Aldose Ketose Functional Group -CHO group C=O at second carbon Structure Carbonyl at C1 Carbonyl at C2 Examples Glucose, Galactose, Ribose Fructose Ribulose Reducing properties Reducing sugars (Strong) Reducing sugars (weak) Cyclization hemiacetal ring hemiketal ring Role in Metabolism Glucose Fructose Aldolases ● Reversible ● Condensation reaction ● Ketose-Aldose ○ Condenses and creates new Ketose ○ Ketose and aldose now in form of Ketose ■ Combined ○ Carbon-Carbon bond ● No carbons are lost ○ New Ketose have same number of Carbon combined from donor Ketone and Aldose ○ Retains donor aldose stereochemistry TransKetolase ● Transfers 2C unit form ketose to aldose ○ Donor ketose becomes aldose ○ Acceptor aldose becomes Ketose ■ 2C longer than the parent aldose ● Retains stereochemistry of Donor Ketose ● Cofactor or TPP needed Transaldolase ● Transfers 3C unit from ketose to aldose ● Shift in Schiff’s Base ● No Cofactor needed ● Donor Ketose becomes aldose ○ 3C shorter ○ Retains stereo chemistry ● Acceptor Aldose becomes Ketose ○ 3C longer than parent aldose Differences ● TPP used as a co-factor in Transketolase while Transaldolases does not ● 2C donation and acception in Transketolase and 3C donation and acception in Transaldolase ● Schiff’s base altered in Transaldolase ● Smooth shift in Transketolase due to TPP