Biochemistry Questions

[buffer]

Hello everyone,
Can anyone please help me with the following questions ,I tried to find answer but could not.

Leucine has a net positive charge at pH:
A. 3 and below
B. 7 (neutral)
C. 10 and above
D. It is never charged
E. More than one of the above

At pH 7, tyrosine has a net charge of​

A. -2
B. -1
C. 0
D. +1
E. +2​

ELISA, enzyme-linked immunosorbent assays, are useful in biochemistry because
A. They are based on the specific binding of a substrate to the enzyme
B. They can be used to detect very small amounts of a specific material
C. They involve a specific recognition between the antibody and enzyme used
in the color formation
D. They can detect the shape of the interacting proteins​

E. They can detect the charge on the proteins

Thanks

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[iomega]

Hello everyone,
Can anyone please help me with the following questions ,I tried to find answer but could not.

Leucine has a net positive charge at pH:
A. 3 and below
B. 7 (neutral)
C. 10 and above
D. It is never charged
E. More than one of the above​

At pH 7, tyrosine has a net charge of
A. -2
B. -1
C. 0
D. +1
E. +2​

ELISA, enzyme-linked immunosorbent assays, are useful in biochemistry because
A. They are based on the specific binding of a substrate to the enzyme
B. They can be used to detect very small amounts of a specific material
C. They involve a specific recognition between the antibody and enzyme used
in the color formation
D. They can detect the shape of the interacting proteins​

E. They can detect the charge on the proteins

Thanks

i dont know the ans for the 1st 2, but ans for the 3rd one in 3, this is the reason y ELISA is used to check if pt is HIV positive during early stage of infection.

 

[buffer]

Thank you so much.
I searched in google for the third question and came up with
Enzyme-linked immunosorbent assay, also called ELISA, enzyme immunoassay or EIA, is a biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample.
But could not correlate my findings with the answer choices.Thank you and I greatly appreciate your help.
The first and second question I have no clue.Hope some one comes up with answer,If I find it I will post it.

Thanks

 

[iomega]

Hello everyone,
Can anyone please help me with the following questions ,I tried to find answer but could not.

Leucine has a net positive charge at pH:
A. 3 and below (
B. 7 (neutral)
C. 10 and above (it is neutral at pH 7, so anything above 7 will give it a positive charge)👍
D. It is never charged
E. More than one of the above​

At pH 7, tyrosine has a net charge of
A. -2
B. -1
C. 0(it is neutral at pH 7)👍
D. +1
E. +2​

ELISA, enzyme-linked immunosorbent assays, are useful in biochemistry because
A. They are based on the specific binding of a substrate to the enzyme
B. They can be used to detect very small amounts of a specific material
C. They involve a specific recognition between the antibody and enzyme used
in the color formation
D. They can detect the shape of the interacting proteins​

E. They can detect the charge on the proteins

Thanks

Hey Buffer,
sorry wht i had explained b4 was for PCR, got confused between ELISA n PCR..
i have corrected my ans above..
plz do correct me if i m wrong..

 

[Raluca]

Leucine has 2 ionizable groups and its iso-electric pH is 6.0. Leucine exists as cation at pH below 6.0 and as anion at pH above 6.0. It exists as a zwitter ion at pH 6.0. So at physiologic ph, leucine is negatively charged and according to the options available, leucine is negatively charged at ph 3 and below.
Tyrosine is neutral at physiologic ph.

 

[iomega]

Leucine has 2 ionizable groups and its iso-electric pH is 6.0. Leucine exists as cation at pH below 6.0 and as anion at pH above 6.0. It exists as a zwitter ion at pH 6.0. So at physiologic ph, leucine is negatively charged and according to the options available, leucine is negatively charged at ph 3 and below.
Tyrosine is neutral at physiologic ph.

i had actually thought 3 an above was the ans, but donno why i changed it later..
thanx for correcting.

 

[buffer]

Thanks iomega and raluca for you answers.
Will the net charge be zero if any other aminoacid other than tyrosine is given?
Thanks raluca for explaining the properties of leucine.then we must know the isolectric point of other aminoacids also.
Thanks a lot

 

[buffer]

Hi all I have answered some question,please check whether these answers are correct and if it is wrong post correct answers.Thanks

1. A biological molecule can serve as a hydrogen bond donor if it contains a
hydrogen atom attached to:
A. phosphorus
B. any nonmetallic atom
C. carbon
D. oxygen or nitrogen
E. zinc

2. Which is an appropriate statement of involvement of the hydrophobic effect in
protein folding?
A. Nonpolar portions of the proteins bind strongly to one another due to
strong van der Waals interactions.
B. Polar portions of the molecule are generally exposed to solvent to interact
effectively with water.
C. Nonpolar portions of the molecule can be placed on the surface of the
molecule only if hydrogen bonded to water.
D. Water molecules form strong hydrogen bonds to the hydrophobic portions
of proteins
E. The hydrophobic effect is a poorly understood interaction between
nonpolar regions of proteins

