chapter 7 Flashcards
Carbohydrates
-Named so because many have formula
-Produced from
-Range from as small as
-Fulfill a variety of functions including:
-Can be covalently linked with
-Named so because many have formula Cn(H2O)n
-Produced from CO2 and H2O via photosynthesis in plants
-Range from as small as glyceraldehyde (Mw = 90 g/mol) to as large as amylopectin (Mw = 200,000,000 g/mol)
-Fulfill a variety of functions including:
–energy source and energy storage
–structural component of cell walls and exoskeletons
–informational molecules in cell-cell signaling
-Can be covalently linked with proteins to form glycoproteins and proteoglycans
Glycoprotein
Proteoglycan
Glycoprotein
-Primarily protein
-CHO chains may be negatively charged
-Present in cell surface
Proteoglycan
-Primarily carbo
-CHO chains always negatively charged
-Present in connective tissue
Aldoses and Ketoses
An aldose contains an aldehyde functionality
A ketose contains a ketone functionality
Trioses
Two common hexoses
Glucose, Fructose
The pentose components of nucleic acids.D-Ribose is a component of ribonucleic acid (RNA), and 2-deoxy-D-ribose is a component of deoxyribonucleic acid (DNA)
Three types of carbohydrates
Monosaccharides
Single polyhydroxy aldehydes/ketone (e.g. glucose)
Disaccharides
Two monosaccharides linked by glycosidic bond; their name ends with suffix “_OSE” (e.g. sucrose)
Polysaccharides
Thousands/millions of mono- units (e.g. cellulose/glycogen)
Enantiomers
Enantiomers
–Stereoisomers that are nonsuperimposable mirror images
In sugars that contain many chiral centers, only the one that is most distant from the carbonyl carbon is designated as D (right) or L (left)
D and L isomers of a sugar are enantiomers
–For example, L and D glucose have the same water solubility
Most hexoses in living organisms are D stereoisomers
Some simple sugars occur in the L-form, such as L-arabinose
Diastereomers? Seterisomers that are not mirrorimages of each other
Drawing Monosaccharides
-Chiral compounds can be drawn using perspective formulas
-However, chiral carbohydrates are usually represented by Fischer projections
-Horizontal bonds are pointing toward you; vertical bonds are projecting away from you
Diastereomers
-Diastereomers: stereoisomers that are not mirror images
-Diastereomers have different physical properties
–For example, water solubilities of threose and erythrose are different
Epimers
-Epimers are two sugars that differ only in the configuration around one carbon atom
Structures to Know
-Ribose is the standard five-carbon sugar
-Glucose is the standard six-carbon sugar
-Galactose is an epimer of glucose
-Mannose is an epimer of glucose
-Fructose is the ketose form of glucose
Hemiacetals and Hemiketals
-Aldehyde and ketone carbons are electrophilic
-Alcohol oxygen atom is nucleophilic
-When aldehydes are attacked by alcohols, hemiacetals form
-When ketones are attacked by alcohols, hemiketals form
Cyclization of Monosaccharides
-Pentoses and hexoses readily undergo
-The former carbonyl carbon becomes a
-The former carbonyl oxygen becomes a
-If the hydroxyl group is on the opposite side
-If the hydroxyl group is on the same side
-Pentoses and hexoses readily undergo intramolecular cyclization
-The former carbonyl carbon becomes a new chiral center, called the anomeric carbon
-The former carbonyl oxygen becomes a hydroxyl group; the position of this group determines if the anomer is α or β
-If the hydroxyl group is on the opposite side (trans) of the ring as the CH2OH moiety the configuration is α
-If the hydroxyl group is on the same side (cis) of the ring as the CH2OH moiety, the configuration is β
Mutarotation
α β interconvertible BUT with breakage of covalent bonds
Pyranoses and Furanoses
-Six-membered oxygen-containing rings are called pyranoses
-Five-membered oxygen-containing rings are called furanoses
-The anomeric carbon is usually drawn on the right side
Chain-Ring Equilibrium and Reducing Sugars
-The ring forms exist in equilibrium with the open-chain forms
-Aldehyde can reduce Cu2+ to Cu+ (Fehling’s test)
