Kurzgesagt – In a Nutshell
Sources – Why are you alive?
We want to thank the following experts for their valuable input:
- Dr James Gurney
Doctor of Microbiology
- Dr Nitai Steinberg
PhD in Microbiology, MSC in Biomedical Communication
- Anonymous
Prof. in Molecular Evolution
– All life is based on the cell.
#What is life?, 2020
Quote: “All living organisms are made up of one or more cells, which are considered the fundamental units of life.”
#What is a cell?, 2014
https://www.nature.com/scitable/topicpage/what-is-a-cell-14023083/
Quote: “Trees in a forest, fish in a river, horseflies on a farm, lemurs in the jungle, reeds in a pond, worms in the soil — all these plants and animals are made of the building blocks we call cells.”
#What is a cell?, 2020
https://ghr.nlm.nih.gov/primer/basics/cell
Quote. “Cells are the basic building blocks of all living things.“
– A cell is filled up with millions of proteins and millions more simpler molecules like water.
#Section 1.2 The Molecules of Life, 2000
https://www.ncbi.nlm.nih.gov/books/NBK21473/
Quote: “To carry this calculation one step further, consider that a liver cell contains about 10,000 different proteins; thus, a cell contains close to a million molecules of each protein on average. In actuality, however, the abundance of different proteins varies widely, from the quite rare cell-surface protein that binds the hormone insulin (20,000 molecules) to the abundant structural protein actin (5 × 108 molecules).”
– Thousands of complex self replicating processes are happening, up to hundreds of thousands of times every second.
This number was quite difficult to calculate, because there are several different self replicating processes. These peer reviewed papers give us some numbers for mitochondrial ATP synthases. They tell us that there are roughly 100 processes per mitochondria, each making around 10 ATP per second and there are 10 mitochondria per cell. That gives us about 10,000 processes just making ATP.
Then there are dimers, which are two copies of proteins that are working together to do a function. Each of these dimers is making ATP in the mitochondria.
#Macromolecular organization of ATP synthase and complex I in whole mitochondria, 2011
https://www.pnas.org/content/108/34/14121
Quote “The number of dimers used in each average was as follows: bovine heart, 84; Y. lipolytica, 136; P. anserina, 24; S. cerevisiae, 138; and potato, 71.”
When you include other self replicating processes like genetic self replication, like DNA to RNA to amino acids, it becomes far more processes per second. Each of these process has hundreds of proteins each whirling around at quite a speed. RNA to amino acids happens at a rate of around 1 second per base pair, a highly expressed gene will have thousands of copies of mRNA at any one time.
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001910
Quote. “We found that the optimal Δν (i.e., the Δνmaximizing the fitness) is −12.2 and −5.3 codons per second for genes with the highest (5,000 mRNA molecules/cell) and lowest (1) expressions considered, respectively.”
Even though it is probably even more, we went with the number of hundreds of thousands of self replicating processes, since this is what we can say for sure.
– For example cells need to keep the molecules around their membranes strictly separated and actively pump out the excess molecules from the inside to the outside.
Protons are positively charged particles, by pushing these outside of the cell the cell makes a difference in charge between inside the cell and outside. Think of the classic experiment of rubbing a balloon on your hair. You are shifting electrons and protons which causes a charge to build up. Or even think of a water dam. The water wants to flow down hill, the proton wants to flow towards the negative space inside the cell. The cell membrane acts like a dam wall and stops the charged particle getting inside. Opening the cell membrane a little lets these protons rush in, the cell uses this physical motion to drive turbines in the cell membrane. That is not an analogy – they really are spinning proteins that act as turbines to drive cellular processes.
#Why Are Cells Powered by Proton Gradients?, 2010
https://www.nature.com/scitable/topicpage/why-are-cells-powered-by-proton-gradients-14373960/
Quote. “Proton gradients are equally central to all forms of photosynthesis, as well as to bacterial motility (via the famous flagellar motor, a rotary motor similar to the ATP synthase) and homeostasis (the import and export of many molecules in and out of the cell is coupled directly to the proton gradient). “
– Energy is the ability of things in the universe to do work, to move or manipulate a thing, to create change. This ability can not be created or destroyed, the set amount of energy in the universe will never change.
That fact that energy can never be created or destroyed is the first law of thermodynamics:
#What is the first law of thermodynamics?, 2020
Quote: “The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system”
– We don’t know a lot about the first cells except that they probably got their energy from breaking down chemicals.
#The Origin and Evolution of Cells, 2000
https://www.ncbi.nlm.nih.gov/books/NBK9841/
Quote: “All cells use adenosine 5′-triphosphate (ATP) as their source of metabolic energy to drive the synthesis of cell constituents and carry out other energy-requiring activities, such as movement (e.g., muscle contraction). The mechanisms used by cells for the generation of ATP are thought to have evolved in three stages, corresponding to the evolution of glycolysis, photosynthesis, and oxidative metabolism (Figure 1.5)”
– And they found the ultimate energy transport system: The energetic building block of life. The molecule Adenosine Triphosphate, or ATP.
