Carbohydrate Digestion (complete) Flashcards
What is central to all digestion
glucose
What is the preferred energy source of the brain
glucose
what is the required energy source for the red blood cells
glucose
What is an essential energy source for exercising muscles
glucose
Glucose is a fundamental precursor to which important compounds
- Lactose
- glycogen
- Nucleic Acids
- Amino Acids
- Steroid hormones
What are is the normal blood glucose range
70 - 100 mg/dL
What is it called when your blood glucose is below 70 mg/dL
hypoglycemia
what is it called when your blood glucose is above 100 mg/dL
hyperglycemia
What is Digestion
the enzymatic conversion of polysaccharides and disaccharides to their corresponding monosaccharides
What are the three main types of carbohydrates in the american diet
- starch
- sucrose
- lactose
What are typical sources of starches
potatoes, rice, corn, wheat
what are typical sources of sucrose
table sugar, desserts, fruit
What are typical sources of lactose
milk, milk products
What % of daily carbs come from starches
60%
what % of daily carbs come from sucrose
30%
what % of daily carbs comes from lactose
10%
How do you differentiate between D and L isomers of sugars
You must find the -OH group that is on they assymetric carbon (the one furthest from the carbonyl carbon)
if it is to the right, then it is a D isomer
if it is to the left, then it is an L isomer
Are all naturally occurring sugars L or D isomers
D isomers
sugars of ___ or more carbons usually under cyclization
5
what are the two types of isomers created by cyclization of sugars
Alpha and Beta isomers
How do you distinguish between alpha and beta isomers of a sugar
in the alpha isomer the hydroxyl group of the anomeric carbon will be below the plane of the ring
in the beta isomer the hydroxyl group of the anomeric carbon will be above the plane of the ring
How does cyclization of a monosaccharide occur
the hydroxyl group of the fifth carbon attacks the carbonyl carbon, and the oxygen of the fifth carbon becomes attached to the carbonyl carbon
what is the anomeric carbon
the carbon that used to be the carbonyl carbon, but then became bonded to the oxygen of the 5th carbon. This is also the carbon used to determine if it is an alpha or beta isomer
besides isomers what is another term used to describe the relationship between the alpha and beta isomers of a monosaccharide
they are anomers
what is a pyranose ring
ring systems with 5 carbons and an oxygen
what is a furanose ring
ring systems with 4 carbons and an oxygen
what is the difference between aldoses and ketoses (types of monosaccharides)
aldoses have the carbonyl carbon as Carbon #1
ketoses have the carbonyl carbon as Carbon #2
What is the difference between the anomeric carbons of ketoses and aldoses when they become cyclized
ketoses have thier anomeric carbon as carbon #2
aldoses have their anomeric carbon as carbon #1
is glucose a ketose or an aldose
an aldose
is fructose a ketose or an aldose
a ketose
is galactose a ketose or an aldose
an aldose
is lactose a ketose or an aldose
an aldose
What is a glycosidic bond
C—O—C
an oxygen between two carbons
where do we find glycosidic bonds
between monosaccharides in di and polysaccharides
What are the steps of naming glycosidic bonds
- name the monosaccharide forming the bond with it’s anomeric carbon
- state what conformation the anomeric carbon is in (alpha or beta)
- state which carbon is the active anomeric carbon (1-6) and state which carbon on the other monosaccharide is participating in the bond
- name the second sugar
Give an example of a glycosidic bond
glucosyl-alpha(1-4)-glucose
what sugar and which isomer make up all starches
alpha-D-glucose
What is amylose
an unbranched chain of alpha-d-glucose
What are the bonds involved in amylose
only alpha (1–>4) bonds
which end of polysaccharides is the reducing end
the end of the polysaccharide with the anomeric carbon exposed (not connected to another monosaccharide by a glycosidic bond)
which end of polysaccharides is the non-reducing end
the end of the polysaccharide where the anomeric carbon is not exposed
how many reducing ends does amylose have
1
how many non reducing ends does amylose have
1
how many reducing ends does amylopectin have
1
how many non-reducing ends does amylopectin have
many
what is the difference between reducing sugars and non-reducing sugars
reducing sugars have an exposed anomeric carbon, non-reducing sugars do not
what is amylopectin
- a branched starch
