Download topic 6.1 digestion notes

6.1 Digestion
6.1.1 Explain why digestion of large food molecules is
essential
Adequate diets provide 3 main functions,
1.fuel to make ATP
2. raw materials for biosynthesis,
3. essential nutrients.- those that the animal cannot
make itself.
Large polymers of carbohydrates, proteins, and fats provide
lots of ATP when they are hydrolysed. Fats liberate twice
the energy of carbohydrates and proteins.
Essential nutrients- Of the 20 amino acids, humans cannot
make 9 of them. It is essential that we obtain them in our
diet.
( Tryptophan, Methionine, Valine, Threonine,
Phenalalanine, Leucine, Isoleucine, Lysine …. Histidine is
required by infants.)
We also cannot make a fatty acid - linoleic acid. It is an
essential fatty acid
It is used to make some of the phospholipids in membranes.
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Vitamins are organic molecules that are required in very
small amounts. Humans require 13 essential vitamins.
These are grouped into the water-soluble and fat-soluble
categories.
Water-soluble vitamins such as Vitamin C are excreted in
urine so overdoses are not usually possible.
Vitamins A,D,E, and K are fat-soluble and when taken in
excess amounts, they can accumulate in fatty tissues to
toxic levels.
Minerals are inorganic nutrients also required in small
amounts.
Calcium, phosphorous, and iron are examples
(see page 855)
6.1.2 Explain the need for enzymes in digestion
[The need for increasing the rate of digestion at body
temperature should be emphasized.]
Enzymes are used to hydrolyse the macromolecules of life
into their monomers. Enzyme function changes with the
temperature. Warm blooded organisms need more energy,
and the warmth increases enzyme function.
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6.1.3 State the source, substrate, products and optimum pH
conditions for one amylase, one protease, and one lipasesee page 864
Carbohydrates--glucose, example: salivary amylase
Carbohydrate hydrolysis begins in the mouth, but the
Stomach acids inactivate the amylase, further hydrolysis
occurs in the small intestine with other enzymes like
pancreatic amylase, sucrase and lactase.
Proteins-- amino acids, example: pepsin in the stomach
pepsin likes acidic environment of the stomach since
the low pH unfolds the proteins making their peptide bonds
more accessible. More protein hydrolysis occurs in the
small intestine.
lipids-- glycerol + fatty acids, example: lipase in small
intestine. Bile salts are secreted from the gall bladder to act
as a detergent in breaking up masses of lipids.
( emulsification)
Nucleic acids-- nucleotides, example: Nucleases in small
intestine. Nucleotides can be broken down further into
ribose sugars, phosphate groups, and nitrogenous bases
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6.1.4 Draw a diagram of the digestive system
[The diagram should show the mouth, esophagus,
stomach, small intestine, large intestine, anus , liver,
pancreas and gall bladder.The diagram should clearly
show the interconnections between these structures. ]
{ see page 863 fig 41.16)
6.1.5 Outline the function of the stomach, small
intestine,and large intestine
Mouth: breaks up the food increases surface area for
enzyme action, saliva lubricates, salivary amylase begins
hydrolyzing carbohydrates.
esophagus: Muscular tube from mouth to stomach. The
epiglottis flap of skin keeps food out of the trachea.Peristaltic
contractions move food towards the stomach. It is not lined with
mucus, so acid from the stomach can ulcerate it.
Stomach: A muscular sack that stores food, sterilizes it with
acid, mechanically and chemically breaks up the food, and
begins the hydrolysis of proteins. Note that the acid environment
and protease enzymes make a dangerous environment for the
stomach itself. Mucus secreted in the stomach protects it from
the acid, the protease is not secreted in its active form. It is
activated by the acid in the stomach. The stomach lining
regenerates every 3 days. The pyloric sphincter separates the
stomach from the small intestine.
Small intestine: Where most of the digestion takes place. The
upper portion, the Duodenum, is where the enzymes from the
pancreas, bile from the gall bladder, and enzymes from glands in
the wall of the small intestine. Most absorption of monomers
and nutrients take place here.
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pancreas: produces enzymes for digestion and transports them to
the small intestine.
liver: digestive function is to produce bile which is stored in the
gall bladder. Bile acts as a detergent breaking up lipid
molecules. The liver also stores glycogen, controls glucose
levels in the blood, neutralizes poisons in the blood and removes
worn out red blood cells.
large intestine: the main function is to re-absorb water that has
been used as a lubricant and solvent in the processing of the
food. Waste becomes more solid as water is removed. Excess
salts can be excreted into the large intestine. Symbiotic Bacteria
Escherichia Coli ( E. Coli) help produce some vitamins, as well
as methane and hydrogen sulfide.
6.1.6 Distinguish between absorption and assimilation
Absorption is when the nutrients are moved into the blood
stream and cells via diffusion and active transport.
Assimilation is when these nutrients are incorporated into
the body. New proteins, new carbohydrates, etc.
6.1.7 Explain how the structure of the villus is related to its
role in absorption of the end products of digestion
see p 865 figure 41.19
Lots of surface area for absorption, 300m2 for humans
Villi have microvilli on them, all closely associated with
blood capillaries. Surfaces have active pumps for many
nutrients.
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