digestion and absorption (+enzymes) Flashcards
Organisms exchange substances with their environment
define digestion
Large (insoluble) biological molecules hydrolysed to smaller (soluble) molecules
that are small enough be absorbed across cell membranes into blood
what is the role of salivary glands in the digestive system?
release salivary amylase enzymes
what is the role of the stomach in the digestive system?
produces HCL and protease enzymes. Also physically churns food
what is the role of the teeth?
physically break food into smaller pieces and increase its surface area
what is the role of the oesophagus?
carries food from the mouth to the stomach
what is the role of the liver?
produces bile
what is the role of pancreas?
Releases pancreatic juice onto food, as it exits the stomach, which contains proteases, lipases and carbohydrases.
what is the role of gall blander?
stores/release bile into ileum
what is the role of ileum?
Produces enzymes to digest food and absorbs products of food digestion into the blood
what is the role of the large intestine?
absorbs water
what are the 2 stages of digestion in a human?
-Physical breakdown by teeth or stomach churning
-Chemical digestion by enzymes
what are the carbohydrase enzymes?
-Salivary Amylase +
Pancreatic Amylase (substrate: starch)
-Maltase (substrate: maltose)
-Sucrase (substrate: sucrose)
-Lactase (substrate: lactose)
Give some examples of proteases involved in digestion
-Endopeptidase (substrate: protein)
-Exopeptidase(substrate: protein)
-Dipeptidase (substrate: dipeptides)
what are the membranes bound enzymes?
-maltase
-sucrose
-lactase
-dipeptidases
what is the function of salivary amylase and pancreatic amylase
- makes maltose
- in salivary glands, pancreas
-acts in the mouth, ileum
-alpha 1,4 and beta 1,6 glycosidic bonds are broken
-the pancreatic amylase hydrolyse starch in the ileum that was not broken down in the mouth.
what is the function of moltase?
-To break down maltose into 2 α-glucose molecules
-made in the ileum lining (stuck at the lining so it can be reused, if not it would be replenished which takes up a lot of energy)
-acts on the ileum
-a 1,4 glycosidic bonds are broken
what is the function of sucrase?
-breaks down sucrose into a-glucose and fructose
-made in the ileum lining
-acts in the ileum
what is the function of lactase?
-hydrolyse lactose into a-glucose and galactose
-made in the ileum lining
-acts in the ileum
what is the function of endopeptidase?
-To hydrolyse the central peptide bonds in a large protein molecule to give smaller peptide molecules.
-made in the stomach and pancreas
-acts in the stomach and ileum
-peptide bonds are broken
what is the function of exopeptidase?
-To hydrolyse the peptide bonds at the ends of peptide molecules, which releases amino acids and dipeptides
-made in the stomach and pancreas
-acts in the ileum and stomach
-peptide bonds broken
What is the function of dipeptidases?
-hydrolyse dipeptides into amino acids
-made in the ileum lining
-acts in the ileum
-peptide bonds broken
what is the function of lipase ?
-hydrolysis of ester bonds in a lipid molecule to form 2 fatty acids and a monoglyceride
-made in the ileum lining
-acts in the ileum
What is meant by egestion?
The removal of faeces via the anus
What is the function of bile salts?
To emulsify large lipid molecules into smaller lipid micelles. To increase the surface area that lipase can act on.
How does physical breakdown aid digestion?
-Creates a larger surface area for enzymes to act on.
-Makes food easier to ingest (swallow).
Starch is not digested when food enters the stomach. Why?
The salivary amylase enzymes are denatured by the hydrochloric acid in the stomach.
What is a membrane-bound disaccharidase?
An enzyme that is part of the epithelial cell surface membranes of the ileum. They break down disaccharides.
What is a gland?
An organ in the body that secretes substances such as enzymes or hormones.
Describe the digestion of starch in mammals
● Amylase (produced by salivary glands / pancreas) hydrolyses starch to maltose
● Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
● Hydrolysis of glycosidic bond
Describe the digestion of lipids in mammals, including action of bile salts
● Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
● This increases surface area of lipids for increased / faster lipase activity
● Lipase (made in pancreas) hydrolyses lipids (eg. triglycerides) → monoglycerides + fatty acids
● Hydrolysis of ester bond
Describe the digestion of proteins by a mammal
● Endopeptidases - hydrolyse internal (peptide) bonds
within a polypeptide → smaller peptides
○ So more ends / surface area for exopeptidases
● Exopeptidases - hydrolyse terminal (peptide) bonds at
ends of polypeptide → single amino acids
● Membrane-bound dipeptidases - hydrolyse (peptide)
bond between a dipeptide → 2 amino acids
● Hydrolysis of peptide bond
Suggest why membrane-bound enzymes are important in digestion
● Membrane-bound enzymes are located on cell membranes of epithelial cells lining ileum
● (By hydrolysing molecules at the site of absorption they) maintain concentration gradients for absorption
what are micelles?
smaller emulsified lipid droplets associated with bile salts which creates a larger surface area for faster lipase action
what are the advantages of micelle formation?
- droplets increase surface area (for lipase/enzyme action)
- so faster hydrolysis/digestion of triglycerides/lipids
3.micelles carry fatty acids and glycerol through membrane to internal epithelial cell
exo and edopeptidases are required for protein hydrolysis - name another enzyme needed to complete protein hydrolysis
dipeptidases
Why does the action of exo and endopeptidases result in more efficient hydrolysis?
endopeptidases create more ends or increase in surface area (for exopeptidases);
Describe the action of membrane dipeptidases
-Hydrolyse peptide bond to release amino acids
(dipeptides cannot cross the cell membrane)
Describe the pathway for absorption of products of digestion in mammals
Lumen (inside) of ileum → cells lining ileum (part of small intestine) → blood
Describe the absorption of monosaccharides in mammals
- sodium removed from epithelial cell by active transport via sodium potassium carrier protein
- into the blood
- maintaining a low concentration of sodium in the cell
- glucose moves into the sodium
- via a co-transporter carrier protein
6.glucose moves into the blood - by facilitated diffusion
Describe the absorption of amino acids in mammals
- sodium removed from epithelial cell by active transport via sodium potassium carrier protein
- into the blood
- maintaining a low concentration of sodium in the cell
- amino acid moves into the sodium
- via a co-transporter carrier protein
- amino acid moves into the blood
- by facilitated diffusion
Describe the absorption of lipids by a mammal, including the role of micelles
● Bile salts combine with monoglycerides and fatty acids to form micelles
○ Micelles make monoglycerides and fatty acids (more) soluble in water
○ Micelles carry fatty acids and monoglycerides to cells lining the ileum, where they break down to
release them
○ This maintains a high concentration of fatty acids and monoglycerides near cells lining the ileum
● Monoglycerides / fatty acids are absorbed (into epithelial cell) by diffusion (as they’re lipid soluble)
● Triglycerides reformed in (epithelial) cells and aggregate into globules
● Globules coated with proteins forming chylomicrons which are then packaged into vesicles
● Vesicles move to cell membrane and fuse with it, releasing chylomicrons via exocytosis
○ Chylomicrons enter lymphatic vessels and eventually return to blood circulation
describe the structures of capillaries and how it aids function
- walls are folded into villi- increase the S.A for faster absorption
- walls are 1 cell thick- short diffusion distance so faster absorption
- epithelial cells have microvilli - increase in S.A for faster absorption
- many capillaries- rich blood supply maintains diffusion gradient
- muscle in villi- maintain diffusion gradient by moving contents of lumen