2. separate chains of alpha-d-glucose that are linked by alpha 1-6 linkages
How often are the glucoses of amylopectin bound to another chain of alpha-d-glucoses by alpha 1-6 linkages as opposed to being bound to another alpa-d-glucose by an alpha1-4 linkage
one of tweny glucoses form alpha 1-6 linkages and create branching
what are the bonds that cause the branching of amylopectin
alpha 1-6 glycosidic bonds
what are starches mixtures of
amylose and amylopectin
what percentage of polysaccharides in starches are amylopectin, and amylose
starches are 85% amylopectin and 15% amylose
What is the only difference between glucose and galactose
glucose has it’s 4th hydroxy group down
galactose has it’s 4th hydroxy group up
what is the relation between galactose and glucose
they are epimers
what are epimers
isomers that differ in orientation at only one carbon
What is glycogen
It is the form of carbohydrate storage in animals. branched, and very similar to amylopectin, just slightly more branched
What are the types of bonds in amylose
only Alpha 1-4
what are the types of bonds in amylopectin
mostly alpha 1-4
some alpha 1-6
what are the types of bonds in glycogen
mostly alpha 1-4
some alpha 1-6
how many reducing ends does glycogen have
1
how many non reducing ends does glycogen have
many
What percent of glycogen bonds are alpha 1-6 as opposed to alpha 1-4 bonds
8% are alpha 1-6 bonds (5% in amylopectin)
what is the plant form of carbohydrate storage
starch
What is cellulose
a linear (unbranched) polysaccharide made up of beta 1-4 linkages
What monosaccharide makes up amylose, amylopectin, glycogen, and cellulose
glucose
what is the type of bond between the glucose monosaccharides in cellulose
beta 1-4
what is significant about the beta 1-4 bonds in cellulose
the human body doesn’t have the enzymes to hydrolize the bond, so the human body can’t digest cellulose
what is hydrolysis of glycosidic bonds
the breaking of the glycosidic bonds that uses H2O
how many reducing ends does cellulose have
1
how many non reducing ends does cellulose have
1
What is sucrose
a disaccharide with glucose and fructose as it’s monosaccharides
what is the glycosidic bond between fructose and glucose in sucrose
it is a alpha beta 1 - 2 bond
what does the alpha beta 1-2 bond in sucrose refer to
the anomeric carbon (#1) of glucose is in the alpha conformation, it is bound to the anomeric carbon (#2) of fructose which is in the beta conformation
what is another name for sucrose
table sugar
what are the bonds in sucrose
Only one alpha beta 1-2 bond
is sucrose a reducing sugar
no
why is sucrose not a reducing sugar
because both of the anomeric carbons are participating in a bond and aren’t exposed.
What is lactose
a galactose bound to a glucose
what is the bond in lactose
a beta 1-4 bond between galactose and glucose
in lactose which end is the reducing sugar
the end with glucose (not galactose)
expound upon the bond between galatose and glucose in lactose
the anomeric carbon (#1) of galactose is in the beta conformation and it binds to the #4 carbon of the glucose
is lactose a reducing sugar
yes
what are the two monosaccharides that make lactose
glucose and galactose
what types of organisms (animals and plants) have lactose
only mammals
What is trehalose
a disaccharide of two glucose molecules
what is the bond like between the two glucoses of trehalose
it is an alpha alpha 1-1 bond
expound upon the alpha alpha 1-1 bond of trehalose
the anomeric carbons of the two glucoses (#1 and #1) are both in the alpha confomation and they are bound to each other
where can trehalose be found
insect blood, mushrooms, and fungi
can the bonds in trehalose be digested in humans
yes
is trehalose a reducing sugar
no
why is trehalose a non reducing sugar
because both of the anomeric carbons are participating in bonds and not exposed
What is the family of enzymes responsible for the digestion of disaccharides and polysaccharides
the Glycosidases
what is another name for the glycosidases
glycoside hydrolases
what do glycosidases or glycodise hyrdolases do
they hydrolize glycosidic bonds
What does it mean to hydrolize glycosidic bonds
to break glylcosidic bonds apart and release H2O as a product
what is the first enzyme to begin to digest cabohydrates
salivary alpha amylase
what kind of glucosidase is salivary alpha amylase
Alpha 1-4 endo glucosidase
what does it mean that salivary alpha amylase is a alpha 1-4 endo glucosidase
it means that it cleaves alpha 1-4 glycoside bonds, and the endo portion means that it cannot cleave terminal alpha 1-4 bonds.
