Amino acids

What is an amino acid theorized to have been created from?

Nature acting on atmospheric gases

What do amino acids link together to form?

Polypeptides (≤50) and proteins (≥50)

What functional groups do amino acids possess?

An amine group (basic) and a carboxylic acid group (acidic)

How many amino acids are used in protein synthesis?

20 (known as the "magic 20")

Why are they called α-amino acids?

Both the amine and acid group are attached to the α-carbon

What is attached to the α-carbon in an amino acid?

A hydrogen atom and a unique R-group

What determines the unique identity of an amino acid?

The R-group

How are amino acids best classified?

According to the nature of their R-group side chain

What are the four R-group classifications?

Non-polar, polar, acidic, basic

What functional groups are most distinguishing in amino acids?

α-amino and α-carboxylic acid groups

What is a zwitterion?

A charged amino acid that simultaneously exists as both a cation and anion

Why are amino acids water soluble?

Because they are charged (zwitterions)

What does it mean for an amino acid to be amphoteric?

They can act as both an acid and a base

How do amino acids behave in acidic solutions?

They are positively charged

How do amino acids behave in basic solutions?

They are negatively charged

Why are amino acids considered pseudo-buffers?

They resist dramatic pH changes due to their amphoteric nature

What role do amino acids play in the body?

They help regulate pH

What forms when amino acids link together?

Polypeptides and proteins

When is a chain officially designated a protein?

When it contains 50 or more amino acids

What are the size ranges of proteins?

From 35,000 g/mol to 55,000,000 g/mol

What are fibrous proteins?

Proteins that give structure to organs, skin, muscle, tendons, and bone

What are globular proteins?

Proteins that act as transporters and biological catalysts (enzymes)

What determines a protein's function?

Its structure

What are the four levels of protein structure?

Primary, secondary, tertiary, quaternary

What is the primary structure of a protein?

The sequence of amino acids

What is another name for primary structure?

Foundational structure

How is primary structure visually represented?

A string of beads (each bead = amino acid)

Which groups are typically placed at the start and end of the sequence?

Amine group at start, acid group at end

What is a disulfide bridge?

A covalent bond between sulfurs from different cysteine amino acids

What was the first protein structure discovered?

Bovine insulin by Frederick Sanger in 1953

What forms secondary structure?

Hydrogen bonding

What are two common types of secondary structure?

Pleated sheet and β-helix

What causes tertiary structure?

Combination of all bonding and interactions between side chains

What forces influence tertiary structure?

Hydrogen bonding, electrostatic interactions, disulfide bridges, hydrophobic and hydrophilic interactions

Where do non-polar side chains go in tertiary structure?

To the protein's interior

Where do polar and ionic side chains go?

On the outside in aqueous environments

What causes protein folding and contortion?

Aqueous environment trying to hide non-polar parts

What is quaternary structure?

Interaction between two or more protein chains (subunits)

What are the protein chains in quaternary structure called?

Subunits

What is hemoglobin an example of?

Quaternary protein structure

How many protein chains does hemoglobin have?

Four: 2 α-chains (141 AA’s) and 2 β-chains (146 AA’s)

What does each hemoglobin chain contain?

One heme molecule

What does heme do?

Binds iron to histidine and oxygen simultaneously

What is hemoglobin's role?

Carries oxygen to cells and CO2 back to lungs

How is myoglobin different from hemoglobin?

One protein strand (153 AA’s) and one heme; has only tertiary structure

What is denaturation?

Loss of all protein structure except primary

What causes denaturation?

Extreme heat, high acid or base

What happens to protein function after denaturation?

It is destroyed

What is an everyday example of denaturation?

Frying an egg

What is putrefaction?

Post-mortem protein, nucleic acid, carbohydrate, and lipid breakdown

What are fibrous proteins made of?

Repeating amino acid units

What makes fibrous proteins stable?

More cross-linking and hydrophobic side chain aggregation

Why are fibrous proteins less water soluble?

Hydrophobic side chains protrude from the molecule

How long do fibrous proteins persist after death?

Several months