Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Today: Signal Transduction the textbook has very little about signal transduction, see http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.section.2743 for more info. Bonus #1 due in class 2/24/09 Bonus #2 due in class on 4/21/09 Five Perceptions of Genes: 1. Genes act as units of heredity 2. Genes are seen as a cause of disease 3. Genes code for proteins 4. Genes act as switches, controlling development 5. Genes are replicators (selfish gene) DNA is used to produce RNA and/or proteins, but not all genes are expressed at the same time or in the same cells. How do cells control which genes are expressed? Protein Cells and organisms must monitor and respond to the environment. Is there anybody out there? Signal Transduction External Stimulus Internal Effector… Effector Effector Effector Response Perception (by receptor) Stimulus Signal transduction step by step: Perception Signal transduction step by step: Transduction Signal transduction step by step: Response – such as changes in cellular components or production of new cellular components Transduction can involve activation or inactivation of proteins. Cellular responses may involve changes in the expression of genes. Blood sugar levels as an example of cellular responses to the environment Why so many steps? Multiple steps allow for signal specificity. Different relay molecules lead to different responses Multiple steps allow for signal amplification: Calcium is a simple method of amplifying signals Calcium is a common effector. Cytoplasmic calcium levels are normally low. During signal transduction, calcium can be released into the cytoplasm: Perception During signal transduction, calcium can be released into the cytoplasm: Transduction During signal transduction, calcium can be released into the cytoplasm: Response During signal transduction, calcium can be released into the cytoplasm General model of Ca++ signaling Multiple steps allow for signal amplification: Calcium is a simple method of amplifying signals Ca++ is involved in many responses Ca++ is involved in signal transduction for responses of: • • • • • • • • • in Plants in Animals Development • Neurons Cold • Muscle movement Guard cell closing • Wounding Osmotic shock • Development Light • Fertilization Fungal infection • Hormones Touch • … Pollen tube growth Wounding… How can there be specificity? Everything has its place… Root nodules: Nitrogen fixation Bacteria and Plants Symbiosis Signaling between bacteria and plants 1nM Nod Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984 10nM Nod A biphasic Ca++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus Bacteria and Plants Symbiosis Bacteria close to root, 10nM Nod, nodule formation . . . . . . . . Bacteria and Plants Symbiosis Bacteria far from root, 1nM Nod, root grows towards bacteria . . . . . . . . 1nM Nod 10nM Nod 1nM Nod 10nM Nod A biphasic Ca++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984 Everything has its place… …and time. 2 hypotheses about how Ca++ signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 Photosynthesis: Plants can make sugar using energy from the sun, water from the ground, and CO2 from the air. Stomata regulate gas exchange: CO2 in, O2 and water out H2 O H2 O Stomata open closed Ca++ fluxes in guard cells in response to hormone or stress that cause stomatal closing. Wildtype vs. det3 and gca2: mutants that fail to close stomata following treatment Fig 5. Sanders et al., The Plant Cell, S401–S417, Supplement 2002 Spike timing is critical for response Fig 2. Allen et al., Nature, Vol 411:1053-1057, 28 June 2001 Duration of spikes for stomata closing Fig 2. Allen et al., Nature, Vol 411:1053-1057, 28 June 2001 2 hypotheses about how Ca++ signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 Signal transduction – such as changes in cellular components or production of new cellular components How do cells express genes? Next: Transcription the textbook has very little about signal transduction, see http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.section.2743 for more info. Bonus #1 due in class 2/24/09 Bonus #2 due in class on 4/21/09