Regulating Gene Expression

• Gene expression can be controlled at the transcriptional level by altering the rate of transcription genes.
• Gene expression is controlled by transcription factors - Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription.
• Factors that increase the rate of transcription are called activators
• Factors that decrease the rate of transcription are called repressors.
• The shape of a transcription factor determines whether it can bind to DNA or not and can sometimes be altered by the binding of some molecules
• The amount of certain molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding.
• In Eukaryotes, transcription factors bind to specific DNA sites near the start of their target genes - The genes they cannot control the expression of.
• In Prokaryotes control of gene expression often involves transcription of factors binding to operons.
• An operon is a section of DNA that contains a cluster of structural genes, that are transcribed together, as well as control elements and sometimes a regulatory gene.
• Structural genes code for useful proteins such as enzymes.
• Control elements include a promotor and an operator.
• A promotor is a DNA sequence located before the structural genes that the RNA polymerase binds to
• An operator is a DNA sequence that transcription factors bind to.
• Genes in Eukaryotic DNA contain sections that don't code for amino acids. These sections of DNA are called introns
• All the bits that do code for amino acids are called exons.
• During transcription the introns and exons are both copied into mRNA. mRNA strands containing these are called primary mRNA transcripts.
• Introns are removed from primary mRNA strands by a process called splicing - Introns are removed and exons joined, forming mature mRNA strands in the nucleus.
• The mature mRNA then leaves the nucleus for translation.
• Some proteins aren't functional straight after they have been synthesised - They need to activated to work
• Protein activation is controlled by molecules, some of these molecules work by binding to cell membranes and triggering the production of cyclic AMP inside the cell.