What is Cell Communication?
-- Cell communication is how cells sense and react to their environment and/or signals from other cells |
-- It can be through direct cell-to-cell contact |
-- It consists of ligands and receptors; ligands are molecules that bind to receptors (signals); receptors are proteins that detect external signals (antenna) |
-- The signal always come from the exterior of the cell (extracellular) |
Steps of Cell Signaling:
1. Reception -- ligand binds to receptor causing receptor to change shape |
2. Transduction -- information transfer from receptor throughout cell |
3. Response -- how the cell changes |
Understanding Pathway Diagrams
-- Pointed arrows means activates |
-- Blunt arrow means inhibit |
-- For multi-step pathways you should simplify into the overall result |
-- Similar to math, if there is two inhibitions it would result in an activation |
Summary of Cell Signaling
-- Different cell types can have different response to the same ligand because they have different receptors |
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RECEPTION
-- Types of receptors: |
-- Cell surface receptors |
Ligand-gated ion channels: |
Receptors are ion channels that open and let ions cross the membrane |
G protein-coupled receptors (GPCR): |
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 |
Receptor tyrosine kinases (RTK): |
Kinases are enzymes that add phosphate groups to other molecules. When a ligand binds it turns on kinase activity of RTKs. |
-- Intracellular receptors |
-- This is when the receptor is in side the cell. Unlike cell surface receptors, the ligands are nonpolar. These regulate gene expression. |
Types of Ligand
-- Ligands can be: gases ions, lipids, proteins, amino acids, nucleotides, etc |
Structure Determines Function
-- Ligand binding to a receptor changes the receptors shape |
-- Change in receptor shape = change in receptor function |
TRANSDUCTION
Amplification |
-- When one ligand binding to one receptor it results in many molecules inside the cell |
-- Each molecule in the signaling pathway can be recycled |
Second Messengers |
-- These activate many enzymes within the cell |
-- For example: Cyclic AMP. The activation of some GPCRs increase cAMP while others decrease cAMP. |
-- Activation of GPCRS regulate the production of second messengers |
-- cAMP can activate other proteins like protein kinase A which is an important regulator of metabolic pathways |
the "first messenger" is the ligand binding to the receptor |
Phosphorylation cascades |
-- Phosphorylation changes the shape of protein, in result changes the function |
RESPONSE
Common cellular response |
Gene expression: |
activation of transcription of specific genes |
Enzyme activation: |
turning on kinases |
Apoptosis: |
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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CELL CYCLE
-- There are four phases to the cell cycle |
G1 (gap 1) = cell growth |
S (synthesis) = DNA replication |
G2 (gap 2) = cell growth, prepare for mitosis |
M (mitosis) = cell division |
Regulation of Cell Cycle
-- Cyclins are proteins that regulate cyclin-dependent kinases (CDKs) |
-- Cyclins/CDKs control which phase of the cell cycle a cell is in |
-- If the cell is not regulated, it can result in cancer which is abnormal growth due to the continuous progression through the cell cycle |
Diagram of The Cell Cycle
Cell Cycle Checkpoints
Checkpoints determine if the cell is ready to progress to the next phase of the cell cycle |
-- G1 checkpoint: |
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. |
-- G2 checkpoint: |
It checks whether DNA has been replicated correctly. If so, the cell continues on to mitosis. |
-- M checkpoint: |
It checks whether mitosis is complete. If so, the cell divides, and the cycle repeats. |
MITOSIS
-- Interphase |
DNA is replicated, cell prepare for mitosis. The nuclear envelop are distant and the chromosomes are in the form of threadlike chromatin. |
-- Prophase |
Chromatin condenses making the chromosomes visible and nuclear envelop breaks down |
-- Metaphase |
The thick, coiled chromosomes, each with two chromatids, become aligned at the equatorial/metaphase plane |
-- Anaphase |
Sister chromatids separate and the daughter chromosomes move toward the poles |
-- Telophase & Cytokinesis |
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. |
Mitosis vs. Meiosis (continued)
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