Transcript 02LecturePresentation

Chapter 2
The Chemical Context of Life
PowerPoint® Lecture Presentations for
Biology
•Organisms are composed
of matter
•Matter is anything that
takes up space and has
mass
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Element - substance that cannot be broken down to other
substances by chemical reactions
Compound - substance consisting of two or more elements in a
fixed ratio
Sodium
Chlorine
Sodium
chloride
Table 2-1
•About 25 of the 92
elements are essential to
life
•Trace elements - required
by an organism in minute
quantities
Fig. 2-4
(a) Nitrogen deficiency
(b) Iodine deficiency
Each element consists of unique atoms, the smallest unit of
matter that still retains the properties of an element
Cloud of negative
charge (2 electrons)
Electrons
Nucleus
•Atomic number - # of protons in its nucleus
•Mass number - sum of protons plus neutrons in the nucleus
•Atomic mass, the atom’s total mass, can be approximated by
the
mass number
Fig. 2-7
•Isotopes - two atoms
of an element that
differ in number of
neutrons
•Radioactive
isotopes decay
spontaneously, giving
off particles and
energy
•dating fossils,
Cancerous
tracing atoms
throat
tissue
through metabolic
processes and
diagnosing medical
disorders
•Energy - capacity to cause change
•Potential energy - energy that matter
has because of its location or structure
•An electron’s state of potential
energy is called its energy level, or
electron shell
Third shell (highest energy
level)
Second shell (higher
energy level)
First shell (lowest energy
level)
(b)
Atomic
nucleus
(a) A ball bouncing down a flight
of stairs provides an analogy
for energy levels of electrons
Energy
absorbed
Energy
lost
Electron Distribution and Chemical Properties
• Valence electrons - those in the outermost
(valence shell)
– determines chemical behavior
– incomplete valence shells can share (covalent =
STRONGEST) or transfer (ionic) valence
electrons
• These interactions usually result in atoms staying
close together, held by attractions called
chemical bonds
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 2-11
Hydrogen
atoms (2 H)
Hydrogen
molecule (H2)
• Molecule consists of two or more atoms held
together by covalent bonds
• The notation used to represent atoms and
bonding is called a structural formula
– For example, H–H
• This can be abbreviated further with a molecular
formula
– For example, H2
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Hydrogen Bonds
• Hydrogen bond - a hydrogen atom covalently
bonded to one electronegative atom is also
attracted to another electronegative atom
– In living cells usually oxygen or nitrogen atoms
• Van der Waals interactions - attractions
between molecules that are close together as a
result of these charges
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 2-18
Natural endorphin
Key
Carbon
Hydrogen
Nitrogen
Sulfur
Oxygen
Morphine
(a) Structures of endorphin and morphine
Natural
endorphin
Brain cell
Morphine
Endorphin
receptors
(b) Binding to endorphin receptors
Biological
molecules
recognize
& interact
with each
other
based on
molecular
shape
Chemical reactions - making and breaking of chemical bonds
•Some chemical reactions go to completion
•All chemical reactions are reversible
2 H2
O2
Reactants
2 H2O
Reaction
Products
•Chemical equilibrium - reached when the forward and
reverse reaction rates are equal