Vet Biochem 4

What Enzymes are in the Small Intestine?

Lipases - break down Triacylglycerides by cleaving Ester linkages

What does the Pancreas secrete?

Lipase

What does the Liver secrete?

Bile

What does the Liver secrete?

Bile

Describe Lipid Absorption.

Free Fatty Acids and Monocylglycerides are diffused across the SI membrane and re-esterfied to form new Triacylglycerides

Describe Transport of Lipids.

Lipoproteins (Triacylglycerides and Cholesterol packaged) are formed as Chylomicrons. They are taken up by Lacteals → Lymphatic Vessels → Veins → Arteries → Capillaries.

What is a Triacylglycerol?

• Glycerol backbone

• Ester linkage

• 3 Fatty Acids

Describe Lipid Digestion.

Bile emulsifies Fat to increase surface area for Enzymes. Lipase breaks down Triacylglycerides into Monocylglycerides and Free Fatty Acids.

What are the major Bile Acids/Conjugates?

• Cholic Acid/Chenodeoxycholic Acid

• Glycocholic Acid/Glycochenodeoxycholic Acid

• Taurocholic Acid/Taurochenodeoxycholic Acid

What are the Lipoproteins from Lowest to Highest Density?

Chylomicrons → VLDL → IDL → LDL → HDL

What are the Characteristics of Chylomicrons?

• Low Protein (1.5-2.5%)

• High Fat (84-89%)

What activates Lipoprotein Lipase?

Insulin

What do Adipose Cells do?

• Store Triacylglycerides then release them as Free Fatty Acids

• Have receptors to detect Insulin and Glucagon which signal release of Fatty Acids by hormone-sensitive Lipase

What does the Liver do to Fatty Acids?

Absorbs them from Blood and packages them into VLDL with Cholesterol

Where do Gluconeogenesis and Lipogenesis occur?

Liver

What is the process that turns Glucose into Fatty Acids?

1. Excess Glucose → Glycogen

2. Glycogen stores filled: Excess Glucose → Fatty Acids

Describe the Exogenous Pathway of Fat Metabolism.

1. Dietary fats and cholesterol enter the small intestine.

2. Bile acids from the liver/gallbladder emulsify fats → form micelles.

3. Micelles deliver fatty acids + cholesterol into intestinal epithelial cells.

4. Inside cells, they are reassembled into triacylglycerols and packaged as chylomicrons.

5. Chylomicrons enter the lymph, then the bloodstream.

6. In blood, lipoprotein lipase (LPL) breaks down triacylglycerides into fatty acids.

7. Fatty acids are taken up by adipose tissue (storage) and muscle cells (energy).

8. Leftover chylomicron remnants (cholesterol-rich) return to the liver.

Describe the Endogenous Pathway of Fat Metabolism.

1. The liver produces cholesterol and packages it into VLDL (very low-density lipoproteins).

2. VLDL enters the bloodstream.

3. LPL removes triglycerides from VLDL → turns into IDL (intermediate-density lipoprotein).

4. IDL is further processed → becomes LDL (low-density lipoprotein).

5. LDL delivers cholesterol to exrahepatic (body) cells.

What returns excess Cholesterol to the Liver?

HDL

What is the first step for Fatty Acid Oxidation?

Fatty Acid + ATP → Acyl CoA + AMP

What carries Acyl groups across the Mitochondrial Membrane?

Carnitine

Describe the process of Carnitine carrying Acyl groups through Mitochondria.

1. Outside Mitochondria: Carnitine + Acyl CoA interact via Carnitine Palmitoyl Transferase I, producing Coenzyme A + AcylCarnitine

2. Coenzyme A + AcylCarnitine diffuse across via Carnitine Carrier Protein

3. Inside Mitochondria: Coenzyme A + AcylCarnitine interact via Carnitine Palmitoyl Transferase II, producing Carnitine + Acyl CoA

4. Carnitine + Acyl CoA diffuse across via Carnitine Carrier Protein

Describe the Beta Oxidation of Fatty Acids.

