1. To gain more appreciation for the range of sizes associated with cellular energy production, let us examine the relative sizes of its many components. Meters are generally the best increment of measurement for our human world. For instance, the smallest features of our existence, e.g. pencil lead and human hair, are measured in millimeters. Micrometers (macrons), at a thousand times smaller are more appropriate for measuring the diameters of cells, bacteria and organelles.
2. At a thousand times smaller still, nanometers are best for relating the size of the large biomolecules of cellular energy production, rubisco, ATP synthase, and ATP. Included in this size frame are building blocks of proteins and DNA – all coming in at a single nanometer.
3. While nanometers are great for the standard biomolecules, picometers, a thousand times smaller, are best for communicating the sizes of the inorganic atoms and molecules of cellular energy production. These include molecules (water, carbon dioxide and oxygen) and atoms (hydrogen, carbon, and oxygen).
4. Smaller still are protons, neutrons, and nuclear radii. Microbiologists have chosen femtometers, a thousand times smaller than the incredibly small nanometers, for the task of size comparison. Then comes electrons and photons, the real stars of cellular energy production. Invisible, not really particles, but more energy packets, scientists can only estimate their relative size at thousands of times smaller than their nucleic friend the proton.
Wow! The range of sizes is awesome - from hair (millimeters) to cells (macrons) to biomolecules (nanometers) to simple inorganic molecules and atoms (picometers) to nuclear particles, e.g. protons, (femtometers) – each a thousand times smaller than the one before. Cellular energy production: random molecular collisions or intelligent design?
1. Micrometers (Macrons): Cells & Organelles
2. Nanometers: ATP, ATP Synthase, Rubisco & Cellular Building Blocks
3. Picometers: Cell’s inorganic molecules & atoms
4. Femtometers: Protons, Neutrons & Nuclear Radii
We’ve been speaking about the components of cellular energy production. This discussion has included everything from the cell itself (both nucleated cells like our own and non-nucleated cells like bacteria), to organelles within the cell (both mitochondria and chloroplasts). We’ve also discussed important biomolecules in the process (ATP, Glucose, ATP synthase, and rubisco) and their molecular components (Water, Carbon Dioxide, and Oxygen). Also significant to this analysis were the atomic components (Hydrogen, Carbon and Oxygen) and even the subatomic components (Protons, Electrons, and Photons).
If you are like me, you envision these elements of cellular energy production as ‘particles’ of different sizes and masses – moving hither and thither in the interior of the cell. Further you probably think of these particles as being of variable sizes from the large organelles floating inside the cell’s protoplasm to the smallest particle – the electron.
Then because we are human, we base our understanding of our world upon our own personal experience. We conceptualize these particles as if they were of the same relative dimensions with regards each other as are the elements of our world – from large airplanes or skyscrapers to the tiny hairs on our head or perhaps the tip of a needle.
Further we magnify the space that all the cellular activity occurs within to be somewhat equivalent, but smaller of course, to the common spaces we inhabit or know of – perhaps the interior of a house or a large factory.
To gain more perspective and appreciation for cellular energy production, let us examine the actual and relative sizes of its many components.
Let’s start with size frames. For humans, a meter could be called a ‘normal’ size referent. Our stride is about a meter. Very small objects in our lives are measured in millimeters, one thousandth of a meter. A bold pencil lead is 1 millimeter in diameter, while a fine pencil lead is one half of a millimeter. Our hair and a sheet of paper are both about one tenth of a millimeter in diameter – 10 x smaller than the bold pencil lead.
Due their smaller, microscopic size, scientists came up with another term for cellular dimensions. Cells are typically measured in micrometers, i.e. macrons. While millimeters are 1 thousandth of a meter, micrometers are 1 millionth of a meter. In other words, there are 1000 macrons in a millimeter. A macron is very small.
A typical human cell is only 10 macrons in diameter. For comparison, a single hair is 100 macrons in diameter. A typical hair is 10x larger than a small human cell. Because volume is proportional to diameter cubed, one thousand human cells could be put in a sphere or ball that was the same size as the width of our hair. Or as another comparison, our little toe contains roughly 3 billion cells.
As a reminder, each of these microscopic cells has a membrane, a cytoskeleton, organelles, and a nucleus. Each of these pinpoints also produces its own energy and synthesizes all the biomolecules it requires to survive. While the membrane is porous to allow nutrients inside and waste to move outside, all the cell’s multiple functions occurs internally – inside this tiny ball whose diameter is 10x smaller than the width of a piece of paper.
