To be more precise, human cell physiology is the study of the mechanical, physical, and biochemical functions of our living cells, all 60 trillion of them give or take a few trillion.
Would you believe that's about 6 times larger than our national debt; the bad news is that the debt is closing fast. Ah, but I digress.
The cell is about in the middle of the journey from gene to clinical medicine.
Starting our journey, the organizational flow is from gene and chromosome to protein to cell to tissue to organ to system to total body clinical medicine.
To firmly establish our foundation, the full set of 24,000 human genes and 23 pairs of chromosomes comprise the genome.
Our genes are carried on our chromosomes and both reside in the nucleus of the cell. We could compare the genome to a library where chromosomes are the books and genes are the paragraphs.
In considering cell physiology, it is necessary to understand the parts that comprise the whole.
The major parts of a typical human cell include the cell membrane, nucleus, mitochondria, Golgi apparatus, smooth and rough endoplasmic reticulum, ribosomes, lysomes, vacuoles and a cytoplasm filling.
In order to understand how our cells take in nutrients and what they do with them, it is necessary to go inside the human cell and dissect it.
Although there are a lot of different types of cells in the human body with vastly different functions, they all have the same basic parts.
Take a microscopic look at a muscle cell or a red or white blood cell or a nerve or a sperm cell and it become very apparent that not all cells are the same.
The illustration below from the NIH shows these differences very well.
To recap, the major parts of human cell physiology are the cell membrane, nucleus, mitochondria, Golgi apparatus, smooth and rough endoplasmic reticulum, ribosomes, lysomes, vacuoles and a cytoplasm filling.
The graphic below depicts the structure of these parts. As you can see, there is a lot of activity going on inside that little galaxy.
We will briefly introduce each human cell component, known as organelles or "little organs", by describing what each one does.
This isn't intended to be a course in cell physiology since the focus of the site is nutrition and lifestyle choices for health. The only purpose in going into the workings of the cell is to show how it uses nutrients for the benefit of the total body.
We will start the piece part discussion of human cell physiology with the CELL MEMBRANE. while it looks like a homogeneous skin covering the cell, there is more than meets the eye.
It is in fact the "skin" of the cell but it's not uniform in construction.
It consists of two building blocks, protein and lipids (fat).
The membrane itself supports and keeps the cytoplasm in and provides a barrier to the outside environment.
Selective transport is its most vital function; nutrients in, waste products out.
Since we mentioned CYTOPLASM above, we will keep it simple and say that it is the gelatin stuff in the human cell that gives it "body" and supports the organelles.
It also contains microtubules that serve as the skeleton of
the cell, much life scaffolding. Scattered throughout the microtubules are structures called ribosomes.
RIBOSOMES play an extremely important role in human cell physiology. They are a complex structure of protein and rRNA (ribosomal ribonucleic acid) whose main function is to make protein.
They do this by expressing the genetic code from nucleic acid into protein, in a process called translation. In the grand scheme of cell physiology, this is how genes coded in our DNA become protein.
Moving further into the cell's interior we encounter the NUCLEUS which contains the code that determines who we are. Of course I'm referring to our DNA, the famous double helix.
DNA resides in our genes which in turn are carried by our chromosomes and all of it in the nucleus. By the way, the nucleus is what sets us apart from plants and bacteria. Only animal cells, which includes human cells, have a nucleus.
Next we might bump into an odd shaped structure called the ENDOPLASMIC RETICULUM (ER).
There is a smooth ER and a rough ER; the rough ER appears "rough" because it has ribosomes on its surface while the smooth ER doesn't.
Its function is mechanical support, synthesis of proteins in the rough ER and transport of certain proteins to the Golgi Apparatus.
Photo: Right - Endoplasmic Reticulum
Photo bottom - Golgi Apparatus (dark semicircles)
The Endoplasmic Reticulum and the GOLGI APPARATUS work hand in hand. The ER is an assembly line in a human cell that delivers its finished product, proteins, to the Golgi Apparatus where they are sorted, packaged and transported to different destinations in the cell.
You could say the Golgi Apparatus is the human cell's post office.
The cell needs energy to do its job and that’s where the MITOCHRONDRIA come in. These are the power plants of the cell. Their main function is the production of Adenosine Triphosphate (ATP) which is the source of energy for the cell.
There are several other smaller organelles also with very specialized functions. The LYSOSOMES are small spheres that contain powerful digestive enzymes whose main purpose is the destruction of damaged cells.
There are CENTRIOLES that play an important role in cell division and VACUOLES that contain water.
