9

transcription of gene into mRNA followed by translation of mRNA into a protein

proteins are needed at the same level all the time

• One controls the activity of preexisting enzymes
• Posttranslational regulation
• Very rapid process (seconds)

• One controls the amount of an enzyme
• Regulate level of transcription
• Regulate translation
• Slower process (minutes)

DNA Binding Protein

• First helix is the recognition helix
• Second helix is the stabilizing helix
• Many different DNA-binding proteins from Bacteria contain helix-turn-helix
• lac and trp repressors of E. coli

DNA Binding Protein

• Protein structure that binds a zinc ion
• Typically two or three zinc fingers on proteins that use them for DNA binding

• Leucine residues are spaced every seven amino acids
• Does not interact directly with DNA unlike helix-turn-helix or Zinc Finger

1)DNA-binding protein may catalyze a specific reaction on the DNA molecule (i.e., transcription by RNA polymerase)

2)The binding event can block transcription (negative regulation)

3)The binding event can activate transcription (positive regulation)

a regulatory mechanism that stops transcription

Repression and Induction

preventing the synthesis of an enzyme in response to a signal

Enzymes affected by any repression make up a small fraction of total proteins in the cell

Typically affects anabolic enzymes (i.e., arginine biosynthesis)

production of an enzyme in response to a signal

• Typically affects catabolic enzymes (i.e., lac operon)
• Enzymes are synthesized only when they are needed so no wasted energy

collective term for inducers and Corepressors (which induce or repress enzyme synthesis)

Effectors affect transcription indirectly by binding to specific DNA-binding proteins

• Repressor molecules bind to an allosteric repressor protein
• Allosteric repressor becomes active and binds to region of DNA near promoter called the operator

cluster of genes arranged in a linear fashion whose expression is under control of a single operator

• Operator is located downstream of the promoter
• Transcription is physically blocked when repressor binds to operator

an enzyme that phophorylates compounds