Metabolism Big Picture Flashcards by Shane Hagen

Most of the energy stored in chemical bonds of food is lost as what?

Heat. Only some of the energy can be converted to useful forms of energy to drive anabolic pathways in synthesis, or maintain cell integrity (ion pumps, transport, etc.).

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T or F. Over 24-hs, blood glucose levels are maintained within a relatively narrow range

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Name 4 metabolic pathways and reactions that increase blood glucose levels

(1) Digestion of dietary carbohydrates
(2) Conversion of dietary sugars other than glucose to glucose
(3) Glycogenolysis - the breakdown (-lysis) of glycogen.
(4) Gluconeogenesis - synthesis of glucose [neo - (new); -genesis (synthesis)]

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Name 4 metabolic pathways that use blood glucose

(1) glycolysis
(2) glycogenesis - the synthesis of glycogen (-genesis) in liver, muscle, and other tissues,
(3) the phosphogluconate pathway, and

(4) other minor pathways.
- The sorbitol (or aldose reductase) pathway, does not involve Glc-6-P, and converts glucose to fructose and sorbitol.

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Glucose-6-phosphatase is only found where?

the liver

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What is the main fuel source for adipose tissue?

TAG (triacylglycerol)- broken down to fatty acids during lipolysis

135,000 kcal

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What is the main fuel source for muscle?

Protein- 24,000 kcal

Gylcogen- 480 kcal (Muscle primarily uses glycogen for severe exercise)

May use blood glucose when insulin is elevated (fed state) or during exercise.

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What is the main fuel source for the liver?

Glycogen- 280 kcal

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What is the main fuel source for body fluids (blood and EFC)?

Glucose- 80 kcal

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Where are TAGs found?

TAG’s are primarily stored on adipose tissue, but also found in liver and muscle.

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What are the substrates and end product(s) of gluconeogenesis? (anabolic)

reactants- lactate, alanine, glycerol

products-glucose

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What are the substrates and end product(s) of glycogenesis? (anabolic)

reactants- Glc-1-P, Glc

products- glycogen

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What are the substrates and end product(s) of protein synthesis? (anabolic)

reactants- amino acids

products- proteins

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What are the substrates and end product(s) of lipogenesis? (anabolic)

reactants- Glc, glycerol, actyl CoA

products- fatty acids, TAG

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What are the substrates and end product(s) of glycolysis? (catabolic)

reactants- glucose

products- pyruvate, ATP

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What are the substrates and end product(s) of CAC and ETC? (catabolic)

reactants- acetyl CoA, OAA

products- NADH, ATP, CO2

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What are the substrates and end product(s) of glycogenolysis? (catabolic)

reactants- glycogen

products- glc-1-p, glc

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What are the substrates and end product(s) of proteolysis? (catabolic)

reactants- proteins

products- amino acids

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What are the substrates and end product(s) of lipolysis? (catabolic)

reactants- TAG -> FAA

products- acetyl CoA, glycerol

What are the substrates and end product(s) of the P-gluconate pathway? (catabolic)

reactants- Glc-6-P

products- pentoses, CO2, NADPH ( -> FA)

What are the stages of the feed-fast cycle?

Fed State: The period during a meal, when lots of food is being ingested and digested.

Post-prandial state: The period after eating. Lasts until last meal is digested. (~2 hrs)

Post-absorptive state: period after the last meal has been digested, and the gut is empty. During this period, we need to add fuels back to the blood. Insulin is low, and glucagon is elevated. The insulin glucagon ratio is low. (~6-8 hrs)

The basal state, sometimes called the early fasting state. After an overnight fast. This is the baseline period for most blood tests, example, fasting blood glucose or blood lipids (lipoproteins). (~12 hrs)

Fasting state: several days without eating. This is the period when we switch to ketones as an important source of fuel. (24-72 hrs)

Starved state: period of extended fasting. May last for weeks or until death. (>72 hrs)

Does the brain require glucose?

Only until levels get low enough to use an alternative (ketone bodies from liver- aka during starved state)

What organ is the source of Ketone bodies?

liver (however, it cannot use them for fuel- KBs can go to muscle and brain (sometimes)- to participate in TCA and ATP production)

How does the liver make Ketone bodies?

from fatty acids from adipose resulting from breakdown of TAG

Which tissues need glucose as an energy source?

brain (can also use ketone bodies) | RBCs (can only use glucose)

Which tissues need AAs as an energy source?

muscle, brain, liver (AAs from breakdown of protein in muscle are needed by the liver to maintain blood glucose during times of fasting)

Which tissues need fatty acids as an energy source?

liver (it uses FA to make glucose and KB) FA come from adipose

Which tissues need ketone bodies as an energy source?

muscle, liver (made by and used by), brain

A system where an organ makes a product and uses it is called?

a futile cycle

What are the major fuel sources during the fed state?

glucose, AAs (depends on what you ate), fatty acids, ketone bodies are very low the brain only uses glucose to complete TCA during this state

What are the major fuel sources during the basal state?

glucose, AAs, fatty acids, ketone bodies starting to grow more

What are the major fuel sources during the fasting state (24-72 hrs)?

glucose (although still replenished by gluconeogenesis when glycogen storage is low) is starting to drop, increase in AAs and fatty acids and ketone bodies (RBCs and brain can't use still) triglycerides release glycerol to produce glucose

What are the major fuel sources during the starving state (>72 hrs)?

Ketone bodies can now be used by the brain (spill over the blood brain barrier). Using ketone bodies is good so the body can conserve AAs for protein synthesis. I.e. the AAs used during this state is actually less than during the fasting state

What is glycogen?

stored glucose (it is a precursor of blood glucose)

What is fat?

Major energy storage

Is protein a stored energy source?

Yes

What are the main events occurring during fed state?

- increased glycogen storage in the liver - increased TAG in adipose - brain using glucose for ATP production

What are the main events occurring during basal state (~12 hrs)?

- in adipose, TAG breaks down to FA, which go to muscle to participate in the TCA to produce ATP and to the liver to make KB (very little amounts still and only travel to muscle to participate in TCA) - in the liver, glycogen breaks down to glucose to go to brain for TCA and ATP production - RBCs secrete lactate to the liver to help in glucose generation - proteins in muscle break down to AAs to travel to liver to make glucose

In the starved state, what is different about KB production

still made in liver from FA from adipose, but main destination is the brain now, not muscle

What are the effects of insulin in muscle?

- increase in Glc uptake and use | - increase in protein synthesis (because the breakdown of proteins would release AAs to go liver for glucose production)

What are the effects of insulin in adipose?

- increased lipogenesis, glc uptake | - decreased lipolysis

What are the effects of glucagon in adipose?

- increased lipolysis

What are the effects of insulin in liver?

- decreased glc output, gluconeogenesis, glycogenolysis, ketogenesis - increased glycogenesis, protein synthesis

What are the effects of glucagon in liver?

- increased glc output, gluconeogenesis, glycogenolysis, ketogenesis - decreased glycogenesis

T or F. glucagon affects protein synthesis in the liver