VIPSolutionsGive step-by-step solution with explanation and final answer: What are the (1) structures and (2) net charges of the following five - amino - acid peptides at pH 12? ( Instruction: Please draw the structures by hand on paper using Chapter 4, slide 4 as a template, and provide a step - by - step explanation on how you determine the net charges; Upload the image file of your work to Canvas) (Hints: you will need concepts from Chapter 2, Chapter 3, Chapter 4 - slides 2 - 4, 1st step: draw the detailed structures of the 5 - amino - acids peptides (use chapter 4, slide 4 as template); 2nd step: identify pKa values and charges of all ionizable functional groups including the primary carboxal and amino groups at the target pH; 3rd step: determine the net charges) WLARK KADFQ
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Give step-by-step solution with explanation and final answer: What are the (1) structures and (2) net charges of the following five - amino - acid peptides at pH 12? ( Instruction: Please draw the structures by hand on paper using Chapter 4, slide 4 as a template, and provide a step - by - step explanation on how you determine the net charges; Upload the image file of your work to Canvas) (Hints: you will need concepts from Chapter 2, Chapter 3, Chapter 4 - slides 2 - 4, 1st step: draw the detailed structures of the 5 - amino - acids peptides (use chapter 4, slide 4 as template); 2nd step: identify pKa values and charges of all ionizable functional groups including the primary carboxal and amino groups at the target pH; 3rd step: determine the net charges) WLARK KADFQ
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Asked by: Rahul
Created at: 2026-01-28 03:28:16
Asked by: Rahul
Created at: 2026-01-28 03:28:16
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# Step-by-Step Solution: Peptide Net Charges at pH 12
Let’s solve for the **structures and net charges** of the following peptides at **pH 12**:
- **WLARK**
- **KADFQ**
We’ll focus on step-by-step charge calculation, as you’ll draw the structures by hand.
---
## 1. List the Amino Acids and Their Ionizable Groups
### Peptide 1: WLARK
| Position | Amino Acid | Side Chain (R) Group | Ionizable? | pKa (approx) | Charge at pH 12 |
|----------|------------|----------------------------------|------------|--------------|-----------------|
| 1 | W (Trp) | Indole (not ionizable) | No | - | |
| 2 | L (Leu) | Isobutyl (not ionizable) | No | - | |
| 3 | A (Ala) | Methyl (not ionizable) | No | - | |
| 4 | R (Arg) | Guanidino | Yes | ~12.5 | (see below) |
| 5 | K (Lys) | ε-amino | Yes | ~10.5 | -1 |
- **N-terminus** (amino): pKa ≈ 9
- **C-terminus** (carboxyl): pKa ≈ 2
### Peptide 2: KADFQ
| Position | Amino Acid | Side Chain (R) Group | Ionizable? | pKa (approx) | Charge at pH 12 |
|----------|------------|----------------------------------|------------|--------------|-----------------|
| 1 | K (Lys) | ε-amino | Yes | ~10.5 | -1 |
| 2 | A (Ala) | Methyl (not ionizable) | No | - | |
| 3 | D (Asp) | β-carboxyl | Yes | ~3.9 | -1 |
| 4 | F (Phe) | Benzyl (not ionizable) | No | - | |
| 5 | Q (Gln) | Amide (not ionizable) | No | - | |
- **N-terminus** (amino): pKa ≈ 9
- **C-terminus** (carboxyl): pKa ≈ 2
---
## 2. Assign Charges at pH 12
**Key rules:**
- At pH **above** pKa, group is **deprotonated**.
- At pH **below** pKa, group is **protonated**.
### Common pKa Values
- N-term (amino): ~9
- C-term (carboxyl): ~2
- Asp/Glu side chain: ~3.9/4.2
- Lys: ~10.5
- Arg: ~12.5
### WLARK
- **N-term**: pH 12 > 9 ⇒ deprotonated ⇒ **** (NH₂, neutral)
- **C-term**: pH 12 > 2 ⇒ deprotonated ⇒ **-1** (COO⁻)
- **R (Arg)**: pH 12 < 12.5 ⇒ still **protonated** ⇒ **+1**
- **K (Lys)**: pH 12 > 10.5 ⇒ deprotonated ⇒ ****
- No other ionizable groups.
**Sum:**
- N-term:
- C-term: -1
- R: +1
- K:
**Net charge:**
\[
+ (-1) + 1 + = \boxed{}
\]
### KADFQ
- **N-term**: pH 12 > 9 ⇒ deprotonated ⇒ **** (NH₂)
- **C-term**: pH 12 > 2 ⇒ deprotonated ⇒ **-1** (COO⁻)
- **K (Lys)**: pH 12 > 10.5 ⇒ deprotonated ⇒ ****
- **D (Asp)**: pH 12 > 3.9 ⇒ deprotonated ⇒ **-1**
**Sum:**
- N-term:
- C-term: -1
- K:
- D: -1
**Net charge:**
\[
+ (-1) + + (-1) = \boxed{-2}
\]
---
## 3. Summary Table
| Peptide | Net Charge at pH 12 |
|---------|---------------------|
| WLARK | |
| KADFQ | -2 |
---
## 4. Drawing Structures
- Draw the backbone for each peptide (N-term left, C-term right).
- Show all sidechains and their charges (as above).
- For reference, see your course’s **Chapter 4, slide 4**.
*(No images included per your instructions; upload hand-drawn images to Canvas.)*
---
## 5. Final Answers
- **WLARK:** Net charge at pH 12 = ****
- **KADFQ:** Net charge at pH 12 = **-2**
---
### Relevant Concepts Used
- **Ionization states** depend on pKa and pH (Chapter 2, 3, 4).
- **Peptide structure** and how to draw (Chapter 4, slide 4).
- **Charge calculation** for each group at specified pH.
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