Exchange and Transport Systems Flashcards
(24 cards)
Define digestion
The hydrolysis of large, insoluble molecules into smaller, smaller molecules that can be absorbed across cell membranes.
What is hydrolysis?
Breaking the chemical bonds of a molecule by adding a molecule of water
What are carbohydrates broken down into?
Disaccharides-> monosaccharides
What are lipids broken down into?
Fatty acids and monoglycerides (has one fatty acid attached)
What are proteins broken down into?
Amino acids
Describe the process of starch digestion.
(s -> m)
Salivary glands secrete saliva = contains amylase = catalyses hydrolysis of starch into maltose = glycosidic bonds broken
In pancreas = starch digestion continues in duodenum = pancreatic amylase secreted from pancreas = catalyses hydrolysis of any undigested starch into maltose = glycosidic bonds broken = substrate is complementary to the shape of the active site
Why can’t maltose be absorbed?
It is a large molecule that is too big to fit through.
Describe the small intestine brush border.
Maltase is an enzyme found in the cell membranes of epithelial cells = catalyses the hydrolysis of maltose into glucose = breaks the glycosidic bonds = substrate is complementary to the shape of the active site
Where is amylase produced?
Pancreas and salivary glands
Describe the digestion of lipids
Bile salts produced by liver = emulsify lipids = increases surface area for lipase to work on
Monoglycerides and fatty acids attach onto bile salts to form micelles
What are micelles?
Monoglycerides and fatty acids attached onto bile salts
Why are fats emulsified?
Provides a larger surface area for faster hydrolysis action by lipase
What do micelles do?
They deliver the monoglycerides, glycerol and fatty acids to the epithelial cells lining the ileum by diffusion
How is the small intestine adapted for absorption?
Contains villi which are surrounded by a network of capillaries- maintain concentration gradient
Epithelial cells are covered with microvilli- large surface area
The epithelial cells are thin- short diffusion pathway
Where is lipase produced?
Pancreas
How are large polypeptides digested?
Endopeptidases
Hydrolyse peptide bonds
Between the amino acids in the central region
Smaller peptide molecules
Where are endopeptidases produced?
Stomach and small intestine
How are smaller polypeptides digested?
Exopeptidases
Hydrolyse peptide bonds
Between terminal amino acids
Dipeptides + amino acids
Where are exopeptidases produced?
Pancreas
Why is it beneficial to digest polypeptides in the middle to produce smaller peptides?
To increase the surface area and provide more “ends” for exopeptidases
How are lipids digested?
Emulsified by bile salts
Lipase hydrolyses the ester bonds
Glycerol and fatty acids (monoglycerides)
What is the role of bile?
Emulsifies fats to provide lipase with a larger surface area to work on
What happens during co-transport?
Sodium is actively transported out of the epithelial cell into the bloodstream
Low con of sodium
Sodium moves into the cell via facilitated diffusion along with glucose due to specific shape of binding site on the co-transport protein
Glucose is transported out of the cell and into the blood via facilitated diffusion
How are lipids absorbed?
Micelles come into contact with epithelial cells
They break down and release fatty acids and glycerol
Fatty acids and glycerol are non-polar so they can easily diffuse into the epithelial cells
Reform to form triglycerides
Transported into the bloodstream via exocytosis
