1.3 Proteins Flashcards
What are proteins made up of?
- Hydrogen, oxygen + carbon.
- Also sometimes nitrogen + sulphur.
What are amino acids?
- Monomers from which polymers (peptides + proteins) are built.
How many AAs join to form a protein?
- 100s or 1000s.
What is a polypeptide?
- Can be used interchangeably w protein.
- When polypeptide is around 50 AA residues long becomes protein.
What is the general formula for amino acids?
- NH2 - CHR - COOH.
What are the 2 functional groups of AAs?
- Amino group (-NH2).
- Carboxyl group (-COOH).
What is an amphoteric molecule?
- One that can ionise as both an acid + base like AAs.
What is a Zwitterion?
- Ion w both +ive and -ive charges.
What is the displayed formula for an AA?
. R O
| //
H2N — C — C
| \
H OH
How do AAs combine?
- Enzyme present.
- Condensation reaction to form dipeptide.
What is a peptide bond?
- Covalent bond between amino group of one AA + carboxyl group of another AA.
- Each peptide bond formed by condensation reaction.
How do we test for the presence of proteins?
- Biuret test –> gives purple colour in presence of peptide bonds.
How do we carry out a biuret test?
- Equal quantity of NaOH solution + test solution.
- Then add a few drop of Copper(II) sulphate solution.
- Gentle mixing should produce purple colour.
What are the four levels of protein structure?
- Primary.
- Secondary.
- Tertiary.
- Quaternary.
What is the primary structure of a protein?
- AA sequence.
- AAs held together by peptide bonds.
- Order of AAs in polypeptide chain controlled by DNA of cell producing it.
What is the secondary structure of a protein?
- Forms immediately after its formation when PP chain becomes twisted and/or folded.
- Alpha helix.
- Beta pleated sheet.
- Permanent + held together by hydrogen bonds.
What is the tertiary structure of a protein?
- Compact unique structure when molecules is further folded + held in 3D shape.
- 3 types of bond.
- Van der Waals forces.
What are Van der Waals forces (bonds)?
- 2 or more atoms very close.
What are the 3 types of bond in tertiary structures of proteins?
- Ionic bonds.
- Hydrogen bonds.
- Disulphide bonds.
What are ionic bonds in tertiary structure of proteins?
- Electrostatic interaction between oppositely charged ions.
- May be broken by changing pH.
What are hydrogen bonds in tertiary structure of proteins?
- Hydrogen atom is shared by two other atoms.
What are disulphide bonds in tertiary structure of proteins?
- Strong covalent bond formed by oxidation of -SH groups of 2 cysteine side chains.
What is the quaternary structure of a protein?
- 2 or more PP join together, forms complex, biologically active molecule.
What are the 2 diff types of protein?
- Fibrous.
- Globular.
What is the shape of fibrous proteins?
- Contain long, coiled PP chains.
- Shaped like rod or wire.
What is an example of a fibrous protein and what is its function?
- Collagen, component of bones + tendons.
- Structural function.
What is the structure of collagen?
- Triple helix - held together by covalent + hydrogen bonds.
Why is the structure of collagen beneficial?
- Resistant to denaturing.
- Provides strength.
What AAs is collagen made up of?
- Every 3rd AA is glycine (smallest AA) and other 2 mostly proline + hydroxyproline.
What is the shape of globular proteins?
- More spherical.
- PP chains wound so that hydrophilic AAs on outside + hydrophobic AAs on outside.
What is an example of a Globular protein?
- Haemoglobin.
What is the function of haemoglobin?
- Respiratory pigment found in RBCs.
- Oxygen binds to iron in haem group.
What is the structure of haemoglobin?
- 4 PP chains, each bound to iron-containing haem group.
How does oxygen bind to haemoglobin?
- O2 binds to 1st haem group, causes change in shape of haemoglobin molecule.
- Makes easier for more O2 to bind.
What is each subunit of haemoglobin made up of?
- Conjugated protein consisting of:
- Protein chain (globin) +
- Prosthetic group (haem).
What is a prosthetic group?
- ‘Helper’ molecule, allows other molecules to be biologically active.
What is the meaning of denaturation?
- Change in shape of protein that alters or destroys ability of protein to carry out function.
- Change results from breakage of bonds holding shape of protein together.
