Dr Irengbam Mohendra Singh
Our abundant life, white puffy clouds, blue skies and beautiful moonlights make me think what a wonderful world we live in. Chemical processes that occur within living organisms make me wonder what a mysterious biochemical compound we are. A compound found mainly in organisms (living things) is known as an organic compound. Carbon though only a handful, is the main element in organic compounds and so, life’s carbon-based.
At the 50th anniversary celebration of NASA on October 1 2008, Stephen Hawking was asked the question, “Are we alone?” His prompt answer was: “probably not.” But the alien life may not be carbon-based. What we normally think of as ‘life’ is based on chains of carbon atoms, with a few other atoms, such as nitrogen and phosphorous. We can imagine that one might have life [alien] with some other chemical basis, such as silicon, but carbon seems the most favourable case, because it has the richest chemistry – added Hawking.
Carbon is such a unique substance that many scientists, currently studying organic compounds and focussing on their molecular structure and reactivity in organic and biological chemistry, can explain why butter is solid while oil is liquid, though their structures are similar. They can identify the major cancer producing agents in grilled meat and cigarette smoke, explain why the widely used Ibuprofen to relieve pain and inflammation takes longer than half an hour to relieve pain, or how consumption of lactose (sugar in milk) can result in mental retardation and how certain groups of antibiotics kill bacteria that are harmful to humans.
Organisms are essentially collections of proteins, which form their structure and carry out all the complex biochemical functions of life. Proteins are made up of smaller building blocks of amino acids (20 of them). These Amino acids are organic compounds containing carbon, and hydrogen bonded (rearrangement of atoms) to each other (see below).
Although most people, apart from medical students and biochemists, know little about chemical processes that go on in our bodies, they are familiar with the phrase, “carbon footprint”. It was labelled by Anindita Mitra (Seattle, US) in 2007, originally “ecological footprint” (Rees & Wackernagel, 1990) as a measure of carbon emission. Carbon footprint refers to manmade production of a series of gases, especially greenhouse gases that help to warm the atmosphere. Globally we produce 40 trillion Kg of carbon dioxide each year, causing the global temperature rise to pass the dangerous 2% limit, set by the Paris climate agreement.
Carbon is the most important component of living organisms. Scientists believe that life evolved in water – the ‘Primordial soup’ as amino acids. Basically, our bodies and their functions are based on carbon compounds viz proteins, carbohydrates and fats that are combinations of carbon and other elements.
Living things cannot live without carbon. Why? Because our human body for instance, contains 18% carbon. Plants need carbon in the form of carbon dioxide (CO2) to produce glucose (sugar), a carbon-based organic molecule that contains carbon. Humans and animals eat plants to survive in the beginning of the food chain. The implication therefore is that, humans need carbon in order to live, grow, and reproduce.
Only in mid-nineteenth century, some scientists knew that carbon-based molecules, the amino acids are the basic fundamental building blocks of life. Research by Haldane (1937) and Oparin (1938) conceived independently, showed how life began on Earth from the primordial soup. Though
there is a widespread scientific consensus on the evolution of first cells from the primordial soup, there is still an unsolved mystery of how the building blocks were first assembled into proteins that formed the machinery of all cells (cf. author’s Points to Ponder. The Origin of life, pp 273-276). Alternatively, there is now an established theory (Panspermia) that meteorites and asteroids were responsible for bringing the first primordial life to Earth along with water(cf. ibid).
So what is carbon? It’s a chemical element with the symbol “c”. Every element has an atomic number. Carbon’s atomic number is “6” (meaning it has 6 protons in its nucleus). Around the carbon nucleus there are 6 electrons. The most common form of carbon known as carbon-12 has a nucleus that also contains 6 electrons, and it is the arrangement of these around the nucleus that determines the chemistry of carbon.
