Upload
clementsra
View
888
Download
0
Tags:
Embed Size (px)
Citation preview
Biology 121 – Concepts of BiologyDr. Fritzler
Chapter 2Chapter 2
Essential Chemistry for Biology
Start with Atoms• Atoms
– Fundamental building blocks of matter
– Composed of three smaller subatomic particles
– Positively charged _______________
– Uncharged (neutral) _______________
– Negatively charged _______________
– # _______________ = # _______________
– Protons and neutrons are part of the nucleus
– Electrons move around the nucleus
Nucleus
Protons
Neutrons
Electrons
Nucleus
Cloud of negativecharge 2 electrons
2
2
2
Proton• Positive charge• Determines element
Neutron• No charge• Determines isotope
Electron• Negative charge• Participates in chemical reactions• Outer-shell electrons determine chemical behavior
Nucleus• Consists of neutrons and protons
Atom
Elements• A pure substance consisting of atoms with the
same number of protons
• _______________ _______________ = quantity of protons (unique for each element)
– Ex: Carbon = 6
Mercury HgCopper Cu Lead Pb
H
Rb
K
Na
Li
Fr
Cs
Sr
Ca
Mg
Be
Ra
Ba
Y
Sc
Ac
La
Zr
Ti
Rf
Hf
Nb
V
Db
Ta
Mo
Cr
Sg
W
Tc
Mn
Bh
Re
Ru
Fe
Hs
Os
Rh
Co
Mt
Ir
Pd
Ni
Uun
Pt
Xe
Kr
Uuo
Rn
Ag
Cu
Uuu
Au
Cd
Zn
Uub
Hg
Ar
Ne
In
Ga
Tl
Al
B
Sn
Ge
Uuq
Pb
Si
C
Sb
As
Bi
P
N
Te
Se
Uuh
Po
S
O
I
Br
At
Cl
F
He
Th
Ce
Pa
Pr
U
Nd
Np
Pm
Pu
Sm
Am
Eu
Lr
Lu
Cm
Gd
Bk
Tb
Cf
Dy
Es
Ho
Fm
Er
Md
Tm
No
Yb
6
C12
Elements•There are 92 naturally occurring elements on
Earth.
• 25 elements are essential to life.
• Four elements make up about 96% of the weight of the human body:
– Oxygen
– Carbon
– Hydrogen
– Nitrogen
Carbon C: 18.5%
Hydrogen H:9.5%
Nitrogen N:3.3%
Calcium Ca: 1.5%
Trace elements: less than 0.01%
Boron B Manganese Mn
Oxygen O:65.0%
Magnesium Mg: 0.1%
Phosphorus P: 1.0%
Potassium K: 0.4%
Sulfur S: 0.3%
Sodium Na: 0.2%
Chlorine Cl: 0.2%
Cobalt CoChromium Cr
Iron FeIodine IFluorine FCopper Cu Silicon Si
Zinc ZnVanadium VTin Sn
Molybdenum MoSelenium Se
Trace Elements•Occur in smaller amounts and are essential
for life
•Deficiencies cause disease
– Example: An Iodine deficiency causes goiter
Isotopes• Atoms of the same element that differ in the
number of neutrons
• Example: 12C (6p and 6n), 13C (6p and 7n), 14C (6p and 8n)
• _______________ _______________ = protons plus neutrons
H
Rb
K
Na
Li
Fr
Cs
Sr
Ca
Mg
Be
Ra
Ba
Y
Sc
Ac
La
Zr
Ti
Rf
Hf
Nb
V
Db
Ta
Mo
Cr
Sg
W
Tc
Mn
Bh
Re
Ru
Fe
Hs
Os
Rh
Co
Mt
Ir
Pd
Ni
Uun
Pt
Xe
Kr
Uuo
Rn
Ag
Cu
Uuu
Au
Cd
Zn
Uub
Hg
Ar
Ne
In
Ga
Tl
Al
B
Sn
Ge
Uuq
Pb
Si
C
Sb
As
Bi
P
N
Te
Se
Uuh
Po
S
O
I
Br
At
Cl
F
He
Th
Ce
Pa
Pr
U
Nd
Np
Pm
Pu
Sm
Am
Eu
Lr
Lu
Cm
Gd
Bk
Tb
Cf
Dy
Es
Ho
Fm
Er
Md
Tm
No
Yb
6
C12
Radioactive Isotopes• _______________– atoms with the same #
protons, but different # neutrons
• Radioactive isotopes are not stable
– Nucleus (protons and neutrons) spontaneously decays into other elements and electrons are emitted
• Can be used as tracers and attached to molecules
– Example: Attach a tracer to glucose to monitor brain activity (PET scan)
Positron-Emission Tomography (PET) Scan
Electron Arrangement and the Chemical Properties of Atoms• Atoms acquire, share and donate electrons
• Some atoms do so easily, others do no
– The number and arrangement of electrons in atoms dictate acquisition, sharing and donation
Electrons and Energy Levels• Atoms have the same # electrons as protons
• Electrons orbit the nucleus of an atom in specific electron shells
• The farther an electron is from the nucleus, the greater its energy
• The number of electrons in the outermost shell determines the chemical properties of an atom
Shell Models
First electron shellcan hold 2 electrons
Outer electron shellcan hold 8 electrons
Hydrogen HAtomic number = 1
Carbon CAtomic number = 6
