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Biochem Ch. 10

Carbohydrates

QuestionAnswer
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