Carbohydrates Flashcards
what is the basic building block of all carbohydrates?
monosaccharides
what are the 4 types of carbohydrates, based on how many monosaccharides long they are?
- monosaccharides: basic unit
- disaccharides: made up of two monosaccharides
- oligosaccharides: 2-10 monosaccharides long (technically disaccharides are in this category)
- polysaccharides: over ten monosaccharides long
what are the 3 types of monosaccharides?
- gluctose
- fructose
- galactose
where is galactose found?
only in milk!!
what is the most common monosaccharide?
glucose
where is fructose found?
in sugary foods like molasses and berries
what are the 3 types of disaccharides? give what they are made of
- maltose = glucose + glucose
- sucrose = glucose + fructose
- lactose = glucose + galactose
describe digestion of carbohydrates in the mouth
salivary alpha amylase begins to breakdown carbohydrates; the longer in the mouth the more digestion occurs
does the digestion that happens in the mouth really play a large role in digestion of carbohydrates?
no; is negligible
does any digestion of carbohydrates occur in the stomach?
NO!!! the stomach contains NOTHING to digest carbs
describe the 4 steps of carbohydrate digestion in the small intestine
- when chyme enters the duodenum the duodenum secretes cholecystokinin (CCK)
- CCK acts on the pancreas to secrete digestive enzymes (pancreatic alpha amylase which breaks polysaccharides into oligosaccharides)
- oligosaccharidases along the brush border break down oligosaccharides into disaccharides
- disaccharidases along the brush border break down disaccharides into monosaccharides, which can finally be digested
give the 3 disaccharidases and what they do in the small intestine for digestion of carbohydrates
- maltase: breaks down maltose into 2 glucoses
- sucrase: breaks down sucrose into glucose + fructose
- lactase: breaks down lactose into one glucose and one galactose
where does digestion of carbohydrates mostly occur in the small intestine and why?
the jejunum; it is the longest part of the SI
how is absorption of carbohydrates accomplished?
through transporters
list and describe the 2 transporters that are responsible for absorption of carbohydrates into cells of the small intestine from the lumen of the SI
- sodium-glucose symporter: on the brush border; transports one glucose and one galactose into the cells along with 2 sodiums
- GLUT5: also on the brush border; will transport fructose into the cell via facilitated diffusion; nothing else transported into cell along with it
list and describe the 2 transporters that transport carbohydrates out of cells of the SI and into the blood stream for absorption
- GLUT2: transports glucose and galactose out of the cell
2. GLUT5: transports fructose out of the cell
in absorption of carbohydrates, what occurs after glucose, fructose, and galactose are transported out of the cells and into the bloodstream?
glucose, fructose, and galactose enter the hepatic portal system and travel to the liver, where fructose and galactose are converted to glucose
how is transport of glucose across cell membranes accomplished?
through 2 types of glucose transport proteins
what are the 2 types of glucose transport proteins?
- insulin independent
2. insulin dependent
name the 3 types of insulin independent glucose transport proteins
- GLUT1
- GLUT2
- GLUT3
name the one glucose dependent transport protein
GLUT4
where is GLUT1 found? (2)
- in small concentrations on every cell
2. in high concentration on erythrocytes and cells in the blood brain barrier
describe GLUT1’s affinity for glucose and what that means
GLUT1 has a high affinity for glucose, which means that is can transport glucose into cells no matter how low the blood glucose concentration is
why is GLUT1 found in high concentrations on erythrocytes and on cells in the blood brain barrier?
because erythrocytes and the blood brain barrier REQUIRE glucose, so they have GLUT1 so they can get glucose no matter what the blood glucose concentration is
where is GLUT3 found?
on neurons in the brain and other neurons
describe GLUT3’s affinity for glucose
also has a high affinity for glucose like GLUT1
where is GLUT2 found? (2)
- on hepatocytes in the liver and
2. on pancreatic cells
describe GLUT2’s affinity for glucose
has a low affinity for glucose, meaning that glucose is only transported when there are high concentrations of blood glucose
when is blood glucose concentration usually high, allowing for GLUT2 to work?
just after a meal, and GLUT2 works because it is found on hepatocytes in the liver and all glucose from the diet goes to the liver first
where is GLUT4 found?
in muscle and adipose cells
when is GLUT4 expressed on muscle and adipose cells?
only when insulin is present
how does GLUT4 work?
glucose will only be transported into muscle and adipose cells when insulin is secreted
when and what causes insulin to be secreted?
insulin is secreted by the pancreas in response to high blood glucose which is sensed due to glucose transport via GLUT2
what is the main effect of insulin and why?
main effect is to lower blood glucose since it is secreted in response to high glucose levels
what are the 2 specific effects of insulin?
