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Chapter 2

Chemistry of Life

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Outline

• Basic Chemistry– Atoms– Molecules and Compounds– Chemical Reactions

• Properties of Water• Acids and Bases• Macromolecules• ATP

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Basic Chemistry

• There are 92 naturally-occurring elements.– Over 90% of human body is composed of

four elements. (CHON)Carbon.Hydrogen.Oxygen.Nitrogen.

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Atoms

• An atom is the smallest unit of matter that retains an element’s physical and chemical properties.– Positively-charged protons and neutral

neutrons are located in the nucleus.– Negatively-charged electrons orbit the

nucleus in shells.

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Atoms

• An element’s atomic number is designated by its number of protons.

• An element’s atomic weight is designated by its protons and neutrons.

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Elements and Atoms

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Molecules and Compounds

• A molecule and compound is a group of atoms bonded together.

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Ionic Reactions

• During an ionic reaction, atoms give up or take on an electron to stabilize their outer shells of the atom.

• Ions are particles that carry a positive (+) or negative (-) charge.– The attraction between oppositely

charged sodium ions and chloride ions forms an ionic bond.

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Ionic “electron stripping” Reaction

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Covalent “electron sharing” Reactions

• In covalent reactions, atoms share electrons in covalent bonds instead of losing or gaining them.– A single bond is formed when atoms

share a single pair of electrons.– A double bond is formed when atoms

share two pairs of electrons.– A triple bond is formed when atoms share

three pairs of electrons.

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Covalent Reactions

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Water and Living Things and a Third type of bond- Hydrogen bond

• The electrons in water spend more time circling the larger oxygen atom than the smaller hydrogen atom.– Water is a polar molecule with the oxygen

end being slightly negative and the hydrogen end being slightly positive.

A hydrogen bond occurs when a covalently bonded hydrogen is positive and is attracted to a negatively charged atom.

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Hydrogen Bonding between Water Molecules

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Some Properties of Water

• liquid at room temperature.

• solvent for polar molecules.

• cohesive.• temperature rises and

falls slowly.

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Acids and Bases

• Acids break down in water and release hydrogen ions (H+).

• Bases/alkaline take up hydrogen ions (H+) or release hydroxide ions (OH-).– Buffers help keep the pH within normal

limits by taking up excess hydrogen ions or hydroxide ions.

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Water can break down to form Ions (atoms with a + or – charge)

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pH Scale

• The pH scale measures acidity or alkalinity of a solution.– Neutral = 7.– Acidic < 7.– Basic > 7.

Logarithmic Scale.

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Log scale

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The pH Scale

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Molecules of Life

• Four categories of molecules are unique to cells.– Carbohydrates.– Lipids.– Proteins.– Nucleic Acids.

• Macromolecules are synthesized by a dehydration reaction, and degraded by a hydrolysis reaction.

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pg.24a

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Synthesis of larger product (macromolecule)

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Breakdown of Molecule to simpler subunits

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• Carbohydrates function for quick and short-term energy storage.– Monosaccharide (simple sugar).

Glucose.– Disaccharide.

Fructose.

Carbohydrates

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Complex Carbohydrates

• Polysaccharides.– Starch (plants).– Glycogen (animals).– Cellulose (plant cell walls).

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Glucose molecule in various forms

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A Disacharride

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Plant Polysaccharide

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Animal polysaccharide

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Lipids

• Lipids contain more energy per gram than any other biological molecule.– Do not dissolve in water.

Absence of polar groups.– Fats.

Animal origin, solid at room temperature.– Oils.

Plant origin, liquid at room temperature.

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Synthesis and breakdown of Fat

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Phospholipids and Steroids

• Phospholipids contain a phosphate head and fatty acid tails.– Polar head and non-polar tails.

Soluble in water.• Steroids are lipids with a backbone of four

fused carbon rings.– Estrogen and testosterone.

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Another Example of a lipid

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Cell membrane

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Other lipid examples

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Fig. 2.15bb

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Emulsyfier

• Bile salts• Tween

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Emulsyfication

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Proteins

• Proteins are macromolecules with amino acid subunits.– An amino acid has a central carbon atom

bonded to a hydrogen and three groups.Peptide bond - Any bond joining two

amino acids. Polypeptide - Single amino acid

chain.

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Building block of proteins

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Fig. 2.16a

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Peptide bond- bond between two amino acids

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Levels of Protein Organization

• Primary Structure.– Linear sequence of amino acids.

• Secondary Structure.– Polypeptide takes on orientation in space.

• Tertiary Structure.– Final three-dimensional shape.

• Quaternary Structure.– Proteins with more than one polypeptide.

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Nucleic Acids

• Nucleic acids are huge macromolecules composed of nucleotides. – A nucleotide is constructed of a

phosphate, a pentose sugar, and a nitrogenous base.

– Deoxyribonucleic acid (DNA).Double-stranded helix.

– Ribonucleic acid (RNA).Single stranded.

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Building block of an Nucleic Acid- A Nucleotide

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DNA Structure

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(ATP) Adenosine Triphosphate

• ATP is the primary cellular energy carrier.– Energy currency of cells.– Breaks down to adenosine diphosphate

(ADP) and a molecule of inorganic phosphate, releasing energy to drive cellular metabolism.

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Another nucleic acid example- ATP and ADP (cell energy)

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Lecture Review

• Give an example of ionic bonding and explain it.• Give an example of covalent bonding and explain

it.• Relate the characteristics of water to its polarity

and hydrogen bonding.• List the four molecules of life and examples of

each.• Fat /triglyceride is composed of______ and

______.• The subunits of Proteins are _______ _______.• List some functions of proteins. What is a

polypeptide?• The subunits of Nucleic acids are ____________.