FOM Flashcards
Examples of locations of receptors
- via plasma membrane (cell surface)
- via intracellular receptors
What are parts that plasma membrane receptors commonly have?
- extracellular domain, transmembrane domain, intracellular domain
Role of Nitric oxide in smooth muscle relaxation
- acts as primary messenger in pathway
- can act as second messenger within cells. Activates guanylyl cyclase which converts GTP to cGMP (vasodilation)
Examples of enzymes used in signalling
- GTPases: bind to GTP to GDP
- phosphodiesterase: breaks phosphodiester bond
- kinase: transfer of phosphate group
- phosphatase: hydrolysis of organic phosphate in specific environment
Structure of GPCRs
- 7 transmembrane alpha helices spanning domain
- specifically binds a G protein
What is signal amplification?
- use chain of other protein messengers to amplify signal.
- complex can activate multiple AC - cascade effect
Role of cAMP
- activated adenylyl cyclase converts ATP to cAMP
- transfers signals of hormones and can simulate different cell activities.
- elicits response via protein kinase A
What are Tyrosine Kinase Receptors (RTK) activated by?
- growth and differentiation factors or metabolic regulators
What occurs at RTKs at the point of ligand-binding?
- form dimer. Auto/cross-phosphorylation occurs at tyrosine residues at intracellular domain
What does RTK autophosphorylation cause?
- receptor able to recognise and activate adaptor proteins
- activated relay proteins can then pass on signal within cell to elicit response
Describe MAP kinase cascade
- GF binding and receptor dimerisation
- autophosphorylation allows Grb to dock
- binds to SOS. Complex activates RAS which activates MAPKKK- MAPKK-MAPK
- MAPK migrates to nucleus and phosphorylates target TFs
Role of RAS
- small G protein functioning as monomer
- SOS transfers GTP to RAS causing activation
- length of RAS activation depends on rate of hydrolysis of GTP to GDP
- mutations locking RAS in active state cause many cancers
What do anabolic enzymes do?
- building of molecules from smaller units into a larger one
What do catabolic enzymes do?
- break down molecules into smaller units
What does a Michaelis-Menten plot represent?
- relationship between the concentration of a substrate and the rate of the corresponding enzyme-controlled reaction
What does Vmax mean?
- rate of reaction when enzyme is saturated with substrate
- maximum rate of reaction
What does Km mean
- substrate conc. at which enzyme works at half its maximum rate.
- used to compare affinity of different enzymes for their substrates
What is a line weaver-burke plot used for?
- determining Vmax and Vm of enzyme kinetics
What comprises a nucleoside?
- nitrogenous base and sugar
What comprises a nucleotide?
- nitrogenous base, sugar and phosphate
What comprises a nucleic acid?
- nitrogenous base, sugar, phosphate and phosphodiester
How do T and U bases differ?
- T on DNA, U on RNA
- T has a methyl group
What are two ways bases in nucleotides can be synthesised?
- de novo
-salvage
What is the start of purine formation?
- Ribose-5-phosphate which derives from pentose phosphate pathway
How is PRPP formed?
- Ribose-5-phosphate is converted into PRPP by PRPP synthesise
What happens in the reaction of PRPP with glutamine?
- glutamine donates one amide group to carbon 1 to form 5-phosphoribosylamine
What atoms are sequentially added to build the purine ring?
- glutamine
-aspartate - CO2
What is the first fully formed purine nucleotide in the de novo pathway?
- IMP, inosine monophosphate
Describe feedback inhibition in purine formation
- ensures balance in purine synthesis
- AMP and GMP inhibit early steps of pathway.
-Cross-regulation
Describe the salvage pathway of purine formation
- recovers purine from normal cell turnover and converts to nucleoside triosphosphate
What enzymes are involved in the salvage pathway of purine formation?
- HGPRT: converts hypoxanthine to IMP and guanine to GMP
- APRT: converts adenine to AMP
What is the only purine nucleoside to be salvaged?
- Adenine
Importance of deoxyribonucletides in nucleotides synthesis
- ribonucleotide reductase converts ribonucleotides to deoxyribonucletides
- Feedback inhibition occurs when dATP is formed
How is orotate produced in pyrimidine formation?
- glutamine, CO2, ATP, aspartate and tetrahydrofolate required in forming pyrimidine ring
- carbamoyl aspartate is oxidised to form orotate
How does the attachment of pyrimidine ring to ribose-5-phosphate occur?
- PRPP provides ribose sugar
- reacts with orotate to form OMP
- enzyme PRPP synthetase converts ribose to PRPP
