chapter02 chemical composition of the body

Chapter 2

Chemical Composition of the Body

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

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

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

Slide number: 1


17p18n

11p12n

11p12n

17p18n+

(+)(–)

Na Cl+ NaCl



Slide number: 2


17p18n

11p12n

Na Cl+



Slide number: 3


17p18n

11p12n

Na Cl+



Slide number: 4


17p18n

11p12n

Na Cl+



Slide number: 5


17p18n

11p12n

Na Cl+



Slide number: 6


17p18n

11p12n

Na Cl+

(+) (–)



Slide number: 7


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

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

4-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

chapter02 chemical composition of the body

Science

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atoms electrons

number of electrons

max number of electrons

number of neutrons

bonded molecule slide

energy levels electrons

covalent bonds atoms