#The Evolution of Electron-Transport Chains, 2002
https://www.ncbi.nlm.nih.gov/books/NBK26849/
Quote: “The Earliest Cells Probably Produced ATP by Fermentation“
– When a cell needs energy, for example to repair a broken micromachine it can break down ATP and use the chemical energy to do work and create change.
#Damage Control: Cellular Mechanisms of Plasma Membrane Repair, 2014
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4252702/
Quote: “Several studies demonstrated that plasma membrane repair is strictly ATP dependent”
– But every living thing we know uses ATP or something very similar to keep its internal machinery running. It is crucial for almost every process plants, fungi, bacteria, and animals need to survive.
#Evolution of proton pumping ATPases: Rooting the tree of life., 1992
https://www.ncbi.nlm.nih.gov/pubmed/24408574
Quote: “Proton pumping ATPases are found in all groups of present day organisms. “
– early life did miss out on the greatest available source of energy: The sun. After hundreds of millions of years of evolution, finally a cell figured out how to eat the sun.
Photosynthesis is the process through which organisms convert inorganic carbon (CO2) to organic compounds, which they then use as food, using sunlight and water. But this was not the only way how the first microorganisms were producing their energy. With low levels of oxygen in the environment early microbes harvested other chemicals to produce their energy without requiring sunlight.
The earliest evidence for photosynthetic life we found dates back 3.2 to 3.5 billion years, but we know that there were earlier forms of life around 3.7 billion years. So, it took at least hundreds of millions of years of evolution to get to that point.
#Early Evolution of Photosynthesis, 2010
http://www.plantphysiol.org/content/154/2/434
Quote: “There is suggestive evidence that photosynthetic organisms were present approximately 3.2 to 3.5 billion years ago, in the form of stromatolites, layered structures similar to forms that are produced by some modern cyanobacteria, as well as numerous microfossils that have been interpreted as arising from phototrophs (Des Marais, 2000). In all these cases, phototrophs are not certain to have been the source of the fossils, but are inferred from the morphology or geological context. There is also isotopic evidence for autotrophic carbon fixation at 3.7 to 3.8 billion years ago, although there is nothing that indicates that these organisms were photosynthetic.”
– It absorbed radiation and converted much of it into neat little chemical packages that it could use to stay alive. We call this process photosynthesis. You take photons that are wobbly with electromagnetic energy and use a part of this energy to merge and combine different molecules together. The electromagnetic energy is converted into chemical energy, stored in the ATP molecule.
#What is Photosynthesis?, 2018
https://www.livescience.com/51720-photosynthesis.html
Quote: “The released electron manages to escape by traveling through an electron transport chain, which generates the energy needed to produce ATP (adenosine triphosphate, a source of chemical energy for cells) and NADPH. The "electron hole" in the original chlorophyll pigment is filled by taking an electron from water. As a result, oxygen is released into the atmosphere.”
– This is so convenient that some cells decided that instead of doing all that pesky photosynthesis work themselves, they would just rip open cells that did and take their glucose and ATP.
#It’s a Cell-Eat-Cell World, 2013
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3589073/
Quote: “The ingestion of one cell by another undoubtedly arose as a feeding mechanism in unicellular organisms. In a twist of fate, proteobacteria and cyanobacteria engulfed by larger archaebacteria managed to survive, giving rise to symbiotic relationships that form the basis of eukaryotic cells.”
– Evolution did its thing but overall things stayed pretty much the same for hundreds of millions of years.
#The Origin and Evolution of Cells, 2000
https://www.ncbi.nlm.nih.gov/books/NBK9841/
Quote: “It appears that life first emerged at least 3.8 billion years ago, approximately 750 million years after Earth was formed (Figure 1.1).”
The scale indicates the approximate times at which some of the major events in the evolution of cells are thought to have occurred:
– Until one day, a cell ate another and did not kill it. Instead they became one cell. Nothing had changed that day but earth would be different forever .
#The origins of Mitochondria, 2010
https://www.nature.com/scitable/topicpage/the-origin-of-mitochondria-14232356/
Quote: “Mitochondria arose once in evolution, and their origin entailed an endosymbiosis accompanied by gene transfers from the endosymbiont to the host. Anaerobic mitochondria pose a puzzle for traditional views on mitochondrial origins but fit nicely in newer theories on mitochondrial evolution that were formulated specifically to take the common ancestry of mitochondria and hydrogenosomes into account. “
#The origins of phagocytosis and eukaryogenesis, 2001
https://www.ncbi.nlm.nih.gov/pubmed/19245710
“The present findings suggest a hypothetical scenario of eukaryogenesis under which the archaeal ancestor of eukaryotes had no cell wall (like modern Thermoplasma) but had an actin-based cytoskeleton including branched actin filaments that allowed this organism to produce actin-supported membrane protrusions. These protrusions would facilitate accidental, occasional engulfment of bacteria, one of which eventually became the mitochondrion.”
