Transcript Chapter 2 Chemistry of Life

Chapter 2
Chemistry of Life
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LEVELS OF CHEMICAL
ORGANIZATION

Atoms (Figures 2-1 and 2-2)

Nucleus—central core of atom
• Proton—positively charged particle in nucleus
• Neutron—non-charged particle in nucleus
• Atomic number—number of protons in the nucleus;
determines type of atom
• Atomic mass—number of protons and neutrons
combined

Energy levels—regions surrounding atomic nucleus
that contain electrons
• Electron—negatively charged particle
• May contain up to eight electrons in each level
• Energy increases with distance from nucleus
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LEVELS OF CHEMICAL
ORGANIZATION (cont.)

Elements, molecules, and compounds

Element—a pure substance; made up of only one
kind of atom
 Molecule—a group of atoms bound together
in a group
 Compound—substances whose molecules have
more than one kind of atom
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CHEMICAL BONDING

Chemical bonds form to make atoms more stable

Outermost energy level of each atom becomes full
 Atoms may share electrons, or donate
or borrow them to become stable
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CHEMICAL BONDING (cont.)

Ionic bonds (Figure 2-3)

Ions form when an atom gains or loses electrons in its
outer energy level to become stable
• Positive ion—has lost electrons; indicated
by superscript positive sign(s), as in Na+ or Ca++
• Negative ion—has gained electrons; indicated by
superscript negative sign(s), as in Cl

Ionic bonds form when oppositely charged ions attract
each other because of electrical attraction
 Electrolyte—molecule that dissociates
(breaks apart) in water to form individual ions;
an ionic compound
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CHEMICAL BONDING (cont.)

Covalent bonds (Figure 2-4)

Covalent bonds form when atoms share their outer
energy to fill up and thus become stable
 Covalent bonds do not ordinarily easily dissociate
in water

Hydrogen bonds

Weak forces hold molecules in folded shapes
(Figure 2-12) or in groups (Figure 2-5)
 Do not form new molecules
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INORGANIC CHEMISTRY


Organic molecules contain carbon-carbon
covalent bonds or carbon-hydrogen covalent
bonds; inorganic molecules do not
Examples of inorganic molecules: water
and some acids, bases, and salts
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INORGANIC CHEMISTRY (cont.)

Water

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Water is essential to life
Water's slightly gluelike nature helps hold the body together
Water is a solvent (liquid into which solutes are dissolved), forming
aqueous solutions in the body
Water is involved in chemical reactions (Figure 2-6)
• Dehydration synthesis—chemical reaction in which water is removed
•
•
•
•
from small molecules and then strung together to form a larger molecule
Hydrolysis—chemical reaction in which water is added to the subunits
of a large molecule to break it apart into smaller molecules
All major organic molecules are formed through dehydration synthesis
and are broken apart by hydrolysis
Chemical reactions always involve energy transfers, as when energy
is used to build ATP molecules
Chemical equations show how reactants interact to form products;
arrows separate the reactants from the products
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INORGANIC CHEMISTRY (cont.)

Acids, bases, and salts

Water molecules dissociate to form equal amounts
of H+ (hydrogen ion) and OH (hydroxide ion)
 Acid—substance that shifts the H+/OH balance
in favor of H+; opposite of base
 Base—substance that shifts the H+/OH balance
against H+; also known as an alkaline; opposite
of acid
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INORGANIC CHEMISTRY (cont.)

Acids, bases, and salts (cont.)

pH—mathematical expression of relative H+
concentration in an aqueous solution
(Figure 2-7)
• pH 7 is neutral (neither acid nor base)
• pH values above 7 are basic; pH values below 7
are acidic

Neutralization—acids and bases mix to form salts
 Buffers—chemical systems that absorb excess
acids or bases and thus maintain a relatively
stable pH
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ORGANIC CHEMISTRY

Carbohydrates—sugars and complex
carbohydrates (Figure 2-8)
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Contain carbon (C), hydrogen (H), oxygen (O)
Made up of six-carbon subunits called
monosaccharides or single sugars
(e.g., glucose)
Disaccharide—double sugar made up of two
monosaccharide units (e.g., sucrose, lactose)
Polysaccharide—complex carbohydrate made up
of many monosaccharide units (e.g., glycogen
made up of many glucose units)
Function of carbohydrates is to store energy
for later use
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ORGANIC CHEMISTRY (cont.)

Lipids—fats and oils

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Triglycerides (Figure 2-9)
• Made up of one glycerol unit and three fatty acids
• Store energy for later use
Phospholipids (Figure 2-10)
• Similar to triglyceride structure, except with only two fatty
acids, and with a phosphorus-containing group attached to
glycerol
• The head attracts water and the double tail does not, thus
forming stable double layers (bilayers) in water
• Form membranes of cells

Cholesterol (Figure 2-11)
• Molecules have a steroid structure made up of multiple rings
• Cholesterol stabilizes the phospholipid tails in cellular
membranes
• Cholesterol is converted into steroid hormones by the body
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ORGANIC CHEMISTRY (cont.)

Proteins

Very large molecules made up of amino acids held
together in long, folded chains by peptide bonds
(Figure 2-12)
 Structural proteins
• Form various structures of the body
• Collagen—a fibrous protein that holds many tissues
together
• Keratin—forms tough, waterproof fibers in the outer
layer of the skin
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ORGANIC CHEMISTRY (cont.)

Proteins (cont.)
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Functional proteins
• Participate in chemical processes of the body
• Examples: hormones, cell membrane channels
and receptors, enzymes
• Enzymes (Figure 2-12)
 Catalysts—help chemical reactions occur
 Lock-and-key model—each enzyme fits a
particular molecule like a key fits into a lock

Proteins can combine with other organic molecules
to form glycoproteins or lipoproteins
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ORGANIC CHEMISTRY (cont.)

Nucleic acids

Made up of nucleotide units:
• Sugar (ribose or deoxyribose)
• Phosphate
• Nitrogen base (adenine, thymine or uracil, guanine,
cytosine)
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ORGANIC CHEMISTRY (cont.)

Nucleic acids (cont.)

DNA (deoxyribonucleic acid) (Figure 2-14)
• Used as the cell’s “master code” for assembling proteins
• Uses deoxyribose as the sugar and A, T (not U), C, and G
as bases
• Forms a double helix shape

RNA (ribonucleic acid)
• Used as a temporary “working copy” of a gene (portion of the
DNA code)
• Uses ribose as the sugar and A, U (not T), C, and G as bases

By directing the formation of structural and functional
proteins, nucleic acids ultimately direct overall body structure
and function
 ATP (adenosine triphosphate)—a modified nucleotide used
to transfer energy from nutrients to cellular processes, thus
acting as an energy-transfer “battery” (Figure 2-15)
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