Lecture 26- chemical digestion Flashcards
What are carbohydrates important for? What are the most common examples?
- Important source of energy
- Starch, glycogen
What is the structure of carbohydrates like?
- Chains of monosaccharides
- Example of monosaccharide is glucose
- Joined by a1-4 glycosidic bonds (at least in the case of starch + glucose)
What are disaccharides and what are some common examples?
- Two monosaccharides joint together
- Sucrose, lactose, maltose
How do we usually ingest carbohydrates and what does this mean?
-Usually ingest as large indigestible molecules (many units joint together) which then have to be broken down to the smallest building block (monosaccharides) to be digested + absorbed.
What are proteins important for?
- Not a source of energy
- Proteins are required as they break down to amino acids (most of our body is made of proteins)
How many amino acids are there in the body? How many can be synthesized? What does this mean?
- 21 amino acids in body
- 12 can be synthesized
- Others essential, cannot be synthesized (or too energy expensive
- These therefore have to be gained from our diet
What are some amino acids that can not be produced by the body?
Histidine, leucine lysine
What is the breakdown of where we source protein?
- 50% Diet
- 50% Endogenous proteins (come from within e.g. enzymes and immunoglobins secreted in the small intestine)
What is the structure of proteins?
- Base unit is an amino acid
- These form long chains via peptide bonds
- It is these long chains that are the proteins
What are lipids important for?
Not essential but…
- Important source of energy
- Source of fat soluble vitamins A, D, E & K
Why do lipids slow gastric emptying?
Because they are complex to digest + absorb (take longer to break down)
What is the main type of lipid? What is it’s structure?
- Mainly triglycerides
- These consist of a Glycerol back bone with 3 fatty acids attached
How does the length of the fatty acids attached to the glycerol backbone vary?
Can be…
- Short chain fatty acids < 6 carbons
- Medium chain fatty acids – 6 to 12 carbons
- Long chain fatty acids – 12 – 24 carbons
Why do we need chemical digestion?
We ingest nutrients in the from of large complex molecules (carbohydrates, proteins, lipids) but can only absorb nutrients as small molecules. Therefore need first mechanical and then chemical digestion to occur so that nutrients can be absorbed and then used.
Chemical digestion utilizes
Digestive enzymes
How does mechanical digestion aid chemical digestion?
Mechanical digestion breaks up food increases surface area available for chemical digestion as enzymes can only act at the surface of the particles.
What are some features of digestive enzymes?
- Are extracellular
- Are organic catalysts
- Very specific (different enzymes are needed for different substrates)
- Have optimum pH
What are the optimum pH's of... -Salivary enzymes -Gastric enzymes -Small intestinal enzymes ??
- Salivary enzymes= 7-8 (Alkaline)
- Gastric enzymes= 1-2 (acidic)
- Small intestinal enzymes = 7-8 (Alkaline)
What are the names of the specific enzyme type that digests... -Carbohydrates -Proteins -Fats ??
- Carbohydrates= Amylase
- Proteins= Proteases
- Fats= Lipases
How do digestive enzymes act as organic catalysts?
- Enzyme combines with substrate to form enzyme-substrate complex. This then produces a product and the enzyme at the end.
- Therefore the enzyme acts as a catalyst as you get it back in the end (is not used up)
Can cellulose be digested? What does this prove about specifity?
- Cellulose is the structural polysaccharide of plants and we have lots in our diet
- Its made of long chains of b 1- 4 glycosidic bonds
- We do not have the enzyme specific to breaking these bonds (only have alpha amylase) and therefore cellulose cannot be digested (acts as dietary fiber)
What are the two general stages of digestion?
- Stage one= Luminal digestion. Initial digestion involving enzymes secreted into lumen. In salivary glands/mouth, stomach, small intestine (via pancreatic enzymes)
- Stage two= Contact digestion. Only occurs in the small intestine completing digestion before absorption. Involves enzymes produced by enterocytes and attached to brush border of enterocytes
Describe stage 1 of carbohydrate digestion…
Luminal digestion:
- Using salivary and pancreatic amylase
- Polysaccharides converted to oligosaccharides and disaccharides (smaller components via breaking bonds)
Describe stage 2 of carbohydrate digestion…
Contact digestion:
- Disaccharides converted to monosaccharides (these can then be absorbed)
- Involves the enzymes (bound to brush border) which are specific to the disaccharide (Sucrase, lactase, maltase)
