Nucleotides and nuclei acids

Question 1

ATP

Answer 1

• used as principal biological transduce of energy
• synthesized by addition of phosphate group to ADP
• ATP consists of molecule adenosine + 2 phosphates
• high energy phosphate ⇒ negative delta G
• transfer of phosphate from or to ATP

Question 2

cAMP

Answer 2

• cyclic nucleotide ⇒ 2nd messenger
• important role in regulation of metabolism
• chemical signals sent by hormone or neurotransmitter binds to G-protein coupled receptor on cell membrane and triggers either increase or decrease in activity of adenylyl cyclase
• membrane bound enzyme, converts ATP⇒ cAMP
• cAMP used for activate protein kinase A

Question 3

GTP

Answer 3

• serves as allosteric regulator and energy source for protein synthesis
• GMP-cGMP is also a cyclic nucleotide, 2nd messenger in response to NO during relaxation of smooth muscle

Question 4

UDP-sugar

Answer 4

• participates in nucleotide-sugar metabolism as an activated form of glucose; precursor of glycogen
• sugars participates in nucleotide sugar metabolism as activated form of glucose⇒ released from liver and kidneys
• alpha-D-glucose attached to UDP is source of all the glycosyl residues that are added to growing glycogen molecule
• elongation of glycogen: glucose to non-reducing end by glycogen synthase. Glycogenin ⇒ acceptor of glucose residues if no pre-existing glycogen chain is present

Question 5

UDP-ribose

Answer 5

• derived from NAD
• diphteria toxin and cholera toxin catalyse ADP ribosylation
• cholera toxin catalyses transfer of ADP-ribose from NAD to subunit of Gs, blocking GTPase activity and rendering Gs permanently active
• results in continuous activation of adenylyl cyclease of intestinal epithelial cells and chronically high cAMP ⇒ triggers secretion of Cl-, HCO3 and water into intestinal lumen ⇒ dehydration + electrolyte loss
• pertussis toxin catalyses ADP-ribosylation of Gi, preventing displacement of GDP by GTP⇒ blocks inhibition of adenylyl cyclase by Gi