Nucleotides, Nucleic Acid Chemistry and Metabolic Integration: every key term you need (+ practice quiz)
25 flashcard terms for Biochemistry Topic 8, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
A nucleoside is a base joined to a sugar; adding one or more phosphates makes it a nucleotide. Only the phosphorylated form is a polymer building block.
Purine
A two-ring base, adenine or guanine, built on a preassembled ribose phosphate so that the ring is constructed directly onto the sugar.
Pyrimidine
A single-ring base, cytosine, thymine or uracil, whose ring is completed before attachment to the sugar, the reverse of purine assembly order.
Phosphodiester backbone
Links the third carbon of one sugar to the fifth carbon of the next, giving the strand a defined direction and a uniformly negative charge.
Complementary base pairing
Adenine pairs with thymine by two hydrogen bonds and guanine with cytosine by three, so a strand's sequence dictates its partner and guanine-rich duplexes melt at higher temperature.
Antiparallel strands
The two strands of a duplex run in opposite directions, which is what forces one strand to be copied discontinuously during replication.
Major and minor groove
The two unequal surface channels of a double helix. The wider groove exposes more distinguishing edge features, so most sequence-specific proteins read it.
Denaturation of nucleic acid
Separation of strands by heat or extreme pH, monitored by increased ultraviolet absorbance as stacking is lost.
Melting temperature
The temperature at which half of a duplex has separated. It rises with length, with guanine-cytosine content and with salt concentration.
Supercoiling
Over- or under-winding of a closed duplex that stores torsional strain. Topoisomerases relieve it so replication and transcription can proceed.
Ribonucleotide reductase
Converts a ribonucleotide to its deoxy form, the committed step of building blocks for replication, and is regulated by an elaborate network of nucleotide effectors.
Salvage pathway
Recycles free bases into nucleotides at a fraction of the energetic cost of building them from scratch, which is essential in tissues with low synthetic capacity.
Purine degradation
Ends in uric acid in humans. Its low solubility is why overproduction or poor excretion deposits crystals in joints.
Nucleotide analogue
A modified nucleotide that inhibits a nucleic-acid enzyme or terminates a growing chain, the basis of many antiviral and anticancer agents.
Transamination
Transfers an amino group to a keto acid using a vitamin-derived cofactor, connecting amino acid nitrogen to carbon skeletons of central metabolism.
Oxidative deamination
Releases nitrogen as free ammonia from glutamate, the collection point that feeds the urea cycle.
Urea cycle
Converts toxic ammonia to urea for excretion, spanning mitochondrion and cytosol and costing several high-energy phosphate bonds per molecule made.
Glucose-alanine cycle
Carries muscle nitrogen to the liver in the form of alanine, whose carbon skeleton is then reused for glucose synthesis.
An amino acid whose carbon skeleton enters metabolism as pyruvate or a cycle intermediate, so it can be converted to glucose.
Ketogenic amino acid
An amino acid degraded to acetyl units or acetoacetate, so it can yield ketone bodies or lipid but never net glucose.
Energy charge
A measure of how fully the cell's adenine nucleotide pool is phosphorylated. It is the master signal that activates catabolic enzymes when low and biosynthetic ones when high.
AMP-activated protein kinase
A sensor switched on by falling energy charge that turns on catabolic pathways and shuts down biosynthesis by phosphorylating key enzymes.
Insulin action
Signals the fed state, promoting glucose uptake, glycogen and fat synthesis, largely through dephosphorylation of the relevant regulated enzymes.
Glucagon action
Signals the fasting state in the liver, raising cyclic nucleotide levels and driving a phosphorylation cascade that mobilizes glycogen and starts glucose synthesis.
Metabolic fuel hierarchy
Circulating glucose is used first, then liver glycogen, then fatty acids and ketone bodies, with protein sacrificed last as starvation is prolonged.