Absorption of carbohydrates and proteins

Question 1

What are carbohydrates?

Answer 1

• Glucose is used to make ATP
• Can use proteins and lipids to make ATP but they are needed so you don’t want to waste them in other processes but carbohydrates are not
• Carbohydrates also are hydrolysed into glucose easily
• Found for diet in plants and milk
• Fibers/cellulose needed for gut health
• Add bulk to food/feel more full
• Complex carbohydrates talk longer to digest so blood glucose level is constant for longer
• Starch is found in plants and is made of glucose- used to make ATP
• Glycogen- glucose storage in animal cells- in liver and muscles ( branching will increase the surface area for hydrolysis)
• Cellulose forms in plants and is used for structural support - can’t be digested as it is too tightly packed together
• Polysaccharides are polymers made up of glucose monomers
• Disaccharides
○ 2 glucose= maltose
○ Glucose+fructose= sucrose
○ Glucose+ galactose = lactose (mainly in milk)
• Fructose is cheaper to produce than glucose ( made of corn but glucose is made of cane ) corn is cheaper than cane

Question 2

How are carbohydrates digested?

Answer 2

1. Chewing increases the surface are of the food for enzyme attachment
   
   2. Salivary amylase break down Polysaccharides into shorter chains. This increases the surface area/ends for enzymes to attach
   3. Amylase are denatured by stomach acid
   4. Pancreatic enzymes hydrolyse the Polysaccharides into disaccharides
   5. Membrane bound disaccharides at the intestinal brush border (e.g. maltase, sucrase, lactase) separates the 2 monomers
   6. Liver will convert fructose and galactose into glucose
      (Glucose in blood will damage the blood vessels) so excess glucose must be stored as glycogen in the muscles or liver
      • Fructose can’t be stored in muscles and liver as glycogen. Must be converted to fat then stored in the liver (causes fatty liver disease- cause of liver cancer)
      •

Question 3

How are monosaccharides absorbed?

Answer 3

1. Glucose moves down a concentration gradient by simple diffusion (passive)-may need a transport proteins
   
   2. Eventually the concentration of glucose outside the cell will be the same as the concentration inside the cell (no net movement of glucose)
      ○ Glucose is too valuable to be wasted/pooped out so all is absorbed
      ○ All glucose must be absorbed (needs active transport)
   3. Na+/K+ ATPase (Na+/K+ pump) will actively (use ATP) to pump Na+ out of the enterocyte and K+ into the enterocyte- active transport
      ○ This will create a concentration/electrochemical gradient of Na+ (higher in the gut than the cell)
   4. The electrochemical/concentration gradient of Na+ causes the cotransport of Na+ and glucose from the lumen into the enterocyte (co-transport) by facilitated diffusion down an Na+ electrochemical/concentration gradient (passive)
   5. Fructose will enter the cell by facilitated diffusion
   6. Glucose, galactose and fructose concentration is higher in the cell then the blood so they move out by facilitated diffusion by the same channel protein
      ○ Some glucose is used by the cell for respiration, create ATP for Na+/K+ pump

Question 4

What are proteins?

Answer 4

• Used to build and repair cells/tissue
• Polypeptides= polymer of animo acid monomers
• Can get energy from proteins (and lipids) when glucose/carbs are not available however this is energy expensive and inefficient
• Loose a lot of protein daily
• Only half of the Proteins in the gut is proteins in diet
○ Cells that have been removed from gut
○ Pathogens
○ Plasma form leaky villi
○ mucus
○ Enzymes
○ (are all proteins)
• Dipeptides and tripeptides and also be absorbed

Question 5

How are proteins digested?

Answer 5

1. In stomach - endopeptidase
   ○ Stomach acid will unfold/ denature the protein to increase the surface area for attachment of peptidase
   ○ HCL in stomach will convert it inactive pepsinogen into active pepsin (pepsin will start digesting the proteins and creating smaller chains)
   § Pepsin breaks large molecules into smaller molecules
   ○ Endopeptidase- hydrolyse peptide bonds in between polypeptides
   § Endopeptidase- break peptide bonds in the middle of the polypeptide to increased surface area for exopeptidase (hydrolyses at the ends)
   § (pancreatic trypsin is produced by the pancreas and is an exopeptidase)
   ○ Gastric pepsin
   
   2. In intestines -exopeptidases
      ○ pancreatic enzymes breaks down polypeptides, intestinal brush border enzymes and enterocytes enzymes
      ○ Exopeptidases hydrolyses bonds at the ends of the polypeptide
      ○ Removes 1 peptide at a time
      • Have luminal and cellular digestion
   3. Dipeptides separate amino acids in dipeptides
   4. although Dipeptides and tripeptides and also be absorbed into the cell they will be broken down into amino acids before entering the blood stream

Question 6

How are animo acids absorbed?

Answer 6

1. Na+/K+ ATPase (Na+/K+ pump) will actively (use ATP) to pump Na+ out of the enterocyte and K+ into the enterocyte- active transport
   ○ This will create a concentration/electrochemical gradient of Na+ (higher in the gut than the cell)
2. The electrochemical/concentration gradient of Na+ causes the cotransport of Na+ and amino acids from the lumen into the enterocyte (co-transport) by facilitated diffusion down an Na+ electrochemical/concentration gradient (passive)
3. Amino acids can also will enter the cell by simple and facilitated diffusion
4. Amino acid concertation is higher in the cell then the blood so they move out by facilitated diffusion by the a transport protein
5. Some amino acids is used by the cell e.g. for protein synthesis
   • Whole proteins may be absorbed
   ○ by newborns who need to absorb maternal antibodies from the milk by pinocytosis (invagination of cell membrane to form vesicles)
   ○ If the junction between cells are leaky can trigger an allergic reaction as the protein may get through into blood
   ○ fructose can make junctions leaky