Protein 3D Structure - Chapter 4 Flashcards
What are the four levels of protein structure?
Primary, secondary, tertiary, and quaternary structures.
What is the primary structure of a protein?
The sequence of amino acids in a polypeptide chain.
What type of bond forms the primary structure of proteins?
Each amino acid is linked to the next via peptide bonds.
Describe the secondary structure of proteins.
spatial arrangement of amino acid residues near one another in the linear sequence; alpha-helix or beta strand
Describe the structure of alpha-helices and beta sheets.
Alpha-helices are coiled and beta-sheets are flat, pleated structures.
What is the tertiary structure of a protein?
spatial arrangement of amino acid residues that are far from each other in the linear sequence, as well as the pattern of disulfide bonds
List some interactions that stabilize tertiary protein structure.
Hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges.
What is the quaternary structure?
The assembly of multiple polypeptide chains into a functional protein complex.
What is an amino acid’s general structure?
An amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain) attached to a central carbon atom.
What are essential amino acids? List them.
Amino acids that cannot be synthesized by the body and must be obtained from the diet.
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
What is a zwitterion?
An amino acid in its neutral form where the amino group is positively charged and the carboxyl group is negatively charged.
What is a peptide bond?
A covalent bond formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water.
How are protein structures experimentally determined?
Techniques include X-ray crystallography, NMR spectroscopy, and cryo-electron microscopy.
Describe the role of chaperones in protein folding?
They assist in the correct folding of proteins and prevent misfolding and aggregation.
What are post-translational modifications? Where do they occur?
Chemical modifications made to proteins after translation, such as phosphorylation, glycosylation, and ubiquitination. They occur in the endoplasmic reticulum and the Golgi apparatus.
Describe the impact of mutations on protein structure.
Mutations can alter the amino acid sequence, potentially disrupting protein folding and function. This can lead to unexpected phenotypic differences (including disease).
What is a domain in a protein?
A distinct functional and structural unit within a protein, often responsible for a specific function.
Explain the role of disulfide bridges in proteins.
Covalent bonds between the sulfur atoms of two cysteine residues that stabilize the protein’s tertiary and quaternary structures.
What is denaturation of a protein?
The process by which a protein loses its native structure due to external stress or conditions, leading to loss of function.
Why does the biosynthesis of peptide bonds require an input of free energy?
The formation of a dipeptide from two amino acids is accompanied by the loss of a water molecule. The equilibrium of this reaction is in thne direction of hydrolysis, rather than synthesis.
