Today: Signal Transduction the textbook has very little about signal transduction, see 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)

Protein 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?

Is there anybody out there? Cells and organisms must monitor and respond to the environment.

Stimulus Signal Transduction Stimulus Perception (by receptor) Effector Response Effector… Effector External Internal

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 Development Cold Guard cell closing Osmotic shock Light Fungal infection Touch Pollen tube growth Wounding… in Animals Neurons Muscle movement Wounding Development Fertilization Hormones … How can there be specificity?

Everything has its place…

Root nodules: Nitrogen fixation

Bacteria and Plants Symbiosis

Signaling between bacteria and plants

Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984 A biphasic Ca ++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus 1nM Nod10nM Nod

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

Fig 3. Shaw and Long, Plant Physiology, March 2003, Vol. 131, pp. 976–984 A biphasic Ca ++ response to Nod factor: 1nM Nod - toward nucleus 10nm Nod - away from nucleus 1nM Nod 10nM Nod 1nM Nod10nM Nod

Everything has its place… …and time.

Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 2 hypotheses about how Ca ++ signals are transduced: Signatures vs. Switches

Photosynthesis: Plants can make sugar using energy from the sun, water from the ground, and CO 2 from the air.

Stomata regulate gas exchange: CO 2 in, O 2 and water out H2OH2OH2OH2O

Stomata closedopen

Fig 5. Sanders et al., The Plant Cell, S401–S417, Supplement 2002 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 2. Allen et al., Nature, Vol 411: , 28 June 2001 Spike timing is critical for response

Fig 2. Allen et al., Nature, Vol 411: , 28 June 2001 Duration of spikes for stomata closing

Fig 1. Scrase-Field and Knight, Current Opinion in Plant Biology 2003, 6:500–506 2 hypotheses about how Ca ++ signals are transduced: Signatures vs. Switches

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 for more info. Bonus #1 due in class 2/24/09 Bonus #2 due in class on 4/21/09