Carbohydrate Meta Flashcards
How quick is carbohydrate digestion and absorbtion?
30-90 mintes
How much monosaccharides can the liver remove from the portal vein
1/3
What are some sources of glucose
- Diet
- gluconeogenic precursors
- glycogen store
What is the fate of glucose in metabolism?
- can be used to produce other carbohydrates (mammoary lactate, ribose for DNA)
- sugar residues for other compounds (glycoproteins)
What cells are very dependent on glucose
- brain
- Rbc
- Nerves
- intestines
- mucosa
What is nomal glucose levels
Upper end: 6mmol/L
Lower end : 4 mmol/L
What are the difference between glycolysis and complete oxidation of glucose?
Glycolysis
- Produces small amount of ATP
- Is an anaerobic process
- occurs in the cytoplasm
Complete oxidation
- occurs in the mitochandria
- Produces alot of ATP
- happens during aerobic conditions
What type of metabolism can occur in muscle cells and why
Muscles can undergo glycolysis, complete oxidation or storage of glycogen
- muscle cells have mitochandria therefore metabolism can go all the way
What type of metabolism can occur is cardiac muscle
- glycolysis –> cytoplasm existent
- Completely oxidation –> yes mitochandria present
What type of metabolism can occur in hepatocytes?
-can do all types (glycolysis, complete oxidation and glycogen storage)
Describe the link between the muscle cells and the liver
- Glucose into the muscle –> G6P (can be converted to glycogen) –> pyruvate
- Pruvate has 2 fates: A. If we are reaching our VO2 max then it is converted into lactate and sent to liver B. Pyruvate can enter the mitochandria where it is converted to oxaloacetate the to citrate (this can occur more effiencient if we are well trained)
- A. Lactate enters the hepatocyte where it is converted into pyruvate where it can be converted into oxaloacetate then citrate –> where it can be converted to fat or CO2
What type of metabolism can occur in red blood
Glucose can only be converted to pyruvate then to lactate because they lack mitochandria
What type of metabolism can occur in the brain
- complete oxidation of glucose BUT cannot store glycogen (big molecule)
- can also oxidize ketones
What type of metabolism can occur in B-cells in pancreas
- complete oxidation of glucose, very effiecient
- High amount of mitochandria
What type of metabolism can occur in adipocytes
- complete oxidation or synthesis of glycerol –> excess glucose to Acetyl CoA –> Fat storage
What organ can raise glucose level
the liver
Do skeletal, cardiac, adipose, brain tissues/cells released glucose to change blood glucose levels?
No, because the respond to the blood glucose changes but do not release glucose into the blood
Why store glycogen in a polymeric form rather than in free form?
- want to store alot while keeping it readily avaible
- Optimized degree of branching and chain length
- more branching than amylopectin
- uses less space and hold more water
What % of storage is glycogen in muscles and liver
muscles - 1%
Liver - 10%
What inhibits glycogensis
- glycogenolysis and maximized glycogen stores
What are the 2 forms of glycogen synthase?
A (GYS1)
B ( GY2)
Describe gycogen sythase A
- found everywhere in the body, RBC, brain, kidney adipose
- more active when phosphorylated
- Used in rapid response to an increase in blood glucose levels in fed state as well exercise
Describe glycogen synthase B
- Only in liver
- Less active when phosphorylated
- ensure that large pools of glycogen avaible for blood glucose concentration
-Lower affinity for UDP- glucose and less sensitive to allosteric activiation by G6P
what activate glycogen phosphorylase
- glucagon
- epinephrine
What is glycogenolysis
use of glycogen when blood glucose levels are low
What increases glycogensis
being in the fed state
What molecules start glycogensis
- high ATP and sugar
- Insulin triggers the increase in glucose uptake
- Glucose enters the cells and transforms to G6P to be used for glycogen storage
- Lactate is perferred to be used as glycogen
What increases glycogenolysis
- fasting state
What triggers glycogenolysis
- Liver is depleted of glycogen
- When no dietary glucose, glycogenolysis is initiated to supply glucose
- Glucagon stimulates in the liver
What is the purpose of glycogen breakdown in the liver?
