Biochemistry: Absorption and Storage of Carbohydrates

carbohydrates are important in:

1. fuel metabolism
2. cell-cell identification
3. structural components of certain tissues

carbohydrate formula

(CH2O)n

carbohydrates range in size from:

monosaccharides to polysaccharides

dietary carbohydrates are made up of the monosacchardies:

1. glucose
2. galactose
3. fructose

dietary carbs are broken down in the digestive tract to _____

monosaccharides

ultimately, all monosaccharides are converted into ___ __or__ ___ intermediates which may then be further metabolized

glucose or glycolytic intermediates

people are either born with or later develop ___ __in aspects of__ ____ which lead to discomfort upon ingestion of that carbohydrate__

defects; carbohydrate digestion

how is glucose stored in the body?

as glycogen

a highly branched polymer of glucose is called?

glycogen

while many tissues have some glycogen, those tissues most abundant in glycogen are:

1. muscle
2. liver
3. kidney

glycogen is synthesized and catabolized by similar pathways in each tissue, but _____ is much different

regulation

regulation reflects the different roles glycogen plays in each _____

tissue

_____ glycogen is preserved for the use of the muscle

muscle glycogen

liver and kidney glycogen is degraded __when blood glucose levels__ __*or when*__ _____ is present__

drop; epinephrine

proteoglycans are proteins with _____ attached

carbohydrates

proteoglycans are important in _____ tissue

connective tissue

what kind of energy is required for the maintenance of blood glucose?

ATP energy

if blood glucose drops too low, a person can enter a state of _____ (which can be life threatening)

unconsciousness

if blood glucose remains elevated, _____ can develop with long-term complications

diabetes mellitus

how do carbohydrates/glucose store energy?

glycogen (polymer of glucose)

where is glycogen most abundant?

liver and muscle

carbohydrates on the cell surface are important for _____ recognition

cell-cell recognition

what is one way to classify carbohydrates?

size

what is another term for monosaccharides?

simple sugars

what are examples of simple sugars?

glucose and fructose

are most monosaccharides sweet/salty?

sweet

what are examples of important monosaccharides and their dietary sources?

1. glucose (starches)
2. galactose (milk/dairy)
3. fructose (table sugar/fruit/honey)

disaccharides are 2 _____ joined together

monosaccharides

what are 2 examples of disaccharides?

lactose and sucrose

what is lactose is composed of?

glucose and galactose

lactose is abundant in _____

milk

lactose is a major source of dietary _____

galactose

what is sucrose composed of?

glucose and fructose

what is a dietary example of sucrose?

common table sugar

sucrose is a major source of dietary _____

fructose

oligosaccharides have _____ of monosaccharides

short chains

oligosaccharides have diverse roles in cells such as:

1. cell attachment
2. cell-cell recognition

polysaccharides have long chains of up to how many units?

10-1000 units

polysaccharides differ in:

1. proteins
2. DNA
3. RNA

what 2 things are polysaccharides essential in?

1. structural roles
2. fuel storage

in polysaccharide fuel storage, glycogen (storage form of glucose) forms compact, dense _____ that are well-suited for cellular storage

granules

in the mouth, saliva contains _____

a-amylase

in the mouth, a-amylase (enzyme) breaks bonds between ___ __in__ ___

sugars in carbohydrates

in the mouth, some glucose can be absorbed _____ across the mucous membranes

directly

the stomach has an acidic environment with a pH range between:

pH 1-3

stomach acid inactivates a-amylase, but _____ in polysaccharides

breaks bonds

is the pH of the small intestine, neutral/basic/acidic?

neutral and slightly basic

what is the PH range of the small intestine

pH 6-8

as food enters the small intestine, the carryover of stomach acid induces secretion of the hormone, _____

secretin

secretin stimulates the ___ __to secrete__ ___ into the small intestine to neutralize stomach acid and buffer the pH

pancreas to secrete bicarbonate

enzyme activity is sensitive to _____

pH

pancreatic amylase is an enzyme that hydrolyzes ___ __and__ ___

starches and glycogen

what has many overlapping specificities?

disaccharidases

what are examples of disaccharidases?

