Final Exam Study Guide
20.1 Enzymes
- Enzymes lower the activation energy for a chemical reaction.
-The actual names of enzymes are derived by replacing the end of the name of the reaction or
compound with the suffix “ase”, for example oxidase
Classification of enzymes:
1. Oxidoreductases-catalyze oxidation-reduction reactions
2. Transferases-transfer groups between two compounds
3. Hydrolases-add water to break bonds
4. Lyases-add or remove groups without hydrolysis or oxidation that may result in a double bond
5. Isomerases-rearrange atoms to form isomers
6. Ligases-join molecules using ATP energy
20.2 Enzyme Action
-Nearly all enzymes are globular proteins
-The tertiary structure plays an important role in how an enzyme catalyzes a reaction
-Typically enzymes are much larger than substrates
-The active site is located on an enzyme and is where a substrate binds to the enzyme
-R groups from specific amino acids interact with R groups on the substrate to form hydrogen bonds.
-The proper alignment of a substrate within the active site form and enzyme-substrate complex.
Lock and key model- describes the active site of having a rigid non-flexible shape
Induced fit model- the active site adjusts to fit the shape of the substrate more closely
20.3 Factors Affecting Enzyme Activity
-The activity of an enzyme describes how fast an enzyme catalyzes the reaction that converts a substrate
to product
-Activity is strongly affected by temperature, pH, concentration of the substrate, and concentration of
the enzyme
-At lower temperature the enzymes show less activity (optimum temperature is 37 degrees Celsius or
body temperature)
-At temperature above 50 degrees Celsius the tertiary structures of proteins are destroyed.
-Enzymes in most cells have an optimum pH around 7.4, however stomach enzymes have a lower PH
around 1.5-2.0 due to their acidic nature
-An increase in substrate concentration and an increase in the enzyme concentration increase the
activity
-When the substrate concentration is high enough to bind with all the enzyme molecules, the rate of the
catalyzed reaction reaches a maximum and the addition of more substrate does not increase the rate of
the reaction
20.4 Enzyme Inhibition
-Inhibitors cause enzymes to lose catalytic activity
-Inhibitors prevent the active site from binding with a substrate
-An enzyme with a reversible inhibitor can regain enzymatic activity but an enzyme attached to an
irreversible inhibitor loses enzymatic activity permanently.
-Reversible inhibitors are related to covalent bonds
-A competitive inhibitor has a structure so similar to the substrate it can bond to the enzyme just like the
substrate. Thus, the competitive inhibitor competes with the substrate for the active site on the enzyme
-Some bacterial infections are treated with competitive inhibitors (Sulfanilamide)
-The structure of noncompetitive inhibitors does not resemble the substrate and does not compete for
the active site. Instead the non competitive inhibitor binds to a different site on the enzyme causing the
shape of the active site to change, which prevents the substrate from binding to the active site.
-The addition of more substrate does not reverse this type of reaction when non competitive inhibitors
are involved.
-In irreversible inhibition, a toxic substance causes an enzyme to permanently lose enzymatic activity
(Insecticides, nerve gas, cyanide, penicillin)
-Antibiotics are irreversible inhibitors used to inhibit bacterial growth.
20.5 Regulation of Enzyme Activity
-Zymogens, or proenzymes are produced as an inactive form and stored in a specific organ until they are
needed
-A zymogen is converted to the active form by the removal of a polypeptide section with up to 40 amino
acids, which uncovers the active site of the enzyme.
-Most protein hormones, such as insulin, as well as digestive enzymes and the enzymes needed for
blood clotting are initially synthesized as zymogens
-Review table 20.7 on page 718
20.6 Enzyme Cofactors and Vitamins
Simple Enzymes-consist only of proteins
-Many enzymes require small molecules such as vitamins or metal ions called cofactors to catalyze
reactions properly
Coenzyme-a small organic cofactor
Vitamins-organic molecules that are essential for normal health and growth
Water soluble Vitamins- have polar groups such as OH and COOH, which makes them soluble in
aqueous environments (B-Vitamins and C-Vitamins)
Fat-Soluble Vitamins- nonpolar compounds, which are soluble in fat components of the body (A, D, E,
and K Vitamins)
21.1 Components of Nucleic Acids
-The bases of nucleic acids are derivative of pyrimidine or a purine.
-In DNA the purine bases with double rings are adenine (A)and guanine (G).
-In DNA the pyrimidine bases with single rings are cytosine (C)and thymine (T).
-In RNA thymine is replaced with Uracil (U).
-In RNA the five carbon sugar is ribose, in the DNA the five carbon sugar is deoxyribose (deoxyribose
does not have a hydroxyl group OH on C2)
Nucleoside- is produced with a pyrimidine or a purine (base) forms a glycosidic bond to C1 of a sugar.
(Base + Sugar= nucleoside)
Nucleotides- formed when the C5 OH groups of ribose or deoxyribose in a nucleoside forms a phosphate
ester. (Base+Sugar+Phosphate group= Nucelotide)
Review Table 21.1 on page 742
21.2 Primary Structure of Nucleic Acids
-The link between sugars in adjacent nucleotides is referred to as a phophodiester bond.
-The sequence or order of based is referred to as the primary structure.
*Know how to recreate the diagrams on page 744
21.3 DNA Double Helix
For DNA: A=T and G=C and vice versa (Complimentary Base Pairing)
-In DNA one strand goes in the 5’-3’ direction and the other strand goes in the 3’-5’ direction.
-Each of the bases along a polynucleotide stand forms hydrogen bonds to a specific base on the opposite
DNA stand, this is referred to as complimentary base pairing.
21.4 DNA Replication
-In DNA replication, the strands in the parent DNA molecule separate, which allows the synthesis of
complementary strands of DNA.
-The replication process begins when an enzyme called helicase catalyzes the unwinding portion of the
double helix by breaking the hydrogen bonds between the complementary bases.
-Eventually the entire double helix of the parent DNA is copied. In each new molecule, one strand of the
double helix is from the original DNA and is one is a newly synthesized stand.
Leading Stand-runs in the 5’-3’ direction
Lagging Stand (Okazaki fragments)-run in the 3’-5’ direction
21.5 RNA and Transcription
-Besides having a different sugar than DNA and having Uracil instead of thymine, RNA also is a single
stranded nucleic acid and are much smaller than DNA molecules
-Review table 21.3 on page 751 for the different types of RNA
Transcription- In the nucleus, the genetic information or DNA is copied to make mRNA.
Translation-tRNA molecules convert mRNA to proteins (amino acids)
When going from DNA to mRNA: G=C, C=G, A=U, T=A
Exons- code for proteins
Introns- do not code for proteins
21.6 The Genetic Code and 21.7 Protein Synthesis: Translation
-The genetic code consists of a series of three nucleotides in mRNA called a codon. Each codon relates to
a specific amino acid. (UUU=Phe, CUU=Leu, GUU=Val, etc….)
-tRNA consists of the anticodons
-Anticodons and codons are complimentary to each other
-View Figure 21.18 on page 759 for an example of tRNA
21.8 Genetic Mutations
-A mutation is a change in the nucleotide sequence of DNA.
Substitution mutation- the replacement of one base in the coding strand of DNA with another base.
Frameshift mutation- a base is added to or deleted from the normal order of bases in the coding strand
of DNA.
-When a protein deficiency is hereditary, the condition is called a genetic disease.
-Know how the disease PKU is affected by genetic mutations (See page 763)