Biochemistry MCAT Chapter 3: Carbohydrates (1/3) 

Hello friend, what a great question! Sorry if I did not elaborate on it further but here's a detailed breakdown: To determine the highest numbered chiral center in a sugar molecule, you need to consider the carbon atoms in the sugar backbone. The numbering of the carbon atoms starts from the carbonyl group (aldehyde or ketone) of the sugar molecule. Here are the steps to determine the highest numbered chiral center: 1. Identify the carbonyl carbon: Locate the carbon atom that is part of the carbonyl group (C=O). In aldoses (sugars with an aldehyde group), the carbonyl carbon is typically at the end of the sugar backbone. In ketoses (sugars with a ketone group), the carbonyl carbon is found within the sugar backbone. 2. Assign numbers to the carbon atoms: Starting from the carbonyl carbon, assign numbers to the carbon atoms in the sugar backbone. The carbonyl carbon is given the lowest number (usually 1), and subsequent carbons are numbered sequentially. 3. Determine the chiral centers: Examine each carbon atom in the sugar backbone and identify those that are bonded to four different substituents. These carbon atoms are chiral centers. 4. Compare the numbers: The highest numbered chiral center is the carbon atom with the largest number. This carbon is farthest from the carbonyl group. By determining the highest numbered chiral center, you can establish whether the sugar has a D or L configuration based on its comparison to a reference compound. For example, in the D/L system, a sugar with the highest numbered chiral center on the right side of the Fischer projection is classified as a D sugar, while if it is on the left side, it is classified as an L sugar.

yes, I accidentally skipped a chapter that I realized later on and its covered at the end. So just follow the chapter names, ignore the numbers.

welcome back my friend!! I hope you enjoy the playlist and the content

Yes you are absolutely correct! The structures formed there are fructofuranose. I left a general comments about it as well!!:)

what's the difference between a furanose or a pyranose? thank you for the great video! @@professoreman2289

Hi, here’s how to tell if a sugar in its ring form is in the D or L configuration: Fischer Projection to Haworth Projection:First, look at the sugar in its Fischer projection, which is a two-dimensional representation where the most oxidized carbon (the carbonyl group) is at the top. In the Fischer projection, if the hydroxyl group on the chiral center furthest from the carbonyl group is on the right, the sugar is a D-sugar. If this hydroxyl group is on the left, it’s an L-sugar. Conversion to Ring Form:When the sugar cyclizes, the Fischer projection is often converted into a Haworth projection, which is a more realistic three-dimensional representation of the cyclic sugar structure. During ring formation, the former carbonyl carbon (C=O) becomes a new chiral center called the anomeric carbon. Determining D or L in Ring Form:In the Haworth projection, look at the anomeric carbon, which is usually labeled as carbon number 1. For D-sugars, the hydroxyl group attached to the anomeric carbon will point up (above the plane of the ring) in a β-configuration or down (below the plane of the ring) in an α-configuration. For L-sugars, it will be the opposite; the hydroxyl group at the anomeric carbon will point down in a β-configuration or up in an α-configuration. Consider the Ring Type: For six-membered (pyranose) rings, the D or L configuration is based on the fifth carbon’s hydroxyl group orientation in the linear form before ring closure. For five-membered (furanose) rings, it’s based on the fourth carbon’s orientation.

Got it, thank you sooo much for the awesome explanation!!

Anytime friend!

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Thank you! 😃 right back at you friend!

No problem:)