Yet our cells are large compared to bacteria. The typical bacteria cell is but 1 macron in diameter. An average nucleated cell is 25 macrons in diameter. As volume is proportional to diameter cubed, over 10,000 bacteria could fit inside a single cell – or one billion bacteria in a cubic inch.
While bacteria don’t contain a nucleus, they produce their own energy and synthesize their biomolecules from simple ingredients found in their immediate environment. Further, it was their microscopic scientists that first developed the processes that our cells employ to produce energy, i.e. photosynthesis and cellular respiration.
These two energy producing processes occur in the mitochondria and chloroplasts, organelles that are inside of nucleated cells (eukaryotes). As they were originally bacteria that were swallowed whole, these organelles are about the size of bacteria. Mitochondria are 0.5 – 1.0 macrons in diameter, while chloroplasts are larger at 5-10 macrons long and 2.5 macrons wide.
For reference, mitochondria are more than a hundred times smaller than the edge of a piece of paper or the width of a single hair. Within this microscopic diameter, the incredibly sophisticated and complicated processes occur that enable us to live. For instance, both mitochondria and chloroplasts have a double membrane – one to separate the organelle from the rest of the cell and the other to generate another interior space within the organelle.
The innermost chamber of the chloroplast is inhabited by granum, which are stacks of oval disks called thylakoid. There are about 5 to 25 thylakoid per granum. Each thylakoid is about 0.30 to 0.55 macron in diameter or 300 to 550 nanometers in diameter. Nanometers?
We employ millimeters to quantify the smallest objects we encounter in our human world. Biologists employ micrometers (macrons) to quantify the size of cells, both eukaryotes and prokaryotes (bacteria), plus their organelles (mitochondria and chloroplasts). Biochemists must take it down a few more orders of magnitude to quantify the sizes of Life’s biomolecules. While micrometers are sufficient for the smallest living things (cells), organic chemists employ nanometers to quantify the sizes of the cell’s building blocks.
While a micrometer is a millionth of a meter, a nanometer is a billionth of a meter. There are a thousand nanometers in a micrometer, a million nanometers in a millimeter and a billion in a meter. A nanometer is unimaginably small.
Let us now focus our attention upon the relative sizes of the diminutive stars of cellular energy production – those whose size is measured in nanometers. The big three for energy are rubisco, ATP synthase and ATP. The first two are enzymes that catalyze incredibly significant chemical reactions in photosynthesis and cellular respiration. The third is the cell’s energy currency.
Rubisco is the enzyme responsible for carbon capture in photosynthesis. During this process, an inanimate carbon molecule is transformed into an organic carbon molecule. This transformed carbon molecule eventually becomes the foundation for all the bioenergy and biomass on our planet.
Due to this highly significant role, rubisco is the most abundant enzyme on the planet. The Earth produces 1000 kilograms per second. Humans supposedly consume their weight in this mega-molecule every day.
Formed from 8 large and 8 small protein subunits, rubisco is also one of the largest enzymes. It is 10.5 nanometers wide and 13 nanometers tall. For comparison, average bacteria are 1 macron in diameter = 1000 nanometers. This immense, protein-filled molecule is a hundred times smaller in width than microscopic bacteria and 1000 times smaller than our human cells. In turn, our cells are 100 times smaller in diameter than the tiny millimeter that we employ to measure the width of hair and pencil lead, i.e. the very small.
ATP synthase, our second star, “provides all cells with the ‘energy currency’ adenosine triphosphate, ATP, which is needed for all processes of life.” It is the enzyme that catalyzes the chemical reaction in the miraculous last stage of cellular respiration. In the entropic urge to balance electromagnetic charges, previously jailed protons rush across a membrane. In so doing, these protons spin this enormous enzyme. This spinning charges an enormous number of ATP molecules, enough to power our human cells.
At 10 nanometers (nm) wide and 20 nm high, skinny ATP synthase is a bit taller and a bit thinner than rounded rubisco. In similar fashion to rubisco, ATP synthase is 2 orders of magnitude smaller than a bacterium.
ATP, the molecule that epitomizes bioenergy, is 10x smaller than these mega-proteins, at 1.4 nanometers in diameter. His partners in energy, the biomolecules that transport electrons around, are bit larger. For instance, the electron carrier, NADP, is almost twice as big at 2.5 nm. Now we have shrunk our gaze to 3 orders of magnitude smaller than the smallest cell.
