Chapter 2Chemical Composition of the Body

Human Physiology

Atoms

•Smallest units of matter that can undergo chemical change.

•Nucleus (center) contains:▫Protons (+ charge)▫Neutrons (no charge)

•Atomic mass:▫Sum of protons and neutrons.

Atoms•Atomic Number

▫Number of protons in an atom•Neutral atom

▫Number of protons = number of electrons•Isotopes

▫Vary in number of neutrons▫Same in atomic number▫Vary in atomic mass

Atoms•Chemical element

▫Includes all of the isotopic forms of a given atom

▫Eg: Element Hydrogen: 3 isotopes Most common: one proton Deuterium: one proton, one neutron Tritium: one proton, two neutrons

Commonly used in research▫106 chemical elements

Elements•Four elements important to living

organisms▫Carbon (C)▫Nitrogen (N)▫Oxygen (O)▫Hydrogen (H)

Atoms

•Electrons (outside the nucleus):▫- charged▫Occupy orbitals surrounding nucleus.

•Valence electrons:▫Electrons in the outer most orbital that

participate in chemical reactions (if orbit incomplete).

▫Form chemical bonds.

Orbitals•Also called shells or energy levels•Electrons usually found within a given

orbital•Levels (and max number of electrons)

▫First shell: 2 electrons▫Second shell: 8 electrons▫Third shell: usually 8 electrons

Chemical Bonds, Molecules, and Ionic Compounds

•Chemical bonds:▫Interaction of valence electrons between 2 or more atoms.

•# bonds determined by # electrons needed to complete outer orbital.

Covalent Bonds

•Atoms share their valence electrons.

•Nonpolar bonds:▫Electrons are equally distributed between the two identical atoms.

▫Strongest bond.▫H2

Covalent Bonds

•Polar bonds:▫Electrons are shared between two different atoms.

▫Electrons may be pulled more toward more atom.

▫Oxygen, nitrogen, phosphate pull electrons towards themselves.

Ionic Bonds

•One or more valence electrons from an atom are completely transferred to a second atom.

•First atom loses electrons, + charged (cation).

•Second atom has more electrons, - charged (anion).

Ionic Bonds

•Cation and anion attract, form ionic compound.

•Weaker than polar bonds.•Dissociate easily when dissolved in H20.

•NaCl Na+ and Cl-

Table Salt, an Ionically Bonded MoleculeSlide number: 1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17p18n

11p12n

11p12n

17p18n+

(+) (–)

Na Cl+ NaCl

Table Salt, an Ionically Bonded MoleculeSlide number: 2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17p18n

11p12n

Na Cl+

Table Salt, an Ionically Bonded MoleculeSlide number: 3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17p18n

11p12n

Na Cl+

Table Salt, an Ionically Bonded MoleculeSlide number: 4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17p18n

11p12n

Na Cl+

Table Salt, an Ionically Bonded MoleculeSlide number: 5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17p18n

11p12n

Na Cl+

Table Salt, an Ionically Bonded MoleculeSlide number: 6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17p18n

11p12n

Na Cl+

(+) (–)

Table Salt, an Ionically Bonded MoleculeSlide number: 7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

NaCl

11p12n

(+)

17p18n

(–)

Interaction with water

•Hydrophilic:▫Formation of hydration spheres.▫Polar covalent bonds.

•Hydrophobic:▫Cannot form hydration spheres.▫Nonpolar covalent bonds.

Hydrogen Bond

• Hydrogen forms a polar bond with another atom, hydrogen has a slight + charge.

• Weak attraction for for a second electronegative atom.

Acids, Bases, and the pH Scale•Acid:

▫Molecule that can release protons (H+).▫Proton donor.

•Base:▫Negatively charged ion that can combine

with H+.▫Proton acceptor.

pH

•pH = log _1__ [H+]

•Normal pH blood = 7.35 - 7.45.

•Buffer:▫System of molecules and ions that act to prevent changes in [H+].

Organic Molecules

•Molecules that contain carbon and hydrogen.

•Carbon has 4 electrons in outer orbital.

•Carbon covalently bonds to fill its outer orbital with 8 electrons.

Organic Molecules•Organic Chemistry: deals with molecules that contain carbon

•More than 5 million organic compounds have been identified

•The carbon atom can form bonds with a greater number of different elements than any other type of atom

Functional Groups•Inactive “backbone” to which more

reactive atoms are attached.

