Cell Respiration

Why does respiration need to be constantly happening in our cells?

ATP has to be constantly regenerated for cells to operate.

What are the three main steps in an aerobic respiration reaction?

• 1. Glycolysis is breaking down glucose into CO₂ and takes place in the cytoplasm

• 2. The citric acid cycle is the oxidation process

• 3. Oxidative Phosphorylation is where ATP is made and converts oxygen into water 

• Gets energy from electrons

What is the energy investment phase in glycolysis?

Spend some ATP to start breaking down glucose and then create more ATP.

What 3 things does glucose break down into?

Pyruvate, ATP, and NADH

How is NADH created and what is its purpose during glycolysis?

• NAD+ reduces by gaining hydrogen ions and electrons to neutralize its charge and create NADH

• NADH represents stored energy that will be transferred later to generate ATP

• Extra electrons are stored in NADH

What is the purpose of pyruvate during glycolysis?

Most of the potential energy contained in glucose is stored in pyruvate

Overall process of glycolysis

• Start with one glucose and spend ATP to destabilize the glucose 

• Product: 4 ATP is formed so 2 ATP molecules are gained, 2 NADH which holds extra electrons, and 2 pyruvate 

Why is glycolysis considered to be one of the first metabolic pathways to have evolved?

It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms 

Describe the citric acid cycle

• Goal is get as much energy out as possible and release carbons as CO₂

• Begins with pyruvate and then breaks carbon skeleton of the glucose molecule into CO₂ 

• In total, from two pyruvates, glycolysis creates 8 NADH, 2 ATP,  2 FADH₂, 6 CO₂ 

What are the two stages in oxidative phosphorylation?

Electron transport chain and chemiosmosis

Describe the electron transport chain

• Contains a series of protein complexes imbedded in the membrane

  • The most important are the 1, 3, and 4th protein complex because they have proton pump capabilities 

• Electrons from NADH and FADH₂ will flow to the protein complexes

• Each time electrons move, they release energy and then at 1, 3, and 4th protein complex, the energy will power proton pumps to pump protons across the membrane and create an electrochemical gradient 

• Overall purpose: use high energy electrons from the carriers to build electrochemical gradient 

What is the purpose of chemiosmosis?

• Uses the electrochemical gradient and protons to power ATP synthase  

• As hydrogen ions flow through the complexes, it will cause the protein to twist and twisting motion will create ATP

What is the role of oxygen during oxidative phosphorylation?

• Functions as terminal electron acceptor 

• After electrons have no energy left after complex 4, they will bind to oxygen and then create water with hydrogen ions floating around  

What is the role of electronegativity during oxidative phosphorylation?

Each subsequent protein is taking electrons from each other because there is an increase in electronegativity which will reduce the power of the electrons 

What is the difference between aerobic and anaerobic respiration?

• Aerobic requires oxygen while anaerobic does not

• They both include all three stages because it is still respiration

What is fermentation?

• Not a form of respiration

• Cells relying solely on glycolysis for ATP production

• As long as glucose is plentiful then single cell organisms will live

• Needs a way to get rid of NADH because there is no process afterwards that can make use of it

  • Takes the high-energy electrons on the NADH and dumps them onto the pyruvate and then release it to regenerate NAD+

Describe anaerobic respiration.

• Electron transport chain follows a similar path as seen in aerobic respiration but the terminal electron acceptor is not O₂

• Alternative acceptors are varied but they are not as electronegative as O₂ so ATP is produced less

• ETC can’t take as much energy from electrons

• Leaves more energy behind so proton pump is weaker which leads to a weaker electrochemical gradient and less ATP production 

What is an example of fermentation and describe it.

• Lactic acid fermentation

  • During fight or flight circumstances, muscles can replace ATP production with lactic acid fermentation because after oxygen is used up during aerobic respiration, there is not enough oxygen available so do lactic acid fermentation for temporary ATP

• Alcohol 

  • Takes yeast, which is a type of fungi, sugar, and wheat and take out all of the oxygen from the container and then the yeast will use up all of the sugar to make ethanol which leads to alcohol