Nitrogen NAtomic number = 7
Oxygen OAtomic number = 8
Electron
Electron Interactions• Atoms whose outermost shell is not completely
full tends to interact with other atoms
– They donate, accept, or share electrons to eliminate vacancies
– Those with the outermost shell filled are chemically inactive and very stable
sodium11p+ , 11e-
chlorine17p+ , 17e-
argon18p+, 18e-
Electrical Charge• An atom with equal numbers of protons and
electrons has no net charge
• _______________ are atoms that carry a charge
– Have either gained (negatively charged) or lost (positively charged) electrons
Sodium atom11p+
11e-
no netCharge (weakly electro-negative)
Sodium ion11p+
10e-
net positivecharge
electronloss
Chlorine atom17p+
17e-
no netCharge (highly electronegative)
Chlorine ion17p+
18e-
net negativecharge
electrongain
Molecules and Mixtures• Molecule – forms when > 2 atoms join in
chemical bonds
• Chemical Bond – attractive force between atoms due to interactions of electrons
• Compounds – molecules consisting of > 2 elements (Ex: water is 2H bound to 1O)
• Mixture – elements intermingle but do not bind (Ex: Sugar into water – sugar dissolves, no bonds formed)
Chemical Bonding and Molecules• Chemical reactions enable atoms to donate,
acquire or share electrons to complete their outer shells.
• Chemical reactions usually result in atoms interacting through three types of bonds
– Ionic bond
– Covalent Bond
– Hydrogen Bond
Ionic Bonds• Strong association between a positive ion and a
negative ion (attraction of opposite charges)
A crystal of table salt isa cubic lattice of many sodiumions and chloride ions.
The mutual attraction ofopposite charges holds thetwo kinds of ions togetherclosely in the lattice.
a
b
A crystal of table salt isa cubic lattice of many sodiumions and chloride ions.
The mutual attraction ofopposite charges holds thetwo kinds of ions togetherclosely in the lattice.
a
b
Outer shellhas 1 electron
Outer shellhas 7 electrons
The outer electron is strippedfrom sodium and completesthe chlorine atom’s outer shell
NaSodium atom
ClChlorine atom
Completeouter shells
The attractionbetween theions—an ionicbond—holdsthem together
Na
Sodium ionCl
Chlorine ion
Sodium chloride (NaCl)
See Animation on Ionic Bonds(Posted to MyCourses)
Covalent Bonds• Form when two atoms share > 1 pairs of outer-
shell electrons
• _______________ covalent bond
– Atoms share electrons equally
• _______________ covalent bond
– Electrons are shared unequally
– Produces polar molecules – one end slightly negative, other slightly positive
Two hydrogen atoms, each withone proton, share two electrons ina single nonpolar covalent bond.
Molecular hydrogen (H—H)
Two oxygen atoms, each with eightprotons, share four electrons in anonpolar double covalent bond.
Molecular oxygen (O=O)
Two hydrogen atoms each share anelectron with an oxygen atom in twopolar covalent bonds. The oxygenexerts a greater pull on the sharedelectrons, so it has a slight negativecharge. Each hydrogen has a slightpositive charge.
Water molecule (H—O—H)
See Animation on Covalent Bonds(Posted to MyCourses)
Hydrogen Bonds•Attraction between a _______________ atom
and another atom
– Both have their own separate covalent bonds
•Are not chemical bonds
– Do not make atoms into molecules
– Weaker than ionic or covalent, and easily form or break
– Used to stabilize structures of large molecules
Hydrogen Bonds• Water is a compound in which the electrons in its
covalent bonds are shared unequally.
– This causes water to be a polar molecule, one with opposite charges on opposite ends.
2 H2 2 H2OO2
Hydrogen
gas
Oxygen
gas
Water
Hydrogen Bonds• The polarity of
water results in weak electrical attractions between neighboring water molecules.
