BCMB 311- Quiz 3

Metabolism is___ + _____

catabolism, anabolism

Define catabolism.

Catabolism→ the breakdown of large molecules into smaller ones. Energy is generally released

Define anabolism.

Anabolism→ the synthesis of large molecules from smaller ones. Energy is generally absorbed

The process of metabolism is a series of consecutive reactions called a metabolic pathway. What two kinds of pathways are there?

Linear and cyclic

Define a linear pathway.

Linear pathway→ the series of reactions that generates a final product different from any of the reactants

Define a cyclic pathway.

Cyclic pathway→ the series of reactions that regenerates the first reaction

What molecules are broken down to produce ATP? Why is this important?

Proteins, lipids, and carbohydrates

• ATP→primary energy-carrying molecule in the body. Energy from burning food is stored as ATP

Why is the stepwise oxidation of sugar in cells advantageous compared to direct burning in nonliving systems?

Stepwise oxidation involves small activation energies overcome by enzymes→ allows some free energy to be stored in activated carriers

Direct burning has a single large activation energy overcome by extreme heat→ all free energy is released as heat/none is stored in a usable form

Describe ATP hydrolysis.

• Removes 1 phosphate group

• Forms ADP and phosphate

• Releases 7.3 kcal/mol of energy (energetically favorable)

Describe ATP phosphorylation.

• Reverse reaction of ATP hydrolysis

• Adds 1 phosphate group to ADP

• Forms ATP

• Requires 7.3 kcal/mol of energy (not energetically favorable)

What must happen to the molecules we consume to produce energy?

It must be “burned”→oxidized

• Carbon-containing molecules (sugars, fats, proteins) can be completely oxidized over many steps

What is the most oxidized form of carbon?

CO₂

What is NAD⁺?

NAD⁺→ a coenzyme acting as an oxidizing agent. It causes an oxidation reaction to occur, so the coenzyme is reduced

• When a coenzyme acts as an oxidizing agent, it gains electrons in the form of H (NAD⁺→NADH)

  • Gains 1 H⁺ and 2 e^- becoming the reduced form (NADH)

What is NADH?

NADH→ a coenzyme acting as a reducing agent. It causes a reduction reaction to occur, so the coenzyme is oxidized

• When a coenzyme acts as a reducing agent, it loses electrons in the form of H (NADH→NAD⁺)

What is FAD/FADH₂?

Coenzymes

FAD→ an oxidizing agent

• Gains 2 H⁺ and 2 e^-

FADH₂→ a reducing agent

What is the result of the oxidation of biomolecules in terms of NADH/NAD⁺/FAD/FADH₂?

The reduction of NAD⁺ to NADH and FAD to FADH₂

• These reduced cofactors can be used to generate ATP by donating electrons to oxygen to form H₂O

An Overview of Metabolism: Stage 1→Digestion

Where does digestion begin? What occurs?

Carbohydrates are hydrolyzed into monosaccharides beginning with amylase enzymes in saliva and continuing in the small intestine

An Overview of Metabolism: Stage 1→Digestion

What occurs during protein digestion and where do these events occur?

• Protein digestion begins in stomach→ stomach acid denatures the protein and pepsin begins cleaving the backbone into smaller peptides

• Next, in the small intestine, trypsin and chymotrypsin cleave the peptides into amino acids

An Overview of Metabolism: Stage 1→Digestion

Where and how are triacylglycerols digested?

Triacylglycerols are hydrolyzed by lipases in the small intestines into 3 fatty acids and a glycerol backbone

An Overview of Metabolism: Stage 2→Formation of Acetyl CoA

Triacylglycerols

1. Digestion: Triacylglycerols→fatty acids + glycerol

2. Fatty acid oxidation: Fatty acids + glycerol→Acetyl CoA

An Overview of Metabolism: Stage 2→Formation of Acetyl CoA

Carbohydrates

1. Digestion: Carbohydrates→monosaccharides

2. Glycolysis: Monosaccharides→Pyruvate + released ATP→Acetyl CoA

An Overview of Metabolism: Stage 2→Formation of Acetyl CoA

Proteins

1. Digestion: Proteins→Amino acids

2. Amino acid catabolism→ Pyruvate + Acetyl CoA

An Overview of Metabolism: Stage 3→Citric Acid Cycle

• Converts Acetyl CoA to CO₂

• Produces ATP, NADH, and FADH₂

• Takes place in the mitochondria

Where in the mitochondria does energy production occur?