1. Fatty Acyl CoA → Trans-delta2-enoyl-CoA using Acyl CoA Dehydrogenase, turning FAD into FADH2

2. Trans-delta2-enoyl-CoA → 3-L-Hydroxyacyl-CoA using Enoyl-CoA Hydratase and H2O

3. 3-L-Hydroxyacyl-CoA → B-Ketoacyl-CoA using 3-L-Hydroxyacyl CoA Dehydrogenase, turning NAD into NADH

4. B-Ketoacyl-CoA → Fatty Acyl CoA (2 atoms shorter) + Acetyl CoA using B-Ketoacyl-CoA Thiolase and CoASH

5. Fatty Acyl CoA (2 atoms shorter) + Acetyl CoA → Fatty Acyl CoA

6. FAD → FADH2

7. FADH2 interacts with ETFox → FAD + ETFred

8. ETFred interacts with ETF Ubiquinone Oxidoreductase(ox) → ETFox + ETF Ubiquinone Oxidoreductase(red)

9. ETF Ubiquinone Oxidoreductase(red) interacts with Q → ETF Ubiquinone Oxidoreductase(ox) + QH2

10. QH2 interacts with Mitochondrial ETC → Q

Where does Beta Oxidation of Fatty Acids occur?

Mitochondria

Fatty Acids to be degraded are linked to CoA in an ATP-dependent reaction. True or False?

True

Fatty Acyl groups are transported into the Mitochondrion via a _____________ for Oxidation.

Carnitine Shuttle

Each round of Mitochondrial Beta Oxidation produces ________________.

• FADH2

• NADH

• Acetyl CoA

• Fatty Acyl CoA (2 atoms shorter)

More enzymes are needed to oxidize Unsaturated Fatty Acids. True or False?

True

The Propionyl-CoA produced by the oxidation of odd-chain Fatty Acids is converted to __________.

Succinyl CoA

What oxidizes Long-chain Fatty Acids, producing H2O2?

Peroxisomes

What are the 3 kinds of Ketone Bodies?

• Acetoacetate

• Acetone

• D-B-Hydroxybutarate

Describe Ketogenesis.

1. Acetyl CoA + Acetyl CoA → Acetoacetyl CoA using Thiolase, releasing Coenzyme A

2. Acetoacetyl CoA → HMG CoA using HMG CoA Synthase

3. HMG CoA → Acetoacetate + Acetyl CoA using HMG CoA Lyase

What does B-Hydroxybutyrate Dehydrogenase do?

Convert Acetoacetate → D-B-Hydroxybutyrate

Describe the conversion of Ketone Bodies to Acetyl CoA.

1. D-B-Hydroxybutyrate → Acetoacetate using D-B-Hydroxybutyrate Dehydrogenase, turning NAD into NADH

2. Acetoacetate → Acetoacetyl CoA using 3-Ketoacyl-CoA Transferase, turning Succinyl CoA into Succinate

3. Acetoacetyl CoA → Acetyl CoA using Thiolase

Acetyl CoA can be reversibly converted to Ketone Bodies in the Liver. True or False?

True

Where does Fatty Acid Biosynthesis occur?

Cytoplasm

Compare Fatty Acid Beta Oxidation and Biosynthesis.

Oxidation:

• Mitochondria

• CoA is acyl group carrier

• FAD is electron acceptor

• L-B-Hydroxyacyl group

• NAD is electron acceptor

• C2 unit product is Acetyl CoA

Biosynthesis:

• Cytoplasm

• ACP is acyl group carrier

• NADPH is electron donor

• D-B-Hydroxyacyl group

• C2 unit donor is Malonyl CoA

Describe Tricarboxylate Transport System.

