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Biochem Ch. 10
Carbohydrates
| Question | Answer |
|---|---|
| What are the simplest carbyohydrates? | monosaccharides |
| monosaccharides | aldehydes or ketones that contain two or more hydroxyl groups (OH) |
| The smallest monosccharides are composed of _#_ carbons | 3 |
| Monosaccharides: aldoses contain a ______ group while ketoses contain a _______ group | aldehyde, keto |
| What are monosaccharides referred to as, based on the number of carbon atoms? | 3= trioses, 4= tetroses, 5= pentoses, etc... |
| What are two common monosaccharides? | the two hexoses, glucose and fructose |
| Carbohydrates can exist in a variety of ________ forms | isomeric |
| Isomeric forms: How do constitutional isomers differ? | in the order of attachment of atoms |
| Isomeric forms: How do stereoisomers differ? | they are connected in the same order but differ in spatial arrangement |
| Isomeric forms: What are two kinds of stereoisomers? | enantiomers and diastereoisomers |
| Stereoisomers: Enantiomers | nonsuperimposable mirror images |
| Stereoisomers: Diastereoisomers | isomers that are not mirror images |
| Stereoisomers: How are the D and L isomers determined? | by the configuration of the asymmetric carbon atom FARTHEST from the aldehyde or keto group |
| Stereoisomers: What are two kinds of diastereoisomers? | epimers and anomers |
| Diastereoisomers: epimers | differ at one of several asymmetric carbon atoms |
| Diastereoisomers: anomers | differ at a new asymmetric carbon atom formed on ring closure |
| What are some important hexoses? (3 aldoses and 1 ketose) | D-Glucose, D-Mannose, D-Galactose (the 3 aldoses) and D-Fructose (the 1 ketose) |
| Using Glucose as the reference sugar, Explain the structure of Mannose. | the 2-epimer of glucose (the H and OH on C2 are on opposite sides) |
| Using Glucose as the reference sugar, Explain the structure of Galactose. | the 4-epimer of glucose (the H and OH on C2 are on opposite sides) |
| How does the ketose, Fructose, differ from the aldose, Glucose? | the C2 carbon contains the keto group (COR) in fructose, while the C2 carbon in Glucose contains an aldehyde group (COH) |
| Many common sugars exist in cyclic forms. What is the chemical basis for ring formation? | the aldehyde or ketone can react with an alcohol to form a ring |
| The chemical basis for ring formation is that the aldehyde can react with an alcohol to form a _______, while a ketone can react with an alcohol to form a _______. | hemiacetal, hemiketal |
| how is an INTRAmolecular hemiacetal formed? | the C1 aldehyde in the open-chain of an aldohexose reacts with the C5 hydroxyl group to form an intramolecular hemiacetal. (Glucose to the 6-membered ring, pyranose) |
| how is an INTRAmolecular hemiketal formed? | The C2 keto group in the open-chain of a ketohexose reacts with either the C5 or C6 hyrdoxyl group to form an intramolecular hemiketal that is either a 5 or 6-membered ring (Fructose to the 5-membered ring, Furanose) |
| The formation of cyclic hemiacetal creates another diastereoisomeric form called an ______ | anomer |
| Hemiacetal anomers: The α form means that the hydroxyl at C1 is _____ the plane of the ring while the β form means that the hydroxyl at C1 is _____ the plane of the ring. | below, above |
| Because the two anomeric forms are in equilibrium with an open chain form, the free open chain form reacts with what? | oxidizing agents |
| Sugars that react with oxidizing agents are called _________ sugars while sugars that do not are called __________ sugars | reducing sugars, nonreducing sugars |
| As a reducing sugar, glucose can react with hemoglobin forming __________ hemoglobin (Hemoglobin A1c) which is fully functional | glycosylated |
| For individuals without diabetes, what is the normal range of Hemoglobin A1c? | 4-6% |
| What do Hemoglobin A1c levels between 5.7% and 6.4% indicate? | increased risk of diabetes |
| What do Hemoglobin A1c levels 6.5% of higher indicate? | diabetes |
| Glycation of hemoglobin is a ____________ reaction occurring between glucose and the N-terminus of the β-chains which forms dioxyfructose | nonenzymatic |
| The chair form of β-D-glucose is more stable than the boat form. Why? | the axial positions are occupied by hydrogen atoms |
