Transcript PPT 1 Biochem

Matter and Energy in the
Web of Life
Chapter 4
What Are Atoms?

1) Smallest particles that retain properties
of an element

2) Made up of subatomic particles:

a) Protons (+)

b) Electrons (-)

c) Neutrons (no charge)`
Atomic Particles
Atomic Number

1) Number of protons
 a) All atoms of an element have the same
atomic number
 1. Atomic number of hydrogen = 1
 2. Atomic number of carbon = 6`
Mass Number
Number of protons
+
Number of neutrons
Isotopes vary in mass number
Mass Number
Isotopes

1) Atoms of an element with different
numbers of neutrons (different mass
numbers)
a) Carbon 12 has 6 protons, 6 neutrons
 b) Carbon 14 has 6 protons, 8 neutrons`

Radioisotopes
1) Have an unstable nucleus that
emits energy and particles
 2) Radioactive decay transforms
radioisotope into a different element


a) Decay occurs at a fixed rate`
Radioisotopes as Tracers

1) A Tracer is a substance with a
radioisotope attached to it
a) Emissions from the tracer can be
detected with special devices
 b) Following movement of tracers is
useful in many areas of biology`

Thyroid Scan

1) Measures health of thyroid by
detecting radioactive iodine taken up by
thyroid gland`
normal thyroid
enlarged
cancerous
PET Scan
What Determines Whether
Atoms Will Interact?
The number and arrangement of their
electrons
Electron Orbitals

1) Orbitals can hold up to two
electrons


a) Atoms differ in the number of
occupied orbitals
2) Orbitals closest to nucleus
are lower energy and are filled
first`
Shell Model


1) First shell

a) Lowest energy

b) Holds 1 orbital with up
to 2 electrons
2) Second shell

a) 4 orbitals hold up to 8
electrons`
CALCIUM
20p+ , 20e-
Shell Model
Shells
Chemical Bonds, Molecules,
& Compounds

1) Bond is union between electron structures of
atoms
 a) Atoms bond to form molecules
 1. Molecules may contain atoms of only
one element
 a. O2
 2. Molecules of compounds contain more
than one element
 a. H2O`
Chemical Bookkeeping

1) Use symbols for elements when writing
formulas

a) Formula for glucose is C6H12O6
 a)
6 carbons
 b)
12 hydrogens
 c)
6 oxygens`
Chemical Bookkeeping

1) Chemical equation shows reaction
Reactants ---> Products

2) Equation for photosynthesis:
6CO2 + 6H2O ---> + C6H12O6 + 6O2
Chemical Equation
Important Bonds in
Biological Molecules
Ionic Bonds
Covalent Bonds
Hydrogen Bonds
Ion Formation

1) Atom has equal number of
electrons and protons - no net
charge

2) Atom loses electron(s), becomes
positively charged ion

3) Atom gains electron(s), becomes
negatively charged ion`
Ionic Bonding
1) One atom loses electrons,
becomes positively charged ion
 2) Another atom gains these
electrons, becomes negatively
charged ion
 3) Charge difference attracts the
two ions to each other`

Ionic Bond
Covalent Bonding
1) Atoms share a pair or pairs of
electrons to fill outermost shell
•Single covalent bond
•Double covalent bond
•Triple covalent bond`
Hydrogen Bonding

1) Molecule held together by polar
covalent bonds has no NET charge

a) However, atoms of the molecule carry
different charges

b) Atom in one polar covalent molecule can
be attracted to oppositely charged atom in
another such molecule`
Hydrogen Bonding
Hydrogen Bond Stability
Properties of Water
Polarity
Temperature-Stabilizing
Cohesive
Solvent
Water Is a Polar
Covalent Molecule



1) Molecule has no net
charge
2) Oxygen end has a
slight negative charge
3) Hydrogen end has a
slight positive charge`
O
H
H
Water Polarity
Hydrophilic & Hydrophobic
Substances

1) Hydrophilic substances
 a) Polar
 b) Hydrogen bond with water
 1. Example: sugar

2) Hydrophobic substances
 a) Nonpolar
 b) Repelled by water
 1. Example: oil`
Temperature-Stabilizing Effects

1) Liquid water can absorb much heat
before its temperature rises


a) Why?
2) Much of the added energy disrupts
hydrogen bonding rather than
increasing the movement of molecules`
Why Ice Floats

1) In ice, hydrogen bonds lock molecules
in a lattice

a) Water molecules in lattice are spaced
farther apart then those in liquid water

b) Ice is less dense than water`
Water Is a Good Solvent
The pH Scale
1) Measures H+ concentration of fluid
 2) Change of 1 on scale means 10X
change in H+ concentration`