Classes According to Functional Groups•Ketone and

aldehyde: carbonyl group

•Organic acid: carboxyl group

•Alcohol: hydroxyl group

Stereoisomers

•Exactly the same atoms arranged in same sequence.

•Differ in spatial orientation of a functional group.▫D-isomers: right-handed▫L-isomers: left-handed

•Enzymes of all cells can combine only with the L-amino acids and D-sugars.

Four main classes of Organic molecules

•Lipids•Carbohydrates•Proteins•Nucleic Acids

Lipids

•GR: Lipos=Fat•Diverse group of molecules.•Insoluble in polar solvents (H20).

•Hydrophobic (nonpolar)•Consist primarily of hydrocarbon chains and rings.

Lipids

•Hydrocarbons•Fatty acids•Triglycerides•Ketone Bodies•Phospholipids•Steroids•Prostaglandins

Hydrocarbons

•Includes oils and gases

•Carbons can be single bonds (saturated)

•Carbons can be double bonded (unsaturated)

Fatty acids•Nonpolar hydrocarbon chain

▫Can be saturated (are stright)▫Can be unsaturated (bend at the double

bond)▫Can be poly unsaturated (multiple

bends)•Carboxyl group on one end•Large group

Triglycerides•Formed by condensation of glycerol

and 3 fatty acids.▫Ester bond

•Fatty acid consists of hydrocarbon chain with carboxylic acid end.▫May be saturated or unsaturated▫Saturated fats:

Mostly animal sources Mostly solid at room temperature

▫Unsaturated fats Mostly plant sources Mostly liquid at room temperature

Nutritional considerations of triglycerides

•Also called fat or neutral fat•Stored in adipose cells•Total fat intake should be about 30% of

total energy intake▫Saturated fat >10%

•Saturated fats are implicated in heart disease and stroke▫Data suggests they promote high blood

cholesterol

Phospholipids•A number of categories•All contain a phosphate group•Most common

▫Glycerol (3 carbons)▫Fatty Acids on carbon 1 and 2▫Phosphate group attached to carbon (and

other polar groups eg.: choline)

Lecithin

Phospholipid•Are amphipathic: contain both polar and

nonpolar domains▫Head:

contains polar groups Hydrophilic

▫Tail: Contains fatty acids (nonpolar) Hydrophobic

Phospholipids•Major component of cell membranes

▫Hydrophylic heads orient to water▫Hydrophobic tails orient to each other

•Kind of phospholipid varies based on cell or organelle

Micelle formation

Ketone Bodies•Results from the hydrolysis of

triglycerides by adipocytes▫Liberates free FA into blood▫FA function as an acid in blood

•Most FA used as energy source by some tissues

•If not, converted by liver into Ketone bodies

Ketone Bodies4-carbon chunks

Ketone Bodies•Produced in the rapid breakdown of FA

▫Low-carbohydrate diets▫Uncontrolled Diabetes mellitus

•Ketosis: Elevated level of FA in blood•Ketoacidosis: ketosis is high enough to lower blood ph

▫Can cause coma, death

•Filtered by the kidney

Steroids•Nonpolar and insoluble in H20.•All have cholesterol as precursor.

Prostaglandins•Prostaglandins:

▫Fatty acid with cyclic hydrocarbon group.

▫Derived from arachidonic acid.

Prostaglandins

Carbohydrates

•Organic molecules that contain carbon, hydrogen and oxygen.

•CH20•General formula:

▫CnH2nOn

•-ose denotes a sugar molecule

Carbohydrates•Supply energy

▫Glucose▫Complex carbohydrates

•Provide structural support▫cellulose

•Part of plasma membrane•Monomer: monosaccarides

Carbohydrates•Monosaccharide: the “simple sugars”

▫Pentoses (5-carbons): Ribose: in RNA Deoxyribose: in DNA

▫Hexoses (6-carbons):structural isomers Glucose, fructose and galactose Characteristics

Soluable Sweet Alcoholic fermentation

Glucose•Also called :

▫Dextrose▫Transportable in the blood

Blood glucose▫C6H12O6

Fructose•Fruit sugar

Galactose▫C6H12O6

Carbohydrates

•Disaccharide: ▫2 monosaccharides joined covalently. Sucrose

Glucose and fructose Maltose

Glucose and glucose Lactose

Glucose and galactose

Disaccharides•Characteristics

▫Sweet▫Soluable▫Can be fermented

•Formation: called condensation▫Requires an enzyme▫Removal of molecule of water▫Also called dehydration synthesis▫Formation of a covalent bond

Formation of Disaccharides

Hydrolysis•Reverse of dehydration synthesis.•Digestion reaction.•H20 molecule split.

