chapter 2: the basics of life lecture outline -...
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Chapter 2: The Basics of Life Lecture Outline Enger, E. D., Ross, F. C., & Bailey, D. B. (2012). Concepts in biology (14th ed.). New York: McGraw-Hill.
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Matter, Energy, and Life
Matter is anything that has mass and occupies space.
Energy is the ability to do work. – There are two types of energy:
Potential energy – Stored energy, available to do work
Kinetic energy – Energy of motion
– Potential energy can be converted to kinetic energy to do work.
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Law of Conservation of Energy
Energy is never created or destroyed. – The first law of thermodynamics
Energy can be converted from one form to another, but the total energy remains constant. – An object at the top of a hill has potential energy
based on its location. – When the object rolls down the hill, the potential
energy is converted to kinetic energy.
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Forms of Energy
There are five forms of energy: 1. Mechanical energy
• Energy of movement 2. Nuclear energy
• Energy from reactions involving atomic nuclei 3. Electrical energy
• Flow of charged particles 4. Radiant energy
• Energy in heat, light, x-rays and microwaves 5. Chemical energy
• Energy in chemical bonds
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What is the nature of matter?
Atoms – The smallest units of matter that can exist
separately Elements
– Chemical substances composed of the same kind of atoms
– Listed on the periodic table – Each element is represented by a symbol of one
or two letters. – The principal elements that comprise living things
are: C, H, O, P, K, I, N, S, Ca, Fe, and Mg.
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The Periodic Table of the Elements
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Atomic Structure
Atoms are composed of: – The atomic nucleus
Protons - positively charged
– Atomic number−the number of protons
– All atoms of the same element have the same number of protons.
Neutrons – no charge – Electrons
Orbit the nucleus in energy levels
Are constantly in motion
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Atomic Structure
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Elements
Atoms of the same element have equal numbers of electrons and protons. – Thus, they have a neutral charge.
Isotopes – Atoms of the same element that have different
numbers of neutrons. – Atomic weight−the average of all of the isotopes in a
mixture. Mass number
– The sum of protons and neutrons in the nucleus.
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Isotopes of Hydrogen
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Electrons
Electrons occupy specific energy levels around the nucleus.
– Electrons closest to the nucleus have the lowest energy.
Energy levels hold specific numbers of electrons. – The first energy level can have up to 2 electrons. – All other energy levels can have up to 8 electrons.
Atoms seek to have a full outer energy level. – Atoms that have full outer energy levels are inert. – Other atoms seek to fill their outer energy levels through
chemical bonds.
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Electrons
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The Formation of Molecules
Molecules consist of two or more atoms joined by a chemical bond.
A compound is a chemical substance made of two or more elements combined in chemical bonds. – The formula of a compound describes the nature
and proportions of the elements that comprise the compound. H2O
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Molecules and Kinetic Energy
Molecules are constantly in motion. Temperature is a measure of the average speed of
the molecules in a substance. – The greater the speed, the higher the temperature. – Measured in Fahrenheit or Celsius
Heat is a measure of the total kinetic energy of molecules.
– Measured in calories (amount of heat that will raise 1g of water 1 degree Celsius).
Heat and Temperature are related. – Add heat energy to a substance and the molecules will
speed up, and the temperature will rise.
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Kinetic Energy, Physical Changes and Phases of Matter
Three phases of matter – Solid – Liquid – Gas
The phase in which a substance exists depends on its kinetic energy and the strength of its attractive forces.
– Solids−strong attractive forces, low kinetic energy, little to no molecular movement.
– Liquid−enough kinetic energy to overcome the attractive forces; more molecular movement.
– Gas−high kinetic energy, little to no attractive forces; maximum movement.
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Chemical Changes—Forming New Kinds of Matter
Chemical reactions – Creating different chemical substances by forming
and breaking chemical bonds. – Remember: Atoms form chemical bonds to fill
their outermost electron energy levels, achieving stability.
There are several types of chemical bonds. – We will discuss:
Ionic bonds Covalent bonds
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Ionic Bonds
Atoms can gain or lose electrons to achieve a full outermost energy level.
– Atoms with charge are called ions. – When an atom gives away an electron, it ends up with more protons than
electrons and gains a positive charge; cation. – When an atom accepts an electron, it ends up with more electrons than
protons and gains a negative charge; anion. – This process is called ionization.
An ionic bond – The attraction between oppositely charged ions
Example: NaCl – Sodium (Na) has one electron in its outer energy level. – Chloride has seven electrons in its outer energy level. – Sodium donates an electron to chloride, each achieving stability. – The positively charged sodium is attracted to the negatively charged
chloride.
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Ion Formation
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Covalent Bonds
Atoms can achieve full outermost energy levels by sharing electrons instead of exchanging them.
A covalent bond is formed by the sharing of electrons. – The atoms sharing electrons sit close enough together so that
their outer energy levels overlap. – Single covalent bond− one pair of electrons is shared.
H2
– Double covalent bond− two pairs of electrons are shared. ethylene
– Triple covalent bond− three pairs of electrons are shared. N2
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Covalent Bonds
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Hydrogen Bonds
The positive hydrogen end of one polar molecule is attracted to the negative end of another polar molecule.
– This attraction is a hydrogen bond. Hydrogen bonds hold molecules together.
– Since they do not hold atoms together, they are not considered true chemical bonds.
Hydrogen bonds are very important in biology. – They stabilize the structure of DNA and proteins. – Water molecules can “stick” together with hydrogen bonds.
