Exam 2: MCB 150 Biology

Cellular Respiration

Catabolic reactions

the breakdown of larger molecules into smaller ones

Anabolic (Biosynthetic) reactions:

synthesis of larger molecules from smaller precursor molecules

Redox reactions

Oxidation: the removal of one or more electrons from an atom or molecule 

Reduction: The addition of one or more electrons to an atom or molecule

Cellular respiration: Main goal, Formula, and three steps

Main goal: To make ATP

Formula: C6H12O6 + 6 O2—--- 6 CO2 + 6H2O + ATP 

Steps:

1. Glycolysis

2. Breakdown of Pyruvate and Citric acid cycle

3. Oxidative Phosphorylation (electron transport train and chemiosmosis)

Glycolysis characteristics (6)

1. endergonic (use cells ATP) up until the first 3 carbon molecules (pyruvate)

2. The remaining steps are exergonic 

3. Catabolic 

4. Has 10 steps that are catalyzed by a different enzyme

5. Step 3 is believed to be the rate-limiting step 

6. essential metabolic pathway

Is NAD+ to NADH oxidation or reduction and exergonic or endergonic? What does this mean for the overall step that this occurred? What if it was flipped?

NAD+ to NADH: reduction and endergonic

• Means the overall step is exergonic because electron left to go to NADH which is a release of energy

NADH to NAD+: Oxidation and exergonic

• Means the overall step is endergonic because electron was brought back in

NADH purpose

to store electrons and harness their energy to later donate the electrons to other molecules

What is Glycolysis main purpose and location

Purpose: to break the 6 carbon glucose into two 3 carbon pyruvate

Location: Cytoplasm of cell

Overview of Glycolysis process under aerobic conditions (with oxygen)

• 6 carbon glucose breaks down into two 3 carbon pyruvates.  

• ADP receives a phosphate and turns into ATP

• During the oxidation of glucose, the electrons that are removed are used to produce the energy intermediates NADH (NAD+ is reduced to NADH)

What is Substrate level phosphorylation? In which steps of cellular respiration is it used?

Definition: The phosphorylated organic molecules and ADP bind to the enzyme and are the enzyme's substrate. The enzyme directly transfers a phosphate from an organic molecule to ADP, therefore making ATP

Used during glycolysis and citric acid cycle

What are the three main problems at the end of glycolysis?

1. Molecules still not at their lowest state

2. Some of our energy is being held in NADH

3. NAD+ is being used up and not replaced

Products of Glycolysis

Net yield 2 ATP

2 NADH molecules

2 pyruvate

Porins

transport proteins located in the outer mitochondrial membrane that let small molecules and ions move freely between the mitochondrion and the cells cytoplasm

Breakdown of a pyruvate process (5) (make sure to include redox and exer/ender for the steps)

1. Pyruvate that was produced in the cytosol as a result of glycolysis is transported into the mitochondrial matrix.  

2. The pyruvate molecules (3C) are broken down (oxidized) by an enzyme (Exergonic)

3. A molecule of CO2 is removed as long as an acetyl group (2C)

4. The acetyl group is attached to an organic molecule called coenzyme A (CoA) to produce Acetyl CoA

5. 2 high energy electrons are removed from pyruvate and transferred to NAD+ together with H+ to produce a molecule of NADH (reduction of NAD+)

Products per one pyruvate molecule in the breakdown of a pyruvate

1 CO2

1 acetyl coa

1 NADH

Location of breakdown of pyruvate

mitochondria matrix

Krebs cycle location

Mitochondrial matrix

Citric acid cycle process (4)

*There is no official start or end to the cycle*

1. The acetyl group (2 carbons) is removed from the acetyl CoA and attached to a four carbon group to become 6 carbons called citric acid

• CoA turns into the energy source that is used rather than using an ATP

2. Two CO2 molecules are released from citric acid (exergonic)

3. Three molecules of NADH, one FADH2, and one ATP made per one pyruvate 

4. Cycle begins again (one cycle per one pyruvate)

What is the main energy source used in the citric acid cycle?

CoA

Products per one pyruvate in the Citric Acid cycle?

• One ATP (Via Substrate level phosphorylation)

• Three NADH 

• One FADH2

• 2 CO2

Problems at the end of the Krebs cycle? (3)

• Still have not replaced NAD+, in fact more NADH has been made

• FADH2 needs to be re oxidized

• Still have not transferred energy carried by cofactors to ATP

Oxidative phosphorylation is the combination of___?

the electron transport chain and chemiosmosis

What is different about Complex 2 in the electron transport train?

• Moves protons only not electrons

• Only FADH2 gives electron to it 

• not an integral protein 

Location of oxidative phosphorylation and electron transport chain?

Oxidative phosphorylation: Protons move from the matrix to the Inner membrane of mitochondria

Electron transport chain: cristae

Electron transport chain process (5) (Include redox)

1. NADH passes its electrons (and is oxidized to NAD+) to the first carrier in the membrane 

• This ends NADH/NAD+ involvement and it can now participate in another redox reaction 

2. FADH2 bypasses complex 1, and passes electrons to a carrier down the line (complex 2)

3. First electron carrier (Complex 1) passes to second, second carrier passes to third and so on

4. The passing of electrons creates the electrochemical gradients of H+

5. From carriers, electron moves to the final electron acceptor, O2, which then makes H2O and this is the final resting place of the electron 

In the electron transport chain, what happens to the complex’s as the electrons continue to move from one to another? Why?

Each complex has a lower energy level as the electron passes by

Why: this is because the energy is released to establish the electrochemical gradient

Chemiosmosis overview

energy stored in an ion H+ electrochemical gradient is used to make ATP from ADP and Pi

Chemiosmosis process

1. The H+ wants to flow back into the matrix due to the unstable proton gradient. The only way back is through ATP synthase

2. ATP synthase uses facilitated transport to make ATP through the energy of H+ passing through 

ATP Synthase Role

 Makes ATP by taking the potential energy in the gradient (H+ stuck in the inner membrane space) and converts it into kinetic energy (the flow of H+) and turns that into mechanical energy which grinds ADP and Pi together to make ATP 

*Not a part of the electron transport chain and is instead a part of chemiosmosis*

Products of oxidative phosphorylation

• Around 30-34 ATP molecules

• 2 H20

• FAD+

• NAD+