Unit 3.1 (carbs) Flashcards
What are carbohydrates? What is their general formula?
Sugars that are polyhydroxyl (lots of OH’s) aldehydes and ketones. They are made up of Carbon and H2O subunits.
Describe the 3 classes of Carbohydrates (monosaccharides, oligosaccharides, and polysaccharides)
Monosaccharides - Single sugars freely soluble in water (sweet taste)
Oligosaccharides - Short chains of single sugars covalently linked
Polysaccharides - Long chains (hundreds or thousands) of single sugars covalently linked
Are all monosaccharides chiral?
Except for dihydroxyacetone, all monosaccharides are chiral
What standard reference compound is used for Fischer notation?
Glyceraldehyde
Are most naturally occurring carbohydrates L- or D- enantiomers?
Most are D-, although some L- do occur
How do you differentiate D vs L enantiomers in monosaccharides?
Which monosaccharides are diastereomers of each other?
Any two monosaccharides with the same number of carbon atoms would be considered diastereomers
What is an Epimer?
A special subset of diastereomers when 2 sugars differ only in the configuration around one carbon
Describe the general structure of D-ketoses
Same as for D-aldoses, except switch C1 C=O and C2 OH (results in one less chiral C)
What process occurs that changes a D-Aldose into a D-Ketose?
Tautomerization
Describe (in detail) hemiacetal and hemiketal formation.
What is an Anomer?
What structure is this?
Pyran Ring
Describe (in detail) the cyclization of Glucose
hemiacetal formation!
Define mutarotation
The interconversion in solution between alpha and Beta anomer forms via the open-chain structure
What is the predominant anomer of glucose in solution?
pyranose beta form
Describe (in detail) the cyclization of fructose
hemiketal formation!
What structure is this?
Furan ring
What does drawing the amino sugar form involve?
Drawing the amino sugar form simply involves replacing the C 2’ OH group and substituting an amino NH2 group in its place
What does drawing the N-acetyl sugar from involve?
Drawing the N-acetyl sugar simply involves adding an acetyl group to the amino NH2 group
How would you draw a 2’ deoxy sugar?
Just convert OH to H at a specified (2’) position
Describe (in detail) acetal and ketal formation
Irreversible!
How are glycosidic linkages formed?
Through acetal formation
How are glycosidic linkages named?
Based on the anomeric carbon in the 1st sugar & the C-OH position # of the 2nd sugar
Describe the summary table of Disaccharides (in detail)
Why is it significant if the anomeric bond is alpha or beta?
Anomeric bond, whether alpha or beta, greatly influences the shape of the molecule, which in tun influences enzyme activity on disaccharide
What do monosaccharides and disaccharides taste like?
Taste sweet
Describe the physical properties of mono/disaccharides
They undergo hydrogen bonding with themselves, as well as with water; They are solids at room temperature and very soluble in water; Highly concentrated solutions of monosaccharides like honey, maple syrup, and molasses are very viscous liquids
Give an overview summary of Acid/Base catalyzed tautomerism
Occurs through Enediol intermediate!!
Give an overview summary of reduction of aldoses to alditols
Reduction of C=O to alcohol with NaBH4
Reduces aldoses and ketoses to alditols
What are alditols?
When the C1=O is reduced to an alcohol (“sugar alcohols”) - These have some sweetness, but are lower in calories (used in gum)
What is the difference between Glucaric Acids and Uronic Acids? (oxidation of sugars with strong [O] agents.
What is D-glucaronic acid important for?
It is a component of polysaccharide hyaluronic acid (vitreous humor of eye)
Describe (in detail) Oxidation of sugars with mild [O] agent
Define a Reducing Sugar
Any sugar that can reduce a mile oxidizing reagent like Tollen’s (requires sugar to be in open chain form so that aldehyde [HC=O] is present
What mild oxidizing reagents are used to test for reducing sugars? (3)
1) Tollen’s Reagent
2) Benedict’s Test
3) Fehling’s Test
Describe (in detail) non-reducing sugars
Describe N Glycosidic bonds
Describe Complex Carbohydrates
Chains of 3 or more single sugar molecules linked together (includes starches & cellulose)
What are the functions of polysaccharides?
Storage, structure, recognition
What is the difference between homopolysaccharides vs. heteropolysaccharides
What is starch?
A plant glucose (energy) storage polysaccharide
What are the two forms of starch?
Amylose and Amylopectin (most starch is 10-30% amylose and 70-90% amylopectin)
What is the difference between amylose and amylopectin? (describe in detail)
Why are branches important in polysaccharides like amylopectin?
Branches allow for quick release (or storing) of glucose units for (or from) metabolism
Describe (in detail) the reaction that releases glucose from a starch polysaccharide
Describe the basis of the “starch” iodine test
Describe (in GREAT detail) the process of the digestion of starch. Include enzymes, bonds broken, and subunits that result from the process.
Describe (in detail) how glucose is absorbed into a cell (GLUT4)
What is Glycogen? Compare/Contrast it to amylopectin
The glucose (energy) storage device in animals!
What reaction is responsible for the releasing of glucose from glycogen?