What polysaccharides and disaccharides can salivary alpha amylase digest
starches and glycogen (poly)
it cannot digest disaccharides
What bonds can’t be cleaved by salivary alpha amylase that are commonly found in poly and disaccharides
- it can’t cleave terminal alpha 1-4 bonds
- it can’t cleave the alpha 1-6 bonds
- in can’t cleave the alpha 1-4 bonds that are adjacent to the branch points of amylopectin and glycogen
What are the possible products after salivary alpha amylase has began the digestion of carbohydrates
- maltose
- maltoriose
- oligosaccharides
- alpha dextrin
What is maltose
a disaccharide with two glucose molecules bound with an alpha 1-4 bond
What is maltotriose
a trisaccharide with three glucose molecules bound with alpha 1-4 bonds
What are oligosaccharides
four or more glucose molecules connected with alpha 1-4 linkages
what is alpha dextrin
four or more glucose molecules (alpha 1-4 linkages) that are linked by a branch point (alpha 1-6 linkage)
from what kind of carbohydrates can alpha dextrin be a product of after it has begun to be digested by salivary alpha amylase
amylopectin and glycogen
what are the most common products formed after salivary alpha amylase begins to digest carbohyrates in the mouth
oligosaccharides and alpha-dextrin
Why are oligosaccharides and alpha-dextrin the most common products formed by salivary alpha amylase
because the salivary alpha amylase only has a few seconds to digest the carbohydrates and doesn’t have enough time to break those down further.
what causes salivary alpha amylases to stop digesting the bolus
the acidity of the stomach is to strong (too low of pH) for salivary alpha amylase to continue functioning
how does the stomach participate in carbohydrate digestion
It does not have glycosidases, but it does do acid hydrolysis of sucrose
What are the two phases of carbohydrate digestion in the small intestine
- The luminal phase
2. The membrane phase
What are the players in the luminal phase of carbohydrate digestion in the small intestine
- Intestinal epithelial cells
- secretin
- pancreas
- bicarbonate
- cystokinin
- Pancreatic salivary amylase
What is the function of the intestinal epithelial cells during the luminal phase of carbohydrate digestion
they secrete secretin which signals to the pancreas to secrete bicarbonate and this enters the intestines and neutralizes the acids from the stomach so that glycosidases can begin to digest carbohydrates
what is the function of secretin
it signals to the pancreas to secrete bicarbonate
what is the function of bicarbonate
it neutralizes the stomach acids in the intestines allowing the pancreatic glycosidases to work
what is the function of cystokinin
it signals to the pancreas to secrete digestive enzymes, specifically pancreatic alpha amylase for carbohydrate digestion
what is the function of pancreatic alpha amylase
it continues the digestion of carbohydrates in the intestines
what are the carbohydates that pancreatic alpha amylase can digest
amylose
amylopectin
glycogen
what are the products after pancreatic alpha amylase digests amylose, amylopectin, and glycogen
- maltose
- maltotriose
- alpha dextrin (from amylopectin and glycogen)
- oligosaccharides (if it doesn’t have the time to fully digest it)
How similar is pancreatic alpha amylase to salivary alpha amylase
they are the same with the exception of where they are located
What bonds can the pancreatic alpha amylase cleave
alpha 1-4 bonds between two glucoses, but only interior bonds
What bonds aren’t cleavable with pancreatic alpha amylase
- terminal alpha 1-4 bonds
- alpha 1-4 bonds adjacent to branch points
- alpha 1-6 bonds
- can’t do the bonds of sucrose, lactose, and trehalose
What are the players in the membrane phase of carbohydrate digestion in the small intestine
- Enterocytes
a. brush border membrane (lumenal membrane)
b. contalumenal membrane - lactase
- trehalase
- glucoamylase complex
- sucrase-isomaltase complex
What are enterocytes
intestinal absorptive cells
what is the membrane of enterocytes that is facing the lumen (the inside of the small intestine)
the lumenal membrane
or the brush border membrane
What is the membrane of the enterocytes that is next to the basement membrane and the capillaries
the contralumenal membrane
What needs to happen in carbohydrate digestion at the enterocytes
- the carbs and remaining structures need to be broken down into monosaccharides
