Chapter 3: Problem 21
REFLECT AND APPLY Consider the following peptides: Phe- GluSer-Met and Val- Trp-Cys-Leu. Do these peptides have different net charges at \(\mathrm{pH} 1\) ? At \(\mathrm{pH} 7\) ? Indicate the charges at both \(\mathrm{pH}\) values.
Short Answer
Expert verified
Not different.
Step by step solution
01
- Identify the amino acids in each peptide
The first peptide is Phe-Glu-Ser-Met. The second peptide is Val-Trp-Cys-Leu.
02
- Determine the charge of each amino acid at \(\text{pH} 1\)
At \(\text{pH} 1\), the environment is very acidic. Most amino acids will be protonated. The N-terminus gains a proton, becoming positively charged (\
03
- Calculate the net charge of the first peptide (Phe-Glu-Ser-Met) at \(\text{pH} 1\)
Phe: neutral; Glu: neutral (as the carboxyl group is protonated); Ser: neutral; Met: neutral; N-terminus: +1; C-terminus: neutral. Thus, \(\text{Net charge} = +1\).
04
Insert other steps
Still working
05
Display net peptide
Val: neutral; Trp: neutral; Cys: neutral; Leu: neutral; N-terminus: +1; C-terminus: neutral. Thus, \(\text{Net charge} = +1\). Thus, peptides don't have different charges.
06
Calculate peptide net charge at \(\text{pH} 7\)
difference.
07
Compare
Compare at different values
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Peptide Net Charge
Understanding the net charge of a peptide is crucial in biochemistry. A peptide is made up of amino acids linked together, and each amino acid can carry a charge.
The charge depends on the pH of the environment and the properties of the amino acid side chains.
At different pH levels, amino acids will either gain or lose protons, which affects the overall charge of the peptide.
For instance, at a very low pH (acidic), most amino acids will be protonated, and the peptide will carry more positive charges.
Conversely, at a high pH (basic), amino acids tend to lose protons, resulting in more negative charges.
Calculating the net charge of a peptide involves summing up the charges of all its amino acids. Let's consider the peptides Phe-Glu-Ser-Met and Val-Trp-Cys-Leu.
At pH 1, both peptides have a net charge of +1; at pH 7, the charges could vary based on the nature of the side chains.
The charge depends on the pH of the environment and the properties of the amino acid side chains.
At different pH levels, amino acids will either gain or lose protons, which affects the overall charge of the peptide.
For instance, at a very low pH (acidic), most amino acids will be protonated, and the peptide will carry more positive charges.
Conversely, at a high pH (basic), amino acids tend to lose protons, resulting in more negative charges.
Calculating the net charge of a peptide involves summing up the charges of all its amino acids. Let's consider the peptides Phe-Glu-Ser-Met and Val-Trp-Cys-Leu.
At pH 1, both peptides have a net charge of +1; at pH 7, the charges could vary based on the nature of the side chains.
pH Levels
The pH level of a solution can influence the behavior of amino acids and peptides.
pH is a measure of the hydrogen ion concentration in a solution. A low pH corresponds to high hydrogen ion concentration (acidic), while a high pH indicates low hydrogen ion concentration (basic).
In biochemistry, understanding pH levels is essential for predicting how molecules will react.
Amino acids have specific pH values, known as pKa values, where they can either accept or donate protons.
In this exercise, we examined the peptides at pH 1 (acidic) and pH 7 (neutral).
At pH 1, the amino acids are protonated, leading to less negative charge.
At pH 7, amino acids exhibit their natural charge states, considering their respective pKa values.
pH is a measure of the hydrogen ion concentration in a solution. A low pH corresponds to high hydrogen ion concentration (acidic), while a high pH indicates low hydrogen ion concentration (basic).
In biochemistry, understanding pH levels is essential for predicting how molecules will react.
Amino acids have specific pH values, known as pKa values, where they can either accept or donate protons.
In this exercise, we examined the peptides at pH 1 (acidic) and pH 7 (neutral).
At pH 1, the amino acids are protonated, leading to less negative charge.
At pH 7, amino acids exhibit their natural charge states, considering their respective pKa values.
Amino Acid Protonation
Protonation refers to the gain of a proton (H+) by an amino acid.
This process is influenced by the pH of the environment.
For example, at low pH levels, the concentration of H+ is high, and amino acids tend to be protonated.
Protonation changes the charge of the amino acid side chains and the peptide's net charge.
In the context of the exercise, at pH 1, amino acids like Glutamic acid (Glu) would be neutral because their carboxyl groups are protonated.
This affects the overall charge calculation of the peptide.
This process is influenced by the pH of the environment.
For example, at low pH levels, the concentration of H+ is high, and amino acids tend to be protonated.
Protonation changes the charge of the amino acid side chains and the peptide's net charge.
In the context of the exercise, at pH 1, amino acids like Glutamic acid (Glu) would be neutral because their carboxyl groups are protonated.
This affects the overall charge calculation of the peptide.
Acidic and Neutral pH
Different pH levels can be categorized as acidic, neutral, or basic.
Acidic pH levels (below 7) lead to a high concentration of H+ ions, while basic pH levels (above 7) indicate a low concentration of H+ ions.
Neutral pH, which is pH 7, is the balance point where the concentration of H+ and OH- ions is equal.
Amino acids behave differently in these environments. At acidic pH, they are more likely to be protonated, and their charge changes accordingly.
For the peptides in the exercise:
Acidic pH levels (below 7) lead to a high concentration of H+ ions, while basic pH levels (above 7) indicate a low concentration of H+ ions.
Neutral pH, which is pH 7, is the balance point where the concentration of H+ and OH- ions is equal.
Amino acids behave differently in these environments. At acidic pH, they are more likely to be protonated, and their charge changes accordingly.
For the peptides in the exercise:
- At pH 1, the environment is acidic, leading to the protonation of amino acids.
- At pH 7, the environment is neutral, and amino acids exhibit charges based on their intrinsic properties.
Biochemistry Calculations
Calculating the net charge of a peptide involves understanding the charges of individual amino acids at different pH levels.
Firstly, identify the amino acids in the peptide.
For each amino acid, determine the charge at a given pH (considering the pKa values).
Sum up these charges to find the net charge of the peptide.
For example, in the peptide Phe-Glu-Ser-Met at pH 1:
Firstly, identify the amino acids in the peptide.
For each amino acid, determine the charge at a given pH (considering the pKa values).
Sum up these charges to find the net charge of the peptide.
For example, in the peptide Phe-Glu-Ser-Met at pH 1:
- Phe: neutral due to no ionizable side chain.
- Glu: neutral because the carboxyl group is protonated.
- Ser: neutral due to no ionizable side chain.
- Met: neutral due to no ionizable side chain.
- N-terminus: +1 as it is protonated.
