FSHN 350 - Carbohydrates (Unit 2.1)

What are the pathways of carb metabolism

What are the pathways of carb metabolism

• glycogenesis

• glycogenolysis

• glycolysis

• gluconeogenesis

What is Glycogenesis

• making glycogen from glucose

What is Glycogenolysis

• break glycogen into glucose

What is Glycolysis

• breakdown of glucose into pyruvate

What is Gluconeogenesis

• produce glucose from a non-carb intermediate

Important tissues for glucose metabolism

• liver

• muscle

The liver

• takes up 20% of glucose

• uses GLUT 2 to transport to get into the cell

The muscles

• take up 80% of glucose

• uses GLUT 4 to transport to get into the cell

How is muscle selfish

• once muscle reaches its glucose limit, it stops taking up more -

• once muscle breaks down glycogen into glu, it does not release it into the blood

Process of making G6P

• glucose enters the cell

• phosphate attached to glucose (ATP --> ADP)

• forming G6P

GLUT transporters

• Glu enters the muscle cell via GLUT 4, phosphorylated by hexokinase -- making G6P

• Glu enters the liver cell via GLUT 2, phosphorylated by glucokinase -- making G6P

Enzymes that make G6P

• hexokinase in the muscle

• glucokinase in the liver

• both phosphorylate glucose into G6P

3 fates of G6P

• G6P --> glycogen (glycogenesis)

• G6P --> back to glucose (glycogenolysis)

• G6P --> glycolysis

What, where and when of Glycogenesis

• glucose --> glycogen

• in muscles and liver

• when in periods of energy excess

• anabolic

• consumes energy

Steps of Glycogenesis with Enzymes

Glucose --(a-b)----> G6P ---(c-e)----> Glycogen a - hexokinase (muscle) b - glucokinase (liver) c - glycogenin d- glycogen synthase e - branching enzyme

What are the steps of Glycogenesis

1. glucose --> G6P

2. G6P --> G1P

3. G1P --> UDP-glucose

4. UDP-glucose + glycogenin = Glycogen (short chain of Glu)

5. Glycogen chains extended w/ glycogen synthase

6. Glycogen adds branching via branching enzyme

Glycogenin

• enzyme in glycogenesis that attaches to UDP-glucose to make a short glu chain

• attaches via α 1-4 bonds

Glycogen synthase

• enzyme that extends the short glu chain (glycogen chain)

• extends via α 1-4 bonds

• when G6P conc. increase, conc. of Glycogen synthase increase, meaning more glycogen is going to be made

Branching enzyme

• enzyme that creates branching points after glycogen has been created

• creates branches via α 1-6 bonds

Regulation of Glycogenesis

• G6P inhibits hexokinase in muscle (negative feedback)

• G6P does NOT inhibit glucokinase in liver

• G6P increases Glycogen synthesis

• Epi and glucagon inhibit Glycogen synthesis

• insulin directly regulates glucose uptake in muscle (via GLUT 4)

• insulin indirectly regulates glucose uptake in liver

• insulin increases activity of glucokinase

• insulin activates glycogen synthase

When would we be using Glycogenolysis

• when we need to break glycogen into glucose

• fasting, starving, working out

What, where and when of Glycogenolysis

• glycogen --> glucose units

• in liver and muscle

• when in periods of energy deficit

• catabolic

• Glycogen phosphorylase will use a phosphate to take Glu off, making G1P

Glycogenolysis (muscle)

• Glycogen --> G1P --> G6P --> Glycolysis

• muscle does not want to give up any Glu so it won't go back to Glu but will go to Glycolysis

Glycogenolysis (Liver)

• Glycogen --> G1P --> G6P --> Glycolysis

• Glycogen --> G1P --> G6P --> Glucose

• will make glucose when the body needs more

• liver is the master Glu regulator

Insulin and glucagon in the pathways

• insulin increases Glycogen synthase (make glycogen)

• glucagon and epi increase Glycogen phosphorylase (make G1P)