-Aldehyde can reduce Ag+ to Ag0 (Tollens’ test)
-Allows detection of reducing sugars, such as glucose
Basis of Fehling’s Reaction = Glucose is Reducing
This is the more sensitive and specific test for glucose
Colorimetric Glucose Analysis
Nowadays, enzymatic methods are used to quantify reducing sugars such as glucose
–The enzyme glucose oxidase catalyzes the conversion of glucose to glucono-δ-lactone and hydrogen peroxide
–Hydrogen peroxide oxidizes organic molecules into highly colored compounds
–Concentrations of such compounds is measured colorimetrically
Electrochemical detection is used in portable glucose sensors
The nonenzymatic reaction of glucose with a primary amino group in hemoglobin
Concentration of GHB is dangerous damage to kidneys, retinas, cardiovascular system
The Glycosidic Bond
Two sugar molecules can be joined via a
The glycosidic bond (an acetal) between monomers is
The disaccharide formed upon
Two sugar molecules can be joined via a glycosidic bond between an anomeric carbon and a hydroxyl carbon
The glycosidic bond (an acetal) between monomers is less reactive than the hemiacetal at the second monomer
Second monomer, with the hemiacetal, is reducing
Anomeric carbon involved in the glycosidic linkage is nonreducing
The disaccharide formed upon condensation of two glucose molecules via 1 → 4 bond is called maltose
Nonreducing Disaccharides
-Two sugar molecules can be also joined via a glycosidic bond between
-The product has two
-There are no
-Trehalose is a
-Two sugar molecules can be also joined via a glycosidic bond between two anomeric carbons
-The product has two acetal groups and no hemiacetals
-There are no reducing ends, this is a nonreducing sugar
-Trehalose is a constituent of hemolymph of insects
–Provides protection from drying
–Resurrection plant (> 15 yrs)
Polysaccharides
-Natural carbohydrates are usually found as
-These polysaccharides can be
-Polysaccharides do not have a defined
-Natural carbohydrates are usually found as polymers
-These polysaccharides can be
–homopolysaccharides (storage forms of monosacc as fuel (starch and glycogen); structural elements in plant cells (cellulose, chitin))
–heteropolysaccharides (provide extracellular support for organism (protection, shape, support to cells, tissues, etc.))
–linear
–branched
-Polysaccharides do not have a defined molecular weight.
–This is in contrast to proteins because unlike proteins, no template is used to make polysaccharides
homopolysaccharides heteropolysaccharides
differ in
Differ in:
mono- units,
chain length
linking bond types
degree of branching
homopolysaccharides heteropolysaccharides
Glycogen
Glycogen is a
-Glucose monomers form
-Branch-points with
-Molecular weight reaches
-Functions as the main
WHY: store glycogen instead of glucose.
Glycogen is a branched homopolysaccharide of glucose
-Glucose monomers form (α1 → 4) linked chains
-Branch-points with (α1 → 6) linkers every 8–12 residues
-Molecular weight reaches several millions
-Functions as the main storage polysaccharide in animals
WHY: store glycogen instead of glucose. The glycogen is insoluble and does not affect the osmolarity of the cell. Glucose is soluble and will affect osmolarity
Glycosidic Linkages of glycogen
Starch
Starch is a mixture of
–Molecular weight of amylopectin is up
-Starch is the main
Starch is a mixture of two homopolysaccharides of glucose
–Amylose is an unbranched polymer of (α1 → 4) linked residues
–Amylopectin is branched like glycogen but the branch-points with (α1 → 6) linkers occur every 24–30 residues
–Molecular weight of amylopectin is up to 200 million
-Starch is the main storage polysaccharide in plants
Mixture of Amylose and Amylopectin in Starch
A cluster of amylose/amylopectin. Strands of amylopectin form double-helical structures with each other or with amylose strands. Amylopectin has frequent (α16) branch points (red). Glucose residues at the nonreducing ends of the outer branches are removed enzymatically during the mobilization of starch for energy production. Glycogen has a similar structure but is more highly branched and more compact.
