Digestion And Absorbsion Flashcards
What is digestion?
When large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes.
What is amylase
Amylase is produced by the pancreas and salivary glands.
It hydrolyses the glycocidic bonds of starch/ polysaccarides producing the disacharide maltose.
What is maltose
Maltose is a disacharide produced in the ileum.
Maltose is hydrolysed into alpha glucose
What are sucrase and lactase?
They are membrane bound enzymes that hydrolyse sucrose and lactose into monosaccharides.
What three enzymess can proteins be hydrolysed by
- endopeptidases
- exopeptidases
- dipeptidates
What do endopeptidases do?
Hydrolise the peptide bond between the central reigon of a protein molecule forming a series of external peptide molecules.
What do exopeptidases do?
Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules. These are formed by endopeptidases and singular amino acids
What do dipeptidases do?
Hydrolyses the bonds between two amino acids of a dipeptide.
Dipeptides are membrane bound being part of the cell surface membrane of the epithelial cells lining the ileum
What is the definition of lacteal
Lymphatic vessels found at the centre of the villi
What is the definition of lumen
A cavity or hollow part of a structure
What is the definition of micelles
Emulsified lipid droplets
What is the definition of chylomicrons
The product of triglycerides associating with cholestrol and lipoproteins
What is the definition of exocytosis
Moving out of the cell
What is the definition of ileum
Small intestine
What is the definition of colon
Large intestine
What is the definition of enzyme
A biological catalyst produced by a gland
What is the definition of hydrolysis
Break down of a compound by a chemical reaction with water
What is the definition of assimulate
Nutrients in food are taken into the cells of the body
What is the definition of monosaccharide
A class of sugars that cannot be hydrolysed to give a simpler sugar
What is the definition of polysacharides
Class of sugars whose molecules contain two monosaccharide residues
What is the definition of polymer
A carbohydrate whose molecules consist of a number of sugar molecules bonded together
What is the definition of monomer
A molecule that can be bonded to other identical molecules to form a polymer
What is the definition of lipid
Molecular structure built up chiefly or completely form a large number of similar units bonded together (fats)
What is the definition of peptide
Compound made of two or more linked amino acids
What is the definition of glycocidic bonds
Bond which directly links carbohydrates to other molecules
What is the definition of emulsification
Breakdown of fat into smaller molecules, this provides a larger surface area
Describe the processes involved in the absorption and transport of
digested lipid molecules from the ileum into lymph vessels.
- Micelles contain bile salts and fatty acids/monoglycerides;
- Make fatty acids/monoglycerides (more) soluble (in water)
Bring/release/carry fatty acids/monoglycerides to cell/lining (of the
Maintain high(er) concentration of fatty acids/monoglycerides to
cell/lining (of the ileum);
- Fatty acids/monoglycerides absorbed by diffusion;
- Triglycerides (re)formed (in cells);
Accept chylomicrons form - Vesicles move to cell membrane;
Accept exocytosis for ‘vesicles move’
Expplain the function of this ATP hydrolase.
ATP to ADP + Pi ) Releases energy;
.
(energy) allows ions to be moved against a concentration gradient
OR
(energy) allows active transport of ions;
The movement of Na+ out of the cell allows the absorption of glucose into
the cell lining the ileum.
Explain how
Maintains/generates) a concentration/diffusion gradient
for Na+ (from ileum into cell);
Accept ‘(Maintains/generates) a lower concentration
of Na+ inside the cell compared with outside the
cell’
.
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
OR
Na+ moving (in) by co-transport, brings glucose with it;
Describe the role of micelles in the absorption of fats into the cells lining
the ileum.
Micelles include bile salts and fatty acids;
Make the fatty acids (more) soluble in water;
Bring/release/carry fatty acids to cell/lining (of the ileum);
Maintain high(er) concentration of fatty acids to cell/lining (of the
ileum);
Fatty acids (absorbed) by diffusion;
Reject if absorbed by facilitated diffusion
Describe the role of enzymes in the digestion of proteins in a mammal.
Reference to) hydrolysis of peptide bonds;
2. Endopeptidase act in the middle of protein/polypeptide
OR
Endopeptidase produces short(er) polypeptides/ increase number of ends;
- Exopeptidases act at end of protein/polypeptide
OR
Exopeptidase produces dipeptides/amino acids;
Dipeptidase acts on dipeptide/between two amino acids
OR
Dipeptidase produces (single) amino acids;
Explain the advantages of lipid droplet and micelle formation.