1. Citrate shuttles through Tricarboxylate Transport System from inside into outside of Mitochondria

2. Outside: Citrate → Oxaloacetate using ATP Citrate Lyase, turning ATP into ADP

3. Oxaloacetate → Malate using Malate Dehydrogenase, turning NADH into NAD

4. Malate → Pyruvate using Malic Enzyme, turning NADP into NADPH

5. Pyruvate shuttles into the inside

6. Inside: Pyruvate → Oxaloacetate using Pyruvate Carboxylase, turning ATP into ADP

7. Oxaloacetate → Citrate using Citrate Synthase, turning Acetyl CoA into Coenzyme A

What Enzyme oxidizes Fatty Acids?

Fatty Acid Synthase

Describe the Biosynthesis of Fatty Acids.

1. Acetyl ACP + Malonyl ACP → Acetoacetyl ACP using B-Ketoacyl ACP Synthase releasing CO2

2. Acetoacetyl ACP → D-B-Hydroxybutyryl ACP using B-Ketoacyl ACP Reductase, turning NADPH into NADP

3. D-B-Hydroxybutyryl ACP → a-B-trans-Butenoyl ACP using B-Hydroxyacyl ACP Dehydrase, releasing H2O

4. a-B-trans-Butenoyl ACP → Butyryl ACP using Enoyl ACP Reductase, turning NADPH into NADP

5. Repeat 6 more times

What is the Temporary Reservoir for Acetyl CoA?

Ketone bodies

What are the requirements for one round of Fatty Acid Biosynthesis?

2 NADPH

What are the requirements for Fatty Acid B Oxidation?

• FAD

• NAD

• H2O

• CoASH

What transfers Acetyl CoA into the Cytosol for Fatty Acid Synthesis?

Tricarboxylate Transport System

What does Fatty Acid Synthesis begin with?

Carboxylation of Acetyl CoA to generate Malonyl CoA

How many reactions does Fatty Acid Synthase carry out?

7

How does Fatty Acid Synthase lengthen a Fatty Acid?

2 carbons at a time

What are Triacylglycerols synthesized from?

Glycerol and Fatty Acids

What are the consequences of excess Fat in Animals?

• Reduced life expectancy

• Diminished quality of life

• Chronic Inflammation

• Kidney dysfunction

• Respiratory disorders

• Skin disorders

• Orthopedic disease

• Cancer

• Metabolic and Endocrine disorders

What are the roles of LDL and HDL?

LDL: transports Cholesterol from Liver to cells/tissues, “Bad” Cholesterol

HDL: absorbs excess Cholesterol and removes it from body, “Good” Cholesterol

Cholesterol Synthesis is regulated by the activity and amount of _____________.

HMG CoA Reductase

The LDL Receptor keeps circulating Cholesterol low or high?

Low

What inhibits and activates Acetyl CoA Carboxylase during Fatty Acid Metabolism?

• Inhibited by AMP, cAMP-dependent Phosphorylation, and Palmitate

• Activated by Insulin-dependent Dephosphorylation and Citrate

What inhibits Carnitine Palmitoyl Transferase I during Fatty Acid Metabolism?

Malonyl CoA

What activates Hormone Sensitive Lipase during Fatty Acid Metabolism?

cAMP-dependent Phosphorylation

Proteins involved in response to physiological activity typically have ________ half-lives than Enzymes involved in structural roles.

Shorter

What ensures Proteins get removed when they are not longer needed?

Ubiquitination Reactions

Describe the Ubiquitination Reactions?

1. Ubiquitin + Ubiquitin-activating Enzyme (E1) → Activated Ubiquitin, turning ATP into AMP + Pi

2. Activated Ubiquitin→ Conjugated Ubiquitin, turning Ubiquitin-conjugating Enzyme (E2) into Ubiquitin-activating Enzyme (E1)

3. Conjugated Ubiquitin→ Ubiquitin-NH-Lys-Condemned Protein using Ubiquitin-ligase Enzyme (E3), turning a Condemned Protein into Ubiquitin-conjugating Enzyme (E2)

What connects Ubiquinone to a Condemned Protein?

