Cell Biology & Signalling Flashcards
What is tyrosine the precursor of?
Epinephrine, dopamine and melanin
What is tryptophan the precursor of?
Serotonin
What are the essential amino acids?
Phenylalanine, F Valine, V Tryptophan, W Threonine, T Isoleucine, I (Methionine, M) Histidine, H (Arginine, R) Leucine, L Lysine, K
Anchored membrane proteins examples
Alkaline phosphatase (glycolipid anchored) RAS (fatty acyl anchored)
Peripheral proteins example
Spectrin (interacts with ankyrin)
Phospholipase A2
What are the different phospholipases?
PLA1,2= FA from phospholipid PLC= phosphate group from glycerol PLD= phosphate group from polar head group
What is the effect of pH on the affinity of Hb for oxygen?
Increase in pH —> increase in affinity
Decrease in pH —> decrease in affinity
What is the effect of BPG on Hb affinity to O2?
Increased BPG —> decreased affinity
Where on hemoglobin does heme bind?
Histidine residues from helixes E7 (distal) and F8 (proximal)
What mutation causes sickle cell anemia?
Glu6 (acidic) to Val (nonpolar) in beta-chains
What are porphyria and thalassemia?
Porphyria: inherited defect in synthesis of heme group
Thalassemia: reduced synthesis of alpha or beta chains
How does protein targeting to the ER happen?
signal sequence at N-terminus, recognised by signal recognition particle (SRP), SRP receptor in ER membrane, translocation channel, signal peptidase cleaves signal sequence
What is the tag for proteins that form lysosomes?
mannose-6-phosphate
How does protein targeting to mitochondria happen?
translated but unfolded protein, chaperones take it to the mitochondria, signal sequence recognised by receptor –> translocation across outer and inner m, cleavage of signal sequence
How does protein targeting to the nucleus happen?
Translation and folding in cytoplasm, nuclear localisation signal (NLS; basic) binds to importin and transported through the nuclear pore, requires G-protein Ran and GTP,
What are glycosyltransferases?
Golgi enzymes that add sugars to proteins
How many actin monomers are needed for a full turn and what is the diameter of the filament?
13; 7 nm
What are the major functions of actin?
Mechanical support, cell shape changes and maintenance, cell motility
What is the diameter of intermediate filaments and what are some examples?
10 nm; keratin, vimentin, glial fibrillary acidic protein, neurofilamin
What is plectin?
protein links IFs to actin and microtubules
How many columns of tubulin polymer are arranged to form the microtubule and what is its diameter?
15; 25 nm
What is required for the assembly of actin filaments and microtubules?
Actin filaments: ATP
Microtubules: GTP
What is responsible for shape of microvilli and stereocilia?
Actin filaments
What is responsible for the organisation the ER of a cell, nucleus support and synaptic vesicle positioning?
ER: microtubules
Nucleus: intermediate filaments
Synaptic vesicles: actin filaments
What molecules are responsible for focal adhesion?
Integrins
What are examples of microtubule based movements?
Cilia and flagellae
9+2 structure + dynein
What motor protein is responsible for movement of lamellipodia?
Myosin II (requires ATP, not processive)
Which motor proteins are responsible for movement of organelles and intracellular contents?
Kinesin (processive motor protein, requires ATP) and dynein (both have heavy and light chain) on microtubules
What are colchicine, vinblastine and taxol?
Anti-cancer therapeutics;
Colchicine and vinblastine: destabilise microtubules
Taxol: stabilises microtubules
What is Tau and what happens to it in Alzheimer’s disease?
Microtubule associated protein
In AD it is hyperphosphorylated and thus cannot bind to MTs
How does the Listeria bacteria interfere with the cytoskeleton of the cell?
F-actin is polymerised at the back of the bacterium providing mobility
What is sphingomyelin composed of?
Ceramide (sphingosine + fatty acyl chain) + phosphate group + choline
What is the partition coefficient?
Equilibrium constant for the partitioning of a molecule between oil and water (the higher the more lipid soluble)
What are the characteristics of GLUT1, 2, 3, 4, 5?
GLUT1: low Km, many tissues, highly expressed in erythrocytes and blood-brain barrier
GLUT2: high Km and large Jmax (high capacity), hepatocytes and pancreatic beta cells.
GLUT3: low Km, high expression in neurons
GLUT4: muscles and adipocytes, regulated by insulin.
GLUT5: fructose transporter
How does ouabain work?
blocks Na+/K+ ATPase –> increase in intracellular sodium –> Na+/Ca2+ antiporter is inhibited –> increase in intracellular Ca2+ –> cardiac muscle contraction
What is SGLUT1 and where is it located?
Na+/glucose transporter; intestinal epithelial cells and proximal tubules of the kidney for reabsorption of glucose
What is the method of action of cholera?
Overacting Gsalpha –> increased cAMP levels –> increased transport of Cl- out of the cell through CFTR –> diffusion of Na+ and water out of the cell –> glucose replacement therapy drives Na+ back through SGLUT1
What type of receptor is the beta adrenergic receptor?
G-protein coupled receptor
How are G-proteins activated?
GTP binds to alpha subunit –> dissociates from beta and gamma subunits
How is PKA activated?
cAMP binds to regulatory subunits (2) –> tetramer dissociates and catalytic monomers are now active
How is glycogen breakdown activated?
Glucagon activates GPCR –> cAMP –> PKA
PKA: phosphorylates and thus activates phosphorylase kinase
Phosphorylase kinase: phosphorylates and thus activates glycogen phosphorylase
Glycogen phosphorylase: phosphorylates glycogen and thus produces glucose-1-phosphate
How is gene transcription activated through GPCR?
PKA phosphorylates CREB –> binds to specific target sequences in target genes and stimulates transcription
How is PLC activated and what does it do?
PLC is activated by GPCRs with Gq subunits (alpha1 adrenergic receptors)
PLC cleaves inositol phospholipids into IP3 and DAG
IP3: activates Ca2+ channels in ER
DAG: together with Ca2+ activates PKC
What receptor does EGF bind to and what cascade does it initiate?
Receptor tyrosine kinase (RTK);
Binding leads to autophosphorylation of tyrosine residues
Adaptor proteins contain phosphotyrosine binding domains: SH2 and PTB
Binding of adaptor proteins (Grb2, Sos) –> activation of Ras through GDP to GTP exchange
What is Ras?
Monomeric G-protein
GTP-Ras triggers kinase cascade:
MAPKKK –> MAPKK –> MAPK –> transcription factor
