Editing Galactose (section)

==Relationship to lactose==
Galactose is a [[monosaccharide]]. When combined with glucose (another monosaccharide) through a [[condensation reaction]], the result is a disaccharide called lactose. The [[hydrolysis]] of lactose to glucose and galactose is [[catalyzed]] by the [[enzyme]]s [[lactase]] and [[beta-galactosidase|β-galactosidase]]. The latter is produced by the [[Lac operon|''lac'' operon]] in ''[[Escherichia coli]]''.<ref>{{Citation |last1=Sanganeria |first1=Tanisha |title=Genetics, Inducible Operon |date=2023 |url=http://www.ncbi.nlm.nih.gov/books/NBK564361/ |work=StatPearls |access-date=2023-10-24 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=33232031 |last2=Bordoni |first2=Bruno}}</ref>

In nature, lactose is found primarily in milk and milk products. Consequently, various food products made with dairy-derived ingredients can contain lactose.<ref>{{cite web |url=http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/ |title=Lactose Intolerance – National Digestive Diseases Information Clearinghouse |last=Staff <!-- Verified: No author provided on page. --> |work=digestive.niddk.nih.gov |date=June 2009 |access-date=January 11, 2014 |archive-url=https://web.archive.org/web/20111125192619/http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/ |archive-date=November 25, 2011 |url-status=dead }}</ref> Galactose [[metabolism]], which converts galactose into glucose, is carried out by the three principal enzymes in a mechanism known as the [[Leloir pathway]]. The enzymes are listed in the order of the metabolic pathway: galactokinase (GALK), galactose-1-phosphate uridyltransferase (GALT), and UDP-galactose-4’-epimerase (GALE).{{Citation needed|date=February 2021}}

In human [[lactation]], galactose is required in a 1 to 1 ratio with glucose to enable the [[mammary glands]] to synthesize and secrete lactose. In a study where women were fed a diet containing galactose, 69 ± 6% of glucose and 54 ± 4% of galactose in the lactose they produced were derived directly from plasma glucose, while 7 ± 2% of the glucose and 12 ± 2% of the galactose in the lactose, were derived directly from plasma galactose. 25 ± 8% of the glucose and 35 ± 6% of the galactose was synthesized from smaller molecules such as glycerol or acetate in a process referred to in the paper as hexoneogenesis. This suggests that the synthesis of galactose is supplemented by direct uptake and of use of plasma galactose when present.<ref name=sunehag>{{cite journal | vauthors = Sunehag A, Tigas S, Haymond MW | title = Contribution of plasma galactose and glucose to milk lactose synthesis during galactose ingestion | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 88 | issue = 1 | pages = 225–9 | date = January 2003 | pmid = 12519857 | doi = 10.1210/jc.2002-020768 | doi-access = free }}</ref>