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•Homework #1 is posted and due 9/20 •Bonus #1 is posted and due 10/25 •For Bonus points, today’s quiz is due T 9/18 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 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… Some Ca++ channels have specific effectors associated with them: Micro-domains Ikeda, Science 12 Oct 2001 Vol 294:318-319 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 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… 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 Opening and closing of stomata 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 2 hypotheses about how calcium signals are transduced: Signatures vs. Switches Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 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? •Homework #1 is posted and due 9/20 •Bonus #1 is posted and due 10/25 •For Bonus points, today’s quiz is due T 9/18