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Unit 3 Study Guide
Biochemistry
Name ____________________
1. I can identify the difference between atoms, ions, and isotopes.
An element is a substance made of only one type of atom. Atoms are the basic unit of all matter. They are made
of protons (positive charge) and neutrons (no charge) in the nucleus and electrons (negative charge) outside the
nucleus. The atomic mass (mass number) is the number of protons plus the number of neutrons (this can change
if the atom gains/loses neutrons). The atomic number is the number of protons (this does not change). A neutral
atom will have the same number of electrons as protons.
Ions are charged atoms. An atom that has lost electrons has a positive charge (cation = positive ion). An atom
that has gained electrons has a negative charge (anion = negative ion). Ions are involved in many biological
processes, such as neuron communication and muscle contraction (see target 5 for more info). Ions dissolve
easily in water but are not able to cross the lipid bilayer of the cell membrane.
Isotopes are atoms that have gained or lost neutrons and therefore have a different mass. Isotopes are
frequently used for biological research because they can be used to tag and trace the activity of cells and
macromolecules.
Chemical bonds are attractions that form between atoms. Covalent bonds form when atoms share electrons.
Ionic bonds form when atoms exchange (give/take) electrons.
positive ion
negative ion
neutral molecule
electron
2. I can explain the pH scale. This means that I can identify an acid or base using Hydrogen ion concentrations.
The pH scale is used to determine whether a substance is a base or an acid based upon H+ ion concentrations. A
pH of 7 (pure water) is considered neutral because the amount of H+ ions is the same as the amount of OH- ions
(water = H2O = H+ + OH-). The concentration changes by a factor of 10 at each pH level. Acids: pH 6-4 = weak
acids; 3-1 = strong acids. A pH of 6 has 10x as many H+ ions. A pH of 5 has 100x as many H+ ions. A pH of 0 is the
strongest acid and 10,000,000x as many H+ ions as OH- ions. As the pH decreases the number of H+ ions
increases and the number of OH- ions decreases by a factor of 10. Bases (aka alkaline): pH 8-10 = weak base; 1114 = strong base. A pH of 8 has 10x fewer (.1) H+ ions. A pH of 9 has 100x fewer (.01) H+ ions. A pH of 14 is the
strongest base and 10,000,000x as many OH- ions as H+ ions (.00000001). As the pH increases the number of H+
ions decreases and the number of OH- ions increases by a factor of 10.
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Unit 3 Study Guide
Biochemistry
Name ____________________
OH-
H+
3. I can explain the properties of water. This means that I know the difference between polarity, cohesion,
adhesion, surface tension, and capillary action.
Water is one of the most important molecules for organisms. Water is made of 1 oxygen atom and 2 hydrogen
atoms. It can disassociate into H+ + OH- ions; this is called ionization. Polarity is caused by the unequal sharing of
electrons. The oxygen atom has a stronger hold on the shared electrons so it has a slightly negative charge. The
hydrogen atoms have a weaker hold on the shared electrons so both hydrogen atoms have a slightly positive
charge. Polarity creates the other properties of water including forming hydrogen bonds and allowing water to
be the universal solvent. Cohesion is the ability for a water molecule to form hydrogen bonds with another
water molecule. These hydrogen bonds can form a mesh-like net of water molecules that is referred to as
surface tension, which allows water to form droplets, support objects, and allows it to “mound up” instead of
spilling over. Adhesion is the ability for a water molecule to form hydrogen bonds with other substances.
Cohesion and adhesion together form the property of capillary action, which is very important to biology.
Capillary action is the ability for water to “climb” against the pull of gravity. This allows water to move from the
roots of a plant to the leaves so that photosynthesis can occur. Transpiration (water evaporating from the leaves
of plants) drives the capillary action; as one water molecule evaporates, the next water molecule is pulled up.
Capillary action also allows blood flow throughout animal tissues.
oxygen
4. I can explain the difference between inorganic and organic compounds. This means that I can identify a
carbohydrate, lipid, protein, or nucleic acid based upon its characteristics.