Lysine

What connects Ubiquitin to NH?

Isopeptide bond

Extracellular and Intracellular Proteins may be digested by _________.

Lysosomal Proteases

Proteins that need to be degraded are first conjugated into _____________.

Ubiquitin

What does a Proteasome do?

Unfolds Ubiquitinated Proteins in an ATP-dependent process and proteolytically degrades them

What does the Carbon Skeleton of an Amino Acid produce?

• CO2

• H2O

• Glucose

• Acetyl CoA

• Ketone Bodies

What do Amino Acids produce?

• Carbon Skeleton

• NH3

Describe Transamination.

1. Amino Acid + a-Ketoglutarate interconverts with a-Keto Acid + Glutamate using Transaminase

2. Glutamate + Oxaloacetate interconverts with a-Ketoglutarate + Aspartate using Glutamate Dehydrogenase, turning NADP into NADPH

What does Oxidative Deamination of Glutamate release?

Ammonia

If an animal has no ready access to Water, what happens to Ammonia?

Ammonia → Urea → Uric Acid

If an animal has a lot of access to Water, what happens to Ammonia?

It is excreted directly without any conversions

Describe the overall Urea Cycle Reaction.

NH3 + HCO3 + Aspartate → Urea + Fumarate, turning 3 ATP into 2 ADP + 2 Pi + AMP + PPi

Describe the entire Urea Cycle.

1. Glutamate (from Transamination) → 2 ATP + Bicarbonate + NH3

2. 2 ATP + Bicarbonate + NH3 → Carbamoyl Phosphate + 2 ADP + Pi using Carbamoyl Phosphate Synthetase

3. Carbamoyl Phosphate → Citrulline using Ornithine Transcarbamoylase, releasing Pi

4. Citrulline transports from Mitochondria to Cytosol via shuttle

5. Citrulline → Argininosuccinate using Argininosuccinate Synthetase and Aspartate, turning ATP into AMP + PPi

6. Argininosuccinate → Arginine using Argininosuccinase, releasing Fumarate

• Fumarate → Malate using Fumarase and H2O

• Malate → Oxaloacetate using Malate Dehydrogenase, turning NAD into NADH

• Oxaloacetate → Gluconeogenesis

7. Arginine → Ornithine using Arginase, turning H2O into Urea

8. Ornithine transports from Cytosol to Mitochondria via shuttle

9. Ornithine → Citrulline using Ornithine Transcarbamoylase

Where does the Urea Cycle occurs?

Cytosol and Mitochondria

How many reactions incorporate Ammonia and an Amino Group into Urea?

5

The rate of the Urea Cycle changes with the rate of __________________.

Amino Acid breakdown

What are the Essential Amino Acids?

• Arginine

• Histidine

• Isoleucine

• Lysine

• Methionine

• Phenylalanine

• Threonine

• Tryptophan

• Valine

What are the Non-essential Amino Acids?

• Alanine

• Asparagine

• Aspartate

• Cysteine

• Glutamate

• Glutamine

• Glycine

• Proline

• Serine

• Tyrosine

What is Heme synthesized from?

Glycine and Succinyl CoA

The synthesis of bioactive Amines begins with ________________.

Amino Acid Decarboxylation

What does Arginine give rise to?

Nitric Oxide

What are the Amino Acid derived Neurotransmitters?

• Epinephrine (adrenaline)

• Norepinephrine

• Dopamine

• Serotonin

• GABA

• Histamine

Describe the synthesis of L-DOPA, Dopamine, Norepinephrine, and Epinephrine.

Tyrosine → L-DOPA → Melanin and Dopamine → Norepinephrine → Epinephrine

What is the purpose of Nitrogen Fixation?

