Activity 7.21 Transcription factors

Transcription

1 Purpose To consolidate understanding of protein synthesis. To explain the role of transcription factors and hormones in switching genes on and off. Play the transcription initiation complex game Regulation of gene expression is vital to ensure the normal development and functioning of an organism. Specific proteins are made at the appropriate time in the appropriate places and in response to specific signals. To switch on expression of a gene, a transcription initiation complex must successfully form which allows transcription of the gene to start. The transcription initiation complex is made up of a group of transcription factors and RNA polymerase which bind onto the promoter region of the DNA adjacent to the gene to be transcribed. The exact order in which these factors bind is not known with certainty. In some experiments the transcription factors seem to bind in a specific order. In other cases, most of the factors are thought to first assemble with the polymerase, with this whole assembled complex then binding to the DNA in a single step. The number of transcription factors found within an organism increases with the size of the genome. There are thought to be approximately 2600 proteins in humans that can bind to DNA. If most of these function as transcription factors then about 10% of our genes must code for transcription factors. This makes transcription factors the largest group of human proteins. The general transcription factors have been highly conserved in evolution, with the same factors occurring in different organisms from humans to simple single-cell organisms. In the transcription initiation complex game you build a complex which involves either a peptide or steroid hormone. The complex switches on a gene. Remember, this is just a theoretical example every transcription initiation complex has a range of different factors with some acting as activators and others repressing expression. How to play the game The aim is to collect all the transcription factors plus RNA polymerase to build a transcription initiation complex. You must collect transcription factors 1, 2 and 3 in order first; you then collect the other pieces in any order. The winner is the first to have a complete transcription initiation complex. 1 Each player selects a transcription initiation complex board; this shows an outline of the complex you have to build and the role of the hormone in forming the transcription initiation complex. 2 Shuffle the cards and lay them face down. 3 Take it in turns to pick up one card. If it is one of the transcription factors, hormones or RNA polymerase that you need to build your initiation complex, keep the card, face up next to you. If it is a card you do not require show it to the other players before replacing it face down. Remember you have to collect transcription factors 1, 2 and 3 first. Once you have these three pieces, you can collect the others in any order. If you turn over a repressor molecule you miss a turn because it binds to your DNA and stops transcription. Remove the repressor from the game by keeping it face up next to you. This sheet may have been altered from the original. 1of 6

2 Once you have a winner View the animation that accompanies this activity, which shows the initiation of transcription occurring, and then complete the tasks below. 1 Trace or cut up your cards to produce an annotated diagram for your notes. Annotate the diagram so it explains the role of transcription factors in the control of gene expression. 2 Find a person who has a different board, exchange annotated diagrams and check their annotations. 3 Draw a flow chart that shows how a a peptide hormone, and b a steroid hormone is produced and can switch on gene expression. Include as much detail as you can. 4 Transcription factors have key roles in development and differentiation. Some human diseases have been linked to mutations of transcription factors. Do an Internet search to find some examples of these diseases. Then try the crossword to revise some of the ideas about hormones and transcription factors. This sheet may have been altered from the original. 2of 6

3 The boards Board A peptide hormone Board B Steroid hormone This sheet may have been altered from the original. 3of 6

4 The cards One set of cards should be provided for each player. This sheet may have been altered from the original. 4of 6

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6 Name Hormones and Transcription Factors Across 1. Property of molecules that can prevent, or make it more difficult, for them to pass through cell membranes 4. Process that takes place at the ribosome 8. Molecule that prevents gene transcription by attaching to the promoter region on the DNA 9. Translation organelle 11. Process that creates specialised cells 12. Sequence of many amino acids linked by peptide bonds 14. Type of hormone with amino acid monomers 17. Catalytic protein Down 2. All the genes in an organism 3. Type of hormone that includes oestrogen and testosterone 4. Factor that is found in all living organisms, essential for gene expression and name of first stage in protein synthesis 5. Programmed cell death 6. This RNA enzyme is essential for gene expression 7. Region of DNA molecule, adjacent to gene, to which transcription initiation complexes bind 10. Ductless glands that produce hormones 13. Peptide hormone with 51 amino acids 15. Specific cells affected by specific hormones 16. Sequence of bases that codes for a particular polypeptide Created with the help of Wordsheets - This sheet may have been altered from the original. 6of 6