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-- Cell communication is how cells sense and react to their environment and/or signals from other cells
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-- It can be through direct cell-to-cell contact
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-- It consists of ligands and receptors; ligands are molecules that bind to receptors (signals); receptors are proteins that detect external signals (antenna)
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-- The signal always come from the exterior of the cell (extracellular)
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1. Reception -- ligand binds to receptor causing receptor to change shape
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2. Transduction -- information transfer from receptor throughout cell
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3. Response -- how the cell changes
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-- Pointed arrows means activates
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-- Blunt arrow means inhibit
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-- For multi-step pathways you should simplify into the overall result
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-- Similar to math, if there is two inhibitions it would result in an activation
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-- Different cell types can have different response to the same ligand because they have different receptors
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-- Types of receptors:
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-- Cell surface receptors
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Ligand-gated ion channels:
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Receptors are ion channels that open and let ions cross the membrane
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G protein-coupled receptors (GPCR):
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Receptors are associated with G protein. When the receptor is activated it causes the G protein to activate. The G protein activates enzymes. ligand --> GPCR --> G protein --> enzyme --> second messengers
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Receptor tyrosine kinases (RTK):
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Kinases are enzymes that add phosphate groups to other molecules. When a ligand binds it turns on kinase activity of RTKs.
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-- Intracellular receptors
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-- This is when the receptor is in side the cell. Unlike cell surface receptors, the ligands are nonpolar. These regulate gene expression.
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-- Ligand binding to a receptor changes the receptors shape
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-- Change in receptor shape = change in receptor function
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Amplification
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-- When one ligand binding to one receptor it results in many molecules inside the cell
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-- Each molecule in the signaling pathway can be recycled
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Second Messengers
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-- These activate many enzymes within the cell
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-- For example: Cyclic AMP. The activation of some GPCRs increase cAMP while others decrease cAMP.
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-- Activation of GPCRS regulate the production of second messengers
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-- cAMP can activate other proteins like protein kinase A which is an important regulator of metabolic pathways
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the "first messenger" is the ligand binding to the receptor
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Phosphorylation cascades
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-- Phosphorylation changes the shape of protein, in result changes the function
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Common cellular response
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Gene expression:
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activation of transcription of specific genes
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Enzyme activation:
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turning on kinases
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Apoptosis:
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programmed cell death in which the cell breaks down while protecting neighboring cells. It is important for development and a normal process in healthy organisms
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-- There are four phases to the cell cycle
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G1 (gap 1) = cell growth
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S (synthesis) = DNA replication
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G2 (gap 2) = cell growth, prepare for mitosis
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M (mitosis) = cell division
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-- Cyclins are proteins that regulate cyclin-dependent kinases (CDKs)
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-- Cyclins/CDKs control which phase of the cell cycle a cell is in
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-- If the cell is not regulated, it can result in cancer which is abnormal growth due to the continuous progression through the cell cycle
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Checkpoints determine if the cell is ready to progress to the next phase of the cell cycle
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-- G1 checkpoint:
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It checks whether the cell is big enough and has made the proper proteins for the synthesis phase. If not, the cell goes through a resting period (G0) until it is ready to divide.
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-- G2 checkpoint:
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It checks whether DNA has been replicated correctly. If so, the cell continues on to mitosis.
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-- M checkpoint:
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It checks whether mitosis is complete. If so, the cell divides, and the cycle repeats.
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-- Interphase
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DNA is replicated, cell prepare for mitosis. The nuclear envelop are distant and the chromosomes are in the form of threadlike chromatin.
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-- Prophase
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Chromatin condenses making the chromosomes visible and nuclear envelop breaks down
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-- Metaphase
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The thick, coiled chromosomes, each with two chromatids, become aligned at the equatorial/metaphase plane
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-- Anaphase
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Sister chromatids separate and the daughter chromosomes move toward the poles
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-- Telophase & Cytokinesis
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The chromosomes are at the poles, and are becoming more diffuse. The nuclear envelop is reforming. They cytoplasm may be dividing. Then the division into two daughter cells.
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Cheatography n. The art of mapping complex subjects into clear, instantly navigable reference guides.