- To increase blood glucose levels or ATP
What is the purpose of glycogen breakdown in the muscle?
For atp for itself NOT THE BLOOD
What biomolecule is used for glycolysis
G6P
What organs contribute to the increase in blood glucose
- liver and kidney
How is glycogen phosphorylase activated in the skeketal tissue
- Phosphorylation control
- Depending on the ratio of phorsphorylase a:b
- A (more active, not sensitive to ATP) : B ( less active dephosphorylated form)
What activates glycogen phosphorylase in the liver?
- Allosteric control
- Glucagon and epinephrine will bind to recpetor and cAMP will induce a response
- Activating Glycogen phosphorylase
How is the rate of glycogen breakdown determined by enzymes in skeletal muscles?
Depends on ratio of phosphorylase A and B
- Exercise can activate phosphorylase kinase that generate phosphorlyase A to stimulate breakdown of glycogen
Why are NAD+ and NADH important to reactions?
they are central for electron movement
What activates working muscles to stimulate glycolysis
NADH, Pi and ADP+AMP
What is regenerated in lactate formation
NAD+
What is the rate-determining step in aerobic metabolism?
PDH
How much ATP is formed during aerobic respiration?
34
What does an increased rate of glycolysis mean?
it means there is a depletion of NAD+
What tissue generate lactate and alanine
peripheral tissues
What does lactate to pyruvate generate?
NADH for gluoconeogensis
What factors impact weather pyruvate enters the CAC
- availbilty of oxygen
- Metabolic state of the cell
How is pyruvate converted into acetyl CoA
via the PDC
What tranporter carrier pyruvate across the mitochandria
monocarboxylate carrier
What is the product and substrate of the CAC?
acteyl CoA to 2 CO2’s
What molecules inhibit CAC
- pyruvate dehydrogenase activity
- ATP avaibility
- Excess NADH
Why would a cell have more mitochandria
to increase cellular respiration
What cells use the pentose pathway?
RBC, adipocyte, liver, and mammary glands
Where does the pentose pathway occur in the cell?
In cystol
What molecule does the pentose pathway generate
NADPH
How is glucose a regulator?
Regulated the activity of enzymes, transcription, hormone secretion, glucoregulatory neuron activity
How is a glucose a substrate?
Acts a signal molecule to control glucose and energy homeostasis
Where are some of the fates of glucose?
Glycogen stores, brain, adipose, muscle
What is the post prandial fate of monosaccharides?
- On the first pass most monosaccharides will be absorbed by the liver
- insulin will initiate a response for use of monosaccharides for energy, glucose for glycogen stores
Skeletal muscle
- insulin will initiate uptake of glucose via GLUT 4 transporter
- glucose will then be used for energy and for glycogen stores
- fructose will also be absorbed
Adipose tissue
- GLUT 4 transporter will uptake, glucose will be used for energy, FA, glycerol, TG if excess glc
Cardiac muscle
- GLUT 4 transporter of glucose, glucose will be used for energy and glycogen synthesis
Other
-Glc can be up-taken (1&3) based on needs
Where and how much is the glucose uptaken
- 1/3 up-taken by the liver, high uptake due to GLUT 2 + glucokinase
- 2/3 up-taken by peripheral tissues after insulin secretion
Which cells are insulin dependent?
Skeletal muscles and adipose tissue
Which cells are insulin independent?
Hepatocytes
How glucose transported to the blood stream from GIT?
- Via SGLUT transporters and GLUT transporters
GLUT 2 ( monosaccharide substrates, sites, affinity, capacity)
MS: Glucose, galactose, mannose, and fructose
Sites: Small intestine, B-pancreas and liver
Affinity: low
Capacity: high
GLUT 4 ( monosaccharide substrates, sites, affinity, capacity)
MS: Glucose
Site: Adipose, muscle,
Affinity: //
Capacity: high
Where is insulin released?
B-cells in the pancreas
Where is glucagon released?
