Cell physiology Part B part 4

Added: 2026-05-09

[00:00:00]in this lecture we're going to review a very important organelle inside the cell called the mitochondrion now the mitochondrion is referred to generally as the PowerHouse of the cell and what this suggests is that this is a site of energy generation and that energy generation comes in the form of adenosine triphosphate or what I refer to as cellular cash cellular money and so the vast amount of ATP that is made by the mitochondrion provides that cell with its what we call its aerobic capacity and I'll detail that here shortly if we take a look on the right hand side we see uh some elements of mitochondrial structure so this is a single mitochondrion uh split in half in this drawing but we see that the mitochondrion is is composed of two separate membranes we have the outer membrane which defines the outer surface of the entire organelle and we see this network uh uh inside the mitochondrion surrounded and formed by an inner membrane and that sets up an inter membrane space which becomes important in mitochondrial function we have what are called Christie which are the folds interior folds of the inner membrane and the inner part of this uh very large compartment uh that takes up the majority of the volume of the Interior volume of the mitochondrion is simply referred to as the Matrix and the Matrix does contain ribosomes much in the same way that the cell cytoplasm contains ribosomes and as indicated just earlier that Christie referred to the folds in the inner membrane and the purpose of folding the inner membrane we believe uh is that nature uses this approach to increase the inner surface area of that interior compartment now why is a micro why is the mitochondrion so important well one example of where the mitochondrion plays a very important role as we can see here in this lower left-hand picture of the slide is a sperm cell so we know that a sperm cell is a motor type of cell which means that it has this long tail that moves and generates Force against the fluid within which that sperm cell exists and that Force against the fluid forces the fluid to push back and that's what provides the sperm cell with propulsion and in order for the sperm cell to operate as a motor cell for those uh tail movements it requires a source of energy and in this expanded view under the microscope we see that the base of the tail near the head of the sperm cell is housed with numerous uh mitochondria and as long as there is a fuel supply and an oxygen supply coming in from the exterior medium within which that sperm cell exists these mitochondria will be able to produce a large amount of ATP to pay for the mechanical action and the motoring action of the tail so overall here when we talk about a cell that contains phytochondria that is a cell that has an energy cost to its function and it pays for those functions by making ATP so just some quick facts on the mitochondrion the mitochondrion is the site inside the human organism that engages in what we call aerobic respiration and aerobic respiration refers to the consumption of molecular oxygen in a series of steps to make ATP in the process carbon dioxide is produced and H2O is produced when that oxygen is consumed uh the second quick fact about the mitochondrion relates to the number how many mitochondria exist inside a cell the more mitochondria that exists inside the cell the greater capability that cell has to making ATP aerobically and we can almost think about the cell having an endless potential to make ATP if it has mitochondria uh and so in this microscopic image uh we it's not quite as clear as the drawing on the previous slide but nevertheless we see an outer membrane forming the outer boundary we see an inner membrane sort of pictured right here uh the interior Matrix which is where a lot of the ATP production takes place and we have those folds referred to as the Christie as well as the inter membrane space once again here not quite as clear as it was in the drawing on the previous slide uh number three here that in order for the mitochondrion to carry out its function it requires enzymes so important is the mitochondrion to the human organism that the mitochondrion this one organelle is equipped with about 2 000 different enzymes that catalyzes various biochemical reactions now recall the enzyme is a protein that speeds up chemical reactions but it's a protein structurally nevertheless and so the question here is where did the mitochondrion obtain its proteins well there are two sources of those mitochondrial proteins the first here in the majority of these proteins are what we call nuclear proteins which means that those proteins were manufactured back in the cytoplasm and the manufacturing was initiated inside the nucleus so basically nature outsources the protein manufacturing for the mitochondrion to the nucleus but it's also important for the mitochondrion to make its own internal proteins and the only way the mitochondria can the mitochondrion can do that is to have its own own set of instructions and so we have two locations of genetic information in the form of DNA inside the cell of course it's in the the nucleus as well as the mitochondria and so mitochondrial DNA is a very different type of DNA molecule where in the nucleus the DNA molecule forms that Alpha Helix type of shape however in the mitochondrion mitochondrial DNA is circular shape and has far less molecules nucleic acids and nucleotides that make up that DNA in the form of 16 000 base pairs where we have millions of base pairs in the nuclear DNA mitochondrial DNA is considered to be a little bit more efficient in that it is mostly made up of what what are called coding regions and those are portions of the DNA molecule that house the specific instructions on how to make a protein uh number four here uh something to understand about the mitochondria is that these are organelles that are very Dynamic and being Dynamic is that these mitochondria undergo changes both in size and in number depending upon the situation when we talk about a short-term change uh the term accommodation is the appropriate term and this is what we typically experience in response to disease in response to uh Rehabilitation and training in one person so when a person undergoes a period of resistance training or weight lifting muscles will start to grow larger and stronger we don't the correct term is not adaptation the correct term is accommodation so the changes that occur through accommodation are reversible when we talk about adaptation that is a long-term permanent change in the characteristics of a cell occurring across many many generations uh now in order for the mitochondria to change uh both in size and the number those mitochondria have to have some sort of stimulation to do that and the stimulus comes from an increase in cellular activity that increase in cellular activity comes from the nervous system activating those cells that elevates the metabolic rate and when metabolic rate is elevated the energetic change also increases now what are these changes that take place uh in mitochondria the first form of that change is what's called mitochondrial fusion and it's Illustrated on the right hand side we see two relatively small mitochondria fused together through the emerging of the outer membranes remember the outer membranes are made up of phospholipid molecules which can form chemical bonds between those molecules quite easily so the fusion is something that does that can't happen quite efficiently provided that there is a stimulus to the cell by activating the cell so uh this is also a process in which damaged DNA can be repaired and so not only do the phospholipids come together but proteins will also combine and help to solidify the new uh membranes of that mitochondria and the mitochondrion and it produces one larger mitochondrion in what we see which which starts with first outer membrane Fusion that will then lead to Inner membrane Fusion producing one larger functional mitochondrion uh the other form of the change is what we call mitochondrial fission uh and mitochondrial fission occurs as you can see in this lower picture where we have a ring of proteins that essentially will pinch that mitochondrion and produce two smaller mitochondria with the idea here that more mitochondria also contributes to an increased capacity to produce ATP uh aerobically and the way it does that is that two smaller mitochondria have an overall greater surface area and volume than one large mitochondria and that will enhance the increase in oxygen and oxygen mediated energy turnover and anxiety indicated just a few seconds ago we have various proteins that function to break that larger mitochondrion into those two smaller organelles so that ends this particular lecture on the mitochondria