Cell Communication

What is direct signal transfer and how it different between animal and plant cells?

• Direct signal transfer is the signal transfer between cells that are direct neighbors

  • Animals use the gap junction which are protein tubes used to pass ions and small molecules through to allow for communication 

  • Plants use plasmodesmata which is a hole in the cell wall that make the plasma membrane of adjacent cells continuous so the signal will slowly diffuse through the cytoplasm 

What is the local signaling-paracrine?

• Local signaling-paracrine signaling is still in an enclosed area but larger 

  • Use vesicles to release a signaling molecule into the area and target adjacent cells will detect it and respond 

What is distance signaling-endocrine?

• Distance signaling-endocrine spreads throughout body

  • Distance signaling-endocrine is a form of cell communication where hormones are released into the bloodstream, allowing them to travel throughout the body and target specific cells equipped to detect and respond to these signals.

What are the three main steps in the generic signaling pathway?

1. Reception: Detection of the signaling molecule by a receptor at the cell membrane

2. Transduction: Conversion of the signal into a cellular response; where the signal is passed to the nucleus

3. Response: Activation of cellular responses that alter behavior or function

Describe how G Protein-Coupled Receptors (GPCR) work.

• 1. Every protein begin inactive 

• 2. GPCR will bind to the signaling molecule so it becomes active then the G protein will drift around and bump into GPCR then activates by throwing away GDP and taking a new GTP 

• 3. G protein will drift to enzyme until touching then enzyme activates 

• 4. Signaling molecule will leave GPCR and turns it off then the G protein will leave enzyme then enzyme turns off and the G protein turns GTP into GDP and turns off

Describe ion channel receptors.

• Ion channel receptors are gated channel proteins 

• If there is no signaling molecule then the gate will be closed but when a signaling molecule binds to the receptor, the gate will open and ions will come in 

• When the signaling molecule leaves, the gate closes

Describe intracellular receptors.

• Rather than detecting at the cell surface, the intracellular receptor detects inside the cell

• Signaling molecule has to be small and nonpolar because they have to travel through the membrane and into the cell on their own 

• Other signaling molecules were detected outside cell so they don’t need to travel across the cell membrane 

• No passing of the message like other pathways because receptor with the signaling molecule inside goes directly to nucleus and triggers the response themselves 

What happens during transduction and what does it involve?

• Once the signal has been received and crosses the membrane it must be carried from the membrane to the portion of the cell that will respond

• Phosphorylation cascade

What 2 types of enzymes are involved in the phosphorylation cascade?

• Kinases which are enzymes that add phosphate groups

• Phosphatases which are enzymes that remove phosphate groups 

Describe the phosphorylation cascade.

• Reception process has activated the relay molecule and it will turn on the phosphorylation cascade for transduction 

• Relay molecule will bind to kinase A and cause it to be active

• Then kinase A will activate kinase B via phosphorylation

• Kinase B will go find the protein it needs to phosphorylate and the active protein will then trigger the cellular response 

• Phosphatases will go in and remove the phosphate groups to turn off all of the kinases and protein once the response is finished   

How does reception trigger transduction?

• Through secondary messengers

  • Secondary messengers are intracellular messengers that help pass signal from the receptor to the signal transduction pathways 

• Primary messenger is the signaling molecule but the receptor will trigger a secondary messenger that will trigger transduction

  • Example is the relay molecule in the phosphorylation cascade 

Describe Cyclic AMP (cAMP)

• Cyclic AMP is a type of secondary messenger (AMP means monophosphate) 

  • An enzyme called adenylyl cyclase takes the ATP and cleaves off two phosphate groups and leaves only one (monophosphate) 

  • Then it builds a bond between the remaining phosphate group and the sugar

Describe cAMP in action.

• GPCR will activate the adenylyl cyclase which will convert ATP into cAMP 

• The cAMP will then activate the first protein in the phosphorylation cascade 

What is signal amplification (part of response)?

• One signal binds to one receptor which will activate very many G-proteins until the signaling molecule detaches 

• Result is a very strong response (1 to 100 instead of 1 to 1) from a very small signal