Also greetings from Germany. I'm taking Biochemistry in German (not my first language) and your videos really are a life-saver for the concepts that are harder for me to translate. Much appreciated!
I'm writing a comment here for my own reference in the future. No other places to take notes right now. ' Aldehydes can be oxidized into carboxylic acids, which are also formally called aldonic acid. Because maltose and lactose have 1,4-glycosidic bonds (regardless of their alpha or beta conformations), this means that there is still at least one anomeric carbon capable of opening up into the open-chain aldehyde form (also known as mutarotation). Thus, it is called a reducing agent (reducing sugar). And sucrose is not a reducing sugar because the anomeric carbons are both taken up in the alpha-1,2-glycosidic linkage, meaning that there's no chance for aldose formation....? Isn't beta-D-fructose a ketose though? I did a bit of googling and I found that ketose sugars can tautomerize (rearranging bonds) resulting in an (enol), a double bond and -OH group. So ketoses also act as reducing sugars by becoming aldoses until a "keto-enol" shift under basic conditions...interesting. aldoses = open chain carbohydrates with aldehyde as their oxidized functional group ketoses = open chain carbon hydrates with ketone hemiacetal = cyclic rings due to intramolecular reactions between an nucleophilic hydoxl group and electrophilic carbonyl carbon in an aldose
In fructose, hydroxyl group in C3 is in the opposite direction as others, as a result, OH resides inside the pentagon ring in C3. But when it becomes Sucrose, i noticed that hydroxyl group is inside of pentagon in C4. Can you please explain why?
Since it's a beta anomer, the OH on C-2 has to face the same side of ring as the CH2OH on C-5. The OH on C-4 also has to face the opposite side of ring as the OH on C-3. That leaves only one option, C3-OH facing down and C4-OH facing up.
A simpler way to think about it is to draw the furanose from the Fischer as you normally would, then flip it left to right (place the paper upside down). All top substituents go to the bottom and vice-versa.
The reason the maltose C1 anomeric carbon is designated alpha is that it's former hydroxyl group, which is now the glycosidic O bond linking the two monsaccharides, is cis to (on the same side of the ring) as the 4th carbon's hydoxyl group. The lecturer was wrong when he referenced it to the position of the CH2OH group attached to carbon no. 5. That group is trans to the glycosidic O bond. The alpha/beta designations refer to the positions of the anomeric hydroxyl group and the hydroxyl group oxygen which is directly bound to the highest numbered chiral carbon in the ring.
My MCAT book defines it the same way he does, as the relationship with respect to the CH2OH (the 5th carbon). If it’s trans or pointing down, it’s alpha and if it’s cis or pointing up with respect to the 5th carbon then it’s beta-anomeric
@@brittopereppadan5503 Please explain how can a single natural disaccharide [Lactose] can have two different monomer units [alpha & beta Glucose] ..and still be called Lactose Thanks
To determine whether the glycosidic linkage is alpha or beta between two monosaccharides ( the first one for Beta and the second one for Alpha) , are we just looking at the first monosaccharide which is beta? (referring to lactose) :) Thanks!
6. If a disaccharide is formed through a (1-> β4) glycosidic bond, it means that ________. A. neither the first nor the second monosaccharide unit needs to be in the β-form B. both monosaccharide units need to be in the β-form C. only the first monosaccharide unit needs to be in the β-form D. None of the above is correct. Can someone help me with this qn?? )):
