carbohydrates Flashcards
describe monosaccharides-
- most common is glucose
- naturally occurring
- can’t be hydrolyzed into a smaller unit
what is the most commonly found monosaccharide
glucose
when is a monosaccharide considered a reducing sugar
- considered a reducing sugar when the anomeric carbon is free
describe disaccharides
- most common is sucrose
- two monosaccharides joined by an acetyl bond (glycosidic)
what kind of bond joins monosaccharides together, forming polysaccharides?
the monosaccharides are joined by an acetyl bond- aka glycosidic bond
what is the ratio of H:O in all CHO
2:1
position of triode monosaccharides?
metabolism of glucose
position of pentose monosaccharides?
components of DNA and RNA
position of hexose monosaccharides
nutritionally the most important
what is a chiral carbon?
a carbon with four different components attached
what are the two types of chiral carbons?
- enantiomers
- diastereomers
what are enantiomers
mirror images
what are diastereomers
not a mirror image
how do you determine a D vs an L sugar
- determined by the -OH group on the highest chiral carbon
- Oh on the right= D
- OH on the left = L
how do you determine the number of stereoisomers for a molecule?
stereoisomers= 2^n
n= # chiral carbons
are D or L sugars more nutritionally important?
D are nutritionally more important because digestive enzymes are stereospecific for D sugars
what are the basic rules for nomenclature in terms of converting towards fischer projection to Haworth model
LAB vs RBa
(left/above/beta)
(right/below/alpha)
describe sucrose
- found in sugar cane and fruits
- product of glucose + fructose
- non-reducing
describe lactose
- found in milk
- product of galactose + glucose
- reducing
describe maltose
- found in beer and liquor
- glucose + glucose
- reducing
describe polysaccharides
- long strings or branches of monosaccharides (min 6) attached by glycosidic bonds
what is the polysaccharide in plants
starch (amylose, amylopectin)
what is the polysaccharide in animal tissue
glycogen
what is the advantage for branched polysaccharides
this provides a larger number of ends from which to cleave glucose when energy is needed
describe cellulose
- both a dietary fibre and functional fibre (naturally occurring but also added to foods for supplement)
- poorly fermented by human gut bacteria
- rich in bran, legumes, nuts, peas
describe hemicellulose
- a heteropolysaccharide that varied between plants
- mixture of alpha and beta glycosidic bolds
describe pectin
- both a dietary and functional fibre
- part of the primary cell wall of plants
- highly fermented by gut bacteria (therefore a good bulking agent in animal feeds)
describe resistant starch
- typically found in plant cell walls
- resistant to amylase activity
- conveys some advantaged to both soluble and insoluble fibres
what are the health benefits of fibre
- maintains function and health of the gut
- insoluble fibres reduce constipation
- soluble fibres increase satiety (the feeling of being full)
describe the correlation between soluble fibre and disease risk
- decrease cardiovascular disease risk by lowering blood cholesterol
describe carb digestion within the mouth
- saliva breaks down alpha-1,4- glycosidic bonds
- produced a few monosaccharides (cellulose and lactose are resistant)
describe carb digestion within the stomach
- alpha amylase (in saliva) digestion continues until pH drops- then enzyme is deactivated
- CHO will not consist of small polysaccharides and maltose
describe carb digestion within the small intestine
- pancreatic alpha-amylase is active at neutral pH
- alpha 1,6 binds are resistant and eventually produce is-maltose
describe people wit more copies of the AMY1 gene
people with more copies of the AMY1 gene gave overall more amylase activity in saliva
describe lactose intolerance
- missing lactase enzyme
- cant convert lactose to glucose and galactose
- rather, once lactose meets the bacteria within the large intestine, fermentation occurs (which produces gasses, organic acids, and other osmotically active molecules)
how do genetics play a factor in lactose intolerance
- ethnicity (asian vs northern europeans)
- variance in the LCT gene (which encodes the lactase enzyme) contributes to an intolerance
what are enterocytes
polarized cells (they have an up and a down)
describe monosaccharide absorption
- nearly all monosaccharides are taken up by enterocytes
- once taken in, small amounts of glucose leak back out into human, and small amounts diffuse into blood through the base lateral membrane, all while the majority of glucose is transported into blood through GLUTZ
- transport of glucose and galactose from lumen into blood is dependent on basolateral Na-K ATPase activity
- fructose is taken up by facilitated transport
- glucose, galactose, and fructose all enter blood via basolateral GLUT2
what is SGLT1
sodium glucose transport
- transports glocose and galactose
on the apical side of the enterocyte, what occurs
uptake of monosaccharides
using the SGLT1 transport
on the basolateral side of the enterocyte, what occurs?