What, where and when of Glycolysis

• break down Glu into pyruvate

• cytoplasm

• when in periods of energy demand

• functions in anaerobic and aerobic conditions

• catabolic

• yields energy

Glycolysis steps (investment phase)

1. Glucose ---(ATP-->ADP)---> G6P

2. F6P ---(PFK)---> F1,6BisP

3. F1,6BisP--> 2 G3P carbon molecules

• 2 mol ATP invested to make 2-G3P

How is PFK regulated

• AMP + (positive feedback, high conc. of AMP, b/c ATP broken down into AMP, so we need more ATP)

• ATP - (negative feedback, high conc. of ATP, so stop making so much)

Glycolysis steps (payoff phase)

6. make ATP from NAD+ ---> NADH

7. make ATP via substrate level

8. making pyruvate + ATP via substrate level

• we use pyruvate kinase to make pyruvate

Product of Glycolysis

• 4 ATP

• 2 NADH

• 2 pyruvate

Regulation of Glycolysis

• AMP -- always increase

• Insulin - increase

• F1,6BisPhosphate -- increase

• ATP -- always decrease

• Citrate -- decrease

• Acetyl CoA -- decrease

How to get electrons into the mitochondria

• Malate-Aspartate shuttle

• Glycerol-Phosphate shuttle

Malate-Aspartate shuttle

• e- passed from NADH to oxaloacetate (OAA), forming malate

• malate easily enters mitochondria

• malate gives e- to new NAD and forms NADH (in the mitochondria)

• NADH goes to the ETC to make ATP

Glycerol-Phosphate shuttle

• e- passed from NADH to DHAP, forming glycerol-phosphate

• glycerol-phosphate easily enters mitochondria

• glycerol-phosphate gives e- to new FAD and forms FADH (in the mitochondria)

• FADH goes to the ETC to make ATP

Liver overview

• Glu enters -- via GLUT 2

• Glu phosphorylated -- via glucokinase (GK)

• insulin activates (GK)

• insulin activates glycogen synthase

• Glycogen phosphorylase -- break Glycogen into G1P

• Glu-6-Phosphatase -- breaks down G6P into Glu

Muscle overview

• Glu enters -- via GLUT 4 (insulin dependent)

• Glu phosphorylated -- via hexokinase (HK) inhibited by G6P (negative feedback)

• G6P has negative feedback on HK

• insulin activates (HK)

• insulin activates glycogen synthase

• Glycogen phosphorylase -- break Glycogen into G1P

Liver story (Glycogenesis)

• Glu enters the cell via GLUT 2

• Glu gets phosphorylated by glucokinase, making G6P

• G6P converted to G1P

• G1P ultimately uses Glycogenin to make a Glu chain

• Glycogen chain extended with Glycogen synthase

• Glycogen branches out with the branching enzyme

• the presence of insulin will activate GK and glycogen synthase

Liver story (Glycogenolysis)

• Glycogen broken down by glucose phosphorylase into G1P

• G1P --> G6P

• G6P --> Glu via Glucose 6 phosphatase

• glucagon receptors help with the release of Glu

what does high G6P mean?

• a lot of G6P means a lot of glycogen can be formed, so a lot of glycogen synthase is going to be needed

Liver story (Glycolysis)

• Glycogen broken down by glycogen phosphorylase into G1P

• G1P --> G6P

• G6P --> Glycolysis

Muscle story (Glycogenesis)

• Glu enters the cell via GLUT 4 (insulin dependent)

• Glu gets phosphorylated by hexokinase, making G6P (G6P has negative feedback on HK)

• G6P converted to G1P

• G1P ultimately uses Glycogenin to make a Glu chain

• Glycogen chain extended with Glycogen synthase

• Glycogen branches out with the branching enzyme

• the presence of insulin will activate HK and glycogen synthase

Muscle story (Glycogenolysis)

• cannot make Glu because muscle has no Glucose 6 Phosphatase

Muscle story (Glycolysis)

