Biochemistry THE FUNDAMENTAL CHEMISTRY OF LIFE

Biochemistry THE FUNDAMENTAL CHEMISTRY OF LIFE

Atomic Structure Elements consist of individual atoms. An atom is composed of three subatomic particles: protons, neutrons, and electrons.

Atomic Structure

Isotopes An isotope is a form of an element that differs in its number of neutrons. What does this mean? These atoms have the same number of protons and electrons, but a different number of neutrons resulting in a different atomic mass. Because isotopes of the same element have the same number of protons and electrons, they behave exactly the same in a chemical reaction.

Isotopes

RADIOISOTOPES The nuclei of some isotopes of an element are unstable and tend to break down, or decay, giving off particles of matter that can be detected as radioactivity. The decay process transforms an unstable, radioactive isotope (radioisotope) into an atom of another element. Radioactive decay continues at a steady rate, with a constant proportion of radioisotope atoms breaking down during a given time interval. This characteristic is known as the radioisotopes half-life.

What are radioisotopes used for? Three useful applications of radioisotopes include: Radiometric dating Radioactive tracers Nuclear medicine

Radiometric Dating Carbon, C, is a major constituent of all living things. Carbon consists of three isotopes: C-12 (account for 99% of the carbon in nature & stable) C-13 (makes up the remaining 1% & stable) C-14 (found in trace amounts & radioactive) When an organism dies, it stops absorbing carbon from the atmosphere. The amount of C-12 remains the same, but the amount of C-14 decreases in a predictable manner because of its radioactive nature (half-life). Consequently, measuring the ratio of C-12 to C-14 in a dead or fossilized organism allows scientists to calculate the time that has elapsed since the organism s death.

Radioactive Tracers Radioisotopes emit radiation as they decay, and their location can be readily detected. Radioactive tracers are radioisotopes used to follow chemicals through chemical reactions and trace their path as they move through the cells and bodies of organisms.

Nuclear Medicine The medical profession have developed techniques to use radioisotopes to help in the diagnosis and treatment of their patients. NORMAL ENLARGED CANCEROUS

Radioisotopes Used in Nuclear Medicine RADIOISOTOPE MEDICAL USES HALF-LIFE Technetium-99 (most commonly used) Iodine-125 Iodine-131 To view the skeleton, heart muscle, and various organs. To evaluate the filtration rate of the kidneys and to determine bone density measurements. To view and treat thyroid, liver, and kidney disease and various cancers. 6.02 hours 42 days 8.0 days Indium-111 To study the brain, the colon, and sites of infection. 2.8 days

Electron Arrangement The arrangement of electrons determines the chemical properties of an atom. An orbital is a region of space that one or two electrons can occupy. Valence electrons are the electrons in an atom s outermost energy shell.

Electron Arrangement

Chemical Bonding Four types of chemical bonds are important in biological molecules: ionic bonds, covalent bonds, and two types of intermolecular forces. An ionic bond results from the attraction between two oppositely charged atoms or molecules. Cations are positive charged ions; anions are negatively charged ions. Covalent bonds form when atoms share one or more pairs of valence electrons. The strength of a covalent bond depends on the electronegativity (a measure of an atom s attraction to shared electrons).

VSEPR Theory Canadian chemist Ronald J. Gillespie developed the Valence Shell Electron Pair Repulsion theory, stating that because electrons are negatively charged, valence electron pairs repel one another and move as far apart from one another as possible. The VSEPR theory can be used to predict the shape of molecules based on the arrangement of the bond angles around the central atom.

VSEPR Theory

Polar Molecules Polar molecules can be described as molecules with an asymmetrical arrangement and an uneven distribution of charges. The unequal sharing of electrons between two atoms with different electronegativity results on a polar covalent bond. Non-polar molecules generally have a symmetrical arrangement and the charge distribution is equal.

Polar Molecules

POLARITY and SOLUBILITY As a rule of thumb: like dissolves like Therefore: polar dissolves polar non-polar dissolves non-polar.

Intermolecular Forces

Chemical Reactions There are four major types of chemical reactions that are common in biological processes: 1. Dehydration (condensation) Reactions 2. Hydrolysis Reactions 3. Neutralization Reactions 4. Redox Reactions

Dehydration (condensation) Reactions A chemical reaction in which subunits of a larger molecule are joined by the removal of water. Also known as condensation reactions and anabolic reactions (build-up reactions).

Hydrolysis Reactions A chemical reaction in which water is used as a reactant to split a larger molecule into smaller subunits. Also known as a catabolic reaction (break-down reaction).

Dehydration & Hydrolysis Reactions

Neutralization Reactions A chemical reaction in which an acid and a base combine to create a salt and water.

Redox Reactions An electron transfer reaction; electrons are lost from one atom and gained by another. The term REDuction refers to the gain of electrons. The term OXidation refers to the loss of electrons. The oxidizing agent is the molecule or atom being reduced (gaining electrons). The reducing agent is the molecule or atom being oxidized (stripped of its electrons).

Redox Reactions