Carbs: Homework and Tophat Flashcards
P1: Be able to identify different carbohydrates (i.e., di- vs. oligosaccharide, homo- vs. heteropolysaccharide, etc.) in images and/or descriptions.
P1: A1C is formed via non-enzymatic glycosylation. What does that mean?
Glucose can non-enzymatically attach to hemoglobin
Via N-terminus or Positively- charged AA residues
Interferes with protein’s oxygen delivery to tissues (poor release)
Glucose also scavenges nitric oxide, altering blood pressure
P1: How do simple carbohydrates differ from complex carbohydrates?
Simple carbohydrates = monosaccharides, disaccharides (sucrose)
Also includes high-fructose corn syrup
Fewer glycosidic bonds so monomers enter glycolysis faster: “quick energy”
Complex carbohydrates = oligosaccharides and larger polysaccharides
Also includes dietary fiber
More glycosidic bonds so monomers enter glycolysis slower
P1: Why is glycogen storage limited within the human body?
-This is due to glycogen’s polarity, and the amount of water that ends up bound to each residue. We couldn’t store all that water alongside the glycogen, but triacylglycerols don’t have this issue, so it is way more efficient!
- Mechanism underlying the hydration process
not entirely understood
P1: Know which conjugated molecule(s) (i.e., glycoprotein, glycolipid and glycoRNA) have O-glycosidic bonds versus N-glycosidic bonds.
- O-glycosidic bond is between carbon-1 and OH group’s oxygen
- N-glycosidic bond is between carbon-1 and NH2 group’s nitrogen
*All three have carbohydrates attached to their exterior surface
*Glycoproteins are both N and O linked, Glycolipids are N linked, and GlycoRNA’s are O linked.
P2: Understand how dietary carbohydrates are digested.
Dietary carbohydrate digestion begins in the mouth as an amylase present
Found within many foods like bread, pasta, fruits and vegetables
Added sugars in many condiments, like ketchup and BBQ sauce
Table sugar (an inorganic food additive) also contains this biomolecule
Brown sugar has sucrose and molasses (with glucose, fructose, etc)
P2: If dietary fiber is indigestible, why is it important we regularly consume it? Be sure to clarify the role of soluble versus insoluble fiber.
enters large intestine mostly intact
Has low-viscosity and is non-fermentable (i.e., metabolically inert)
- Evidence also suggests INsoluble fiber helps improve the bioavailability of water-soluble vitamins within large intestine
- Recall soluble fiber has high-viscosity and is fermentable (good source for bacteria in LI)
– Resulting short chain fatty acids
mostly absorbed through colonic
lumen
P2: Does insulin stimulate the liver to synthesize or metabolize glycogen?
Insulin triggers insulin signal transduction pathway in muscle and fat cells
Also stimulates liver activity
P2: Know the four metabolic pathways involved in cellular respiration.
Glycolysis: glucose (primary input); pyruvate and NADH (outputs)
Pyruvate oxidation: pyruvate (primary input); acetyl CoA and NADH
(outputs)
Citric acid cycle: acetyl CoA (primary input); NADH and FADH2 (outputs)
Oxidative phosphorylation: NADH and FADH2 are the primary inputs
P2: During starvation, how does the brain obtain glucose?
only fuel the mammalian brain uses under non-starvation conditions is glucose.
Body cannibalizes muscle (protein) and fat (triacylglycerol), gluconeogenesis synthesizes glucose from non-carbohydrate sources
P2: If you’re on a low-carb diet, how does the brain obtain glucose?
Brain still requires glucose
Non-carbohydrate precursors for gluconeogenesis obtained from dietary lipids and proteins
Consumed fats also source of acetyl CoA used for ketone body synthesis
P3: Where does glycolysis occur in prokaryotes? What about in eukaryotes?
Both prokaryotes and eukaryotes within the cytoplasm
P3: Define the term “isozyme”. How do isozymes differ from isomers?
enzyme with different primary structure but catalyzes same reaction
they’re different atoms making up composition
P3: Understand how each of the allosteric enzymes involved in glycolysis is regulated in the muscle versus in the liver.
Muscle -
Hexokinase: feedback inhibition by glucose-6-phosphate, but glucose 6-phosphate not solely a glycolytic intermediate. Impacted by phosphofructrokinase activity
Phosphofructokinase: most important control site in mammalian glycolytic pathway, allosterically inhibited by ATP, changes in pH, and citrate. Stimulated by AMP - signal for low- energy state
Pyruvate kinase: allosterically inhibited by ATP, alanine and phosphorylation of select serine residues. stimulated by fructose 1,6-biphosphate- product of reaction catalyzed by phosphofructokinase
Liver -
Hexokinase: enzyme not present in the liver; reaction performed BY glucokinase (isozyme, with low glucose affinity), not subject to feedback inhibition by glucose 6-phosphate
Glucokinase: only phosphorylates glucose when blood-glucose levels high, ensures brain has priority for the monosaccharide. Regulated via interaction with glucokinase regulatory protein, when bound it’s inactivated and localized to nucleus
phosphofructokinase: different isozyme in liver than in muscle, allosteric inhibition in liver due to citrate not ATP or pH. Nucleotide levels don’t fluctuate as much in liver as in other tissues. lactate not produced in the liver, so remains physiologically neutral.
pyruvate kinase: different isozymes in different tissues. L isozyme allosterically inhibited by phosphorylation by PKA. dephosphorylation by a protein phosphatase
P3: Where does pyruvate oxidation occur in prokaryotes vs. in eukaryotes?
