BIOL 1010 Lecture Notes - Lecture 5: G Protein–Coupled Receptor, Signal Transduction, Cell Signaling
Cell Communication
September 30, 2014
Signaling can be through direct contact through means of:
➢ Gap Junctions, in which small molecules can pass
➢ Cell-Cell Recognition, in which one cell recognizes another cell (widely used by cells
of our immune system containing receptors)
Signaling can also be local through means of:
➢ Paracrine Signaling
➢ Synaptic Signaling (neurotransmitter)
Signaling can be long-distance through means of:
➢ Endocrine Signaling
• Molecules (hormones) move far away from the secreting cell (endocrine
cell), through the blood to receptor cells
Three Stages of Cell Signaling:
1. Reception
• Signaling molecule binds to its receptor which causes the receptor to
undergo a conformational change
• This receptor is specific to the molecule
2. Transduction
• Relay molecules sends signal in a pathway
3. Response
• Activation of a cellular response
• The cell may grow, divide, eat, kill itself, etc.
Occasionally, the receptor is found inside the cell. This mostly happens with ligands that are
steroids (like sex hormones) because they can easily pass through the cell membrane. Once
the ligand is inside the cell, it binds with the receptor to make a complex. The ligand
hormone-receptor complex can then move into the nucleus and act as a transcription factor.
This causes an increase in mRNA production and eventually leads to synthesis of new
protein.
Receptors in the Cytoplasmic Membrane:
1. G Protein Coupled Receptors (GPCRs)
• Have 7 transmembrane domains
• Asymmetric (specific orientation)
• Many are sensory receptors (most often is perception)
• Named respectively because they interact with G proteins
o Bind GDP its in inactive state
o When activated, it releases GDP and binds with GTP
o GTPase is an enzyme
STEPS:
i) G protein is inactive and is bound to GDP. Ligand binds to GPCR.
ii) Once ligand binds, the receptor changes shape. This new shape means the G
protein can bind to the receptor. When the G protein binds to the receptor, the G
protein changes its shape so that GTP replaces GDP.
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Document Summary
Signaling can be through direct contact through means of: Gap junctions, in which small molecules can pass. Cell-cell recognition, in which one cell recognizes another cell (widely used by cells of our immune system containing receptors) Signaling can also be local through means of: Endocrine signaling: molecules (hormones) move far away from the secreting cell (endocrine cell), through the blood to receptor cells. Occasionally, the receptor is found inside the cell. This mostly happens with ligands that are steroids (like sex hormones) because they can easily pass through the cell membrane. Once the ligand is inside the cell, it binds with the receptor to make a complex. The ligand hormone-receptor complex can then move into the nucleus and act as a transcription factor. This causes an increase in mrna production and eventually leads to synthesis of new protein. Steps: g protein is inactive and is bound to gdp. Ligand binds to gpcr: once ligand binds, the receptor changes shape.
