Digestion and Absorbption Flashcards
Why are large biological molecules
e.g starch and proteins
in food
can’t be absorbed from the gut into the blood?
They are too big to cross the cell membranes
What happens during digestion?
Large molecules are broken down into smaller molecules (e.g glucose,amino acids)
They can move across the cell membrane and be easily absorbed
What type of reaction that large molecules can be broken down into smaller molecules?
Hydrolysis reaction - break bonds by adding water
Process of hydrolysis of carbohydrates:
- Disschardies
- Monosaccharides
Process of hydrolysis of proteins
Proteins
Amino acids
Process of hydrolysis of lipids
Fatty acids
Monoglycerdies
Where is the variety of different digestive enzymes?
Produced by specialised cells in digestive systems of mammals
These enzymes are released into the gut to mix into the food
Why are different enzymes needed to catalyse the breakdown of food molecules?
Enzymes only work with specific subtrates
What is amlyase?
Digestive enzyme that catalyses the conversation of starch (polysaccharide)
into the smaller sugar maltose (disaccharide)
This involves the hydrolysis of glycosidic bonds
Where is the amylase produced?
By salivary glands (release amylase into the mouth)
and also by pancreas (release amylase into the small intestine)
What are membrane-bound disaccharides?
Enzymes that are attached to the cell membrane of epithelial cells lining the ileum (final part of the small intestine)
Help to break down disaccharides (e.g maltose, sucrose and lactose) into monosaccharide
Hydrolysis of glycosidic bonds
What is the disaccharidase for maltose?
Maltase
What is the disaccharidase for sucrose?
Sucrase
What is the disaccharidase for lactose?
Lactase
Hydrolysis of maltose
Alpha glucose + Alpha glucose
Hydrolysis of lactose
glucose + galactose
Hydrolysis of sucrose
glucose + fructose
How can monosaccharides be transported across the cell membrane of ileum epithelial cells?
via specific transporter proteins
What does lipase enzyme catalyse?
The breakdown of lipids into monoglycerides and fatty acids
Involve the hydrolysis of ester bonds in lipids
What is a monoglyceride?
Glycerol molecule with one fatty acid attached
Where are the lipase made?
In pancreas
Where do lipase work?
In small intestine
Where are bile salts produced?
In the liver
What do bile salts do to lipids?
Emulsify lipids - cause lipids to form small droplets
Why are bile salts so important for lipid digestion?
Several small lipid droplets have a bigger surface area than a single large droplet (same vol)
formation of small droplets increase SA of lipid that’s available for lipase to work on
Lipids broken down : monoglycerides and fatty acids stick to bile salts to form tiny structures called micelles
Are proteins broken down by a combination of different proteases/peptidases?
Yes
What do the combination of proteases/peptidases do to break down proteins?
Hydrolysing the peptide bonds between the amino acids
Different types of protein enzymes
- Endopeptidase
- Exopetidases - Dipeptidases
What does endopeptidases act?
Hydrolyse peptide bonds within a protein
What are examples of endopeptidases?
- Trypsin
- Chymotrypsin
- Pepsin
What are the properties of trypsin and chymotrypsin
- Synthesised in pancreas
- Secreted into small intestine
What is properties of pepsin?
- Released into the stomach by cells in the stomach lining
- Only works in acidic conditions - provided by hydrochloric acid in the stomach
How do exopeptidases act?
To hydrolyse peptide bonds at the end of protein molecules
They remove single amino acids from proteins
What are dipeptidases?
They are exopeptidases to work specifically
They act to separate the two amino acids that make up dipeptide by hydrolyzing the peptide bonds between them
Where is dipeptidases often located?
In cell-surface membrane of epithelial cells in small intestine
How is monosaccharides transported?
- Glucose is absorbed by active transport with sodium ions via co-transport protein
- Glucose is absorbed in the same way using the same co-transport protein
- Fructose is absorbed via facilitated diffusion via different transporter protein
How is monoglycerides and fatty acids transported across ileum epithelium into the bloodstream?
Micelle help to move monoglycerides and fatty acids towards the epithelium
monoglycerides and fatty acids are lipid soluble - diffuse directly across the epithelial cell membrane
Micelle constantly break up and reform so they can release monoglycerides and fatty acids allowing them to be absorbed - whole micelle not taken up in epithelium
How are amino acids transported across the ilem epithelium into the bloodstream?
Amino acids are absorbed via co-transport
Sodium ions are actively transported out of ileum epithelial cells into blood
creates sodium ion concentration gradient
Na+ ions can diffuse from lumen of the ileum into the epithelial cells through sodium-dependent transporter protein , carrying amino acids with them.
Some people suffer from lactose intolerance
This is caused by an inability to break down lactose in upper small intestine
a) Suggest which disaccharidase enzyme is deficient or missing in people who are lactose intolerant
Lactase
Some people suffer from lactose intolerance
This is caused by an inability to break down lactose in upper small intestine
b) How are the digestion products of lactose absorbed across the epithelial cells of the ileum?
The digestion products of lactose/glucose and galactose are absorbed across the epithelial cells by active transport with sodium ions via a co=transport protein
Where in the body would you find sucrase?
