Gene Regulation

• Proteins are produced on polyribosomes
• Multiple ribosomes simultaneously translate the same mRNA, boosting efficiency
• Targets of antibiotics
• Subtle differences in the way bacteria and eukaryotes synthesize RNA and proteins
• Many common antibiotics were first isolated from fungi because fungi and humans are both eukaryotes
• Post-translational modifications
• Proteins fold into the correct three-dimensional shape either spontaneously or with the help of chaperone proteins
• Newly synthesized proteins require post-translational modifications to become fully functional
• Some proteins are covalently modified with phosphoryl (phosphorylation) or glycosyl (glycosylation) groups
• Some proteins bind or associate with small molecule co-factors or other protein subunits
• Lifespan of a protein
• Proteases are enzymes that degrade proteins by hydrolyzing peptide bonds between amino acids
• The lifetime of proteins must be kept short
• Damaged or misfolded proteins must be recognized and removed
• In eukaryotic cells, proteins are broken down in proteasomes
• The central cylinder of proteasomes is made up of proteases, and stoppers bind the proteins destined for degradation
• Proteases are housed inside the proteasome cylinder to confine their activity
• Proteins are directed to the proteasome for degradation through the covalent attachment of a small protein called ubiquitin
• Specialized enzymes tag proteins with a short chain of ubiquitin molecules for degradation
• RNA can serve as information storage and catalysts
• The ribosome, the protein synthesizing machinery, is a ribozyme, providing evidence that RNA can catalyze the synthesis of proteins
• Gene regulation
• Cells become different from each other based on the proteins they produce
• Every somatic cell nucleus contains the complete genome established in the fertilized egg
• Gene expression in eukaryotes is controlled at transcription, processing, RNA transport, translational, and post-translational levels
• Transcription regulators recognize a part of the promoter and recruit RNA pol II to form a pre-initiation complex
• Transcription depends on regulatory sites (enhancer or silencer) on the DNA, recognized by transcription factors
• Transcription factors are DNA-binding proteins that regulate transcription by binding to regulatory DNA sequences
• Transcription factors direct the modification of local chromatin structure to facilitate transcription initiation
• Combinations of transcription factors work together to determine gene expression through combinatorial control
• A single transcription factor can play a key role in switching a particular gene on or off
• In the presence of cortisol hormone, liver cells increase the expression of many genes to produce glucose
• Enhancers are regions of DNA that can be located far away from the promoter but still affect its activity.