Download 2.1 What Does Life Require?

Chapter 2
Are We Alone in the Universe?
PowerPoint lecture prepared by
Steve McCommas
Southern Illinois State University
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Are We Alone in the Universe?
 Martian rock found on Earth
 Is there evidence of life on Mars?
 How would we know?
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2.1 What Does Life Require?
A Definition of Life
 There is no simple definition of life.
 But, all Earth organisms…
 have a common set of biological molecules
 can maintain homeostasis
 Homeostasis- the ability to maintain a stable
internal environment.
 require liquid water
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2.1 What Does Life Require?
Some Basic Chemistry
 Elements: fundamental forms of matter
 Listed on periodic table in appendix A-2
 Atoms: the smallest units of an element
 Atoms are composed of protons, neutrons,
and electrons
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2.1 What Does Life Require?
 Protons (positive
charge) + neutrons =
nucleus
 Electrons (negative
charge) are outside
the nucleus.
Atomic number = number of protons
Atomic mass = number of protons + number of neutrons
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Figure 2.3
2.1 What Does Life Require?
 Molecule: two or more atoms held together
by chemical bonds
 Water molecule: two hydrogen atoms bonded
to one oxygen atom
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2.1 What Does Life Require?
The Properties of Water
 Water is a good solvent (helps chemical
reactions)
 Solute: what is being dissolved
 Solution: the solute in the solvent
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2.1 What Does Life Require?
The Properties of Water
 Water is a polar
molecule:
 Oxygen side is slightly
negative
 Hydrogen side is slightly
positive
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Figure 2.4
2.1 What Does Life Require?
The Properties of Water
 Hydrogen bond: the weak attraction
between the hydrogen atom of one water
molecule and the oxygen atom of another
 Water molecules tend to stick together:
cohesion
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2.1 What Does Life Require?
The Properties of
Water
 Water can dissolve
salts and hydrophilic
(water–loving)
molecules because it
is polar.
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Figure 2.6
2.1 What Does Life Require?
The Properties of Water
 Water can dissolve acids and bases.
 The pH scale is a measure of the relative
amounts of acids and bases in a solution.
 pH greater than 7 = basic
 pH lower than 7 = acidic
 Pure water = 7 - neutral
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Figure 2.7
2.1 What Does Life Require?
The Properties of Water
 Nonpolar molecules such as oil, do not
contain charged atoms.
 These atoms are called hydrophobic
(water–hating).
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2.1 What Does Life Require?
Organic Chemistry
 All life on Earth is based on organic
chemistry: the chemistry of the element
carbon.
 Carbon makes up most of the mass of living
organisms
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2.1 What Does Life Require?
Organic Chemistry
 Carbon: a molecular TinkerToy
 Can bond to 4 different atoms at once
 Covalent bonds: strong bonds from sharing
electrons
 Carbon can make macromolecules
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Organic Macromolecules
 There are four types of macromolecules that
are important to living organisms.




Carbohydrates
Proteins
Lipids
Nucleic Acids
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2.1 What Does Life Require?
 Carbohydrates:
molecules of carbon,
oxygen, and
hydrogen
 Major source of
energy for cells
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Figure 2.12
2.1 What Does Life Require?
 Proteins: polymers
of amino acids;
joined by peptide
bonds
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Figure 2.13
2.1 What Does Life Require?
 Proteins are made up of carbon, oxygen,
hydrogen, and nitrogen.
 There are 20 different amino acids, with
different chemical properties.
 Different combinations of amino acids give
proteins different properties.
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2.1 What Does Life Require?
 Lipids: hydrophobic; composed mostly of
carbon and hydrogen
 Three types:
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Figure 2.14
2.1 What Does Life Require?
 Nucleic acids: polymers of nucleotides
 Nucleotide: sugar + a phosphate + a
nitrogenous base
 There are 4 nitrogenous bases in DNA.
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Figure 2.15c
2.1 What Does Life Require?
Structure and Function of Macromolecules
 Nucleotides are of two types: RNA and DNA,
depending on the sugar.
 DNA is the hereditary material in nearly all
organisms.
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2.1 What Does Life Require?
 The structure of a
DNA molecule is a
double helix.
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Figure 2.15a
2.1 What Does Life Require?
 Bonding between
bases on opposite
strands follows strict
base-pairing rules:
 A with T
 G with C
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Figure 2.15b
Cells
 A cell is the smallest unit of a living organism.
 All living things are made up of cells.
 There are single celled organisms and
organism made up of trillions of cells.
 Cells in different organisms are approximately
the same size. The difference between a mouse
and an elephant is the number of cells not the
size of the cells.
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2.2 Life on Earth
Prokaryotic and Eukaryotic Cells
 All cells on Earth are either prokaryotic or
eukaryotic.
 Prokaryotic cells are smaller and simpler in
structure.
 They probably resemble the earliest cells to
arise on Earth.
 Some structures in the Martian meteorite
resemble them.
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2.2 Life on Earth
Prokaryotic and Eukaryotic Cells
 All cells are surrounded by a plasma
membrane.
 The plasma membrane is Semipermeable:
some molecules can cross and some can’t
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2.2 Life on Earth
Prokaryotic and Eukaryotic Cells
 Prokaryotes do not have a true nucleus.
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Figure 2.17b
2.2 Life on Earth
Prokaryotic and Eukaryotic Cells
 Eukaryotic cells are much more complex.
 Have true nuclei surrounded by a membrane
 Also have membrane-bound organelles with
specialized jobs
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2.2 Life on Earth
Eukaryotic Cells
 Mitochondria: provide energy for the cell, using
oxygen
 Chloroplasts: sites of photosynthesis
 Endoplasmic reticulum: involved in protein or
lipid synthesis
 Golgi apparatus: modifies and sorts proteins
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2.2 Life on Earth
Eukaryotic Cells (Check out Table 2.1 on
page 45 in your textbook.)
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Figure 2.18
2.2 Life on Earth
The Tree of Life and Evolutionary Theory
 All Earth organisms share many similarities:
 Same basic biochemistry, with same types of
macromolecules
 All organisms consist of cells
 Cells always have phospholipids bilayer plasma
membrane
 Eukaryotes share most of the same organelles.
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