More Questions Flashcards
what is standard free energy equation
delta G’ = -RTlnK
a chemical reaction for which the associated enthalpy change is positive:
A) cannot occur spontaneously
B) may occur spontaneously if coupled to reaction in which enthalpy change is negative and of greater magnitude
C) raise surrounding temp
D) inevitably occur spontaneously
B
a chemical reaction for which the associated free energy change delta G is large and negative A) cannot occur spontaneously B) is likely to be irreversible C) will inevitably occur spontaneously D) will occur rapidly
B -
when is delta G small and reversible
when all difference in ratio to products
small conc change in reactants/products can reverse delta G
when is delta G large and irreversible
when large differences between reactants/products
what statement about ATP is correct
A) ATP can diffuse through membranes
B) ATP is considered a low energy phosphate compound
C) ATP is present at high conc in cell
D) Hydrolysis of ATP is strongly exergonic
D
Which of the following statements best describes how a reaction is likely to behave if it has a large, negative value for G?
a) The reaction will be at equilibrium.
b) The reaction is likely to happen to a small extent, with only a small amount of product formed.
c) The reaction will happen to a moderate extent, with about as much product being formed as reactant being left.
d) The reaction is likely to happen to a large extent, with large amounts of product formed
D G is large and negative equilibrium lies towards right favours foward reaction product formation spontaneous reaction
At Keq the value of the change in free energy for a chemical reaction is:
a) zero
b) greater or less than zero but remains at a stable value
c) does not change with respect to energy transfer from coupled reactions
d) The point at which the concentration of reactants and products are equal.
A g K is equilibrium constant determined from [C][D]/[A][B] products/reactants no net free energy transfer
what is delta G when a reaction is at equilibrium
delta G = 0
forward rate = backwards rate
What is the value of DGo’ (kJ/mol) at equilibrium for the reaction
A + B C + D with the following conditions:
A = 0.1mol.l-1 B=0.25mol.l-1 C=0.3mol.l-1 D=0.6mol.l-1 R= 8.3 JK-1.mol-1 T= 298 K
WATCH UNITS
must divide -RT by 1000
-RT = -(8.3 x 298)/1000 = -2.5kJ.K-1.mol-1
Keq = ((0.3x0.6)/(0.1x0.25)) = 1.8/0.025 = 72mol.l-1
ln(72)= 4.3
DGo’ = -2.5 x 4.3 = -10.6kJ.mol-1
if delta G is negative is reaction spontaneous
yes
larger the value more change of being irreversible
more products are formed
Which of the following options provides the correct value of DGo’ (kJ/mol) at equilibrium for the reaction A + B C + D with the following conditions:
A = 0.75mol.l-1 B=0.15mol.l-1 C=0.08mol.l-1 D=1.2mol.l-1 R= 8.3 JK-1.mol-1 T= 298 K
a) +0.43kJ.mol-1
b) -0.43kJ.mol-1
c) +0.88kJ.mol-1
d) -0.88kJ.mol-1
A
What is a polar molecule?
a) a molecule with no charge
b) a molecule with opposite charges at opposite ends
c) a molecule with identical charges at opposite ends
d) molecule with an unequal number of protons and electrons
A
What how does water arrange around ions?
a) the more negative atoms attach to positive ions
b) the more positive atoms attach to negative ions
c) water forms a hydration shell
d) all of these answers are true
D
Which is TRUE regarding the structure of hydrogen bonds?
a) Hydrogen bonds can only arise from the covalent interaction between oxygen and hydrogen atoms.
b) It is only the hydrogen atoms of a water molecule which interact with polar molecules
c) Hydrogen bonds involve a linear arrangement of one hydrogen atom between two electronegative atoms
d) Hydrogen bonds are angled at 104.3o
C
how are hydrogen bonds formed
hydrogen atoms are shared between 2 electronegative atoms
bonds are linear
Which of the following statements about amino acids is correct?
a) Amino acids are classified according to the structures and properties of their side chains.
b) Amino acids are uncharged at neutral pH.
c) Amino acids in proteins are mainly in the D-configuration.
d) Twenty four amino acids are commonly used in protein synthesis.