- the monosaccharides need to be carried into the enterocytes
- the monosaccharides need to cross the contralumenal membrane into the capillaries
What breaks the carbohydrates down into monosaccharides
the digestive enzymes embedded into the lumenal membrane
What are the enzymes in the lumenal membrane
lactase
trehalase
sucrase-isomaltase complex
glucoamylase complex
What is the structures of these enzymes that are embedded in the lumenal membrane of enterocytes
they have a structural part inside the membrane and a catalytic portion sticking out into the lumen
what kind of bonds does lactase cleave
beta 1-4 bonds between glucose and galactose (the bonds of lactose)
What kind of bonds does trehalase cleave
alpha alpha 1-1 bonds between two glucose molecules (the bonds of trehalose)
What are the products given off of lactase
galactose and glucose
what are the products given off of trehalase
two glucoses
What kinds of bonds does the glucoamylase-complex digest
alpha 1-4 bonds (EXO)
meaning that it cleaves terminal alpha 1-4 bonds between glucose
from what end does the glucoamylase-complex cleave alpha 1-4 bonds
from the non-reducing end
What things can the glucoamylase-complex cleave
- maltose
- malotriose
- alpha 1-4 bonds adjacent to branch points
what can’t the glucoamylase complex cleave
- alpha 1-6 bonds
2. bonds of sucrose, lactose, and trehalose
What kinds of bonds does the sucrase-isomaltase complex cleave
- alpha beta 1-2 bonds of sucrose (glucose and fructose)
- alpha 1-6 bond of alpha-dextrin
- alpha 1-4 bonds between glucose molecules (maltose, maltotriose)
What carbs can the sucrase-isomaltase complex digest
1, sucrose
- maltose
- maltotriose
- isomaltose
What is isomaltose
two glucose molecules linked alpha 1-6 ( the branch point of amylopectin and glycogen)
What are the two enzymes that can cleave maltose and maltotriose
- glycoamylase complex
2. sucrase-isomaltase complex
what are the potential products of sucrase-isomaltase digestion of carbs
- glucose
2. fructose
would we be able to digest carbs if we didn’t have salivary alpha amylase
yes (we have pancreatic alpha amylase)
what are dietary fibers
carbohydrates or carbohydrate derivatives that can’t be digested by our digestive enzymes
What are the two different kinds of dietary fibers
- soluble
2. insoluble
what is an example of insoluble fiber
cellulose
what are examples of soluble fiber
pectin and gums
What is an important characteristic of soluble fibers
they absorb water
What happens to the more soluble types of fibers
they move down to the colon and are digested by bacteria in the colon
What are the products of bacterial digestion of soluble fibers in the colon
- Gases (CO2, H2, Methane)
- Short chain fatty acids (acetic, propryonic, and butyric)
- Lactate
What are the 5 main benefits of dietary fibers
- they can bind carcinogens in the colon and take them out in the stool
- they can bind bile acids and take them out in the stool, so instead of reabsorbing them like it usually does the body has to remake them from cholesterol. this lowers our cholesterol
- they slow the absorption of glucose, preventing the spiking in blood glucose in diabetics
- they absorb more water, which makes stool softer, which helps a lot in diverticular disease
- they absorb more water so for people with IBS it is helpful in softening the stool as well
are monosaccharides polar or non-polar
polar
What is needed for monosaccharides to cross the lumenal membrane into the enterocytes
transport proteins are needed
What are the two membranes that monosaccharides have to cross to reach the capillaries
- lumenal membrane
2. contralumenal membrane
What are the two kinds of transporters that assist in transporting monosaccharides across the lumenal and contralumenal membranes
- SGLT
2. GLUT
What are SGLT transporters
sodium dependent transporters that use active transport
Which SGLT transporter aids in the abosrbtion of monosaccharides
SGLT 1
What monosaccharides does SGLT-1 transport
glucose and galactose
What does SGLT-1 do
it brings galactose and glucose from the lumen into the enterocyte
How does SGLT-1 work
sodium goes down it’s own gradient into the cell and brings glucose and galactose into the cell (AGAINST their concentration gradient)
Why is it important the SGLT-1 brings glucose and galactose into the enterocyte against their concentration gradients
because this means that no matter the concentration of glucose and galactose outside of the cell, it will still be absorbed into the enterocyte
