Chemistry of Microbes

LECTURES IN MICROBIOLOGY

LESSON 2

Sofronio AgustinProfessor

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Topics

Fundamental Building Blocks

Macromolecules

The Cell

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Fundamental Building Blocks

Atoms

Elements Molecules and compounds

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Atoms

Subatomic ParticlesProton = positive chargeNeutron = neutralElectron = negative charge

Atomic number = no. of protons Atomic mass = no. of protons and neutrons

5Models of Atomic Structure

Atomic Structure

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Isotopes

Atoms with same number of protons but differ in number of neutrons are called isotopes.

Example: 12C, 13C, and 14C are isotopes of carbon.

Radioisotopes emit radiation in the form of alpha or beta or gamma rays or photons.

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Major Elements of Life

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Molecules and Compounds

Molecule = combination of two or more elements (e.g.H2)

Compound = combination of two or more different elements (e.g. H2O)

Molecules are held together by chemical bonds

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Chemical Bonds

Covalent

Ionic Hydrogen

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Chemical Bonds

Chemical bonds involve atoms sharing, donating or accepting electrons

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Covalent Bonding

Examples of covalent bonding

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Polar Covalent Bond

Polarity occurs when atoms electrons unequally due to differences in electronegativities. This is seen in water (H2O).

More electronegative atoms tend to pull electrons toward them creating a polar molecule.

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Ionic Bonding

Sodium chloride (table salt) is an example of ionic bonding, that is, electron transfer among atoms or redox reaction.

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Ionization

Molecules formed by ionic bonding breakup (ionization) when dissolved in water (solvent), producing separate positive (cation) and negative (anion) ions.

These ions conduct electricity and thus called electrolytes.

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Hydrogen Bond

Hydrogen bonding is formed between the partially positive (hydrogen) end of a polar molecule and the negative end of another (e.g. O2 or N2).

Example : Water molecules

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pH

pH – measurement of the H+ ion concentration in a solution.

General rule: Acidic = excess H+ ions in solution Basic = excess OH- ions in solution Neutral = equal amounts of H+ and OH- ions

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The pH Scale

The pH of an environment (exterior or interior of a cell) is important for living systems.

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Molecules

Molecules important to life consist of inorganic and organic substances.

Inorganic – either C or H maybe present (e,g, CO2, H2)

Organic- C and H (hydrocarbons) are present

(e.g. CH3)

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Organic Molecules

Carbon, a tetravalent atom, is an ideal element for life because it serves as the skeleton for macromolecules.

Functional groups (R) attached to these carbons confer unique properties to these macromolecules.

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Macromolecules

Carbohydrates Lipids Proteins Nucleic acids

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Carbohydrates

Simple Sugars

Disaccharides

Polysaccharides

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Classes of Carbohydrates

Major sugars (monosaccharides) in the cell are glucose, galactose and fructose.

Several sugars bonded together are called polysaccharides.

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Glycosidic Bond

Sugars are bonded by special kind of covalent linkage called glycosidic bonds.

Water is released (dehydration) after the bond is formed.

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Polysaccharides

Peptidoglycan in bacteria is an example of a polysaccharide.

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Lipids

Fats Phospholipids

Steroids

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Fats

Synthesis and structure of a triglyceride (fat), a storage molecule.

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Phospholipids

Phospholipids serve as a major structural component of cell membranes.

It is an amphiphatic molecule. Its phosphate “head” is hydrophilic and its fatty acid “tail” is hydrophobic.

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Cholesterol: An Alcoholic Steroid

Cholesterols are associated with cell membranes of some cells such as those of eukaryotes.

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Proteins

Proteins are the predominant organic molecules in cells.

Proteins consist of a series of amino acids (e.g. peptides, polypeptides)

Peptide bonds link amino acids together. Examples: hormones, enzymes, antibodies, etc.

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Amino Acids

An amino acid has a central carbon, to which carboxylic, amino and R groups are attached.

Amino acid types vary according to the reactive (R) groups present.

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The 20 Naturally Occurring Amino Acids

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A peptide bond (covalent) forms between the amino group on one amino acid and the carboxyl group on another amino acid with the accompanying loss of water.

Peptide Bond

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Levels of Structures of Protein

Proteins take on a variety of shapes due to extensive folding of the molecule. This enable them to perform specific functions and interactions with other molecules.

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Nucleic acids

Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA contains genetic information and

transfers it to RNA RNA translates the DNA information into

proteins

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Nucleic Acid Polymers

Nucleic acids are polymers of repeating units called nucleotides.

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The Sugars and Nitrogenous Bases

The pentose sugars and nitrogen bases determine whether a molecule will be DNA or RNA.

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The DNA configuration is a double helix similar to “a spiral staircase”

Sugar and phosphate backbones are held together by hydrogen bonds formed between nitrogenous bases.

The DNA Molecule

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DNA : The Molecule of Inheritance

DNA serves as a template for the synthesis of new DNA strands as well as mRNA, tRNA and rRNA.

DNA replication is an important step in cell reproduction.

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The Cell

Fundamental characteristics shared by all living organisms: Reproduction Metabolism Motility (Response to molecules) Protection and Storage (Cell wall or

membrane) Nutrient transport