Carbohydrates: Metabolism I

polysaccharides

broken into oligosaccharides by alpha-amylase in the saliva in the mouth

oligosaccharides

get broken into disaccharides by alpha-amylase in the pancreas - dextrins and maltotriose broken down

a-amylase

enzyme in saliva and the pancreas that break down polysaccharides and oligosaccharides

disaccharides

broken into monosaccharides by their specific enzyme in the small intestine; ex: sucrase, lactase, maltase, a-glucosidase

monosaccharides

get absorbed from the intestines into the blood to be used by tissues

ex: glucose, fructose, galactose

glycemic index

measure of digestibility of starchy food, based on the extent to which it raises the blood concentration of glucose compared with a reference food such as white bread or boiled rice

1 (100%)

starches readily hydrolyzed in the small intestine such as white bread have a glycemic index of _________

0

carbohydrates that are not hydrolyzed at all have a glycemic index of ________

lactose intolerance

condition where the body does not produce enough lactose to break lactose into D-glucose and D-galactose; the lactose stays in the intestines and gets fermented instead of being digested - produces toxic metabolites that result in cramping and diarrhea

galactosemia

defect in an enzyme that phosphorylizes/isomerizes D-galactose so it can't be converted to glucose-6-phosphate and enter glycolysis; galactose accumulation in tissues (eyes and CNS) can cause cataracts and growth/mental retardation

glucose

energy-rich hexose that is a source of numerous metabolic intermediates; can be stored as a polysaccharide having no effect on osmotic pressure of cell

glycolysis

can occur in aerobic or anaerobic conditions; occurs in the cytoplasm of many tissues

GLUT

cell membrane protein transporter that moves glucose inside of the cell prior to the first step of glycolysis

preparatory

in the _____________ stage of glycolysis, energy is consumed (2 ATP)

payoff

in the _____________ stage of glycolysis, energy is generated (2 net ATP)

irreversible

steps 1, 3, and 10 of glycolysis are _____________

hexokinase

catalyzes step one of glycolysis (irreversible), in which glucose is phosphorylated to prevent it from leaving the cell

Phosphofructokinase (PFK)

catalyzes step three of glycolysis (irreversible) in which fructose-6-phosphate is phosphorylated into fructose-1,6-bisphosphate, forming a high-energy molecule

pyruvate kinase

catalyzes step 10 of glycolysis in which phosphoenolpyruvate is dephosphorylated into pyruvate, producing 2 ATP

fluoride

poisons enolase; no formation of phosphoenolpyruvate

induced fit

mechanism of interaction in step 1 of glycolysis between glucose and hexokinase in which the enzyme folds in on glucose after it binds, resulting in a tight fit. The whole glucose molecule is surrounded by hexokinase except for C-6, which enhances the specificity of the reaction (eliminates any water molecules that may interfere with the phosphorylation reaction)

coupling

mechanism of interaction in step 6 of glycolysis involving glyceraldehyde-3-phosphate dehydrogenase, which couples two reactions through the intermediates to overcome the energy barrier

thioester

____________ intermediate in step 6 of glycolysis allows for the bypassing of large energy dip

glycose-6-phosphate

trapped inside the cell; product of the phosphorylation of glucose

oxidation

the exergonic reaction in step 6 of glycolysis is an _______________ reaction

phosphorylation

the endergonic reaction in step 6 of glycolysis is a ____________________ reaction

iodoacetate

suicide inhibitor of glyceraldehyde-3-phosphate dehydrogenase; prevents the continuation of glycolysis (environmental poison)

substrate level phosphorylation

mechanism of interaction in steps 7 and 10 of glycolysis in which phosphorylated compounds (substrates of kinases) act as energy rich sources of phosphate groups (phosphorylate ADP); produces 2 ATP molecules each step (4 total)

cytoplasm

location of substrate level phosphorylation in glycolysis (does not require mitochondria or electron transport chain)

NAD+

oxidizing agent that gets depleted fast in the glyceraldehyde-3-phosphate dehydrogenase reaction; glycolysis will stop if it is not regenerated

pyruvate

NAD+ gets regenerated through ___________ metabolism

aerobic

in _________ conditions, pyruvate gets converted to acetyl-CoA which enters the citric acid cycle. In oxidative phosphorylation, NAD+ gets regenerated

lactate

in anaerobic conditions in mammals, NAD+ gets regenerated by converting pyruvate to ______________

ethanol

in anaerobic conditions in microbes, NAD+ gets regenerated by converting pyruvate to acetaldehyde and then to ___________________

anaerobic

accumulation of lactate due to vigorous exercise, septic shock, or cancer cachexia in ________________________ conditions, impacting erythrocytes, the brain, GIT, renal medulla, retina, and skin

