Chapter 2Chemical Basis of Life

Molecular model of a Phospholipid

PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 10th edition, edited by S.C. Wache for Biol2064.01

You are responsible for the following figures and tables:

Tab. 2.1 - important definitions.  Tab. 2.3 - the first ten elements of the periodic table of elements, TB, p. 969.

Fig. 2.3 - Learn how to distribute proteons and electronsFig. 2.4 - learn how to distribute protons and electrons

Fig. 2.8 - hydrogen bonds; example H2O.Fig. 2.6 - examples of structural and molecular formulas

Read TB, p.44, on chemical reactions.Define 'isotope'. Tb, p.39. See Clin. Appl. 2.1, TB, p. 41. What is 131 I used for ?

Tab. 2.4, 2.5; Fig. 2.10 - Study pH, bases and acids.

Tab. 2.6: small inorganic molecules like water and carbon dioxide Tab. 2.8 – Macromolecules.

Fig. 2.11 and 2.12; Fig. 2.15 and 2.16; Fig. 2.17 and 2.18 - note the formation of the covalent bond; Fig. 2.21.

Chemistry and Biochemistry

• Chemistry is the study of non-living matter and how it changes.

• Biochemistry is the chemistry of living organisms.

• It has been important in explaining physiological processes and in improving medicine.

Matter and Elements

Definition: Matter is anything that has weight and

takes up space.

• All matter is composed of elements.

• Elements exist in their pure form or in chemical combinations called compounds or, more specifically, molecules

• Elements are composed of atoms.

Atomic Structure

Def. Atom: It consists of many different types of particles and has a nucleus.

• Nucleus: center of the atom, containing protons and neutrons• Protons: positively charged particles• Neutrons: particles which lack charge• Electrons: very small, negatively charged particles which encircle the nucleus.

Fig. 2.1

Isotopes• Atoms that have the same atomic number, but

different atomic weights are isotopes. For example, 131 I and 125I are isotopes of iodine (see textbook,

Clinical Applications 2.1). 131 I is a heavy radioactive isotope of iodine that has the mass number

131 and a half-life of eight days. It emits beta particles and gamma rays, and is used especially in the form of its sodium salt in the diagnosis of thyroid disease and the treatment of goiter.

125I is a light radioactive isotope of iodine that has a mass number of 125 and a half-life of 60 days. It gives off soft gamma rays, and is used as a tracer in thyroid studies and as therapy in hyperthyroidism.

• Atomic number is the number of protons. It is the same for all atoms of an element.

• Atomic weight is the number of protons and neutrons.

Stable and Radioactive Isotopes

Definition Stable Isotopes: Isotopes that do not

decompose are called stable isotopes.

Definition Radioactive Isotopes: Isotopes that have

unstable nuclei that decompose are called

radioactive isotopes.

• Radioactive isotopes release energy or particles until they reach a stable form.

Atomic Radiation

• Alpha radiation consists of particles from atomic nuclei, two protons and two neutrons. These particles are heavy, move slowly, and do not penetrate matter.

• Beta radiation consists of smaller electrons that travel fast and penetrate matter.

• Gamma radiation is similar to X-radiation and is the most penetrating of these forms.

Ex: 131 I

• Two or more atoms / elements combine to form a molecule or compound.

• Molecules are distinctive from the elements of which they are composed.

• A molecular formula, such as H2O, illustrates the number and type of atoms found in a molecule.

• A structural formula shows the spatial arrangement of the atoms in a molecule (see Fig. 2.2)

* see Fig. 2.6 for examples of molecular and structural formulas

Fig. 2.2

Atomic Structure

• Atoms, such as Helium, whose outermost electron shells are filled, have stable structures and are chemically inactive or inert.

•Atoms with incompletely filled outer shells tend to gain or lose electrons in ways that empty or fill their outer shells and create a stable structure.

• Ions carrying a positive or negative charge are formed when atoms gain or lose electrons.

Fig.2.4: Ions are formed when atoms gain or lose electrons. Ionic bonds are formed by the attraction of oppositely charged

ions

Fig.2.5: Covalent bonds are formed by the sharing of electrons between atoms.

Fig.2.8: Hydrogen bonds are weak bonds between polar molecules.

• Molecular bonding leads to the formation of small molecules.

• Further molecular bonding results in the synthesis of larger molecules and macromolecules.

• Synthetic and degradative chemical reactions make up metabolism which underlies the physiological functioning of the human body.

From Small To Large Molecules

Chemical Reactions• Synthesis Reaction: A + B AB• Degradation Reaction: AB A + B

• Reversible Reactions can proceed in either direction

Definition: Metabolism is the sum of all chemical reactions in the human body and is necessary for physiological processes to proceed.

Many chemical reactions are reversible. • The direction in which the reaction proceeds

depends on many factors such as:

- the proportions of products

- reactants

- amount of energy

- presence of catalysts

- molecules that influence the rate of reaction, but are not consumed in the reaction.