- GLUT4 expression (on muscle and adipose cells)
2. activation of metabolic pathways that utilize/store glucose (keep it out of the bloodstream)
when insulin is secreted and blood glucose is high immediately after a meal, what state is the animal in?
Fed State
when is glucagon secreted and what is it secreted by?
glucagon is secreted by the pancreas when insulin is not being secreted
what two things is the pancreas always secreting to regulate blood glucose levels?
insulin or glucagon
what is the main effect of glucagon?
to MAINTAIN blood glucose
what is the specific effect of glucagon?
activation of metabolic pathways that synthesize glucose and release glucose from storage (add removed glucose back to bloodstream for cells that require it)
how long will the fasted state last?
until all body reserves have been used up
what is the main goal of glycolysis?
to convert one molecule of glucose (a 6 carbon molecule) into 2 molecules of pyruvate (3-carbon molecules) for ATP (energy)
where does glycolysis take place and what does this mean?
takes place in the cytoplasm, meaning that any cell can perform glycolysis, do not need organelles like mitochondria to provide energy
what MUST happen in order for glycolysis to take place?
glucose MUST get into the cell
write out the entire process of glycolysis (11 steps)
every time you see this card, get a whiteboard and WRITE IT!!!! does not matter if studying for a quiz or exam or what, just DO IT
name the 4 ways of regulation of glycolysis
- glucose transport
- glucokinase
- phosphofructokinase-1
- pyruvate kinase
for what cells is the glucose transport regulation of glycolysis relevant for? why?
only on cells with GLUT2 and GLUT4 due to their low affinity for glucose meaning they require certain conditions in order for glucose to enter
describe the regulation of glycolysis that occurs via the glucose transporter GLUT2
GLUT2 will only transport glucose into liver and apncreatic cells when there are high concentrations of glucose outside those cells due to their low affinity for glucose; so glycolysis will only occur in those cells when there are high concentrations of glucose
describe the regulation of glycolysis that occurs via the glucose transporter GLUT4
GLUT4 will only tranposrt glucose into muscle and adipose cells when INSULIN IS PRESENT, so glycolysis will only occur in these cells when INSULIN IS PRESENT
describe the affinity for glucose of glucokinase, which catalyzes the first step of glycolysis in liver cells and what this means for glycosis
has a low affinity for glucose, so glycolysis will only be initiated in these cells when there are high concentrations of glucose inside those cells
describe the affinity for glucose of hexokinase, which catalyzes the first step of glycolysis in all cells except liver cells and what this means for glycolysis
has a high affinity for glucose, so will always be active in the presence of glucose
what does phosphofructokinase-1 do in glycolysis?
converts fructose 6-phosphate into fructose 1,6-bisphosphate in the first committed step of glycolysis
what does it means when we refer to the first committed step of glycolysis?
after the conversion of fructose 6-phosphate into fructose 1,6-bisphosphate, the only pathway that can now occur is glycolysis, the product must move on in conversion to pyruvate
how is phosphofructokinase-1 regulated (2)
- inhibited by a buildup of ATP
2. reactivated by fructose 2,6-bisphosphate
when phosphofructokinase-1 is inhibited by a buildup of ATP, what happens to the glucose that would have entered glycolysis
it is stored as glycogen
can the liver hold all the stored glycogen in the world? what does this mean?
no, so phosphofructokinase-1 is reactivated by fructose 2,6-bisphosphate
when is fructose 2,6-bisphosphate synthsized?
when insulin is present
what does pyruvate kinase do?
converts phosphoenol pyruvate into pyruvate in the final step of glycolysis
how is pyruvate kinase regulated (2)
- activated by fructose 1,6-bisphosphate becauase products are now committed to glycolysis
- inhibited by glucagon
how much ATP is produced by glycolysis?
