Transcript BIOL-2404-Holes-chapter02_lecture_7e

Lecture Outline
Chemistry of Life
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2.1 Basic Chemistry
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Matter – anything that takes up
space
States of matter
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Solid
Liquid
Gas
Basic Chemistry
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Elements – basic substances that
make up matter
Four elements that make up
>90% of the human body
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Carbon (C)
Nitrogen (N)
Oxygen (O)
Hydrogen (H)
Basic Chemistry
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Atoms
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Smallest unit of an element that has
chemical and physical properties of
that element
Smallest unit to enter into chemical
reactions
Structure
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Central nucleus
Outer shells (energy levels)
Basic Chemistry
Subatomic particles
oIn nucleus
• Protons – positive
charge
• Neutrons – no charge
oIn shells
• Electrons – negative
charge
• Innermost shell can
have 2 electrons
• Outer shells can have
up to 8 electrons
• Number of electrons in
outer shell determines
the chemical properties
of an atom
Basic Chemistry
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Atomic number
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Number of protons in the nucleus
Denoted as a subscript to the lower
left of the atomic symbol
Atomic weight
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Number of protons plus the number
of neutrons
Denoted as a superscript to the upper
left of the atomic symbol
Basic Chemistry
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Mole
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Measurement for the number of
atoms or molecules of a compound
Avogadro’s number 6.02 x 10 23
Based on the number of atoms in
exactly 12 grams of carbon atoms
Basic Chemistry
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Isotopes
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Variations of one type of atom
Differ in number of neutrons
Radioactive isotopes
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Unstable isotopes that break down over
time
Releases detectable energy
Low levels of radiation can be used as
tracers
High levels of radiation can be harmful to
cells, but can also be useful
Basic Chemistry
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Molecules – form when atoms
bond to each other
Compounds – formed when atoms
of different elements bond
Basic Chemistry
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Ionic bonds
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Created by electrical attraction between ions
Ions form when an atom gains or loses
electrons in its outer energy level to become
stable
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Positive ion—has lost electrons; indicated by
superscript positive sign(s), as in Na+
Negative ion—has gained electrons; indicated by
superscript negative sign(s), as in Cl–
Can dissociate (separates into ions) when
dissolved in water and are then referred to
as electrolytes.
Basic Chemistry
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Covalent bonds
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Created when atoms share electrons
Atoms can share more than one pair
of electrons
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Double bonds – atoms share two pairs of
electrons
Triple bonds – atoms share three pairs of
electrons between them
Polar covalent bonds result when
there is an unequal sharing of
electrons between atoms
2.2 Water, Acids, and Bases
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Water
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Most abundant molecule in living
organisms
Is an inorganic molecule (does not
contain carbon atoms)
Is a polar molecule
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Oxygen has a slight negative charge (δ-)
Hydrogen atoms have a slight positive
charge (δ+)
Attraction between slightly positive
hydrogen atoms and slightly positive
oxygen atom results in hydrogen bonds
Water, Acids, and Bases
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Properties of Water
Water is a solvent (liquid into which ions
are dissolved)
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Facilitates chemical reactions
Molecules that dissolve in water are said to be
hydrophilic (water-loving)
Molecules that do not dissolve easily in water
are said to be hydrophobic (water fearing)
Water, Acids, and Bases
Water molecules are cohesive and
adhesive
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Water molecules cling together (cohesion)
because of hydrogen bonding
Water molecules cling to other substances
(adhesion)
Water flows freely, allowing it to distribute
evenly
Allows for transport
Water, Acids, and Bases
Water has a high specific heat capacity
and a high heat of vaporization
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Specific heat capacity is the amount of energy
needed to change an object’s temperature by
1C
Heat of vaporization is the amount of energy
needed to turn water into steam
Both allow for thermoregulation body
temperature
Water, Acids, and Bases
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Acids and Bases
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When water molecules break up, an
equal number of hydrogen ions (H+)
and hydroxide ions (OH-) are released
Acids are substances that release
hydrogen ions (H+)
Bases are substances that release
hydroxide ions (OH-)
Water, Acids, and Bases
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Salt
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A salt is an electrolyte formed when
an acid and a base are combined.
Water also forms.