A
All amino acids contain an alpha carbon bonded to the following structures:
a) an amino group (-NH2), a carboxyl group (-COOH), a hydrogen (-H), a side chain (-R)
b) an amide group (-CONH2), a carboxyl group (-COOH), a hydrogen (-H), a side chain (-R)
c) an amino group (-NH2), a carboxyl group (-COOH), a hydroxyl group (-OH), a side chain (-R)
d) an amide group (-CONH2), a hydrogen (-H), a side chain (-R)
A
what are proteins and polypeptides in humans made up of
20 different L-amino acids
define hydrophobic
no net charge
what are Aliphatic (linear hydrocarbon chain) or aromatic (unsaturated chemical compounds characterized by
one or more planar rings of atoms joined by covalent bonds side groups
describe methionine
amino acid the starts translation
contains sulphur
describe polar amino acids
soluble in water
class capable of creating redox sensitive disulphide bridges
one N,O, S in R side chain d
what are electron donors in hydrogen bonds
N, O, S in side chain
describe acidic amino acids
hydrophilic
carboxylic acid side group = proton donating
at pH 7, 3 groups ionised charged difference -1
when ionised side chain forms ionic bond salt bridges and H bonds
free glutamate functions as neurotransmitter
describe basic amino acids
hydrophilic
each side chain contains basic group - proton accepting
charge difference +1
why is histidine an amino acid that makes up active site of protein enzymes
imidazole side chain of histidine = acid and base catalysis
no other amino acid has this
Which of the following statements is true about a peptide bond (RCONHR’)?
a) It is non planar.
b) It is capable of forming a hydrogen bond.
c) Thecisconfiguration is favoured over thetransconfiguration.
d) Single bond rotation is permitted between nitrogen and the carbonyl group.
D
During the formation of the peptide bond which of the following takes place?
a) The α-amino group of one amino acid acts as a nucleophile to displace the hydroxyl group of another amino acid forming a peptide bond.
b) Hydrogen atom is lost from its carboxyl group of one amino acid and a hydroxyl group is lost from its amino group of another amino acid
c) Hydroxyl group is lost from its carboxyl group of one amino acid and a hydroxyl group is lost from its amino group of another amino acid
d) Hydrogen atom is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid
A
what is [H+] pure water
10 to the power of -7
pH equation
pH = -long[H+]
what is K
dissociation constant
[H+]{OH-]/[H2O]
what is conc of water
55.5M
what is Kd/Kw
ion product pure water
10 to the power of -14
defines limits of pH scale
what happens if [H+] decreases
[OH-] increases
describe neutral pH
H = OH
what is Ka
acid dissociation constant
tendency of an acid [HA] to donate [H]
Ka = [H][A]/[HA]
what does pKa allow
allows calculation of ratio of unprotonated:protonated acid at any pH
pH = -logKa
acid is 50% dissociated if pH = pKa
what us the Henderson hasselbalch equation
pH = pKa + log [A]/[HA]
Compare solution A with pH =4 to solution B with pH = 6.
The concentration of [H+] in solution A is twice that in solution B.
Solution A has greater buffering capacity than solution B.
The concentration of [H+] in solution A is 100 times that in solution B.
The hydroxide concentrations are equal in the two solutions since pH only measures the concentration of H+.
C
Two weak acids, A and B, have pKa values of 4 and 6, respectively.Which statement is true?
Acid A dissociates to a greater extent in water than acid B.
For solutions of equal concentration, acid B will have a lower pH.
B is the conjugate base of A.
Acid A contains more ionizing groups than acid B.
The equivalence point of acid A is higher than that of acid B
A
strong acids favour [H]{A] so ratio to [HA] gives a larger value
since pKa = -logKa what happens to pKa with increasing acid strength
pKa value becomes smaller
A solution of HCl with a concentration of 4x10-4 mol.L-1 has a pH of which of the following?
a) 2.67
b) 3.21
c) 3.40
d) 4.00
d) 4.31
Answer:
pH = -log[H+].