4 ATP
how much ATP is used by glycolysis?
2 ATP
how much ATP is 1 NADH + H+ molecule worth?
1 NADH + H+ is worth 2.5 ATP
how much ATP comes from the NADH + H+ molecules produced in glycolysis?
2 NADH + H+ molecules x 2.25 = 5 ATP
how much NET ATP is produced from one molecule of glucose undergoing glycolysis? is this a lot?
net 7 ATP from one molecule of glucose, which isn’t a lot
what is glycogen? (2)
- a complex polymer of glucose molecules
2. the storage form of glucose in the LIVER and MUSCLE
where is the glucose chain attached in glycogen?
to glycogenin
what is glycogenin?
a core protein where glucose attaches in glycogen
why is glycogen highly branched?
to allow miltiple glucoses to be able to attach for storage and use
describe the structure of glycogen
chain of glucoses that are linked via alpha 1,4-linkages on the straight chain and glucoses are linked by alpha 1,6-linkages at the branched points
why does the liver store glucose as glycogen? she’s selfless
to be able to releace glucose into the bloodstream during the fasted state to maintain blood glucose levels (the selfless. altruistic angel)
how much glycogen does the liver store?
enough to maintain blood glucose levels during an overnight fast
why does the muscle store glucose as glycogen? selfish
for a quick energy soure when needed, selfish
when do both the liver and muscle store glucose as glycogen?
after a meal, in the fed state
give the 4 steps of the glycogenesis pathway
- glucose in coverted to glucose 6-phosphate by glucokinase in the liver and hexokinase in the muscle and the conversion input of one ATP to one ADP
- glucose 6-phosphate is converted to glucose 1-phosphate by phosphoglucomutase
- glucose 1-phosphate is converted to UDP-glucose by UDP-glucose phosphorylase and the conversion input of one UDP to PPi
- UDp-glucose is converted to (Glucose)n+1, or added to glycogen chain, by glycogen synthase and the input conversion of (Glucose)n to UDP
what is UDP glucose?
the primed glucose that is ready to be added to an existing glycogen chain
how does glycogen synthase work?
only adds glucose to existing glycogen chain at alpha-1,4-linkages
since glycogen is highly branched, what else is required in the glycogenesis pathway?
branching enzyme
how does branching enzyme work?
once a glucose chain is at least ELEVEN glucoses long, a segment of SEVEN glucoses will be removed and will be added to another chain at an alpha-1,6-linkage that is itself at least 4 glucoses away from an existing branch
what creates chains in glycogen?
alpha-1,4-linkages
what creates branches in glycogen?
alpha-1,6-linkages
in what two ways is glycogenesis regulated?
- through glucose transport
2. through glycogen synthase
what must happen in order for glycogenesis to occur?
glucose MUST get into the cell
describe how glycogenesis is regulated via glucose transport in liver cells
GLUT2 has a low affinity for glucose, so glucose will only get into the cell when there are high concentrations of blood glucose, so glycogenesis will only happen when there is high blood glucose (Fed state)
describe how glycogenesis is regulated via glucose transport in muscle cells
GLUT4 is insulin dependent, so glucose will only enter muscle cells when insulin is present, so glycogenesis will only occur in these cells when insulin is present (Fed state)
will glycogenesis happen in the Fasted state?
NO!! glycogenesis will only occur in the Fed state
describe how glycogenesis is regulated via glycogen synthase
- glycogen synthase in inactive when it is phosporylated, so the enzyme protein phosphatase-1 (PP1) dephosporylates it to become active
- conversely, protein kinase A (PKA) phosphorylates glycogen synthase to inactivate it
when is protein phosphatase-1 activated? what does this indicate and what is the result?
by insulin, in the fed state, indicates that glycogenesis can occur and dephosphorylates glycogen synthase
what is protein kinase A (PKA) activated by? what does this indicate and what is the result?
activated by glucagon, indicating a fasted state where glycogenesis should NOT occur, so it phosphorylates glycogen synthase and prevents glycogenesis from occurring
what determines if glycolysis or glycogenesis occurs?
