Download Human Physiology

Chapter 2
Chemical composition of the body
Remon Wahba, MD
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Chapter 2 Outline
Atoms
Chemical
Bonds
Acids, Bases & the pH Scale
Organic Molecules
Carbohydrates
Lipids
Proteins
Nucleic Acids
Atoms
2-3
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Atoms
Smallest
units of the
chemical elements
Composed
of:
Nucleus contains:
Protons (+ charge)
Neutrons (no charge)
Electrons
Shells:
 Electrons(- charge)
2-4
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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
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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
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Atoms - Electron Shells
Valence
Electrons
Electrons present in the outermost shell
These
can participate in chemical reactions &
form bonds
2-7
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electron shell
Carbon (C)
Oxygen (O)
Phosphorus (P)
Calcium (Ca)
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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
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Types of Atoms
There are 2 types of atoms:
1. Inert
 The
outermost electron shell is completely full.
2. Reactive
 The
outermost electron shell is partially full
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electron
nucleus
Hydrogen (H)
Helium (He)
Chemical Bonds
2-9
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Chemical Bonds
Atoms
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
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Chemical Bonds
Atoms
unite together by Bonds
Number
of bonds determined by number of
Electrons needed to complete (saturate)
the outermost shell
2-10
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Chemical Bonds
1. Covalent Bonds
Non-Polar Covalent Bonds
Polar Covalent Bonds
2. Ionic Bonds
3. Hydrogen Bonds
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Covalent Bonds
when atoms Share valence
electrons
Occur
Two
Types:
1. Non-polar Covalent Bonds:
2. Polar Covalent Bonds
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Covalent Bonds
1- Nonpolar Bonds:
Electrons are shared
equally between the two
atoms
E.g. in:
H 2
02
Fig 2.2
2-11
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(a)
nonpolar covalent
bonding
Hydrogen (H–H or H2),
a nonpolar molecule
Oxygen (O=O or O2),
a nonpolar molecule
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Covalent Bonds
(continued)
2- Polar Covalent Bonds:
Electrons are shared unequally
Pulled more towards one atom
Molecules
Oxygen,
Have (+) and (–) poles
Nitrogen, Phosphorous have strong pull
so tend to form polar molecules
E.g. H20
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(b)
polar covalent
bonding
(slightly negative)
(slightly positive)
Water (H–O–H or H2O),
a polar molecule
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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
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Ionic Bonds
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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
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Ionic Bonds
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Hydrophilic Vs. Hydrophobic
Hydrophilic
molecules are Soluble in Water
Because readily form hydration spheres
E.g. glucose & amino acids
Hydrophobic
molecules are nonpolar, cannot
form hydration spheres (Insoluble in Water)
2-15
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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.
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Hydrogen Bonds
Forms
between
Adjacent H20
Molecules
Create
Surface
Tension
2-16
Acids, Bases, & The pH Scale
2-17
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Acids and Bases
Water
is very stable but few molecules
constantly break into Ions
A Hydrogen ion ( H+ )
A Hydroxide Ion (OH- )
As
the numbers of H+ and OH- are equal,
water is considered Neutral
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water
(H2O)
hydroxide ion
(OH – )
hydrogen ion
(H+)
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Acids & Bases
Acids:

Release (H+) in a solution (proton donor)
Bases:

Absorb (H+) of a solution (proton acceptor)
2-18
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Acids & Bases
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pH Scale
Is
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
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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
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Blood pH
Normal
range of Blood pH is 7.35
Maintained
– 7.45
by buffering action
Acidosis
occurs if pH < 7.35
Alkalosis
occurs if pH > 7.45
2-22
Organic Molecules
2-23
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Organic Molecules

Contain Carbon & Hydrogen

Carbon has 4 electrons in outer shell
Bonds Covalently to fill outer shell with 8
electrons
Carbon Serves as “Backbone” to which more
reactive Functional groups are added

