Are We Alone
in the Universe?
What Does Life
Definition of Life
is no simple definition of life!
is “defined” by the possession of a number of complex
living Earth organisms…
a common set of biological molecules
Properties of Water
- Elements: fundamental forms of
- Atoms: the smallest units of
are composed of protons, neutrons, and electrons
- Protons (positive charge) + neutrons
- Electrons (negative charge) are
outside the nucleus.
- Molecule: two or more atoms held
together by chemical bonds
molecule: two hydrogen atoms bonded to one oxygen atom
bond made by sharing of electrons is called a covalent
is a polar molecule:
side is slightly negative
side is slightly positive
molecules have no charges, they are nonpolar
is a good solvent (a liquid that helps chemical
- Solute: what is being dissolved
- Solution: the solute in the
solvent (a mixture)
the weak attraction between the hydrogen atom of one water
molecule and the
oxygen atom of another
bonds are the weakest form of chemical bond
molecules tend to stick together: cohesion
molecules tend to stick to charged molecules: adhesion
can dissolve salts and hydrophilic (water–loving)
molecules because it
is polar (partially charged).
can dissolve acids and bases.
- The pH
scale is a measure of the relative amounts of acids and
bases in a solution.
greater than 7 = basic (more base)
lower than 7 = acidic (more acid)
water has a pH of 7 = neutral
molecules, such as oil, do not contain charged atoms.
atoms are called hydrophobic (water–hating).
life on Earth is based on organic chemistry: the
chemistry of the
makes up most of the mass of living organisms.
a molecular “TinkerToy”
bond to up to 4 different atoms at once
strong bonds from sharing electrons
can make macromolecules, or molecules that are large
comprised of smaller subunit molecules
and Function of Macromolecules
- Carbohydrates: molecules of carbon,
oxygen, and hydrogen
source of energy for cells
- Proteins: polymers of amino
acids; joined by peptide bonds
have a mix of hydrophilic and hydrophobic portions
are made up of carbon, oxygen, hydrogen, and nitrogen.
are 20 different amino acids, with different chemical
combinations of amino acids give proteins different
amino acid sequence in a protein determines the shape of the
hydrophobic; composed mostly of carbon and hydrogen
acids: polymers of nucleotides
sugar + a phosphate + a nitrogenous base
are of two types: RNA and DNA, depending on
is the hereditary material in nearly all organisms.
is heavily involved with protein synthesis - converting the
DNA code into a
structure of a DNA molecule is a double helix.
strands of DNA are held together by hydrogen bonds
between bases on opposite strands follows strict base-pairing
Life on Earth
and Eukaryotic Cells
cells have the following:
surrounding the cell (this is a phospholipid bilayer)
- Cytoplasm (cytosol) inside the
membrane; chemical reactions take place here
information in the form of DNA
- Ribosomes for the production of
proteins, made up of RNA and proteins
cells on Earth are either prokaryotic or eukaryotic.
cells are smaller and simpler in structure.
probably resemble the earliest cells to arise on Earth.
structures in the Martian meteorite resemble them.
cells are surrounded by a plasma membrane.
of a phospholipids bilayer: hydrophobic tails orient
membrane, away from water
lipids and proteins can move about within the membrane
- Semipermeable: some molecules can
cross and some can’t
have DNA but do not have a nucleus (membrane-bound structure
that contains the
cells are much more complex.
true nuclei surrounded by a membrane
have membrane-bound organelles with specialized jobs
The Tree of
Life and Evolutionary Theory
Earth organisms share many similarities:
basic biochemistry, with same types of macromolecules
organisms consist of cells
always have phospholipids bilayer plasma membrane
share most of the same organelles.
unity of life is best explained by a tree of life,
species having evolved from common ancestors.
history of Humans.