Protiens Flashcards
What elements are amino acids built out of?
Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulphur.
What is the name given to the sub-units that proteins are constructed out of?
Amino acids
What does the structure of an amino acid consist of?
An amino group (NH2), Carboxyl acid (COOH) and a variable “R” group (facing upwards) bonded to a central carbon with a hydrogen bonded to it.
What are these variations due to?
Changes in the composition of the R(radical) side group
What are the three simplest amino acids?
- ) Glycine where R=H
- ) Alanine where R=(C-H3)
- ) Valine where R=(C3-H7)
What happens when an amino acid dissolves in water and what is the importance of this property?
It becomes a dipole (amide=-ve and Carboxyl=+ve)
Because of this proteins and amino acids act as pH buffers in the cytoplasm of cells which keeps enzymes stable by maintaining a pH close to 7.0
How are dipeptides formed?
Through a condensation reaction between the Carboxyl group of one amino acid and the amide group of another to create a peptide bond in which Nitrogen and Carbon are bonded together. These dipeptides then undergo further condensation reactions to create linear polypeptide chain which is the basis of all protiens.
What is the primary structure of a polypeptide?
This refers to the the formation of a linear chain of amino acids.
How does primary structure vary?
In the length of the chain and the sequence of amino acids.
Why is there an almost infinite variety of protiens?
Because the are normally 2-300 amino acids in the polypeptide chain and so the number of possible polypeptide sequences approaches infinity.
What is secondary structure?
This involves the folding of a single polypeptide chain due to the formation of hydrogen bonds.
What is the name for proteins that remain at the secondary level and what are their identifying feaures?
These are called secondary proteins and are identified by two features;
1-involve hydrogen bonding only
2-No “R” group bonding occurs.
What are the two most common types of secondary protein?
The alpha helix and Beta pleated sheet.
Describe the structure of an alpha helix.
This type of protein is held in in a anticlockwise helix by hydrogen bonds which form between the amide and carboxylic groups of the amino acids in the polypeptide chain.
How many types of amino acid are there?
22
Describe the structure of a beta-pleated sheet.
In this type of protein at least three polypeptide chains are held together by hydrogen bonds, creating a pleated structure which although strong is more elastic than alpha helices.
Give an example of an alpha helix.
Keratin which forms hair, nails, skin, fur, claws and feathers.
Explain the term tertiary structure.
This refers to the complex folding of a secondary protein to create a tertiary protein with a unique 3D shape.
What is ultimately responsible for the 3D structure of the tertiary protein?
The sequence of amino acids in the primary chain which in turn controls the “R” group sequence and therefore the bonds that occur and the folds that created and the final 3D shape of the molecule.
What determines the function of a tertiary protein?
As most tertiary proteins are enzymes their 3D shape dictates what substrates they interact with and therefore their function.
What are the three primary types of bonding in a tertiary protein? Strongest to weakest.
Disulphide bridges
Ionic bonds
Hydrogen bonds
What other types of forces are present?
Van der Walls forces
Covalent bonds
And many other repulsion forces.
What is the advantage of a tertiary protein being so compact?
They are able to move easily and as such can take part in chemical reactions.
What are the two biggest groups of tertiary proteins
Enzymes and hormones.
Outline Quaternary structure.
Tis refers to the bonding of two or more tertiary proteins together to form macro-molecules such as heamaglobin.
Describe the structure of heamaglobin.
It has a mass of 68000 and consists of four tertiary molecules two alpha and two beta subunits. In the centre of each those subunits there is a a prosthetic iron group called the heam group
Describe the structure of the heam group.
This consists of one iron molecule which is held in place by four nitrogen atoms.
What are the four main protein functions.
1-Regulation of metabolic processes.
2-Communication
3-Structural functions
4-pH buffers.
How do proteins help regulate metabolic processes?
Enzymes in the body are used to speed up chemical processes.
How are proteins involved in communication?
Many hormones are proteins. These molecules act as chemical messenger molecules allowing parts of the body to communicate with each other e.g insulin (two alpha helices).
What are the structural functions of proteins?
Secondary fibrous proteins are used to build structures in the body such as tendons and ligaments.
How do enzymes act as pH buffers?
As amino acids and proteins are dipoles they help to maintain pH close to 7.0 by removing both excess +ve and -ve charge. This allows intracellular enzymes to work at their optimum pH.
Give an example of a beta pleated sheet.
Fibroin which is found in a spiders web.