| Monosaccharides (sugars) are joined to alcohols and amines through _________ bonds at the anomeric carbon | glycosidic |
| A bond formed between the anomeric carbon of glucose and the oxygen atom of an alcohol is called a O-glycosidic bond, and the resulting product is called a _________ | glycoside |
| The anomeric carbon atom of a sugar cab be linked to the nitrogen atom of an amine to form an _____________ bond | N-glycosidic bond |
| Carbohydrates can also form an ester linkage to ___________, one of the most prominent modifications in carbohydrate metabolism | phosphates (like the phosphorylation of glucose) |
| Monosaccharides are linked to form complex ________________ | carbohydrates |
| Glycosidic bonds can join one monosaccharide to another. How is this possible? | because sugars contain many hydroxyl groups |
| Oligosaccharides | contain two or more monosaccharides linked by O-glycosidic bonds |
| Oligosaccharides: Glycosidic bonds are formed how? | when the hydroxyl group on one anomeric carbon of a sugar reacts with the elimination of water with any hydroxy group of another sugar |
| Specific _________ are responsible for Oligosaccharide assembly | enzymes |
| These specific enzymes catalyze the formation of glycosidic bonds. What are these enzymes called? | glycosyltransferases |
| There is no DNA template for the synthesis of polysaccharides. The glycosyltransferases' substrate and acceptor molecule __________ determine which sugar and linkage is added to an existing molecule | specificity |
| The monosaccharide substrates for glycosyltransferases are in many cases, what? | sugar nucleotides (UDP-Glucose, GDP-Mannose, GDP-Glucose, ADP-Glucose, CMP-Sialic Acid, etc.) |
| The monosaccharide acceptor molecule can be what? | a simple monosaccharide, a complex polysaccharide, or a serine, threonine, or asparagine residue of a protein |
| a ____________ consists of two sugars joined by an O-glycosidic bond. | disaccharide |
| What are three abundant disaccharides that we encounter frequently? | sucrose, lactose, and maltose |
| Sucrose | table sugar (α-glucose and β-fructose joined by their anomeric carbon atoms) |
| lactose | milk sugar (galactose joined to glucose by a β1-,4 linkage) |
| maltose | comes from the hydrolysis of large polymeric oligosaccharides such as starch and glycogen (two glucoses joined by an α- 1,4 linkage) |
| ______ cleaves sucrose, ______ cleaves lactose, and ______ cleaves maltose. | Sucrase, lactase, maltase |
| sucrase, lactase, and maltase are located where? | on the outer surfaces of epithelial cells lining the small intestine (to cleave common disaccharides) |
| the cleavage products of sucrose, lactose, and maltose can be further processed to provide energy in the form of _____ | ATP |
| Large polymeric oligosaccharides, formed by the linkage of multiple monosaccharides are called ______________ | polysaccharides |
| Polysaccharides play vital roles in what? | energy storage and in maintaining structural integrity of an organism |
| if all the monosaccharides in the polysaccharide are the same, the polysaccharide is called a ___________ | homopolymer |
| What is the most common homopolymer? | glycogen |
| glycogen | storage form of glucose in animal cells |
| Most glucose units in glycogen are linked by α1 → _#_ (~90 %) glycosidic bonds with branches formed by α1 → _#_-glycosidic bonds (~10 %). | 4, 6 |
| In plants, glucose is stored as _____ of which there are two forms. | starch |
| What are the two forms of starch? | amylose and amylopectin |
| amylose | unbranched (linear) type of starch consisting of glucose residues linked by α-1, 4-glycosidic bonds. |
| amylopectin | branched form of starch with an α-1, 6-glycosidic bond for every 30 α-1, 4-glycosidic bonds. |
| What is another major polysaccharide of glucose found in plants? | cellolose |
| Cellulose serves a ________ rather than nutritional role as an important component of the plant cell wall | structural |
| Cellulose is among the most ________ organic compounds in the biosphere | abundant |
| Cellulose is an unbranched homopolymer of glucose residues joined by what? | of glucose units linked by β-1, 4-glycocidic bond. (in contrast with linkages seen in starch and glycogen) |