Droplets increase surface areas (for lipase /
enzyme action);
2. (So) faster hydrolysis / digestion (of
triglycerides / lipids);
3. Micelles carry fatty acids and glycerol /
monoglycerides to / through membrane / to
(intestinal epithelial) cell;
How is golgi appuratus involved in absorbtion of lpids
Golgi (apparatus);
2. Modifies / processes triglycerides;
3. Combines triglycerides with proteins;
4. Packaged for release / exocytosis
OR
Forms vesicles;
Cells lining the ileum of mammals absorb the monosaccharide glucose by
co-transport with sodium ions. Explain how.
Sodium ions actively transported from ileum cell to blood;
Maintains / forms diffusion gradient for sodium to enter cells from gut
(and with it, glucose);
Glucose enters by facilitated diffusion with sodium ions;
What are proteins
Proteins are large polymer molecules that can be hydrolysed by three enzymes:
What are the three enzymes proteins can be hydrolysed by
- Endopeptidases (hydrolyse peptide bonds between amino acids in the middle of a polymer chain)
- Exopeptidases (hydrolyse peptide bonds between amino acids at the end of a polymer chain)
- Membrane-bound dipeptidases (hydrolyse peptide bonds between two amino acids).
Where does protein digestion start
Protein digestion starts in the stomach, continues in the
duodenum and is fully digested in the ileum.
What are lipids
Lipids are digested by lipase and the action of bile salts.
Lipase is produced in the pancreas and it can hydrolyse the ester bond in triglycerides to form the monoglycerides and fatty acids.
Bile salts are produced in the liver and can emulsify lipids to form tiny droplets, micelles. This increases the surface area for lipase to act on.
What are the two stages of lipid digestion
Two stages of lipid digestion -
Physical (emulsification & micelle formation)
Chemical (lipase)
What is the physical stage of lipid digestion
Physical -
Lipids are coated in bile salts to create an emulsion.
Many small droplets of lipids provides a larger surface area to enable the faster hydrolysis action by lipase.
What is the chemical stage of lipid digestion
Lipase hydrolyses lipids into glycerol and fatty acids (some monoglycerides)
What are micelles
Micelles are water soluble vesicles formed of the fatty acids, glycerol, monoglycerides and bile salts.
Micelles deliver the fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorbtion
Monosaccharide and amino acid absorbtion
To absorb glucose and amino acids from the lumen to the gut there must be a higher concentration in the lumen compared to the epithelial cell (for facilitated diffusion).
BUT
There is usually more in the epithelial cells.
That is why active transport and co-transport are required.
Where are products of digestion absorbed in mamals
n mammals the products of digestion are absorbed across the cells lining the ileum.
The ileum wall is covered in villi, which have thin walls surrounded by a network of capillaries and epithelial cells have even smaller microvilli.
These features maximise absorption by increasing the surface area, decreasing the diffusion distance and maintaining a concentration gradient.
What happens when lipids are digested
Lipids are digested into monoglycerides and fatty acids by the action of lipase and bile salts.
These form tiny structures called micelles
When the micelles encounter the ileum epithelial cells, due to the |n-polar nature the fatty acids and monoglycerides, they can simply diffuse across the cell surface membrane to enter the cells of the epithelial cells.
Once in the cell, these will be modified back into triglycerides inside of the endoplasmic and Golgi body.
What do lipase do
Triglycerides are broken down by lipase. Lipases are produced by the pancreas. They hydrolyse the ester bonds in triglycerides which forms fatty acids and monoglycerides (one fatty acid + one glycerol)
Adaptations for the small and large intestine
Most absorption takes place in the small and large intestine - many digested food in the small intestine and water in the large intestine.
The intestines are long providing a large surface area for absorption to occur. There are large numbers in the villi in the mucosa furthermore increasing surface area. There are a large number of goblet cells searching mucus of food.
Adaptations of villi
The villi posses smooth muscle fibres which contract and relax mixing up the contents and bringing the epithelial cells into contact with digested food.
Each villus has an extensive capillary network so absorbed food is transported away quickly maintaining a concentration gradient.
There are lacteal in each villus to which fats are absorbed.
As tips of the villi are constantly damaged by passage of food, these cells can easily be replaced by cells from the base of the villi.
These cells migrate to the surface and gradually move up the villus until being shed from the tip.
Process of digestion
Process of digestion
•Saliva mixed with food
•Contains salivary amylase (SA).
•Starch → maltose (hydrolysis). Salts help maintain a neutral pH (optimum enzyme pH for SA).
•Food enters stomach, acid denatures SA to prevent further breakdown of the starch.
•Food passed to ileum, mixes with pancreatic juice.
•Pancreatic juice contains pancreatic amylase, this ensures the remaining starch is hydrolysed to maltose.
•Alkaline salts produced by the ileum and pancreas ensure optimum pH for enzyme
Process of digestion 2
Ileum muscles push the food along (peristalsis).
The lining of which produce maltase (a disaccharidase).
•Maltase is released into the lumen of the ileum, but also forms part of the lining to the ileum.
