3. Cell Signaling, Growth And Divison Flashcards
Purpose of Cell Signalling
Cells require basic signaling to survive and in the absence will undergo apoptosis
Abnormal signaling - lead to unregulated growth or cancer or in an ineffective response to an extrinsic stress - shock
Regardless of type of signaling - protein is required for effective transmission
Paracrine Signalling
Cells in immediate vicinity are affected
Ex: NMJ - muscle contraction
Autocrine Signalling
When molecules secreted by the cell affect the same cell
Ex: T-cells stimulate themselves to release cytokines
Synaptic Signaling
Activated neurons secrete neurotransmitters at specialized cell junctions (synapses) into target cells
Ex: nerve impulse
Endocrine Signaling
Hormone is released into bloodstream and acts on a target at distant site
Intracellular receptors
Present inside cell, cytoplasm or nucleus
EX: vit D and steroid hormones
Vit D and Intracellular Receptors
Inactive Vit D in skin goes through processing in the liver and kidneys and is converted to active Vit D
Active Vit D binds to receptors in nucleus and increases transcription of genes required for calcium absorption
Calcium absorption is increased
Steroid hormones work similarly
Cell surface receptors
These include transmembrane proteins with extracellular domains that bind to solvable secreted liagnds
Functions of Receptors
Open ion channels and activate an associated G protein - required for drug binding
Activate an endogenous associated enzyme (RTK) - receptor tyrosine kinase, when ligand binds to receptor it causes phosphorylation of tyrosine residues that activate signaling pathways
Trigger proteolytic event or change in protein binding/stability that activates a latent transcription factor
Growth Factors
Key molecule that activates specific genes required for cell survival and division - promote growth
Functions of growth factors
Promoting cell cycle entry
Relieving blocks in cell cycle progression
Preventing apoptosis
Enhancing biosynthesis of cellular components required for cell divison
Importance of Balancer between Proliferation and Differentiation
Decided the baseline population of cells
- Proliferation rate : how fast cells multiply
- Differentiation rate: how fast cells can regenerate from stem cells
- Apoptotic rate: how fast cells die
- Regeneration rate: how fast cells differentiate and become mature cells, depends on cell cycle
Phases of Cell Cycle
Last 24 hours:
G0- inactive Phase
INTERPHASE:
G1- pre-synthetic growth (11hours)
S- DNA synthesis (8 Hours)
G2- pre-mitosis growth, make sure DNA synthesis happened properly (4 hours)
MITOTIC PHASE
M- mitotic phase (1 hour)
C- cytokinesis
Factors contributing to cell cycle activation or arrest
Each stage requires completion of previous step as well as activation of necessary factors
errors in DNA replication or cofactors deficiency result in arrest of various transition positions
Cell cycle is regulated by activators and inhibitors - cyclin dependent kinases (CDK)
Modifying activators = abnormal expression of CDK - continue to phosphorylation and drive cell cycle forward= cancer (unchecked growth)
Stem cells
Groups of primitive cells that differentiate and form tissues during development
Must meet 3 properties:
- Self-renewal: eternal cell division to maintain numbers
- Clonogenic: ability of one cell to form others
- Multipotent : can develop into more than one cell type
