Protein Chemistry, Structure, Function, Synthesis, and Maturation Flashcards
Describe the basic cellular/physiological role of several diverse proteins, including specific examples.
Enzymes - regulate metabolic pathways (Glycolysis)
Signalling molecules - (kinases, cAMP)
Modify existing proteins - (kinases, phosphatases)
Structural proteins - (actin, tubulin)
Extracellular matrix - collagin, elastin
Movement - motor proteins (myosin, dynein, kinesin)
Cell Signalling - cell receptors
Draw the generalized structure amino acids and polypeptides.
AA General structure: COOH-CH2(NH3)-R
Peptide General structure:
-NH-C(R)-CO-
Describe the four levels of protein structure.
Primary- amino terminal (5’), carboxyl (3’)
Secondary - alpha helices, beta-pleated sheets
Tertiary - functional structure w/ only one polypeptide
Quaternary - structure with more than one polypeptide
Explain what is meant by the phrase post translational modification of proteins and give three reasons why such modifications are biologically important.
post translational modification is important for the proper folding of the polypeptide (increases half life and changes function of polypeptide)
ex: glycosylation (the addition of sugars) - O-linked(occurs on serine, threonine) and N-linked (on asparagine)
O-antigen (H-substance) - depending on the person, the o-antigen is converted to A or B or nothing at all
*Addition of lipid tail to protein helps it incorporate into the lipid membrane
Outline the important factors that help a protein fold.
Final conformation is largely dictated by:
primary sequence
non-covalent forces
clustering of hydrophobic amino acids*
*Chaperones prevent hydrophobic AA from sticking together prematurely
Describe the process of translation as it occurs in eukaryotic cells, utilizing the following terms: initiation factors, tRNA, mRNA, E site, P site, A site, elongation factors, ATP, start codon, stop codon, anticodon.
- initiation factors work with 40S ribosomal subunit and recognizes the start codon (AUG) on the mRNA
- tRNA with the anticodon methionine enters the P site.
- Elongation factors enters the A site, and a peptide bond is formed.
- the ribosome moves down the strand, and a tRNA is expelled from the E site.
- this occurs until a stop codon is reached
Describe the intracellular movement of a secreted protein starting with its translation in the cytosol and give specific examples of human proteins that are targeted through the secretory pathway.
- synthesized in the cytosol
- moved to ER membrane for modification
- trafficked to golgi apparatus
- Packaged for excretion
Describe the cellular mechanisms for targeting proteins to mitochondria, nuclei, peroxisomes, and the plasma membrane.
proteins have a “zip code” designating its final destination. chaperonins denature the protein and bring it to the site
Describe what is meant by receptor-mediated endocytosis and give examples of how of how defects in this process can lead to disease.
Example: LDL particle binds to LDL receptor in a clathrin coated pit. The membrane invaginates due to clathrin and brings the particle to an endosome
If there is a mutation and the LDL is not imported properly, it sticks around in the blood and increases the chance of cardiovascular disease
Describe the role ubiquitin and proteasomes have in regulating protein levels.
Proteasomes - main method of cytosolic protein degradation
E3 determines the specificity of proteins meant for destruction, and tags them with ubiquitin. proteins can become polyubiquitinates and become targeted by a proteasome.
Explain the properties of the genetic code.
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