• This is how it gets its name membrane-bound disaccharidase.
• This hydrolyses maltose into alpha glucose (which would have originally come from starch)!
Carbohydrates
Carbohydrates require more than one enzyme to hydrolyse them into monosaccharides:
Amylases
Membrane-bound disaccharidases.
Amylase is produced by the pancreas and salivary glands. It hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds.
Sucrase and Lactase are membrane-bound enzymes that hydrolyse sucrose and lactose into monosaccharides.
Describe the differences between the villi and the microvilli”
single villi within the small intestine will be made up of intestinal epithelial cells each of the cells will have multiple hair like projections from cells within a microvilli.
• “ describe how the diffusion is maintained across the villus”
the capillary network is closely associated with the villi. Anything absorbed is quickly transported away to continuously provide a low concentration of absorbed substances in the villi.
Describe how digested lipids are absorbed and then transport to the ileum and lymphatic system. [5]
- Micelles are made of bile salts, fatty acids and monoglycerides
- Micelles carry the fatty acids to the epithelial cells of
the ileum - Fatty acids are absorbed into the cells of the ileum by simple diffusion
- Triglycerides or chylomicrons are formed
- Vesicles am questiond by exocytosis
Describe the importance of micelles in absorbing lipids into the epithelial cells of the ileum. [3]
- Micelles are made of bile salts fatty acids and monoglycerides
- Micelles make fatty acids more soluble in water
- Micelles carry fatty acids to the epithelial cells of the ileum
- The fatty acids are released from the micelles and absorbed into the cell by simple diffusion
When lipids are digested, they first form smaller droplets and then micelles are formed
Explain the advantages of these two stages.
Lipid droplets the increase surface areas for lipase
2. This speeds up hydrolysis / digestion
3. The micelles bring the fatty acids, monoglycerides and glycerol to the epithelial cell
How are golgi apparatus involved in the absorbtion of lipids
- They modify triglycerides
- They combine proteins with triglycerides to form chylomicrons
- These are packaged into vesicles.
What do endopeptidases do
Hydrolyse internal peptide bonds within polypeptides
So more surface area for exopeptidases
What do exopeptidases do
Hydrolyse terminal peptide bonds at end of polypeptide
To make single amino acids
Suggest why membrane bound enzymes are important in digestion
Membrane bound enzymes are located on the cell membranes of the epithelial cells lining the ileum
By hydrolysing molecules at site of absorption, they maintain a concentration gradient for absoption
Describe pathway for absorption of producrs of digestion in mamals
Lumen inside of ileum —> cells lining ileum —> blood
Describe how proteins are digested in the human gut.
Hydrolysis of peptide bonds;
Endopeptidases break polypeptides into smaller peptide chains;
Exopeptidases remove terminal amino acids;
Dipeptidases hydrolyse / break down dipeptides into amino acids.
Most blood glucose comes from starch and disaccharides in the diet.
Describe a test you could use to check if food in the diet contained starch.
Add iodine / potassium iodide solution;
Reject if heated
2. Blue-black colour (with starch);
Accept black
E xplain how digestion of starch in the gut (small intestine) leads to an increase in the
concentration of glucose in the blood.
Hydrolysed by enzymes / hydrolysed by amylase / maltase;
Produces glucose (in the gut);
Small enough to cross the gut wall (into the blood) / monomers / monosaccharides
(can) cross the gut wall (into the blood);
Describe the difference between the structure of a triglyceride molecule and the structure of
a phospholipid molecule.
In phospholipid, one fatty acid replaced by a phosphate;
Describe the role of the enzymes of the digestive system in the complete breakdown of
starch
Starch) to maltose:
Maltase;
Maltose to glucose;
Hydrolysis;
(Of) glycosidic bond;
Decribe the processes involved in the absorption of the products of starch digestion.
Glucose moves in with sodium (into epithelial cell); Via (carrier / channel) protein / symport;
Sodium removed (from epithelial cell) by active transport / sodium- potassium pump; Into blood;
Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium concentration gradient (between lumen and epithelial cell);
Glucose moves into blood; By (facilitated) diffusion;
The epithelial cells that line the small intestine are adapted for the absorption of glucose.
Explain how.
icrovilli provide a large / increased surface area;
Many mitochondria produce ATP / release or provide energy (for activetransport);
Carrier proteins for active transport; Channel / carrier proteins for facilitated diffusion;
Co-transport of sodium (ions) and glucose or symport / carrier protein for sodium (ions) and glucose
Membrane-bound enzymes digest disaccharides / produce glucose;
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction.
Active site (of enzyme) has (specific) shape / tertiary structure / active site
complementary to substrate / maltose;
- (Only) maltose can bind / fit;
To form enzyme substrate complex.
