chapter 2 chemical composition of the body remon wahba, md

Chapter 2Chemical composition of the

body

Remon Wahba, MD

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

Chapter 2 Outline

AtomsChemical BondsAcids, Bases & the pH ScaleOrganic Molecules

CarbohydratesLipidsProteinsNucleic Acids

Atoms

2-3


Atoms Smallest units of the

chemical elements

Composed of: Nucleus contains:

Protons (+ charge)Neutrons (no

charge)

Electrons Shells: Electrons(- charge)

2-4


Atoms continued

Atomic mass is sum of protons &

neutrons in an atom

Atomic number is number of

protons in an atom is unique for every

element

2-5


Electron Shells

Electron shells or Orbitals are in layers around the nucleus

Number of Electrons = Number of Protons

Number of shells depends on atomic number

First shell can have 2 Electrons only

Second shell can have up to 8 Electrons


Atoms - Electron ShellsValence Electrons

Electrons present in the outermost shell

These can participate in chemical reactions & form bonds

2-7


electron shell

Carbon (C) Oxygen (O) Phosphorus (P) Calcium (Ca)


Isotopes Are different forms of the Same Atoms

Contain same number of Protons

Contain different numbers of Neutrons

Atomic number is the same,Atomic mass is different

2-8


Types of Atoms

There are 2 types of atoms:1. Inert

The outermost electron shell is completely full.

2. ReactiveThe outermost electron shell is partially

full


electron

nucleus

Hydrogen (H) Helium (He)

Chemical Bonds

2-9


Chemical BondsAtoms unite together to form Molecules

Molecules form by chemical bonding between valence electrons of atoms

An Atom, with a partially full outermost electron shell is a Reactive atom

Atoms react with each other to Complete (Saturate) their outermost electron shell


Chemical BondsAtoms unite together by Bonds

Number of bonds determined by

number of Electrons needed to

complete (saturate) the outermost

shell

2-10


Chemical Bonds

1. Covalent BondsNon-Polar Covalent BondsPolar Covalent Bonds

2. Ionic Bonds

3. Hydrogen Bonds


Covalent Bonds

Occur when atoms Share valence electrons

Two Types:1. Non-polar Covalent Bonds:2. Polar Covalent Bonds


Covalent Bonds

1- Nonpolar Bonds: Electrons are shared equally between the two atoms E.g. in:

H2

02

Fig 2.22-11


(a)nonpolar covalentbonding

Hydrogen (H–H or H2),a nonpolar molecule

Oxygen (O=O or O2),a nonpolar molecule


Covalent Bonds (continued)

2- Polar Covalent Bonds: Electrons are shared unequallyPulled more towards one atom

Molecules Have (+) and (–) poles

Oxygen, Nitrogen, Phosphorous have strong pull so tend to form polar moleculesE.g. H20


(b)polar covalentbonding

(slightly negative)

(slightly positive)

Water (H–O–H or H2O),a polar molecule


Ionic Bonds Occur when valence electrons are transferred

from one atom to another; (Losing OR Gaining) Forming charged atoms (ions)

An Atom that loses electrons becomes a Cation (+ charged )

An Atom that gains electrons becomes an Anion (- charged)

Bonds form by attraction of (+) & (-) charges


Ionic Bonds


Ionic Bonds

Ionic bonds are weaker than Polar Covalent Bonds

Dissociate when dissolved in H20

Because H20 forms Hydration spheres around ions

E.g. NaCl


Ionic Bonds

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

Hydrophilic molecules are Soluble in Water Because readily form hydration spheresE.g. glucose & amino acids

Hydrophobic molecules are nonpolar, cannot form hydration spheres (Insoluble in Water)

2-15


Hydrogen Bonds- Hydrogen Bonds form between Molecules

with Polar Covalent Bonds- Water Molecules:

The negatively charged Oxygen atom attracts the positively charged hydrogen atoms of The Adjacent Molecules

- Hydrogen bonds are weaker than Ionic and Covalent Bonds.