[H+] = 0.0004M
-log [0.0004] = 3.39794 or 3.40
A buffer solution contains ethanoic acid and its conjugate base; the pKa of ethanoic acid is 4.74. At what pH does the solution buffer?
a) 3.0
b) 4.0
c) 5.0
d) 6.0
C
A strong acid will display a larger Ka but smaller pKa value compared to a weak acid. True or false?
a) True
b) False
A
An Amino acid can act as an acid or a base?
a) True
b) False
A
carboxyl group donated H = acid
amino group accepts H so acts as base
what are zwitterions in neutral solution
amino acids without charges
no net charge
contain two titratable goups
define isoelectric point
pH at which molecule has no net charge
uncharged amino acids have 2 titratable groups so 2 pKa values
Which statements about the zwitterionic amino acids are correct?
a) Reducable atoms in the amino acid side group side group enable zwitterions to alter charge depending upon prevailing pH
b) Zwitterions are dipolar molecules which act as buffers of acids and bases.
c) Charge differences at amino and carboxyl residues of zwitterions balance each other such that the molecule is non-polar.
d) Zwitterion ion charge may be positive or negative depending upon prevailing pH.
e) Zwitterions display a single pKa
f) The overall charge of a zwitterion is neutral at a pH equivalent to the isoelectric point, pI.
B
D
F
Which type of bonding is responsible for the secondary
structure of proteins?
a) Disulphide bridges between cysteine residues.
b) Hydrogen bonding between the C=O and N-H groups of peptide bonds.
c) Peptide bonds between amino acids.
d) Salt bridges between charged side chains of amino acids.
B
Which term below best defines the ‘quaternary structure’ of a protein?
a) The arrangement of two or more polypeptide subunits into a single functional complex
b) The folding of the polypeptide backbone in three-dimensional space.
c) The interaction of amino acid side chains.
d) The sequence of amino acids in a polypeptide chain.
A
Which term below best defines the ‘quaternary structure’ of a protein?
a) The arrangement of two or more polypeptide subunits into a single functional complex
b) The folding of the polypeptide backbone in three-dimensional space.
c) The interaction of amino acid side chains.
d) The sequence of amino acids in a polypeptide chain.
A
Which of the following statements about collagen is correct?
a) Collagen contains a high proportion of hydroxylated proline residues.
b) Collagen is a globular, intracellular protein.
c) Post-translational modification of collagen involves vitamin A.
d) The structure of collagen consists of a superhelix of three α helices twisted together.
A
Which of the following amino acids is mostly likely to disrupt an alpha helix?
a) Proline.
b) Leucine.
c) Glycine.
d) Valine.
A
Which of the following most accurately describes how secondary structures in proteins are stabilised?
a) Through ionic bonds operating between oppositely charged amino acid side chains.
b) Through covalent bonds joining different parts of the peptide backbone.
c) Through hydrogen bonds between different amino acid side chains.
d) Through hydrogen bonds joining different parts of the peptide backbone.
D
Which of the following pairs of amino acids might contribute to protein conformation by forming electrostatic interactions?
a) Glycine and leucine.
b) Glutamate and lysine.
c) Phenylalanine and tyrosine.
d) Lysine and arginine.
B
Which amino acid can form disulphide bonds?
a) Glycine.
b) Proline.
c) Glutamate.
d) Cysteine.
D
Which of the following best describes a protein domain?
a) The α-helical portion of a protein.
b) A discrete region of polypeptide chain that has folded into a self-contained three-dimensional structure.
c) The β-pleated sheet portion of a protein.
d) A feature that rarely occurs in globular proteins.
B
Which of the following statements correctly describes the effect of glutamic acid to valine substitution upon the quaternary structure of hemoglobin?
a) The heme domain is acidified causing iron to move from its normal Fe(II) to Fe (III)
b) Hydrophobic interactions between hemoglobin tetramers cause aggregation.
c) charge differences result in a and b subunit disaggregation
d) Electron transfer between a and b subunits and the heme domain no longer occurs.
B
