Cellular Respiration Background

Mitochondria

Mitochondria are one of the two energy-converting organellestructures within a cell that perform specialized functions. in a eukaryotic cell. Recall from a previous module that the other organelle is a chloroplast. Students often think that plants contain chloroplasts and animals contain mitochondria, but this is untrue. All eukaryotic cellsThe basic structural and functional units of life. contain mitochondria, plant cells included.
Let’s focus on the structure of one of these organelles. Mitochondria are these little jelly bean-shaped organelles and are always orange in any book from which I’ve ever taught. Each mitochondrion has a double membrane, which makes a structure like a bag in a bag. But think of the inner bag; it’s all wrinkled and doesn’t fit to the outer bag perfectly. This is true. The inner membrane has much more surface area. You can see this in the bottom left corner. Here, enzymesProteins that speed up chemical reactions in the body. are embedded in the inner membrane.

The inner membrane is filled with a gooey substance of enzymes called the matrix. Between the membranes is a space we call the intermembrane space. The prefix inter means between, whereas intra means within. And then remember, this isn’t a cell, so this organelle would be found in the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol. of a cell.

They are very common in muscle cells. These cells are also called muscle fibers. You require a massive amount of energyThe capacity to do work or cause change. conversion to power contractions. Moving from the outside to the inside of a mitochondrion, we’d first hit the outer membrane. Next, we encounter the intermembrane space. Then, the inner membrane is reached. Finally, we reach the gooey matrix.

Phosphorylation

Phosphorylation is, in general, the process of generating ATPThe energy currency of cells used for muscle contraction..  There are three types of phosphorylationaddition of a high-energy phosphate to a compound, usually a metabolic intermediate, a protein, or A and the names indicate what is used in the process of generating that ATP.  You have to think of ATP as a coiled spring.  Coiling, or compressing that spring is the process called phosphorylation.  When that energy trapped in the ATP is used, the ATP undergoes hydrolysis. A waterThe universal solvent essential for life. molecule is used to split one phosphate group off the ATP. This converts it into ADPA molecule produced when ATP releases energy..  When you eat food, energy from your food powers the coiling of the spring again. It bonds the last phosphate group to the ADP to make ATP.  You are one big ATP recycling bin. 

Substrate phosphorylation occurs with an enzyme and makes very little ATP, not enough to power many eukaryotic cells.  Oxidative phosphorylation uses oxygen and a specific enzyme called ATP synthasemembrane-embedded protein complex that adds a phosphate to ADP with energy from protons diffusing th. This enzyme is embedded in the inner membrane of the mitochondria. It makes lots of ATP very quickly.  The final type, photophosphorylation is discussed with photosynthesis in the next module.

Redox Reactions

Redox reactions are pretty simple.  In Biology.  They get a bit more complex if you take chemistry, but this is not chemistry, so we’ll keep it simple.  This concept is deceptive because it uses a word with which you are already familiar: reduction.  Don’t neglect the significance of this work here. To reduce is to become more negative. This would also mean to gain negative charges or electronsNegatively charged subatomic particles found in atoms..  Of course, if a molecule accepts an electron or is reduced, the electron must come from somewhere. Right?  Yes, these would be the donors, who, by losing electrons become more positive, or oxidized.

Glucose is our electron donor.  When glucoseA simple sugar that is the main source of energy for cells. becomes oxidized, it turns to carbon dioxide. Molecular oxygen is our electron acceptor.  When it becomes reduced, it turns to water.

Electron Infidelity

Understanding electron infidelity is important for reading the chapter. It is also crucial for understanding the rest of what we’re going to talk about with cellular respirationThe process of gas exchange, including ventilation, external and internal respiration..  Think of what a hydrogen atom is: one proton surrounded by one electron there are no neutronsElectrically neutral particles in an atom’s nucleus..  The problem is that every other atom that’s out there that isn’t a hydrogen atom has more protons.  And so that one lonely electron is unfaithful.  It sees atomsThe smallest units of matter that retain the properties of an element. and ionsCharged atoms or molecules. with more positive charges. It is attracted to these atoms or ions.  Therefore, we refer to hydrogen as a hydrogen ion or hydrogen cation. Sometimes it’s called just a proton.  If the electron leaves then all that’s left is this nucleusThe control center of the cell that contains DNA and directs cellular activities. with one proton in it.  Essentially what we have is a hydrogen cation.

Two Location Challenge

When we get into cellular respiration we are going to find out that there are 3 significant steps.  The first of the steps occurs in the cytoplasm second and third of these steps occurs in the mitochondria.  During the first step electrons are stripped from glucose.  Electron stripping continues in the second step in the mitochondria.  Those electrons from the first and second step are used in the third step that’s also in the mitochondria.  The problem is transporting the electrons between the first and the third step and the second and the third step.  Electrons can just float about freely, I mean they can, but they’ll never get to where they’re going.  What we have is kind of like an usher or a taxi for these electrons.

NAD+ and NADH

There are many analogies out there. They explain how electrons are taxied from one location to another location inside of his cell.  I like this analogy with this actual taxi in the picture.  The taxi is a molecule called NAD+ indicating that it’s a cation and that it has lost an electron somewhere.  Don’t worry where.  These 2 people here are 2 electrons.  These are electrons stripped from glucose. They come from other breakdown compounds during the first and second steps of cellular respiration.  The electrons are loaded into the taxi, changing the taxi from NAD+ to NADH.  When the electrons are loaded into NAD+, the hydrogen protons also kind of come along.  Taxis can then take all of these substances from one area of the cell into the mitochondria. They can also move substances from one area of the mitochondria to another.  Once the taxi gets to its destination, it can offload the electrons. It turns back into NAD+. NAD+ can circle back to pick up more electrons. It turns into NADH. It circles back to the mitochondria. It’s just a big cycle.