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| Pregunta | Respuesta |
| All the cells in an organism carry the same genes (DNA), but the structure and function of different cells varies. Why? | Not all the genes in a cell are expressed (transcribed and used to make a functional protein) - they are selectively switched on or off |
| Name the 3 levels in which gene expression is controlled | Transcriptional level control Post-transcriptional level control Post-translational level control |
| Complete the sentences: Gene expression can be controlled at the transcriptional level by altering the ______ of transcription of ______. For example, increased transcription produces more ______, which can be used to make more protein. | Gene expression can be controlled at the transcriptional level by altering the RATE of transcription of GENES. For example, increased transcription produces more MRNA, which can be used to make more protein. |
| What are transcription factors? | Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription |
| What is the name for transcription factors that start transcription? | Activators |
| What is the name for transcription factors that stop transcription? | Repressors |
| TRUE OR FALSE: The shape of the transcription factor has no effect on its ability to bind to DNA | FALSE The shape of a transcription factor determines whether or not it can bind to DNA |
| Where do transcription factors bind to in eukaryotes? | In eukaryotes, transcription factors bind to specific DNA sites near the start of their target genes - these are the genes they control the expression of |
| Where do transcription factors bind to in prokaryotes? | Control of gene expression often involves transcription factors binding to operons |
| What is an operon? | An operon is a section of DNA that contains a cluster of structural genes that are all transcribed together, as well as control elements and sometimes a regulatory gene |
| What does the structural gene on an operon code for? | The structural genes code for useful proteins, such as enzymes |
| What are the control elements on an operon composed of? | A promoter (a DNA sequence located before the structural genes that RNA polymerase binds to) An operator (a DNA sequence that transcription factors bind to) |
| What does the regulatory gene on an operon code for? | The regulatory gene codes for an activator or a repressor |
| Complete the sentences: E. coli is a ___________ that respires glucose, but it can use _________ if glucose isn't available. The lac operon has three structural genes - ______, ______ and ______. The lac operon is around ________ base pairs long. | E. coli is a BACTERIUM that respires glucose, but it can use LACTOSE if glucose isn't available. The lac operon has three structural genes - LAC Z, LAC Y and LAC A. The lac operon is around 6000 base pairs long. |
| Describe the structure of the lac operon |
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| Outline what happens at the lac operon when lactose is NOT present |
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| Outline what happens at the lac operon when lactose IS present |
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| What is post-transcriptional level control? | Control of gene expression that takes place after genes have been transcribed |
| Complete the sentences: After transcription, mRNA in eukaryotic cells is ________ - that's because genes in eukaryotic DNA contains sections that don't code for _________ ______. These sections are called _________. The rest of the DNA that do code for amino acids are called ________. | After transcription, mRNA in eukaryotic cells is EDITED - that's because genes in eukaryotic DNA contains sections that don't code for AMINO ACIDS. These sections are called INTRONS. The rest of the DNA that do code for amino acids are called EXONS. |
| What happens to the introns and exons during transcription (before the mRNA strand exits the nucleus)? | They are both copied into mRNA Introns are removed from primary mRNA strands by a process called splicing - introns are removed and the exons are jointed together to form mature mRNA strands. This takes place in the nucleus. The mature mRNA then leaves the nucleus for translation. |
| What are mRNA strands containing introns and exons called? | Primary mRNA transcripts |
| What does post-translational level control involve? | Protein activation E.g. in protein synthesis, protein activation is controlled by molecules like hormones and sugars |
| Describe how some molecules control protein activation using cAMP | Some molecules that control protein activation work by binding to cell membranes and triggering the production of cyclic AMP (cAMP) inside the cell. cAMP then activates proteins inside the cell by altering their 3D structure. |
| PKA is an enzyme made of four subunits. What happens when cAMP binds? What happens when cAMP does NOT bind? | When cAMP isn't bound, the four units are bound together and are inactive When cAMP binds, it causes a change in the enzyme's 3D structure, releasing the active subunits |
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