Lecture 13: Absorption and Storage of Carbohydrates Flashcards
Carbohydrates can allow for formation of ___, which is present in connective tissues and joints
proteoglycans
True or False: Carbohydrates are important for cell to cell recognition
True
Glucose is stored as ___
glycogen
Glucose, Fructose, and Galactose are _____ (single units)
monosaccharides
Lactose is a disaccharide made up of ___ and ___
Sucrose is a disaccharide made up of ___ and ___
galactose + glucose
glucose + fructose
____ are short chains of monosaccharides that are particularly important for cell recognition and attachment
Oligosaccharides
Polysaccharides can be stored as ___
glycogen
True or False: polysaccharides make up make components of DNA/RNA
True
___ is a fuel source of glucose and polysaccharide
Glycogen
Saliva contains ____, which begins the breakdown of large carbohydrates
alpha amylase
True or False: A small portion of glucose can be absorbed indirectly across mucus membrane of the mouth
False - A small portion of glucose can be absorbed DIRECTLY across mucus membrane of the mouth
After leaving the mouth, carbohydrates enter stomach and begin mixing in stomach acid. What enzyme is inactived by stomach acid?
A-amylase
Secretin is release from _____ cells in response to the ____ ____ entering the small intestine
intestinal cells; stomach acid
Secretin sends a signal to ___ that food is entering the stomach. In response, the above mentioned organ releases ____
pancreas; bicarbonate
Secretin stimulates pancreas to release ___into the small intestine to ___ and _____
neutralize and raise pH
As HCO3 is being released, the pancreas also secretes ___into the small intestine
pancreatic amylase
(continues to digest large carbohydrates)
Pancreatic amylase digests carbohydrates while they are in the _____
small intestine
If bicarbonate were not secreted by pancreas, ___ could not be produced
pancreatic amylase
What are examples of two types of disaccharidases found on the surface of intestinal cells?
Sucrase + Lactase
Sucrase breaks sucrose into ___ and ___
glucose + fructose
What is the benefit of having disaccharidases on surface of intestinal cells?
Once disaccharides are broken down into single units, they can be absorbed
Once digested and absorbed, ____ and ___ are metabolized in the liver
fructose + galactose
Lactose intolerance is an example of disaccharide deficiency
True
When one lacks lactase, unabsorbed disaccharides attracts____ to the intestine, leading to diarrhea
water
True or False: In lactose intolerance, disaccharides are not digested and, as such, move through intestines without being absorbed
True
In lactose intolerance, unabsorbed disaccharides that reach the large intestine are acted on by what organism?
What is generated as a result of interaction?
Intestinal bacteria
Gas and Bloating
Deficiency in liver enzyme involved in ____ metabolism will cause ill feeling after consuming milk/dairy (this is rare!)
As a result of this deficiency, there is a build up of _____
galactose
Deficiency in liver enzyme involved in ___ metabolism will lead to feeling ill after ingesting what three food items?
In this disorder, there is a build up of ___
sucrose
honey, fruit, and sugar
fructose
True or False: Bacteria in the large intestine will digest some substance that cannot be digested by humans
True
Where does nutrient, water, and electrolyte absorption occur?
Large Intestine
____, such as: cellulse, is an undigestable carbohydrate in humans and is excreted
Dietary fiber
____: Classifications of foods based on ability to raise glucose after consumption
Glycemic Index
True or False: The Glycemic Index is based on how a food is digested or absorbed
True
What two factors LOWER the GI of a food?
Fat and Fiber
An orange has a ___ GI while orange juice has a ___ GI
low; high
A plain piece of toast has a ____ GI while one with butter has a ____GI
high; low
True or False: Glycogen consists of a polymerized glucose, which forms a circular structure
True
Although a majority of glycogen is made up of linear chains, ~10% of glycogen molecules contain ____ ____
branch points
Cellular location of glycogen?
Cytosol (forms granules)
What kind of glycogen is the fuel source for the entire body?
Liver glycogen
Glycogen in skeletal muscle is only for ____
skeletal muscle
What are the two primary sites of glycogen?
