The levels of structural organization of proteins.

What is the name for the variable region of the 20 amino acids?

• Carboxil group

• Amino group

• R-group

• Alpha carbon

Answer explanation

Every amino acid contains a central (α) C, surrounded by a H, an R group (variable group), an amino group, and a carboxyl group.

What functional group must be present in the R group of an acidic (-) amino acid?

• Carboxyl group

• Amino group

• Hydroxyl group

• Carbonyl group

• Sulfahydryl group

Answer explanation

Carboxyl groups behave asacids because they dissociate to release H+ ions.  The amino acids aspartic acid & glutamic acids have a carboxyl group in their group, so they are acidic aminoacids.

What functional group must be present in the R group of a basic (+) amino acid?

• Carboxyl group

• Amino group

• Hydroxyl group

• Carbonyl group

• Sulfahydryl group

Answer explanation

Bases either release OH-     OR     accept H+ ions when dissolved in aqueous solution. In both cases, bases reduce the H+: OH- ratio  to less than 1.0 

The amino group in an amino acid’s R group acts as a base, accepting a proton.  The amino acids arginine and lysine act as bases

What functional group is most often present in a neutral, yet hydrophilic, amino acid’s R group?

• Carboxyl group

• Amino group

• Hydroxyl group

• Carbonyl group

• Sulfahydryl group

What functional group in cysteines allows them to form strong covalent bonds that stabilize a protein’s tertiary structure?

• Carboxyl group

• Amino group

• Hydroxyl group

• Carbonyl group

• Sulfahydryl group

Answer explanation

Disulfide bridge

(S-S) between cysteine amino acids

How do alpha helices and Beta pleated sheets compare?

• They are both forms of protein secondary structure

• They are both formed due to formation of H bonds between N-H and C=O groups along the backbon of polipeptide chain

• The beta sheets are more rigid and strong because they form more abundant H bonds

• All of the avobe

Answer explanation

Haemoglobin is a globular protein with quaternary structure.

Fig 1.1 is a diagram of the haemoglobin molecule.

Determine the name of the labelled X ?

• haem

• amino group

• carboxyl group

• radical

Answer explanation

Hemoglobin comprises four subunits, each having one polypeptide chain and one heme group. All hemoglobins carry the same prosthetic heme group.

Which arrow points to a peptide bond?

• a

• b

• c

• d

Answer explanation

Which amino acids tend to cluster in the center of an aqueous protein, but to be located on the outer edges of proteins located within a cell membrane’s lipid bilayer?

• Acidic amino acids

• Basic amino acids

• Disulfide bridge forming cycteines and methionones

• Polar, hydrophilic amino acids

• Nonpolar, hydrophobic amino acids

R group interactions control which levels of protein folding?

• Ptimary structure and secondary structure

• secondary structure only

• Tetiary structure and quaternary structure

• Tetiary structure only

• quaternary structure only

Answer explanation

R group interactions control tertiary & Quarternary structure