L20: carbohydrates Flashcards
what are glycoconjugates?
they stabilize and regulate membranes
main roles of carbohydrates
energy and structure
what are monosaccharides?
simplest sugars
what are oligosaccharides?
short chains of sugar subunits joined by glycosidic bonds
what are polysaccharides?
sugar polymers with thousands of monosaccharide units
what is the basic carbohydrate chemistry?
they are either polyhydroxy aldehydes or ketones
properties of monosaccharides:
- colorless crystalline solid
- freely soluble in water; insoluble in nonpolar solvents
- unbranched (linear) carbon chains
- typically end in -ose
do monosaccharides have chiral centers?
yes, making them optically active
how do you figure out how many stereoisomers there are for a molecule?
2^n
n= chiral centers
what is an epimer?
a sugar that differs in configuration at only 1 carbon
what does alpha mean when naming hemiacetals/hemiketals
alpha means the hydroxy group is pointing down (opposite side of the ring from C6)
what does beta mean when naming hemiacetals/hemiketals
beta means the hydroxy group is pointing up (same side of the ring from C6)
which is the anomeric carbon?
C1- forms when C-5 OH attacks C=O
what kind of substituents experience less steric hindrance?
equatorial substituents
how can conversion between anomers occur?
spontaneously in water or via mutarotation (ring opens and recloses)
what is a glycoside?
any molecule possessing an O-, N-, or S- glycosidic bond
glycoside bonds involve _____?
anomeric carbons
stability of glycoside bonds?
thermodynamically unstable
kinetically stable
what is amylose?
unbranched homopolymer of glucosyl units
what do homopolysaccharides contain?
they contain a single type of monosaccharide and are used for energy storage as well as structural elements
what do heteropolysaccharides contain?
they contain 2 or more varieties of monosaccharides and provide extracellular support for microorganisms
do polysaccharides have variable molecular weight?
yes; they are known as indefinite polymers
sugars are very ___
water-soluble due to large number of OH groups
branched molecules are ___
highly soluble
what does starch do?
it serves as an important energy storage in plants
what is starch made up of?
it is made up of unbranched amylose and highly-branched amylopectin
starch is ______
enzymatically broken down from the non-reducing ends to produce glucose for energy production
what is the main sugar in our body that’s located in the liver?
glycogen
what does glycogen provide?
it provides long-term energy storage in animals and fungi
how is glycogen synthesized?
it is synthesized on a protein anchor that localizes it within the cytoplasm
what is cellulose?
it is an unbranched polymer of D-glucose units that are connected by beta glycosidic bonds
what kind of bonding is present in cellulose?
there is extensive intramolecular H-bonding as well as H-bonding between cellulose chains
what are some examples of animals that lack enzymes that can cleave cellulose?
- termites: rely on microorganisms
- ruminants: have an extra stomach compartment containing bacteria that secrete cellulases
- fungi produce cellulases
