Proteins Flashcards
What are the levels of organisation of proteins? (3)
o All are made from a sequence of amino acids
o Although proteins are diverse polymers, they are all still made from the same 20 amino acids
o Polymers of amino acids (monomers, building blocks)—> polypeptides
What is the primary structure of a protein? (3)
• Primary structure:
o R group side chain
o Can carry a charge
o Determines how the polypeptide will fold
What is the secondary structure of a protein?
o Polypeptide chains twisting due to H bonds in the backbone (can be helix or pleating)
What is the tertiary structure of a protein? (2)
• Tertiary structure: represents the overall shape of the polypeptides
o Interaction between R groups
o Interactions reinforced by disulphide bridges
What is the quaternary structure of a protein?
Quaternary structure: represents the overall protein structure
o Results from the aggregation of the polypeptide subunits
What does the primary structure of proteins consist of? (2)
> The simplest level of protein structure, primary structure, is simply the sequence of amino acids in a polypeptide chain
Each chain has its own set of amino acids, assembled in a particular order
How is the sequence of a protein determined?
> The sequence of a protein is determined by the DNA of the gene that encodes the
protein (or that encodes a portion of the protein, for multi-subunit proteins).
What is the effect of the change in the gene’s DNA? (2)
> A change in the gene’s DNA sequence may lead to a change in the amino acid sequence of the protein.
Even changing just one amino acid in a protein’s sequence can affect the protein’s overall structure and function.
What does the secondary structure of a protein refer to?
> Refers to local folded structures that form within a polypeptide due to interactions between atoms of the backbone. (The backbone just refers to the polypeptide chain apart from the R groups – so all we mean here is that secondary structure does not involve R group atoms.)
What are the most common types of secondary structures? (2)
> The most common types of secondary structures are the α helix and the β
pleated sheet.
Both structures are held in shape by hydrogen bonds, which form between
the carbonyl O of one amino acid and the amino H of another
> The overall three-dimensional structure of a ______ is called its tertiary structure, due to interactions between the ___ _____ of the amino acids that make up the protein.
polypeptide
R groups
> R group interactions that contribute to tertiary structure include: (4)
- hydrogen bonding
- ionic bonding
- dipole-dipole interactions
- London dispersion forces
- R groups with like charges ____ one another, while those with opposite charges can form
an ____ _____. - Similarly, polar R groups can form _____ bonds and other ____-_____ interactions.
repel
ionic bond
hydrogen
dipole-dipole
What is the important of the hydrophobic interactions in the tertiary structure?
- Also important to tertiary structure are hydrophobic interactions, in which amino acids with nonpolar, hydrophobic R groups cluster together on the inside of the protein, leaving hydrophilic amino acids on the outside to interact with surrounding water molecules.
Finally, there’s one special type of covalent bond that can contribute to tertiary structure:
the disulfide bond. What is the disulfide bond?
Disulfide bonds, covalent linkages between the sulfur-containing side chains of cysteines, are much stronger than the other types of bonds that contribute to tertiary structure—> They act like molecular “safety pins,” keeping parts of the polypeptide firmly attached to one another)
