition of cap and tail Cap Adding a cap and tail Removing introns Splicing exons together RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Figure 10.14

Transcription and translation Are the processes whereby genes control the structures and activities of cells

Triplets of bases Specify all the amino acids Are called codons

The Genetic Code The genetic code is the set of rules relating nucleotide sequence to amino acid sequence Figure 10.11

The genetic code is shared by all organisms Figure 10.12

Translation: The Players Is the conversion from the nucleic acid language to the protein language

Messenger RNA (mRNA) mRNA Is the first ingredient for translation

An mRNA molecule has a cap and tail that help it bind to the ribosome Start of genetic message End Cap Tail Figure 10.17

Transfer RNA (tRNA) tRNA Acts as a molecular interpreter Carries amino acids Matches amino acids with codons in mRNA using anticodons Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Anticodon Figure 10.15

A fully assembled ribosome holds tRNA and mRNA for use in translation Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA (b) Figure 10.16b

The process of elongation Amino acid Polypeptide P site Anticodon mRNA A site Codons 1 Codon recognition Elongation 2 Peptide bond formation New peptide bond mRNA movement 3 Translocation Figure 10.19

Sickle-cell hemoglobin Mutations A mutation Is any change in the nucleotide sequence of DNA Normal hemoglobin DNA Mutant hemoglobin DNA mRNA mRNA Normal hemoglobin Sickle-cell hemoglobin Glu Val Figure 10.21

Mutations may result from Mutagens Mutations may result from Errors in DNA replication Physical or chemical agents called mutagens

DNA can be damaged by ultraviolet light The enzymes and proteins involved in replication can repair the damage Figure 10.7

Although mutations are often harmful They are the source of the rich diversity of genes in the living world They contribute to the process of evolution by natural selection Figure 10.23

VIRUSES: GENES IN PACKAGES Viruses sit on the fence between life and nonlife They exhibit some but not all characteristics of living organisms Figure 10.24

Bacteriophages, or phages Attack bacteria Head Tail Tail fiber DNA of virus Bacterial cell Figure 10.25

Viruses that infect plants Plant Viruses Viruses that infect plants Can stunt growth and diminish plant yields Can spread throughout the entire plant Protein RNA Figure 10.27

VIRUS Protein spike Viral RNA (genome) Protein coat Envelope 1 Plasma membrane of host cell Entry 2 Uncoating RNA synthesis by viral enzyme 3 4 Protein synthesis 5 RNA synthesis (other strand) mRNA Template New viral genome 6 Assembly New viral proteins Exit 7 Figure 10.29

Signaling between biomolecules

Gene therapy