The human cell physiology is wondrous but that doesn't make it immortal...yet! Yes, cells do wear out in fact they have a preprogrammed lifespan and when their job is done, they die. The whole process is called apoptosis.
The amazing thing is the sheer numbers of cells that die and get replaced each day. Different sources give different estimates, ranging from from 50 to 70 billion per day to a high of 300 billion per day.
On the high end, that would be over 200 million cells getting regenerated every minute.
It follows that nutrition would play an important role in all that cell replacement. If any of the essential nutrient building blocks are missing, then it is probable that defective cells could be replacing those dead cells.
As shown in the chart below, human cell physiology does not allow immortality.
At this point, a paragraph on telomeres seems to be in order.
Telomeres are small bits of DNA that reside on the ends of our chromosomes and whose purpose seems to be one of protecting the chromosome. They are frequently compared to the small plastic caps on the ends of shoelaces that keep them from unraveling.
At last check there were over 800 book titles about telomeres on Amazon and too many of them carried tantalizing titles alluding to immortality and dramatically slowing down aging. The book shown above right seems to be one of the more rational treatments of the subject.
Observations show that each time the cell divides, the telomeres on the new cells are shorter than the parent cell. As cell division continues, the telomeres become so shortened that the cell loses its ability to divide and it dies.
Thus telomeres seem to be closely linked to apoptosis and may be the actual body clock that controls a cells lifespan.
Numerous research efforts are underway to discover how to prevent the shortening of the telomeres after cell division and thus bestow immortality on the cell. There is a tremendous potential for therapeutical applications in degenerative diseases at the cellular level but there seems to be a large potential for unintended consequences as well.
What other cell types are immortal? Does cancer come to mind? It should. Programmed cell death is a normal function of a healthy body and tinkering with that natural process could have the same result in the body as eliminating the brakes from your car.
What could possibly go wrong? Let's hope the cellular biologists doing the tinkering know what they are doing.
Ever wonder how all that food we swallow gets from our stomach to our cells and where it goes from there? Not to worry, not many other people lose sleep over this aspect of human cell physiology either.
Ok, just for fun let's imagine we are a meal; say a salad, a rib-eye, baked potato and a sliver of hot apple pie with ice cream on top. After the waitress delivers us to the table, what fate is in store for us.
It's not a pretty picture; you may want to ask the kids to leave the room.
First off, we get ripped apart and ground up by cutting, grinding teeth while our fats and carbohydrate parts are being slowly dissolved by saliva full of enzymes.
Then it’s down the tube, or esophagus, we go to a bag full of hydrochloric acid called a stomach (novel name) where we are squeezed and squished around in the acid until we are a liquid; this torture goes on for four hours or so.
Our protein content has been spared so far but now more powerful enzymes go to work breaking our protein apart.
Next we get squirted out to a 20 foot long tube, the small intestine, where even more chemicals go to work on us and our remaining molecules are torn asunder even more.
As we get to the last two sections of this tube our molecules have been ripped apart about as small as they can get.
Now we get absorbed through tiny finger-like projections, called villi, on the walls of this tube and just when we think it can't get any worse, we end up in a river of blood; OK, so it's a tube full of blood.
Finally we find ourselves at a big red blob called a liver where we are filtered out of the blood. Some of our vitamins, glucose and other parts get stored until we are called on to supply energy to the body or a cell puts in an order for us.
We have been transformed from an appetizing meal to raw material for a biological assembly line. Alcohol, ammonia and other disagreeable stuff was also filtered out by the liver and eliminated.
The part of us that didn't get absorbed in the small intestine, gets shuttled through to a large intestine, called a colon, where the water we picked up along the way and our minerals get absorbed.
Now we are just a collection of vitamins, minerals, sugars, amino acids and fatty acids biding our time waiting to be put to work.
Now let's get rid of the tongue-in-cheek routine and have a serious discussion on how human cell physiology takes nutrients, the raw materials, which have been stored in the liver and elsewhere in the body and converts them to structure.
Imagine an assembly line in our human cell, a biological assembly line as it were.
We will refer to this assembly line while following the path of nutrients, in this case, the essential bio-active sugars, through the assembly line.
Trehalose is one such bioactive sugar that the Endowment for Medical Research has done extensive work on uncovering its health bestowing secrets.
Hopefully we will come to understand in principle, the step-by-step cell physiology of how basic nutritional building blocks become complex molecules or structures required to carry out the functions of the body.
