cell structure and signalling , Lecture notes of Biology

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Eukaryotic Cell Signalling

Cell and Microbiology 4LMS

Meggie Nikolić

m.nikolic@herts.ac.uk

C

Aims

 Understand the following terms :

• Signalling
• Ligand
• Receptor
• Signalling pathways
• Signal transduction

 Understand the importance of signalling in the context of

development, adult function and disease

 Understand the basic principles of different signalling pathways

and their regulation

• Understand the principles of signal diversity
• Understand some regulatory steps in protein function that

operate during signalling

Signalling is activated by ligands

Ligand ( ligare = to bind; Latin )

receptor

ligand

Signal transduction

Cell Receptor proteins regulate most aspects of cell differentiation, cell proliferation and cell death

Ligands are most often proteins/peptides that bind to specific receptors on the cell surface and thus trigger a cascade of protein changes in inside the cell, thus altering the behaviour of the cell

Regulation of the cytoskeleton is fast

No transcription or translation are needed for the initial response

Signalling can affect cell shape and movement by controlling the assembly and disassembly of the cytoskeleton (very fast)

It can also affect what proteins are made in the cell – controlling gene expression (slower)

Development Cell proliferation, cell migration and differentiation, cell death, cell/tissue specification and function, cell response to the environment

Adulthood Cell function, cell death, cell replacement, cell response to the environment

Alterations in signalling can cause developmental defects

Alterations in signalling can cause cell loss (e.g. neurodegeneration) or cell gain (e.g. cancer)

e.g. Development of the central nervous system (CNS) is hugely dependent on correct signalling between cells

ABNORMAL SIGNALLING:

Cells STOP responding to the environment; however,

they still affect it.

This can be over short or long distances

• Cell survival and cell division
• Cell Differentiation (muscle cells, nerve cells, blood cells, etc.)
• Morphogenesis (organization of differentiated cells into tissues and organs). Cell fates.
• Programmed cell death

What do signalling

pathways entice cells

to do?

Many signalling pathways are activated by extracellular ligands binding cell surface receptors

Consequently, the receptor protein will trigger the activation of one or more cytoplasmic signalling molecules = signalling pathways; ONE IS SHOWN

Upon the activation of specific effector proteins (the ones that will actually cause the cell response), changes will be evident in the responding cell ( target cell responses ).

Once a receptor is activated (by binding to a ligand), this information is relayed through the cell by a cascade of molecular changes.

The cytoplasmic molecules (often proteins) that relay the information can amplify, transduce, integrate and distribute the incoming signal with the final result – a cellular change.

Types of signalling

http://philschatz.com/biology-book/contents/m44451.html

1. Direct cell signalling (cells have to be in close contact with each other so their interactions are via plasma membrane-associated molecules)
2. Indirect cell signalling (via secreted molecules) a. Autocrine (cells signal to themselves) b. Paracrine (cells signal to other nearby cells) c. Endocrine (cells signal through the blood stream to others that are further away = long distance signalling)

autocrine

paracrine

endocrine

Specificity of signalling – cells have to have the correct receptors

More than 50 different hormones are secreted from glands including the thyroid, pancreas, gonads and more

They only act on cells with appropriate receptors

e.g. endocrine signalling