Inorganic compounds do not contain carbon. Organic compounds contain carbon and have many important
properties such as the ability to form a variety of carbon skeleton arrangements. This is because carbon can
form up to 4 covalent bonds with other atoms including single bonds (1 pair of electrons is shared), double
bonds (2 pairs of electrons are shared), and triple bonds (3 pairs of electrons are shared). Organic compounds
Variety of Carbon Skeleton Arrangements
Unit 3 Study Guide
Biochemistry
Name ____________________
make up all living things. There are 4 major types of organic macromolecules: proteins, nucleic acids, lipids, and
carbohydrates. These can be found as monomers (atoms stablely bonded together to form single units) and
polymers (many single units bonded together to make a large molecule).
Double bond
Triple bond
Single bonds
Carbohydrates are the primary source of energy for living things and can be broken down so that the cell can
make ATP. Carbohydrates are made of carbon, hydrogen, and oxygen in a 1:2:1 ratio (ex: C6H12O6). Typically the
compound names end with “-ose.” Carbohydrates are generally found as ring structures. A single ring
(monomer) is called a monosaccharide (including glucose and fructose); these have a sweet taste and are easily
metabolized for quick energy. Glucose and fructose are isomers, which means that they have the same chemical
formula but a different arrangement of atoms. A double ring (dimer) is called a disaccharide (including sucrose,
lactose and maltose); these can also be sweet and easily metabolized. Many rings bonded together (polymer) to
form one large molecule is called a polysaccharide (including cellulose, chitin, and glycogen); these are referred
to as starches which can be structural or store energy because they are metabolized slowly. Cellulose is the
starch found in plant cell walls. Fungi have cell walls made of the starch called chitin. Animal cells use the starch
glycogen for energy storage and is broken down to fuel muscle cell contraction.
Lipids are large molecules that are made of fatty acids, which are long unbranched chains of carbons and
hydrogens. A saturated fatty acid has a carbon skeleton with only single bonds (fully saturated with hydrogen);
these are generally plant based and are better from a health standpoint. An unsaturated fatty acid has a carbon
skeleton with at least one double bond (not fully saturated with hydrogen); these are generally animal based
and are worse from a health standpoint. The double bonds of unsaturated fatty acids causes the carbon
skeleton to bend at a slight angle instead of being straight. Lipids include fats, oils, waxes, steroids, and some
vitamins. One important lipid is a phospholipid, which is the primary component of cell membranes. Another
important lipid is cholesterol, which is a steroid that gives stability to cell membranes but can also be dangerous
at high levels. Lipids do not dissolve (not soluble) in water because they are nonpolar and hydrophobic; this
means that they can form a waterproof barrier. Lipids can also be used to store energy for long periods of time
and are hard to metabolize.
Unit 3 Study Guide
Biochemistry
Name ____________________
cholesterol
phospholipid
Nucleic acids are polymers made of nucleotides which contain carbon, hydrogen, oxygen, nitrogen, and
phosphorus. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the 2 types of nucleic acids. They are
used to store and transmit genetic information. DNA is double stranded and contains the sugar deoxyribose and
the following nucleotides: Guanine, Cytosine, Adenine, and Thymine. DNA contains the instructions for making
for making proteins and is used to pass genetic information to the next generation. RNA is single stranded and
contains the sugar ribose and the following nucleotides: Guanine, Cytosine, Adenine, and Uracil. RNA is used
during protein synthesis.
Proteins are
polymers made of amino acids which
contain carbon, hydrogen, oxygen, and nitrogen. Proteins are also called polypeptides because of the peptide
covalent bonds that form between the amino acids. Proteins are important because they can be used to
transport substances (ex: hemoglobin transporting oxygen); control the rate of chemical reactions (ex: enzymes
like amylase); build tissues (ex: bone and muscle); fight infections (ex: antibodies); and are involved in cell
communication. Proteins are made by ribosomes using the instructions contained in the cell’s DNA.