Human Cells = 10,000 nm
Bacteria = 1000 nm
ATP synthase 10 nm x 20 nm
Rubisco 10.5 nm x 13 nm
NADP 2.5 nm
ATP 1.4 nm
Let us complete our discussion of biomolecular size by briefly mentioning the building blocks of DNA and proteins. Life’s building block molecules (amino acids, nucleotides, energy carriers) are small molecules that are best quantified in nanometers. In fact, their dimensions surround 1 nanometer. For instance, most individual proteins range between 2 to 7 nanometers is size, while their components (amino acids) are a little under 1 nanometer.
Others of our highlighted biocharacters also measure their dimensions in nanometers. The cellular membrane is between 7.5 to 10 nanometers thick and the microfilaments in the cell’s cytoskeleton are about 5 to 7 nanometers wide.
How about the famous IMPs - the cell’s sensory motor network and the material substrate of Attention? These Integral Membrane Proteins (IMPs) are embedded in the cellular membrane to both sense and interact with both the external and internal environment of the cell. In order to perform their interactive functions, these proteins are much larger than the membrane they are embedded in. IMPs range in length from 30 to 160 nanometers.
Cellular Membrane = 7.5 - 10 nm
Microfilaments in Cytoskeleton = 5 - 7 nm
Proteins = 2 – 7 nm
DNA chain = 2.2 – 2.6 nm
Amino acids = 0.4 – 1 nm
Nucleotide pair = 0.34 nm
To gain perspective, let us take a step back. Humans employ millimeters to characterize the very small in our visible world (pencil lead and gems). Cells, if they could, would employ nanometers to characterize the very small in their microscopic world (membranes and building block biomolecules). The very small in the human world is 6 orders of magnitude (one million times) larger than the very small in the cellular universe.
Nanometers to Cells ≈ Millimeters to Humans
But our shrinking process still has a way to go. Each of these organic biomolecules is composed of a multitude ‘inanimate’ atoms and molecules. And as we know, the cell’s energy-producing process specializes in the deployment of even smaller particles - hydrogen atoms, protons and even electrons. But we are getting ahead of ourselves. Let us first examine the dimensions of the extraordinarily ordinary molecules in the cell’s basic energy producing process.
Recall the equations that describe the energy conversions that allow us to live:
6 Water + 6 Carbon Dioxide + Sunlight = Glucose + 6 Oxygen
Glucose + 6 Oxygen = Bioenergy + 6 Water + 6 Carbon Dioxide
The indisputable stars of these complementary processes are ‘ordinary inanimate’ molecules: Carbon Dioxide, Oxygen and Water. The cellular factory converts these common substances into a large biomolecule, Glucose, the source of all the biomass and bioenergy on our planet.
To provide a relative sense of the size of our star molecules (the ones we have highlighted in our discussions), we list their dimensions in both nanometers and picometers. While a nanometer (nm) is a billionth of a meter, a picometer (pm) is a trillionth of a meter.
Glucose diameter = 1000 pm = 1 nm
180 Protons & Neutrons
CO2 = Carbon Dioxide diameter = 330 pm = 0.33 nm
44 Protons & Neutrons
O2 = Oxygen molecule = 292 pm = 0.292 nm
32 Protons & Neutrons
H2O = Water = 270 pm = 0.270 nm
18 Protons & Neutrons
All of our molecules are between a quarter and a third of a nanometer, while glucose is considerably larger at a full nanometer. We are referring to diameters. As such, the glucose molecule contains approximately 27 times more volume than carbon dioxide, the largest of our inanimate stars. This is reasonable as glucose contains many more atoms (24) than the others (3, 2, 3), subsequently more protons and neutrons (180 vs. 44, 32, 18).
But these are molecules. We can’t forget the three fundamental atoms to cellular energy production – hydrogen, carbon, and oxygen. Recall that the cell finds them in the air.
When we get to the size of atoms and chemical bonds, picometers become more convenient. Indeed, atoms are between 62 and 520 picometers (a billionth of a meter) in diameter. The relative dimensions of our star atoms are listed below.
