10 Questions
What is the function of a chaperone in the protein cycle after translation?
Assisting in the folding of the polypeptide into its native conformation
What process involves attaching several ubiquitin molecules to a protein?
Degradation
What can trigger an enzyme to adopt a catalytically active conformation?
Binding an allosteric effector
Which event is most likely to occur during the processing phase of the protein cycle?
Formation of disulfide bonds
What happens during the degradation phase of the protein cycle?
Degradation to amino acids for new protein synthesis
What determines the tertiary structure of a protein?
Sequence of amino acids in the chain
What is the primary factor in favoring the formation of alpha helices?
DELIMA amino acids
Which type of protein has a structure that is nearly entirely a-helical?
Keratin
How is a beta-pleated sheet stabilized?
H-bonding between amide N's and carbonyl C's
What defines the secondary structure of a protein?
Sequence of amino acids forming intramolecular bonds
Study Notes
Protein Cycle
- Translation: synthesis of a polypeptide chain on a ribosome (RER) with its primary structure determined by an mRNA template
- Folding/Refolding: nascent polypeptide folds into its native conformation with the assistance of chaperones to prevent misfolding
Processing
- Accompanied by processing events such as:
- Proteolytic cleavage of an N-terminal leader sequence
- Formation of disulfide bonds (S-S)
Covalent Modification
- Removing unneeded polypeptides
- Attaching a fatty acid molecule, for example
Translocation
- Modified peptide is translocated to a membrane
- Examples: hemoglobin for the circulatory system
Activation/Catalysis
- Binding an allosteric effector triggers a catalytically active conformation
- Enzymes are involved in this step
Aging
- Proteins become damaged by chemical attacks, deamidation, or denaturation
Ubiquitination
- Proteins may be labeled by the covalent attachment of several ubiquitin molecules (Ub)
Degradation
- Ubiquitinated protein is degraded to its component amino acids (reused for new protein synthesis)
- Proteasome is involved in this step
Four Levels of Protein Structure
- Primary Structure: sequence of amino acids and disulfide links
- Secondary Structure: formed by hydrogen bonding, examples: alpha helix and beta-pleated sheet
- Tertiary Structure: complete 3-D conformation of a protein
- Quaternary Structure: association of two or more polypeptide chains
Protein Structure Examples
- Alpha Helix:
- Produces a helical coiling of the peptide backbone
- R-groups lie on the exterior of the helix and perpendicular to its axis
- Approximately 11 amino acids long (3.6 per complete turn)
- DELIMA (amino acids) favor alpha helix formation
- GP favors disruption of the helix
- Beta-Pleated Sheet (B-Sheet):
- Composed of 2 or more regions of stretches of at least 5-10 amino acids
- Stabilized by H-bonding between amide N's and carbonyl C's
- Found in both fibrous and globular proteins
This quiz covers the protein cycle involving translation on a ribosome, folding with the help of chaperones, and processing events like proteolytic cleavage. Test your knowledge on how polypeptides are synthesized, folded, and processed during protein synthesis.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