– These interactions are called hydrogen bonds.
Hydrogen bond
Water – The Most Important Molecule
• Without water, there would be no life
• Life on Earth began in water and evolved there for 3 billion years
– Modern life remains tied to water
– Your cells are composed of 70%–95% water
• The abundance of water is a major reason Earth is habitable
Polarity of the Water Molecule• Water molecules are polar
– Form hydrogen bonds with each other and with other polar molecules
– Hydrophilic (water-loving) substances are polar– Hydrophobic (water-dreading) substances are
nonpolar (ex. Oils)
+ +
HH
O
-−slight negative charge on the
oxygen atomThe positive and negative charges balance each other; overall, the molecule carries no charge.
slight positive charge on the hydrogen
atoms
See Animation on Water Structure(Posted to MyCourses)
Water’s Life-Giving Properties• The polarity of water molecules and the
hydrogen bonding that results explain most of water’s life-supporting properties:
– Water molecules stick together.
– Water has a strong resistance to change in temperature.
– Frozen water floats.
– Water is a common solvent for life.
The Cohesion of Water• Hydrogen bonding provides _______________
(resistance of molecule separation)
Microscopic tubes
Cohesion due tohydrogen bondsbetween watermolecules
Evaporation from leaves drives the flow of water up and through the
plant
SE
M
Flow
of
wat
er
See Animation on Water Transport
(Posted to MyCourses)
Water Moderates Temperature• Because of hydrogen bonding, water has a strong
resistance to temperature change.
• Heat and temperature are related, but different.
– _______________ is the amount of energy associated with the movement of the atoms and molecules in a body of matter.
– _______________ measures the intensity of heat.
• Water can absorb and store large amounts of heat while only changing a few degrees in temperature.
•Earth’s giant water supply causes temperatures to stay within limits that permit life.
•Evaporative cooling removes heat from the Earth and from organisms.
The Biological Significance of Ice Floating
• When water molecules get cold enough, they move apart, forming ice.
• A chunk of ice has fewer molecules than an equal volume of liquid water.
• Ice floats because it is less dense than the liquid water around it. Hydrogen bond
Liquid water Ice
• If ice did not float, ponds, lakes, and even the oceans would freeze solid.
• Life in water could not survive if bodies of water froze solid.
The Biological Significance of Ice Floating
Water as the Solvent of Life• A _______________ is a liquid consisting of a
homogeneous mixture of two or more substances.
– The dissolving agent is the _______________.
– The dissolved substance is the _______________.
• When water is the solvent, the result is an aqueous solution.
Sodium ion in solution
Chloride ion in solution
Salt crystal
Na
Na
Cl–Cl–
Solvents form “spheres of hydration” around solutes
Acids, Bases, and pH• Ions are dissolved in fluids both inside and
outside each living cell
• _______________ ions are the most influential
– Chemically active
– Tons of them – they are everywhere
How do Acids and Bases Differ?• A chemical compound that releases H+ to
solution is an _______________.
• A compound that accepts H+ and removes it from solution is a _______________.
Basicsolution
Neutralsolution
Acidicsolution
Acids, Bases, and pH• pH scale
– Indicates hydrogen ion (H+) concentration of a solution
– Ranges from 0 (most acidic, most H+) to 14 (most basic or alkaline, least H+)
– At pH 7 (neutral) H+ and OH- concentrations are equal
Neutral
Basic
Acidic
pH scale
14
7
0
Lower H+
concentration
H+ = OH–
Greater H+
concentration
Buffers Against Shifts in pH• Enzymes and biological molecules function
properly only in a narrow range of pH
• Cells must quickly respond to pH shifts otherwise cellular processes halt
• Most cells and body fluids are buffered in order to maintain a constant pH
• A set of chemicals (an acid or base AND its salt) that keeps the pH of a solution stable
• A “salt” is any compound that dissolves easily in water, and releases ions other than H+ and OH-
– Form when an acid interacts with a base (Ex: NaCl)
HCl + NaOH NaCl + H20
Na+ + Cl- + H2O
Buffer System
• Buffers help maintain homeostasis
• Most biological processes proceed only within a narrow pH range, usually near neutrality (blood pH = 7.3 – 7.5)
– Acidosis: decline in blood pH
– Alkalosis: increase in blood pH
– Both are potentially lethal
Functions of Buffer Systems
Evolution Connection: The Search for Extraterrestrial Life• If life similar to ours has
evolved elsewhere in the universe, then it too would depend upon water.
• Recent NASA missions to Mars have detected evidence that liquid water flowed over the planet’s surface.