PARTICLE PHYSICS OF THE HUMAN

Fourteen billion years ago, when the hot, dense speck that was our universe quickly expanded, all of the matter and antimatter that existed should have annihilated and left us nothing but energy. And yet, a small amount of matter survived.

We ended up with a world filled with particles. And not just any particles—particles whose masses and charges were just precise enough to allow human life. Here are a few facts about the particle physics of you that will get your electrons jumping.

The particles we’re made of

About 99 percent of your body is made up of atoms of hydrogen, carbon, nitrogen and oxygen. You also contain much smaller amounts of the other elements that are essential for life.

While most of the cells in your body regenerate every seven to 15 years, many of the particles that make up those cells have actually existed for millions of millennia. The hydrogen atoms in you were produced in the big bang, and the carbon, nitrogen and oxygen atoms were made in burning stars. The very heavy elements in you were made in exploding stars.

The size of an atom is governed by the average location of its electrons. Nuclei are around 100,000 times smaller than the atoms they’re housed in. If the nucleus were the size of a peanut, the atom would be about the size of a baseball stadium. If we lost all the dead space inside our atoms, we would each be able to fit into a particle of lead dust, and the entire human race would fit into the volume of a sugar cube.

As you might guess, these spaced-out particles make up only a tiny portion of your mass. The protons and neutrons inside of an atom’s nucleus are each made up of three quarks. The mass of the quarks, which comes from their interaction with the Higgs field, accounts for just a few percent of the mass of a proton or neutron. Gluons, carriers of the strong nuclear force that holds these quarks together, are completely massless.

If your mass doesn’t come from the masses of these particles, where does it come from? Energy. Scientists believe that almost all of your body’s mass comes from the kinetic energy of the quarks and the binding energy of the gluons.

The particles we make

Your body is a small-scale mine of radioactive particles. You receive an annual 40-millirem dose from the natural radioactivity originating inside of you. That’s the same amount of radiation you’d be exposed to from having four chest X-rays. Your radiation dose level can go up by one or two millirem for every eight hours you spend sleeping next to your similarly radioactive loved one.

You emit radiation because many of the foods you eat, the beverages you drink and even the air you breathe contain radionuclides such as Potassium-40 and Carbon-14. They are incorporated into your molecules and eventually decay and produce radiation in your body.

When Potassium-40 decays, it releases a positron, the electron’s antimatter twin, so you also contain a small amount of antimatter. The average human produces more than 4000 positrons per day, about 180 per hour. But it’s not long before these positrons bump into your electrons and annihilate into radiation in the form of gamma rays.

The particles we meet

The radioactivity born inside your body is only a fraction of the radiation you naturally (and harmlessly) come in contact with on an everyday basis. The average American receives a radiation dose of about 620 millirem every year. The food you eat, the house you live in and the rocks and soil you walk on all expose you to low levels of radioactivity. Just eating a Brazil nut or going to the dentist can up your radiation dose level by a few millirem. Smoking cigarettes can increase it up to 16,000 millirem.

Cosmic rays, high-energy radiation from outer space, constantly smack into our atmosphere. There, they collide with other nuclei and produce mesons, many of which decay into particles such as muons and neutrinos. All of these shower down on the surface of the Earth and pass through you at a rate of about 10 per second. They add about 27 millirem to your yearly dose of radiation. These cosmic particles can sometimes disrupt our genetics, causing subtle mutations, and may be a contributing factor in evolution.

In addition to bombarding us with photons that dictate the way we see the world around us, our sun also releases an onslaught of particles called neutrinos. Neutrinos are constant visitors in your body, zipping through at a rate of nearly 100 trillion every second. Aside from the sun, neutrinos stream out from other sources, including nuclear reactions in other stars and on our own planet.

Many neutrinos have been around since the first few seconds of the early universe, outdating even your own atoms. But these particles are so weakly interacting that they pass right through you, leaving no sign of their visit.

You are also likely facing a constant shower of particles of dark matter. Dark matter doesn’t emit, reflect or absorb light, making it quite hard to detect, yet scientists think it makes up about 80 percent of the matter in the universe.

