Ch20: Carbs' Structure & Function

SPR26 OSU BIOPHRM 3312

Carbohydrates are organic compounds made up______-, and they serve as a key source of energy for the body.

of carbon, hydrogen, and oxygen

4 main categories of carbs

reflecting increasing complexity

• monosaccharides

• disaccharides

• oligosaccharides

• polysaccharides

sugar unit # and examples: monosaccharides

• 1

• Glucose, Fructose, Galactose

sugar unit # and examples: disaccharides

• 2

• sucrose, lactose

sugar unit # and examples: oligosaccharides

• 3-10

• raffinose, stachyose

sugar unit # and examples: polysaccharides

• >10

• starch, cellulose, glycogen

simplest form of carbohydrates, consisting of a single sugar unit.

monosaccharides

a primary energy source for cells

Glucose

part of lactose in dairy products

Galactose

sugar found in fruits

Fructose

Monosaccharides are absorbed directly in the ______ into the bloodstream and are quickly used for energy

small intestine

ID this structure:

glucose

ID this structure:

galactose

ID this structure:

fructose

glucose and galactose are _____ of each other

isomers

Monosaccharides, often referred to as simple sugars, are polyalcohols that contain either an ________ or a ________. Structurally, they can exist in both _______ forms.

• aldehyde (called aldose)

• ketone group (called ketose)

• straight-chain and ring

Disaccharides are formed by two monosaccharide molecules linked together by a _______ bond.

glycosidic

Give this disaccharide’s common name/formation & its sugar subunit: sucrose

• table sugar

• a-D-glucose – b-D-fructose

Give this disaccharide’s common name/formation & its sugar subunit: lactose

• milk sugar

• b-D-galactose – b-D-glucose

Give this disaccharide’s common name/formation & its sugar subunit: maltose

• formed during the breakdown of starch

• a-D-glucose – a-D-glucose

Disaccharides must be broken down into monosaccharides by ________ before they can be absorbed and used by the body

enzymes

________ are often found in certain vegetables, legumes, and grains, which are not fully digested by humans and can cause gas when consumed, as they are fermented by bacteria in the large intestine.

Oligosaccharides

Oligosaccharides covalently modify (via attachment) proteins and lipids to generate _________ involved in cell recognition and signaling

glycoproteins and glycolipids

In glycoproteins, they are bonded to specific ______, while in glycolipids, they are linked to _______molecules

• amino acid residues

• lipid

________ are common membrane components with carbohydrate chains exposed on the extracellular surface for recognition and signaling

Glycoproteins and glycolipids

_______are large, complex carbohydrates made up of many monosaccharide units linked together

Polysaccharides

________, a storage form of glucose in plants

Starch

___________, the storage form of glucose in animals that are found mainly in the liver and muscles

Glycogen

__________, a major structural component of plant cell walls that is not digestible by humans but acts as dietary fibers

Cellulose

___________ are composed of glucose units but differ in their anomeric forms, their structures, function, and the types of bonds that link the glucose units together

Starch, glycogen, and cellulose

Energy production – _______are the major source of energy for our body

Carbohydrates

Energy storage - Excess ________is stored as glycogen (the majority of which is stored in the muscle and liver) providing energy in between meals or during intense activity

glucose

Building blocks of macromolecules: ________ are essential building blocks of important macromolecules, such as RNA, DNA, NAD, FAD and ATP

ribose and deoxyribose

Cell Recognition and Signaling: Cell surface __________ are crucial for recognition and signaling, participating in cell adhesion, immune responses, and intercellular communication

glycoproteins and glycolipids

Systematic Names of Monosaccharides: Monosaccharides are named according to the presence of either an aldehyde (prefix _________) or ketone (prefix _______) functional group, the carbon chain length, and usually conclude with the suffix __________

• Aldo-

• Keto-

• -ose

Monosaccharides typically have a carbon count ranging from ________—

three to six

Trioses with 3 carbons are the smallest _______

monosaccharides

Formula C3H6O3 that can correspond to two sugars: ________________. These two sugars are constitutional isomers.

