7 - Carbohydrates Flashcards
What are 5 functions of carbohydrates?
- Coating of cell surfaces
- Modification of secreted proteins
- Part of receptors for some pathogens
- Form the basis of human blood groups
- Allows a tremendous amount structural diversity.
What is the general formula for sugars and what groups do sugars include?
General formula is CH2On when n is between 3 and 7.
Sugars include aldehyde groups (-CHO) or ketone groups (C=O).
What are 3 nutritionally important monosaccharides?
Glucose
Galactose
Fructose
How does glucose go from its open chain form to the ring form?
The formation of a hemiacetal through the reaction of the aldehyde group and the alcohol group results in the formation of the ring structure.
What is an example of a sugar alcohol, how is it formed, and what is it used for ?
Sorbitol - found in mountain ash fruit.
Formed by the reduction of the aldehyde group of glucose to a hydroxyl group
Used in foods for diabetics.
What does the addition of a phosphoryl group do to a monosaccharide?
Makes the sugar anionic.
Traps sugars within the cell.
Creates a reactive intermediate of sugar metabolism.
What are disaccharides, oligosaccharides, intrinsic sugars and extrinsic sugars?
Disaccharide - Formed by condensation between two monosaccharides (O-glycosidic bond).
Oligosaccharides - 3-10 bonded monosaccharides
Intrinsic sugars - Sugars contained within plant cell walls. (healthy)
Extrinsic sugars - Sugars that are free in solution. (unhealthy)
What are 5 examples of disaccharides, where do they come from and what is their formula?
Maltose - glucosyl-glucose - cane or beet sugar.
isomaltose - isoform of maltose - 1-6
Trehalose - 1,1-glucosyl-glucose - found in mushrooms.
Sucrose - glucosyl-fructose - malt.
Lactose - glucosyl-galactose - milk
Formula - C12H22O11
What is starch, what are its two forms and how do the forms differ?
Starch - large storage molecule with variable number of glucose units - storage carb of plants.
Amylose - unbranched chain of glucose molecules α-1,4
Amylopectin - glucose chain α-1,4. every 30th glucose branches to other glucose residues α-1,6
What is glycogen?
Storage carb of mammalian muscle and liver
Similar to amylopectin, but branch every 10th glucose
What are 3 examples of non-starch polysaccharides and how do they differ from starch?
Not digested by humans
Cellulose
Chitin
Pectin
How is starch broken down in humans?
Starch is broken down by amylase by hydrolysis.
What causes milk intolerance and what effects can it have?
An inability to metabolise lactose resulting in gastrointestinal disturbance.
Microorganisms in the colon use the unmetabolized lactose as an energy source:
Lactose -> lactate + methane and hydrogen gas
Lactate causes flatulence, diarrhea as it draws water into the intestine
Why is it said that polysaccharides have directionality?
Polysaccharides have a reducing and a non-reducing end.
What causes the formation of the non-reducing end?
An acetal - molecule with two single bonded oxygens attached to the same carbon.
The acetal prevents the opening of the chain to the aldehyde form rendering this end non-reducing.