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Water: The Essence of Life
Water has special properties that make it an essential molecule for life. – H2O – Electrons are shared unequally by hydrogen and
oxygen. This is a polar covalent bond. Oxygen has more protons than hydrogen.
– The electrons spend more time around oxygen than around hydrogen.
– The oxygen end of water is more negative. – The hydrogen end of water is more positive.
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Hydrogen Bonds
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Mixtures and Solutions
A mixture – Matter that contains two or more substances that are not in set
proportions A solution is a homogeneous mixture of ions or
molecules of two or more substances. – Components are distributed equally throughout. – The process of making a solution is called dissolving. – The solvent is the substance present in the largest amount.
Frequently the solvent is a liquid. – The solutes are the substances present in smaller amounts.
Aqueous solutions are solids, liquids, or gases dissolved in water.
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Mixtures vs. Pure Substances
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Water and Life
The following properties of water make it essential for life:
– High surface tension Water molecules stick to each other via hydrogen bonds. Capillary action moves water through streams, soil, animals
and plants. – High heat of vaporization
A lot of heat is required to break the hydrogen bonds holding water together.
Large bodies of water absorb a lot of heat. – Temperate climates – Evaporative cooling
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Water and Life
Unusual density properties – Ice is less dense than water, so ice floats. – Allows aquatic life to survive in cold climates.
The universal solvent – Water can form hydrogen bonds with any polar or
ionic compound. – Therefore, many things can be dissolved in water.
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Chemical Reactions
A chemical change: – When the bonds of compounds are made or
broken, new materials with new properties are produced.
– Happens via chemical reactions. In a chemical reaction the elements remain
the same, but the compounds they form and their properties are different.
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Chemical Reactions and Energy
Chemical reactions produce new compounds with less or more potential energy. – Energy is released when compounds are made with
less potential energy. – Energy is used to make compounds with more
potential energy.
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Chemical Equations
A chemical equation is a method of describing what happens in a chemical reaction. – For example, photosynthesis is described by the
following equation: Energy + 6CO2 + 6H2O → C6H12O6 + 6H2O
Reactants−substances that are changed, usually on the
left side of the equation. Products−new chemical substances formed, usually on
the right side of the equation.
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Five Important Chemical Reactions in Biology
1. Oxidation–reduction 2. Dehydration synthesis 3. Hydrolysis 4. Phosphorylation 5. Acid–base reactions
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Oxidation-Reduction Reactions
Oxidation−reduction reactions – Reactions in which electrons (and their energy) are transferred from
one atom to another. – Oxidation
An atom loses an electron. – Reduction
An atom gains an electron. For oxidation to occur, reduction must also occur. Example:
– Respiration Sugar is oxidized to form carbon dioxide and oxygen is reduced to form
water. Energy is released in the process.
C6H12O6 + 6O2 → 6H2O + 6CO2+ Energy Sugar + oxygen → water+ carbon dioxide + energy
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Dehydration Synthesis Reaction
When two small molecules are joined to form a larger molecule, – A molecule of water is released.
Example: – Joining amino acids to form proteins. NH2CH2CO-OH + H-NH CH2CO-OH NH2CH2CO-NH CH2CO-OH + H-OH
amino acid 1 + amino acid 2 = protein + water
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Hydrolysis Reactions
When a larger molecule is broken down into smaller parts, – A water molecule is split – Opposite of a dehydration synthesis
Example: – Digesting proteins into amino acids. NH2CH2CO-NH CH2CO-OH + H-OH NH2CH2CO-OH + H-NH CH2CO-OH
Protein + water = amino acid 1 + amino acid 2
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Phosphorylation Reactions
When phosphate groups are added to other molecules, – Phosphate groups are clusters of oxygen and phosphate
atoms.
Bonds between phosphate groups and other molecules contain high potential energy.
– When these bonds are broken, the energy that is released can be used by the cell to do work.
– Phosphorylation reactions are commonly used to transfer potential energy.
Q-P + Z Q + Z-P
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Acid-Base Reactions
Occurs when ions from an acid interact with ions from a base.
This type of reaction allows harmful acids and bases to neutralize one another.
H+Cl- + Na+OH- → Na+Cl- + H+OH-
Hydrocloric + Sodium Sodium + Water acid hydroxide chloride
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Acids, Bases and Salts
An acid – Ionic compounds that release hydrogen ions (H+) into a solution – Phosphoric acid, hydrochloric acid
A base – Compounds that release hydroxide ions (OH-) into a solution – Sodium hydroxide, ammonia
Because bases are negatively charged, they will react with a positively charged hydrogen in solution.
The strength of an acid or base is determined by how completely it will dissociate in water.
– Strong acids release almost all of their hydrogen ions into water. – Strong bases release almost all of their hydroxide ions into water.
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Some Common Acids, Bases and Salts
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Salts
Neither acids nor bases Usually formed when acids and bases react
– The dissociated hydrogen ions and hydroxide ions join to form water.
– The remaining ions form ionic bonds, creating a salt. – This is an example of neutralization:
H+Cl- + Na+OH- → Na+Cl- + H+OH-
Hydrocloric + Sodium Sodium + Water acid hydroxide chloride
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pH
A measure of hydrogen ion concentration Solutions with high hydrogen ion concentrations
– Have low pH – Are acidic
Solutions with low hydrogen ion concentrations – Have a high pH – Are basic
There is a 10-fold difference in hydrogen ion concentration between solutions that differ by one pH unit.
– A solution with pH 4 has ten times as many hydrogen ions as a solution with pH 5.
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The pH Scale