2-24
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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
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Organic Molecules
Carbohydrates
Lipids
Proteins
Nucleic
Acids
continued
Carbohydrates
2-28
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Photosynthesis
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Carbohydrates
Are
organic molecules containing Carbon,
Hydrogen & Oxygen in ratio of CnH2n0n
Types:
Monosaccharides
Disaccharides
Polysaccharides
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Monosaccharides
Simple
One
sugars:
molecule of Sugar
 Such as
 Glucose
 Fructose
 Galactose
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Disaccharides
Disaccharides
are 2 Monosaccharides joined
covalently
Examples:
Sucrose (glucose + fructose) or Table Sugar
Lactose (glucose + galactose) or Milk Sugar
Maltose (2 glucoses) or Malt Sugar
2-30
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Polysaccharides
Complex
Carbohydrates
Chains of Monosaccharides joined together by
covalent bonds
Starch In plants
Glycogen In animals
Stored in:
Liver
Skeletal
Muscles
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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
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Formation of Disaccharides
Occurs
by removing water molecule out of Two
Monosaccharides
 H+ & OH- are removed, producing H20
This
is called Dehydration
2-32
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Digestion of Polysaccharides
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
Occurs
2-33
Lipids
2-34
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Lipids
Are
insoluble in polar solvents such as water
Hydrophobic
Consist
primarily of hydrocarbon Chains &
Rings
2-35
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Triglycerides
Formed by condensation (Dehydration
 One Alcohol molecule (Glycerol)
 Three Fatty Acids
There are 2 Types of Fatty Acids:
Saturated
 Hydrocarbon chains of fatty
Reaction) of:
acids are joined by
Single Covalent Bonds
Unsaturated
There are Double
chains
Bonds within the hydrocarbon
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Fatty Acids
2-37
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Monounsaturated Fatty Acid
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
omega end
One double bond
alpha end
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Polyunsaturated Fatty Acid
H H H H H
H
H H H H H HH 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
omega end
> 2 double bonds
alpha end
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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
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Ketosis & Ketoacidosis
Occurs
when the body depends of Fats as the
main source of Energy
In cases of:
Severe
Low
un-controlled Diabetes Mellitus
Carbohydrate Diets
Starvation
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Ketosis & Ketoacidosis
Ketone
bodies can easily convert to Acetone
which gives a Fruity smell to the breath
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Phospholipids
Are
lipids that contain a Phosphate group
The
Plasma membrane that surrounds each
cell is made up of double layer of
Phospholipids
Phosphate
Lipid
part is polar & Hydrophilic
part is nonpolar & Hydrophobic
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Phospholipids
Aggregate
into
Micelles in water
Polar part interacts
with water;
nonpolar part is
hidden in middle
micelle
Fig 2.21
Act
as Surfactants by
reducing surface
tension (in the lungs)
2-40
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Steroids
Are
Nonpolar &
insoluble in water
All
have three 6carbon rings joined to
a 5-carbon ring
Fig 2.22
Cholesterol
is:
 Precursor for
steroid hormones
 Component of cell
membranes
2-41
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Cholesterol
Cholesterol
is carried in the blood by 2
Lipoproteins:
LDL
( Low Density Lipoproteins) Bad
HDL
( High Density Lipoproteins) Good
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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
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Prostaglandins
Are
Fatty Acids with
cyclic hydrocarbon
group
Produced
& active in
most tissues
Serve
many
Regulatory functions
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Hydrogenation of Oils
Adding
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
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Proteins
Proteins
are the building blocks of the body
Important
for the manufacture of hormones and
enzymes
Important
Important
for the production of antibodies
for maintaining fluid and electrolyte
balance of the body
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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 body
Nonessential:
Can be produced from other amino acids
2-44
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Proteins - Peptides
Are
short chains of amino acids
Amino acids are linked by peptide bonds
Formed
by Dehydration reactions
2-45
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Proteins - Peptides
Two
Amino Acids are called Dipeptide
Three
If
<100 amino acids is called a Polypeptide;
>100
A
Amino Acids are called Tripeptide
amino acids, is called a Protein
typical protein contains about 1000 amino acids
2-46
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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
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Nucleic Acids
DNA
Deoxyribonucleic Acid
RNA
Ribonucleic Acid
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Nucleic Acids
Fig 2.29
Are
made of long chains of
Nucleotides.
Each
Nucleotide is made up of:
Sugar
Phosphate group
Nitrogenous base
Pyrimidines ( C & T)
Purines (G & A)
2-54
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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
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Deoxyribonucleic acid (DNA)
2-57
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Ribonucleic Acid (RNA)
 Consists
of a long chain of
nucleotides joined together
by sugar-phosphate bonds
Fig 2.32
 Its
Ribose sugar is bonded
to 1 of 4 bases:
 Guanine or Adenine
 Cytosine or Uracil
(replaces thymine)
Single-stranded
2-58
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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
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DNA and RNA
 DNA

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
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DNA & RNA