What are the GLUT transporters
glucose transporters that work by facilitated diffusion
What are the GLUT transporters involved in carbohydrate absorption in the gut
GLUT 5 and GLUT 2
what does GLUT 5 do
it brings fructose into the enterocyte
can GLUT 5 bring glucose into the enterocyte as well as fructose
yes, it can bring glucose into the enterocyte, but it has a much higher affinity to fructose
What does GLUT 2 do
it transports glucose, galactose, and fructose across the contalumenal membrane into the capillaries
Where is GLUT 1 active
in red blood cells, blood-brain barrier
Where is GLUT 2 active
in the liver, pancreatic Beta-cells, contralumenal membrane of intestinal epithelial cells
Where is GLUT 3 active
in the neurons of the brain
where is GLUT 4 active
adipose tissue, skeletal muscle, heart muscle (insulin sensitive transporter)
Where is GLUT 5 active
Intestinal epithelial cells (from lumen into cells), sperm (fructose transporter)
Where is SGLT-1
Intestinal epithelial cells
Where is SGLT-2
Kidney (tubular epithelial cells)
What does the Glycemic Index measure
it measures how quickly you see a rise in blood glucose after food is consumed.
What are things with a high glycemic index
things that are quickly digested, which leads to a quick spike in blood glucose
is it better to eat things of high glycemic index or a low glycemix index
a low glycemic index
What is the flaw with the Glycemic index
it doesn’t figure in the serving size
What Is Glycemic load
The glycemic index multiplied by the standard serving of that food
What causes lactose intolerance
a lactase deficiency
What happens when you can’t properly digest lactose
- lactose draws in water, increasing fluid load
- in the colon we get gas, short chain fatty acids, and lactic acid from bacterial digestion of lactose
- lactic acid draws in more water, greatly increasing fluid load
- bloating, fullness, cramps, and pain are symptoms of the pressure in the gut
- distension of the walls leads to increased peristalsis
- peristalsis increase and increased water = diarrhea
- quick passing of things through the gut leads to decreased absorption of nutrients
- Dehydration, loss of electrolytes
- all this leads to malnutrition
What are the 5 classifications of lactose intolernace
- congenital lactase deficiency in infants and children
- temporary lactase deficiency in premature infants
- Acquired isolated lactase deficiency
- Lactase deficiency secondary to intestinal diseases
- Lactase deficiency secondary to insufficient mucosal contact time
What is congenital lactase deficiency in infants and children
Children born with low levels of lactase
what is temporary lactase deficiency in premature infants
Children that haven’t yet developped enough lactase
What is acquired isolated lactase deficiency
AKA late onset lactase deficiency or adult hypolactasia
With age our lactase levels decrease, especially in cultures that don’t consume much lactose
What is lactase deficiency secondary to intestinal disease
AKA secondary lactase deficiency
damage to intestinal mucosa that leads to decreased lactase ability
What is lactase deficiency secondary to insufficient mucosal contact time
if stuff isn’t in the intestine long enough then it can’t digest the lactose enough
How do you diagnose lactose intolerance
Easy way = take lactose away see if symptoms dissapear. if they do give it back, see if the symptoms come back
Other way = test the amount of hydrogen in their breath after giving them a test meal with lactose
what is the normal glucose tolerance curve like
blood glucose reaches a peak between 30-60 minutes after consumption, then it returns to its fasting level in about two hours
What is the difference between sucrose and sucralose (the artificial sweetener)
sucralose is a alpha beta 1-2 linkage between galactose and fructose, (not glucose and fructose like sucrose) this makes it indigestable
What can digest maltose
sucrase-isomaltase complex
glucoamylase
what can digest maltotriose
sucrase-isomaltase complex
glucoamylase
what can digest isomaltose
sucrase-isomaltase
what can digest lactose
lactase
what can digest trehalose
trehalase
what can digest sucrose
sucrase-isomerase complex
how does fiber help with diabetes
it slows the absorption of glucose into the blood
Which one of the following compounds is NOT produced from dietary starch by α-amylase?