The same reaction that accounts for the release of glucose from starch!!!
What is the most abundant STRUCTURAL POLYSACCHARIDE on earth?
Cellulose
Describe the structure of Cellulose
Linear and unbranched, containing 10,000 to 15,000 D-glucose units that are linked with a B(1-4) linkage; Structure consists of several chain slying side by side, resulting in fibers with high tensile strength (water insoluble)
Does Cellulose produce a positive Iodine Test?
No, it produces a negative iodine test because it is linear. Because it does not cyclize, there is nowhere for the Iodine to bind
Why is it significant that cellulose is a component of insoluble (dietary) fiber?
Promotes regular bowel movement
What enzyme is required to digest Cellulose? What organisms have this enzyme?
What is the second most abundant polysaccharide on earth? Describe its structure and glycosidic bonds.
What is a Glycoconjugate?
Carb + Lipid/Protein (carb. covalently linked to nonsugar moiety)
Describe Peptidoglycan (Murein)
Glycoconjugate
Bacterial Cell Wall
Provides strength and rigidity for the organism (prevents osmotic lysis)
Determines the gram staining characteristic of the bacteria
Describe the structural characteristics of bacterial cell wall
A structural glycoconjugate
Bacterial cell walls are heteropolysaccharide of alternating (B1-4) linked NAG & NAM
Has polypeptide cross-links
Describe the last step in Peptidoglycan synthesis
How do Penicillin drugs work?
Penicillins resemble D-Ala - D-Ala substrate of transpeptidase (enzyme necessary for the last step of the formation of bacterial cell walls) - Penicillins are irreversible inhibitors of transpeptidase
Penicillin Drugs have B-lactam rings (structurally similar to 2 D-Ala’s)
Stops bacterial cell wall synthesis
What are some examples of B-Lactam antibiotics
What is unique about a Staph infection?
Staph strains are resistant to ALL penicillins
Describe Antibiotic Resistance (B-lactamases)
B-Lactamases are bacterial enzymes which hydrolyse B-lactam rings
Defense because they destroy B-lactam antibiotics
What is an example of a B-lactamase inhibitor?
Clavulanic Acid - reacts with B-lactamases, irreversibly inhibitting them (thus, they cannot hydrolyze B-lactam antibiotics & efficacy of drugs is restored)
Describe Glycoproteins
Glycoconjugate
Proteins with covalently linked oligo- and polysaccharides
Modified proteins include structural proteins, enzymes, receptors, transport proteins, and immunoglobins
What are the 2 types of Glycoproteins?
- O-linked to Ser, Thr, hydroxyLys, hydroxyPro
- N-linked to Asn (only) - longer chains
When does carb attachment take place for glycoproteins?
Carb attachment is co/post translational modification (occurs in ER & golgi)
Define the significance of Sialic acid in glycoproteins
Sialic acid is often found as a terminal residue of oligosaccharide chains of glycoproteins
Imparts negative charge to glycoproteins, because carboxyl group is negatively (-) charged a physiological pH
Describe Glycosaminoglycans (GAGs)
A component of Proteoglycans
Linear polysaccharides consisting of a repeating disaccharide (normally an acetylated amino sugar alternating with a uronic acid)
Often negatively (-) charged from added sulfate and uronic acid (COO-)
What are the diverse function of GAGs?
Heparin: Stop blood clotting
Hyaluronate: Eye juice and knee oil
Chondroitins/Keratans: Connective tissue
What are proteoglycans?
Glycoproteins whos carb. moieties are linear, O-linked GAGs
What is the role of proteoglycans?
Either fill extracellular matrix (ECM) or “decorate” cell membrane
Contribute flexibility/resiliency and organization/physical properties
What are 2 Proteoglycans that are prominent in the ECM? Describe their structure.
Aggrecan and Versican (structural components of ECM)
Both have a bottle-brush structure
What is unique about Proteoglycans found in connective tissue?
“SHOCK ABSORBERS”
Highly branched = gel; GAGs give ability to absorb/release H2O
Account for shock absorption & lubricant properties (“knee oil”)
What are syndecans? What is their role?
Cell surface proteoglycans
Involved in signaling regulation
What are Lectins?
PROTEINS (not carbs)
= Proteins that bind specific cell surface carbohydrate patterns
Play a role in biological recognition involving cells and proteins
What is one example of a Lectin? What is it important for?
Mannan-binding Lectin (MBL) - Binds cell surface carbohydrates of disease-causing microorgansims, promoting their phagocytosis
***Some bacteria & viruses (influenza) use lectins to attach themselves to the cells of the host organism during infection
What are the two classes of surface protein?
Hemaglutinin (HA) (a lectin) and Neuraminidase (NA)
Describe (in detail) how a flu infection works
For a flu virus to penetrate the cells of the respiratory tract, its thron-like hemaclutinin (HA) molecules must dock to N-acetylneuraminic acid (a siliac acid) molecules on the surface of the host cell
Causes the host cell to ingest the virus
How does Tamiflu work?
Tamiflu is a Competitive Inhibitor of Neuraminidase (resembles siliac acid)
Stops infection!
