Proteins Flashcards
What is the monomer of proteins?
Amino acids.
What polymer do amino acids form?
Polypeptides.
How many amino acids occur naturally in proteins?
20/ about 100 identified- this is indirect evidence for evolution.
What is the amino group?
(-NH2) - The basic group from which the ‘amino’ part of the name is derived.
What is the carboxyl group?
(-COOH) - An acidic group which gives the ‘acid’ part of the name.
What is the R group?
A variety of different chemical groups. Each amino acid has a different R group. This is where amino acids differ from each other.
How do amino acids form dipeptides?
Condensation reactions. - The water is made by combining the -OH from the carboxyl group and then -H from the amino group of another amino acid.
What bond holds two amino acids together?
Peptide bond. (Between the carbon atom of one amino acid and the nitrogen atom of the other.)
How can a peptide bond be broken?
Hydrolysis - this gives two constituent amino acids.
What does a sequence of amino acids in a polypeptide chain dictate?
The primary structure of a protein.
What is the sequence of amino acids in a polypeptide chain determined by?
DNA.
What does the primary structure determine?
Shape and hence function of protein.
What charge does the hydrogen of the -NH group have?
Overall positive.
What charge does the O of the -C=O group have?
Overall negative.
What are the bonds between the -NH and the -C=O called? Are they weak or strong?
Hydrogen bonds, weak.
What do hydrogen bonds cause?
The polypeptide chain to be twisted into a 3-D shape, such as the coil known as an α-helix.
What is the tertiary structure maintained by?
A number of different bonds.
Which bonds are formed in the tertiary structure?
disulfide bridges, ionic bonds, hydrogen bonds.
How strong are disulfide bridges?
Fairly strong and not easily broken.
Where are the ionic bonds formed in a protein?
Between any carboxyl and amino groups that are not involved in forming peptide bonds. These are weaker than disulphide bonds and are easily broken by changes in pH.
What is important when it comes to the function of a protein?
The 3-D structure as it makes each protein distinctive and allows them to recognise, and be recognised, by other molecules. It can then interact with them in a specific way.
Describe the primary structure of a protein. What does it do?
Primary structure is a sequence of amino acids found in its polypeptide chains. This sequence determines properties and shape.
Describe the secondary structure of a protein. What does it do?
The secondary structure is the shape which the polypeptide chain forms as a result of hydrogen bonding. This is most often a spiral known as the α-helix, although other configurations occur.
Describe the tertiary structure of a protein. What does it do?
The tertiary structure is due to the bending and twisting of the polypeptide helix into a compact structure. All three types of bond contribute to the maintenance of the tertiary structure.
