Abstract
This chapter focuses on the chemical foundations of life. Matter is made up of elements classified into major and minor elements. Elements are made up of atoms which in turn are made up of sub-atomic particles called protons, electrons and neutrons. Chemical bonds are unions of electron structures when atoms lose, gain or share one or more electrons with other atoms. Water is important to life and has unique properties making it ideal to life on Earth. The pH of a substance is a measure of the balance between H+ and OH- ions ranging from 0 to 14 on a log scale. Most metabolic reactions that maintain life occur in living organisms involve five types of chemical reactions. Macromolecules are large complex molecules made up of repeating units (monomers) of sometimes the same molecule or of different molecules joined together by chemical bonds to form very long chains (polymers).
TopChapter Outline
2.1 Matter and Chemical Elements
2.2 Chemical Bonds and Life
2.3 Water, pH Balance and Life
2.4 The Central Role of Carbon
2.5 Chemical Reactions Governing Life
2.6 Life’s Macromolecules
2.6.1 Carbohydrates
2.6.2 Lipids
2.6.3 Proteins
2.6.4 Nucleic Acids
Chapter Summary
TopLearning Outcomes
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Understand the nature of matter and chemical basis of life
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Explain chemical bonds and bonds important to life
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Understand the role of water in life
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Demonstrate the bonding behaviour of carbon and its importance in life
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Illustrate the nature and the different types of macromolecules in life
Top2.1 Matter And Chemical Elements
Physicists define matter as anything that occupies space (volume) and has mass. Mass is different from weight in that it does not change depending on where you are. For example, in outer space, people experience ‘weightlessness’; but they still have the same mass as when on Earth. Matter includes air, soil, water, bacteria, plants, animals, clouds, snow, ice, etc. but not energy (as in the electromagnetic spectrum). Matter is made up of elements, which are comprised of atoms. Atoms in turn are made up of smaller sub-atomic particles.
In living organisms, we identify major elements and minor elements. The major group includes four central elements carbon, nitrogen, oxygen and hydrogen, which make up to 96% of the dry weight of organisms. The minor group includes elements required in minor proportions by living organisms and comprising about 4% of the dry weight of organisms. These are elements like iron, calcium, copper, zinc, iodine, and phosphorous. Remember, “wet weight” is the weight you get on the scale, which includes watery fluids in your body. If all water were to be removed from your body entirely, you would get the dry weight. In research, scientists typically use the dry weight of organisms, which does not fluctuate as much as the wet weight.
All named elements are organized together in a periodic table. Most periodic tables of the elements common in many undergraduate college lecture halls list 104 elements identified by chemists. The list is comprised of 94 natural elements occurring on Earth, with the remainder being synthetic elements made in chemical laboratories around the world. Elements are made up of atoms. Atoms combine to form molecules, which in turn combine to form chemical compounds. Inside atoms are the sub-atomic particles called protons, electrons and neutrons (Figure 1). Both protons and neutrons have mass and are found in the nucleus of the atom, while electrons are weightless and are conceived as occupying a three-dimensional space around the nucleus in distinct shells or levels. Protons are positively charged particles counterbalanced by the negatively charged electrons. Thus, the numbers of protons always equal the numbers of electrons making an atom electrically neutral. Neutrons have no charge.
Figure 1. Model of an atom showing sub-atomic particles
Structurally, electrons are best visualized as occupying defined “rings” around the nucleus like planets around the sun as seen here for hydrogen and helium (Figure 2).
Key Terms in this Chapter
Covalent Bond: A type of chemical bond involving the sharing of electrons between atoms.
Ester Bond: A bond formed from a dehydration reaction between a carboxylic acid and an alcohol.
Peptide Bonds: A type of covalent bond formed through a condensation reaction of two amino acids.
Isotopes: Atoms that share the same number of protons but differ in the number of neutrons.
Hydrocarbon: A compound consisting of hydrogen and carbon atoms.
Macromolecules: Large complex molecules made up of repeating units of the same or different molecules.
pH: A logarithmic scale that quantifies the acidity or basicity of an aqueous solution.
Phosphodiester Bond: The bond that forms between two phosphate groups of nucleotides.
Chemical Bonds: A union between atoms in a molecule.
Chaperonins: A protein that aids the assembly and folding of other protein molecules in living cells.
Glycosidic Bond: A covalent bond between the anomeric carbon of a sugar and an alcohol or amine of another molecule formed by a dehydration reaction.
Ionic Bond: A type of chemical bond formed between oppositely charged particles and electrostatic attraction.
Periodic Table: A table of chemical elements arranged by respective characteristics/properties, including atomic number, mass, electronegativity, etc.
2:8:8:8 Octet Rule: A rule in electron configuration that focuses on the tendency of atoms to bond in a way that mimics the number of valence electrons in inert gases.
Atoms: Smallest unit of matter.
Lipoproteins: A lipid and protein complex that aids in the transport of lipids throughout the lymph and blood.
Particulate Matter: The mixture of solid and liquid particles suspended in the air.
Fatty Acids: Long hydrocarbon chains with either single or double bonds between carbon atoms and a carboxyl functional group at one end.
Hydrogen Bond: A weak chemical bond involving the interaction of a hydrogen atom.