Carbohydrates•Polysaccharides:

▫Many monosaccharides joined covalently.

▫General formula: (C6H10O5)n

▫Characteristics: Devoid of taste Do not form solutions Iodine test

Iodine +starch+blue

Polysaccarides•Kinds:▫Starch

Glucose subunits branched

▫Dextrins▫Glycogen (animal starch)

Glucose subunits Branched

▫Cellulose Glucose subunits Long, unbranched chains

Proteins

•General Information:▫GR: proteios=first rank▫~50% of the organic material of the body

▫Functions Structural:

Cell structures, CTs Functional:

Enzymes, hormones, Hb, etc!

Proteins•Protein Structure▫Large molecules (polymers) composed of amino acid sub-units (monomers).

▫Amino Acid structure amino group (NH2) carboxylic acid group (COOH) Radical group (R): functional group H

Proteins•20 different standard amino acids.▫Based on the properties of the functional group

▫E.g.:

Proteins

•Dehydration synthesis:▫Amino end of one amino acid combines with hydroxyl group of carboxylic end of another amino acid.

•Peptide bond:▫Bond between two adjacent amino acids.

Peptide bond

Proteins•Dipeptide: 2 amino acids•Tripeptide: 3 amino acids•Polypeptide: many amino acids

▫Number of amino acids varies▫Up to 100 aa

•Protein▫Over 100aa▫Great variety!

Protein structure•Four structural levels

▫Primary structure Based on amino acid sequence Amino acid sequence determined by DNA

▫Secondary structure Based on hydrogen bonding between close

aa▫Tertiery structure

3-D shape▫Quaternary structure

Only in proteins with 2 or more polypeptide chains

Secondary structure (2o)

•Based on the primary structure•Weak hydrogen bonds form between

hydrogen and oxygen of a different amino acid.

•Two main kinds of secondary structure:▫Alpha helix: Bond cause chain to twist in a

helix.▫Beta pleated sheet: interactions between

lengths of the polypeptide chain

Secondary structures

Tertitary structure

•Polypeptide chains bend and fold.▫Based on interactions with aa in different

parts of the polypeptide chain disulfide bonds: covalent Hydrogen bonds: weak

•Produce 3 -dimensional shapes.•Chemical interaction of each protein

produces own characteristic tertiary structure

•Denaturing protein▫Irreversible disruption of tertiary structure

Bonds responsible for 3o structure

Tertiary structure

Quaternary Structure

•Number of polypeptide chains covalently linked together.

•Insulin, hemoglobin

Conjugated proteins•Protein combined with another type of

molecule•Glycoproteins: carbohydrate with

protein▫Membranes, hormone

•Lipoproteins: Lipid and protein▫Membranes, blood plasma

•Hemoproteins: iron and protein▫Hemoglobin, cytochromes

Nucleic Acids•Include the macromolecules:

▫DNA: deoxyribonucleic acid▫RNA: ribonucleic acid

•Involved in heredity and genetic regulation

•Are polymers:▫Monomeric subunit:nucleotides▫Bonded together in a dehydration synthesis

reaction

Nucleic Acids

Nucleotides•Structure of a nucleotide: 3 subunits▫Pentose sugar▫Phosphate group▫Nitrogenous base

Purines: two rings Guanine Adenine

Pyrimidines: one ring Cytosine Thymine Uricil

Nucleotide Structure

Nitrogenous Bases

DNA•Huge molecules with simple structure•Big time data storage!•Structure

▫Nucleotides Pentose sugar: Deoxyribose Bases:

Purines: G and A Pyrimidines: C and T

▫Form double-stranded helix

DNA•Nucleotide strands: 2

▫Sugar-phosphate backbone▫Bases stick out▫Bases bond to each other

•Base pairing: ▫A – T▫G – C▫Called law of complementary base pairing

Nitrogenous Bases

DNA

RNA•Means by which DNA directs cellular activities

•Structure▫Pentose sugar: ribose▫Bases: uracil (not thymine)▫Single stranded

•Three main types▫Messenger RNA (mRNA)▫Transfer RNA (tRNA)▫Ribosomal RNA (rRNA)

DNA vs RNA