the excess ATP produced by glycolysis inhibits phosphofructokinase-1, which shuttles everything back to glucose-6 phosphate and causes glycogenesis to occur instead
where does glycogenesis occur?
in the cytosol; like glycolysis
what is glycogenolysis?
the breakdown of glycogen
what is glycogen broken down into in the liver through glycogenolysis? what can use this? selfless
glucose, whole body can use
what is glycogen broken down into in the muscle through glycogenolysis? what can use this? selfish
glucose 6-phosphate, only muscles can use
describe the 3 steps of glycogenolysis in the LIVER
- (Glucose)n is converted to glucose 1-phosphate by glycogen phosphorylase, with the input on an inorganic phosphate (Pi) and releasing (Glucose)n-1, or the glycogen chain with one less glucose molecules
- glucose 1-phosphate is converted to glucose 6-phosphate by phosphoglucomutase
- glucose 6-phosphate is converted to glucose by glucose 6-phosphatase, with the input of one H2O and the release of a Pi, then the glucose enters the bloodstream
describe the 2 steps of glycogenolysis in the MUSCLE
- (Glucose)n is covnerted to glucose 1-phosphate by glycogen phosphorylase with the input of an inorganic phosphate (Pi) and the release of (Glucose)n-1
- glucose 1-phosphate is converted to glucose 6-phosphate by phosphoglucomutase, and this glucose 6-phosphate enters glycolysis for energy production in the muscles
what does glycogen phosphorylase do in glycogenolysis?
removes alpha-1,4-linkages
at the same time as the pathway is occurring in glycogenolysis, what is also working?
debranching enzyme
how does debranching enzyme work in glycogenolysis?
when only FOUR glucoses remain on a branch, a chain of THREE are removed and will be added at the end of another chain, while the ONE remaining glucose is release as free glucose to go through glycogenolysis; removes alpha-1,6-linkages
how is glycogenolysis regulated?
through glycogen phosphorylase, using the same enzymes as glycogenesis
describe regulation of glycogen phosphorylase for glycogenolysis
- glycogen phosphorylase is inactive when it is DEphosphorylated, so protein kinase A phosphorylates and activates it
- protein phosphatase-1 dephosphorylates and inactivates glycogen phosphorylase
what causes secretion of protein phosphatase-1 and deactivation of glycogen phosphorylase through dephosphorylation? relate to glycogenesis
the presence of insulin, which indicates that there is extra glucose and glycogenesis occurs instead and PP-1 dephosphorylates and activates glycogen synthase instead
what causes secretion of protein kinase A and activation of glycogen phosphorylase through phosphorylation? relate to glycogenesis
PKA is activated by glucagon (greater effect in the liver) and epinephrin (greater effect in muscle). This indicates that there is a fasted state and glycogenolysis must occur instead of glycogenesis, so PKA also deactivates phycogen synthase by phosphorylation
can glycogenesis and glycogenolysis occur at the same time? why?
nope! they are regulated conversely by the same enzymes. Protein kinase A deactivates glycogenesis and activates glycogenolysis through phosphorylation and protein phosphatase-1 activates glycogenesis and deactivates glycogenolysis through dephosphorylation
what is gluconeogenesis?
biosynthesis of glucose
where does gluconeogenesis occur? (2)
- liver
2. kidney
what is the goal of gluconeogenesis?
to maintain blood glucose
what is the onnly source of energy that can be broken down and stored in anaerobic conditions?
glucose
when does gluconeogenesis occur and where?
when fasting longer than what the liver has glycogen stored for, gluconeogenesis occurs first in the LIVER and if continue on to extreme starvation, gluconeogenesis will occur in the kidneys as well
what are the 3 precursors for gluconeogenesis?
- lactate/lactic acid
- glycerol
- amino acids
when is lactate produced?
due to the anaerobic metabolism of glucose
how is lactate produced?
one glucose is converted to 2 molecules of pyruvate through glycolysis and then the pyruvate is converted to lactate which enters the bloodstream and is removed by the liver
under what conditions/locations is lactate most often produced? (2)
- when exercising anaerobically or during fight or flight response
- in erythrocytes, which are RBCs with no mitochondria, so they use lactate instead
how and when is glycerol produced?
from the breakdown of fats (triglycerides); when fatty acids are removed from glycerol to mobilize fat in the fasted state, glycerol is released from adipose and is removed by the liver (from the bloodstream)
how and when are amino acids produced in the body to be a precursor for gluconeogenesis?
