Carbohydrate Structure Aldopentoses and Ketopentoses

The video tutorial explores the cyclization of carbohydrates, focusing on aldoses and ketoses, particularly pentoses like D-ribose and ribulose. It explains the stability of different ring structures, emphasizing the preference for five-membered furanose rings in ribose due to hydrogen bonding. The tutorial also discusses the limited cyclization of ribulose and general rules for carbohydrate cyclization, highlighting the instability of four-membered and seven-membered rings.

What is the primary focus when studying pentoses in the context of aldoses and ketoses?

• Their cyclization and stability

• Their role in protein synthesis

• Their ability to form disaccharides

• Their interaction with lipids

Which carbon in D-ribose is involved in the nucleophilic attack during cyclization?

• Carbon 1

• Carbon 5

• Carbon 2

• Carbon 4

Why is the furanose form of ribose more stable than the pyranose form?

• It forms a larger ring

• It is less soluble in water

• It has fewer carbon atoms

• It has more hydrogen bonding

What is the role of the hydroxymethyl group in ribose stability?

• It forms a double bond

• It destabilizes the pyranose form

• It stabilizes the furanose form

• It increases hydrophobicity

What is a key difference between ribose and ribulose?

• Ribulose has difficulty cyclizing

• Ribulose is an aldo pentose

• Ribose forms a stable pyranose

• Ribose is a keto pentose

Why are four-membered rings generally unstable?

• They have significant angle strain

• They are too large to form

• They have excessive hydrogen bonding

• They are too hydrophilic

What is a characteristic of ribulose in the pentose phosphate pathway?

• It is not involved in the pathway

• It is found in a cyclic form

• It is primarily in a linear form

• It forms a stable pyranose

What is the most stable form for pentoses like ribose?

• Pyranose form

• Furanose form

• Linear form

• Tetrahydrofuran form

Which type of ring is generally not formed due to instability?

• Six-membered rings

• Five-membered rings

• Eight-membered rings

• Four-membered rings

What is a common feature of stable carbohydrate rings?

• They have an even number of carbons

• They are either five or six-membered

• They contain a double bond

• They are always linear