Topic 3 Organisms exchange substances. Digestion and Absorption Flashcards
What is digestion
The hydrolysis of large insoluble molecules into smaller molecles that can be absorbed across cell membranes.
e.g lipids proteins carbohydrates
Which enzymes are involved in carbohydrate digestion where ate they found?
Amylase in mouth (produced in the pancreas and salivary glands)
Maltase, sucrase, lactase in membrane of small intestine.
(membrane bound disaccharidases)
What does Amylase do in the giestion of carbohydrates
Hydrolyses polysaccharides into disaccharide maltose by hydrolysising glycosidic bonds
maltose-into 2x glucose
sucrase and lactase hydrolyses sucrose and lactose into monosacchairdes
sucrase- sucrose into glucose and fructose
lactase- lactose into glucose and galactose
What are membrane-bound disaccharidases, and where are they located?
Membrane-bound disaccharidases, such as maltase, sucrase, and lactase, are enzymes attached to the epithelial cells lining the ileum
What are proteins and what are the three enzymes they can be hydrolysed by
Endopeptidases: hydrolyse peptide bonds between amino acids in the middle of a polymer chain.
Exopeptidases: hydrolyses peptie bonds between amino acids at the end of a poylmer chain
membrane bound dipeptidases: hyrolyse pepride bonds between two amino acids
Describe where protein digestion takes place
Starts in the stomach and continues in the duodenum and is fully digested in the illeum
What needs to happen before lipids can be digested (physical stage)
They must be emulsified by bile salts produced in the liver. this breaks down large fat molecules into smaller soluble molecules called micelles increasing surface area for lipase to act on.
lipids coated in bile salts to create an emulsion many small droplet of lipids provides a larger surface area to enable faster hydrolysis by lipase
How are lipids digested (chemical stage)
Lipase produced in the pancreas, hydrolyses the ester bond in trigylcerides to form the monoglycerides(glycerol) and fatty acids
What is a micelle and what do they do
Micelles are water soluble vesicles formed of the fatty acids and glycerol, monoglycerides and bile salts
they deliver fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorbtion
Where in mammals are products of digested absorbed?
absorbed across the cell linings of 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 micro villi.
these maximise absorbtion by maintaining conc gradient increaseing sa and decreasing the diffusion distance
How are monosaccharides and amino acids absorbed
Why do monosaccharides and amino acids require co transport to be absorbed
Because to absorb glucose and amino acids into 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 so active transport and co transport are required.
How are fatty acids and monoglycerides absorbed
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 non polar nature of fatty acids and monoglycerides they can simply diffuse across the cell surface membreane to enter the cells of the epithelial cells.
once in the cell these will be modified back into triglycerides inside of the endoplasmic reticulum and golgi body
Describe the process of co transport of glucose and sodium ions in the ileum (amnio acids and monosaccharides)
- Sodium ions actively transported (sodium potasium pump) out of the epithelial cells into the blood.
- This reduces the sodium ion concentration in the epithelial cell. creating conc gradient
- Sodium ions can diffuse from the lumen down the concentration gradient into the epithelial cell
- The protein the sodium ions diffuse through is a co transported protein so amino acids or glucose can attatch and are transported into the epithelial cell against their concentration gradient.
- glucose then moves via facilitated diffusion via carrier protein from the epethilial cell to the blood
Explain the advantagges of lipid droplet and micelle formation
- Droplets increases Surface area for lipase enzyme action
- So faster hydrolysis of lipids
- micelles carry fatty acids and glycerol through membrane to epithelial cell
