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UNE Biochemistry Midterm Exam – Q&A (Rated A+)
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UNE Biochemistry Midterm Exam – Q&A (Rated A+)Primary Structure function Correct Ans - -Linear sequence of
amino acids in polypeptide chain
-Written from the amino terminus to the carboxyl terminus
bends, turns, and loops Correct Ans - Short stretches areas of the
polypeptide chain form these structures that are stabilized by hydrogen
bonds (these are not random)
Alpha helix function Correct Ans - - Formed when the carbonyl
group of peptide bond forms a hydrogen bond with the amide nitrogen of
another peptide bond four amino acids down the polypeptide chain
- The peptide backbone is formed by hydrogen bonds between each
carbonyl oxygen atom and the amide hydrogen located 4 residues down the
chain. This unique bonding sequence results in an alpha helix structure
that is highly compact and rigid.
- Comprises about 1/3 of all secondary structures.
- Proline is not typically found in these structures as it forms a non-
traditional peptide bond and adds a 'kink' in the helix.
Tertiary structure function Correct Ans - - Total 3-D conformation
of an entire polypeptide chain including interactions between alpha-
helices, beta-sheets and any other loops, turns, or bends. (Rossman fold is
an example)
- Motifs are common arrangements of secondary structures to generate a
tertiary arrangement
- Tertiary structures can be stabilized by a variety of interactions including:
disulfide linkages, hydrophobic interactions, van der Waals forces,
electrostatic interactions and ionic bonding.
structural domains Correct Ans - A section of protein sufficient to
perform a particular chemical or physical task. These are defined regions
with specific function that are conserved in function and sequence across
other proteins
Quaternary Structure and function Correct Ans - A combination of
two or more tertiary subunits that work together as one functioning unit.
,Homologous proteins Correct Ans - - have similar primary
sequences and functions
- Both bind oxygen
- Both contain at a heme ring stabilized by histidine
- Like all proteins, the tertiary and quaternary structures are stabilized by
hydrophobic interaction, hydrogen bonds, and salt bonds
Hemoglobin Correct Ans - - Hb is a heterotetramer (four "mers"
and at least one monomer is different from the others).
- Hb is composed of 2 α and 2 β subunits.
- Each subunit has its own heme; hemoglobin can bind 4 oxygen molecules
- travels in the blood inside a red blood cell to deliver oxygen to tissues
Myoglobin Correct Ans - - Is a monomer that has 8 α-helices linked
together by α -turns
- It has a hydrophobic pocket containing heme with a ferrous iron atom
(Fe+2) at its center for oxygen binding.
- Fe2+ is always bound to a histidine R-group of the α-helix. This binding
stabilizes the reduced state of iron when it binds to oxygen
- Heme is tightly bound to the globin, it is termed a prosthetic group.
- Myoglobin binding 🡪 hyperbolic
-remains in the heart and skeletal muscle cells to bind oxygen released by
hemoglobin.
apoprotein Correct Ans - A protein missing its ligand or ligands.
Example: hemoglobin lacking heme - porphyrin ring
holoprotein Correct Ans - A protein with its ligand so it is able to
function. Example: hemoglobin bound to heme
Cooperativity Correct Ans - - when an enzyme (such as
hemoglobin) consisting of several subunits is altered by the substrate
- When O2 binds to the Fe2+ at one of the Hb binding sites, it pulls on the
histidine, which pulls on the α-helix, changing the conformation of the
globin slightly. This slight movement changes the conformation of the other
three chains in the Hb.
- When oxygen binds to one heme, the other hemes are more likely to bind
a second molecule of oxygen.
, reverse of positive cooperativity Correct Ans - When oxygen is
released from hemoglobin, the loss of one molecule of oxygen facilitates the
loss of additional oxygen molecules
Hemoglobin in T-state Correct Ans - - Hb has a low affinity for O2.
- Allosteric inhibitors stabilize the T conformation
Hemoglobin in R-state Correct Ans - - Hb has a high affinity for O2.
- Allosteric activators stabilize the R conformation
Salt bridges Correct Ans - are broken between the transitions
between the T and R state
bohr effect Correct Ans - - the impact of pH on oxygen binding
hemoglobin. A decrease in pH decreases hemoglobin saturation
- Effectors to know: 2,3-bisphosphoglycerate (BPG), pH, protons and CO2
substrate specificity Correct Ans - - the ability of an enzyme to
select one or a few substrates from a group of similar substrates
- The active site contains functional groups that participate in the reaction.
- The reaction takes place away from water solution.
- The enzyme usually changes conformation due to the interactions
between the amino acid side chain groups of the enzyme and the functional
groups of the substrate, so that the outside solution can't take part in the
reaction
- Enzymes increase the rate of the reaction by decreasing the activation
energy, i.e., stabilizing the transition state.
Oxdioreductase Correct Ans - Catalyze oxidation reduction
reactions. At least one substrate becomes oxidized and at least one
substrate becomes reduced.
transferase Correct Ans - Catalyze group transfer reactions - the
transfer of a functional group from one molecule to another.
Example: amino acid transferases use ping-pong reaction that requires
pyridoxal phosphate
hydrolase Correct Ans - C-O, C-N, and C-S bonds are cleaved by
addition of H2O in the form of OH- and H+ to the atoms forming the bond.
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