• Glycogen broken down by glycogen phosphorylase into G1P

• G1P --> G6P

• G6P --> Glycolysis

3 fates of pyruvate

• make Acetyl CoA

• make lactate

• make ethanol

Pyruvate --> Acetyl CoA

• CO2 released

• NADH created (NAD+ --> NADH)

• via PDH enzyme

• inhibited by ATP, NADH and Acetyl CoA

Pyruvate --> Lactate

• NADH --> NAD+

• via LDH enzyme

When do we make lactate

• when the rate of pyruvate formation, exceeds the rate of Acetyl CoA formation

What pathways need NAD to function

• Glycolysis

• TCA

• pyruvate --> Acetyl CoA

Importance of NAD+ in forming lactate

• we need NAD for the TCA

• the pyruvate --> lactate reaction allows for other reactions to occur because NAD+ is produced in this reaction (NADH --> NAD+)

• other reactions: the ones mentioned above

Lactate transportation

• intracellular lactate shuttle

• intercellular lactate shuttle

Intracellular lactate shuttle

• stays in the cell that made it

• lactate goes to mitochondria to undergo oxidation to pyruvate via mitochondrial LDH

Intercellular lactate shuttle

• lactate can enter the circulation and go to other tissues

• via the Cori Cycle

Lactate misconceptions

• it is a waste product produced by metabolism

• is formed only under anaerobic conditions

• is the cause for muscle soreness

• all are wrong

Cori Cycle

• intercellular shuttle

• if rate of lactate production in cell is too high, it ships it out

Cori Cycle story

• lactate accumulates in skeletal muscle and skeletal muscle lacks glucose 6 phosphatase

• it ships the lactate to the liver so the lactate can be converted into Glu via gluconeogenesis

MCT

• intracellular

• lactate enters the mitochondria via the MCT

• lactate then forms pyruvate

• then go to the TCA and make ATP

What, where, when of Gluconeogenesis

• making Glu from non-carb

• liver, kidney, intestine

• when low blood Glu

• consume energy

• yield NADH

When does Gluconeogenesis happen

• when we are fasting

Gluconeogenesis story

• say you ate at 7:00 and then went to bed

• immediately after - the body will break down that food for Glu

• 4 hours after - glycogen stored in the liver will be broken down

• 12-18 hours after - glycogen stores are empty so body goes through gluconeogenesis to increase blood Glu

What enters Gluconeogenesis

• pyruvate

• lactate

• glycerol from mono, di and triglycerides

• glycogenic amino acids

Steps of Gluconeogenesis

• pyruvate --(1+2)--> phosphoenolpyruvate --> reverse to glycolysis --> Fructose 1,6 BisPhosphate --(3)--> Fructose 6 phosphate --> G6P --(4)--> Glucose

Gluconeogenesis enzymes

1. pyruvate carboxylase

2. PEP carboxykinase

3. fructose 1,6 bisphosphatase

4. glucose 6 phosphatase

Regulation of Gluconeogenesis

• opposite of glycolysis

• AMP -

• ATP +

• Citrate +

Pentose phosphate pathway

• detour off glycolysis

• NO ATP made

• produce NADPH and R5P

• high after a carb high diet

NADH in pentose phosphate pathway

• used for lipid synthesis

R5P in pentose phosphate pathway

• used for synthesis of nucleotides and nucleic acids

• can lead to increased levels of uric acid

Glycogen storage diseases

1. McArdle's Disease (GSD-V)

2. Von Gierke's Disease (GSD 1)

McArdle's Disease (GSD-V)

• exercise intolerance

• low lactate levels after intense exercise

• happens in skeletal muscle

• no glycogen phosphorylase (so glycogen cannot be broken down when exercising)

Von Gierke's Disease (GSD 1)

• most common glycogen storage disease

• severe hypoglycemia (low blood Glu)

