Biological Molecules - Proteins

Question 1

What is The General Structure of an Amino Acid?

Answer 1

• Carbon-Hydrogen-R Group : Variable R Group Can be Anything From Hydrogen, to Alcohol, to a More Complex Ring Structure - Makes it Specific
• NH2 : Amine/Amino Group on Left
• COOH : Carboxyl/Carboxylic Acid Group on Right

Question 2

Describe How to Test for Proteins in a Sample

Answer 2

Biuret Test Confirms Presence of Peptide Bonds:

1. Add Equal Volume of Sodium Hydroxide to Sample at Room Temperature.
2. Add Drops of Dilute Copper (II) Sulphate Solution and Swirl.
3. Step 1 & 2 Makes Biuret Agent.
4. Positive Result = Blue Solution Turns Purple/Violet

Question 3

How Many Amino Acids are There? How do They Differ from One Another?

Answer 3

20

Differ Only by Side of R Group (Polar or Non-Polar)

Question 4

How do Dipeptides and Polypeptides Form?

Answer 4

Condensation Reactions Between 2 or More Amino Acids Forms Dipeptides (-CONH-) and Eliminates Molecule of Water

Dipeptide : 2 Amino Acids
Polypeptide : 3 or More Amino Acids

Question 5

How Many Levels of Protein Structure are There?

Answer 5

4

Question 6

Define Primary Structure of a Protein

Answer 6

• Sequence, Number & Type of Amino Acids in Polypeptides

- Determined by Sequence of Codons of on mRNA

Question 7

Define Secondary Structure of a Protein

Answer 7

Hydrogen Bonds Form Between Amino Acids at Different Locations in Polypeptide Chain

Question 8

Describe The 2 Types of Secondary Protein Structure

Answer 8

Alpha Helix:

• All N-H Backbones Hydrogen Bond to All C=O Backbones
• Spiral Shape
• Hydrogen Bonds Parallel to Helical Axis

Beta-Pleated Sheet:

• Two or More Segments of Polypeptide Chain Line Up Next to Each Other Gradually Forming a Sheet-Like Structure
• N-H and C=O Groups Alternate from One Side to the Other

Question 9

Define The Tertiary Structure of a Protein and Name The Bonds Present

Answer 9

3D Structure Formed by Further Folding of Polypeptide

• Disulphide Bridges
• Ionic Bonds
• Hydrogen Bonds

Question 10

Describe Each Type of Bond in The Tertiary Structure of Proteins

Answer 10

• Disulphide Bridges : Strong Covalent S-S Bonds Between Molecules of the Amino Acid Cysteine
• Ionic Bonds : Relatively Strong Bond Between Charged R Groups (ph Changes Cause These Bonds to Break)
• Hydrogen Bonds : Numerous but Easily Broken

Question 11

Define Quarternary Structure of a Protein

Answer 11

• Functional Proteins May Consist of More Than One Polypeptide
• Precise 3D Structure Held Together by the Same Types of Bond as Tertiary Structure
• May Involve Addition of Prosthetic Groups (eg: Metal Ions or Phosphate Groups)