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Carbohydrates, Glycolisys, and Krebs
Terms in this set (23)
nomenclature of monosaccharides (e.g. ketohexose, aldopentose)
aldose ends with CHO
ketose ends w/ CH2OH
triose, tetrose, pentose, hexose
stereoisomers, number of possible stereoisomers for aldoses and ketoses
L (left side OH on linear) and D (right side on linear)
- D-, L- nomenclature refers to absolute configuration of asymmetric 'C' furthest away from the carbonyl group
- D-sugars predominate over L-sugars in biology
- D-glucose only aldose that commonly occurs in nature as a monosaccharide
formulas of glucose and fructose in normal and Haworth projections
In solution, a monosaccharide is not in an open chain but predominantly
"cyclizes" into rings due to the reaction between alcohol group and
aldehyde or ketone group
Ring is perpendicular to paper,
with heavy shaded area closest to us
definition of epimers and anomers
-epimers are sugars that differ only by the configuration about one C atom triose vs tetrose
-Anomers are from cyclization creating an additional asymmetric 'C' center. Alpha is below the ring and Beta is above the ring.
conformations of pyranose
-The pyranose ring may assume a boat or a chair conformation.
The relative stabilities of these conformations depend on the
stereochemical interactions between the substituents on the ring.
-Substituents extending parallel to the symmetry axis - axial (a)
Substituents extending outward from the symmetry axis - equatorial (e)
glycosidic bonds; reducing versus non-reducing sugars
Cyclic and linear forms of aldoses and ketoses readily interconvert - sugars undergo reactions typical for aldehydes and ketones. The saccharides bearing anomeric carbon atoms not forming a glycosidic bond are termed reducing sugars (Tollens' reagent - Ag+ in ammonia solution is reduced).
-A glycosidic bond is when the anomeric hydroxyl of a sugar reversibly condenses with alcohols to form glycosidic bonds.
structure of cellulose, chitin, starch (α-amylose, amylopectin)
-Cellulose is a linear polymer
of up to 15,000 D-glucose residues linked by β(1-4) glycosidic bonds.
-Chitin is a
β(1-4) linked homopolymer of N-acetyl-D-glucosamine.
-α-amylose has several thousands glucose
residues linked by a (1® 4) bonds, helically coiled conformation
-amylopectin is -composed of mainly a(1® 4) residues, branched every 24-30 residues
with a(1® 6) bonds, up to 106 glucose residues per
structure of glycogen
structure similar to amylopectin...branches every 8-12 glucose
residues, hence more branched
composed of mainly a(1® 4) residues, branched every 24-30 residues
with a(1® 6) bonds
N and O glycosidic attachments
Oligosaccharides bind to protein by an 'N'-linkage to the amide nitrogen of Asn, or 'O'-linkage to the oxygen of Ser/Thr.
All N-glycosidic protein attachments occur through β-N-acetylglucosamino-Asn bond in the sequence Asn-X-Ser/Thr
The most common O-glycosidic attachment involves the disaccharide
β-galactosyl-(1-3)-α-N-acetylgalactosamine α-linked to the OH group
of Ser or Thr.
bacterial cell walls, Gram + and - bacteria
Gram-positive bacteria have a thick (~250Å) cell wall surrounding their
Gram-negative bacteria have a thin (~30Å) cell wall covered by a complex
Bacterial cell walls consist of covalently linked polysaccharide and polypeptide chains. The framework is known as peptidoglycan (murein) consisting of alternating β(1-4) N-acetylglucosamine and N-acetylmuramic acid linked to a tetrapeptide. The units are crosslinked through their tetrapeptide chains.
describe mechanisms of action of penicillin and lysozyme
Lysozyme - an enzyme present in tears, mucus, and other body secretions.
Catalyzes the hydrolysis of the β(1-4) glycosidic linkage.
Treatment of gram-positive bacteria with lysozyme degrades their cell walls.
specifically binds and inactivates enzymes that function to
cross-link the peptidoglycan strands of bacterial cell walls. Since cell wall
expansion requires partial cell wall degradation, penicillin causes cell
describe the biochemical basis for ABO blood group determinants
ABO blood group determinants are present on the glycolipids of red blood cells and other plasma membranes.
explain how large proteoglycan complexes contribute to the resilience of cartilage
Colagen - provides strength
Proteoglycans - provide
elasticity and resilience
Central strand of hyaluronic
acid binds up to 100 aggrecan
chains, each of which covalently
binds ~30 keratan sulfate chains
(250 disaccharide units) and
~100 chondroitin chains
Pneumococcal polysaccharide vaccine: unconjugated polysaccharides; current standard is 23-valent vaccine (Pneumovax).
The immunogenicity of pneumococcal polysaccharides is greatly enhanced by coupling them to a highly antigenic protein such as Diphtheria protein - conjugate pneumococcal vaccine. 13 polysaccharides included in recent polyvalent vaccine (Prevnar 13).
