BIOL 304 Chapter 11: Carbohydrates and Glycoproteins Part 1

What are carbohydrates?

carbon-based molecules high in hydroxyl groups

What is the empirical formula for carbohydrates?

(CH2O) n

True or False: carbohydrate groups can have additional groups or modifications.

True!

What oxidized molecules are found in carbohydrates?

polyhydroxy aldehydes and ketones

What are monosaccharides composed of?

aldehydes or ketones that contain two or more hydroxyl groups; can exist in many isomeric forms

How long are monosaccharides?

between 3 to 7 carbons long

What is another name for monosaccharides?

simple sugars,

What does the prefix "ose" mean in regard to carbohydrates?

this carbohydrate is some type of sugar

Which carbohydrate isomer is used in the most amount in the body?

the D conformation

What is nomenclature of a monosaccharide based on?

carbon-chain length and identity of oxidized group

What are trioses?

three carbon lengths

What are tetroses?

four carbon lengths

What are pentoses?

five carbon lengths

What are hexoses?

six carbon lengths

What are heptoses?

seven carbon lengths

What is a ketose?

in a carbohydrate, the keto (ketone) group is oxidized

What is an aldose?

in a carbohydrate, the aldehyde group is oxidized

What are constitutional isomers?

molecules with identical molecular formulas that differ in how the atoms are ordered

What are stereoisomers?

molecules that differ in spatial arrangement but not bonding order

True or False: stereoisomers can have either a D or L configuration

True!

What is an enantiomer?

isomers that are mirror images of each other

What is a diastereoisomer?

isomers that are not stereoisomers of each other

How can the number of isomers that can possibly be produced from one molecule be determined?

with the equation 2n (n = number of asymmetric, or chiral, carbon atoms)

What are epimers?

sugars that are diastereoisomers differing in configuration only at a single asymmetric center

True or False: most monosaccharides exist as interchanging cyclic forms

True! form cyclic molecules when reacted with certain molecules

How is a hemiacetal created?

by reacting aldehyde with alcohol

How is a hemiketal formed?

by reacting a ketone with an alcohol

How is pyranose produced?

by reacting the hydroxyl group on carbon 5 of a sugar with the aldehyde of carbon 1, which forms a hemiacetal

Why does pyranose formation occur?

a specific group in sugar (C5) reacts with aldehyde due to the presence of the specific aldehyde group

What is pyranose formation an example of?

interchanging cyclic forms within sugar

How is furanose produced?

by reacting the hydroxyl group on carbon 5 of a sugar with the ketone of carbon 1, which forms a hemiketal

What is furanose formation an example of?

interchanging cyclic forms

What is an anomer?

a diastereoisomeric form of sugars that forms when a cyclic hemiacetal is formed, and an additional asymmetric center is created

In glucose, which molecule becomes the asymmetric center when a cyclic hemiacetal is formed?

C1, since it becomes the anomeric carbon atom

What happens when the asymmetric center in glucose is created?

two ring structures are formed

What two ring structures are formed from the creation of the asymmetric center in glucose?

D-glucopyranose and beta-D-glucopyranose

What is D-glucopyranose?

hydroxyl group attached to C-1 is on the opposite side of the ring as C-6

What is beta-D-glucopyranose?

hydroxyl group attached to C-1 is on the same side of the ring as C-6

True or False: D-fructose rapidly interchanges between four distinct ring structures

True! different variants can form based upon how the ring is put together; some structure, even though they're possible, are not favored biologically, so they don't form

In D-fructose, which carbon is the anomeric carbon?

C-2

Which ring structure of glucose predominates over the other forms?

pyranose, since it has reduced steric hinderance

Which ring structure of fructose predominates over the other forms?

furanose

Why are pyranose rings not planar?

saturated carbon atoms of the ring cause tetrahedral geometry, some are squashed, while others cannot be squashed due to steric hinderance

Which two types of conformations can pyranose and furanose adopt?

boat and chair

How are the substituents on the carbon ring atoms oriented?

in either the axial or equatorial position

What is the axial position of the chair form?

nearly perpendicular

What is the equatorial position of the chair form?

nearly parallel

In the chair form, which position for substituents leads to the most steric hinderance?

axial substituents, specifically on the same side of the ring

Which form predominates for beta-D-glucose?

the chair form, since all axial positions are occupied by hydrogens

Why is the boat form disfavored by beta-D-glucose?

this form is more sterically hindered and it is harder to access certain molecules

What is blood sugar?

