Login
Copyright

Cellular Respiration in Yeast

Instructor: Amanda Robb
In this lesson, we'll learn about cellular respiration in yeast. Here, we'll cover what yeast is and the two ways that it uses cellular respiration to make energy.

What Is Yeast?

Picture a calm Sunday in the kitchen. The smell of freshly baked bread rises from the oven. By mixing yeast, flour, sugar and water you were able to turn these simple ingredients into a loaf of bread. If you've ever made bread you know it takes a long time. After mixing the dough, it needs time to rise. Almost like magic your bread doubles or even triples in size over an hour or two.

A chef prepares fresh bread in the bake shop
baking bread

How does this happen? The key ingredient for making fluffy bread is yeast. Yeast is a single-celled fungus, which is alive and must make its own energy to survive. The yeast in your bread uses a process called cellular respiration, where glucose is converted to ATP and carbon dioxide. The carbon dioxide is what causes the bread to rise. The yeast produces this gas and the bread puffs up, incorporating the gas in between the flour. Today, we'll learn about this process, which requires oxygen, called aerobic respiration, and another process of yeast called anaerobic respiration.

A teaspoon of baking yeast
bakers yeast

Aerobic Cellular Respiration

Aerobic cellular respiration is cellular respiration that requires oxygen. There are three main steps to this process: glycolysis, the citric acid cycle, and oxidative phosphorylation. Here, we will look at each step in more detail.

Step 1: Glycolysis

During the first step of cellular respiration, glucose, a simple sugar, enters the cell. The yeast uses the glucose and creates two ATP, two NADH (a molecule that carries electrons to be used later), and two pyruvate needed for the next step.

Glycolysis
glycolysis

Step 2: Citric Acid Cycle

In the citric acid cycle, the pyruvate are converted to a molecule called acetyl-CoA in the mitochondria, the powerhouse of the cell. This molecule is regenerated during this step, hence the cycle part of the name. During this conversion each pyruvate releases one carbon dioxide molecule. Next, acetyl-CoA is converted to several other molecules before being regenerated. During these reactions, two GTP, which are later converted to ATP, are made. This step also makes six NADH, the most of any step in cellular respiration, and one FADH2, a similar molecule. At this stage, two additional carbon dioxide are released.

Citric acid cycle
citric acid cycle

Step 3: Oxidative Phosphorylation

Oxidative phosphorylation is the big energy payoff for yeast. This step occurs at the inner membrane of the mitochondria. All of the NADH and FADH2 created come to the membrane to drop off their electrons. They deliver them to proteins in the electron transport chain. Each protein likes each electron more than the one before it, so the electrons keep getting passed down the chain. At the end of the chain is oxygen, the ultimate electron acceptor. Oxygen takes two electrons and two hydrogen ions from the mitochondria and turns into water.

You might still be wondering how energy is made. The secret is the electron transport chain. As the electrons are passed down, they use the energy to pump hydrogen ions into the intermembrane space between the inner and outer mitochondrial membrane. These hydrogen ions build up like water behind a dam. Like a dam, there is only one way for them to flow down their concentration gradient to release the stored energy. The hydrogen ions flow through a protein called ATP synthase, which spins like a turbine to create ATP.

Oxidative phosphorylation
oxidative phosphorylation

Aerobic respiration is the most efficient and releases the most energy, 36 to 38 ATP per glucose molecule.

To unlock this lesson you must be a Study.com Member.
Create your account

Register for a free trial

Are you a student or a teacher?
I am a teacher
What is your educational goal?
 Back

Unlock Your Education

See for yourself why 10 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back

Earning College Credit

Did you know… We have over 79 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it free for 5 days!
Create An Account
Support