The Henderson-Hasselbach equation shows that
A. Dilution of a buffer increases its pH
B. Stronger buffers have higher pKa values
C. pH is a function of temperature
D. pH is independent of the dissociation constant of the acid
E. pH equals the pKa when an acid is half neutralized

SDS-PAGE separates proteins based on:
A. Mass
B. Shape
C. Charge
D. Number of disulfide binds in the protein
E. None of the above

Edman degradation can be used to detect the sequence of a
A. Protein
B. DNA
C. RNA
D. Polysaccharide
E. Binding events during catalysis
11. Three-dimensional structure of a protein can be determined by
A. Western Blotting
B. Mass Spectrometry
C. High-pressure Liquid Chromatography
D. Ultracentrifugation
E. NMR Spectroscopy
12. A reaction has an equilibrium constant, Keq, of 50. When performed in the
presence of an appropriate enzyme, the forward rate constant is increased 20-fold.
What will happen to the reverse rate constant?
A. It will be unaffected
B. It will increase 20-fold
C. It will decrease 20-fold
D. It will increase 50-fold
E. It will decrease 50-fold
I don’t have any clue about this question
Which of the following statements is true regarding the role an enzyme plays in
catalysis?
A. An enzyme increases the equilibrium constant.
B. An enzyme decreases the activation energy
C. An enzyme increases the energy of the transition state so that it breaks
down more rapidly.
D. An enzyme decreases the difference of free energy between substrate and
product
E. All of the above

In the Michaelis-Menten equation, KM is defined as
A. Equal to the dissociation constant for the enzyme substrate complex
B. Equal to the substrate concentration at which reaction rate is one third of
the maximal value
C. Equal to the substrate concentration at which reaction rate has reached
the maximal value
D. Equal to the half-maximal reaction rate
E. None of the above

 

[buffer]

Hey Buffer,
sorry wht i had explained b4 was for PCR, got confused between ELISA n PCR..
i have corrected my ans above..
plz do correct me if i m wrong..

In google book search Biological Thermodynamics (page 154) it says ELISA is a useful method in detecting small amounts of proteins and other specific material.
But ELISA also shows the presence of antigens through color change.So I dont know which one is correct.two of ur answer seems to be correct.I would probably go with the answer they can be used to detect small amounts of material.

 

[Be positive]

In google book search Biological Thermodynamics (page 154) it says ELISA is a useful method in detecting small amounts of proteins and other specific material.
But ELISA also shows the presence of antigens through color change.So I dont know which one is correct.two of ur answer seems to be correct.I would probably go with the answer they can be used to detect small amounts of material.

I agree with u
In decks it has given as ''The detection of a specific protein''.

 

[buffer]

Can someone please help me with this question.

What is the pH of a phosphate solution made by the addition of 2.6 equivalents of NaOH to an intial solution of phosphoric acid? The pKavalues are pK1 = 2.12, pK2 =7.20, pK3 =12.40
a) 7.4
b) 10.6
c) 12.6
d) 8.8
Thanks

 

[Czarcasm]

I'm sorry to bump this thread, but I came across it after searching for some answers on immunoassay techniques, but I started reading some of the responses here and noticed some of you guys (@iomega and @Raluca) giving wrong information.

Leucine has a net positive charge at pH:
A. 3 and below
B. 7 (neutral)
C. 10 and above
D. It is never charged
E. More than one of the above

The correct answer to this question is A (3 and below). Not C as two others have pointed out. For an amino acid with two ionizable groups, as is the case for Leucine, it will have an overall positive charge when the carboxyl end is protonated. While the carboxyl end carries no charge (as -COOH), the amino terminus does -- a positive charge and so in extremely acidic environments, more specifically, when the pH is below the pKa of the carboxyl terminus, -COOH is fully protonated and NH3+ carries a positive charge. Therefore A is the correct answer.

 

[Czarcasm]

Can someone please help me with this question.

What is the pH of a phosphate solution made by the addition of 2.6 equivalents of NaOH to an intial solution of phosphoric acid? The pKavalues are pK1 = 2.12, pK2 =7.20, pK3 =12.40
a) 7.4
b) 10.6
c) 12.6
d) 8.8
Thanks

This thread is ancient but in case anyone google's:

Phosphoric Acid has 3 pKa's. The first equivalent of NaOH will fully deprotonate H3PO4 to H2PO4. The second equivalent of NaOH will fully deprotonate H2PO4- to HPO42-. And the final 0.6 of NaOH will create a buffer solution of conjugate acid and base (0.6 M PO43- (Conjugate Base) and 0.4 HPO42- (Conjugate acid).

pKa1 describes the equilibrium between H3PO4 and H2PO4-
pKa2 describes the equilibrium between H2PO4- and HPO42-
pKa3 describes the equilibrium between HPO42- and PO43- (This is what we'll use for the HH equation).

Therefore: pH = pKa3 + log (conjugate base / conjugate acid)
pH = 12.40 + log (0.6/0.4)
pH = 12.57 which is ~12.6 (Choice C)

You didn't really need to do the calculation if you realized that buffer solutions are within +1/-1 of the pKa range it's buffering.