Cytoplasm for Prokaryotes
Mitochondria for Eukaryotes
P3: Understand how pyruvate oxidation is regulated.
allosterically inhibited by phosphorylation of select serine residues, PDH phosphatase stimulated by calcium and insulin. Also regulated by NADH, acetyl CoA and ATP
P4: Where does the CAC occur in prokaryotes? What about in eukaryotes?
Cytoplasm for prokaryotes
Mitochondria for eukaryotes
P4: How do the α-ketoglutarate dehydrogenase complex and the pyruvate dehydrogenase complex differ? How are they similar?
α-ketoglutarate dehydrogenase - reaction removes carboxyl group containing carbon-1 and forms thioester linkage with CoA. Allosteric enzyme with 3 distinct enzyme; each has own active site, same structure and mechanism as pyruvate dehydrogenase complex
P4: ATP is generated via substrate-level phosphorylation in glycolysis and the CAC. Why is the reaction in the CAC considered unusual?
No kinase or donor molecule with phosphoryl-transfer potential (substrate-level phosphorylation)
only example of substrate-level phosphorylation within mitochondria
P4: Understand how each of the allosteric enzymes involved in the citric acid cycle is regulated. Do certain effectors regulate both enzymes?
Isocitrate dehydrogenase - (IDH1, IDH2, IDH3), IDH1 and IDH2 both reduce NADP+ while IDH3 reduces NAD+, IDH1 in cytoplasm and peroxisomes; IDH2 and IDH3 in mitochondria. IDH3 involved in CAC; requires a metal cofactor for activity
regulation- allosterically inhibited by ATP and NADH, muscle unique in hwo much its metabolic rate varies, stimulated by ADP, citrate and calcium (muscle only)
α-ketoglutarate dehydrogenase complex- allosteric enzyme with 3 distinct enzymes; each has own active site, same structure and catalytic mechanism as pyruvate dehydrogenase complex
regulation - different α-KGDH isozyme in brain than in muscle and liver, allosteric inhibition from ATP, NADH, succinyl CoA, reactive oxygen species
P5: Where does oxidative phosphorylation occur in prokaryotes? What about in eukaryotes?
Plasma membrane for prokaryotes
Inner mitochondrial membrane for eukaryotes
P5: NADH and FADH2 are the primary inputs for the ETC. Which complex in the ETC accepts electrons from NADH? What about from FADH2?
Complex 1
P5: Understand how electrons flow within the ETC.
Complex 2
P5: Which amino acid must be neutralized for ATP synthase’s c ring to turn?
amino acid gluatmate
P5: Understand how oxidative phosphorylation is regulated.
activity of ETC and ATP synthase tightly coupled, NADH and FADH2 oxidation linked with ADP phosphorylation, known as acceptor control or respiratory control
when ADP concentration low, NADH and FADH2 produced by earlier parts of cellular respiration not oxidized back to NAD+ or FAD
Does the monosaccharide shown below contain all six of the major elements required for life?
No, it does not. (only had CHO in the aromatic ring)
The polysaccharide shown below contains 4 sugar residues connected by:
O-glycosidic bonds (-O-)
Below is glycosylated hemoglobin, with glucose in blue and hemoglobin in black. The monosaccharide is attached to the protein via:
the side chain of an amino acid residue
Unlike standard monosaccharides, amino sugars also contain the chemical element:
nitrogen
A carbohydrate is comprised of 7 sugar residues: 3 galactosamine (GalN) and 4 mannose (Man). Based on this information, the carbohydrate would be categorized as a/an:
heteropolysaccharide
Which statement about dietary fiber is incorrect?
Dietary fiber includes cellulose (from plants) and gristle (from animals).
correct
-dietary fiber includes both water-soluble and water-insoluble types
-soluble fiber can be fermented by gut bacteria
-insoluble fiver cannot be fermented by gut bacteria
True or false: The glycoprotein shown contains a compound sugar.
This is false. (compound sugar: also known as disaccharides or double sugars, are molecules made of two bonded monosaccharides)
In the glycoglycerolipid shown below, select the oxygen participating in the O-glycosidic bond.
(on O connecting ring and side chain)
The amylase present in your saliva cleaves:
alpha-1,4-glycosidic bonds
True or false: In the small intestine, alpha-dextrinase cleaves alpha-1,4-glycosidic bonds.
This is false.
Bacteria in the large intestine convert soluble fiber into short chain fatty acids. This process would likely involve:
fatty acid synthesis
A redox reaction involving glucose is shown below. The electrons being transferred are associated with hydrogen. Glucose is a reducing sugar, which means it:
loses electrons and is oxidized in the reaction
