Topic 2: Enzymes and The Digestive System

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  • Created on: 12-03-14 21:37
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Topic 2: Enzymes and The Digestive System
Topic 2.1 Enzymes and Digestion
Major Components of the digestive system
Oesophagus
Responsible for movement of food from the mouth to
the stomach
Adapted for transport
Consists of a thick muscular wall
Stomach
Muscular sac lined with a layer that secretes enzymes
and mucus
Responsibility of storing and digesting food
Mucus production prevents the stomach from being
digested by its own enzymes
Enzyme From To
Carbohydrase
(e.g. Amylase) Carbo-hy Mono-sacc
drates harides
Lipase Lipids Glycerol &
fatty acids
Protease Proteins Amino
Acids
Small Intestine
Long muscular tube
Digested further by enzymes secreted by its walls and surrounding glands
Inner layer folded into villi, which contain projections of microvilli.
Surrounded by epithelial cells
Increased surface area to volume ratio
Surrounded by numerous capillaries.
Large Intestine
Absorption of water
Water absorbed here is mainly due to secretions of enzymes
Formation of faeces, much drier and thicker in consistency
Rectum
Purpose of storage before being removed (egestion)
Salivary Glands
Situated near the mouth
Secretions pass via a duct
Main enzymes include amylase.
Pancreas
Gland which secretes pancreatic juice
Situated below the stomach
Secretion contains enzymes; proteases for proteins, lipase for lipids and amylase for carbohydrates
Digestion
Physical Digestion
Shivani BarotPage 1
13F

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Topic 2: Enzymes and The Digestive System
Breaking down of components by physical movement, such as the churning in the stomach by muscles
movements, and chewing of food
Increases surface area
Chemical Digestion
Breaking down large molecules into much smaller molecules with the addition of water.
Hydrolysis ­ the function of digestive enzymes (hydrolases is the term given to digestive enzymes)
Molecules are absorbed into the body, and assimilated, where they are incorporated into body tissues
and used in processes.
2.…read more

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Topic 2: Enzymes and The Digestive System
2.3 Carbohydrates ­ Disaccharides and Polysaccharides
Monosaccharides combine to form disaccharides as a result of condensation reactions, which form
glycosidic bonds.
The formation of polysaccharides is a result of multiple condensation reactions
Condensation reactions remove water molecules; to break down polysaccharides, hydrolysis adds water
to the polymer. The diagram below shows an
example.
Testing for non-reducing sugars
Similar to reducing sugars, Benedict's reagent is
used, whereas for non-reducing sugars, the
substance needs to be broken into reducing
sugars.…read more

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Topic 2: Enzymes and The Digestive System
The epithelial lining of the small intestine secretes maltase, which is used for the hydrolysis of maltose
into -glucose.
Digestion ­ Disaccharides
Sucrose
Found contained in cells, which is physically
broken down by the teeth.
Epithelial lining produces sucrase which is used
to hydrolyse sucrose into fructose and glucose.
Hydrolysis breaks the glycosidic bonds in
sucrose.
Lactose
Sugar found in milk
Hydrolysed in the small intestine as a result of
the lactase secretions in the small intestine.…read more

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Topic 2: Enzymes and The Digestive System
Hydrolysis breaks down the peptide bonds (similar to that of carbohydrates)
Primary Structure ­ Polypeptides
Amino acid monomers joined together from a number of condensation reactions (condensation
polymerisation)
Formation of a polypeptide, which is the primary structure of a protein.
There is no set number of possible primary structures, as there are a limitless number of combinations.…read more

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Topic 2: Enzymes and The Digestive System
Hydrogen bonds - these are found in high proportions to the other bonds, but these are the most easily
broken bonds.
Quaternary Structure
These are proteins that contain prosthetic (non-protein groups)
An example of a quaternary structure for a protein is haemoglobin, where the haem group (iron containing
group) is incorporated into the protein.…read more

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Topic 2: Enzymes and The Digestive System
One important limitation that was recognised was the fact that a lock (in this case, a substrate) is of a rigid
structure.
From the evidence given by scientists, it was observed that a substrate was able to place itself into an
area on the enzyme which was not its active site.…read more

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Topic 2: Enzymes and The Digestive System
Figure 2: Observation of Disappearance
The initial reading will be high, as the reaction will not have begun.
Will begin to plateau at lower points, as the reactant is being used (and converted into products)
As the reaction progresses, the reactant will be used up as a result of successful collisions.…read more

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Topic 2: Enzymes and The Digestive System
When there is a low substrate concentration, there are empty active sites, and so the rate of reaction is not as
efficient as it can be, as the active sites are not being used to its full extent.
When the substrate concentration is equal to the number of active sites, the rate of reaction is at its most
efficient, as the active sites are all being used constantly.…read more

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Topic 2: Enzymes and The Digestive System
Shivani BarotPage 10
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