The cellular membrane, the skin of the cell, is a double layer of lipid molecules, protein, cholesterol and carbohydrates. The membrane is the doorway for nutrients to enter the cell.</p>
<p>Non-polar molecules, water and some small polar molecules can cross the membrane without assistance.
Most polar compounds such as amino acids, organic acid and inorganic salts must be transported across the membrane by protein molecules.
The physiology of the human cell membrane is extremely complex in its construction and function and the membrane itself is synthesized within the biological assembly line in the cell.
It is constructed such that nutrients come in through the membrane as needed and waste products go out through the membrane while keeping out everything else that doesn't belong. These decisions are controlled by proteins; receptor proteins and effector proteins, all doing their jobs in reaction to stimulus from the environment.
The bottom line is that we are not captives of our genes but to the environment.
Dr. Bruce Lipton,Ph.D, has documented his research into the new biology of Epigenetics in which genes and DNA do not control our biology, that instead DNA is controlled by signals from outside the cell for which the membrane is the key. Whether we agree or not, the book is a mind-blower and will change the way you think about who you are.
Recall that the nucleus contains the chromosomes composed of DNA chains that carry the genetic code that tells the cell what molecules to build and how to build them.
Because the nucleus houses DNA, historically it was viewed as the cell's brain. However, when the nucleus is removed from the cell it goes on living and carrying out its activities of daily living except for repairs and reproduction, both of which require DNA. If any part of the cell deserves to be called its brain, it is the membrane.
The structure above is a cross-section of the cellular membrane showing the membrane proteins. In one sense, the cells membrane is equivalent to a liquid crystal semiconductor with gates and channels which are either open or closed, depending on charges that control them.
The biological assembly line uses ribosomes to carry RNA to the assembly stations; the endoplasmic reticulum and on to the Cis, Middle and Trans Golgi.
Photo right: Secretory Flow from Nucleus to ER to Golgi
Passing down the assembly line, each station uses nutrients to build up molecules as they pass from the ER to the three sections of the Golgi apparatus.
In this case we are looking at how glycoproteins are synthesized using molecules of mannose and other essential sugars.
The whole physiology of the human cell structure starts in the cytoplasm where the three major steps in the assembly process take place in the ribosomes, followed by the ER and Golgi.
Amino acids get polymerized in the ribosome as the mRNA is pulled through the organelle and read like blueprint to start the construction process of forming peptides and protein chains.
Defining a couple of terms, polymerization is just a fancy word than means small molecules, or parts of them, are chemically combined to form larger chains or networks of molecules.
A peptide is just a polymer made up of pieces of amino acids and amino acids are just the building blocks of protein. In our doofus example above, they are what's left of that rib-eye steak that we ate.
The peptide chain then goes to the ER and glycosylation starts by adding 9 molecules of mannose organized in three chains.
Glycosylation is that part of cell physiology where sugars are added to a protein or lipid (fat). The three chain domain becomes the basis for coding the bio-information that is sent to the cell membrane receptors.
Next the mannose-rich glycoform is then taken to the Golgi for final assembly and code modification that involved the substitution of seven additional sugars (or more) for positions where mannose had been originally connected.
A glycoform in a human cell is a structure made up of the essential sugar molecules and a protein or lipid backbone.
Glycosylation in the Golgi includes coding for a timer and address to determine the lifespan of the just-constructed complex molecule and where in the body it is to be sent.
The complex sugar code on the three chains mentioned earlier, convey charge and stereometric confirmation and provide a means to communicate with other cells by fitting into receptor sites on cellular membranes.
The component parts of the cellular membranes, including the receptor sites where cytokines interact, are also made on the assembly line.
Stereometric or stereometry is a technique for measuring volume or shape of an object. So in the description above, "stereometric confirmation" can be thought of as the final inspection step or quality control performed by the cell's production process.
It makes sure that the glycoform that was just created has the electrical charge and size and shape that the blueprint specified.
If it doesn't, it would not fit into its designated receptor
and cell-to-cell communication would break down.
Just click the image link above or the book cover for more information.
There you have it. The physiology of a human cell detailed above described the production of a glycoform destined to reside on the surface of the cell and perform communication and signaling functions.
In this case it used sugars and amino acids as the nutrient raw material. The biological assembly process is the same for any type of structure the cell is called on to construct.
If any of you have ever worked in a factory environment where production depends on sequential steps being performed in a timely and correct manner, you will see the similarity to human cell physiology.
You will also know that there is a lot of room for error. The same is true of our biological production line and "errors of glycosylation" do occur and has become a hot area of research in glycobiology.
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