On the cell membrane of epithelial cells lining the ileum
What is the role of sucrase in body?
Sucrase catalyses the hydrolysis of sucrose into glucose and fructose
Smaller molecules/monosacharides can be absorbed across the ileum epithelium into bloodstream
Diagram of human digestive system labelled
What is the oesophagus?
Carries food from the mouth to the stomach
What is the stomach?
Muscular sac with an inner layer that produces enzymes
Its tole to store and digest food , especially proteins
Has glands to produce enzymes to digest proteins
What is the ileum? (small intestine)
Long muscular tube
Food is further digested in the ileum by enzymes produced by its walls and glands pour secretions into it
Inner walls are folded into villi - giving a large surface area
surface area increased by microvilli on epithelial cells of each villus
Adapts for absorbing products of digestion into the bloodstream
What is the large intestine?
Absorbs water
Most of the water that is absorbed from secretions of the many digestive glands
What is rectum?
Faces stored in here before periodically removed by the anus in a process called egestion
What is salivary glands?
Situated near the mouth
They pass their secretions via the duct into mouth
These secretions contain the enzyme amylase which hydrolyses starch into maltose
What is pancreas?
Large gland is situated below the stomach
It produces a secretion called pancreatic juice
Secretion contains proteases to hydrolyses proteins
lipase to hydrolyse lipids
amylase to hydrolyse starch
What are the two types of digestion?
Physical breakdown
Chemical breakdown
What is physical breakdown?
If food is large
Broken down into smaller pieces by means of structure such a teeth
provides a large surface area for chemical digestion
food is churned by muscles in the stomach wall and physically breaks it up
Explain why the stomach does not have villi or microvilli?
Villi and microvilli increase the surface area to speed up the absorption of soluble molecules
As food in the stomach has not yet been hydrolysed into soluble molecules they cannot be absorbed and so villi and microvilli are unnecessary
Name the final product of starch digestion in the gut
Alpha glucose
List the three enzymes produced by the epithelium of the ileum:
Maltase
Sucrase
Lactase
Suggest the process by which microorganisms produce a large volume of gas in lactose intolerant individuals
Respiration
Suggest a reason why a gas is unlikely to be carbon dioxide
CO2 is formed in aerobic respiration
whereas conditions in colon is anaerobic
Suggest an explanation why lactose intolerance is a problem for modern day humans but wasn’t for our ancestors?
Modern storage and distribution methods mean that milk and milk products are readily available
Without these ancestors rarely consumed milk as adults
Explain how the lowering of water potential in the colon cause diarrhoea?
Low water potential in colon causes the water to move from epithelial cells into the lumen of the colon creating watery stools
Which process by which fatty acids and glycerol enter the intestine epithelial cells?
Diffusion
Explain the advantages of lipid droplet and micelle formation:
Droplet increases surface area for lipase enzyme action
Faster rate of hydrolysis reaction
Micelles carry fatty acids and glycerol through the intestine epithelial cell
Name how Golgi apparatus involved in the absorption of lipids
Modifies and processes triglycerides
Combine triglyceride with proteins
Form vesicles
Packaged for release/exocytosis
Sodium ions from salt(sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with carrier protein called NHE3.
NHE3 actively transport one sodium ion into the cell in exchange for one proton (one hydrogen ion) out of the cell
Use your knowledge of transport across cell membrane across cell membrane to suggest how NHE3 does this
Co-transport
Uses of hydrolysis - ATP needed
Sodium ion and protein bind to protein
Protein changes shape to move sodium ion and/or proton across the membrane
Explain why pH decreases when the lipase is added to the milk
Fatty acids are produced
Suggest why pH remained constant after 2 minutes
No more fatty acids are produced
All triglycerides/fat/lipids/substrate used up/enzyme denatured
Name the part of a pancreatic cell that produces an inactive form of trypsin
Ribosome/ RER - rough endoplasmic reticulum
Suggest an advantage of producing trypsin in an inactive form inside cells of the pancreas
Does not digest protein inside cells
So (pancreatic) cells/tissues/function does not get destroyed/damaged
Name the type of bond hydrolysed when the short chain of amino acids is removed
Peptide bonds
Sometimes trypsin can become activated inside a pancreatic cell.
A competitive inhibitor in the cell then binds to the trypsin and stops it working
Explain how the competitive inhibitor stops trypsin from working
Inhibitor has similar shape to the substrate
The inhibitor blocks the active site/complementary to the active side/binds to the active site of trypsin
Substrate cannot bind to active site/fewer ES complexes formed
Surgery is sometimes carried out to remove the gall bladder.
Explain why a change in diet is required after removal of gall bladder
Less fat in the diet
Bile emulsifies lipids/ produces smaller droplets
Increase surface area for (action of enzyme) lipase
Pancreatic enzyme becomes active when they reach the lumen
If the pancreatic duct becomes blocked, enzymes can become active in the pancreas
Suggest how activation of these enzymes in the pancreas can affect the pancreas
Protease/lipase digest (pancreatic tissue)
Where is maltase produced?
Small intestine
Where is amylase produced?
Pancreas
Salivary glands