Starch Detection: Iodine Reaction
Theiodinetest is used to test for the presence ofstarch.Starchturns into an intense “blue-black” colour upon addition of aqueous solutions of the triiodide anion, due to the formation of an intermolecular charge-transfer complex.
Metabolism of Glycogen and Starch
-Glycogen and starch often form
-Granules contain
-Glycogen and amylopectin have
-Enzymatic processing occurs
-Glycogen and starch often form granules in cells
-Granules contain enzymes that synthesize and degrade these polymers
-Glycogen and amylopectin have one reducing end but many nonreducing ends
-Enzymatic processing occurs simultaneously in many nonreducing ends
Dextrans
-Bacterial and yeast polysaccharides made of D-glucose connected by α1→6 linkages and branchpoints at α1→3, α1→2, α1→4, linkages .
-Makes a crosslinked matrix that is insoluble and of various porosities- used to separate macromolecules (size-exclusion chromatography).
Cellulose
-Glucose monomers form
-Hydrogen bonds form
-Additional H-bonds
-Structure is now
-Most abundant
-Cotton is nearly
Cellulose is a linear, unbranched homopolysaccharide (10,000 – 15,000 D-glucose unit)
-Glucose monomers form (β1 → 4) linked chains
-Hydrogen bonds form between adjacent monomers
-Additional H-bonds between chains
-Structure is now tough and water-insoluble
-Most abundant polysaccharide in nature
-Cotton is nearly pure fibrous cellulose
Hydrogen Bonding in Cellulose
When aligned, they form H-bonds and fit like Leggo’s blocks to become insoluble.
Cellulose Metabolism
-The fibrous structure and water-insolubility make
-Fungi, bacteria, and protozoa secrete
-Most animals cannot
-Ruminants and termites
-Cellulases hold
-The fibrous structure and water-insolubility make cellulose a difficult substrate to act on
-Fungi, bacteria, and protozoa secrete cellulase, which allows them to use wood as source of glucose
-Most animals cannot use cellulose as a fuel source because they lack the enzyme to hydrolyze (β1 →4) linkages
-Ruminants and termites live symbiotically with microorganisms that produces cellulase
-Cellulases hold promise in the fermentation of biomass into biofuels
Cellulase is Only produced by
Cellulase is Only produced by Some Fungi and Some Bacteria
Chitin
-N-acetylglucosamine monomers form
-Forms extended
-Hard,
-Structure is
-Found in
Chitin is a linear homopolysaccharide of N-acetylglucosamine
-N-acetylglucosamine monomers form (β1 → 4)-linked chains
-Forms extended fibers that are similar to those of cellulose
-Hard, insoluble, cannot be digested by vertebrates
-Structure is tough but flexible, and water-insoluble
-Found in cell walls in mushrooms, and in exoskeletons of insects, spiders, crabs, and other arthropods
Peptidoglycan
-The rigid component of
-Has interpeptide
-Composed of a
-Linear polymers lie
-Produces a strong
-Lysozyme hydrolyses
-The rigid component of bacterial cell walls
-Has interpeptide bridge
-Composed of a heteropolymer of N- acetylglucosamine and N-acetylmuramic acid in a β1→4 linkage
-Linear polymers lie side by side in cell wall and are crosslinked by short peptides
-Produces a strong sheath to protect bacteria
-Lysozyme hydrolyses the β1→4 linkage
Peptidoglycan
inhibitor of cell wall synthesis: penicilllins
-block cross-linking of peptidoglycan
-beta-lactam ring
-different spectra of action
-often cause allergic reactions
Agar and Agarose
-Agar is a complex
-Agar serves as
-Agarose is one component of
-Agar solutions form
-Agarose solutions form gels that are commonly used in
-Agar is a complex mixture of hetereopolysaccharides containing modified galactose units
-Agar serves as a component of cell wall in some seaweeds
-Agarose is one component of agar with fewest charged groups
-Agar solutions form gels that are commonly used in the laboratory as a surface for growing bacteria
-Agarose solutions form gels that are commonly used in the laboratory for separation DNA by electrophoresis