Aldotriose (AKA Glyceraldehyde) and Ketotriose (Dihydroxyacetone)

ID this structure’s trivial name:

glyceraldehyde (intermediate in glycolysis)

ID this structure’s trivial name:

dihydroxyacetone (intermediate in glycolysis)

Sugars are predominantly recognized by their _______ names, each unique to a specific sugar

common or trivial

The limitation of trivial names is their lack of information regarding the sugar's __________

structure, carbon count, or functional groups

Carbohydrates has a general formula _______, with exceptions

(CH₂O)_n

________are compounds that share identical molecular and structural formulas but exhibit distinct spatial arrangements of atoms, resulting in different shapes

Stereoisomers

________are stereoisomers that are not mirror images of each other and differ at one or more (but not all) chiral centers

Diastereomers

achiral means?

not chiral (duhhhh lol)

_______carbon is a carbon that bonds to four different groups

Chiral

A structure with n stereocenters will have a maximum of _________ different stereoisomers

2ⁿ

Glyceraldehyde has two stereoisomers; more specific they are _______; non-superimposable mirror images

enantiomers

In conventional naming, a sugar is designated as an ____ if the –OH group on the last chiral carbon is on the left, and as a __________ if it is on the right. Only the _____ on chiral carbons are considered when identifying mirror images

• L-isomer

• D-isomer

• –OH groups

The prevalent form for naturally occurring sugars is the _______

D-form

In a molecule with multiple chiral carbons, the chiral carbon ______ is chosen for determining the L- or D-forms

farthest from the carbonyl carbon

_______are stereoisomeric pair that serves as mirror images of one another. They share identical properties, trivial names, but vary based on the L- or D-form. Examples: _______

• Enantiomers

• D-Allose and L-Allose; D-Glucose and L-Glucose

_______specifically refer to stereoisomers differing solely in the absolute configuration at a singular chiral center known as the ______ carbon. Examples: ________

• Epimers

• epimeric

• D-Allose and D-Glucose are C3 epimers

An alcohol group reacts with a carbonyl group to form a _____; compounds with –OH and –OR bond to what was once the carbonyl carbon of an aldehyde/ketone

hemiacetal / hemiketal

How does an alcohol group react with a carbonyl group to form a hemiacetal/hemiketal? (i.e., what is it about these two groups that would encourage this arrangement?)

Alcohols (ROH) are weak acids, and carbonyl groups are polar (O partial^(-) & C partial⁽⁺⁾).

Case of opposites attract: Alcohol H+ bonds to Carbonyl O-, and Alcohol RO- bonds to Carbonyl C+.

The open-chain, monosaccharide form is mostly converted to _______ form (more than 99% in a mixture of aqueous solution).

cyclic hemiacetal (rings)

The carbonyl carbon is called the ____ carbon in the ring form.

anomeric

Glucose contains both alcohol and aldehyde functional groups that readily undergo an ________- reaction.

intramolecular addition

Depending on how the ring was closed, D-Glucose can form two molecules: ____________. The two forms are called _______ since they are isomers at the _______ center/carbon.

• α-D-Glucose and β-D-Glucose

• "anomers"

• anomeric

In the α-form of cyclic glucose, the -OH group at the anomeric center is on the _________ the -CH₂OH group

opposite side to

In the β-form of cyclic glucose, the -OH group at the anomeric center is on the _________ the -CH₂OH group

same side (besides) as

Mutarotation is the spontaneous change in the specific ________of a sugar solution due to interconversion between its______ forms through the ______ form.

• optical rotation (OR)

• α- and β-anomeric

• open-chain

Example: a-D-Glucose ←→ Open-chain form ←→ b-D-Glucose

Simple sugars, such as glucose and fructose, predominantly adopt ring/cyclic structures when in a solution. Only the cyclic form, as opposed to the open-chain form, participates in ________.

polymerization

D-Glucose (C6H12O6) AKA blood sugar, aldohexose, is the most important sugar in human metabolism b/c energy ________.

extraction starts with glycolysis

D-Glucose (C6H12O6) AKA blood sugar, aldohexose, is produced ________in plant, and by _______in humans, and it serves as building block of biopolymers: ______(plants) and ________(animals).

• photosynthesis

• gluconeogenesis

• Starch

• glycogen

D-Glucose (C6H12O6) AKA blood sugar, aldohexose, levels in the blood are primarily regulated by two hormones: _______. An imbalance of these, leads to elevated blood glucose levels, associated with ________.