a. maltose b. maltotriose c. fructose d. oligosaccharides e. α-dextrins
fructose
After digestion of a piece of cake that contains flour, milk and sucrose as its primary ingredients, the major carbohydrate products entering the blood are:
a. glucose b. fructose and glucose c. galactose and glucose d. glucose, fructose, and galactose
glucose, fructose, and galactose
A patient has a genetic defect that causes intestinal epithelial cells to produce disaccharidases of much lower activity than normal. Compared to a normal person, after eating cake (flour, milk, sucrose) this patient will have higher levels of:
a. maltose, sucrose, and lactose in the stool b. starch in the stool c. galactose and fructose in the blood d. lactose in the blood e. sucrose in the blood
maltose, sucrose and lactose in the stool
Which of the following disaccharides cannot be digested by the sucrase-isomaltase complex?
a. glucose α-1,4 glucose
b. glucose α-1,6 glucose
c. glucose α,α-1,1 glucose
d. glucose α,β-1,2 fructose
glucose alpha alpha-1,1 glucose
Dietary fiber refers to carbohydrates or carbohydrate derivatives of plant origin that are not hydrolyzed by human digestive enzymes. Which of the following statements about soluble fiber is correct?
a. Soluble fiber accelerates the rate of absorption of glucose from the gut into intestinal epithelial cells.
b. Soluble fiber is converted by intestinal bacteria to short chain fatty acids, lactic acid, and gas (CO2, CH4, and H2).
c. Soluble fiber is detrimental to patients with diverticular disease because it causes increased pressure on the colonic wall.
d. When consumed in large quantities, soluble fiber is associated with an increased incidence of colon cancer.
e. Soluble fiber is thought to increase blood cholesterol levels.
b. Soluble fiber is converted by intestinal bacteria to short chain fatty acids, lactic acid, and gas (CO2, CH4, and H2).
Galactose is transported across the brush border (luminal) membrane of the intestinal epithelial cells with the aid of:
a. SGLT-1
b. GLUT-1
c. GLUT-2
d. GLUT-4
e. GLUT-5
SGLT-1
. An infant shows symptoms of abdominal fullness, bowel cramps, and diarrhea when fed food sweetened with sucrose. A hydrogen analysis of his exhaled breath showed a 40-fold increase in the production of H2 an hour after consuming 40 g of sucrose dissolved in water. Consumption of a like amount of fructose showed a normal production of H2. The child most likely suffers from:
a. a GLUT-5 deficiency
b. a GLUT-2 deficiency
c. an α-amylase deficiency
d. a sucrase deficiency
e. a lactase deficiency
a sucrase deficiency
- Drug X, a potent inhibitor of the Na+-dependent monosaccharides cotransport system, is administered to a patient. Which of the following monosaccharides would the patient have difficulty in absorbing into intestinal epithelial cells?
a. glucose
b. galactose
c. fructose
d. A and B are correct.
e. A, B and C are correct.
A and B are correct
- A patient is suspected of having a lactase deficiency. Lactose (75 g) dissolved in water was administered orally after an overnight fast and the following blood glucose results were obtained:
Time (min) Blood Glucose (mg/dl) 0 85 30 110 60 140 90 115 120 85
These results indicate:
a. normal lactase activity.
b. lactase deficiency.
normal lactase activity
- Chronic use of dairy products by individuals with a lactase deficiency may result in:
a. diarrhea
b. rapid intestinal transit time.
c. malabsorption of drugs.
d. A and B are correct.
e. A, B, and C are correct
A, B, and C are correct
- Which of the following statements are correct?
a. Not all carbohydrates contained in food are digested at the same rate.
b. The glycemic index refers to the effect of 50 g of carbohydrate in a particular food on blood glucose compared to 50 g of glucose.
c. The higher of glycemic index of a particular food, the slower the rise of blood glucose after the food is consumed.
d. A and B are correct.
e. A, B, and C are correct.
A and B are correct
What can inflammation and damage to the gut cause, and how does that affect abosrption
it can cause gaps or tears in the intestine
this can result in absorption of things that aren’t normally absorbed. (disaccharides)
Which membrane carbohydrate enzyme is the most easily damaged, and the slowest to recover
lactase
