3.3.3 Digestion and Absorption (Unit 3 Exchange) Flashcards
The 2 stages of digestion in humans are…
Physical breakdown by teeth or stomach churning
Chemical digestion by enzymes
Give some examples of proteases involved in digestion
Endopeptidase
Exopeptidate
Dipeptidase
Identify the part of the digestive system
Oesophagus
What is meant by chemical digestion?
When large food molecules are hydrolysed into smaller molecules by enzymes.
Give some examples of carbohydrases involved in digestion
Salivary Amylase
Pancreatic Amylase
Maltase
Sucrase
Lactase
Name the cell membrane-bound protease
Dipeptidase
Bile salts are produced by the…
liver
What is the function of maltase?
To break down maltose into 2 α-glucose molecules
What is the function of salivary amylase?
To hydrolyse starch into maltose
What is the function of lipase?
To hydrolyse the ester bonds in triglycerides to give fatty acids and monoglycerides
How does the body break down maltose?
The lining of the ileum has maltase enzymes bound to their membranes.
Identify the part of the digestive system
Pancreas
What is the function of exopeptidases?
To hydrolyse the peptide bonds at the ends of peptide molecules, which releases amino acids and dipeptides.
Name the 3 membrane-bound disaccharidases…
Maltase
Sucrase
Lactase
What is the function of dipeptidases?
To hydrolyse the peptide bonds between dipeptides.
They are membrane bound enzymes.
What is the function of the ileum (small intestine)?
Produces enzymes to digest food
Absorbs the products of digestion into the blood.
What is the function of the oesophagus?
To carry food from the mouth to the stomach
What is the function of the large intestine?
To absorb water
Identify the part of the digestive system
Salivary Glands
What is meant by egestion?
The removal of faeces via the anus
Identify the part of the digestive system
Ileum (small intestine)
Identify the part of the digestive system
Large Intestine
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.
What is the function of lactase?
To hydrolyse the glycosidic bond in a lactose molecule to give glucose and galactose.
What is the function of pancreatic amylase?
To hydrolyse starch in the ileum that was not broken down in the mouth.
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 the function of endopeptidase?
To hydrolyse the central peptide bonds in a large protein molecule to give smaller peptide molecules.
Name the 3 categories of enzymes.
Carbohydrases
Proteases
Lipases
Which type of bond does amylase break?
α 1-4 glycosidic bonds
What is meant by hydrolysis?
When a water molecule is added to a molecule to break a chemical bond.
What is the function of sucrase?
To hydrolyse the glycosidic bond in a sucrose molecule to give glucose and fructose.
Which enzyme is produced by the salivary glands?
Salivary Amylase
Enzymes are secreted by…
glands
What is a monoglyceride?
A glycerol molecule with 1 fatty acid attached.
Name the 3 proteases (peptidases) that are involved in protein digestion.
Endopeptidase
Exopeptidase
Dipeptidase
Bile salts emulsify large lipid molecules into smaller lipid molecules called…
micelles
What is a membrane-bound disaccharidase?
An enzyme that is part of the epthelial 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.
Identify the part of the digestive system
Stomach
What is the function of the salivary glands?
They secrete the enzyme salivary amylase, which hydrolyses starch into maltose.
How is glucose absorbed by co transport in the GUT with Na ions?
- co transport
- Na ions actively transported from ileum cell to the blood
- maintains a diffusion gradient for Na to enter the ileum cell from the gut lumen (bringing glucose with it)
- glucose enters with Na
- glucose enter to blood by facilitated diffusion
exo and edopeptidases are required for protein hydrolysis - name another enzyme needed to complete protein hydrolysis
dipeptidases
what do endopeptidases do?
Endopeptidases hydrolyse internal peptide bonds
What do exopeptidases do?
Exopeptidases remove amino acids/hydrolyse bonds at end(s);
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)
define digestion
HYDROLYSIS of LARGE insoluble molecules into SMALLER soluble molecules
How is the golgi involved in the absorption of lipids?
modifies triglycerides
adds protein on/.forms lipoproteins
packages them for their release
/forms vesciles
Explain the advantage of lipid droplet and micelle formation
droplets increase SA for enzyme action so FASTER hydrolysis
micelle formation carries FA and glycerol through the intestinal membrane
How do fatty acids and glycerol molecules enter the intestinal epithetial cell?
Diffusion
What is a carrier protein?
- A protein spanning a cell membrane that specific molecules or ions bind to, which causes the protein to change shape and carry the molecule onto the other side of the membrane.
- Involved in facilitated diffusion and active transport.
What happens to chylomicrons when they enter the lymphatic system?
They are hydrolysed by an enzyme and enter the blood
What is meant by a chylomicron?
A triglyceride associated with cholesterol and a lipoprotein which aids lipid transport into the lymphatic system.
What is the function of the golgi apparatus in lipid absorption?
An organelle in the epithelial cells lining the ileum where triglycerides association with cholesterol and lipoproteins takes place.