A- cells in the pancreas
What does insulin do?
Stimulate hepatic uptake and storage
What response does glucagon have on the liver?
Increase liver output of glucose but can be catabolic
Where are the A and B cells found ?
Islet of langerhans
Explain how glucagon raises blood sugar
- decrease in bloods glucose
- breakdown glycogen into glucose in the liver
- breakdown fats to fatty acids and ketones in the liver (ketogenesis)
- breakdown non carbohydrates to produce glucose (gluconeogensis)
Increases blood glucose concentration
Explain how insulin promotes energy storage?
Raising blood glucose levels
Anabolic effects
- uptake of skeletal muscles and adipose tissue for energy
- convert glucose to glycogen for storage
-promote synthesis of muscle
- promote synthesis of fat
How is GLUT 4 impacted by insulin?
Once insulin binds to its receptor, it send a response to the transporter to move to the membrane of the cell and to bring the extra cellular glucose into the cytoplasm
What does the rate of glucose transport depend on in muscle and adipose tissue?
How long glut 4 is on cell surface and amount
Explain the process of how insulin is secreted.
- glucose enters the cells via GLUT 2 and gets phosphoryl aged by glucokinase
- Pyruvate is made and undergoes the transformation inside the mitochondria (PDH -> A CoA -> CAC)
- the increase of ATP: ADP ratio cause depolarization, which opens up the CA+ channels. Ca2+ fusion of insulin vesicle to be released via exocytosis
How is insulin production coupled with glucose
Via ATP production
What can stimulate insulin production?
GLUCOSE
-certain aa
-Parasympathetic stimulation
-incretin hormones
Does fructose cause an insulin response, why or why not?
Fructose enters cells via GLUT 5 which not present in the pancreas therefore I’ll not initiate a response
What enzymes/transporters senses blood glucose levels?
GLUT 2 and glucokinase/ rate of glycolysis
Explain glucose homeostasis during the fed state
- pancreas will increase insulin production and decrease glucagon production
- increased glucose utilization (glycogenesis and lipogenesis ) and decrease glucose production (gluconeogensis and glycogenolysis )
- muscle will uptake glucose and utilize
Explain glucose homeostasis during the fasted state
- Pancreas will produce glucagon and decrease insulin production
- liver will increase glucose production (lipogenesis and glycogenesis ) and decrease glucose utilization ( gluconeogenesis and glycogenolysis )
- muscle will decrease uptake and utilization
What are normal glucose ranges
4-6mmol/l
70-110 mg/dl
What is insulin resistance?
Increase insulin secretion for the same response in GLUT 4 transporters
What does insulin resistance lead to?
Hyperglycaemia and hyperinsulimeia
What are Catecholamines effect on glucose levels?
Increased glycogenolysis and gluconeogenesis
What are Glucocorticoids effect on glucose levels?
Increased hepatic glucose output & expression of gluconeogenic genes
What are the effects of Tri-iodothyronine (T3) on glucose levels?
Can modulate or amplify many other hormones & actions, increases gene expression for enzymes to regulate metabolism (both anabolic & catabolic systems; INCR BMR)
What happens to glucose metabolism during starvation
- Increased glucagon secretion
- increase glycogenolysis and gluconeogensis
- decreased up p take of glucose by muscles and adipose, switches to fat oxidation
What is glycemic index?
The incremental area under the blood glucose response curve of a 50 g carbohydrate portion of a test food expressed as a percent of the response to the same amount of carbohydrate from a standard food taken by the same subject
What’s the difference between a high glycemic response and a low glycemic response?
Low glycemic response has a smaller more controlled increase in blood glucose but high glycemic response and a high spike in blood glucose filled by a dip which leads to a drop. High glycemic response put pressure on the pancreas to produce more insulin
What is glycemic load?
takes into account BOTH GI and the amount of food in a given serving
GL=GI/100x(gofCHO/serving)
What is the glucose sparing effect?
Glucose uptake by muscle and adipose tissue decreases and switches to lipid fuels
