protein catabolism Flashcards
(12 cards)
outline the excretion of protiens (3)
- amino acids can’t be stored in body and can’t be directly excreted
- excess amino acids have their amino group removed
- allows them to be converted to urea (dna pyrimidines) and uric acid (purines) before excretion
outline the process of dietary protein degradation (4)
stomach:
- acidic environment (HCl) denatures protein
- pepsin breaks peptide bonds
intestines:
- proteolytic enzymes from pancreas
- proteases located in plasma membrane of intestinal cells
identify zymogens
suffix = 'ogen' prefix = 'pro'
outline zymogen activation (2 + 4 steps)
- requires activation by cleavage
- hydrolyses proteins -> amino acids
- activated by eating/digesting
- cells lining in duodenum secrete enteropeptidase
- cleaves and activates trypsinogen -> trypsin
- trypsin can activate further trypsinogens and zymogens
why is important that preteolytic enzymes are initially zymogens
zymogens inactive
- important they are activated where they are needed NOT where they are synthesised
outline regulation of trypsin
why is it important to regulate trypsin
- pancreas produces trypsin inhibitory protein
- competitive inhibition
- accidental activation of trypsinogen activates all the other zymogens
- leads to pancreatitis
why and when does protein turnover occur
why:
- protein degradation regulates biological functions (gene transcription, circadian rhythm)
when:
- constantly occurs
- proteins have varying half-lives (eg. crystallin lasts lifetime)
identify the 2 key enzymes involved in cellular protein turnover and their functions (1)
- ubiquitin
- places a target on protein to be degraded - proteasome
- degrades marked protein
outline the role of ubiquitin in protein turnover (4 + 2E)
- enables protein turnover to be tightly regulated
- found in all eukaryotic cells
- requires ATP
- chain of 4 or more Ub enhances signal of protein to be degraded
- attaches to target proteins with help of enzymes: E1, E2 & E3
- E3 reads and recognises protein to be targeted
what determines whether ubiquitin is attached (3)
specific amino acid sequence notifies Ub:
- N terminal residue
- PEST boxes
- Cyclin destruction boxes
what common diseases are associated to errors in Ub controlled protein degradation
- parkinson’s
2. HPV associated cervical cancer
outline the steps taken by proteasome to degrade a Ub-marked protein
- Ub-tagged proteins are unfolded and digested
- multiple rounds of ATP hydrolysis occurs
- peptide fragments and Ub is produced (Ub reused)
- peptide fragments can then be further degraded into amino acids
