carbohydrates

Created by mcostakis 

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biochemistry

study of the chemical substances found in living organisms and the chemical interactions of these substances.

carbohydrates (general)

1. half come from plants
2. ex. cotton, linen, wood-shelter and paper

carbohydrates plants

1. produced by photosynthesis
2. two uses = cellulose (structural) and starch/glycogen (energy reserve for the plant

functions of carbohydrates

1. oxidation provides energy
2. storage - in form of glycogen, provides short-term energy
3. supply carbon atoms for synthesis of other products (proteins, lipids & nucleic acids)
4. part of framework for DNA
5. linked to lipids, structural of cell membranes
6. linked to proteins function in cell-cell & cell-molecule recognition

carbohydrates definition

a polyhydroxy aldehyde, a polyhydroxy ketone or a compound that yields such substances upon hydrolysis
CnH₂nOn (n=number of atoms)

carbohydrates: monosaccharides

1. one single polyhydroxy aldehyde or ketone
2. can't be broken down to simpler substances by hydrolysis
3. 3-7 carbons, 5-6 are more common
4. water soluble, white crystalline solids

oligosaccharides

1. 2-10 polyhydroxy monosaccharide units
2. disaccharides most common (table sugar & milk sugar)
3. crystalline, white soluble substances
4. with proteins & lipids for structural & regulatory

polysaccharides

1. polymers that may contain thousands of mono units
2. ex. cellulose & starch

mirror images: 2 categories

1. superimposable on mirror images: images that coincide at all points when the images are laid upon each other (ex. plates)
2. non-superimposable: chiral (handedness) will exist in "left-handed" and "right-handed" forms

chirality "handedness"

1. any organic compound that contains a carbon atom with 4 different groups has handedness

chiral center

1. an atom in a molecule that has 4 different groups tetrahedrally bonded to it
2. a molecule that has a chiral center is a chiral molecule
- if 2 hydrogens than can't be chiral molecule

stereoisomers

1. isomers that have same molecular & structural formula but differ in orientation of atoms in space.

stereoisomers: structural features

1. presence of chiral center
2. structural rigidity (cis-trans isomers)

stereoisomers: 2 types

1. enantiomers: stereoisomers whose molecules are non-superimposable mirror images of each other
- molecules with a single chiral center
2. diastereoisomers: molecules are not mirror images of each other
- cis-trans isomers
- some molecules with more than one chiral center

fischer projections

1. vertical line represent bonds to groups directed into the printed page
2. horizontal lines represent bonds to groups directed out of the printed page.
3. functional groups w/highest priority are at the top (aldehyde & ketone)
4. presence of a chiral center means there can be two enantiomers
5. # carbons from carbonyl (top) & go down

glyceraldehyde

D-glyceraldehyde
1. smallest monosaccharide
2. one chiral center & 2 enantiomers

# of chirals = ? stereoisomers

2n
ex. 3 chirals = 2³ = 8 stereoisomers

epimers

distereomers whose molecules differ only in the configuration at one chiral center

properties of enantiomers

have same properties except for 2 areas:
1. their interaction w/plane polarized light
-a pair of enantiomers will rotate light to the same extent but in opposite directions
2. their interaction with other chiral substances
- a pair will react differently w/other chiral molecules (ex. left & right handed baseball gloves)
- solubility will be different
- will have the same BP, MP & density
- our bodies react differently. one may react higher & one might be inactive

dextrorotatory

1. a chiral compound rotates light to the right in a polarized plane
2. denoted as a "+"

levorotatory

1. a chiral compound rotates light to the left in a polarized plane
2. denoted as a "-"

aldoses

a monosaccharide that contains an aldehyde functional group

ketones

a monosaccharide that contains a ketone functional group

triose monosaccharides (2)

a. smallest monosaccharide that exist
b. intermediates in the glycolysis process

1. D-glyceraldehyde = chiral
2. dihydroxyacetone = non-chiral

glucose

1. aldohexose, monosaccharide
2. most abundant & most important nutritionally
3. grapes are a good source
4. aka grape sugar, dextrose & blood sugar

galactose

1. aldohexose, monosaccharide
2. epimer of glucose
3. synthesized from glucose, then combined with glucose to make disaccharide lactose
4. present in chemical marker than determines blood type

fructose

1. most important ketohexose (monosaccharide)
2. sweetest of all sugars
3. found in many fruits & honey
4. used as dietary sugar

ribose

1. aldopentose, monosaccharide
2. component of a variety of complex molecules
Ex. RNA, DNA, ATP

cyclic forms

1. dominant form of monosaccharide w/5 or more carbons is cyclic
2. cyclic forms are in equilibrium w/open chain forms
3. formed by the reaction of carbonyl group (C=O) with hydroxyl (-OH) group on carbon 5
4. the chemical reaction forms a hemiacetal

cyclic forms of D-glucose (2)

1. alpha form: -OH of C₁ and CH₂OH of C₅ are on opposite sides (CH₂OH above ring & -OH below ring)
2. Beat form: -OH of C₁ and CH₂OH of C₅ are on same side (CH₂OH & -OH above ring)

cyclic forms of monosaccharides

1. intramolecular cyclic hemiacetals no restricted to glucose
2. all aldoses w/5 or more carbons establish equilibria but w/different percentages of α, β and open chain forms

