Examine the picture above. 1. Describe the cell membrane. 2. Does the above process use ATP? 3. Name the type of cellular transport being shown above.
Why do we need oxygen, and what purpose do we need it for?
Cellular respiration is the process of harvesting energy (ATP) from food on the cellular level. During cellular respiration, oxygen will be added to glucose to make carbon dioxide and water. See the formula below: C 6 H 12 O 6 + O 2 → CO 2 + H 2 O ◦ Note that this equation is almost the opposite of the formula for photosynthesis!
Cellular respiration takes place in the mitochondrion. Mitochondria are organelles that process ATP from nutrients. As stated before, mitochondria were once living organisms. ◦ They have their own circular DNA. ◦ They can make their own protein, and divide like bacteria. ◦ They have a double cell membrane.
The mitochondria have both an outer and an inner membrane. The space inside the inner membrane is called the matrix. This is the site of cellular respiration.
The space in between the outer and inner membranes is called the intermembranous space. This area is vital for the electron transport chain, which we will talk about later.
Note that the inner membrane is folded in upon itself. This is to increase the surface area of the inner membrane. ◦ This also becomes important when discussing the electron transport chain.
Cellular respiration is divided into several phases, depending on the organism: Eukaryotes: ◦ Glycolysis, the conversion of glucose to pyruvate. ◦ Krebs or TCA cycle, the oxidation of pyruvate. (Electrons are loaded unto NADP + at this time.) ◦ Electron transport chain, where the collected electrons are used to “kick” protons out of the matrix. The protons re-enter the matrix, which charges ADP to ATP.
Cellular respiration is divided into several phases, depending on the organism: Prokaryotes: ◦ Glycolysis, the conversion of glucose to pyruvate. ◦ Fermentation, the process of converting pyruvate to acid and alcohol. Prokaryotes conduct fermentation, as they completely lack mitochondria. ◦ Be aware that eukaryotes also conduct fermentation in the absence of oxygen. We’ll discuss that later.
Glycolysis Krebs cycle Electron transport Fermentation No mitochondria, OR no oxygen Mitochondria AND oxygen present
Glycolysis is the process of converting glucose to pyruvate. In the process, both 2 ATP and 2NADPH will be produced. ATP is used for energy, and NADPH will be used later in electron transport.
Notice that ONE molecule of pyruvate is converted to TWO molecules of pyruvate. This is important to keep in mind when we discuss the Krebs cycle.
The Krebs/TCA/ citric acid cycle is the set of reactions that oxidizes pyruvate. Oxidation is the harvesting of electrons, so our main product is NADPH and FADH 2.
Note that this process also creates carbon dioxide (CO 2 ) as a waste product. You need to remember that CO 2 is released as a waste product in respiration!
Also, note that each molecule of pyruvate makes 3 NADPH, 1 FADH 2 and 1 ATP. Since we had two molecules of pyruvate, we end up with 6 NADPH, 2 FADH 2 and 2 ATP.
The electron transport chain is the process of harvesting energy from collected electrons.
ALL of our collected electrons (e - ) will be used up to pump protons (p + ) OUT of the matrix. ◦ Since we CANNOT destroy matter, the electrons have to be disposed of. We bind them to oxygen gas and add hydrogen, which creates water. ◦ This is why respiration requires oxygen!!! The protons then re-enter the matrix through an ion channel. This recharges ADP, converting it to ATP.
Fermentation is the process of converting pyruvate to acids, alcohols and other compounds. ◦ This is a way of using up pyruvate WITHOUT the addition of oxygen. Fermentation is mainly conducted in bacteria and yeast, and is the reason why we can ferment drinking alcohol. ◦ However, eukaryotes can also conduct fermentation – if they do NOT have access to oxygen!
In bacteria and yeast, alcohol is a very common byproduct of fermentation.