Topic 1.3 - Proteins Flashcards
What is an amino acid?
The monomer from which dipeptides, polypeptides and proteins are made
How many different amino acids are there?
20
What are amino acids made up of?
Amine group (NH2) and a carboxyl group (COOH) which are attached to the same C. Also an R group
What does amphoteric mean?
Molecules that can ionise as both an acid and a base
What is a zwitterion?
An ion with both positive and negative charge
What’s the difference between a polar molecule and a zwitterion?
A polar molecule doesnt have a formal charge, some atoms just pull harder on electrons than others thus creating a slight charge
What is a dipeptide?
A molecule consisting of two amino acids joined by a single peptide bond
What is a peptide bond?
A covalent bond that forms between the amine group of one amino acid and the carboxyl group of another
What is a condensation reaction?
A reaction by which two molecules are joined together to make a larger, more complex molecule with the loss of water
Explain the formation of a dipeptide
The OH of one carboxyl group and the H of another amine group join together to form water. A peptide bond forms between the C and the N, joining the two amino acids together
What test is used to test for proteins?
The biuret test
Explain the biuret test
Add an equal amount of sodium hydroxide solution to the test solution. Add a few drops of 0.5% copper sulfate solution. if it turns purple then there is protein present.
What are some of the important functions of protein?
Structural component, antibody/immunoglobins enzymes and hormones
What is the primary structure of proteins?
The order of the amino acids
How is the type of amino acid determined?
By the order of the bases on the DNA
How does changing one amino acid affect the protein?
It changes the properties of the entire protein
What is a polypeptide chain?
Amino acids linked together by peptide bonds in a chain
What is a protein?
Multiple polypeptide chains
What is the secondary structure?
When the polypeptide chain folds or twists
What is an alpha helix?
When the polypeptide twists into the shape of a helix
What is a beta pleated sheet?
When the polypeptide chain becomes folded
How is the secondary structure held together?
By hydrogen bonds between the OH and H of the amino acids
What is the tertiary structure?
When the polypeptide is further folded into a 3D structure which determines its function
What are the types of 3D structures?
Globular and fibrous proteins
In what structure do the R groups interact?
The tertiary structure
What bonds are found in the tertiary structure?
Hydrogen, disulfide, ionic bonds
What is the quarternary structure?
When two or more polypeptides are held together to form a molecule
What is a fibrous protein?
Long coiled polypeptide chains
What is an example of a fibrous protein?
Collagen
What is the structure of collagen and how does this contribute to its properties?
3 polypeptide chains held together by covalent and hydrogen bonds makes collagen resistant to denaturing + strong
What are the properties of fibrous proteins?
Insoluble, have structural roles like keratin (skin and teeth) and collagen
What are globular proteins?
Spherical proteins
What is an example of a globular protein?
Haemoglobin
What is the structure of globular proteins?
Polypeptide chains wind so hydrophillic amino acids are at the surface and hydrophobic amino acids are at the core
How does the structure of globular proteins help its function
Allows it to be soluble and therefore can be transported around the body
What is haemoglobin?
A respiratory pigment found in red blood cells
What is the structure of haemoglobin?
Four polypeptide chains (2 alpha chains and 2 beta chains) each bound to a haem group
What is a prosthetic group?
An attachment that isn’t made from the protein
What is in haem that allows it to carry oxygen?
Iron
How does haem bind with oxygen?
The Fe2+ binds with an O2 molecule which changes the shape and allows more O2 molecules to bind to the haem
When does haemoglobin have a high affinity for O2?
When there are high O2 conditions eg in the lungs
When does haemoglobin have a low affinity for O2?
When there are low O2 conditions eg in the tissues where respiration has consumed O2
What is transamination?
The conversion of one amino acid into another
What are the essential amino acids?
The amino acids that can only be obtained from diet
What is denaturation?
A change in shape of a protein that alters or destroys the ability of a protein to carry out its function
