Food Chem Exam 2: Proteins

What are proteins?

Highly complex polymers, comprised of 20 different amino acids

What is special about proteins? (compared to carbs, lipids, & H₂O)

Contain nitrogen

What are the two protein compositions?

Homoproteins and Conjugated proteins

What are the two protein shapes?

Globular and Fibrous

What are globular proteins?

Spherically shaped, resulting from folding or collapsing of polypeptide chain on itself

What are fibrous proteins?

Rod-shaped molecules containing twisted linear polypeptide chains

Why are proteins biologically important?

Enzyme catalysts, transfer, signaling, structural, antibodies

Why are proteins important in food?

Nutrition, enzyme activity, transporters, structural (gels, emulsions, foams)

How are amino acids differentiated?

R group, confers unique characteristics

What is contained in the structure of an amino acid?

Amino group (NH2), Carboxyl group (COOH), R group (20 different kinds)

How does the R group vary?

Size, composition, structure, polarity, charge, chemical reactivity

What happens to amino acids when in the presence of low pH?

Become protonated, gain H, (+) charge

What happens to amino acids when in the presence of high pH?

Become de-protonated, donate H, (-) charge

What quality determines protein structure, interactions, and functionality?

Hydrophobicity

If a side chain is polar, is it hydrophobic or hydrophilic?

Hydrophilic

If a side chain is non-polar, is it hydrophobic or hydrophilic?

Hydrophobic

What is a peptide bond?

Covalent bond between N of one amino acid and C of carboxyl group of another amino acid

What are the two types of secondary structures formed by proteins?

alpha helix and beta sheet

What stabilizes alpha helix and beta sheet?

Hydrogen bonds

How would you define the primary structure of proteins?

Sequence of amino acids

How would you define the secondary structure of proteins?

alpha helix or beta sheet

How would you define the tertiary structure of proteins?

Hydrophobicity of R groups fold chain

What are the three common types of tertiary protein structures?

Globular, disordered, fibrous

What are the six forces involved in the stability of protein structure?

Steric hindrance, van der waals, hydrogen bonds, electrostatic interaction, hydrophobic interaction, and covalent bonds

What is steric hindrance?

No two atoms or functional groups can occupy the same space

What are van der waals forces?

Interaction between temporary dipoles, attractive, very weak, short range

What are hydrogen bonds?

Strong interactions between molecular groups w/ strong dipoles, attractive, medium strength, short range

What are electrostatic interactions?

Interactions between charged groups, attractive to repulsive, weak to strong, short to long range

What are hydrophobic interactions?

Tendency for non polar groups to associate when surrounded by H2O, attractive, strong, long range

What are covalent bonds?

Sharing of electrons between atoms, attractive, strong, short range

_________ the isoelectric point, the amino acid is deprotonated, and the amino acid is ____________ charged

Above, negatively

What is the primary structure of proteins?

It is the sequence of amino acids of a protein

What are the primary and secondary structures of proteins stabilized by?

Primary stabilized by covalent bonds, secondary by hydrogen bonds

__________ ___________ drive the folding of globular proteins

Hydrophobic interactions

Denaturing of proteins does not affect which structure?

primary structure

Primary structures of proteins can break through ________ which break the _______ bonds

Hydrolysis; peptide

Irreversible denaturing of protein happens at the ___________

aggregation

What is an example of a heat-set protein gel?

Boiled egg