An element is a substance that is made up of tiniest particles called atoms, which cannot be broken down chemically into simpler substances. Protons and neutrons inside the nucleus are subatomic particles ie smaller than atoms. Carbon is not particularly plentiful, about only 0’025% of the Earth’s crust. Yet it forms more compounds than all other elements combined, either in pure form or in combination with other elements, as it shares electrons easily with them. The commonest one is hydrogen, forming hydrocarbon groups of compounds.
Organic compounds that are essential for living things and created by living things are found throughout the world in soils, seas, commercial products and in all the cells in the human body. They are of 4 types: (1) carbohydrates; (2) lipids; (3) proteins; and (4) nucleotides (vide infra). That’s why it forms the basis of all known life on Earth.
All the carbon atoms, including those we have in our body, were created in the stars after the Big bang, 14 billion years ago. There are 94 naturally occurring elements on earth, to which another 24 synthetic elements have been added to make up a total of 118 elements. Synthetic elements are radioactive elements, such as Technetium (1936) and Promethium (1945).
Carbon is the fourth most important abundant element in the Universe after hydrogen, helium and oxygen, and the 15th most abundant element in the Earth’s crust. Carbon is naturally available in organic chemical forms, like diamond and graphite. Though diamonds can be mined eg in South Africa, synthetic diamonds can be made from ashes eg the cremation ashes of your beloved ones.
Protein, fat and carbohydrates are mainly made of carbon. Protein plays a crucial role in the biological process in the living cells. A large proportion of our cells in muscles, tendons, and other tissue is made up of proteins which in turn is made up of amino acids – their building blocks. Amino acid is a simple organic compound that contains carbon (C), hydrogen (H), Oxygen (O), and nitrogen (N). Some may contain sulphur (S) and phosphorous (P).
The construction of proteins from their amino acid building blocks is at the heart of life in the primordial soup. Proteins are built up from sequences of amino acids based on the DNA code in a series of chemical processes (Molecular Biology). The centre of an amino acid is the carbon, called the alpha carbon that is bonded to four element groups.
Molecular biology is the study of life at molecular level such as DNA and RNA. The phrase, “DNA makes RNA makes proteins”, first used by Francis Creek in 1958, feels too vertiginous for me. It probably means information transfer from DNA is through RNA (messenger) to protein. Genes made up of nucleic acids (DNA and RNA) contain instructions for making proteins by transcription, but enzymes made of proteins are needed to replicate genes.
Besides amino acids, there is a complex organic substance that’s present in all living cells, which is vital for all life forms on Earth. These are nucleic acids which is of two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acids are small biomolecules, composed of nucleotides containing carbon, sugar, phosphate and a nitrogen base. They allow organisms to transfer genetic information from one generation to the next.
DNA contains the blueprint of life ie genetic instructions encoded that an organism needs to develop, live and reproduce. Various types of RNA help carry out this blueprint’s guidance in protein production. This is because DNA stays in the nucleus of a cell, while protein-making machinery is outside the nucleus in the cell. The RNA template can leave the nucleus carrying the information to make protein. The actual work of making an organism is done by proteins. The difference between DNA and RNA is that DNA is a double helix while RNA is a single helix.
Proteins have diverse roles in our body. Apart from the protein that we are familiar with in our daily diet, they come in all sorts of shapes and sizes. For example, hair and fur is made from a protein called keratin; haemoglobin in our blood that carries oxygen is a protein; so are enzymes in our saliva and stomach that digests food. Muscle protein is called actin, and a protein called myosin enables us to walk, breathe and blink our eyes.
The continuance of life is possible, because carbon is a finite source that cycles through the Earth in many forms, and is available to all living organisms in balance with carbon in the atmosphere and the water, because of what is called the “Carbon cycle”, which is a series of processes by which carbon compounds are converted into each other in the environment. That includes plants bringing CO2 back by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and burning of fossil fuels like charcoal, petroleum etc.
So carbon is essential both for scaffolding, creating and continuing of human life.
The writer is based in the UK Email: firstname.lastname@example.org Website: www.drimsingh .co.uk