Topic 3 — B: More Exchange and Transport Systems Flashcards
What is digestion, and why is it essential?
breaks down large biological molecules (e.g., starch, proteins) into smaller molecules that can cross cell membranes, allowing nutrients to be absorbed from the gut into the bloodstream and transported around the body for cellular use.
What is a hydrolysis reaction?
break down polymers into monomers by adding water. For example, carbohydrates are broken into monosaccharides, fats into fatty acids and monoglycerides, and proteins into amino acids.
Which enzymes are involved in carbohydrate digestion, and where are they produced?
Amylase, produced by the salivary glands and pancreas, catalyzes starch breakdown into maltose. Membrane-bound disaccharidases, located on the ileum’s epithelial cells, break down disaccharides into monosaccharides
Describe the role of amylase in carbohydrate digestion.
Amylase catalyzes the hydrolysis of glycosidic bonds in starch, producing maltose. It’s secreted into the mouth (by salivary glands) and the small intestine (by the pancreas).
What are membrane-bound disaccharidases? Give an example.
These enzymes, attached to the cell membranes of ileum epithelial cells, break down disaccharides into monosaccharides. For example, sucrase breaks down sucrose into glucose and fructose.
Explain the digestion process of lipids
Lipase enzymes break down lipids into monoglycerides and fatty acids by hydrolyzing ester bonds. Lipases are mainly made in the pancreas and secreted into the small intestine
What role do bile salts play in lipid digestion?
Bile salts, produced by the liver, emulsify lipids, increasing the surface area for lipases to act by breaking lipids into smaller droplets, facilitating their breakdown.
What are micelles, and what is their function in lipid absorption?
Micelles are tiny lipid-bile salt structures that help deliver monoglycerides and fatty acids to the ileum epithelium for absorption. Micelles break up and reform, releasing their contents for absorption.
Describe the process of protein digestion.
Proteins are broken down by peptidases, which hydrolyze peptide bonds. Endopeptidases act within proteins, exopeptidases remove amino acids from protein ends, and dipeptidases work specifically on dipeptides.
Provide examples of endopeptidases and their locations.
Trypsin and chymotrypsin (from the pancreas, active in the small intestine) and pepsin (from the stomach lining, active in acidic stomach conditions).
What are dipeptidases, and where are they located?
membrane-bound exopeptidases that hydrolyze dipeptides into amino acids. They are located in the cell-surface membrane of the small intestine’s epithelial cells.
How is glucose absorbed in the ileum?
Glucose is absorbed by active transport with sodium ions via a co-transporter protein in the ileum epithelial cells.
How are monoglycerides and fatty acids absorbed?
they are lipid-soluble and diffuse directly across the epithelial cell membrane after being transported to the epithelium by micelles.
Explain amino acid absorption in the ileum.
Sodium ions are actively transported out of epithelial cells into the ileum and then diffuse back in, carrying amino acids with them through sodium-dependent transporter proteins.
What is the main role of haemoglobin in the circulatory system?
Haemoglobin in red blood cells carries oxygen throughout the body. It binds oxygen in the lungs and releases it to respiring tissues where oxygen concentration is low
Describe haemoglobin’s quaternary structure and its oxygen-binding capacity.
has four polypeptide chains, each with a haem group that contains an iron ion, which allows each haemoglobin molecule to carry up to four oxygen molecules.
What is the relationship between pO₂ and haemoglobin’s affinity for oxygen?
Haemoglobin’s affinity for oxygen increases with higher pO₂ (e.g., in the lungs) and decreases with lower pO₂ (e.g., in respiring tissues).
Explain the terms “loading” and “unloading” in relation to haemoglobin and oxygen.
Loading” (association) occurs when oxygen binds to haemoglobin, forming oxyhaemoglobin, typically in the lungs. “Unloading” (dissociation) occurs when oxygen is released to tissues.
What is the oxygen dissociation curve, and why is it S-shaped?
shows the percentage saturation of haemoglobin at different pO₂ levels. Its S-shape reflects cooperative binding, where binding the first O₂ molecule makes it easier for additional molecules to bind
Describe the Bohr effect and its importance in oxygen unloading.
occurs when high pCO₂ (from active respiration) shifts the dissociation curve to the right, lowering haemoglobin’s oxygen affinity and promoting oxygen release to tissues.
How does haemoglobin adaptation help animals in different environments?
Animals in low-oxygen environments (e.g., underground or high altitudes) have haemoglobin with a higher oxygen affinity, while highly active animals have haemoglobin with lower affinity for efficient oxygen unloading.
What is haemoglobin and its primary role?
Haemoglobin is a protein in red blood cells that binds to oxygen in the lungs and releases it at tissues for respiration.
How does haemoglobin’s affinity for oxygen change?
Its affinity changes based on oxygen concentration (partial pressure of oxygen), CO₂ concentration, and pH (Bohr effect).
Define partial pressure of oxygen (pO₂).
Partial pressure of oxygen is a measure of oxygen concentration; high in the lungs and low in respiring tissues.
Explain the oxygen dissociation curve.
It shows haemoglobin saturation with oxygen at different pO₂. The curve is sigmoidal due to cooperative binding.
What is cooperative binding in haemoglobin?
When one oxygen molecule binds to haemoglobin, it increases the affinity for more oxygen molecules to bind.