Hydrogen BondsForms between

Adjacent H20 Molecules

Create Surface Tension

2-16

Acids, Bases, & The pH Scale

2-17


Acids and BasesWater is very stable but few molecules

constantly break into IonsA Hydrogen ion ( H+ )A Hydroxide Ion (OH- )

As the numbers of H+ and OH- are

equal, water is considered Neutral


hydroxide ion(OH – )

hydrogen ion(H+)

water(H2O)


Acids & BasesAcids:

Release (H+) in a solution (proton donor)

Bases: Absorb (H+) of a solution (proton acceptor)

2-18


Acids & Bases


pH ScaleIs symbol for H+ concentration of a

solution

pH scale runs from 0 to 14

Pure H20 is Neutral & has pH of 7

Acids have a pH less than 7 (pH 0 - 7)

Bases have a pH More than 7 (pH 7 - 14)2-19


Buffers Are molecules that prevent changes in pH by

either combining with or releasing H+s E.g. the Bicarbonate Buffer System in blood:

H20 + C02 H2C03 H+ + HC03-

This buffers pH because reaction can go in either direction depending upon concentration of H+s

2-21


Blood pHNormal range of Blood pH is 7.35 – 7.45

Maintained by buffering action

Acidosis occurs if pH < 7.35

Alkalosis occurs if pH > 7.452-22

Organic Molecules

2-23


Organic Molecules

Contain Carbon & Hydrogen

Carbon has 4 electrons in outer shellBonds Covalently to fill outer shell with 8

electrons

Carbon Serves as “Backbone” to which more reactive Functional groups are added

2-24


Organic Molecules continued

Functional groups: Carbonyl group

forms ketones & Aldehydes

Hydroxyl group forms Alcohols

Carboxyl group forms Organic Acids (Lactic & Acetic acids) Fig 2.11

2-26


Organic Molecules continued

Carbohydrates

Lipids

Proteins

Nucleic Acids

Carbohydrates

2-28


Photosynthesis


Carbohydrates

Are organic molecules containing Carbon, Hydrogen & Oxygen in ratio of CnH2n0n

Types:

Monosaccharides

Disaccharides

Polysaccharides


Monosaccharides

Simple sugars:

One molecule of Sugar Such as

Glucose Fructose Galactose


DisaccharidesDisaccharides are 2 Monosaccharides

joined covalentlyExamples:

Sucrose (glucose + fructose) or Table

Sugar

Lactose (glucose + galactose) or Milk

Sugar

Maltose (2 glucoses) or Malt Sugar 2-30


PolysaccharidesComplex CarbohydratesChains of Monosaccharides joined

together by covalent bondsStarch In plantsGlycogen In animals

Stored in:

LiverSkeletal Muscles


Glycogen Stored in the Liver

Can be converted into Free Glucose which can be released into the blood stream to be used by All Body Cells as a source of energy

Stored in the Skeletal Muscles Can be converted into Glucose 6 Phosphate

which is trapped inside the muscle fibers to be used by the Skeletal Muscles Only to get energy

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

Occurs by removing water molecule out of Two Monosaccharides H+ & OH- are removed, producing H20

This is called Dehydration

2-32

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

Occurs by Hydrolysis (reverse of dehydration)H20 molecule is split and added, H+ added to

one Monosaccharide, OH- to other Polysaccharide are hydrolyzed into

Disaccharides, then to Monosaccharides

2-33

Lipids

2-34


Lipids

Are insoluble in polar solvents such as water

Hydrophobic

Consist primarily of hydrocarbon Chains & Rings

2-35


Triglycerides Formed by condensation (Dehydration Reaction) of:

One Alcohol molecule (Glycerol) Three Fatty Acids

There are 2 Types of Fatty Acids: Saturated

Hydrocarbon chains of fatty acids are joined by Single Covalent Bonds

Unsaturated There are Double Bonds within the hydrocarbon chains


Fatty Acids

2-37


Monounsaturated Fatty Acid

omega end alpha end One double bond

H H H H H H H H H H H H H H H O

H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H


Polyunsaturated Fatty Acid

omega end alpha end > 2 double bonds

H H H H H H H H H H H H H O

H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH

H H H H H H H H H H H H H H H H H


Ketone Bodies Hydrolysis of Triglycerides releases free fatty

acids which can be either: Used for energy Converted in the Liver to ketone Bodies

High levels = ketosis

Ketoacidosis occurs when ketone bodies in blood lower pH


Ketosis & Ketoacidosis

Occurs when the body depends of Fats as the main source of Energy

In cases of:

Severe un-controlled Diabetes

Mellitus

Low Carbohydrate Diets

Starvation


Ketosis & Ketoacidosis

Ketone bodies can easily convert to Acetone which gives a Fruity smell to the breath


