4. Carbohydrates

Question 1

Know structures of D-glucose and D-fructose

Answer 1

Know em by heart. Glucose has 4 chiral centers, fructose has 3 chiral centers

Question 2

How do you know if they’re D vs L?

Answer 2

Look at furthest chiral C, -OH on right vs -OH on left (IF H IS POINTING AT YOU)

Question 3

What happens when you make a disaccharide (what type of rxn). What kind of bond forms and which C’s form the bond?

Answer 3

condensation rxn; O-glycosidic bond forms, usually C1 of 1st sugar and C4 of 2nd sugar => 1,4 glycosidic linkage. Linkages can be either alpha or beta

Question 4

What are anomers? How to find anomeric C?

Answer 4

alpha vs beta sugars (not D/L). Carbonyl C = anomeric C; If hydroxyl = opposite side of C6 –> alpha, if hydroxyl = same side of C6 –> beta

Question 5

What do lines of a Fischer projection mean?

Answer 5

horizontal lines = pointing towards you, vertical lines = point away from you

Question 6

How do you know how many stereomers something has?

Answer 6

2^n = X stereomers; n = # of chiral C

Question 7

What happens when alcohol attacks aldehydes or ketones? What happen when alcohol attacks hemiacetals or hemiketals?

Answer 7

You get hemiacetals or hemiketals. And then you get acetals or ketals

Question 8

When linear sugar becomes a ring, how do you know if it’s D or L?

Answer 8

-OH = right –> down, -OH = left –> up (DOWNRIGHT UPLEFTING). -CH2OH = up –> D, -CH2OH = down –> L.

Question 9

In water, hemiacetal/hemiketal rings can open and close spontaneously; what is this process called? What factors causes ring to close?

Answer 9

Mutarotation. When it opens, C1 and C2 rotates; when it closes, it can switch between alpha or beta anomers. Some amount of acid, base or H2O can close it

Question 10

Pyranose vs furanose

Answer 10

6 ring (5 carbon + O) sugar vs 5 ring (4 carbon + O) sugar

Question 11

Cellulose (plants) vs starch (plants but can be digested in animals) vs glycogen (animals). Beta vs alpha amylase

Answer 11

polysaccharide made of repeating glucose via beta-1,4-glycosidic bonds vs polysaccharide made of repeating glucose via alpha-1,4-glycosidic bonds => amylose; some alpha-1,6-glycosidic bonds –> branching => amylopectin vs polysaccharide made of repeating glucose via some alpha-1,4-glycosidic bonds; lots of alpha-1,6-glycosidic bonds –> branching
Cleaves at nonreducing ends (end of acetal) —> yields maltose vs cleaves randomly —> yields maltose and glucose

Question 12

Homopolysaccharide vs heteropolysaccharide

Answer 12

made up of one type of monosaccharide vs made up of more than one type of monosaccharide

Question 13

What are some common disaccharides/dimers?

Answer 13

sucrose (glucose-α-1,2-fructose), lactose (galactose-β-1,4-glucose), and maltose (glucose-α-1,4-glucose)

Question 14

How to name disaccharides?

Answer 14

1. Name non reducing end, add suffix –osyl
2. Identify connection (NR –> R)
3. Name reducing end

Question 15

Which C’s in glucose bond to go from linear to ring? Why?

Answer 15

C5 bonds w/ C1 –> Carbonyl O bonds w/ H
C5 is better because it’s thermodynamically stable. Using C4 hydroxyl would result in 5 members ring (not 6) —> less stable

Question 16

What’s the difference b/w alpha vs beta glycosidic bonds? What type of rxn occurs to make a glycosidic bond?

Answer 16

both groups = same side vs both groups = opposite sides (A down, B up); dehydration

Question 17

How are beta linkages broken down?

Answer 17

Only by bacteria

Question 18

Glycogen synthase vs branching enzyme vs glycogen phosphorylase vs de branching enzyme

Answer 18

Makes alpha 1,4 glycosidic link vs makes alpha 1,6 glycosidic link vs creates G1P by breaking alpha 1,4 link vs makes alpha 1,4 link (instead of alpha 1,6), breaks branches

Question 19

Postprandial vs postabsorptive states vs starvation

Answer 19

Well fed, high insulin and low glucagon vs fasting, high glucagon and low insulin vs really high glucagon and catacholamines released, keto genesis

Question 20

How to move groups from Haworth projection to chair conformation

Answer 20

Up groups become equatorial and down groups become axial

Question 21

What are aldonic acids? What are alditols?

Answer 21

Aldoses can be oxidized to CAs => aldonic acids; aldonic acids have been reducing sugars. Ketones can’t be oxidized to CAs directly but they can tautomerize into aldoses and then get oxidized
Aldoses that have been reduced to alcs

Question 22

Esterification vs glycoside formation

Answer 22

When hydroxyl group of carb reacts with CA or CA derivative to make ester vs when hemiacetal reacts with alcs to make acetal aka glycoside

Question 23

Tollens vs Benedict’s reagent

Answer 23

There’s aldehyde because it’s silver vs there’s aldehyde because it’s copper

Question 24

Can fats be converted to glucose during starvation? Can glucose be converted to fats?

Answer 24

No, humans don’t have the enzymes to do so. Yes, in the liver: glu = converted to FAs, which are converted to triacylglycerides

Question 25

Common ratio for monosaccharide chemical formula

Answer 25

C:H:O = 1:2:1

REMEMBER WHEN JOINING MONO’s TO MAKE A DISACCHARIDE, SUBTRACT A H2O MOLEC

Question 26

Where is glycogen produced and stored? Where is glycogen broken down into glucose?

Answer 26

Produced and stored in liver and skeletal muscle; can also be stored in brain. Only in liver to inc blood sugar b/c skeletal muscle don’t have glucose-6-phosphatase; skeletal muscle uses glycogen for high intensity exercise (epinephrine tells skeletal muscles to do glycogenolysis and glycolysis), brain uses glycogen as cerebral source for emergencies

Question 27

Cyclic monosaccharides are what?

Answer 27

Hemiacetals/ketals