Origami Organelles tm

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1 Mighty Mitochondria Cat no OO-001 Origami Organelles tm 折り紙オルガネラ We d love to hear any feedback, comments or questions you have! Post: Discovering DNA Ltd, PO Box 280 Hertford, SG13 9DG, UK info@ tel: +44 (0)

2 Thanks for purchasing an Origami Organelle Downloadable! What is an Origami Organelle tm Downloadable set? When you purchase a set you will receive two PDF files to download. One of these files is the full colour manual that includes scientific background information, illustrated assembly instructions and observation questions for students. The other file contains the template pages for the model. Downloading is essentially just clicking on link that is ed to you and then copying the files to your computer. You will be able to download the PDF files once for a period 7 days. Once the files are on your hard drive you can print them as many times as you like! Can I order pre-printed Origami Organelle sets? Yes! We supply Origami Organelles sets with 20 copies of templates and student guides, plus a teacher s guide. The sets also include additional supplies as needed, such as gems, Velcro, paper fasteners or paper clips. Please visit for more information. I ve accidentally deleted or lost my download, can I download it again? Yes. Please contact us at info@ for more information. Can I print out on to US Letter sized paper? Yes. Origami Organelles are designed for A4 (210 x 297mm). To print on your printer simply select scale to fit paper. Can I share the files with a friend? Once you have made your Origami Organelle it is understandable that you would want to share the files with a friend. Please don t. Dominic and Melanie Delaney have invested a lot of time and money in the development of these sets. In order for us to continue bringing you innovative sets your support is vital. We hope you enjoy the model! Thanks for your support! 2

3 Mighty Mitochondria The mitochondria (singular mitochondrion) are the power stations of the cell. They take up oxygen and use it to generate energy through the oxidation of food molecules (pyruvate and fatty acids). The structure of a mitochondrion plays an essential role in its function as we shall see with this model. The evolution of mitochondria is interesting in its own right as they are the result of an ancient symbiotic event. Endosymbiosis theory Mitochondria (and chloroplasts) are thought to have evolved from free living bacteria that formed a symbiotic partnership inside another cell (endosymbiosis). For mitochondria, this event is thought to have happened when earth's atmosphere became oxygen rich about 1.5 billion years ago. At this time one or more aerobic bacteria were engulfed by an anaerobic ancestral eucaryotic cell. However, the aerobic bacteria were not digested but evolved symbiotically within their host and have been passed on ever since in their progeny. Much evidence supports this idea. For instance, mitochondria are a similar size to bacteria, have their own circular DNA genome (as do bacteria) and they even possess bacteria-like 70S ribosomes. Thus, it seems that mitochondria gained safety and food in return for their production of ATP. It is interesting to speculate what life would have been like had this not happened. Mitochondria number and shape Mitochondria are very dynamic organelles changing shape, dividing and fusing frequently. A mammalian liver cell has per cell but they vary greatly in number in different cell types. Their division is not in sync with the host cell division cycle but daughter cells get the correct number so it must be closely coordinated. Mitochondria genome The circular mitochondria genome is small at just 16,500 base pairs long in mammals. Part of the reason for this size may be that many key mitochondrial 3

4 proteins are encoded by the host cell genome (such as, mitochondrial DNA replication enzymes, soluble enzymes of citric acid cycle). Structure of mitochondria A mitochondrion is enclosed by a double membrane each comprised of a phospholipid bilayer. Between these membranes is the intermembrane space. The central region of a mitochondrion is the matrix. We will consider each structure in turn. Cristae ATP synthase Matrix Ribosome Outer membrane Inner membrane Proton pumps Intermembrane space Outer membrane The outer membrane contains a large protein channel so it is permeable to all small molecules. This means the molecules needed for energy production (such as ADP, inorganic phosphate, etc) can freely move in and out of the mitochondrion. The outer membrane is also where lipid synthesis happens and where the machinery for mitochondrial division is to be found. Matrix The matrix is a large internal space filled with a high concentration of enzymes needed for oxidation of pyruvate and fatty acids and for the citric acid cycle (or Krebs cycle or tricarboxylic acid cycle, TCA). There are also several identical copies of the mitochondrial genome, mitochondria specific ribosomes, trnas and enzymes needed for gene expression. 4