PhospholipidsAre lipids that contain a Phosphate

group

The Plasma membrane that surrounds each cell is made up of double layer of Phospholipids

Phosphate part is polar & Hydrophilic

Lipid part is nonpolar & Hydrophobic


Phospholipids Aggregate into

Micelles in waterPolar part

interacts with water; nonpolar part is hidden in middle

Act as Surfactants by reducing surface tension (in the lungs)

micelle Fig 2.21

2-40


Steroids Are Nonpolar &

insoluble in water

All have three 6-carbon rings joined to a 5-carbon ring

Cholesterol is: Precursor for

steroid hormones Component of

cell membranes

Fig 2.22

2-41


Cholesterol

Cholesterol is carried in the blood by 2 Lipoproteins:

LDL ( Low Density Lipoproteins) Bad

HDL ( High Density Lipoproteins) Good


Cholesterol, HDL & LDL

Recommended Levels:Total Cholesterol: Less than 200 mg / dL

HDL: Over 40 mg / 100ml

LDL: Less than 100 mg / 100ml

Triglycerides: Less than 100 mg /100ml


Prostaglandins Are Fatty Acids with

cyclic hydrocarbon group

Produced & active in most tissues

Serve many Regulatory functions


Hydrogenation of OilsAdding Hydrogen to oil (hydrogenated oils)

Changing Unsaturated Fatty Acids into Saturated Fatty Acids

Oils become solid at room temperature (margarine)

To prolong the shelf-life of processed foods

Proteins

2-43


Proteins Proteins are the building blocks of the body

Important for the manufacture of hormones and enzymes

Important for the production of antibodies

Important for maintaining fluid and electrolyte balance of the body


Proteins - Amino Acids Are made of long chains of Amino Acids

There are 20 different amino acids

Two Types:Essential:

Can not be produced inside our bodyNonessential:

Can be produced from other amino acids

2-44


Proteins - Peptides Are short chains of amino acids

Amino acids are linked by peptide bondsFormed by Dehydration reactions

2-45


Proteins - Peptides Two Amino Acids are called Dipeptide

Three Amino Acids are called Tripeptide

If <100 amino acids is called a Polypeptide;

>100 amino acids, is called a Protein

A typical protein contains about 1000 amino acids

2-46


Protein - Structure Many proteins are conjugated with other groups

Glycoproteins Contain Carbohydrates

Lipoproteins Contain Lipids

Others proteins like Hemoglobin contain a pigment

2-52

Nucleic Acids

2-53


Nucleic Acids

DNADeoxyribonucleic Acid

RNARibonucleic Acid


Nucleic Acids

Are made of long chains of Nucleotides.

Each Nucleotide is made up of: Sugar Phosphate group Nitrogenous base

Pyrimidines ( C & T)Purines (G & A)

Fig 2.29

2-54

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Deoxyribonucleic acid (DNA)

Contains the Genetic code Its Deoxyribose sugar (5C) is covalently bonded to 1 of 4

bases: Guanine or Adenine (purines) Cytosine or Thymine (pyrimidines)

Chain is formed by sugar of one nucleotide bonding to phosphate of another

Each base forms hydrogen bonds with other bases which holds 2 strands of DNA together

The 2 strands of DNA twist to form a Double Helix

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Deoxyribonucleic acid (DNA)

2-57


Ribonucleic Acid (RNA) Consists of a long chain

of nucleotides joined together by sugar-phosphate bonds

Its Ribose sugar is bonded to 1 of 4 bases: Guanine or Adenine Cytosine or Uracil

(replaces thymine)

Single-stranded

Fig 2.32

2-58


Ribonucleic Acid (RNA)

3 types of RNA are synthesized from DNA & allow it to direct activities of a cell:Messenger RNA – mRNA

Transfer RNA – tRNA

Ribosomal RNA - rRNA

2-59


DNA and RNADNA

Contains the sugar Deoxyribose Contains Thymine instead of Uracil Controls protein synthesis Double Stranded

RNA

Contains the sugar Ribose Contains the nitrogen base Uracil instead of

Thymine Carries the message from the nucleus to the

cytoplasm to direct protein synthesis Single stranded


DNA & RNA

chapter 2 chemical composition of the body remon wahba, md

Documents

bonds number of bonds

mcgrawhill companies

chemical bonds atoms

outermost electron shell

md slide

valence electrons of

hydrogen bonds

ionic bonds