– The formerly independent cell in the inside could stop trying to survive. It could concentrate on one thing: Make ATP. It became the powerhouse of the cell, the first mitochondria. The host cell’s job became to ensure survival in the dangerous world and provide the mitochondria with food. The host cell’s job became to ensure survival in the dangerous world and provide the mitochondria with food.
The host cell provides glucose, the mitochondria turns that into ATP for both of them:
#The origins of Mitochondria, 2010
https://www.nature.com/scitable/topicpage/the-origin-of-mitochondria-14232356/
Quote: “The mitochondria typical of mammalian cells respire O2 during the process of pyruvate breakdown and ATP synthesis, generating water and carbon dioxide as end products”
– Mitochondria basically reverse photosynthesis, in a similarly complex process: They take sugar molecules that we got from eating other living things, combust them with oxygen and precursor molecules to make new, energy rich ATP molecules. This process works like a tiny furnace and spits out waste products like CO2, Water and a little bit of kinetic energy that you experience as body heat.
#The origins of Mitochondria, 2010
https://www.nature.com/scitable/topicpage/the-origin-of-mitochondria-14232356/
Quote: “The Krebs cycle and the electron transport chain in the inner mitochondrial membrane enable the cell to generate about 36 moles (mol) of ATP per mole of glucose, with the help of O2–respiring mitochondria”
– At some point these cells began to form small groups or communities. Which leads to multicellular life and finally to you.
#The Origin and Evolution of Cells, 2000
https://www.ncbi.nlm.nih.gov/books/NBK9841/
Quote. “Multicellular organisms evolved from unicellular eukaryotes at least 1.7 billion years ago. Some unicellular eukaryotes form multicellular aggregates that appear to represent an evolutionary transition from single cells to multicellular organisms. “
– Today you are a pile of trillions of cells, filled with dozens if not hundreds of little machines, that provide you with usable energy to stay alive. If this process is interrupted, even for a few minutes, you die.
#An estimation of the number of cells in the human body, 2013
https://www.ncbi.nlm.nih.gov/pubmed/23829164
Quote: “RESULTS: A current estimation of human total cell number calculated for a variety of organs and cell types is presented. These partial data correspond to a total number of 3.72 × 10(13).”
– Every day your body produces and converts about 90 million, billion, billion molecules of ATP. About your own body weight. You need an entire second you of ATP to make it through a single day.
#Chapter 10 - Adenosine Triphosphate Energetic, 2016
https://www.sciencedirect.com/science/article/pii/B9780128096857000101
Quote: “It is estimated that the human body uses roughly 2 × 1026 transient molecules of ATP or more than the bodies weight; 160 kg of ATP in a day.”
–Even storing enough ATP to last you a few minutes is basically impossible.
#ATP synthesis and storage, 2012
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3360099/
Quote: “because of the high rate of ATP-dependent processes, together with its low stability in water, ATP content could quickly be depleted if it were not immediately replenished by glycolysis and oxidative phosphorylation. ATP cannot be stored easily within cells, and the storage of carbon sources for ATP production (such as triglycerides or glycogen) is the best choice for energy maintenance.
– An ATP molecule is really good for shifting energy around quickly but it is terrible for storage, since it has only one percent of a glucose molecule’s energy at three times its mass.
ATP has a mass of 507.18 g/mol
#Adenosine-5'-triphosphate, 2020
https://pubchem.ncbi.nlm.nih.gov/compound/Adenosine-5_-triphosphate
The mass of a glucose molecule is of 180.16 g/mol, which is roughly one third of the mass of a ATP molecule:
#Molar Mass Of Glucose (C₆H₁₂O₆), 2019
https://sciencetrends.com/molar-mass-of-glucose-c%E2%82%86h%E2%82%81%E2%82%82o%E2%82%86/
1 molecule of glucose can make a net of 2 ATP (and 2 NADH which will later be made into ATP) during glycolysis, this then feeds into the citric acid cycle which produces 30 molecules of ATP. ATP is 3.06 times the weight of glucose (atp = 551 daltons, glucose = 180 daltons) and produces the same energy as 30 ATPs. We will round this down to ATP which is 3 times the weight of glucose.
30 ATP molecules make the same energy as 1 glucose molecule. So to get 30 worth of energy from ATP the weight would be 30 * 551 = 16530 daltons. To get the same we need 1 Glucose molecule (180 *1 = 180). To get the percentage we do 180/16530 = 0.01 or 1%.