The human body requires inorganic and organic

molecules to function properly and

physiologically.

• Inorganic molecules serve vital functions as electrolytes in the body fluids.

• Organic molecules are mostly used in metabolic reactions that lead to storage or release of chemical energy and, ultimately, growth processes to resume.

Inorganic and Organic Molecules

Inorganic Substances: Salts (Fig. 2.9)• Inorganic

substances include H2O, O2, CO2 and the salts.

• Polarity of water causes dissociation of salts and the release of ions.

• They are called electrolytes.

Inorganic Acids, Bases, Salts

Electrolytes release ions in water as do acids and

bases.

• Acids release hydrogen ions (H+).

• Bases release hydroxyl ions such as OH - which combine with H+ to form H2O.

pH

• Def. pH: It is the hydrogen ion concentration of a solution which is measured in grams of ions per liter of solutions.

• The pH scale illustrates the H+ concentration in a convenient form. The lower the pH, the higher the H+ concentration and the more acidic the solution.

• Pure water ionizes only slightly and results in equal numbers of hydrogen and hydroxyl ions and a pH 7 which is chemically neutral.

Hydrogen Ion Concentration or pH

• Solutions with more hydrogen ions than hydroxyl ions are acidic and have pH values of less than 7.

• Solutions with more hydroxyl ions than hydrogen ions are basic and have pH values of greater than 7.

pH Changes Affect the Physiological Processes of the Human Body

• Fluids in the human body function in a narrow ph range.

• Normal blood pH is pH 7.4. This is also called the physiological pH.

• A blood pH of 7.5 to 7.8 is alkalosis, resulting in agitation and dizziness.

• A blood pH of 7.0 to 7.3 is acidosis, resulting in disorientation and fatigue.

Fig. 2.10

Organic Substances• Organic substances are any such molecules

that contain a combination of C, O, and H.

• Organic compounds that dissolve in water usually do not release ions into water and therefore they are not electrolytes with the exception of proteins.

• Important groups of organic substances in cells include carbohydrates, lipids, proteins, nucleic acids.

• Carbohydrates: water-soluble molecules containing carbon, hydrogen, oxygen

• Sugars: mono-saccharides, disaccharides, polysaccharides

Fig. 2.11 – Carbohydrates are slightly polar because of the attached hydroxyl or OH- groups. They suspend in water.

Fig. 2.12: starch, fiber, glycogen are polysaccharides that are built of simple sugars.

Lipids or fats are nonpolar – they do not suspend in water or in blood. • 3 fatty acids combine with glycerol to form triglyceride.• Shown are stearic and oleic acids attached to a glycerol backbone

Fig. 2.14

Oleic acid

Stearic acid

• Fatty acids can be saturated (stearic acid) or unsaturated (oleic acid, alpha-linolenic acid).

• Phospholipids contain two fatty acids and a phosphate group.

Fig. 2.15

• Steroids are lipids. They composed of three 6- carbon rings and one 5-carbon ring just like their precursor cholesterol.

• The building blocks of cholesterol are small fatty acid precursors.

Fig. 2.16

Saturated vs. Unsaturated FatsA diet rich in saturated fat such as stearic acid increases a person’s risk of atherosclerosis. • It is healthy to substitute stearic acid for unsaturated fats such as oleic or linoleic acid. • Saturated fats are found in fatty foods that are solid at room temperature as in lard. • Unsaturated fats are found in foods that are liquid at room temperature as in olive oil or plants.

Proteins• Wide range of functions• Polar or hydrophilic in nature -suspend in water or

blood.• Chain of amino acids of varying lengths that carries

positive and negative charges on attached groups• Amino acids consist of a central carbon to which is

attached an amino group, a carboxyl group, and a side chain (R group)

• Amino acids are linked in a peptide bond which is a covalent bond which connects the amino group of one amino acid and the carboxyl group of a second amino acid.

Fig. 2.18

Levels of Protein Structure

• Primary: amino acid sequence

• Secondary: coil or sheet formed by hydrogen bonds between the amino acids

• Tertiary: three dimensional shape created by hydrogen and covalent bonds

• Quarternary: association of several separate protein chains

Fig. 2.19

Nucleic acids, such as DNA and RNA, are another group of macromolecules.

• DNA and RNA are large, complex, charged molecules that suspend easily in water or plasma

• Chains / strands of nucleotides

• Their building blocks are nucleotides which are composed of a sugar, a phosphate group (carries a negative charge), and one of five nitrogen bases (A, T, C, G, U).

Nucleic Acids

• RNA

• ribose

• single strand

• aid in protein synthesis

• Bases: ACGU

• DNA

• deoxyribose

• double stranded

• store genetic information

• Bases: ACGT

Fig. 2.21a - RNA

: DNA

Note the hydrogen bonds that hold the two strands together.