3.3.3 (digestion) Flashcards
Digestion
Hydrolysis of large biological molecules into smaller, soluble molecules that can be absorbed across cell membranes
What are the 2 types of digestion?
Physical= chewing and churning by muscles of stomach wall
Chemical= hydrolysis by enzymea
Name the 2 enzymes involved in starch digestion
Amylase
Maltase
Describe what amylase does
Hydrolyses alternate glycosidic bonds to produce disaccharides (maltose)
Describe what maltase does
Hydrolyses maltose into monosaccharides (alpha glucose)
Why does salivary amylase stop working when food is swallowed?
Hydrochloric acid in stomach denatures enzymes
Tertiary structure of active site changes due to high concentration of H+ ions
Interact with charges on ions and hydrogen + ionic bonds
Amylase’s active site is no longer complementary preventing enzyme-substrate complexes forming
How does the body compensate for salivary amylase denaturing when swallowed?
Pancreas secretes pancreatic amylase to continue the hydrolysis of starch into maltose
Enters the ileum (of small intestine) along with alkaline bile salts to maintain a neutral pH
Why is maltase membrane bound?
Not released into lumen of ileum as membrane bound (part of cell surface membrane of epithelial cells)
Prevents enzymes being lost with gut contents
Leads to more effective absorption of products formed by these enzymes
Name the enzymes that hydrolyse each disaccharide
Maltose = maltase
Sucrose = sucrase
Lactose = lactase
Name the 3 types of proteases
Endopeptidases
Exopeptidases
Dipeptidases
Where are endopeptidases made?
Stomach and pancreas
What do endopeptidases do?
Hydrolyse peptide bonds between amino acids in the central region of the polypeptide chain creating shorter polypeptide chains
Where are exopeptidases produced?
Pancreas
What do exopeptidases do?
Hydrolyse peptide bonds at the terminal regions of the polypeptide chain producing dipeptides and amino acids
Where are dipeptidases produced?
Ileum - are membrane bound so part of cell surface membrane of ileum’s epithelial cells
What do dipeptidases do?
Hydrolyse the peptide bonds between two amino acids in a dipeptide
Describe lipase action
Enzymes produced in the pancreas
Catalyse hydrolysis of ester bonds in triglycerides
Forms fatty acids and a monoglyceride
What is a monoglyceride?
A glycerol ester bonded to a single fatty acid
Describe how lipids are emulsified
Lipids are split into many tiny droplets called micelles
Done by bile salts which are produced in the liver
Increases surface area
Describe the absorption of lipids
Micelles contact epithelial cells that line ileum and break down releasing monoglycerides and fatty acids which diffuse across the phoshpolipid bilayer
Inside cells these molecules travel to endoplasmic reticulum forming triglycerides then travel to golgi where thy are modified, processed and associated with cholesterol and lipoproteins in order to package the molecules to be released by exocytosis in the form of chylomicrons
What are chylomicrons and what do they do?
Specialised particles adapted for transport of lipids
Move out of cells by exocytosis and enter lymphatic capillaries (lacteals)
Chylomicrons pass into blood from lymphatic vessels
Triglycerides in chylomirons are hydrolysed by an enzyme in endothelial cells of blood capillaries
Fatty acids diffuse into cells
Describe the adaptations of the ileum
Layer of endothelial cells one cell thick- short diffusion pathway
Microvilli- increased surface area so more membrane bound enzymes
Network of blood capillaries - maintained high conc gradient
Presence of muscles- mechanical digestion/churning
