Transcript The Living World - Chapter 3 - McGraw Hill Higher Education

Essentials of
The Living World
First Edition
GEORGE B. JOHNSON
3
The Chemistry of Life
PowerPoint® Lectures prepared by Johnny El-Rady
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3.1 Atoms
Matter is any substance in the universe that
has mass and occupies space
All matter is composed of extremely small
particles called atoms
Every atom has the same basic structure
Core nucleus of protons and neutrons
Orbiting cloud of electrons
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Fig. 3.1
e- determine the
chemical behavior
of atoms
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3.1 Atoms
Atomic number
Number of protons
Atomic mass
Number of protons and neutrons
Element
A substance that cannot be broken down by
ordinary chemical means
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Electrons
Energy is the ability to do work
Electrons have energy due to their relative
orbital position (potential energy)
Fig. 3.2
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Electrons
Each electron shell has a specific # of orbitals
Each orbital holds up to two electrons
Fig. 3.3
Atoms with incomplete
electron orbitals are
more reactive
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3.2 Ions and Isotopes
Ions are atoms in which the number of
electrons does not equal that of protons
Fig. 3.4
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3.2 Ions and Isotopes
Isotopes are atoms with the same number of
protons but different numbers of neutrons
Fig. 3.5
99% of all
carbon
Different
atomic mass
Same atomic
number
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Radioactive Decay
The nucleus of an unstable isotope breaks
down into particles with lower atomic numbers
Radioactive isotopes are used in
1. Medicine
Tracers are taken up and used by the body
Emissions are detected using special lab equipment
2. Dating fossils
The rate of decay of a radioactive element is constant
The amount of decay can be used to date fossils
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Fig. 3.7 Radioactive
isotope dating
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3.3 Molecules
A molecule is a group of atoms held together
by energy
The holding force is called a chemical bond
There are three kinds of chemical bonds
1. Ionic bonds
2. Covalent bonds
3. Hydrogen bonds
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Ionic Bonds
Formed by the attraction of oppositely
charged ions
Two key properties
1. Strong
But not as strong as covalent bonds
2. Not directional
They are not formed between particular ions in the
compound
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Ionic Bonds
Everyday
tablesalt
NaCl
Crystal
Fig. 3.8 The formation of the ionic bond in table salt
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Covalent Bonds
Formed when two atoms share electrons
Two key properties
1. Strong
The strength increases with the number of shared
electrons
2. Very directional
They are formed between two specific atoms
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Covalent Bonds
Fig. 3.9 Water molecules contain two covalent bonds
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Hydrogen Bonds
Formed by the attraction of opposite partial
electric charges between two polar molecules
Two key properties
1. Weak
They are not effective over long distances
2. Highly directional
Polar molecules must be very close for the weak
attraction to be effective
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Hydrogen Bonds
Fig. 3.10 Hydrogen bonding in water molecules
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3.4 Hydrogen Bonds Give Water
Unique Properties
Water molecules are polar molecules
They can thus form hydrogen bonds with each
other and with other polar molecules
Each hydrogen bond is very weak
However, the cumulative effect of enormous
numbers can make them quite strong
Hydrogen bonding is responsible for many of
the physical properties of water
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3.4 Hydrogen Bonds Give Water
Unique Properties
Heat Storage
A large input of thermal energy is required to
disrupt the organization of liquid water
This minimizes temperature changes
Ice Formation
At low temperatures, hydrogen bonds don’t break
Water forms a regular crystal structure that floats
High Heat of Vaporization
At high temperatures, hydrogen bonds do break
Water is changed into vapor
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3.4 Hydrogen Bonds Give Water
Unique Properties
Cohesion
Fig. 3.12
Attraction of water molecules
to other water molecules
Example: Surface tension
Adhesion
Water strider
Attraction of water molecules
to other polar molecules
Example: Capillary action
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3.4 Hydrogen Bonds Give Water
Unique Properties
High Polarity
Polar molecules are termed hydrophilic
Water-loving
All polar molecules that dissolve in water are termed
soluble
Nonpolar molecules are termed hydrophobic
Water-fearing
These do not form hydrogen bonds and are therefore
not water soluble
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Salt dissolves
when all ions
have separated
from the crystal
Fig. 3.13 How salt dissolves in water
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3.5 Water Ionizes
Covalent bonds within a water molecule
sometimes break spontaneously
H 2O
OH–
hydroxide
ion
+
H+
hydrogen
ion
This process of spontaneous ion formation is
called ionization
It is not common because of the strength of
covalent bonds
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pH
A convenient way to express the hydrogen ion
concentration of a solution
pH = _ log [H+]
The pH scale is logarithmic
A difference of one unit represents a ten-fold change in
H+ concentration
Acid
Dissociates in water to increase H+ concentration
Base