- produced from the breakdown of protein
2. major source of energy during extreme starvation, when there are no more fat stores
what kind of muscle is broken down first to be a precursor for gluconeogenesis? why?
skeletal muscle; least essential. keep heart beating and brain getting energy first
when do the precursors of amino acids and lactate enter gluconeogenesis? where does this occur?
at the first step when pyruvate is converted to oxaloacetate by pyruvate carboxylase with the input of a bicarbonate and the input conversion of one ATP to ADP + Pi; in the mitochondria
when does the precursor glycerol enter gluconeogenesis? where does this occur?
when one glyceraldehyde 3-phosphate is converted into one dehydroxyacetone phosphate by triose phosphate isomerase; in the cytosol
when does gluconeogenesis move out of the mitochondria and into the cytosol?
once pyruvate has been converted to oxaloacetate
how many molecules of each precursor must enter into gluconeogenesis and why?
2 of each because it comes from 2 pyruvate molecules which will eventually become two glyceraldehyde 3-phosphate molecules that then move on
at what kind of steps is gluconeogenesis regulated?
at the steps that differ from glycolysis
by what 4 enzymes is gluconeogenesis regulated? what do these enzymes normally do?
- pyruvate carboxylase, which converts pyruvate into oxaloactate
- phosphoenol pyruvate carboxykianse, which converts oxaloacetate into phosphoenol pyruvate
- Fructose 1,6-bisphosphatase, which converts fructose 1,6-bisphosphate into fructose 6-phosphate
- glucose 6-phosphatase, which converts glucose 6-phosphate into glucose
how does pyruvate carboxylase contribute to regulation of gluconeogenesis?
it is activated by increase in breakdown of fat, which indicates that some time has passed after the last meal so something needs to be done to maintain blood glucose, so this enzyme is activated to start gluconeogenesis
how does phosphoenol pyruvate carboxykinase contribute to regulation of gluconeogenesis? (2)
- it is activated by glucagon and glucocorticoids like cortisol (under stress) and contributes to maintaining blood glucose levels
- it is inhibited by insulin, which indictaes that the body has plenty of glucose, and when inhibited, it by passes the pyruvate kinase reaction on glycolysis to prevent addition of glucose to the bloodstream
how does fructose 1,6-bisphosphatase contribute to regulation of gluconeogenesis?
it is inhibited by fructose 2,6-bisphosphate, which normally activates phosphofructokinase-1 in glycolysis so we can use the glucose we have instead of making more
how does glucose 6-phosphatase contribute to regulation of gluconeogenesis?
it is inhibited by insulin, because now we want to use the glucose, not make it
give the 11 steps of gluconeogenesis
- in the mitochondria, amino acids and lactate enter and 2 pyruvate molecules are converted to 2 oxaloacetates by pyruvate carboxylase and input of a bicarbonate and inpit conversion of one ATP to ADP + Pi
- now in the cytosol, 2 oxaloacetates are converted to 2 phosphoenol pyruvates by phosophoenol pyruvate carboxykinase, input conversion of one GTP to GDP and release of CO2
- 2 phosphoenol pyruvate are converted to 2-phosphoglycerate by enolase and input of H20
- 2 molecules of 2-phosphoglycerate are converted 2 3-phosphoglycerates by phsophoglycerate mutase
- 2 3-phosphoglycerates are converted to molecules of 1,3-bisphosphoglycerate by phosphpglycerate kinase and input conversion of one ATP to one ADP
- 2 molecules of 1,3-bisphosphoglycerate and glycerol if it is the precursor are converted to 2 molecules of glyceradehyde 3-phosphate by gluceraldehyde 3-phosphate dehydrogenase and input conversion on one NADH + H+ to NAD+ and and Pi is released
- one of the glyceraldehyde 3-phosphate molecules is converted to dihydroxyacetone phosphate by triose phosphate isomerase
- one molecule of glyceraldehyde 3-phosphate and one molecule of dihydroxyacetone phosphate is converted to 1 molecule of fructose 1,6-bisphosphate by aldolase
- fructose 1,6-bisphosphate is converted to fructose 6-phosphate by fructose 1,6-bisphosphatase
- fructose 6-phosphate is converted to glucose 6-phosphate by phosphoglucose isomerase
- glucose 6-phosphate is converted to glucose by glucose 6-phosphatase with the input of H2O and release of a Pi
why is the normal blood glucose range so narrow?