D-glucose circulating in the blood

What parts of the body primarily utilize D-glucose for fuel?

the brain in non-starvation conditions and red blood cells

What is the first possible reason why D-glucose is an important fuel source?

glucose is formed from formaldehyde under prebiotic conditions and may have been available as a fuel source for primitive biochemical systems

What is the second possible reason why D-glucose is an important fuel source?

glucose is relatively inert (stable and does not readily participate in chemical reactions with other substances)

What is the third possible reason why D-glucose is an important fuel source?

the most stable ring structure is beta-D-glucopyranose

How do we know that D-glucose is a reducing sugar?

in its linear form, glucose can react with oxidizing reagents

What ion is needed in order to determine if a molecule is a reducing sugar?

Cu2+

What is Fehling's solution?

solutions of Cu2+ that test for the presence of sugars that adopt an open structure

What are reducing sugars?

sugars that react with oxidizing agents

True or False: all monosaccharides that can adopt linear structures in solution are reducing sugars.

True!

What are non-reducing sugars?

sugars that do not react with oxidizing agents

What is glycation?

nonenzymatic addition of a carbohydrate to another molecule (non-carbohydrate)

What is an example of glycation?

reducing sugars nonspecifically react to free animo groups with Lys or Arg residues to form stable covalent bonds

Under what conditions will D-glucose participate in glycation?

if concentrations of sugars and protein are very high for long periods of time

What are advanced glycation end products (AGEs)?

products resulting from cross-linking following the primary modification by glycation

Advanced glycation end products (AGEs) are usually associated with what conditions?

aging, arteriosclerosis, diabetes, and other pathological conditions

What happens when D-glucose reacts with hemoglobin?

glycated hemoglobin (A1C, A1c) is formed

What effect does glycated hemoglobin have on O2 binding?

has no effect >:)

What percent of hemoglobin is glycated in non-diabetics?

less than 6%

What percent of hemoglobin is glycated in uncontrolled diabetics?

almost 10%

Why is it important to measure the level of glycated hemoglobin in the blood?

high levels of glycated hemoglobin can indicate high levels of glucose in the blood, which can help identify underlying conditions like diabetes :D

Which molecules can modify the biochemical properties of monosaccharides?

alcohols, amines, and phosphates

True or False: modifications can increase biochemical versatility.

True! they can serve as signal molecules and can facilitate metabolism

What is O-glycosidic linkage?

covalent linkage formed between the anomeric carbon atom of a carbohydrate and the oxygen atom of an alcohol

What is N-glycosidic linkage?

covalent linkage formed between the anomeric carbon atom of a carbohydrate and the nitrogen atom of an amine

What is phosphorylation commonly used for?

modifying sugars in metabolic reactions

What is the first purpose of phosphorylation in metabolic reactions?

makes sugars anionic to prevent crossing the lipid-bilayer membranes and interacting with transporters of the unmodified sugar

What is the second purpose of phosphorylation in metabolic reactions?

blocks the formation of alternative ring formation

What is the third purpose of phosphorylation in metabolic reactions?

creates reaction intermediates that more readily undergo metabolism

What are oligosaccharides?

sugars that contain two or more monosaccharides linked by O-glycosidic bonds

How is directionality determined in oligosaccharides?

by their reducing and nonreducing end

What is a reducing end?

has a free anomeric carbon atom that can form the open chain form

What is the non-reducing end?

has an anomeric carbon in a glycosidic linkage that can not covert to the open-chain form

What is alpha-1,4-glycosidic linkage?

glycosidic linkage between the alpha-anomeric form of C-1 on one sugar and the hydroxyl oxygen atom on C-4 of the adjacent sugar

What is a disaccharide?

two sugars joined by an O-glycosidic linkage

Why are disaccharides important?

the cleaved product can be processed and used to make energy in the form of ATP :D

What is sucrose?

disaccharide of sugar cane or sugar beets that consists of glucose linked to fructose

How is sucrose structured?

the anomeric carbon of glucose is linked to the anomeric carbon of fructose

What are the configurations of glucose and fructose in sucrose?

glucose is in the alpha configuration and fructose is in the beta configuration

Is sucrose a reducing sugar?

No! so it cannot react with Cu2+

How is sucrose cleaved?

by using sucrase (invertase)

What is lactose?

disaccharide of milk that consists of a galactose linked to a glucose

How is galactose and glucose linked in lactose?

through beta 1,4-glycosidic linkage

How can lactose be hydrolyzed?

by lactase in humans and beta-galactosidase in bacteria

What does a lack of lactase lead to?

intolerance to lactose (lactose intolerant lol)

What is maltose?

a disaccharide resulting from the hydrolysis of large oligosaccharides that consists of two linked glucose molecules

How are the glucose molecules in maltose linked?

by an alpha-1,4-glycosidic linkage

How can maltose by converted to glucose?

through hydrolysis by maltase

What happens after eating a meal?

starch and glycogen are degraded by alpha-amylase to create oligosaccharides

What role does maltase play in the digestion of glycogen and starch?

maltase breaks down the oligosaccharides generated by alpha-amylase from glycogen and starch