Today: Signal Transductionthe 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)

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 thereanybodyout there?

Cells and organisms must monitor and respond to the environment.

Stimulus

Signal Transduction

Stimulus

Perception(by receptor)

EffectorResponse

Effector…

EffectorEffector

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 nucleus10nm Nod - away from nucleus

1nM Nod 10nM 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 nucleus10nm Nod - away from nucleus

1nM Nod 10nM Nod

1nM Nod 10nM 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 CO2 from the air.

Stomata regulate gas exchange: CO2 in, O2 and

water out

H2OH2O

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 411:1053-1057, 28 June 2001

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 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: Transcriptionthe 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