The area enclosed by the inner membrane called the matrix

An Overview of Metabolism: Stage 4→The Electron Transport Chain

• Occurs in mitochondria→ produces lots of ATP from ADP

• NADH and FADH₂ are oxidized to NAD⁺ and FAD

• O₂ is converted to H₂O

• Process is called “oxidative phosphorylation”→ generates ATP

  • Oxygen accepts electrons from NADH and FADH₂, converting them back to NAD⁺ and FAD

  • When oxygen gains electrons in the form of hydrogen, water is released

  • Phosphorylation: ADP + Pi→ ATP

An Overview of Metabolism: Summary

1. Sugars, proteins, and fats are broken down into basic building blocks (Digestion)

2. Building blocks are broken down into Acetyl CoA (Fatty acid oxidation, glycolysis, amino acid catabolism)

3. Acetyl CoA enters the citric acid cycle→ produces NADH and FADH₂ and releases CO₂ (Citric Acid Cycle)

4. Electron transport chain uses oxygen as final electron acceptor releasing water→ NAD⁺ and FAD (oxidized forms) are regenerated→ ATP is produced via phosphorylation (Oxidative phosphorylation)

Where in the cell do glycolysis and fatty acid synthesis occur?

Cytoplasm

Where in the cell do the citric acid cycle and fatty acid oxidation occur?

Mitochondrial matrix

Where in the cell does oxidative phosphorylation occur?

Inner mitochondrial membrane

Describe the process of fatty acid degradation (oxidation). What enzymes are involved? What is the effect of hormones?

1. Triacylglycerol→ glycerol + 3 fatty acids

• Done by hormone-sensitive lipase (HSL)

  • Activated by epinephrine

  • Inhibited by insulin

2. Break down of fatty acid chains into Acetyl CoA in mitochondria

• Long FA chains broken down into 2-carbon units

What is coenzyme A?

A thiol containing coenzyme that is neither an oxidizing nor a reducing agent (HS-CoA)

What must be done before glycolysis can begin? What is involved?

• Glucose must be transported from the bloodstream to the cytoplasm

  • This is done by Glucose Transporter Protein (GLUT)

  • Glucose is transported into the cell via facilitated transport→ a form of passive transport facilitated by membrane proteins (no energy input required)

  • Must have concentration gradient-: concentration on one side of membrane>concentration on other side of the membrane

What is the role of insulin in regulating glycolysis?

Insulin stimulates glucose uptake by translocating GLUT protein to the plasma membrane

What is glycolysis? Where does it occur? What is produced?

• Main pathway for monosaccharide catabolism (glucose, fructose, galactose)

• All reactions occur in the cytoplasm

• Glucose is oxidized

• NAD⁺ reduced to NADH

• End result is pyruvate

• ATP is produced

• Glycolysis is ANAEROBIC→ produces ATP in the absence of oxygen

What is the net reaction of glycolysis?

Glucose + 2 NAD⁺ + 2 ADP + 2 Pi→ 2 Pyruvate + 2 NADH + 2 H⁺ + 2 ATP

• 2 ATP used, 4 generated→ net production is 2 ATP

True or False: After a meal insulin levels are high which causes hormone-sensitive lipase (HSL) to be activated.

False→ HSL is activated during fasting/low-insulin states to break down stored triglycerides into fatty acids.

True or False: NADH and FADH2 in this form are said to be oxidized.

False→ these are the reduced forms. NAD⁺ and FAD are the oxidized forms

True or False: During glycolysis each glucose produces 2 pyruvates.

True→ glucose (6 carbons) is broken down into 2 pyruvate molecules (3 carbons each)

Glycolysis: Steps 1-5

Steps 1-5→ energy investment phase, where 2 ATP molecules are hydrolyzed

• The 6-carbon glucose molecule is converted into 2 3-carbon segments (step 4)

Glycolysis: Steps 6-10

Steps 6-10→ the energy-generating phase, producing 1 NADH and 2 ATP for each pyruvate formed

What happens to the products of glycolysis?

• Net ATP (2) are used for energy

• 2 NADH are made in cytoplasm→ must be transported to the mitochondria to join the ETC and make ATP

• Fate of 2 Pyruvate depends on O₂ availability

What is pyruvate converted into under aerobic/anaerobic conditions and in fermentation?

