20 Amino Acids: Structures and Functions

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Questions and Answers

What is the abbreviation for Glycine?

  • Val, V
  • Ala, A
  • Gly, G (correct)
  • Pro, P

What type of amino acid is Glycine?

Small, Aliphatic, Non-polar

Which amino acid has a ring as the R-group?

  • Glutamate
  • Tryptophan
  • Phenylalanine (correct)
  • Alanine

How many carbon atoms are there in Valine?

<p>5</p> Signup and view all the answers

What is unique about the structure of Proline?

<p>Imino acid, kinks the peptide backbone</p> Signup and view all the answers

Which of the following amino acids is positively charged at physiologic pH?

<p>Lysine (D)</p> Signup and view all the answers

What is the functional group present in Aspartate?

<p>Carboxylic acid group</p> Signup and view all the answers

Which amino acid is the first added during translation?

<p>Methionine</p> Signup and view all the answers

Isoleucine has the same number of carbons as Leucine.

<p>True (A)</p> Signup and view all the answers

What type of amino acid is Tyrosine?

<p>Aromatic (B)</p> Signup and view all the answers

Which amino acid has an imidazole ring?

<p>Histidine</p> Signup and view all the answers

What type of bond can cysteine form?

<p>Disulfide bond</p> Signup and view all the answers

Flashcards

Glycine (Gly, G)

The smallest amino acid, with a simple structure and no chiral center. It is often found in tight turns in peptide chains due to its small size.

Alanine (Ala, A)

An amino acid with a simple methyl group attached to its carbon backbone. It is non-polar but does not exhibit hydrophobic properties.

Valine (Val, V)

A branched-chain amino acid with two methyl groups close to the peptide backbone, giving it a distinctive 'V' shape. Its bulkiness makes it hydrophobic.

Leucine (Leu, L)

A branched-chain amino acid similar to valine but with one extra carbon. Its branching at the gamma carbon contributes to its hydrophobic nature.

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Isoleucine (Ile, I)

An amino acid that shares the same carbon count as leucine but with a unique distribution of its methyl groups at the beta and gamma positions. It is hydrophobic.

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Phenylalanine (Phe, F)

An amino acid containing an aromatic ring, making it hydrophobic. It is structurally more complex than alanine.

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Tryptophan (Trp, W)

An amino acid featuring two aromatic rings. It is less hydrophobic than phenylalanine and contains an indole group, impacting its function in proteins.

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Tyrosine (Tyr, Y)

An amino acid that exhibits both hydrophobic and hydrophilic properties depending on its location within a protein. It also contains a hydroxyl (-OH) group, which influences its interactions.

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Histidine (His, H)

An amino acid containing an imidazole ring with two nitrogen atoms. It can act as a base due to its ability to accept a proton under physiological conditions.

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Lysine (Lys, K)

A basic amino acid that gains a positive charge at physiological pH. Its function is similar to histidine in terms of proton acceptance.

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Arginine (Arg, R)

A basic amino acid that carries a positive charge at physiological pH due to a guanidinium group. It is classified with histidine and lysine as a key basic amino acid.

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Aspartate (Asp, D)

An amino acid that acts as an acid. It carries a negative charge at physiological pH and serves as the conjugate base of aspartic acid, containing a four-carbon structure.

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Study Notes

Amino Acids Overview

  • Glycine (Gly, G): Smallest amino acid, achiral; important for fitting into tight turns in peptide chains without affecting hydrogen bonding with water.
  • Alanine (Ala, A): Comprises three carbons with a simple methyl group; does not exhibit hydrophobic properties despite being non-polar.
  • Valine (Val, V): Branched and bulky, hydrophobic with a distinctive "V" shape due to two methyl groups close to the peptide backbone.
  • Leucine (Leu, L): Similar to valine but with one additional carbon; branched at the gamma-carbon, contributing to its hydrophobic nature.
  • Isoleucine (Ile, I): Shares the same carbon count as leucine but with a unique methyl group distribution at the beta and gamma positions.

Aromatic Amino Acids

  • Phenylalanine (Phe, F): Contains an aromatic ring, making it hydrophobic similar to alanine but with increased complexity in structure.
  • Tryptophan (Trp, W): Features two aromatic rings; less hydrophobic than phenylalanine and includes an indole group, impacting its function in proteins.
  • Tyrosine (Tyr, Y): Possesses both hydrophobic and hydrophilic properties based on location within proteins, also contains a hydroxyl (-OH) group influencing its interactions.

Polar Amino Acids and Their Characteristics

  • Histidine (His, H): Contains an imidazole ring with two nitrogen atoms, capable of acting as a base due to protonation under physiological conditions.
  • Lysine (Lys, K): Basic amino acid that gains a positive charge at physiological pH; functions similarly to histidine in terms of proton acceptance.
  • Arginine (Arg, R): Basic and positively charged at physiological pH due to a guanidinium group; classified with histidine and lysine as key basic amino acids.

Acidic Amino Acids

  • Aspartate (Asp, D): Acts as an acid, carrying a negative charge at physiological pH; functions as the conjugate base of aspartic acid, containing a four-carbon structure.
  • Glutamate (Glu, E): Similar to aspartate but possesses five carbons; acts as an acid and negatively charged under physiological conditions, serving as the conjugate base of glutamic acid.

Additional Amino Acids

  • Asparagine (Asn, N): Polar amino acid functioning as an amide derivative of aspartate; includes a reactive sulfhydryl group, contributing to disulfide bond formation.
  • Methionine (Met, M): Non-polar amino acid with a thioether linkage; serves as the first amino acid introduced during the protein translation process.
  • Proline (Pro, P): Distinguished by its imino acid structure, causing kinks in peptide backbones; facilitates structural changes due to its unique bonding involving the alpha-amino group.

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