because major deviations can cause death
why do ruminants have a lower normal blood glucose range?
a majority of the carbs from their diet are not broken down to glucose so ruminants rely solely on gluconeogenesis
compare the blood glucose range of a chicken to other animals
much higher and no one knows why
where does blood glucose come from? (3)
- dietary carbohydrates in the fed state
- liver glycogen in the fasted state
- gluconeogenesis in the fasted state
does muscle glucose 6-phosphate contribute to blood glucose?
nope
when does glucose become blood glucose?
when it enters the bloodstream
what are the 4 gluconeogenesis precursors that contribute to blood glucose?
- lactate
- amino acids
- glycerol
- proprionate
describe the cyclical nature of lactate contributing to blood glucose
glucose is broken down to lactate in anaerobic conditions and then travels through the bloodstream to the liver where it is converted to glucose which then tracels through the bloodstream and is broken down to lactate again
describe how glycerol contributes to blood glucose
when fat is broken down, glycerol is released which travels through the bloodstream to the liver where it is converted to glucose which travels to cells for use
describe how amino acids contribute to blood glucose
protein in muscle if broken down into amino acids which travel through the bloodstream to the liver where they are converte to glucose which travels through the bloodstream to cells for use
what is the precursor for gluconeogenesis for ruminants and nonruminant herbivores?
propionate
where does proprionate come from?
microbial fermentation
describe how proprionate contributes to blood glucose
proprionate is absorbed from the rumen wall then travels through the hepatic portal vein to the liver where it is converted to glucose and sent to cells for use
in what 5 ways is blood glucose regulated?
- glucose transport
- glucokinase
- insulin
- glucagon
- other hormones like GH, ACTH, and epinephrine
when are the glucose transporters GLUT2 and GLUT4 active?
when trying to lower blood glucose
how do GLUT2 and GLUT4 regulate blood glucose? the abridged version
only active in high concentrations of glucose (GLUT2) and presence of insulin (GLUT4), lower blood glucose by transporting out of bloodstream and into cells
how does glucokinase regulate blood glucose when there are large amounts of blood glucose?
glucokinase will prevent glucose from leaving the cells when blood glucose is high by converting it to glucose 6-phosphate for glycolysis
how does glucokinase regulate blood glucose when there are low amounts of blood glucose?
this means gluconeogenesis or glycogenesis has occured, so glucokinase is inactive and glucose can enter the bloodstream instead of getting used by liver cells
how does insulin regulate blood glucose (generally and then give 3 mechanisms)
lowers blood glucose
- activates GLUT4 to remove glucose from blood
- activates glycogenesis by activating PP-1 and activate glycolysis which will keep glucose from returning to bloodstream
- inhibits gluconeogenesis and glycogenesis which also prevents glucose from returning to blood
how does glucagon regulate blood glucose? (generally and then give 2)
opposite of insulin, maintains blood glucose
- activates gluconeogenesis and glycogenolysis to allow glucose to enter blood
- inhibits glycolysis and glycogenesis, keeps liver and muscles from storing or using glucose
how does growth hormone regulate blood glucose?
enhances gluconeogenesis to provide energy for growth as more glucose enters the bloodstream
how does ACTH regulate blood glucose?
stimulates release of glucocorticoids, like cortisol from adrenal cortex and cortisol enhances gluconeogenesis so glucose enters the blood
how does epinephrine regulate blood glucose?
stimulates/activates glycogen phosphorylase for glycogenolysis and glucose enters the blood
what cells secrete insulin?
pancreatic beta cells
what cells secrete glucagon?
pancreatic alpha cells
