Proteins, Health and Disease Flashcards
What are the 7 main functions of proteins
DNA binding proteins
Hormones
Enzymes
transport proteins
Structural proteins
Receptors
Antibodies
What type of protein are most enzymes
Globular
Are enzymes chemically altered by reactions
No
What is the function of enzymes
Biological catalysts that enable reactions which would not take place otherwise
What is the active site
Point of catalysis where the reaction is energetically most favourable and an enzyme substrate complex forms
What is the induced fit model
Contact between part of the binding site and substrate induces change in shape of active site
What is activation energy
Initial large input of energy required for the reaction to proceed
How do enzymes catalyse reactions
Minimise activation energy so reaction proceeds much faster
What are proteases secreted as
Zymogens (inactive precursors)
What are the functions of the zymogens
Protects host against auto digestion until active form required
What zymogen is secreted by the stomach
Pepsinogen
What zymogens are secreted by the pancreas
Chymotrypsinogen, trypsinogen, procarboxypeptidase, proelastase
Describe the mouth stage of protein digestion
Protein is homogenised by chewing and protein passes to stomach still intact (mostly)
Describe protein digestion in the stomach
Protein entering stomach stimulates release of gastrin from gastric mucosa, gastrin stimulates parietal cells to secrete HCL and chief cells to secrete pepsinogen, dietary proteins are denatured by acid which exposes their internal peptide bonds for hydrolysis
Describe enzyme action in the stomach
At low pH pepsinogen is activated into pepsin (endopeptidase) to hydrolyse internal peptide bonds (long to smaller PP chains)
How is pepsinogen activated
Removal of N-terminal ‘activation peptide’ from active site
Describe protein digestion in the small intestine
Hormone secretin triggers release of bicarbonate from pancreas into SI as stomach contents enter to neutralise
Peptides pass to duodenum
CCK stimulates zymogen release from pancreas
Intestinal cells secrete proteolytic enzyme enteropeptidase to produce trypsin
What is the function of enteropeptidase
Catalyses conversion of trysinogen to trypsin
What is the duodenum
Upper SI
Describe enzyme action in the small intestine
Trypsin activates more trypsinogen to trypsin and other pancreatic zymogens
Further hydrolysis of peptides produced by pepsin in stomach by 3 highly specific enzymes (trypsin, elastase and chymotrypsin to produce oligopeptides
Carboxypeptidases A&B are exopeptidases and release single AA
What are exopeptidases
Hydrolyse peptide bonds adjacent to C-terminus to release AA
What are the main pepsin cleavage points
Phe, trp, tyr (N-terminal side)
What are the main trypsin cleavage points
Lys, arg (C-terminal side)
Why are the main chymotrypsin cleavage points
Phe, trp and tyr (c-terminal side)
