Reaction done by bacteria that produce ATP and small organic molecules in the absence of oxygen - in the gut they breakdown glucose to produce acetate, lactate, butyrate, and other gases

Carbohydrates Flashcards by Emmaly Smith

What is the big picture of Energy Metabolism?

Burn sugar when available or use lipids when sugar absent. (see picture)

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What is the history of catabolism?

Photosynthetic bacteria were able to breakdown glucose (glycolysis) in a time before oxygen

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Fermentation

Reaction done by bacteria that produce ATP and small organic molecules in the absence of oxygen

in the gut they breakdown glucose to produce acetate, lactate, butyrate, and other gases

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What are the chemical properties of glucose?

-Water soluble, small - easy to transport in aq environment of cells

osmotically active - drives H2O in and can dehydrate
Has aldehyde group that makes it reactive

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Maillard reaction

Sugars bond with amino acids

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Why is glucose reactive?

The aldehyde group on the C1 anomeric carbon which undergoes ring conversion or mutarotation. In the linear form, sugars spontaneously react with amino groups

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Which way is the OH group in alpha-glucose?

Down

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Which way is the OH group on Beta Glucose?

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How do we detect reducing sugars?

Benedict’s reagent - used for detecting reducing sugars in urine (glucose, galactose, and fructose).

Sugar reduces the copper and coverts it to an acid (glucose to glucuronic acid)

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Glycation

Glucose reacting with amino groups on proteins.

Spontaneous rxn and dependent on glucose conc.

Produces early glycation products (hemoglobin A1c)

Further reactions produce advanced glycation end products (AGEs) that bind to receptors and have signaling function

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How can glycation cause damage?

Reactions from oxidative, metabolic, or radical stress cause more advanced glycation. The sugars can accumulate in areas or hang on to proteins where they are not supposed to be like blood vessel wall proteins

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Glycosidic Bond

Bond connecting a sugar to a hydroxl group on another molecule

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How do glycosidic bonds form?

First a sugar substrate is activated using energy (UTP) and catalyzed by UDP-Glucose pyrophosphorylase

Then, glycosyltransferase form glycosidic bonds using activated sugar nucleotides as substrates and UDP is released.

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What happens to C1 after glycosidic bond has formed?

The ring does not open anymore so no more mutarotation.

Hydroxyl group on C1 remains in either alpha or beta position.

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How are glycosidic bonds named?

Sugar contributing to anomeric carbon
Position of hydroxyl goup
Positional number of carbons connected by bond
Sugar contributing hydroxyl group

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What is the nomenclature for maltose?

Glucose-alpha(1,4)-glucose

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What is the nomenclature for lactose?

Galactose-beta(1,4)-glucose

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What is the nomenclature of sucrose?

Glucose-alpha(1, beta2)-fructose

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What are the two ways to break a glycosidic bond?

Hydrolysis

Phosphorolysis

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Phosphorolysis - where does it occur and what does it do?

Use phosphate to cleave bond. Conserves energy of glycosidic bond in a phosphate ester bond

Requires regulated enzymes and phosphate

Occurs inside of cells during breakdown of storage carbs

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Hydrolysis - what it does and where it occurs?

Use of water to cleave bond. Does not conserve the glycosidic bond energy

Occurs in the intestine during digestion of complex carbs

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What are large digestible polysaccharides?

Starch/amylopectin in plants

Glycogen in animal tissue

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What does starch consist of?

alpha(1,4)-linked glucose

What does glycogen and amylopectin consist of?

alpha(1,4)-linked glucose with alpha (1,6)-linked glucose branches

What are indigestible carbohydrates?

Cellulose

What is cellulose made of?

Beta(1,4) linked glucose

What occurs with indigestible cellulose?

Gut bacteria ferment all carbs and produce short chain fatty acids and gas

What is the presentation and what are diagnostic clues for patients with carbohydrate digestion disorders?

Pt presents with chronic digestive difficulties following intake of carb; diarrhea, bloating, and gas. Diagnostic clue is the trigger of episodes

What is the pathology of patients with carbohydrate digestion disorders?