Liver and skeletal muscle
___ can help to maintain glucose levels
Glycogen
True or False: There are separate pathways for glycogen synthesis and degradation
True
True or False: Genetic conditions involving defects in glycogen storage or release can cause numerous pathologies
True
____ is the protein at the center of the glycogen molecule that uses UDP-glucose (activated form of glucose)
Glycogenin
How does glycogenin start glycogen synthesis?
Adds glucose molecule to itself
Once glycogenin acts, ____ will add additional glucose units to growing end
Glycogen Synthase
True or False: Glycogen Synthase can only add to an EXISTING chain of glucose. In other words, needs glycogenin to add additional units before it can work.
True
_____: activated form of glucose that is used in the cell to build glycogen
UDP-glucose
Steps of Glycogen Synthesis?
1) Activation of UDP-glucose
2) Glycogenin adds glucose molecules to itself using UDP-glucose
3) Glycogen synthase catalyzes addition of more glucose units
4) Branching Enzyme will periodically move a block of 5-8 glucose molecules from growing end and reattach it to another point => BRANCH POINT (increases the growing number of growing ends for glycogen molecule) => two growing ends
Glucose can only be added to a ___ end
growing
What enzyme will remove glucose units with a phosphate attached when active (has a role in glycogenolysis)?
Glycogen phosphorylase
(uses phosphate to work)
Glycogen phosphorylase will remove glucose units one by one until only __ units on branch remain
4
(at this point: it can no longer break down glucose)
Using its transferase activity, the transferase/debranching enzyme will remove ____ glucose molecules, adding them to a different chain
outer three
Using its debranching enzymes, the transferase/debranching enzyme uses water to remove remaining ______ glucose
branch point
How does the amount of glycogen breakdown affect glucose units that will become available for use?
The more glycogen that is broken down, the more individual glucose units will be available for use
Cooperation between what two enzymes allows for glycogen breakdown?
Glycogen phosphorylase
Transferase/De-branching enzyme
Importance of having numerous glycogen branch points and growing ends?
Allows glycogen to be synthesized or broken down FAST!
What enzyme is expressed in liver cells and allows for GLUCOSE to be exported to the blood and be made available to the body?
Glucose 6 phosphatase
True or False: Skeletal muscle expresses G6P
False - it does NOT. As a result, glucose made in skeletal muscle is only made available to the muscle itself
Three general regulatory mechanisms for glycogen metabolism?
1) Hormones - insulin, epinephrine, glucagon
2) Allosteric regulation
3) Substrate availability (glucose)
In a well-fed state, insulin stimulates ____ synthesis in the liver
If blood glucose is low, glucagon will stimulates ___ degradation
glycogen
glucagon
How will epinephrine affect glycogen?
Epinephrine will stimulates glycogen degradation
Insulin will stimulate ___ in muscle
Epinephrine will stimulate ___ degradation in muscle
Insulin will stimulate glycogen synthesis in muscle
Epinephrine will stimulate glycogen degradation in muscle
Why is skeletal muscle not sensitive to glucagon?
Muscle cannot help with low glucose levels because it cannot release glucose due to LACK of G6P
Is glycogen synthesized at rest? In motion?
At rest: glycogen synthesis
In motion: glycogen degradation
What two hormones stimulate PKA?
Epinephrine and Glucagon
Upon activation, PKA phosphorylates which two enzymes?
Glycogen Synthase
Glycogen Phosphorylase
Phosphorylation of glycogen synthase turns it ___
Phosphorylation of glycogen phosphorylase turns it ___
Net effect?
OFF
ON
Glycogen degradation
Epinephrine will stimulate glycogen breakdown in ___ and ___
Glucagon will only cause glycogen breakdown in ___
liver and skeletal muscle
liver
Insulin activates ____, which remove phosphate groups from ___ and ___
phosphatases
glycogen synthase = ON
glycogen phosphorylase = OFF
What is glycated hemoglobin?
Hemoglobin with glucose attached
-Marker of glycemic control over 3 to 4 months (long-term)
-HbA1C test