| This simple different in stereochemistry yields 2 molecules with very different properties and biological functions. The β linkage yields a straight chain capable of what? | of interacting with other cellulose molecules to from strong fibrils. |
| The α linkages of starch and glycogen form compact hollow cylinders suitable for The α linkages of starch and glycogen form compact hollow cylinders suitable for what? | for accessible storage. |
| Although mammals cannot digest cellulose (lack cellulase), cellulose and other plant fibers are still important component of dietary fibers. What does a soluble fiber such as pectin do? | slows the movement of food through the gastrointestinal tract, allowing improved digestion and absorption of nutrients. |
| Carbohydrates are commonly __________ to proteins | conjugated |
| Carbohydrates may be linked to what 3 protein residues? | asparagine, serine, or threonine residues |
| specific enzymes link the oligosaccharide units on proteins to either the side-chain ozygen atom of a ______ or ______ residue, or to the side-chain amide nitrogen atom of an ________ residue | serine or threonine, asparagine |
| If the protein component is predominant, the conjugate of protein and carbohydrate is called a __________ | glycoprotein |
| many glycoproteins are components of what? | cell membranes, where they take part in processes such as cell adhesion and the binding of sperm to eggs |
| Proteins bearing covalently linked glycosaminoglycans are called __________ | proteoglycans |
| Proteoglycans: what are glycosaminoglycans? | polymers of repeating disaccharides |
| Proteoglycans: The glycosaminoglycan makes up as much as 95% of the biomolecule by weight. What does this mean in regards to what the proteoglycan resembles most? | the proteoglycan resembles a polysaccharide (carbohydrate) more than a protein |
| Proteoglycans: what do proteoglycans function as? | lubricants and structural components in connective tissue (also mediates cell adhesion to extracellular matrix, and regulate cell proliferation) |
| Proteoglycans: What are the properties of proteoglycans determined by? | the glycosaminoglycan component |
| Proteoglycans: many glycosaminoglycans are made of repeating units of disaccharides containing a derivative of an amino sugar, either _______ or ________ | glucosamine or galactosamine |
| Proteoglycans: At least one of the two sugars in the repeating unit has what? | negatively charged carboxylate or sulfate group |
| Mucoproteins, like proteoglycans, are what? | predominantly carbohydrate by weight |
| Mucoproteins: The protein component is heavily O-glycosylated with ______________ joining the oligosaccharide to the protein | N-acetylgalactosamine |
| Mucoproteins: What do mucoproteins serve as? | lubricants |
| Blood groups are based on what? | protein glycosylation patterns |
| The human ABO blood groups reflect the _________ of glycosyltransferases | specificity |
| All of the blood groups share the oligosaccharide foundation called the ___ antigen | O-antigen |
| The A and B antigens differ from the O antigen by the addition of one extra _____________ | monosaccharide |
| Type A, _______________ is added to the O by a specific glycosyltransferase | N-acetylgalactosamine |
| Type B, _________ is added to the O by another transferase | galactose |
| Type O | no active glycosyltransferase |
| Carbohydrate structures are the __________ sites for a special class of proteins | recognition |
| such proteins, termed _______-binding proteins, bind specific carboydrate structures on neighboring cell surfaces | glycan-binding proteins |
| Carbohydrates on the cell surface are recognized by proteins called _______ | lectins |
| What is the chief function of lectin? | to facilitate cell-cell contact |
| How can lectin facilitate cell-cell contact? | a lectin usually contains 2 or more carbohydrate-binding sites, allowing lectins on the surface of one cell to interact with carbohydrates displaced on the surface of another cell |
| Lectins and carbohydrates are linked by a number of weak __________ interactions that ensure specificity yet permit unlinking as needed. | noncovalent |
Created by:
cmccartney2
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