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a. Write the structure of histidine when...

a. Write the structure of histidine when `pHlt1.82 and pHgt1.82.`
b. What is the `pH` range of neutral `A A` at the isoelectric point?
c. The `pH` range in cellular fluid is `6` to `7`. In what form (dipolar,cation, or anion) do the amino acids in each class predomiate in the cell?

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a.
b. All those amino acids with neutral `(R )` groups (e.g., hydrocarbon, alcohol, and amide) have `pl` in the same range `5.5-6.3.`
c. The amino acids are in the dipolar form because the cellular `pH` is very close to their `pI's`.
i. `pl` for acidic `A A's` are in the acidic range `(pH=6-7)`. they act as acids and exist mainly as anions.
ii. `pI` for basic A A's are in the basic range `(pH=6.7)`. they accept `H^(o+)` in the cell and exist mainly as cations.
iii. `pI` for very weakly acidic `A A'a` e.g., cysteine (with its `SH`) and tyrosine (with its phenolic `OH`), are in the acidic range `(pH=5-6)`. they are classified with neutral `A A's`
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