Combines with H+ when dissolved in water
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Acidic solutions
Neutral solutions
Balance between
H+ and OH–
Basic solutions
Fig. 3.14 The pH Scale
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Buffers
Hydrogen ion reservoirs that take up or
release H+ as needed
The key buffer in blood is an acid-base pair
Favored reaction
when [H+] is low
Fig. 3.16
–
+
+
H2O
Water
CO2
Carbon dioxide
H2CO3
Carbonic acid
HCO3–
Bicarbonate
ion
Favored reaction
when [H+] is high
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+
H+
Hydrogen
ion
3.6 Forming Macromolecules
Fig. 3.17
An organic molecule
consists of a carbonbased core with
special groups
attached
These groups have
special properties
and are referred to
as functional groups
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3.6 Forming Macromolecules
Organisms are primarily made of four kinds
of molecules
Proteins
Nucleic acids
Carbohydrates
Lipids
These are termed macromolecules
They constitute the building materials and
machinery of the cell
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Macromolecules are
made by a process
termed dehydration
synthesis
Macromolecules are
broken down by a
process termed
hydrolysis
Fig. 3.18a
Fig. 3.18b
H2O
H HO
HO
H2O
H
HO
H
Energy
HO
H
Energy
HO
H HO
Both types of processes require enzymes
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H
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3.7 Proteins
Fig. 3.19
Made up of
subunits called
amino acids Six amino
acids
Six amino
acids
There are 20
common amino
acids, and they fall
into one of four
general groups Five amino
acids
Three amino acids
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3.7 Proteins
Fig. 3.20
Amino acids
are linked
together by
peptide bonds
Long chains of
amino acids
are called
polypeptides
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Protein Structure
Determined by the sequence of its amino
acids
There are four general levels
Primary
Secondary
Tertiary
Quaternary
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Protein Structure
Primary structure
The specific amino acid sequence of a protein
Secondary structure
The initial folding of the amino acid chain by
hydrogen bonding
Tertiary structure
The final three-dimensional shape of the protein
Quaternary structure
The spatial arrangement of polypeptides in a
multi-component protein
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Fig. 3.21 Levels of
protein structure
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Protein Structure
Changes in a
protein’s
environment can
cause a protein
to denature
It loses its threedimensional
structure
And becomes
inactive
Fig. 3.22
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Protein Structure
Proteins can be divided into two classes
1. Structural
2. Globular
Long cables
Provide shape/strength
Fibrin
Grooves and depressions
Enzymes
Keratin
Silk
Fig. 3.23
Fig. 3.24
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Chaperone Proteins
Help newly-produced proteins to fold properly
Fig. 3.25
Chaperone protein deficiencies may play a role in
certain diseases
Cystic fibrosis and Alzheimer’s disease
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3.8 Nucleic Acids
Serve as information storage molecules
Long polymers of repeating subunits termed
nucleotides
A nucleotide is composed of three parts
Five-carbon sugar
Nitrogen-containing base
Phosphate
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Fig. 3.26 The structure of a nucleotide
Nitrogenous bases
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3.8 Nucleic Acids
Two varieties
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
RNA
DNA
Sugar = Ribose
Sugar = Deoxyribose
Bases = A, G, C, U
Bases = A, G, C, T
Single-stranded
Double-stranded
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Fig. 3.27 How DNA
differs from RNA
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Space-filling
model
Fig. 3.28
The DNA
double helix
Nucleotide sequence
specifies the amino
acid sequence of
proteins
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3.9 Carbohydrates
Also referred to as sugars
Provide building materials and energy storage
Are molecules that contain carbon, hydrogen
and oxygen in a 1:2:1 ratio
Are of two main types
Simple carbohydrates
Complex carbohydrates
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Simple Carbohydrates
1. Monosaccharides
2. Disaccharides
Consist of one subunit
Fig. 3.29
Consist of two subunits
Fig. 3.30
Formed by a
dehydration
reaction
Glucose
Chemical formula: C6H12O6
Sucrose
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Complex Carbohydrates
Consist of long polymers of sugar subunits
Also termed polysaccharides
Examples:
Starch provides energy storage in plants
Glycogen provides energy storage in animals
Cellulose is found in the cell walls of plants
Chitin is found in the cell walls of fungi
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3.10 Lipids
Large nonpolar molecules that are insoluble
in water
Three major types
Fats
Phospholipids
Steroids
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Fats
Used for long-term
energy storage
Also termed
triglycerides or
triacylglycerol
Composed of
three fatty acid
chains linked to
glycerol
Fig. 3.33
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Fats
Fatty acids can be saturated or unsaturated
Most plant
fats
Most animal
fats
Fig. 3.33
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Phospholipids
A modified fat
One of the three fatty acids is replaced by a
phosphate and a small polar functional group
Fig. 3.34a
In water, phospholipids aggregate to form a
lipid bilayer
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Steroids
Composed of four carbon rings
Examples:
Cholesterol
Found in most
animal cell
membranes
Fig. 3.34b
Male and female sex hormones
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