Purines and Pyrimidines

Purine numbering

-CCW in 6 membered ring -CW in 5 membered ring

Pyrimidine numbering

-CW staring with N at bottom

Describe how the activity of G-proteins is regulated by GTP.

-G proteins are involved in many cellular processes including cell signaling, protein synthesis, intracellular transport and microtubule assembly -G proteins have an active conformation when bound to GTP that promotes interactions with effectors to regulate biological processes -Hydrolysis of GTP to GDP+Pi changes conformation of G-protein to an inactive state which no longer interacts w/effectors -Guanine nucleotide-exchange factors (GEFs) stimulate dissociation of GDP+Pi from G protein and loading of GTP to produce active conformation -GTPase-activating proteins (GAPs) stimulate hydrolysis of GTP to GDP+Pi to produce inactive conformation and dissociation from effectors

Cytosine

-Pyrimidine -carbonyl (C=O) at position 2 -amino (-NH₂) at position 4

Identify the secondary messengers generated from ATP and GTP and specify the kinases that they activate.

-cyclic adenosine monophosphate (cAMP) is generated from ATP -cyclic guanosine monophosphate (cGMP) is generated from GTP -cAMP binds to and activates cAMP-dependent protein kinase A (PKA) -cGMP binds to and activates cGMP-dependent protein kinase G (PKG)

Hypoxanthine

-modified base -amino group of Adenine at position 6 replaced w/carbonyl group

Differentiate btwn a nucleoside and nucleotide.

-nucleoside is nitrogen base and sugar ring -nucleotide is nitrogen base, sugar ring, and at least on phosphate group

Guanine

-purine -amino (-NH₂) at position 2 -carbonyl (C=O) at position 6

Adenine

-purine -amino (-NH₂) at position 6

Uracil

-pyrimidine -carbonyl (C=O) at position 2 -carbonyl (C=O) at position 4

Thymine

-pyrimidine -carbonyl (C=O) at position 2 -carbonyl (C=O) at position 4 -methyl (-CH₃) at position 5

Differentiate btwn ribose and deoxyribose

-ribose and deoxyribose differ only at one position on the ring -deoxyribose has an oxygen atom removed at 2' position

Differentiate btwn syn and anti conformation of the glycosidic bond.

-rotation about the N-glycosidic bond allows for two conformations -electronegative oxygen causes bond to rotate to form the anti conformation most of the time

Describe the molecular properties of purines and pyrimidines

-weak bases -flat or planar in shape b/c resonance w/bonds (double bond character) -absorbe UV light -hydrophobic at neutral pH -base stacking interactions -H bonding btwn base pairs

Distinguish btwn the α, β, and γ phosphates in a nucleoside triphosphate molecule.

-α is the phosphate group connected to the sugar molecule via a phosphoester bond -β is the 2nd phosphate group in the chain -γ is the 3rd and final phosphate group in the chain

Name the two components of a nucleoside. Differentiate btwn a nucleoside and a deoxynucleoside.

Nucleoside: consists of nitrogen base and sugar ring (ribose or deoxyribose) -nucleoside has ribose sugar and deoxynucleoside has a deoxyribose sugar

Describe how nucleotides fxn as a) chemical energy carriers, b) coenzymes, and c) intermediates in glycogen synthesis.

Chemical energy carriers: hydrolysis of the phosphoanhydride bonds and the phosphate bond provides energy for cellular rxns. Structural components of coenzymes: many types of coenzymes, for ex. NAD⁺ & FAD, contain adenosine as a structural component of the molecule. Adenosine in the coenzyme binds to a nucleotide binding domain or fold in target enzymes Intermediates in glycogen synthesis: a sugar molecule is formed by attachment of C1 to a nucleotide. Ex. UDP-glucose serves as the sugar donor for glycogen synthesis in the liver by enzyme Glycogen synthase