Question

How is the reciprocal use of nucleotides useful in purine synthesis?

Which vitamin supplement is taken during the first trimester of pregnancy to prevent the birth defect known as spina bifida?

How is a chloroplast similar to a mitochondria in regard to energy production?

Why are reactions of the Calvin cycle called the “dark reactions”?

Answer 1

The body is cheap so, if it can salvage nucleotides it will not have to synthesize as many purines and use as ATP to do so. Through salvage pathways adenine, guanine and hypoxanthine are recycled. These can then react with PRPP ( Phosphoribosyl pyrophosphate) and a mediating enzyme. Adenine + PRPP with APRT (Adenine Phosphoribosyltransferase) forms AMP +PPi. Hypoxanthine + PRPP with HGPRT ( Hypoxanthine-Guanine Phosproribosyltransferase) forms IMP+ PPi and GMP + PPi respectively. Once these nucleotides are phosphorylated again they can power Purine synthesis.

Folic acid, taken in supplement form starting at least one month before conception and continuing through the first trimester of pregnancy, greatly reduces the risk of spina bifida and other neural tube defects.

The common pathway used by mitochondria, chloroplasts, and procaryotes to harness energy for biological purposes operates by a process known as chemiosmotic coupling—reflecting a link between the chemical bond-forming reactions that generate ATP (“chemi”) and membrane-transport processes (“osmotic”). The coupling process occurs in two linked stages, both of which are performed by protein complexes embedded in a membrane.

Calvin cycle:

Photosynthesis starts out using the energy from sunlight to get things started, but it ends with the dark reactions, which don't need sunshine to complete sugar production. In the Calvin cycle, ATP and NADPH from the light reactions are used to produce sugars.