Looking at the density of dark matter throughout the universe, scientists calculate that hundreds of thousands of these particles might be passing through you every second, colliding with your atoms about once a minute. But dark matter doesn’t interact very strongly with the matter you’re made of, so they are unlikely to have any noticeable effects on your body.

The next time you’re wondering how particle physics applies to your life, just take a look inside yourself.

What is your body made of ?

Your first thought might be that it is made up of different organs—such as your heart, lungs, and stomach—that work together to keep your body going. Or you might zoom in a level and say that your body is made up of many different types of cells. However, at the most basic level, your body—and, in fact, all of life, as well as the nonliving world—is made up of atoms, often organized into larger structures called molecules.

Atoms and molecules follow the rules of chemistry and physics, even when they're part of a complex, living, breathing being. If you learned in chemistry that some atoms tend to gain or lose electrons or form bonds with each other, those facts remain true even when the atoms or molecules are part of a living thing. In fact, simple interactions between atoms—played out many times and in many different combinations, in a single cell or a larger organism—are what make life possible. One could argue that everything you are, including your consciousness, is the byproduct of chemical and electrical interactions between a very, very large number of nonliving atoms!

So as an incredibly complex being made up of roughly 7,000,000,000,000,000,000,000,000,000 atoms, you'll probably want to know some basic chemistry as you begin to explore the world of biology, and the world in general.

Matter and elements

The term matter refers to anything that occupies space and has mass—in other words, the “stuff” that the universe is made of. All matter is made up of substances called elements, which have specific chemical and physical properties and cannot be broken down into other substances through ordinary chemical reactions. Gold, for instance, is an element, and so is carbon. There are 118 elements, but only 92 occur naturally. The remaining elements have only been made in laboratories and are unstable.

Each element is designated by its chemical symbol, which is a single capital letter or, when the first letter is already “taken” by another element, a combination of two letters. Some elements follow the English term for the element, such as C for carbon and Ca for calcium. Other elements’ chemical symbols come from their Latin names; for example, the symbol for sodium is Na, which is a short form of natrium, the Latin word for sodium.

The four elements common to all living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), which together make up about 96% of the human body. In the nonliving world, elements are found in different proportions, and some elements common to living organisms are relatively rare on the earth as a whole. All elements and the chemical reactions between them obey the same chemical and physical laws, regardless of whether they are a part of the living or nonliving world.

The structure of the atom

An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, a gold coin is simply a very large number of gold atoms molded into the shape of a coin, with small amounts of other, contaminating elements. Gold atoms cannot be broken down into anything smaller while still retaining the properties of gold. A gold atom gets its properties from the tiny subatomic particles it's made up of.

An atom consists of two regions. The first is the tiny atomic nucleus, which is in the center of the atom and contains positively charged particles called protons and neutral, uncharged, particles called neutrons. The second, much larger, region of the atom is a “cloud” of electrons, negatively charged particles that orbit around the nucleus. The attraction between the positively charged protons and negatively charged electrons holds the atom together. Most atoms contain all three of these types of subatomic particles—protons, electrons, and neutrons. Hydrogen (H) is an exception because it typically has one proton and one electron, but no neutrons. The number of protons in the nucleus determines which element an atom is, while the number of electrons surrounding the nucleus determines which kind of reactions the atom will undergo. The three types of subatomic particles are illustrated below for an atom of helium—which, by definition, contains two protons.

Structure of an atom.

The protons (positive charge) and neutrons (neutral charge) are found together in the tiny nucleus at the center of the atom. The electrons (negative charge) occupy a large, spherical cloud surrounding the nucleus. The atom shown in this particular image is helium, with two protons, two neutrons, and two electrons.

Protons and neutrons do not have the same charge, but they do have approximately the same mass, about 1.67 × 10^{-24}1.67×10−241, point, 67, ×, 10, start superscript, minus, 24, end superscript grams. Since grams are not a very convenient unit for measuring masses that tiny, scientists chose to define an alternative measure, the dalton or atomic mass unit (amu). A single neutron or proton has a weight very close to 1 amu. Electrons are much smaller in mass than protons, only about 1/1800 of an atomic mass unit, so they do not contribute much to an element’s overall atomic mass. On the other hand, electrons do greatly affect an atom’s charge, as each electron has a negative charge equal to the positive charge of a proton. In uncharged, neutral atoms, the number of electrons orbiting the nucleus is equal to the number of protons inside the nucleus. The positive and negative charges cancel out, leading to an atom with no net charge.

