Section D - Introduction to Metabolism

Dr. Olson

What are the chemical building blocks for our cells and their metabolism?

Macronutrients

What is the main function of Proteins?

Proteins provide essential Nitrogen, Carbon, electrons, and AAs that the body cannot synthesize on its own

What is the main function of Carbohydrates?

Do we need carbohydrates in our diet?

Carbohydrates provide carbons and electrons

There are NO ‘essential’ carbohydrates required in the diet

What is the main function of Lipids?

Lipids provide carbons, electrons, and essential lipids that the body cannot synthesize on its own

What is responsible for allowing someone to grow from an infant to an adult, thereby accruing increases in fat and protein?

METABOLISM

Metabolism allows us to accrue fat, protein, and all other components that make up our bodies as we grow

What are the two most fundamental metabolic states?

Describe them.

1. Fed State

• Aka the Absorptive State

• Lasts for 2-4 hours after a meal

• Ends when the last nutrient has been absorbed by the intestine

2. Fasted State

• Aka the Post-Absorptive State

• Fasting lasts until food is next consumed

What is Fed Metabolism?

What is the driving hormone in this process?

Fed Metabolism is when food that is consumed gets assimilated and stored for later use

Driving hormone is Insulin

What does the Intestine send to the Liver during Fed Metabolism?

To the Adipose Tissue?

Intestine sends the Liver (1) Glucose and (2) Amino Acids

Intestine sends the Adipose Tissue (1) dietary fat

What does the Liver send to the Skeletal Muscle during Fed Metabolism?

To the Adipose Tissue?

Liver sends the Skeletal Muscle (1) Newly Synthesized lipids and (2) Glucose and AAs

Liver sends the Adipose Tissue (1) Glucose and AAs

What is Fasting Metabolism?

What are the driving hormones in this process?

Fasting Metabolism is when energy that is stored is moved around the body

The driving hormones in this process are Glucagon and Adrenaline

What does the Adipose Tissue send to the Liver during Fasting Metabolism?

To the Skeletal Muscle?

Adipose Tissue sends the Liver (1) Glycerol and Fatty Acids

Adipose Tissue sends the Skeletal Muscle (1) Fatty Acids

What does the Liver send to the CNS during Fasting Metabolism?

To the Skeletal Muscle?

Liver sends the CNS (1) Glucose during Fasting Metabolism

Liver sends the Skeletal Muscle (1) Ketones during Fasting Metabolism

What does the Skeletal Muscle send to the Liver during Fasting Metabolism?

Skeletal Muscle sends the Liver (1) Amino Acids during Fasting Metabolism

What are the general reactants and products of Glycolysis?

Gluconeogenesis?

Beta-Oxidation?

Krebs Cycle & ETC?

Glycolysis — Glucose to Acetyl CoA

Gluconeogenesis — Glycerol and AAs to Glucose

Beta-Oxidation — FAs to Acetyl CoA

Krebs Cycle & ETC — Acetyl CoA to CO2, H2O, and ATP

What is Metabolism?

How is it regulated?

All chemical processes that occur in the living cell to maintain life

These processes are regulated by extracellular signals from hormones, growth factors, and Cytokines

What are the two classifications of metabolic pathways?

1. Catabolic — energy rich to energy poor; energy is captured, usually in the form of ATP

2. Anabolic — synthesis of complex molecules from precursors; requires energy input, usually in the form of ATP

What is meant when catabolic reactions ‘pay’ for anabolic reactions?

The energy they capture is used to ‘pay’ / contribute to anabolic reactions, thereby allowing the synthesis of ATP in coupled reactions

How does free energy explain metabolism?

Free energy changes of coupled reactions are additive

This is what makes metabolism possible!!

How is Catabolic Metabolism carried out in our bodies?

Carried out by flux through the Krebs Cycle and ETC

Glucose —> Pyruvate (puts off ATP)

Pyruvate and Fatty Acids —> Acetyl CoA

Acetyl CoA —> into the Krebs Cycle —> release of CO2, e-, ATP, and H2O

Which two processes are used to support Anabolism?

1. Glycolysis

2. Krebs Cycle

Which side-products are made in the conversion of Glucose to Pyruvate?

1. UDP-sugars

2. ATP

3. Ribose-5-Phosphate

4. NAD, NADP

5. Nucleic Acids

6. Serine, Sphingolipids

What products are made in the conversion of Acetyl CoA through the Krebs Cycle?

1. Amino Acids

2. Citrate

3. Fatty Acids

4. Cholesterol

What is required for us to grow and proliferate?

What specific things does this allow for?

We require flux through anabolic pathways to grow and proliferate

Specifically, it allows us to:

• Synthesize new membranes and organelles

• Synthesize new proteins and enzymes

• Provide substrates for post-translational modification

What five main survival activities require ATP?

1. Maintaining membrane gradients

2. AT of solutes against their conc. gradient

3. Muscle contraction

4. Membrane trafficking and secretion

5. Cellular turnover

Which tissues (with a reference of a 72kg male) have the highest metabolic demand?

1. Liver — 18 moles of ATP / day

2. Resting Skeletal Muscle — 17 moles of ATP / day

3. Brain — 17 moles of ATP / day

4. Heart — 10 moles of ATP / day

5. Kidneys — 7 moles of ATP / day

What energy resource do the Kidney and Brain prefer?

They prefer Glucose (they are not very metabolically flexible)

Which substrates can the Liver, Heart, and Skeletal Muscle use?

Can use both Glucose and Fat, but they mainly switch from Glucose to Fat when going from Fed to Fasting (metabolically flexible)

Why are the Liver, Heart, and Skeletal Muscle referred to as being metabolically flexible?

They change energy substrate depending on availability

How do Skeletal Muscle, Liver, and the Heart sense when to switch the substrate that they are oxidizing?

Changes in Insulin levels and Nutrient Transporters