Post on 26-Dec-2015
transcript
Topic 1:Chemicals of life
1. Molecules and Atoms2. Water3. Carbon and other elements
1. Atoms and Molecules
1.1 Elements and Compounds1.2 Elements of Life 1.3 Chemical and Physical Bonds1.4 Importance of Carbon, Nitrogen, and
Water
Organisms are composed of matter.
Matter is made up of elements.
Elements combine to form compounds.
anything that has mass and takes up space
cannot be broken down to other substances by chemical reactions
1.1 Elements and Compounds
Sodium Chloride Sodium Chloride
+
compounds have characteristics different from those of their elements
Emergent Properties
Essential Elements(elements required by living organisms)
macroelements• C, H, O, N• 96% of living matter
microelements• Na, K, Ca, Mg, P, S, Cl• 4% of living matter
trace elements• Fe, I, Cu, Mn, etc.• required in minute (tiny) amounts
1.2 Elements of Life
the properties of elements depend on the chemical characteristics of their atoms
chemical characteristics of atoms depend on the arrangement of electrons in electron shells (electron configuration)
Electronegativity• the attraction of an atom for electrons from other atoms• important property of elements of life
Bonds
Chemical Bonds
Physical Bonds
form between elements form between molecules
Covalent Ionic Dipole Interactions Van der Waals
1.3 Chemical and Physical Bonds
Chemical Bonds
Covalent BondsIonic
Bondselements of similar electronegativity share pairs of electrons
elements of very different electronegativity transfer electrons, creating ions (anions and cations)
The properties of a compound (solubility, melting point, etc.) depend on the type of bonding involved.
Covalent bonds are the most important in biological molecules because they allow for a variety of properties
they can be single, double, or triple bonds
H Hsingle covalent bond
O Odouble covalent bond
N Ntriple covalent bond
Covalent bonds can be classified as non-polar or polar
create dipoles - molecules with partial negative ( -) and positive ( +) charges at 𝛿 𝛿opposite ends
non-polar covalent bonds(elements of the same or almost the
same electronegativity)
ethane
polar covalent bonds(elements of slightly different
electronegativity)
water
weak attractions between molecules (not the result of chemical reactions)
Physical Bonds
There are two major types of Physical Bonds
Dipole InteractionsAttraction between opposite poles
of polar molecules (dipoles)
Van der Waals Interactions
(aka London Dispersion Forces) Caused by momentary asymmetric
distribution of moving electrons in large non-polar molecules.
– +
+
Water(H2O)
Ammonia(NH3)
OH
H
+
–
N
HH H
+ d+
Hydrogen Bonds
• the most important dipole interaction in biology
• forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom from a different molecule
bonds determine the shape of the molecule
Shape of a Molecule
• determines the biological function• Differently-shaped molecules have different functions• similar shape molecules can mimic the function of another
molecule (morphine/endorphins)
• Carbon is the element most widely used in biomolecules due to its special properties.
• Organisms can obtain carbon in two ways:
inorganic carbon (CO2)autotrophs
organic carbon (glucose)heterotrophs
1.4 Importance of C, N, and H2O
• Nitrogen is also essential to living organisms, making part of proteins and nucleic acids.
• Organisms can obtain nitrogen in two ways:
inorganic nitrogen (N2)atmosphere – microorganisms, fungi
minerals – nitrates for plants
organic nitrogen from other organisms
Water
• fundamental to life• organisms are composed mostly of water (65% in humans, 99% in
jellyfish)• most chemical reactions in organisms take place in water (wet
chemistry)