Protons, neutrons, and electrons are very small, and most of the volume of an atom—greater than 99 percent—is actually empty space. With all this empty space, you might ask why so-called solid objects don’t just pass through one another. The answer is that the negatively charged electron clouds of the atoms will repel each other if they get too close together, resulting in our perception of solidity.

The periodic table

By convention, elements are organized in the periodic table, a structure that captures important patterns in their behavior. Devised by Russian chemist Dmitri Mendeleev (1834–1907) in 1869, the table places elements into columns—groups—and rows—periods—that share certain properties. These properties determine an element’s physical state at room temperature—gas, solid, or liquid—as well as its chemical reactivity, the ability to form chemical bonds with other atoms.

In addition to listing the atomic number for each element, the periodic table also displays the element’s relative atomic mass, the weighted average for its naturally occurring isotopes on earth. Looking at hydrogen, for example, its symbol, \text{H,}H,start text, H, comma, end text and name appear, as well as its atomic number of one—in the upper left-hand corner—and its relative atomic mass of 1.01.

The periodic table of the elements

Differences in chemical reactivity between elements are based on the number and spatial distribution of their electrons. If two atoms have complementary electron patterns, they can react and form a chemical bond, creating a molecule or compound. As we will see below, the periodic table organizes elements in a way that reflects their number and pattern of electrons, which makes it useful for predicting the reactivity of an element: how likely it is to form bonds, and with which other elements.

Elements are placed in order on the periodic table based on their atomic number, how many protons they have. In a neutral atom, the number of electrons will equal the number of protons, so we can easily determine electron number from atomic number. In addition, the position of an element in the periodic table—its column, or group, and row, or period—provides useful information about how those electrons are arranged.

If we consider just the first three rows of the table, which include the major elements important to life, each row corresponds to the filling of a different electron shell: helium and hydrogen place their electrons in the 1n shell, while second-row elements like Li start filling the 2n shell, and third-row elements like Na continue with the 3n shell. Similarly, an element’s column number gives information about its number of valence electrons and reactivity. In general, the number of valence electrons is the same within a column and increases from left to right within a row. Group 1 elements have just one valence electron and group 18 elements have eight, except for helium, which has only two electrons total. Thus, group number is a good predictor of how reactive each element will be:

Electron shells and the Bohr model

An early model of the atom was developed in 1913 by the Danish scientist Niels Bohr (1885–1962). The Bohr model shows the atom as a central nucleus containing protons and neutrons, with the electrons in circular electron shells at specific distances from the nucleus, similar to planets orbiting around the sun. Each electron shell has a different energy level, with those shells closest to the nucleus being lower in energy than those farther from the nucleus. By convention, each shell is assigned a number and the symbol n—for example, the electron shell closest to the nucleus is called 1n. In order to move between shells, an electron must absorb or release an amount of energy corresponding exactly to the difference in energy between the shells. For instance, if an electron absorbs energy from a photon, it may become excited and move to a higher-energy shell; conversely, when an excited electron drops back down to a lower-energy shell, it will release energy, often in the form of heat.

Bohr model of an atom, showing energy levels as concentric circles surrounding the nucleus. Energy must be added to move an electron outward to a higher energy level, and energy is released when an electron falls down from a higher energy level to a closer-in one.

Atoms, like other things governed by the laws of physics, tend to take on the lowest-energy, most stable configuration they can. Thus, the electron shells of an atom are populated from the inside out, with electrons filling up the low-energy shells closer to the nucleus before they move into the higher-energy shells further out. The shell closest to the nucleus, 1n, can hold two electrons, while the next shell, 2n, can hold eight, and the third shell, 3n, can hold up to eighteen.

The number of electrons in the outermost shell of a particular atom determines its reactivity, or tendency to form chemical bonds with other atoms. This outermost shell is known as the valence shell, and the electrons found in it are called valence electrons. In general, atoms are most stable, least reactive, when their outermost electron shell is full. Most of the elements important in biology need eight electrons in their outermost shell in order to be stable, and this rule of thumb is known as the octet rule. Some atoms can be stable with an octet even though their valence shell is the 3n shell, which can hold up to 18 electrons.