• Insulin and glucagon

• diabetes

galactose is commonly found in milk as a component of the disaccharide _______, and in glycolipids

lactose

galactose is an epimer of glucose and can be converted into glucose or enter _______—to yield energy when needed.

glycolysis

_______ is a rare genetic disorder due to the deficiency of any enzymes involved in breaking down galactose, which may cause liver failure, mental retardation and cataracts. This is treated by a galactose-free diet

Galactosemia

________ is present in fruits and honey, and can be produced by the hydrolysis of corn starch to make high-fructose corn syrup.

Fructose, also known as fruit sugar,

_______ often serves as a sweetener in beverages and processed foods

Fructose

Phosphorylated fructose is an intermediate in the _______ pathway

glycolytic

_________is primarily metabolized in the liver, where it bypasses key regulatory steps in glycolysis (unlike glucose). This can lead to an overproduction of triglycerides, contributing to _______ (NAFLD).

• Fructose

• non-alcoholic fatty liver disease

ID this structure:

ribose, C5H10O5

ID this structure:

deoxyribose, C5H10O4

________is part of larger biomolecules, such as DNA, RNA, NAD⁺, FAD, coenzyme A, and ATP.

Ribose

______, w/ the -OH at carbon 2 of ribose replaced by -H (lacking oxygen).

Deoxyribose

Aldoses are _______sugars because they contain an aldehyde functional group that can be oxidized to carboxylic acid.

reducing

In aqueous solution, although aldoses exist primarily in a cyclic hemiacetal form, they are in equilibrium with __________ group. This aldehyde can act as reducing agents by being oxidized.

a small amount of the open-chain form that contains a free aldehyde

In alkaline solution, ketoses undergo rearrangement to become aldoses via the intermediate _________

enediol

An _______is an alkene with an -OH group attached to each of the two carbon atoms forming the double bond.

enediol

Ketoses by converting to aldoses can also act as _________.

reducing sugars

All _______ including both aldoses and ketoses are reducing sugars.

monosaccharides

In a monosaccharide, the…

hemiacetal group + alcohol → acetal + H2O

What is the acetal group called, and what is its significance?

It is called glycoside, and they are no longer reducing sugars b/c the anomeric C is locked in the acetal linkage.

When the…

hemiacetal group of one sugar + hydroxyl group from another sugar → disaccharide + H2O

…what is the linkage called?

glycosidic linkage

_______is formed from rxn b/t a hemiacetal group on one glucose and the hydroxyl group at C4 on another glucose. The linkage is called _____, w/ H2O released in the process.

• maltose

• α-1,4 glycosidic bond or α-1,4link

Maltose retains a free ______ group at Glucose 2, hence it is a reducing sugar

hemiacetal

Maltose is produced during the enzymatic digestion of ______ (Stage 1 of Food catabolism).

starch and glycogen

ID this structure:

maltose

Glycosidic linkages are named by reading from left to right:

• Position (a or b) of the anomeric –OH (left glucose)

• followed by numbers that correspond to the locations of the carbons involved in the glycosidic bond (C1 to C4)

Lactose AKA milk sugar, constituting 2-8% of human milk by weight and comprises a ______ bond.

β-D-galactose linked to a β-D-glucose through a β-1,4

Lactose is classified as a reducing sugar due to the presence of a _______

hemiacetal in glucose

Lactose intolerance results from the inability to hydrolyze lactose, caused by an _______. In the colon, normal bacteria interact with undigested lactose, leading to symptoms such as diarrhea, gas, and bloating

enzyme (lactase) deficiency

Patients with _____ should avoid ingesting lactose.

Galactosemia

Sucrose, also known as table sugar, is composed of _______ link.

α-D-glucose and β-D-fructose linked by an α-1,2

The hemiacetal of α-D-glucose reacts with the hemiketal of β-D- fructose.

Sucrose is a ______ because both of its anomeric carbons are involved in the glycosidic bond, leaving no free hemiacetal or hemiketal group.

non-reducing sugar

Sucrose is hydrolyzed in the small intestine by _____ yielding a 50:50 mixtures of glucose and fructose

sucrase

The hydrolysis of disaccharides involves the breaking of the ______ that connects the two monosaccharide units in the disaccharide molecule, resulting in the formation of individual monosaccharides

glycosidic bond

This hydrolysis of disaccharides reaction takes place during digestion of carbohydrates catalyzed by a class of enzyme known as _____. Sugar specific enzymes are named after the sugar.

hydrolases