Topic 1.6 - Proteins Flashcards
What are the basic monomers that make up proteins?
Amino acids
What is an amino acid made up of?
- Central carbon (to which it is all attached to)
- Amino group (NH2)
- Carboxyl group (COOH)
- Hydrogen atom (H)
- R (side group) = a variety of different chemical groups
What is the primary structure of proteins?
- The sequence in which the amino acids are ordered in to form a polypeptide
What are amino acids joined by?
Peptide bonds
How are peptide bonds formed?
Through condensation reactions, where water is produced as a product.
- The -OH comes from the carboxyl group of one amino acid and the other -H comes from the amino group of another amino acid when they bond together.
How many amino acids naturally occur?
20
What is the secondary structure of proteins?
Where the sequence bends/folds to form a 3D shape
What does the primary protein structure look like? And what bond joined them?
A long chain of amino acids (a polypeptide) joined by peptide bonds
What two types are there of secondary structure?
- Alpha helix
- Beta sheet
What bonds form/hold together the secondary structure of proteins?
Hydrogen bonds
What is the tertiary structure?
Where most proteins form their final, specific shape.
The 3rd protein structure is further folded and twisted to give it a more complex 3D structure
If it is not folded correctly, it cannot perform its intended biological activity.
What bonds or interactions form/hold the tertiary structure?
- Ionic bonds
- Hydrogen bonds
- Disulfide bridges (covalent so are stronger than other bonds)
- Hydrophilic/hydrophobic interactions
Give an example of a protein that has a quaternary structure.
- Haemoglobin
What is the quaternary structure of proteins?
Where multiple polypeptide chains can be joined together, and sometimes prosthetic groups can be added too (non-protein, e.g. HAEM group, iron ion in haemoglobin is a prosthetic group)
What enzymes are needed in protein digestion and why?
Endopeptidases - break polypeptide into smaller chains
Exopeptidases - remove end terminal amino acids
Dipeptidases - hydrolyse dipeptides into amino acids
What makes a dipeptide?
2 amino acids bonded together with a peptide bond
What makes a polypeptide?
Multiple amino acids joined together through polymerisation (a series of condensation reactions)
What is the test for proteins?
Biuret test
How would you conduct a test for proteins?
- Add 2cm cubed of sample and 2cm cubed (equal amounts) of sodium hydroxide into a test tube
- Add a few drops of very dilute (0.05%) copper (||) sulphate and mix gently
- The presence of a peptide bond will be indicated when the solution turns from blue to purple
What does the biuret test detect?
Peptide bonds
How are the weak hydrogen bonds form?
The slightly positive charge on the hydrogen and the slightly negative charge of the oxygen are attracted to each other
What does the primary structure of a protein determine?
It’s shape and function
What changes in the structure of different amino acids?
The R group changes, but all amino acids have the same general structure
What is a glycoprotein?
When a carbohydrate combines with a protein
What is formed when a lipid and protein combine?
A lypoprotein
What is a fibrous protein?
A protein with a elongated shape forming a rod or wire like shape, that are usually inert structural or storage proteins
What are globular proteins?
Proteins formed by compact amino acid chains, then folded into intricate chains that resemble spheres
They usually have metabolic functions.
Give an example of a fibrous protein
Collagen, Keratin, Elastin
Are fibrous proteins soluble or insoluble in water?
Insoluble
Are globular proteins soluble in water?
Soluble
What do fibrous proteins provide?
Structural support for cells and tissues
Give an examples of a globular protein and what it does:
Haemoglobin - transports oxygen around the body
Immunoglobulins - antibodies which white blood cells produce to attack pathogens
Many enzymes - hydrolyse/catalyse in metabolism to make up/break down nutrients we need
