Unit 1-Communication And Signalling Flashcards
Why is it essential that cells communicate within multicellular organisms?
In order to get required integration and co-ordination for cellular activities
What are the two principle forms of communication?
HormonalNervous
Where are the receptor proteins for hydrophobic signals?
Within the cell/nucleus
Why do hydrophyllic signals require cell surface receptor proteins?
Cannot pass through the membrane
What are hormones?
Extracellular signalling molecules that are secreted by one tissue into the blood
What are the two types of hormones?
Hydrophobic and Peptide
Give examples of hydrophobic hormones?
Steroid HormonesThryoxine
Give examples of hydrophyllic hormones
Peptide Hormones
What are neurotransmitters?
Signals that are released into the synaptic gap between a nerve cell and its neighbour
What are the receptor proteins for steroid hormones?
Transcription factors
What is a transcription factor?
Protein that binds to DNA and controls the rate of transcription
Give an example of a steroid hormone
Testosterone, Oestrogen
What happens to the metabolism of a cell in the absence of thyroxine?
Metabolic rate is lower
What happens when thyroxine binds to its receptor protein?
Receptor undergoes conformational changeCan no longer bind to DNAGene for sodium potassium pump is transcribed
What are the two ways a cascade is activated once a hydropyllic signalling molecule binds to a receptor protein?
G proteinsPhosphorylation by Kinase Enzymes
Give examples of peptide hormones
InsulinGlucagon
What are G protein coupled receptors linked to?
A G protein
What is the difference between a G protein being on or off?
Whether GTP or GDP is attached
What happens when a hydrophyllic signalling molecule binds to the extracellular side of GPCR?
GTP replaces GDP and the G protein becomes active
What happens when a G protein is active?
G protein stimulates enzymes leading to a response in the cell
Why is the response only temporary if the G protein triggers the response?
G protein is a GTPase and hydrolyses the GTP into GDP making the G protein inactive again
What is the insulin receptor?
Kinase linked receptor
Where is the insulin receptor found?
Cell membrane of fat and muscle cells
What happens once insulin binds its receptor?
Signal is transduced and a series of phosphorlyation events trigger the recruitment of GLUT4 to the cell membrane
What does GLUT4 allow?
Allows glucose to enter the cell
What is Diabetes Mellitus?
Medical Condition caused by a failure at some stage of insulin signalling pathway
What is the difference between Type 1 and Type 2 diabetes?
Type 1 - Failure to produce insulin Type 2 - Loss of receptor function
How is type 1 diabetes treated?
Injections of Insulin
How does exercise improve type 2 diabetes?
Triggers recruitment of GLUT4
What do organisms use light energy for?
Generating ATPDetect changes in their enviroment
What prosthetic group is present in rhodopsin?
Retinal
Where does retinal absorb energy from?
Photons
Where do the hydrogen ions diffuse back through?
ATP Synthase
What is retinal?
Prosthetic group covalently bonded to polypeptide called opsin
What are the two classes of photoreceptor cells found in the retina of vertebrates?
Cone and Rod cells
What do cone cells contain?
Photopsins
Which class of photoreceptor cells is responsible for colour vision?
Cone cells
Why are cone cells less sensitive than rod cells?
They have about 1000x less photoreceptor molecules
How many types of photopsins are found in human cells?
3
What are the colours each type of photopsin have maximal sensitivity to?
Red, blue and green
How are different photopsins formed?
Combining retinal with different forms of opsins
What do Rod cells produce when no light has been absorbed?
Cylic GMP
Where does cGMP bind to?
Ligand gated Na+ channels
What happens when a photon of light is absorbed by a retinal molecule?
Conformational change in rhodopsinActivates hundreds of G proteins which activates hundred of enzymes
What do the enzymes do when activated by G proteins?
Catalyse breakdown of cGMP
What does the breakdown of cGMP cause?
Na channels closeMembrane will become hyperpolarizedNerve impulse is generated
What provides a high degree of amplification?
Protein cascade
What are the steps in the protein cascade?
RhodopsinG proteinsEnzymes Channels
What is a photoreceptor?
Name given to proteins which are capable of sensing and responding to light