Enzyme deficiencies impair digestion and uptake of particular carb - no rise in serum glucose following ingestion Osmotic activity of undigested molecules - draws water into intestine, diarrhea Microbiome activity produces gas and acids (H2, CO2, bloating, pain)

Digestion of polysaccharides

Complex carbohydrates are hydrolyzed to monosaccharides

What happens to monosaccharides after they are hydrolyzed from complex carbs?

Monosaccharides are taken up by glucose transporters in the intestinal epithelium

What two types of enzymes do humans have for carb digestion?

alpha-amylases disaccharidases

alpha-amylases

Break down large, alpha-linked polysaccharides (glycogen and starch granules) Starts in mouth (saliva) and continues in intestine

Disaccharidases

Break down the three main dietary disaccharides

What are the three dietary disaccharides? What monomers are they made of?

Lactose - milk, Gal-Glu Sucrose - fruit, Glu-Fru Maltose - starch, Glu-Glu

What enzymes break down the three dietary disaccharides and what do they produce?

Lactose - Lactase - Galactose, Glucose Maltose - Maltase - Glucose, Glucose Sucrose - Sucrase/Isomaltase - Fructose, Glucose

What are the microbes in the gut and what do they do?

Most are anaerobes and operate by fermentation Actively convert complex carbs to short chain fatty acids like butyrate, H2, CO2, methane

Case: A 24 year old presents with complaints of recurring abdominal pain for 4 months. Pain occurs after eating at favorite ice cream shop but also after having dairy. Pt has no rise in blood sugar, H2 detectable in breath, and acidic stool. What is the dx? Explain onset and what helps

DX: Lactase non-persistance or Lactose intolerance Lactase activity decline with age and eventually becomes insufficient. Early adult onset typically, but can have congenital lactase deficiency (lactase mutation, rare, present at birth) Lactase preparations can help

What are legumes rich in? Can this be digested?

Raffinose. Raffinose has alpha-1,6-galactosidic bond and cannot be digested Galactosidase supplements can help

What 3 carbohydrates are taken up efficency?

Glucose Galactose Fructose

How is glucose taken up?

Uptake of glucose in cells of intestine and kidney is secondary active (against gradient) Uptake into all other tissues is by facilitated diffusion (with gradient, requires phosphorylation)

What carbs share transporters?

Glucose and galactose. Fructose has separate transporter

How does facilitated diffusion of glucose occur?

Works if there is a concentration gradient. The cells keep the gradient by keeping the concentration of glucose very low by phosphorylating it to glucose 6-phosphate

Glucose --> Glucose 6-phosphate How does this occur?

Most cells use hexokinases Liver uses glucokinase

Hexokinases

Convert glucose to glucose 6-phosphate in most cells. Inhibited by its end products and uptake of glucose stops when glucose 6-phosphate cannot be processed

Glucokinase

How liver converts glucose to glucose 6-phosphate. Not inhibited by end product and liver takes up glucose all the times

What happens to unphosphorylated glucose?

Coverted to sorbitol, which is osmotically active

What is the distribution of glucose and fructose?

Serum glucose kept constant, at high level. Glucose uptake needs active transport to concentrate glucose in epithelial cells Serum fructose concentration is low - passive uptake uses gradient

What protein absorbs glucose from the intestinal lumen into the intestinal epithelium?

SGLT1. Sodium pumped out of epithelium through use of ATP

What protein transports glucose into circulation?

GLUT2. Follows conc. gradient

How does glucose get transported from intestinal lumen to the cells?

Glucose via SGLT1 enters intestinal epithelium Glucose then enters circulation via GLUT2 Glucose then heads to cells where it becomes glucose 6-phosphate

What protein transports fructose into the intestinal epithelium from the lumen?

GLUT5, follows conc. gradient

How does fructose get transported from intestinal lumen to the liver?

Fructose enters epithelium via GLUT5 Fructose enters circulation and then the liver where it becomes fructose 1-phosphate

Where does secondary active transport for uptake of carbs occur?

Intestine - SGLT1 Kidney -SGLT2

What transporters allow uptake by facilitated diffusion? What are the different types?

GLUT GLUT2 - active in liver, intestine, pancreas GLUT4 - insulin-inducible transporter GLUT5 - fructose transporter