Forensic biology - Cell signalling and communication

  • Created by: aarafa11
  • Created on: 31-05-20 17:33
Individual cells must
Communicate with their neighbours; Monitor internal and external environmental conditions; Respond appropriately to many stimuli that may potentially affect them; Communicate with other cells
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how do cells comunicate
cell signalling
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What are the signals that come from external environment
light, temperature & chemicals e.g. CO2, H+
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What are the signals that come from internal environment
hormones; neurotransmitters; cytokines - immuno-chemicals; physical stress
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What do cells use to communicate
contact-dependant; paracrine; synaptic; endocrine
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Received signal has to be transmitted to its recipient via
Release of secondary signal molecules; Initiation of a signal transduction pathway
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What are the signal transductions chemical reaction
One reaction initiates the reaction below; Characterised by enzymes changing from inactive to active state; Often due to phosphorylation (Control & communication within a cell is a very similar)
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Intra-cellular receptors
Receptor protein is inside the cell; signal chemical (ligand) must be able to diffuse into the cell; Must be non-polar and not too large
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categories of receptors on the surface of eukaryotic cells
Ion channel receptors; Enzyme coupled receptors; G Protein- coupled receptors
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How does ion channel receptors work
Ligand binds to receptor, causing it to change shape – opens the gate
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What type of signals does the ion channel receptors use
light, sound and various chemical ligands such as hormones; neurotransmission
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How does enzyme coupled receptors work
Activated phosphokinase phosphorylates a specific cytoplasmic protein; signal transferred into cell; Signal continues as long as the ligand and receptor protein remain bound – this amplifies the signal
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Types of enzyme coupled receptors
Protein kinases; Receptor tyrosine kinase (Phosphorylates other proteins); Phosphorylates other proteins (phosphorylates tyrosine amino acid residues)
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How does The signal transduction pathway work
All signals down the signal transduction pathway to the effector; Each reaction results in an enzyme becoming activated; substrate of the newly activated enzyme is the inactive enzyme below in the pathway
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How does Protein kinase cascade trigger for cell division
Receptor autophosphorylates (kinase activated); Activated adaptor protein catalyses GTP binding to Ras, which is then activated; Activated Ras activates Raf; Activated Raf activates MEK; MEK phosphorylates MAP kinase; MAP kinase enters nucleus
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What does MAP do when it enter the nucleus - triggering cell division
MAP kinase enters nucleus and phosphorylates further proteins, including transcription factors
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What are the ligand of the G-Protein coupled receptors (GPCRS)
hormones, neurotransmitters and light
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Examples of G-Protein coupled receptors (GPCRS)
Anti-histamines; Β –blockers; Opiates – heroin, morphine; Drugs of abuse - THC
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The G-Protein coupled receptors (GPCRS) receptor structure
Single protein made up of 7 sub-units; Each sub-unit passes through the plasma membrane; Form cylindrical structure with ligand-binding site at centre
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Why does G-Protein coupled receptors (GPCRS) have 2 binding site
1)for the receptor 2) for the nucleoside GDP/GTP (Guanosine diphosphate/ Guanosine triphosphate)
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What is G-Protein coupled receptors (GPCRS) madeof
3 sub-units (α,β & γ); Two sub-units are tethered to the plasma membrane by short lipid “tails”; It is membrane mobile
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How to activate G-Protein coupled receptors (GPCRS)
GDP is replaced by GTP; α sub-unit of G-protein with GTP attached breaks free from G-protein which travels along plasma memb until it binds an effector protein; This activates or inhibits the effector protein
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When is G-Protein coupled receptors (GPCRS) inactive
GDP is bound to it
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What happens when there is a mutation of G-Protein coupled receptors (GPCRS)
none function or continual function in the absence of the signal ligand; Continual activation of the G protein can cause cells to divide uncontrollably = carcinoma
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What substance can diffuse through cytoplasm
Water soluble
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How does secondary messengers work
but activate enzymes by binding to them and causing conformational change
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Examples of secondary messengers
cAMP (cyclic adenosine monophosphate); Ca2+; nitric oxide; some lipids (IP3)
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How does cAMP (cyclic adenosine monophosphate) act as a secondary messenger
works by activating cyclic-AMP dependant protein kinase (PKA); PKA activates target proteins by phosphorylation; Also regulates ion channels
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How does Ca2+ act as a secondary messenger
activates proteins associated with cell movement, transcription, fertilisation, metabolism
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How does Nitric oxide act as a secondary messenger
activates protein that dilates blood vessels
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How does some lipids (IP3) act as a secondary messenger
released by G protein activation of the enzyme phospholipase C-β; Diffuses through cytoplasm in to smooth ER; Where it activates an ion channel to release Ca2+
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How to form cAMP
The enzyme adenylyl cyclase catalyses the convertion of ATP into cAMP
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Secondary messengers in Olfactory signalling
G Protein activated by receptor; G protein activates the enzyme adenyl cyclase to synthesises cAMP from ATP; cAMP activates the ion channel protein to open
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The end result of the signal
Ion channels opened/closed; Enzyme activity changed; Different genes are transcribed; Transcription of genes increased or decreased
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An example of regulation of gene expression
G-Protein Linked Receptor receives signal & activates cAMP production; PKA translocates into the nucleus, where it phosphorylates the protein CREB (cAMP response element-binding protein); Phosphorylated CREB binds to DNA at the CREB response element
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What is CREB
transcription factor
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What does cAMP cause
glycogen breakdown in liver cells; triglyceride breakdown in fat cells; relaxation in smooth muscle
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Types of Ending signal transduction
Spontaneous termination; Inhibition of Ligand-receptor binding due to inhibitory proteins/ meds; Phosophatases to end enzymic activity; GTP hydrolysed to GDP so proteins become deactive
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