H2O = Water = 270 pm = 0.270 nm
Carbon diameter = 154 pm = 0.154 nm
Carbon-carbon bond =150 pm = 0.15 nm
Oxygen = 132 pm = 0.132 nm
Hydrogen = 100 pm = 0.1 nm
Let’s start this brief comparison with the famous atomic megastar, everyone’s favorite atom – carbon. Carbon’s diameter is about one half that of water. And the ubiquitous carbon-carbon bond, that is the stable foundation of glucose as well as many other important biomolecules, is about the same size. While a little smaller, the atoms of oxygen and hydrogen are in the same order of magnitude. All are between 100 to 154 picometers in diameter. For comparison, the enormous Rubisco enzyme is over a 100x the width of a hydrogen atom, which translates into a million times larger in volume.
Although orders of magnitude smaller than microscopic, Life’s building block molecules and atoms are gargantuan in comparison with the cell’s subatomic superstars – protons and electrons. Recall that the cellular transport system is regularly moving these tiniest of ingredients around strategically to serve the cell’s energy needs.
Millimeters (thousandths of a meter) are the measurement increment that best describe the tiniest objects in our human realm (pencil lead); micrometers (millionth) are employed for bacteria and cellular size. Nanometers (billionth) are best for the tiny molecular building blocks of the cellular realm; while picometers (trillionth) best capture the sizes of the inanimate atomic particles that are important to the cell. Each of these measurement increments are 1000 times (3 orders of magnitude) smaller than the one before. As such, atomic sizes are a billion times (9 orders of magnitude) smaller than a millimeter.
However, to conveniently characterize the sizes of protons, we must introduce yet another even smaller measurement increment – the femtometer. A femtometer is a quadrillionth of a meter – a thousand times smaller than tiny atom-oriented picometers and 15 orders of magnitude (10-15) smaller than a meter. Femtometers are primarily employed to characterize nuclear sizes. For instance, carbon’s nucleus is 4 femtometers (fm) in diameter, while lead’s nucleus is 15 fm.
Yet an atom’s nucleus is composed of both protons and neutrons. Our cell’s primary energy producing process (chemiosmosis) deals in single protons. To charge enough ATP to power our multicellular systems, a single photon energizes a single electron to push a single proton (a hydrogen ion) across a membrane. Rather than atomic nuclei, the cell is primarily interested in their building blocks - protons.
The diameter of a proton, as well as a neutron, is 0.84 femtometers across (10 x -15 meters or a quadrillionth of meter). For comparison, the diameter of the hydrogen atom in which it is contained is 100,000 times larger (10-10 Meters); a microscopic water molecule is a million times larger; and one of our cells that employs this subatomic particle to power its engine is a billion times larger (9 orders of magnitude). And the bold pencil lead that we employ to scratch out notes is colossal at a trillion times larger (12 orders of magnitude).
Following is a list of the relative size of our cellular stars in femtometers (fm).
Proton/Neutron diameter = 0.84 fm
Carbon nucleus: diameter = 4 fm
Lead nucleus: diameter = 15 fm (10-15 meter)
Hydrogen atom: diameter = 100,000 fm
Water Molecule diameter = 1 million fm
Cell = 1 billion fm
Bold Pencil Lead = 1 trillion fm
In addition to protons, the cell also employs single electrons in its energy production process. While the proton is small, the electron is smaller still. Or is it?
Certainly one of the more unusual denizens of our fair planet, the electron resists quantification in the usual ways (Galileo’s Big 3: weight, location, and time). Before delving into the bizarre characteristics of the mysterious electron, let us provide a relative figure that biologists have proposed for those of us with an obsession with quantification by size.
Some have made approximate extrapolations showing that an electron is a ten thousand times smaller than a proton. Others say 100 million times smaller. Why the variance in proposed size? Four orders of magnitude difference between the smallest and largest estimate. This variation is just one indication of the uncertain status of our friend the electron.
Following are the relative sizes of our subatomic superstars, along with some comparative values.
Hydrogen atom: diameter = 100,000 femtometers (fm) (10-15 meter)
Lead nucleus: diameter = 15 fm
Carbon nucleus: diameter = 4 fm
Proton/Neutron: diameter = 0.84 fm
Electron = 0.0001 fm or 0.00000001 fm (10-18 > 10-22 Meters)
With these unimaginably small dimensions in mind, let us now talk a little about the enigmatic electron. In fact, there is so much to say that we have devoted an entire chapter to this essential and ubiquitous ‘subatomic particle’.