What are the essential amino acids?
PVT TIM HLL
Phe, Val, Thr, Trp, Ile, Met, His, Leu, Lys
What are the non-essential amino acids?
Asp, asn, alanine, glu, ser
What are the conditional amino acids and what are their precursors?
Need them in some conditions when an organ that produces them is damaged/not working.
Pro (Glu), Arg (Gln, Glu, Asp), Gln (Glu), Cys (Ser, Met), Tyr (Phe)
How does digestion of protein occur?
- None in mouth
- A little in stomach (by HCl which exposes bonds by denaturing, and pepsin which gets activated by HCl to self-cleave)
- Most in small intestine (release enzymes like trypsinogen by pancreas which gets activated by enteropeptidase on brush border cells, which themselves get activated by secretin and CCK). Trypsin then cleaves procarboxypeptidase A/B, proelastase, chymotrypsinogen to activate them as well.
Cut peptide bond within peptide (ex. elastase, chymotrypsin, pepsin, enteropeptidase)
Cut peptide bond at N-terminus or C-terminus (ex. carboxypeptidase A/B, dipeptidase, aminopeptidase)
Sodium-dependent AA transport (for free AA)
(1) Sodium binds a sodium-aa transporter
(2) This increases affinity for an aa, which then also binds the transporter
(3) Both of them binding creates a sodium-aa cotransporter
(4) A conformational change occurs and puts both Na+ and AA inside the cell
(5) Na+/K+ ATPase pumps Na+ back out of cell
Why can supplemental amino acids be bad for you?
Some aa share the same transport system, so if you ingest an aa orally. That would mean it would be in higher quality and be absorbed more readily than the other one. This would lead to an imbalance in aa absorption.
How are di/tri-peptides transported into cells?
PEPT1 H+ cotransporter:
(1) Peptides and H+ transported inside the cell together
(2) H+ gets pumped out and Na+ gets pumped in by another transporter
(3) Na+ gets restored via Na+/K+ ATPase
This is more energy efficient and faster than free aa transport
How are aa transported into cells?
- Insulin causes uptake of free aa into tissue by active transport
- Insulin causes uptake of free aa into liver by active transport IN FED STATE
- Glucagon causes uptake of aa out of muscle for gluconeogenesis
What are amino acids catabolized to?
What happens to most of the aa absorbed by the intestine?
Most of these are used for protein synthesis right along the villus:
- Lipoprotein formation
- Digestive enzymes
- N-containing compounds
What is the function of glutamine?
- Essential fuel for intestinal cells
- Initiates synthesis of heat shock proteins
- Stimulate growth of GI via proliferation
What are heat shock proteins?
Proteins that "monitor" other proteins to make sure they are functioning properly, the upregulation of these proteins is done by:
- High temp - Infection - Hypoxia - Inflammation - Starvation - Water deprivation
What do heat shock proteins do?
As part of the cellular stress/heat shock response, they are responsible for helping proteins to fold and for carrying old proteins for recycling.
How does the cellular stress response work?
(1) Proteins get denatured (hypoxia, heat, etc.)
(2) Gets detected and this causes upregulation of HSP synthesis
(3) HSPs go and help reformation of damaged proteins that have unfolded
What is the job of chaperonins?
Prevent aggregation by providing favourable folding of newly synthesized proteins.
Why is protein turnover done even though it is so energetically expensive?
(1) Allow body to adapt to changing conditions regardless of aa coming (free aa pool reflects aa coming in + protein degradation aa)
(2) Allow some proteins to change in conc rapidly (ex. protein turnover in regulatory proteins is high while structural proteins is low)
(3) Prevent bad proteins from building up (ex. damaged, denatured, etc.)
(4) Allow for a free aa pool that is available when it is needed
What do the different protein synthesis and degradation rates cause?
Protein synthesis = protein degradation: No change in protein mass
Protein synthesis > protein degradation: Gain in protein mass
How is protein synthesis regulated?
It is tissue specific but is done by glucagon and insulin
Glucagon:Insulin ratio high = increased gluconeogenesis, increased protein breakdown, decreased protein synthesis