L20: carbohydrates

Question 1

what are glycoconjugates?

Answer 1

they stabilize and regulate membranes

Question 2

main roles of carbohydrates

Answer 2

energy and structure

Question 3

what are monosaccharides?

Answer 3

simplest sugars

Question 4

what are oligosaccharides?

Answer 4

short chains of sugar subunits joined by glycosidic bonds

Question 5

what are polysaccharides?

Answer 5

sugar polymers with thousands of monosaccharide units

Question 6

what is the basic carbohydrate chemistry?

Answer 6

they are either polyhydroxy aldehydes or ketones

Question 7

properties of monosaccharides:

Answer 7

• colorless crystalline solid
• freely soluble in water; insoluble in nonpolar solvents
• unbranched (linear) carbon chains
• typically end in -ose

Question 8

do monosaccharides have chiral centers?

Answer 8

yes, making them optically active

Question 9

how do you figure out how many stereoisomers there are for a molecule?

Answer 9

2^n

n= chiral centers

Question 10

what is an epimer?

Answer 10

a sugar that differs in configuration at only 1 carbon

Question 11

what does alpha mean when naming hemiacetals/hemiketals

Answer 11

alpha means the hydroxy group is pointing down (opposite side of the ring from C6)

Question 12

what does beta mean when naming hemiacetals/hemiketals

Answer 12

beta means the hydroxy group is pointing up (same side of the ring from C6)

Question 13

which is the anomeric carbon?

Answer 13

C1- forms when C-5 OH attacks C=O

Question 14

what kind of substituents experience less steric hindrance?

Answer 14

equatorial substituents

Question 15

how can conversion between anomers occur?

Answer 15

spontaneously in water or via mutarotation (ring opens and recloses)

Question 16

what is a glycoside?

Answer 16

any molecule possessing an O-, N-, or S- glycosidic bond

Question 17

glycoside bonds involve _____?

Answer 17

anomeric carbons

Question 18

stability of glycoside bonds?

Answer 18

thermodynamically unstable

kinetically stable

Question 19

what is amylose?

Answer 19

unbranched homopolymer of glucosyl units

Question 20

what do homopolysaccharides contain?

Answer 20

they contain a single type of monosaccharide and are used for energy storage as well as structural elements

Question 21

what do heteropolysaccharides contain?

Answer 21

they contain 2 or more varieties of monosaccharides and provide extracellular support for microorganisms

Question 22

do polysaccharides have variable molecular weight?

Answer 22

yes; they are known as indefinite polymers

Question 23

sugars are very ___

Answer 23

water-soluble due to large number of OH groups

Question 24

branched molecules are ___

Answer 24

highly soluble

Question 25

what does starch do?

Answer 25

it serves as an important energy storage in plants

Question 26

what is starch made up of?

Answer 26

it is made up of unbranched amylose and highly-branched amylopectin

Question 27

starch is ______

Answer 27

enzymatically broken down from the non-reducing ends to produce glucose for energy production

Question 28

what is the main sugar in our body that’s located in the liver?

Answer 28

glycogen

Question 29

what does glycogen provide?

Answer 29

it provides long-term energy storage in animals and fungi

Question 30

how is glycogen synthesized?

Answer 30

it is synthesized on a protein anchor that localizes it within the cytoplasm

Question 31

what is cellulose?

Answer 31

it is an unbranched polymer of D-glucose units that are connected by beta glycosidic bonds

Question 32

what kind of bonding is present in cellulose?

Answer 32

there is extensive intramolecular H-bonding as well as H-bonding between cellulose chains

Question 33

what are some examples of animals that lack enzymes that can cleave cellulose?

Answer 33

• termites: rely on microorganisms
• ruminants: have an extra stomach compartment containing bacteria that secrete cellulases
• fungi produce cellulases