Molecular Basis for Relationship between Genotype and Phenotype DNA RNA protein genotype function organism phenotype DNA sequence amino acid sequence transcription translation

Molecular Basis for Relationship between Genotype and Phenotype DNA RNA protein genotype function organism phenotype DNA sequence amino acid sequence transcription translation

Protein Synthesis: Initiation in Eukaryotes eIF4A, eIF4B, and eIF4G associates with 5’ end, then with 40S subunit and initiator tRNA. mRNA is unwound by movement of this complex in 5’ -> 3’ direction. 60S subunit associates with initiation complex when start codon is recognized. Initiation factors are released when the two ribosomal subunits associate.

Important Features of Ribosome A - aminoacyl site P - peptidyl site E - exit site

Proteins and RNA Molecules Compose the Two Subunits of a Ribosome

EF-Tu associates with aminoacyl-tRNA to form a ternary complex. Protein Synthesis: Elongation Amino acid in P site is transferred to amino acid in A site. Translocation requires GTP and EF-G. EF-G enters A site, shifting tRNAs. When EF-G leaves, A site is open for a new ternary complex. A new ternary complex associates with A site, and deacylated tRNA leaves from E site. Correct match of ternary complex with codon in A site (decoding center) changes conformation of ribosome. EF-Tu leaves ternary complex, and peptide bond is formed between amino acids as amino acids are positioned together in peptidyltransferase center.

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 for Relationship between Genotype and Phenotype DNA RNA protein genotype function organism phenotype DNA sequence amino acid sequence transcription translation

Molecular Basis for Relationship between Genotype and Phenotype DNA RNA protein genotype function organism phenotype DNA sequence amino acid sequence 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 Transfer Genetic code is essentially identical for all organisms. There are exceptions. System AUA UGA “universal” isoleucine termination mammalian mitochondria methionine tryptophan yeast 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.