5 types of reactions of monosaccharides

1. oxidation to acidic sugars
2. reduction to sugar alcohols
3. glycoside formation
4. phosphate ester formation
5. amino sugar formation

oxidation to acidic sugars

-can yield 3 different types depending on oxidizing agent

3 types of acidic sugars

1. weak oxidizing agents → oxidize the aldehyde end to form an acid (aldonic acid)
a. a reducing sugar= gives a positive test w/a weak oxidizing agent such as Tollens (Ag+) & Benedicts (Cu)
2. strong oxidizing agents → oxidize both ends of mono at the same time to produce a dicarboxylic acid, known as aldaric acids
3. enzymes can oxidize the primary alcohol end w/o oxidation of the aldehyde group, producing an alduronic acid

reduction to sugar alcohols

1. carbonyl group (aldose or ketose) is reduced to a hydroxyl group using H as reducing agent.
-product is the corresponding polydydroxy alcohol (CH₂OH) = sugar alcohol
2. D-glucose →D-sorbitol. used as moisturizing agent in food & cosmetics. sweetener in gum
3. any time 2 mono are bonded thru a (1-4) linkage

glycoside formation

1. cyclic monosaccharides are hemiacetal & they can react w/alcohol to form acetals.
2. monosaccharide acetal = glycoside
3. can exist in both alpha & beta forms

phosphate ester formation

hydroxyl groups of a mono can react w/inorganic oxyacids to form inorganic esters (hemiacteal group C₁ and the primary alcohol group C₆)

amino sugar formation

1. one of the hydroxyl groups of a mono is replaced with an amino group
2. important building blocks of polysaccharide such as chitin

disaccharides

1. 2 monosaccharides reacting together
2. it is the formation of an acetal
3. one mono acts as a hemiacetal & other is an alcohol
4. the connection = a glycosidic linkage (always a C-O-C bond in a disaccharide)

maltose

1. maltose is produced when the polysaccharide starch breaks down
2. has two D-glucose units (one has to be α), H₂O is given off
3. hydrolysis (digestion) occurs b/c we have enzymes that break down the α (1-4) linkage
4. maltose & other reducing sugars exist in 3 forms:
α maltose, β maltose & open chain form

cellobiose

1. produces as intermediate in hydrolysis of polysaccharide cellulose
2. has 2 β-D-glucose units linked thru β(1-4) glycosidic linkage.
3. we don't have enzymes to break down

lactose

1. β-D-galatose + β-D-glucose→joined by a β(1-4) glycosidic linkage
2. principal carb in milk (milk sugar)
3. lactose intolerance = no enzyme to hydrolyse to galactose & glucose

sucrose

1. table sugar, plant kingdom, made from sugar cane (20% by mass) & sugar beets (17% by mass)
2. α-D-glucose + β-D-fructose
3. (1-2) linkage. the -OH on the C₂ of fructose-5 ring (the hemiacetal + the -OH on the C₁ of glucose (hemiacetal)
4. non-reducing sugar b/c it doesn't have a hemiacetal

polysaccharide

1. many mono bonded by glycosidic (acid) linkages
2. not sweet, negative w/Tollens & Benedicts b/c so many mono the concentration of aldehydes are low
3. limited water solubility
4. ex. cellulose, starch in plants, glycogen in animals, chitin in arthropods

polysaccharide: 2 types

1. linear & branched
2. homo- and hetero-polysaccharides

storage polysaccharides

1. a storage form for monosaccharides & is used as an energy source in cells
2. provides lower osmotic pressure than storing monos (↑ molarity → ↑ osmotic pressure) better to store 1 poly than thousands of mono
3. two important = starch (in plant cells) & glycogen (in animal & human cells)

storage polysaccharide: starch

1. glucose is monomeric unit
2. storage polysaccharide in plants
3. 2 types
a. amylose
b. amylopectin

storage polysaccharide: starch - amylose

*1. straight chain polymer
*2. makes up 15-20% of starch
3. usually α(1-4)bonds, 300-500 units

storage polysaccharide: starch - amylopectin

*1. branched chain polymer
*2. makes up to 80-85% of starch
3. α(1-4) for straight & α(1-6) for branch

storage polysaccharide: glycogen

1. storage polysaccharide for humans & animals
2. only glucose units
3. branched polymer, α(1-4) in straight chain, α(1-6) in branched
3. 3 times more highly branched than amylopectin
4. molecular mass: 3,000,000

storage polysaccharide: glycogen excess

1. stored in liver & muscles
2. glucose →glycogenesis→glycogen
3. glycogen→glycogenolysis→glucose

structural polysaccharide

1. serves a structural element in plant walls & animal exoskeletons
2. cellulose & chitin (both homopolysaccharides)

structural polysaccharide: cellulose

1. linear, homopolysaccharide w/ β(1-4) linkage
2. up to 5,000 glucose units
3. difference btw amylose (α1-4) & cellulose (β1-4) is that amylose is spiral & cellulose is straight/linear
4. linear align & form water-insoluble fibers
5. humans don't have enzyme to digest β(1-4) linkage but need fiber
6. cotton 95% cellulose, wood 50% cellulose

structural polysaccharideL chitin

1. linear, with all β (1-4) linkages & an N-acetyl amino derivative of glucose
2. give rigidity to exoskeletons of crabs, lobsters, etc.

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