BIOB34H3 Lecture Notes - Lecture 7: Cecum, Protein Precursor, Portal Venous System
HYDROLYTIC DIGESTION
- Carbs come in 3 diff types:
mono/di/poly
-Monosaccharides are not
digested simple enough
to be absorbed as is
-Disaccharides have to be
digested à just break the
bonds and digest à need
enzyme that can break the
bond between them à use a disaccharidase (eg. Lactase to break down lactose)
- The breaking down is happening in the midgut à once bonds are broken, the compounds
are simply absorbed
not a simple process however: monosacchrides are hydrophillic à cannot simply diffuse
through cells (b/c hydrophobic core) à thus need transporters à thus: digestion can only
take place in areas where those transporters are found: midgut
MONOSACCHARIDE DIGESTION
- 2 major types involved in the absroption:
-SGLT- sodium/glucose co-transporters à couple the uptake of glucose to the uptake of
sodium
- There is an NA/K ATPase à pumps sodium from cells into the outside à Sodium conc. In
the cell decreases à diffusion gradient à co-transporter links the uptake of sodium to the
uptake of glucose à is an active process
-Glucose-transporters (can absorb other tpye of sugars as well)
- Lots of them
- Do it in a passive process
- Are just channels in the membrane that allow for glucose to enter the cell through
facilitated diffusion à it’s only when the conc. Of glucose in the gut goes down, that the
co-transporter is used
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- The exact same process occurs with water
soluble vitamins
Usually transporters that couple the
uptake of Vitamin B/C with the uptake of
sodium
-Hydrophillic compounds cannot diffuse
through PM in the intestinal cells require
transporter for absorption only absorb in
areas where these transporters are
present (usually midgut)
TYPES OF CARBOHYDRATES
-Polysaccharides are complex sugars (have
lots of monosacchrides linked together)
-3 major kinds that animals consume:
starch, glycogen, and cellulose
- One thing similar between all 3, is that they are all just polymers
of glucose
-Starch is an energy storage compound for plants (eg. If you see
potato that are tubing, they’re using their starch to continue
growth)
-Glycogen: energy storage molecule for animals, stored in liver,
muscles
-Cellulose: structural molecule, gives plants their
structural strength (animals use proteins like
collagens for structural parts)
-Linear chain of glucose typically becomes in a
ringed-form in body à when glucose goes from
linear molecule to a ring, and forms a hydroxyl
group that either ends up above the ring or below
the ring
-Alpha is below
-Beta is above
- Starches are glycogen are comprised of alpha-
glucose à form alpha-glycosidic bonds
- Cellulose has beta-glucose à form beta-glycosidic bonds
HYDROLYTIC DIGESTION OF POLYSACCHARIDES
-Starch and glycogen are digested by hydrolytic
digestion à animals themselves produce enzymes
necessary to digest them à the enzyme is amylase
(it can break alpha-glycosidic bonds)
- Called an endopolysacchraide à means: amylase
can only break internal bonds, not terminal bonds
- Won’t directly produce glucose, will create things
like maltose
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- Can sometimes create Limit dextrins à branches
- Starch and glycogen are easy compounds to digest
à alpha-glucose molecule cannot be easily packed
together à create a very spacious structure à
there’s lots of space for amylase to break those
internal bonds b/c ease of access, thus makes it
easier to digest
FERMENTATIVE DIGESTION
-Cellulose is beta-glucose à beta-glycosidic bonds between indiv. Glucose
à require a diff. enzyme to break them: cellulase à most animals cannot
produce this
- Thus digestion of cellulose requires: microbial-symbiosis à strategy most
herbivores take is harbor microbes (eg. Protists/archae etc.) à these
produce cellulase à occurs via fermentative digestion (when the enzyme is
being produced by a microbe, rather than by the animal itself)
- When see strcture of cellulose vs glycogen, molecules are more compact b/c b-glucose
molecules allows for it to be packed much tigther cellulose is much harder to digest
- Thus: Herbivores require larger, more complex digestive systems to be able to break
down the cellulose
FOREGUT FERMENTATION
- Two types of fermentative digestion: foregut (rumination, go over again/regurgitate)
and hindgut digestion
- Foregut
- More times mechincally break down molecules by ruminaition, the more successful the
digestion will be
- Examples: eg. Cows, goats, sheeps etc. à all these mammals do this fermentative
digestion in their foregut (stomach) and ruminate their food
- Digastric Stomach
- rumen and reticulum = fermentative digestion
- symbiotic microorganisms present
- omasum and abomasum = hydrolytic digestion
- - digestive enzymes = “true stomach”
-Animals with this mechanism have a digastric stomach: have 2 major
compartments of your stomach // 1st part: RUMEN (in the back
portion), 2nd part: RETICULUM // together make up the
fermentative digestion parts of the stomach, are the parts where
you’ll find the greatest density of microorganisms
- As food comes in, it goes to the rumen first, then into the reticulum à then food is
ruminated and is brought back to the mouth to be chewed again
- > i.e fermentative digestion occurs first, then goes into the mouth for food again à once
chewed for 2nd time, food bypasses the rumen and goes into the omasum and then
abomasum à these are the hydrolytic compartments of the cow // thus there are 4
major parts of the stomach
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Document Summary
Monosaccharides are not digested simple enough to be absorbed as is. Disaccharides have to be digested just break the bonds and digest need enzyme that can break the bond between them use a disaccharidase (eg. lactase to break down lactose) The breaking down is happening in the midgut once bonds are broken, the compounds are simply absorbed. Not a simple process however: monosacchrides are hydrophillic cannot simply diffuse through cells (b/c hydrophobic core) thus need transporters thus: digestion can only take place in areas where those transporters are found: midgut. Sglt- sodium/glucose co-transporters couple the uptake of glucose to the uptake of sodium. There is an na/k atpase pumps sodium from cells into the outside sodium conc. In the cell decreases diffusion gradient co-transporter links the uptake of sodium to the uptake of glucose is an active process. Glucose-transporters (can absorb other tpye of sugars as well)