HCl + NaOH → NaCl + H2O
Water, Acids, and Bases
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pH Scale
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Used to indicate the acidity and basicity
(alkalinity) of a solution
pH 7 is neutral (an equal number of
hydrogen ions and hydroxide ions are
released)
pH above 7 is a base (more hydroxide
ions are released than hydrogen ions)
pH below 7 is an acid (more hydrogen
ions are released than hydroxide ions)
Water, Acids, and Bases
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pH of body fluids
Normal pH of blood is 7.4
Acidosis – blood pH less than 7.35
Alkalosis – blood pH greater than 7.45
Blood pH needs to be maintained within a
narrow range
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Respiratory and urinary systems
Buffers (chemicals that take up excess
hydrogen or hydroxide ions)
Carbonic acid and bicarbonate ions
Water, Acids, and Bases
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Electrolytes
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Substances that release ions when put
into water
The balance of electrolytes in the blood
affects the functioning of vital organs
2.3 Molecules of Life
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Four categories of molecules are
unique to cells (called
macromolecules)
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Carbohydrates
Lipids
Proteins
Nucleic acids
Synthesis of macromolecules
involves a dehydration reaction
Breakdown of macromolecules
involves a hydrolysis reaction
2.4 Carbohydrates
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The ratio of hydrogen (H) atoms to
oxygen (O) atoms is
approximately 2:1
Function for quick, short-term
cellular energy
Carbohydrates
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Simple carbohydrates
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Low number of carbon atoms (3-7)
Monosaccharides
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Glucose
Fructose – found in fruits
Galactose – found in milk
Disaccharides
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Two monosaccharides joined together
Sucrose (table sugar) – formed when
glucose joins with fructose
Lactose – formed when glucose joins with
galactose
Carbohydrates
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Complex carbohydrates
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Contain many glucose
(monosaccharide) units
Starch – storage form of glucose in
plants
Glycogen – storage form of glucose in
animals
Cellulose
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Found in plant cell walls
Humans are unable to digest (passes
through digestive tract as fiber)
2.5 Lipids
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Contain more energy per gram
than other biological molecules
Some function as long-term
energy storage in organisms
Do not dissolve in water
Consist mostly of carbon and
hydrogen atoms; contain few
oxygen atoms
Lipids
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Fats and Oils
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Formed when one glycerol molecule
reacts with three fatty acid molecules
Fats
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Usually of animal origin
Solid at room temperature
Used for long-term energy storage,
insulation, and cushioning
Oils
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Usually of plant origin
Liquid at room temperature
Lipids
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Emulsification – cause fats to mix
with water
Saturated and Unsaturated Fatty
Acids
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Fatty acid (carbon-hydrogen chain ending
with an acidic group –COOH
Saturated fatty acids have only single
covalent bonds; lard and butter are
examples
Unsaturated fatty acids have double
bonds between carbon atoms wherever
fewer than two hydrogens are bonded to
a carbon atom; vegetable oils
Lipids
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Phospholipids
• Contain a
phosphate group
• Have a hydrophilic
head and
hydrophobic tails
• Form backbone of
cellular
membranes
Lipids
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Steroids
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Structure consists of four fused
carbon rings with attached functional
groups
Cholesterol
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Structural component of animal cell
membrane
Precursor of several other steroids
2.6 Proteins
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Function of proteins
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Fibrous structural proteins
Hormones
Muscle contraction
Transport
Protection
Enzymes
Proteins
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Structure of proteins
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Made of amino acid subunits
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Amino group
Acid group
R (Remainder) group – differentiates
amino acids
Dipeptide – two amino acids joined
together
Polypeptide – three or more amino
acids joined together
Proteins
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Amino acids joined together by a peptide
bond
Secondary structure – due to hydrogen
bonding that may occur in a polypeptide
Tertiary structure results from bonding
between R groups
Quaternary structure – arrangement of
individual polypeptides in a protein
containing more than one polypeptide
Denaturation – irreversible change in the
normal shape of a protein due to extremes
in heat and pH
Proteins
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Enzymatic Reactions
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Metabolism - sum of all chemical
reactions that occur in a cell
Enzymes (protein catalysts that
enable metabolic reactions)
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Named for their substrate(s)
The shape of the active site determines
specificity of enzyme
Many require cofactors that assist an
enzyme
Proteins
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Types of Reactions
Synthesis Reactions
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Degradation (Decomposition) Reactions
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Two or more reactants combine
Require energy
Dehydration synthesis
Larger, more complex molecule breaks down
into smaller, simpler products
Hydrolysis reactions
Replacement (Exchange) Reactions –
involve both degradation and synthesis
2.7 Nucleic Acids
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Huge macromolecules composed
of nucleotides
Nucleotides composed of 3 subunit
molecules:
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A phosphate
A pentose sugar
A nitrogen-containing base
Two classes of nucleic acids
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DNA
RNA
Nucleic Acids
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Two classes of nucleic acids
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DNA
Make up genes
Contain pentose sugar deoxyribose
Nitrogen-containing bases
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Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Usually double stranded
Nucleic Acids
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RNA
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Intermediary in process of protein
synthesis
Contain pentose sugar ribose
The nitrogen-containing base uracil (U)
replaces thymine
Usually single stranded
Nucleic Acids
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ATP (Adenosine Triphosphate)
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Primary energy carrier in cells
Cells break down glucose and convert
released energy into ATP
Used when cellular reactions require energy
Breakdown of ATP results in one molecule of
ADP (adenosine diphosphate) and one
molecule of inorganic phosphate
ATP is rebuilt by the addition of inorganic
phosphate to ADP
One glucose molecule can build 36 ATP
molecules