• high glycogen in the liver and kidney

• can lead to an enlarged liver -- hepatomegaly

• can't get rid of glycogen once its formed

• glucose 6 phosphatase is inhibited

• eat lower carb diets to solve issue

Fructose metabolism

• absorption into the cell via GLUT 2

• not insulin dependent

• liver takes 20% Glu and 75% fructose

• fructose --fructokinase--> fructose 1 phosphate

Where does fructose join glycolysis

• fructose enters at the 2-G3P step

• so after the investment phase

• it bypasses the rate limiting step (which has PFK)

Once fat is created the liver can

• burn it

• store it

• package into VLDL

• VLDL carries and ships triglycerides

3 ways fructose increases risk of disease

• increase fatty liver

• increase risk heart disease b/c of VLDL

• increase levels of uric acid

Increase of fructose meaning

• means ATP depletion

• which makes AMP

• AMP creates uric acid

What is uric acid

• risk factor for heart disease and gout

• gout -- painful inflammation

• linked to diabetes

Glucose vs Fructose metabolism

• both use GLUT 2 to enter cell

• both phosphorylated by glucokinase and fructokinase

• fructose dangerous b/c its a fast pathway (b/c it bypasses PFK)

How fructose increase risk of heart disease

• increases gout b/c ATP depletion

• increase VLDL

What does fructose lead to

• it bypasses PFK and increases Acetyl CoA conc.

• this is converted to fat and can lead to:

• obesity, fatty liver and increased VLDL

What is Type 1 diabetes

• the body can not make insulin

What is Type 2 diabetes

• the body can make insulin, it just cannot utilize it

Type 1 effect

• no insulin means:

• GLUT 4 transporters do not work - so tissues starve for Glu

• Glu stuck outside the cells

• people must inject Glu

• lack of insulin = increase break down of fat

• high fate loss = high ketone production (dangerous)

Type 2 effect

• cannot use insulin means:

• Glu cannot get into the cell

What leads to Type 2

• over nutrition leads to type 2

• obesity is the biggest risk factor

• most common type (95% of people get this one)

4 areas impacted by lack of insulin

• fat

• liver

• muscle

• blood

Fat

• increase lipolysis -- breakdown of fat

Liver

• increase hepatic glucose output -- increased Glycogenolysis, so Glu

• increase VLDL -- bad cholesterol

Muscle

• decreased Glu uptake

• decreased glycogen synthesis

Blood

• decreased vasodilation

First step towards diabetes

• insulin intolerance

Insulin intolerance effects

• less Glu taken by insulin

• so body makes more insulin to compensate

• increased intolerance leads to increased production of insulin

Insulin intolerance story

• insulin production increases as insulin resistance/tolerance goes up

• Glu will stay normal (during this time) b/c of increased insulin production

• pancreatic beta cells reach Beta Cell Failure as resistance goes up and production cannot meet that

• this is when diabetes occurs

Diagnosing diabetes (3 tests)

• check A1C

• being over 126 mg/dL (fasting)

• being over 200 mg/dL (75g Glu)

A1C test

• the percent of hemoglobin in blood, that is bound to Glu

• over 6.5% = you have diabetes

Fasting test

• test bloog Glu after 8 hrs of fasting

• over 126 mg/dL = you have diabetes

75g Glu test

• take a 75g sugary drink in water, wait 2 hours

• over 200 mg/dL = you have diabetes

Limitations of these tests

• you could have fasting blood Glu and be on your way to diabetes

• there are different reactions for those that drink 75g (different body sizes)

• A1C cannot be used in pregnant moms

• b/c has a wide snapshot range, detects for 3 month range, not for right this second

Glucagon and diabetes

• increases gluconeogenesis

• increases glycogenolysis

Types 1 and 2

• both have increased glucagon

• associated with hyperglucagonemia

What does high glucagon mean for diabetes

• glucagon means more Glu from non carbs and more Glycogen broken into Glu

• all this Glu makes diabetes worse because insulin already can't do it's job

Gestational diabetes

• women that are not diabetes, end up having high blood Glu during pregnancy