chapter02 chemical composition of the body
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Chapter 2
Chemical Composition of the Body
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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.
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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
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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
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Elements
Four elements important to living organisms Carbon (C) Nitrogen (N) Oxygen (O) Hydrogen (H)
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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.
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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
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Chemical bonds: Interaction of valence electrons
between 2 or more atoms. # bonds determined by #
electrons needed to complete outer orbital.
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Covalent Bonds
Atoms share their valence electrons.
Nonpolar bonds: Electrons are equally distributed
between the two identical atoms.
Strongest bond. H2
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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.
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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).
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Ionic Bonds
Cation and anion attract, form ionic compound.
Weaker than polar bonds. Dissociate easily when
dissolved in H20. NaCl Na+ and Cl-
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Table Salt, an Ionically Bonded Molecule
Slide number: 1
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17p18n
11p12n
11p12n
17p18n+
(+)(–)
Na Cl+ NaCl
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Table Salt, an Ionically Bonded Molecule
Slide number: 2
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17p18n
11p12n
Na Cl+
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Table Salt, an Ionically Bonded Molecule
Slide number: 3
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17p18n
11p12n
Na Cl+
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Table Salt, an Ionically Bonded Molecule
Slide number: 4
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17p18n
11p12n
Na Cl+
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Table Salt, an Ionically Bonded Molecule
Slide number: 5
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17p18n
11p12n
Na Cl+
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Table Salt, an Ionically Bonded Molecule
Slide number: 6
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17p18n
11p12n
Na Cl+
(+) (–)
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Table Salt, an Ionically Bonded Molecule
Slide number: 7
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NaCl
11p12n
(+)
17p18n
(–)
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Interaction with water
Hydrophilic: Formation of hydration spheres. Polar covalent bonds.
Hydrophobic: Cannot form hydration spheres. Nonpolar covalent bonds.
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Hydrogen Bond
Hydrogen forms a polar bond with another atom, hydrogen has a slight + charge.
Weak attraction for for a second electronegative atom.
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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.
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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+].
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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.
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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
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Functional Groups Inactive “backbone” to which more
reactive atoms are attached.
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Classes According to Functional Groups
Ketone and aldehyde: carbonyl group
Organic acid: carboxyl group
Alcohol: hydroxyl group
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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.
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Four main classes of Organic molecules Lipids Carbohydrates Proteins Nucleic Acids
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Lipids
GR: Lipos=Fat Diverse group of molecules. Insoluble in polar solvents (H20). Hydrophobic (nonpolar) Consist primarily of hydrocarbon
chains and rings.
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Lipids
Hydrocarbons Fatty acids Triglycerides Ketone Bodies Phospholipids Steroids Prostaglandins
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Hydrocarbons
Includes oils and gases
Carbons can be single bonds (saturated)
Carbons can be double bonded (unsaturated)
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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
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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
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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
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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)
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Lecithin
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Phospholipid
Are amphipathic: contain both polar and nonpolar domains Head:
contains polar groups Hydrophilic
Tail: Contains fatty acids (nonpolar) Hydrophobic
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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
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Micelle formation
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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
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Ketone Bodies
4-carbon chunks
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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
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Steroids Nonpolar and insoluble in H20. All have cholesterol as precursor.
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Prostaglandins
Prostaglandins: Fatty acid with cyclic
hydrocarbon group. Derived from arachidonic acid.
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Prostaglandins
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Carbohydrates
Organic molecules that contain carbon, hydrogen and oxygen.
CH20 General formula:
CnH2nOn
-ose denotes a sugar molecule
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Carbohydrates
Supply energy Glucose Complex carbohydrates
Provide structural support cellulose
Part of plasma membrane Monomer: monosaccarides
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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
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Glucose
Also called : Dextrose Transportable in the blood
Blood glucose C6H12O6
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Fructose
Fruit sugar
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Galactose
C6H12O6
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Carbohydrates
Disaccharide: 2 monosaccharides joined
covalently. Sucrose
Glucose and fructose Maltose
Glucose and glucose Lactose
Glucose and galactose
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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
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Formation of Disaccharides
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Hydrolysis Reverse of dehydration synthesis. Digestion reaction. H20 molecule split.
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Carbohydrates
Polysaccharides: Many monosaccharides joined
covalently. General formula: (C6H10O5)n
Characteristics: Devoid of taste Do not form solutions Iodine test
Iodine +starch+blue
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Polysaccarides
Kinds: Starch
Glucose subunits branched
Dextrins Glycogen (animal starch)
Glucose subunits Branched
Cellulose Glucose subunits Long, unbranched chains
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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!
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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
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Proteins
20 different standard amino acids. Based on the properties of the
functional group E.g.:
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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.
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Peptide bond
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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!
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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
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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
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Secondary structures
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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
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Bonds responsible for 3o structure
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Tertiary structure
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Quaternary Structure
Number of polypeptide chains covalently linked together.
Insulin, hemoglobin
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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
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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
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Nucleic Acids
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Nucleotides Structure of a nucleotide: 3 subunits
Pentose sugar Phosphate group Nitrogenous base
Purines: two rings Guanine Adenine
Pyrimidines: one ring Cytosine Thymine Uricil
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Nucleotide Structure
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Nitrogenous Bases
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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
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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
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Nitrogenous Bases
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DNA
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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)
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DNA vs RNA
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