Proteins Flashcards
What are the monomers from which proteins are made called?
- Amino acids.
How many types of amino acids are there in all organisms?
- 20 amino acids
How is peptide bond formed?
- Peptide bond formed by condensation reaction between two amino acids.
What are dipeptides formed by?
- Dipeptides formed by condensation reaction of two amino acids.
- Peptide bond forms between OH of carboxyl group (on amino acid) and H of the amine group.
What are polypeptides formed by?
- Polypeptides are formed by the condensation of many amino acids.
- Peptide bond forms between OH (of carboxyl group) and H of the amine group.
What is the only part of the amino acid monomer that changes depending on the type of amino acid?
- The R (variable) group.
What are the components of an amino acid monomer, ie. the groups in an amino acid monomer?
- C and H atom in centre
- Amine group (NH₂)
- Carboxyl group (COOH)
- R- group (variable) side chain.
What type of protein contains one or more polypeptides?
- Functional protein may contain one or more polypeptides.
What is a hydrogen bond?
- Chemical bond often between slight negative oxygen atoms and slight positive hydrogen atoms (in water.) (oxygen = slightly negative as it has more electrons than hydrogen.)
() - extra info for clarification
What are the 4 levels of structure in proteins?
1.) Primary
2.) Secondary
3.) Tertiary
4.) Quaternary
Definition of primary structure of protein.
- The sequence of amino acids in a polypeptide chain.
Definition of secondary structure of a protein.
- Sequence of amino acids (ie. primary structure) are bent into alpha helix shapes or folded into beta pleated sheets (this is known as secondary structure.)
- Hydrogen bonds hold the secondary structure of protein.
Where are hydrogen bonds formed in the secondary structure of a protein?
- Hydrogen bonds form between the C=O groups (part of peptide bond of 1 amino acid) and the NH group (in the peptide bond of another amino acid.)
Definition of** tertiary structure** of proteins.
- The further folding of the secondary structure (forms the tertiary structure.)
- Folding forms a unique 3D shape.
- Tertiary structure held in place by ionic, hydrogen and disulphide bonds/ bridges.
What 3 types of bonds hold the tertiary structure of proteins in place?
- Ionic
- Hydrogen
- Disulphide
Where are ionic and disulphide bonds formed in the tertiary structure?
- Ionic/ disulphide bonds = formed between the R groups of different amino acids.
True or False
Disulphide bonds/ bridges are always present in the tertiary structure of a protein.
- False.
- Disulphide bridges only sometimes occur (when there is a sulphur in the R groups of the amino acids.)
Definition of **quarternary structure ** of protein.
- More than one polypeptide chain.
What happens to the tertiary structure of a protein when it is **denatured? **
- The bonds which hold the tertiary structure in place break (ionic/ hydrogen bonds break) and therefore the unique 3D shape is lost/ collapses back into the secondary structure.
Two conditions that would denature a protein:
1.) Too high temperature ( too much kinetic energy - of amino acids - can cause bonds to break.)
2.) Too high/ low a pH (ie. too many H+ or OH- : will lead to imbalance in charge which can break the bonds.)
What is the importance of the primary structure of a protein?
- Primary structure: sequence of amino acids.
- If sequence of amino acids changes (ie. from a mutation), it will cause the ionic/ hydrogen/ disulphide bonds to form in different locations (in the tertiary structure.)
- This will result in a different 3D shape.
What is the issue with the shape of a 3D protein (ie. enzymes/ carrier proteins) changing ?
- Enzymes: will have different shapes active site (will be non-functioning.)
- Carrier proteins: will have different shapes binding site (molecules = no longer complementary/ cannot be transported across membranes.)
What is the test for proteins?
- Add Biuret (solution) to sample.
- A positive result = Biuret goes from blue to purple.
Atoms involved in peptide bond?
– COHN
How does the charge of amino acids affect the protein?
- Change in charge of an amino acid may change the tertiary structure of the protein.
- Ie. Ionic bond only between positively-charged/ negatively-charged amino acids. Mutation (change in amino acid to another amino acid) may change the charge so the ionic bond will break.