sucrase and lactase

sucrase breaks sucrose into ___ __and__ ___

fructose and galactose

lactase breaks lactose into ___ __and__ ___

galactose and glucose

galactose and fructose are absorbed in the ___ __tract, travel in the blood, and are taken up by the__ __*where they are converted to*__ ______

GI tract, liver, glucose

what can cause ill effects (GI discomfort) when following consumption of corresponding carbohydrate

lack of disaccharidase

___ __disaccharides in GI tract cause loss of water leading to__ ___

unabsorbed disaccharides, diarrhea

any ___ __that make it to the large intestine will be used by bacteria which generate__ ___

metabolic fuels, gas

relatively common condition that mainly causes discomfort in the GI tract is due to _____

lack of absorption

what is an example of lack of absorption?

lactose intolerance

lactose intolerance is the inability to break down ___ __in the__ ___

lactose, small intestine

lack a liver enzyme involved in either ___ __or__ ___ metabolism

glucose or fructose metabolism

lacking a liver enzyme (involved in either galactose or fructose metabolism) is an uncommon condition with serious, potentially life threatening complications due to _____

lack of metabolism

what are 2 conditions where you lack a liver enzyme?

1. galactosemia


1. hereditary fructose intolerance

in galactosemia, individuals lack an enzyme that _____ following absoprtion

metabolizes galactose

if galactose and its metabolites build up, it can cause _____

toxicity

in hereditary fructose intolerance, individuals lack an enzyme involved in the ___ __of__ ___

metabolism of fructose

if fructose and its metabolites build up, it can cause _____

toxicity

conditions such as galactosemia and hereditary fructose intolerance can lead to serious complications including effects on:

1. growth and development
2. nervous system complications
3. damage to organs (especially the liver)
* main treatment is avoidance of the corresponding sugar

intestinal bacteria (E coli) in the large intestine digest substances including _____ that humans are not able to digest

complex polysaccharides

some nutrients are absorbed in the large intestine including:

1. H2O
2. electrolytes
3. anything left over from the rest of the GI tract

some carbohydrates such as _____ are not absorbed and are excreted in the large intestine

fiber

dietary fiber is a digestible/undigestible carbohydrate in humans

undigestible

the glycemic index is a way of classifying foods based on their ability to _____ after consumption

raise blood glucose

a food with a high GI will raise blood glucose more than consumption of a food with a _____

low GI

true or false, foods range in GI?

true

examples of high GI foods

white bread/bagel/white rice

examples of medium GI foods

whole grain breads/oats/brown rice

examples of low GI foods

lentils/most fruits/non-starchy vegetables

___ __and__ ___ tend to lower the GI of a good

fat and fiber

_____ of a food matters (juice has a higher GI than whole fruit)

processing

_____ a food is eat matters: putting butter on bread lower GI of the toast

how

GI matters b/c people with _____ try to maintain normal blood glucose levels

diabetes mellitus

GI also matters b/c studies show that people with high GI diets have increased risk of developing _______

type 2 diabetes mellitus

glycogen is a readily accessible _____

storage form of glucose

glycogen structure: _____ polymer of glucose residues

large and branched

approximately 90__% of glucose molecules in glycogen are__ ___

linear

approximately 10% of glucose molecules in glycogen are _____

branched

the existence of glycogen makes glucose readily available between ____ __and__ during _____

between meals and during muscular activity

glycogen exists as _____ in the cytosol (where glycolysis and most carbohydrate metabolism occur)

granules

glycogen is present in a number of cells in small/large amount

small amounts

however, glycogen is stored in large amounts in:

1. liver


1. purpose: fuel reserve for the body
2. muscle


1. purpose: fuel reserve ONLY for muscle

although glycogen is more concentrated in the _____, there is more muscle tissue than liver in the body; therefore, there is approximately 2x more glycogen in total muscle than liver

liver

glycogen plays an important role in the _____ of blood glucose levels

maintenance

the ___ __and__ ___ are highly dependent on glucose

brain and nervous tissue

synthesis and degradation of glycogen are same/different pathways

different pathways

_____ regulate the pathways that synthesize and degrade glycogen

hormones

genetic/inherited _____ defects in glycogen pathways result in disease

enzyme