BS1030 Topic 1 Lecture 2 Protein Structure 2 – Amino Acids

Give examples of the functional roles of proteins in living systems.

Structural support, enzymes, signaling, transport, immune defense, and movement.

What determines a protein's unique structure and function?

The DNA sequence of its gene.

What are the building blocks of proteins?

Amino acids.

How do proteins form from amino acids?

They fold spontaneously from linear chains of amino acids.

Are amino acids water soluble?

Yes, most amino acids are water soluble and electrically charged at physiological pH.

What are amino acid isomers?

Enantiomers (D and L forms) based on the geometry around the asymmetric carbon atom.

Which amino acid isomer is found in life?

The L-isomer.

How many amino acids are common to all living organisms?

20.

What are the two standard codes used to represent amino acids?

Three-letter and one-letter codes.

What part of the amino acid determines its properties?

The side chain (R group).

How can amino acids be classified based on side chains?

Polar charged, polar uncharged, or nonpolar.

What does "polar" mean in chemistry?

Unequal distribution of charge within a molecule, creating partial or full positive and negative charges.

Why does polarity matter for proteins?

Most proteins exist in aqueous environments and must interact with water.

What are hydrophilic side chains?

Charged or polar side chains that can interact with water ("water-loving").

What are hydrophobic side chains?

Nonpolar side chains that avoid water ("water-hating").

Why do nonpolar side chains cluster inside folded proteins?

To reduce contact with water, increasing entropy and stabilising folding.

What are polar charged side chains?

Side chains that carry full positive or negative charges at physiological pH and interact strongly with water.

What are polar uncharged side chains?

Side chains with partial charges that can form hydrogen bonds with water.

What are nonpolar side chains?

Uncharged side chains that cannot bond with water; they are hydrophobic.

What are the three main groups of amino acids by polarity?

Polar charged (hydrophilic), polar uncharged (hydrophilic), and nonpolar (hydrophobic).

Which eight amino acids should you be able to draw at pH 7?

Glycine, Alanine, Serine, Tyrosine, Glutamate (Glutamic acid), Glutamine, Lysine, and Cysteine.

Which amino acid has no L or D isomer?

Glycine (side chain is H).

Which amino acids can be phosphorylated on the side chain OH group?

Serine, Tyrosine, and Threonine.

Why is phosphorylation important?

It plays a key role in cell signaling.

Which amino acid acts as a neurotransmitter?

Glutamate.

Which amino acid has a similar structure to glutamate but with an amide group?

Glutamine.

Which amino acid is important in histone proteins for gene regulation?

Lysine.

Which amino acid can form disulphide bridges?

Cysteine.

Why are disulphide bridges important?

They stabilise the tertiary and quaternary structure of proteins.

Which amino acids are structural isomers?

Leucine and isoleucine.

Which amino acid group absorbs UV light at 270-280 nm?

Aromatic amino acids (e.g., tyrosine, tryptophan, phenylalanine).

Why do aromatic R groups absorb UV light?

Due to conjugated ring structures; this property is used to measure protein concentration via spectrophotometry.

What property distinguishes cysteine from other polar uncharged amino acids?

It can form covalent disulphide bonds.

Which amino acid's side chain joins onto the α-amino group?

Proline, forming a "kink" in the backbone.

Where are hydrophilic amino acids found in cytosolic proteins?

On the outside surface.

Where are hydrophobic amino acids found in cytosolic proteins?

On the inside, away from water.

Where would hydrophobic amino acids be found in membrane proteins?

In the transmembrane regions interacting with lipid tails.

What are the "special" amino acids mentioned in the lecture?

Glycine, Cysteine, and Proline.

What are the properties of glycine?

Small, flexible, no L or D form, allows tight turns in protein structure.

What are the properties of cysteine?

Can form disulphide bonds, contributes to structural stability.

What are the properties of proline?

Side chain links back to amino group, introduces kinks or turns in proteins.

What determines whether an amino acid is on the inside or outside of a folded protein?

The hydrophobic or hydrophilic nature of its side chain.

At physiological pH, what happens to amino acids?

They exist as zwitterions - both the amino and carboxyl groups are charged.