All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #4 : Help With Acid Base Chemistry And P H
A researcher adds acid to . The concentration of hydrogen ions is __________ as the concentration of hydroxide ions.
the same
half as much
three times as much
twice as much
the same
Hydrochloric acid () and sodium hydroxide () are both strong reagents. Adding equal amounts of strong acid to a strong base neutralizes the solution and gives the solution a neutral pH of 7. This means that the concentration of hydrogen ions and hydroxide ions are equal to each other. If pH was greater than 7 (basic pH), then the hydroxide ion concentration would be higher and if pH was less than 7 (acidic pH) then hydrogen ion concentration would be higher.
Example Question #2 : Help With Acid Base Chemistry And P H
Solution A contains a weak acid and a weak base whereas solution B contains a weak acid and a strong base. What can you conclude about these two solutions?
I. Solution B will have a higher
II. Solution B will have a higher pOH
III. Solution A will have a lower concentration of hydroxide ions
I and II
None of these
II and III
III only
III only
Solution A has two weak reagents whereas solution B contains a strong base. This means that solution B will be more basic, will have a higher concentration of hydroxide ions, and a higher pH. is a constant and is not altered by the relative reagents (it is always equal to ). Recall that pOH is defined as
This equation suggests that pOH decreases as the hydroxide ion concentration increases. Since it has the higher hydroxide ion concentration, solution B will have a lower pOH.
Example Question #93 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
What is the pH of a solution composed of acetic acid and acetate?
for acetic acid is
Since this problem involves both the acid and the conjugate base of the acid, we can use the Henderson-Hasselbach equation in order to determine the pH of the solution:
Example Question #11 : Chemical Reactions
If a solution of hydrofluoric acid is created, what fluoride ion concentration must be present in order to make the new pH of the solution equal to ?
for hydrofluoric acid is
In order to determine what concentration of fluoride is needed, we can use the Henderson-Hasselbach equation:
Example Question #21 : Biochemistry
Which of the following properties is NOT a feature of the genetic code?
Degenerate
Unambiguous
Universal
Overlapping
Overlapping
The genetic code refers to the sequence of DNA that codes for genes and proteins in the body. The genetic code is composed of three-nucleotide codons, each used to recruit an amino acid during translation and protein synthesis. Each codon codes for one and only one amino acid, making the code unambiguous; however, some amino acids have more than one codon that can be used to recruit them. This feature of the genetic code is known as degeneracy. Finally, the genetic code is universal. All living organisms use the same genetic material (DNA) in their cells and produce proteins through transcription and translation. Though the processes may change slightly between organisms, the general genetic code is universal to all cells.
The genetic code is not overlapping, meaning that the code is linear. Transcription of DNA has a fixed starting point and proceeds in a linear fashion, as does translation of mRNA. There is no overlapping or reverse reading of the genetic code.
Example Question #22 : Biochemistry
For amino acids, the phi () angle refers to the bond between __________ and the alpha carbon while the psi () angle refers to the bond between the alpha carbon and __________.
the amine nitrogen . . . the carbonyl carbon
the carbonyl carbon . . . the R group's first carbon
the carbonyl carbon . . . the amine nitrogen
the amine nitrogen . . . the R group's first carbon
the amine nitrogen . . . the carbonyl carbon
These bonds are specifically referring to the invariable portions of the amino acid and, thus, do not involve the R group (functional group).
This is more of a definition-based answer. The phi angle refers to the bond between the amine nitrogen and the alpha carbon, while the psi angle refers to the bond between the alpha carbon and the carbonyl carbon of the carboxylic acid. These bonds play important roles in determining possible protein structures.
Example Question #103 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Which of the following amino acid sequences is most likely to form an alpha-helix?
GCCDPCQRRTSHM
GAADQAAPSAAEDAA
GAADEAAQSAATYP
GQQGGCACTYFGGG
GAADEAAQSAATYP
Amino acid sequences with a lot of alanine (A) residues are higly likely to form alpha-helices. Glycine (G) and proline (P) residues often cap alpha-helices, though glycine can sometimes be found inside alpha-helices as well.
Proline is never found inside an alpha-helix due to the conformational hindrance caused by the hydrogen bonding within the residue. Proline is usually found in bends in a protein structure.
Example Question #3 : Macromolecules And Enzymes
Which of the following is true regarding the protonation of histidine at a pH of 7?
The carboxyl group is deprotonated, the R-goup is deprotonated, and the amine group is deprotonated
The carboxyl group is deprotonated, the R-goup is protonated, and the amine group is protonated
The carboxyl group is deprotonated, the R-goup is deprotonated, and the amine group is protonated
The carboxyl group is protonated, the R-goup is protonated, and the amine group is protonated
The carboxyl group is deprotonated, the R-goup is protonated, and the amine group is protonated
Histidine has the following pKa values:
COOH - 1.82
R-group - 6.00
NH3 - 9.17
Any pH below the pKa will cause the molecule to be protonated, while any pH above the pKa will cause the molecule to deprotonate. At a pH of 7, the COOH group to deprotonate, but the NH3 and R-group will remain protonated.
Example Question #3 : Macromolecules And Monomers
Which part of its amino acid mediates the interactions that form the tertiary structure of a protein?
The alpha carbons
The polypeptide backbone
The amino groups
The R-groups
The carboxyl groups
The R-groups
Tertiary structure of a protein is determined by interactions between the R-groups of the amino acids that make up that protein. The secondary structure of a protein is mediated by the backbone atoms of the polypeptide chain which includes the carboxyl and amine groups. The alpha carbon are what the R-groups are attached to an do not directly contribute to any level of protein structure.
Example Question #106 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology
Interactions between which of these mediates the secondary structure of a protein?
The polypeptide backbone
The amino groups
The R-groups
The alpha carbons
Disulfide bonds
The polypeptide backbone
Hydrogen bonds between repeating units of the polypeptide backbone (namely the amino groups and carboxyl groups) mediate secondary structure in proteins.
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