LPS is present in the cell walls of gram-negative bacteria. It is a prototypical pyrogen
(substance that induces fever).
-Lethal toxin, mediates septic shock, induces fever
-Induces cytokine storm (TNF-α, IL-1)
-Activates complement and clotting cascade
-B cell mitogen
chiral is used to describe an object (molecule) which is non-superimposable on its mirror image
-Anomers are from cyclization creating an additional asymmetric 'C' center on the first carbon of aldehydes typically
Describe the reactions of glycolysis from glucose to lactate, Stage I and Stage II;
- a series of 10 enzymatic reactions in which glucose is converted via fructose-1,6-bisphosphate into pyruvate with the generation of 2 ATPs.
Stage 1 (investment) is reactions 1-5: A preparatory stage in which the hexose is phosphorylated and cleaved to yield two molecule of the triose glyceraldehyde-3-phosphate. This process uses two ATPs
Stage 2 (payoff) is reactions 6-10: The two molecules of glyceraldehyde-3-phosphate are converted to pyruvate with the concomitant generation of four ATPs
Describe the fate of pyruvate under the conditions of aerobic oxidation, anaerobic
homolactic fermentation and alcoholic fermentation.
Under aerobic conditions, the pyruvate is further oxidized by the citric acid cycle and oxidative phosphorylation to CO2 and water.
Under anaerobic conditions, the pyruvate is instead converted to a reduced end product, which is:
- lactate in muscle (homolactic fermentation)
In muscle, during vigorous activity when the oxygen has been depleted, lactate
dehydrogenase (LDH) catalyzes the oxidation of NADH by pyruvate to yield NAD+ and lactate. H4 is better adapted to oxidize lactate to pyruvate, which is than used as fuel. M4 is optimized to convert pyruvate to lactate, to allow glycolysis to proceed under anaerobic conditions.
- ethanol + CO2 in yeast (alcoholic fermentation).
Explain the principles of the Cori cycle, draw the scheme.
In contracting skeletal muscle under anaerobic conditions, the rate of production of pyruvate by glycolysis exceeds the rate of oxidation of pyruvate by the citric acid cycle. Moreover, the rate of formation of NADH is greater than the rate of its oxidation by the respiratory chain. Continuation of glycolysis depends on the availability of NAD+. The accumulation of both NADH and pyruvate is reversed by lactate dehydrogenase, which oxidizes NADH to NAD+ as it reduces pyruvate to lactate.
Lactate is a dead end in metabolism. The formation of lactate buys time and shifts
part of the metabolic burden from muscle to liver. Lactate diffuses to blood and
is carried to liver where it is converted to glucose by gluconeogenesis. Glucose
then enters the blood and is taken to the skeletal muscle.
When tissues such as muscle are rapidly consuming ATP, they regenerate it almost
exclusively by anaerobic glycolysis.
Skeletal muscle consists of slow-twitch and fast-twitch fibers.
Fast twitch fibers - predominate in muscles capable of short bursts of rapid activity,
are nearly devoid of mitochondria - all ATP from glycolysis (white fibers).
Slow twitch fibers - rich in mitochondria, obtain most ATP through oxidative phosphorylation
(red fibers- heme-containing cytochromes).
Major metabolic processes in the liver after a meal and after an overnight fast.
After a meal: The liver is stimulated by insulin to uptake glucose in the blood for G6P to be used for Glycocen, FA synthesis, or fuel
After a fast: The liver is stimulated by glucagon. It breaks down its Glycogen reservoir, dephosphatases its G6P and releases it into the blood. Fatty acid can also be used by the liver as fuel.
- How many ATPs per glucose are generated by anaerobic fermentation and how many
by glycolysis coupled to oxidative phosphorylation?
For the lactate fermentation, 2 molecules of ATP are produced for every molecule of glucose used
-Describe the regulation of glycolysis, activators and inhibitors.
In heart muscle under physiolo-
gical conditions , only three reactions function with large negative free energy changes: those catalyzed by hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK). Those reactions are the candidates for the flux-control points.
HK: G6P inhbits
PFK: ATP, citrate, and PEP inhibits. ADP, AMP, F6P, F2,6P, P activates.
PK (muscle): ATP inhibits. AMP, PEP, FBP activates.
-What is the main purpose of gluconeogenesis? Where does it take place? Under what conditions is the gluconeogenesis pathway most active?
A pathway through which noncarbohydrate precursors such as lactate, pyruvate, glycerol, and amino acids are converted to glucose.
Liver's glycogen is only sufficient to supply brain with glucose for ½ - 1 day.
In fasting, most of the body's glucose needs is met by gluconeogenesis (ketone bodies are made during prolonged starvation).
Only liver and kidney can release glucose to blood (express glucose-6-phosphatase) - "buffer" of glucose. Gluconeogenesis occurs mainly in liver and, to a smaller extent, kidney.
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