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An Overview of Fuel Metabolism; Digestion and Transport of Carbohydrates


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What are the sugar constituents of Sucrose?
Fructose and Glucose
What are the sugar constituents of Starch?
Glucose polymer (amylose + amylopectin)
What are the sugar constituents of Lactose?
Glucose and Galactose
What are the sugar constituents of Maltose?
Glucose and Glucose
What are the sugar constituents of Amylose?
Amylose is a linear poly-maltose consisting of Glucose-Glucose in 1-4 linkage
What bond does ∂-amylase hydrolyze?
1-4 linkage between glucose units of starches (amylose).
1. What inhibits ∂-amylase in the stomach?

2. T/F ∂-amylase is a exoglycosidase that can hydrolyze many different type of monomers.
1. Low pH of the stomach = HCl

2. False, it is a endoglycosidase with specificity to glucose polymers
What prevents the denaturing of pancreatic ∂-amylase, due to stomach acid?
Where is ∂-amylase actively hydrolyzing starch?
Mouth and intestines
What is a glycosidase?
An enzyme that hydrolyzes bonds between sugars.
What is an endonuclease?
It is an enzyme that hydrolyzes internal bonds of a complex, e.g., ∂-amylase.
Will ∂-amylase hydrolyze isomaltose (an isomer of maltose)?
No, since isomaltose has a ∂-1-6 linkage. It requires isomaltase... THUS, maltase and isomaltase are needed to complete the breakdown of starch that was started by ∂-amylase
1. What is the name of the branch of glucose polymer that is connected by a ∂, 1-6 linage?

2. which two polysaccharides make up starch?
1. Amylopectin

2. amylopectin and amylose
What type of bond holds the fructose and glucose together in sucrose?
Alpha 1-2, linkage
What type of bond holds the galactose and glucose together in lactose?
ß-1,4 linkage
What is the function of the sucrase-isomaltase complex? And where is it found?
It metabolizes sucrose and isomaltose and is found in membrane of the gut.
What is the function of glucoamylase?
It hydrolyzes ∂, 1-4 linkage between glucose-glucose in maltose.
What is the function of lactase?
It hydrolyzes ß, 1-4 linkage between galactose-glucose in lactose.
Why does the lack of lactase (ß-glycosidase) cause diarrhea?
If the enzyme that breaks up lactose is present on the brush border of the intestines then the galactose and glucose are absorbed, if not BACTERIAL FERMENTATION breaks LACTOSE --> Galactose + Glucose --> which further breaks down into CO2, CH4, H2 and osmotically active products and you get more molecules in the gut⬦ thus water flows out of the cell and into the gut.
What are the products resulting in the gut in the absence of lactase?
Galactose, glucose, CO2, CH4, H2
What is the conclusive measurement of lactase deficiency?
H2 content of exhalation⬦ produced by microbial flora.
How long does it take for the symptoms of lactase deficiency present after consuming milk?
45-60 minutes
What is a channel protein?
A protein that makes a hole in the membrane and facilitate the flow of molecules down their concentration gradient.
1. What is gated channel?

2. In which disease do gated channel proteins play an important role?
1. A protein channel that can be opened or closed in response to metabolic signals.

2. cystic fibrosis
What is involved in facilitative diffusion?
Stuctrural change in the protein in response to substrate specificity.
What type of curve represents simple diffusion?
Linear (slow)
In facilitated diffusion, what type of kinetics are observed?
Saturation kinetics (hyperbolic curve), which will show increases in diffusion as concentration increases, then tapper off, then stop increasing as the protein reaches it V-max.
In a hyperbolic cure (facilitated diffusion), where do you find the Km?
x-int of 1/2 v-max.
Which has higher affinity, low or high Km?
What type of Glut do you find in⬦ a. RBC, or barriers (blood/brain)⬦ b. Intestines, Liver, kidney, pancreas
a. Glut 1⬦ b. Glut 2
Which Glut has higher affinity and lower capacity GLUT 1 or 2? And what effect will this have?
a. Glut 1⬦ b. Glucose will cross the barrier whenever it is near.
a. Which Glut (1 or 2) has lower affinity and higher capacity? And what effect will this have?
a. Glut 2⬦ b. Glucose will only be taken up when [glucose] are high.
What can the body do to modulate the V-max?
Make more transporters
How can V-max and Km be modulated?
V-max: make more transporters

Km: allosteric modulation
1. What is the Na+ to glucose ratio at the Na+/glucose cotransporter?

2. what is the Na+ to k+ ratio at the sodium/potassium ATPase transorter?
1. 2 Na+ in to 1 glucose in b) 2 K+ out of the cell.

2. 3 Na+ out to 2 K+ into the cell
Detail how cholera causes diarrhea (5 steps)
a. Cholera bacterium (vibrio cholerae) releases an endotoxin that catalyzes a ADP-ribosylation rxn⬦ b) A-subunit binds to adenylate cyclase⬦ c)Adenylate cyclase will constitutively produce cAMP⬦ d) cAMP activates PKA⬦ e) PKA stimulate Chloride transport (CFTR) and Cl- flows out of the cell⬦ f) Na+ and water follows into the gut lumen.
What is CFTR?
Cystic fibrosis transmembrane regulator protein
What is the treatment of cholera?
Water, sodium and glucose⬦ taking advantage of the Na/K cotransport system. (also Cl- and HCO3-)
What significance does cycstic fibrosis have in cholera?
even if the cholera bacterium attaches causes adenylate cyclase constituent activity, the transporter is nonfunctional... thus CF individuals are protected against cholera
With respect to chlorine channels, what is the sequence of events after cAMP is produced?
a) PKA is activated⬦ b) PKA stimulate chlorine channel transport, via the CFTR, into the luman
What does a high Vmax indicate?
The enzyme works fast.
What is the percentage of CF heterozygotes in the Caucasian Northern European population?

How many of this same population has homozygous affected/


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