Conversion of free Nitrogen to Ammonia via Nitrogenase

How is Ammonia incorporated into Amino Acids?

Glutamate Synthase

What is the only way that Nitrogen is incorporated into food chain?

Root Nodules

Describe the electron flow in Nitrogenase-catalyzed N2 Reduction.

1. Ferredoxin ox → Ferredoxin red using Photosynthesis or Oxidative ETC

2. Ferredoxin red + Fe Protein ox → Ferredoxin ox + Fe Protein red

3. Fe Protein red + MoFe Protein ox → Fe Protein ox + MoFe Protein red, transporting 2 ATP through into 2 ADP + 2 Pi

4. MoFe Protein red + N2 + 8 H → MoFe Protein ox + 2 NH3 + H2

What are the products of electron flow in Nitrogenase-catalyzed N2 Reduction?

• 16 ATP

• 2 Ammonia

Describe the Glutamate Synthase reaction.

1. NADPH + FAD → NADP + FADH2

2. FADH2 + FMN → FAD + FMNH2

3. Glutamine → NH3 + Glutamate, releasing H

4. NH3 channels into a-Iminoglutarate using a-Ketoglutarate

5. a-Iminoglutarate → Glutamate using FMNH2 + H

Describe the Nitrogen Cycle.

1. Atmospheric N2 → Ammonia (Nitrogen Fixation)

• Ammonia → N-containing Biomolecules (Assimilation)

• N-containing Biomolecules → Ammonia (Decomposition)

2. Ammonia → Nitrite (Nitrification)

3. Nitrite → Nitrate

4. Nitrate → Atmospheric N2 (Denitrification)

OR

1. Nitrate → Nitrite using Nitrate Reductase

2. Nitrite → Ammonia using Nitrite Reductase (Ammonification)

3. Ammonia → Atmospheric N2 using Nitrogenase

What are the only ways for the Brain to get Energy?

• Ketone bodies

• Glucose

What ATP sources does the body use in order during exercise?

1. ATP

2. (Phosphocreatine) ATP from Phosphagen

3. ATP from Anaerobic Glycolysis

4. (Oxidative Phosphorylation) ATP from Aerobic Catabolism using Glycogen and Glucose

5. ATP from Aerobic Catabolism using Lipids

What is Hexokinase?

• Present everywhere

• Glucose → G6P

• Needs a little bit of Glucose to be activated

What is Glucokinase?

• Only in Liver

• Specific to Glucose

• Allows local control of Metabolism

• Needs a lot of Glucose to be activated

What are the fates of G6P?

• Glycogen

• Glucose

• Acetyl CoA

• R5P

Describe the Cori Cycle.

1. Glucose from Liver transports through the Blood into the Muscle

2. Muscle: Glucose → Glycogen

3. Glycogen → Lactate via Glycogenolysis and Glycolysis, turning Pi + ADP into ATP

4. Lactate transports from Muscle into the Liver

5. Liver: Lactate → Glucose via Gluconeogenesis, turning ATP + GTP into ADP + GDP + Pi

Describe the Glucose-Alanine Cycle.

1. Glucose from Liver transports through the Blood into the Muscle

2. Muscle: Glucose + Glycogen → Pyruvate

3. Pyruvate → Alanine via Transamination, turning a-Amino Acid into a-Keto Acid

4. Alanine transports from Muscle into the Liver

5. Liver: Alanine → Pyruvate, releasing Ammonia (which releases Urea)

6. Pyruvate → Glucose via Gluconeogenesis

What converts Pyruvate into Alanine?

Muscle Aminotransferases

The major metabolic pathways for Glucose, Fatty Acids, and Amino Acids center on ______________.

Pyruvate and Acetyl CoA

What is the primary fuel for the Brain?

Glucose

Muscles can generate ATP only aerobically. True or False?

False

Anaerobically and Aerobically

What makes all types of fuel available for other tissues?

Liver