low

when there are __________ levels of ATP, glycolysis will increase

feedback inhibition

glucose-6-phosphate regulates hexokinase with ___________________________ while at rest

phosphofructokinase

the pacemaker of glycolysis

allosterically

high levels of ATP or citrate ______________________ inhibit phosphofructokinase

feedforward stimulation

accumulation of fructose-1,6-bisphosphate provides _______________ _______________ for pyruvate kinase during exercise

pyruvate kinase

allosterically inhibited by high levels of ATP or Alanine

gluconeogenesis

the formation of glucose from non-carbohydrate molecules. Major precursors include glycerol, lactate, and amino acids

cori cycle

involved in gluconeogenesis by redirecting lactate from muscle to be converted to glucose in the liver

glucose crosses through the blood from the liver to muscle, and lactate crosses through the blood from the muscle to liver

4 ATP, 2 GTP

energy expenditure of gluconeogenesis

pyruvate carboxylase

enzyme that catalyzes the first irreversible reaction (part 1) in gluconeogenesis in which the enzyme requires biotin to carry CO2; converts pyruvate to oxaloacetate

phosphoenolpyruvate carboxykinase

enzyme that catalyzes the first irreversible reaction (part 2) in gluconeogenesis in which oxaloacetate is converted into phosphoenolpyruvate

biotin

carries carbon dioxide; needs allosteric activation of pyruvate carboxylase by acetyl-CoA

Fructose-1,6-bisphosphatase

enzyme that catalyzes the second irreversible reaction in gluconeogenesis converting fructose-1,6-bisphosphate to fructose-6-phosphate

glucose-6-phosphatase

enzyme that catalyzes the third irreversible reaction in gluconeogenesis, converting glucose-6-phosphate to glucose

liver, kidney

while glycolysis can occur in any cell cytosol, gluconeogenesis only occurs in the ___________ and _________

Fructose-2,6-bisphosphate (F-2,6-BP)

enzyme involved in the regulation of phosphofructokinase in glycolysis and fructose-1,6-bisphosphatase in gluconeogenesis

phosphofructokinase

fructose-2,6-bisphosphatase activates _____________________

Fructose-1,6-bisphosphatase

fructose-2,6-bisphosphatase inhibits ________________

insulin

secreted to maintain blood glucose levels by stimulating expression of glycolysis enzymes and preventing expression of phosphoenolpyruvate carboxykinase

type 2 diabetes

condition in which glycolysis is still active but gluconeogenesis is not inhibited (non-insulin dependent diabetes); have high levels of phosphoenolpyruvate carboxykinase because it is resistant to insulin, even though it is being produced by the pancreas

hyperglycemia

excessive sugar in the blood

pancreatic

type 2 diabetes can progress into type 1 diabetes when _______________________ cells get burnt out and stop producing insulin

glucose-6-phosphatase

enzyme present mainly in liver and kidney but not in other tissues like the brain or muscle because those tissues require glucose and don't want it to get rehydrolyzed back into glucose so that it can leave the cell

glycogen

readily mobilized storage form of glucose that can be broken down to yield glucose as needed

10-14

branching in glycogen occurs every _____________ glucose units

glycogen phosphorylase

glycogenolysis enzyme that breaks off one glucose-1-phosphate at a time on the branches (phosphorylates glucose)

phosphoglucomutase

enzyme that converts glucose-1-phosphate into glucose-6-phosphate and vice versa

glycogen transferase

enzyme that takes the last three glucose molecules off a glycogen branch and moves them to the end of the branch they were attached to

a-1,6-glucosidase

enzyme that undergoes hydrolysis and is realesed as glucose; gets phosphorylated and enters glycolysis

a-1,4-bonds

bonds that link glucose molecules together in glycogen

a-1,6-bonds

bonds that link glycogen to its branch extending from it

UTP

molecule that glucose-1-phosphate reacts with in the first step of glycogen sysnthesis

UDP-glucose pyrophosphorylase

enzyme that converts glucose-1-phosphate to UDP-glucose in glycogen sysnthesis

glycogen synthase

enzyme that adds UDP-glucose to an existing glycogen branch, forming glycogen + UDP

branching enzymes

makes the alpha 1,6 branches found in glycogen

hydrolyses the alpha 1,4 glycosidic linkage and than attaches those few chained glucose molecules to another spot of the chain and forms a alpha 1,6 bond to finish the branch

glucagon and epinephrine

activate glycogenolysis to synthesize more glucose; occurs during fasting or exercise

insulin

activates glycogen synthase to convert extra glucose into storage as glycogen after meals; glucose also activates glycogen synthase