5 In the cytosol, glycolysis anaerobically converts glucose to pyruvate and releases two molecules of ATP per molecule of glucose. In the mitochondria, much more energy is released as pyruvate (and fatty acids) are oxidised by O 2 to CO 2 and H 2 O releasing 30 molecules of ATP from each molecule of glucose. Pyruvate and fatty acids are transported into the matrix and converted into acetyl coenzyme A (acetyl CoA) by enzymes there. Acetyl CoA is oxidised via the citric acid cycle converting the carbon atoms to the waste product CO 2. This oxidisation generates high energy electrons which are captured by diffusible molecules, such as NAD+ (and also FAD). NAD collects two electrons (plus a proton) forming NADH. NADH then carries the electrons to the inner membrane where they are taken up by an electron transport chain. Inner membrane The inner membrane is folded into numerous cristae (singular crista) that increase the surface area for ATP synthesis. The membrane has proteins for three functions, for electron transport, ATP synthesis and transport in and out of the matrix. Pyruvate, fatty acids, inorganic phosphate and ADP are moved into the matrix. ATP is pumped out. Electron transport chain The electron transport chain (or respiratory chain) uses NADH as the source of high energy electrons which are used to drive a series of proton pumps in the inner mitochondrial membrane. These move protons as described below. Each passing step reduces the energy of the electron. Electrons are carried by the proteins ubiquinone and cytochrome c that shuffle back and forth between the proton pumps. As an aside, the poison cyanide works by blocking the electron transport chain in the inner mitochondria membrane. Proton pumps The proton pumps are really complexes made of made many polypeptide chains. They move protons from the matrix into the intermembrane space. This creates a potential difference in proton concentration between the matrix (low) and the intermembrane space (high). Such a potential gradient is a form of stored energy that is released when the protons are allowed to flow back into the matrix later on. Protons are readily available in cells as they are naturally formed from water. Thus, they are an easily available substrate for a creating a potential gradient in the mitochondria. 5

6 The third proton pump catalyses the transfer of electrons to oxygen that is used to make water. ATP synthase As the inner membrane is impermeable to ions, the protons in the intermembrane space are only able to get back into the matrix by passing through a channel in a protein machine called ATP synthase that is embedded in the inner membrane. As the name suggests, ATP synthase makes ATP using the stored energy in the proton potential. Much like a turbine in a power station, ATP synthase uses the kinetic energy of the proton gradient to drive production of ATP. ATP synthase has a lollipop like structure with a spherical head on a stalk. The stalk is embedded in the inner membrane and the head is in the matrix. There is a channel through the stalk so protons can flow from the intermembrane space to the matrix through ATP synthase. As the protons travel through the central channel, they turn a rotating protein inside the stalk converting the kinetic energy into mechanical energy. Next, the mechanical energy is converted into chemical energy as the movement causes changes in protein conformation that causes ADP and inorganic phosphate that are bound to the ATP synthase to react and form ATP. 100 molecules of ATP are produced per second in this way! ATP is taken out of the matrix by the same carrier protein that brings ADP in. Oxidative phosphorylation The production of ATP in this way is called oxidative phosphorylation: NADH + ½O 2 + H+ è NAD+ + H 2 O energy conversion process in membranes ADP + P è ATP 6

7 Genetics of mitochondria In humans, mitochondria are only passed down the maternal side. The reason for this is that although mitochondria are in both eggs and sperm, they are not in the sperm head that fuses with the egg so do not pass into the embryo. As such, mitochondria have been used to trace maternal inheritance. Such studies have led to theories about human evolution and even the idea that the human population derives from just one female about 200,000 years ago - the Mitochondrial Eve! Mitochondria transfer has been proposed as a way to cure severe genetic conditions that affect the mitochondria (mitochondrial myopathies). This transfer is controversial because the embryo receives mitochondria from an egg donor that includes the mitochondrial DNA in addition to a maternal and paternal genomic DNA - so called "three parent babies". Thus, transferring mitochondria also transplants a limited amount of genetic information that is passed onto future generations. These issues are an active area of ethical discussion. If you are pleased with this Origami Organelles tm set and its learning outcomes, why not go to and easily download and print another quality set from our growing range! Each set comes with full instructions and templates for you to print for your students. Please contact us with any suggestions or comments regarding this or future sets that you would like to see developed. Thank you for your support. Dr Dominic Delaney Dr Melanie Delaney 7

8 Mighty Mitochondria - Lesson Guide Components Dark blue outer membrane sheet Light blue inner membrane sheet Requirements Glue - glue stick recommended (or double sided tape) Glue dots (3mm) recommended for gems Tape - magic tape recommended Scissors Gems (optional) 3 small pink, 6 small blue and 2 large purple Outer membrane - dark blue 1 Cut out around the shape along the solid lines: 2 Fold the outer edges inwards to the middle dotted line. 8

9 3 Create the side walls by folding the sides into the middle......and out again. Then tape the centre to secure: 4 Fold triangular corners to make the first curved end and tape to secure: 5 Repeat step 4 at the other end: 9

10 6 Fold in the end flaps to cover the curved framework by crossing over and tape to secure: 7. Repeat with each of the other 3 flaps and tape them all: Inner membrane - light blue 1 Cut out the template along the solid lines. 10

11 2 Fold in half lengthwise along the dotted middle line. 3 Apply double sided tape (or glue stick) on the both sides on the inside of the outer membrane: 4 Attach the inner membrane creating four cristae: 5 Repeat with the other strip of inner membrane. Nicely shows expanded surface area of inner membrane due to cristae. 11

12 6 Optional - bejewel your mitochondrion! You can glue in gems using glue dots or a glue stick to represent the following features on your mitochondrion: Ribosomes - three spread out across base of matrix floor (pink) Proton pumps - in triplet on the matrix side of inner membrane (blue) x 2 sets ATP synthase - single next to proton pumps (purple) x 2 Congratulations! You have now finished your model! Observation questions You should now be able to identify the locations of these features in the mitochondrion you have just made: Outer membrane Intermembrane space Inner membrane Matrix Cristae ATP synthase Proton pumps Genome. Describe what happens in each location of the mitochondrion. 12