Molecular Basis forRelationship between Genotype and Phenotype

DNA

RNA

protein

genotype

function

organismphenotype

DNA sequence

amino acidsequence

transcription

translation

Molecular Basis forRelationship between Genotype and Phenotype

DNA

RNA

protein

genotype

function

organismphenotype

DNA sequence

amino acidsequence

transcription

translation

Proteins and RNA Molecules Compose the Two Subunits of a Ribosome

Protein Synthesis: Termination

tRNA molecules do not recognize stop codons.

Termination codons are recognized by release factors. (RF1, RF2, RF3 in bacteria)

UAA and UAG are recognized by RF1.

UAA and UGA are recognized by RF2.

RF3 assists in release activity.

Release factors bind to a stop codon in the A site by association between codon and tripeptide of RF.

Polypeptide is released from P site when RF fits into A site.

Release of polypeptide is followed by dissociation of ribosomal subunits.

Molecular Basis forRelationship between Genotype and Phenotype

DNA

RNA

protein

genotype

function

organismphenotype

DNA sequence

amino acidsequence

transcription

translation

Molecular Basis forRelationship between Genotype and Phenotype

DNA

RNA

protein

genotype

function

organismphenotype

DNA sequence

amino acidsequence

transcription

translation

All Protein Interactions in an Organism Compose the Interactome

Proteome: Complete set of proteins produced by genetic material of an organism.

Interactome: Complete set of protein interactions in an organism.

Alternative Splicing Produces Related but Distinct Protein Isoforms

Posttranslational Events

Protein Folding: Translational product (polypeptide) achieves appropriate folding by aid of chaperone proteins.

Modification of Amino Acids: * Phosphorylation/dephosphorylation* Ubiquitination

Protein Targeting:Directing proteins to specific locations (for example, nucleus, mitochondria, or cell membrane) is accomplished by tagging of proteins (signal sequence for secreted proteins, nuclear localization sequences for nuclear proteins).

Posttranslational Events

Protein Folding: Translational product (polypeptide) achieves appropriate folding by aid of chaperone proteins.

Modification of Amino Acids: * Phosphorylation/dephosphorylation* Ubiquitination

Protein Targeting:Directing proteins to specific locations (for example, nucleus, mitochondria, or cell membrane) is accomplished by tagging of proteins (signal sequence for secreted proteins, nuclear localization sequences for nuclear proteins).

Phosphorylation and Dephosphorylation of Proteins

Kinases add phosphate groups to hydroxyl groups of amino acids such as serine and threonine.

Phosphatases remove phosphate groups.

Ubiquitinization Targets a Protein for Degradation

Short-lived proteins are ubiquitinated:• cell-cycle regulators• damaged proteins

Posttranslational Events

Protein Folding: Translational product (polypeptide) achieves appropriate folding by aid of chaperone proteins.

Modification of Amino Acids: * Phosphorylation/dephosphorylation* Ubiquitination

Protein Targeting:Directing proteins to specific locations (for example, nucleus, mitochondria, or cell membrane) is accomplished by tagging of proteins (signal sequence for secreted proteins, nuclear localization sequences for nuclear proteins).

Signal Sequences Target Proteins for Secretion

Signal sequence at the amino-terminal end of membrane proteins or secretory proteins are recognized by factors and receptors that mediate transmembrane transport. Signal sequence is cleaved by signal peptidase.

Nuclear localization sequences (NLSs) are located in interior of proteins such as DNA and RNA polymerases. They are recognized by nuclear pore proteins for transport into nucleus.

Universality of Genetic Information TransferGenetic code is essentially identical for all

organisms.There are exceptions.

System AUA UGA“universal” isoleucine terminationmammalian mitochondria methionine tryptophanyeast mitochondria isoleucine tryptophan

Comparison of Gene Expression

Prokaryotes

One type of RNA polymerase synthesizes all RNA molecules.

mRNA is translated during transcription.

Genes are not split. They are continguous segments of DNA.

mRNAs are often polycistronic.

Eukaryotes

Three different types of RNA polymerases synthesize different classes of RNA.

mRNA is processed before translation.

Genes are often split. They are not continguous segments of coding sequences.

mRNAs are mostly monocistronic.