• Aerobic: Pyruvate→ Acetyl CoA

• Anaerobic: Pyruvate→ Lactate

• Fermentation: Pyruvate→ Ethanol

Pyruvate conversion: Aerobic

• Pyruvate is oxidized by NAD⁺ in the presence of coenzyme A to form Acetyl CoA

• Pyruvate + HS-CoA + NAD⁺→ Acetyl CoA + CO₂ + NADH + H⁺

• NADH formed needs O₂ to return to NAD⁺, so without O₂ no additional pyruvate can be oxidized

Pyruvate conversion: Anaerobic

• In anaerobic conditions there is an abundance of NADH

• NADH acts as a reducing agent, reducing pyruvate to lactate

• Pyruvate + NADH + H⁺→ Lactate + NAD⁺

  • NAD⁺ can reenter glycolysis at step 6

How does lactate formation relate to what occurs during strenuous exercise?

• During strenuous exercise→ ATP needs are high and not enough O₂ is being inhaled to re-oxidize NADH in the ETC

• The lactate formed by anaerobic pyruvate metabolism builds up in muscle cells→ results in soreness and cramping

How does lactate formation relate to what occurs during a heart attack? What can high blood lactate levels indicate?

• The pain felt during a heart attack is caused by an increase in lactate in the heart and areas near the heart are cut off from oxygenated blood

• A higher-than-normal blood lactate level can indicate lung disease, congestive heart failure, or serious infection

Under low oxygen conditions (hypoxia or vigorous exercise), the main reason pyruvate is converted to lactate is:

– To maintain glucose levels in blood

– To reverse the process of glycolysis

– To maintain NAD level in cytoplasm

– To prevent decrease in pH

To maintain NAD level in cytoplasm

Citric Acid Cycle: Overview

• Main function→ produce reduced coenzymes for ETC

• CAC begins when 2 C of Acetyl CoA react with a 4 C substrate to form a 6 C product (Step 1)

• 2 C atoms are sequentially removed to form 2 CO₂ molecules (Steps 3 and 4)

• 4 molecules of reduced coenzymes (3 NADH and 1 FADH₂) are formed (Steps 3, 4, 6, and 8)

• 1 GTP is produced in step 5 (similar to ATP)

CAC overall reaction

Acetyl CoA + 2 H₂O + 3 NAD⁺ + FAD + GDP + HPO₄^2- → 2 CO₂ + HSCoA + 3 NADH + 3 H⁺ + FADH₂ + GTP

• CO₂ released as gas

• Coenzyme A re-enters the cycle

• Reduced coenzymes enter ETC

  • 3 NADH= 3×2.5 ATP

  • 1 FADH₂= 1.5 ATP

  • 1 GTP= 1 ATP

  • 10 ATP total

• GTP is energy source

CAC: Key enzymes/steps

1. Citrate Synthase

• Inhibited by: ATP, NADH, Succinyl CoA

3. Isocitrate Dehydrogenase

• RATE-LIMITING STEP

• Inhibited by: ATP and NADH

• Activated by: ADP

4. a-Ketogluterate Dehydrogenase

• Inhibited by: ATP, GTP, NADH, Succinyl CoA

How many enzyme complexes are involved in the ETC and where are they located? Why are they located there?

• 4 enzyme complexes (I, II, III, IV)

• Located along the mitochondrial inner membrane

  • Complexes pump protons from matrix to intermembrane space→ forms proton gradient

What occurs in the ETC?

• Electrons from NADH and FADH₂ are donated to enzyme complexes, regenerating NAD⁺ and FAD

• Electrons move from one complex to the next, enzyme complexes use the energy to pump protons

• Protons are pumped from matrix to intermembrane space to create a proton gradient

Describe the movement of electrons in the ETC from NADH and FADH₂.

NADH: Complex I→ Complex III→ Complex IV→ O₂

FADH₂: Complex II→ Complex III→ Complex IV→ O₂

How do the events in the ETC lead to energy production?

• Enzyme complexes transfer electrons from NADH and FADH₂ to O₂

• In the pr

During oxidative phosphorylation, the concentration of protons in the ______ becomes higher than that _________

intermembrane space, inside the matrix