Biological Molecules - Proteins Flashcards
What are the monomers (the basic building blocks) of proteins?
amino acids
What is the basic structure of an amino acid?
- a carboxyl group -COOH
- an amine group -NH2
- R-group (the variable side group)

What’s a dipeptide?
two amino acids joined
What’s polypeptide?
Many amino acids joined together.
How many types of amino acids do living things use?
20
Describe a peptide bond
When amino acids join together (covalently) they release a water molecule (condensation reaction)
The bonds formed are call peptide bonds
Describe a protein primary structure
flat and straight

Describe a protein secondary struture
Hydrogen bonds form between amino acids (slightly polar) which causes the chain to coil and bend into:
alpha helix structure
or beta pleated sheet

Describe a tertiary protein structure
More bonds now operate - hydrogen and ionic bonding (and disulfide bonding bonds in the case of cysteine)
A 3-D structure now forms

Describe a quaternary protein structure
several polypeptide chains all held by bonds in a basic origami mess!

Name four functions of proteins
enzymes - break/synthesise large molecules
antibodies - immune response
transporting - sitting in cell membranes to help molecules and ions cross the membrane
structural - scaffolding jobs such as keratin (hair, fingernails), collagen (connective tissue)
Explain the Biuret test
Into a test tube with the food sample
Few drops of an alkaline solution - sodium hydroxide
Add copper (II) sulfate solutions
turns purple if present, or stays blue if not

What are conjugated proteins?
A protein to which another chemical group or molecule has been attached, typically with covalent bonds to conjugate (join) molecules to proteins.
Conjugated proteins can be attached to carbohydrates, lipids, organic complexes and stabilized metal ions.
E.g., haemoglobin and myoglobin are associated with an iron containing group
What are free proteins? (1pt)
Proteins that contain only amino acids (as opposed to conjugated proteins that contain other chemical groups)
What are globular proteins?
Spherical protein structures (eg enzymes)
Why are globular proteins useful? (2pts)
- They are soluble (due to hydrophilic tails) and are hence important in metabolic reactions.
- Being three dimensional, they have a critical role in binding to other substances
Describe the haemoglobin structure (4 pts)
- Haemoglobin transports oxygen so:
- it has four polypeptide chains
- each associating with an iron haem group
- oxygen attaches to the iron groups
(it’s also known as a conjugated protein)
Describe fibrous proteins
Long protein chains
There are polypeptide chains that cross link creating more strength
Insoluble
Examples: skin, tendons, bones, cartilage, blood vessel walls
Describe collagen
- Fibrous protein
- Three polypeptide chains wind around each other creating a rope-like strand held by hydrogen bonds
- The strands are also staggered creating more strength