Chapter 9 Flashcards
cell communication
- cells require this to survive
- known as cell signaling
- incoming and outgoing signals
- cells live in an environment: body is a huge environment and cells need to know how to talk to each other and outside world. Blood cells live in an environment, its important for BC to know whats going on around it
Cell communication; Plasma membrane
- PM isolates the cell
- a cell cannot survive if it cannot sense and respond to environmental changes
- PM is a boundary layer btw the cells and environment
- need a message from outside world for activity to take place
- thirsty
Why do cells need to respond to signals?
1.
- need to respond to a changing environment
- adaptation or a cellular response is critical for survival
- cells need to adapt to the change
- yeast cell- single cell, proteins inside
- glucose comes in and binds to the receptors and tells the cell something about the environment. enough glucose biding to cells present, cell responds by making glucose transporters
Why do cells need to respond to signals?
2.
- cells need to communicate with each other
- cell to cell communication
- coordinate cellular activities in multicellular organisms
Phototropism
- cells in the growing shoot tip sense light and send a signal (auxin) to cells on the nonilluminated side of the shoot.
- cells located below the growing tip receive this signal and elongate, thereby causing a bend in the shoot. In this way, the tip grows toward the light
5 methods of cell to cell communication; 1. Direct intercellular signaling
-cell junctions allow signaling molecules to pass from one cell to another
5 methods of cell to cell communication: 2. contact dependent signaling
-some molecules are bound to the surface of cells and serve as signals to cell coming in contact with them
5 methods of cell to cell communication; 3. autocrine signaling
-cells secrete signaling molecules that bind to their own cell surface and/or neighboring cells of the same type
5 methods of cell to cell communication; 4. Paracrine signaling
- signal does not affect cell secreting the signal but does influence cells in close proximity
- neuronal signaling, blood clotting
5 methods of cell to cell communication; 5. endocrine signaling
- signals (hormones) travel long distances
- hormones are released into the bloodstream
- can travel virtually anywhere in the body/organism
- usually slower acting, but longer lasting; estrogen, insulin etc
Stage one of cell signaling; 1. receptor activation
- signaling molecule (ligand) binds to its cellular receptor (protein)
- receptor undergoes a conformational/ structural change
Stage two of cell signaling; 2. signal transduction
- activated receptor stimulates sequence of cellular changes
- a group of proteins form a signal transduction pathway
- often a multi-step process
Stage three of cell signaling; 3. cellular response
- activation of a cellular response
- a huge range of responses
- alter activity of enzymes; alter cellular structure, gene expression
Ligand
- signaling molecule (key)
- steroid, peptide or protein
- hydrophilic and/or large; cannot cross the membrane easily
- binds noncovalently to receptor (lock) with high degree of specificity
- binding and release between receptor and ligand is relatively rapid
Ligand- Botex
- binding and release is not always rapid
- Clostridium botulinum
- produces most potent toxin known to human kind as a defense mechanism
- inhibits muscle cell receptors
ligand cont.
-ligands alter receptor structure 0conformation change; different structure= different function -ligand-receptor complex is activated -can initiate a cellular response -unbound receptor is not activated
enzyme linked receptor; cell surface receptor (3)
- found in all living species
- extracellular domain binds signal
- causes intracellular domain to become functional catalyst
- most protein kinases
G-protein coupled receptors (GPCR); cell surface receptor (3)
- common in eukaryotes
- protein receptor contains 7 transmembrane segments
- activated receptor binds to G protein
- releases GDP and binds GTP instead
- GTP causes G protein to disassociate
G-protein coupled receptors in mammals
- largest class of cell surface receptors in mammals
- 1000 genes in humans code for GPCRs (3% total genome)
- 300-400 mediate effects of endogenous ligands
- many are for exogenous ligands
ligand-gated ion channels; cell surface receptors (3)
- the receptor is an ion channel
- ligand binding causes ion channels to open and ions to flow through the membrane
- important for signals between nerve and muscle cells, between 2 nerve cells
Intracellular receptors
- most receptors are on the plasma membrane, but some are inside the cell
- estrogen receptors is a steroid which is a lipid and is made up of…
- steroid receptors- estrogen receptors (ERs)
- ligand is hydrophobic
- passes through membrane and binds to receptor in nucleus
- estrogen-receptor complexes bind to DNA
- activates transcription of specific genes
what produces the cellular response to signals?
- signal transduction pathway
- may involve cascade of kinases
- or generation of second messengers
Receptor Tyrosine Kinases
- enzyme-linked receptors in animal cells
- recognize various signaling molecules
- ex: EGF (epidermal growth factor)
- stimulates cells to divide
Receptor activation (step 1)
- two EGF molecules bind to 2 EGF receptor subunits, causing them to dimerize and phosphorylate each other on tyrosine’s
Relay between the receptor and protein kinase cascade (step 2)
- Grb binds to the phosphorylated receptor and then to Sos. Sos. stimulates Ras to release GDP and bind to GTP
Protein kinase cascade (step 3)
Ras activates Raf, which starts a protein kinase cascade in which Raf phosphorylates Mek, and then Mek phosphorylates Erk
Activation of transcription factors (step 4)
Erk enters the nucleus and phosphorylates transcription factors, Myc and Fos
Cellular response (step 5)
Myc and Fos stimulate the transcription of specific genes, the mRNAs are translated into proteins that cause the cell to progress through the cell cycle and divide
EGF and cancer
- overactive EFG receptor observed in some cancers
- targeted therapies being developed to inhibit activity
GPCR’s and Second Messengers
- signals binding to cell surface are first messengers
- very diverse range of first messengers
- many signal transduction pathways lead to production of second messengers
- much more limited range of second messengers
- relay signals inside cells
- ex: cAMP
cAMP (a second messenger)
- cyclic adenosine moniphosphate
- signal binding to GPCR activates pathway leading to synthesis of cAMP
cAMP
- activates protein kinase A (PKA)
- then PKA goes on to phosphorylate several proteins
cAMPs- signal amplification and speed
-binding of signal to single receptor can cause the synthesis of many cAMP that activate PKA, each PKA can phosphorylate many proteins
Caffeine
- inhibits cAMP removal
- causes cAMP to persist longer
- so heart beats faster
Hormonal signaling
- what is a hormone?
- type of cellular response caused by a given signaling molecule depends on the type of cell responding to the signal
epinephrine
- dilates pupils
- inhibits salivation
- stimulates glucose release from glycogen in skeletal muscle cells
- constricts blood vessels
- relaxes airways
- speeds heat rate
- stimulates sweating
- fight or flight
ADH??
-antiduretic hormone
apoptosis
-programed cell death
0cell shrinks and forms a rounder shape due to destruction of nucleus and cytoskeleton
-plasma membrane forms blebs- irregular extension that breaks away
steps of apoptosis
- cell beginning apoptosis
- condensation of nucleus and cell shrinkage
- multiple extensions of the plasma membrane
- further blebbing
Apoptosis- intrinsic vs. extrinsic
??