Glycosaminoglycans
-_____ polymers of
-One monomer is either
-Negatively charged
-Extended hydrated
-Forms meshwork with
-Linear polymers of repeating disaccharide units
One monomer is either
-N-acetyl-glucosamine or
-N-acetyl-galactosamine
Negatively charged
-Uronic acids (C6 oxidation)
-Sulfate esters
Extended hydrated molecule
-Minimizes charge repulsion
Forms meshwork with fibrous proteins to form extracellular matrix
-Connective tissue
-Lubrication of joints
Heparin and Heparan Sulfate
-Heparin is linear
-Heparan sulfate is
-Highest
-Prevent
-Binding to various
-Can also bind to
-Heparin is linear polymer, 3–40 kDa
-Heparan sulfate is heparin-like polysaccharide but attached to proteins
-Highest negative charge density biomolecules
-Prevent blood clotting by activating protease inhibitor antithrombin
-Binding to various cells regulates development and formation of blood vessels
-Can also bind to viruses and bacteria and decrease their virulence
Glycoconjugates: Glycoprotein
A protein with small
-Carbohydrate attached via
-About half of
-Carbohydrates play role in
-Only some bacteria
-Viral proteins heavily
A protein with small oligosaccharides attached
-Carbohydrate attached via its anomeric carbon
-About half of mammalian proteins are glycoproteins
-Carbohydrates play role in protein-protein recognition
-Only some bacteria glycosylate few of their proteins
-Viral proteins heavily glycosylated; helps evade the immune system
Glycoconjugates: Glycolipids
-Parts of plant and animal
-In vertebrates,
-In gram-negative
A lipid with covalently bound oligosaccharide
-Parts of plant and animal cell membranes
-In vertebrates, ganglioside carbohydrate composition determines blood groups
-In gram-negative bacteria, lipopolysaccharides cover the peptidoglycan layer
Glycoconjugates: Proteoglycans
Sulfated glucoseaminoglycans attached to a large rod-shaped protein in cell membrane
-Syndecans: protein has a single transmembrane domain
-Glypicans: protein is anchored to a lipid membrane
-Interact with a variety of receptors from neighboring cells and regulate cell growth
Proteoglycans
-Different glycosaminoglycans are
-Linkage from anomeric carbon of
-Our tissues have many
Proteoglycan structure, showing the tetrasaccharide bridge
-Different glycosaminoglycans are linked to the core protein
-Linkage from anomeric carbon of xylose to serine hydroxyl
-Our tissues have many different core proteins; aggrecan is the best studied
Proteoglycan structure, showing the tetrasaccharide bridge. A typical tetrasaccharide linker (blue) connects a glycosaminoglycan—
in this case chondroitin 4-sulfate (orange)—to a Ser residue in the core protein. The xylose residue at the reducing end of the linker is joined by its anomeric carbon to the hydroxyl of the Ser residue.
Proteoglycan Aggregates
-Hyaluronan and aggrecan form huge (Mr > 2*108) noncovalent aggregates
-Hold lots of water (1000× its weight); provides lubrication
-Very low friction material
-Covers joint surfaces: articular cartilage
Reduced friction
Load balancing
Extracellular Matrix (ECM)
-Main components
ECM is a barrier for
-Material outside the cell
-Strength, elasticity, and physical barrier in tissues
-Main components
–Proteoglycan aggregates
–Collagen fibers
–Elastin (a fibrous protein)
ECM is a barrier for tumor cells seeking to invade new tissues
-Some tumor cells secrete heparinase that degrades ECM
Interaction of the Cells with ECM
-Some integral membrane proteins are
-Other integral membrane proteins are
These proteins link cellular cytoskeleton to the
-Some integral membrane proteins are proteoglycans
–Syndecans
-Other integral membrane proteins are receptors for extracellular proteoglycans
–Integrins
These proteins link cellular cytoskeleton to the ECM and transmit signals into the cell to regulate:
-cell growth
-cell mobility
-apoptosis
-wound healing
