CELLULAR RESPIRATION! AP BIO

What is cellular respiration?

Cells harvest chemical energy stored in organic molecules and use it to generate ATP

What is the major source of fuel for animals?

Starch --> breaks down into glucose

Is cellular respiration an anabolic or catabolic reaction?

Catabolic --> breakdown of glucose

Write the formula for cellular respiration.

C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy (ATP and heat)

Which reactant is oxidized in cellular respiration?

C6H12O6 oxidized --> 6CO2

Which reactant is reduced in cellular respiration?

6O2 reduced --> 6H2O

Why is glucose necessary for cellular respiration?

The oxidation of glucose transfers e- to a lower energy state, releasing energy to be used in ATP synthesis.

What is the ultimate electron acceptor?

OXYGEN

Trace the path of electrons in energy harvest.

Most electrons follow this "downhill" exergonic path:
Glucose --> NADH --> ETC (Electron Transport Chain) --> Oxygen

Describe how glucose is broken down to harvest energy.

1) Electrons are taken from glucose at different steps
2) Each e- taken travels with a proton (H+)
3) Dehydrogenases (oxidizing agent for glucose) take 2e- and 2H+ from glucose
--> Transfers 2e- and 1H+ to coenzyme NAD+, reduces to NADH (stores the energy)
--> Other H+ is released into surrounding solution
4) NADH carries e- to the (ETC) electron transport chain

What is the electron transport chain (ETC)?

Sequence of membrane proteins that shuttle electrons down a series of redox reactions

What is the function of the ETC?

Releases energy used to make ATP.
Transfers e- to O2 (final e- acceptor) to make H2O --> releases energy.

List the 3 stages of cellular respiration.

1. Glycolysis
2. Pyruvate oxidation and Citric Acid cycle (Krebs cycle)
3. Oxidative phosphorylation: ETC and chemiosmosis

Where does glycolysis occur?

Cytosol outside the mitochondria

What does glycolysis do?

Splits glucose (6C) into 2 pyruvates (3C)

What are the 2 stages of glycolysis?

Energy investment and energy payoff

Describe the stages of glycolysis.

1) Energy investment: cell uses ATP to phosphorylate (attach a phosphate group) compounds of glucose.
2) Energy payoff: Energy is produced by substrate level phosphorylation
--> Net yield per 1 glucose = 2 ATP, 2 NADH

Summarize the pathway of glycolysis.

Energy investment: 2 ATP --> 2 ADP + P
Energy payoff: 4 ADP + P --> 4 ATP
2 NAD+ + 4e- + 4H+ --> 2 NADH + 2H+
Net: 2 pyruvate + 2 H2O, 2 ATP, 2 NADH + 2H+

How many net ATP are produced in glycolysis?

2 net ATP

Describe pyruvate oxidation.

If oxygen is present, the pyruvate enters the mitochondria (eukaryotic cells).
1) Pyruvate is oxidized into Acetyl CoA --> Acetyl CoA is used to make citrate in the Citric Acid cycle.
2) 2 CO2 + 2 NADH are produced.

Summarize the pyruvate oxidation pathway.

Pyruvate oxidized --> Acetyl CoA (for Krebs cycle) --> 2 CO2 + 2 NADH produced

Citric acids cycle is also known as the…

Krebs cycle

Where does the Citric Acid cycle occur?

Mitochondrial matrix

Describe the citric acid cycle.

Turns acetyl CoA into citrate
--> Releases CO2, ATP synthesized, electrons are transferred to NADH and FADH2

Summarize the pathway of the Citric Acid cycle (per glucose molecule)

2 acetyl CoA --> 2 ATP + 6 NADH + 4 CO2 + 2 FADH2

What is the net ATP production in the Citric Acid cycle?

2 net ATP

Oxidative phosphorylation consists of…

Electron transport chain (ETC) and chemiosmosis

Where is the ETC located?

intermembrane of mitochondria

How does the ETC work?

As the electrons "fall", proteins alternate between reduced (accepts e-) and oxidized (donates e-) state.
Oxygen is the final electron acceptor

each O pairs with 2H+ and 2e- to form H2O.

What is the function of cristae in the ETC?

Increases the surface area for reactions to occur.
Does not produce ATP directly --> it helps manage the release of energy by creating several smaller steps for the "fall" of electrons.

Identify and describe the major function of the ETC.

Creates a proton (H+) gradient across the membrane.
1) As proteins shuttle electrons along the ETC, they also pump H+ into the membrane space and use the exergonic flow of electrons from NADH and FADH2.
2) This gradient will power chemiosmosis as they use H+ to power cellular work.

What is ATP synthase?

Enzyme that makes ATP from ADP + P.

What is chemiosmosis?

H+ ions flow down their gradient through ATP synthase.

Explain the steps of chemiosmosis.

1) ATP synthase uses energy from the H+ gradient across the membrane
--> H+ ions flow down their gradient through ATP synthase.
2) ATP synthase acts like a rotor
--> When H+ binds the rotor spins.
3) This activates catalytic sites to turn ADP + P into ATP.
--> Produces about 26-28 ATP per glucose.

How is the proton gradient formed across the inner mitochondrial membrane?

The exergonic flow of electrons from NADPH and FADH2 powers the proteins in the ETC to pump H+ into the intermembrane space.

Identify the inputs and outputs of Glycolysis.

Input: 1 glucose
Outputs: 2 pyruvate + 2 ATP + 2 NADH

Identify the inputs and outputs of Pyruvate Oxidation.

Input: 2 pyruvate
Outputs: 2 acetyl CoA + 2 CO2 + 2 NADH

Identify the inputs and outputs of the Citric Acid cycle.

Input: 2 acetyl CoA
Outputs: 4 CO2 + 2 ATP + 6 NADH + 2 FADH2

Identify the inputs and outputs of Oxidative Phosphorylation.

Inputs: 10 NADH + 2 FADH2
Outputs: 26-28 ATP

How much net ATP is gained from cellular respiration?

Net gain: 30-32 ATP

What is the oxygen important in the ETC?

In cellular respiration, oxygen is the final electron acceptor.
--> It drives electrons down the ETC.

How do organisms produce ATP in the absence of oxygen?

Anaerobic respiration or fermentation

What is anareobic respiration?

Generates ATP using an ETC without oxygen present.

Where does anarobic respiration occur?

In prokaryotic organisms that live in environments with no oxygen.

What are the final electron acceptors in anaerobic respiration?

Sulfates or nitrates.

What is fermentation?

Generates ATP without an ETC without oxygen present.
Recycles NAD+

Where does fermentation occur?

Cytosol

What are the 2 types of fermentation?

Alcoholic fermentation and lactic acid fermentation

What is alcohol fermentation?

Pyruvate is converted --> ethanol.

Give examples of alcohol fermentation.

Bacteria, yeast

What is lactic acid fermentation?

Pyruvate is directly reduced by NADH --> lactate.

Give an example of lactic acid fermentation.

Muscle cells

Explain what happens when muscle cells run out of oxygen.

When muscle cells run out of oxygen, they can go through lactic acid fermentation to produce ATP.
--> Causes the burning sensation you feel when performing strenuous exercise.

Explain the breakdown of lactate.

1) Muscles produce lactate which goes into the blood, and is broken down back to glucose in the liver.
--> When lactate is in the blood, it lowers pH.
2) If lactate builds up and is unable to be broken down it can lead to lactic acidosis.
--> Leads to excessively low blood pH.