The following very basic information about cells might help you understand a little bit more about them and the important role they play.

Cells

Cells are a miniature microcosm of man. They have organs within a protective skin. They have a brain, can interact with their environment, make decisions, accomplish tasks, repair and reproduce themselves. There are a lot of reasons why cells stop responding they could be damaged, diseased or have abnormal cell tissue. When a cell starts to mutate they could accumulate into tumors

Cell Structure

Visualize a “typical” cell as a round circle. The outside of the circle is called the membrane. The membrane encloses the inner workings of the cell. This is similar to our body’s skin encompassing our internal organs. There are about 100 trillion cells in our body grouped together into different organs and functions.

Cell Membrane

The membrane contains proteins called Integral Membrane Proteins (IMP). Two important types are called receptor proteins and effector proteins. The receptor IMPs are the cell’s sense organs, the equivalent of our eyes, ears, nose, taste buds, etc.

Receptors function as individual molecular mini “Nano-antennas”, each tuned to respond to specific environmental signals. Some of these receptor proteins extend from the cell’s outer surface, monitoring external signals.

In addition to responding to physical signals, receptor “antennas” can read vibrational energy fields such as light, sound, radio frequencies and thought.

The receptor proteins provide an awareness and reaction to environmental signals, but the need also exists to create a life-sustaining response to the inner functions of the cell. This is the task of the effector proteins. Taken together the receptor-effector proteins provide a stimulus-response mechanism.

The membrane acts as the brain of the cell (hence membrane). Research has demonstrated that when the nucleus of the cell is removed the cell continues with reduced functioning. But, when the membrane is removed, the cell quits functioning and the cell dies. The membrane makes the decisions for the cells.

When a cell gets activated it heals, it detoxifies by expunging toxins from within the cell through the membrane.

The body then directs more blood to the area, to remove the toxins, this is why a warming feeling is felt by some people.

Regulatory proteins on the outside of each cell’s membrane sense external environmental signal as well which activate DNA / RNA (genes).

Inner Cell

Cells are made up of four types of large molecules: complex sugars, fats, nucleic acids (DNA/RNA), and proteins.

Most of the cell’s structures are referred to as organelles, which are “miniature organs” suspended within a jelly-like cytoplasm. They include the nucleus and the mitochondria.

Hereditary information is passed on via chromosomes, which are used when a cell divides into replacement cells. The chromosomes are incorporated in the nucleus. Genes are found on chromosomes. Chromosomes are singular pieces of DNA, which contain many genes, regulatory elements and other nucleotide sequences. The chromosomes contain two types of molecules – DNA and protein.

DNA, (deoxyribonucleic acid) is a nucleic acid that carries the genetic information in the cell and is capable of self-replication and synthesis into a very similar molecule called RNA (ribonucleic acid). When a gene is read by a cell the DNA sequence is copied into the RNA.

DNA consists of two long chains of repeating units twisted into a double helix and joined by hydrogen bonds. These units are four types of nucleotides: adenine, thymine, cytosine, and guanine (A, T, C, and G). The sequence of nucleotides stores information in an alphabet called the genetic code and determines individual hereditary characteristics.

A gene is the molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA. These stretches are really “codes” for either a type of protein or for an RNA chain section that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism's cells and pass genetic traits to offspring.

Some organelles (e.g. mitochondria) are self-replicating and do not require coding by the organism's DNA.

The function of genes is to provide the information needed to make the proteins in cells. Genes give the instructions and the proteins carry out the instructions, tasks like creating a new cell or repairing an existing damaged, diseased or abnormal cell! Genes tell cells what to do by telling them which proteins to make and in what amounts. Genes are expressed by being transcribed into RNA, and this RNA is then translated into proteins.

A protein is any of a group of complex organic macromolecules that contain carbon, hydrogen, oxygen, nitrogen, and usually sulfur and are composed of one or more chains of amino acids. Proteins are made of a chain of 20 different types of amino acid molecules. Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies that are necessary for the proper functioning of an organism. They are essential for the growth and repair of tissue.