What is happening at stage 1 in the diagram?
- Sodium ions are actively transported out of the epithelial cell by a sodium-potassium pump.
- Potassium ions are actively transported into the cell.
- This creates a lower sodium ion concentration in the epithelial cell than in the ileum.
Why can monoglycerides and fatty acids enter the epithelial cells of the ileum via simple diffusion?
Because they are non polar molecules so can bypass the non polar fatty acid section of the cell membrane.
By what process is glucose absorbed from the ileum and into the blood?
Facilitated diffusion
Co-transport (indirect active transport)
Define diffusion
the net movement of molecules or ions from a region where they are highly concentrated to a region where they are less concentrated until evenly distributed.
Bile salts emulsify fatty acids into smaller structures called…
micelles
How do monoglycerides and fatty acids enter the epithelial cells lining the ileum?
Simple diffusion
Micelles are created by an association between bile salts and triglycerides. After lipase has acted on micelles of triglyceride we are left with…
Micelles of monoglycerides and fatty acids (still asociated with bile salts)
What does the diagram show?
Facilitate diffusion via a channel protein from high to low concentration
What happens to monoglycerides and fatty acids after they have entered the epithelial cells lining the ileum?
They are transported to the endoplasmic reticulum where they are recombined into triglycerides.
How does the thin wall of the ileum help to optimise absorption?
Less distance for nutrients to diffuse across before reaching the blood
How is the ileum adapted to carry out the process of absorption of nutrients?
Its wall contains many villi, which greatly increases the area for nutrient absorption
Which other product of digestion is absorbed into the blood via the same method as glucose?
Amino acids
Where are the products of digestion absorbed?
Ileum (small intestine)
Name the products of digestion
Monosaccharides
Amino Acids
Monoglycerides
Fatty Acids
What is facilitated diffusion?
- Diffusion of molecules or ions aided by carrier proteins or protein channels.
- Does NOT use ATP (energy),
What is a protein channel?
A protein that spans a cell membrane and will only allow specific molecules to pass through. Involved in facilitated diffusion.
Identify the label on the diagram and the type of transport that take place.
Sodium-Potassium Pump (carrier protein)
Active Transport
Describe the process of active transport.
- Molecule or ion binds to carrier protein.
- ATP binds to carrier protein, gives a phosphate and ADP is released.
- Carrier protein changes shape and moves molecule to opposite side of membrane.
- Phosphate is released from carrier protein and protein reverts back to start position.
What is a lacteal?
A lymphatic capillary that is found in the centre of each villus of the small intestine.
What is happening at stage 2 in the diagram?
- Sodium ions are moving into the epithelial cell through a cotransport carrier protein via facilitated diffusion.
- A glucose molecule is carried through the cotransport carrier protein by the sodium ion (still facilitated diffusion)
- The sodium ion moves down a concentration gradient
- Glucose moves against its concentration gradient.
How are villi adapted to optimise absorption of nutrients?
- They increase the surface area for diffusion
- Very thin walls so less diffusion distance to the blood.
- Many blood capillaries- blood can carry nutrients away and maintain diffusion gradients.
- Epithelial cell lining contains microvilli increasing surface area for absorption further.
- They contain muscle so can move contents of the ileum to maintain concentration gradients.
What is happening at stage 3 in the diagram?
Glucose is moving into the blood stream via facilitated diffusion through a carrier protein.
What happens to the chylomicrons that are produced in the epithelial cells lining the ileum?
They exit the cells via exocytosis and enter the lymphatic system via lacteals.
What does the diagram show?
Facilitated diffusion via a carrier protein from a high to low concentration
Define active transport
the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP (energy) and carrier proteins.
Identify the label on the diagram and the type of transport that take place.
Sodium-Glucose co-transport carrier protein
Facillitated diffusion
What does the diagram show?
The path taken by glucose/amino acids through the epithelial cells of the ileum and into the blood.
Identify the label on the diagram.
A capillary within a villus
Why does having many capillaries optimise absorption in the ileum?
Nutrients absorbed in the blood are carried away quickly which maintains the concentration gradient between the ileum and the blood.
What is the function of the endoplasmic reticulum in lipid absorption?
- An organelle in the epithelial cells lining the ileum where monoglyerides and fatty acids are recombined to make triglycerides.
- Triglycerides begin to associate with cholesterol and lipoproteins here also.
Identify the label on the diagram and the type of transport that take place.
Glucose carrier protein
Facilitated diffusion
Diffusion and facilitated diffusion are both passive processed. What is meant by this?
They do not require ATP (energy)
What does the diagram show?
Simple diffusion through a cell membrane from a high to low concentration
What happens to triglycerides which have been reformed in the endoplasmic reticulum of epithelial cells lining the ileum?
They are associated with cholesterol and lipoproteins to form chylomicrons.
What does the diagram show?
Active transport of molecules by a carrier protein against a concentration gradient.