absorption
using GLUT2
what are the functions of carbs within the body?
- primary source of energy
- they “spare” protein
- prevent ketosis (and therefore acidic blood)
- primary source fo energy for therein and red blood cells
what I ketosis
- when carbs are limited, fats are broken down for energy
- leads to the production of ketone bodies- causing the body’s pH to become slightly acidic
how do carbs spare protein
- prevents the breakdown of protein for energy
- allows protein to concentrate on building, repairing, and maintaining body tissue
(if carbs are low, body will breakdown protein to keep the Krebs cycle going)
why are red blood cells dependent on glucose
they dont have mitochondria- and since things cant be oxidized without mitochondria- no energy will be formed
what are the three fates of glucose in cells
- enters glycigenisis for energy storage
- enters glycolysis for energy production
- enters hexose monophosphate shunt to generate precursors for biogenesis
what is glycogenin
an enzyme that serves as a scaffold on which to attach glucose molecules to build glycogen
how does glycogenin work?
- initially attaches glucose molecules to itself before glycogen synthase takes over and adds glucose to the growing glycogen store
how many glucose molecules can be contained in a single glycogen store
30 000 + glucose molecules can be contained in a single glycogen store
where is energy produced in the cell?
- substrate-level phosphorylation (Krebs cycle) occurs in the mitochondria
- oxidative phosphorylation (glycolysis) occurs in the cytoplasm
what is glycolysis
turning glucose into pyruvate
what is the first committed step in glycolysis
phosphofructokinase
what is the net energy yield from on glucose that undergoes glycolysis
2 NADH + 2 ATP
equivalent to ~8 ATP
describe lactic acid production
- occurs in muscle during prolonged exercise and in RBC
- pyruvate is converted into lactic acid in the cell’s cytosol
- regenerates NAD+, which allows glycolysis to continue
- a net of 2 ATP is produced when glucose is converted to lactic acid
describe how ethanol is produced
(doesn’t happen in body)
- yeast breaks down pyruvate into CO2 and ethanol
- regenerated NAD+, which allows glucose to continue being broken down in glycolysis
when does the Cori Cycle occur
the cori cycle occurs in times where oxygen is unavailable in the muscle- which leads to the production of lactate
describe what happens in the Cori Cycle
- used when oxygen is unavailable
- lactate is transported back to the liver- where gluconeogenisis allows for the conversion of pyruvate back to glucose
- for two molecules of lactate to form glucose, the cell consumes 6 ATP molecules
how much ATP does it take to convert 2 molecules of lactate
it takes 6 ATP to convert 2 lactate molecules
what is the function of the hexose monophosphate shunt
produces important molecules (ie- NADPH, ribose sugars)- that all other cells will use
what is pyruvate dehydrogenase?
the “gatekeeper” to the Krebs cycle
describe the Krebs cycle
- over 90% of the energy in food is released in this process
- a common and final catabolic pathway for products of protein, lipid, and carbs
- takes place in mitochondrial matriculates
how much energy do you get from 1 molecule of glucose
38 ATP
describe gluconeogenisis
- pathway that is active when glucose is needed in the body
- very active in liver (but can also happen in the kidney during starvation)
- muscle and adipose tissue lack enzymes for gluconeogenisis
- high physical activity produced muscle lactate- which travels to liver tin the cori cycle
