AQA BIOLOGY B2 Digestion

B2 PART 2.. It has all the information about digestion and enzymes

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Enzymes are biological catalysts. There are optimum temperatures and pH values
at which their activity is greatest. Enzymes are also proteins, and usually
denatured above about 45ºC.
Enzymes are important in respiration. Aerobic respiration releases energy from
What are enzymes?
Enzymes are biological catalysts - catalysts are substances that increase the rate of
chemical reactions without being used up. Enzymes are also proteins that are folded into
complex shapes that allow smaller molecules to fit into them. The place where
these substrate molecules fit is called the active site.
If the shape of the enzyme changes, its active site may no longer work. We say the
enzyme has been denatured. They can be denatured by high temperatures or extremes
of pH. Note that it is wrong to say the enzyme has been killed. Although enzymes are
made by living things, they are proteins, and not alive.
Temperature and enzymes
As the temperature increases, so does the rate of reaction. But very high temperatures
denature enzymes.
The graph shows the typical change in an enzyme's activity with increasing temperature.
The enzyme activity gradually increases with temperature until around 37ºC, or body
temperature. Then, as the temperature continues to rise, the rate of reaction falls
rapidly, as heat energy denatures the enzyme.
Temperature and enzyme activity
pH and enzymes
Changes in pH alter an enzyme's shape. Different enzymes work best at different pH
values. The optimum pH for an enzyme depends on where it normally works. For example,
intestinal enzymes have an optimum pH of about 7.5. Enzymes in the stomach have an
optimum pH of about 2.

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H and enzyme activity
Enzymes and respiration
Enzymes in cells catalyse photosynthesis, protein synthesis - joining amino acids
together, and aerobic respiration.
Aerobic respiration
Respiration is not the same thing as breathing. That is more properly called ventilation.
Instead, respiration is a chemical process in which energy is released from food
substances, such as glucose - a sugar.
Aerobic respiration needs oxygen to work. Most of the chemical reactions involved in the
process happen in tiny objects inside the cell cytoplasm, calledmitochondria.…read more

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Enzymes are important in digestion. Digestion is the breakdown of carbohydrates,
proteins and fats into small soluble substances that can be absorbed into the
Lipases and proteases are used in biological detergents, and enzymes are used in
the manufacture of food and drink.
The digestive system
Digestion is the breakdown of large molecules into smaller, soluble molecules that can be
absorbed into the body. Digestion happens inside the gut, and relies on enzymes.…read more

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Enzymes and digestion
The enzymes involved in respiration, photosynthesis and protein synthesis work inside
cells. Other enzymes are produced by specialised cells and released from them; the
digestive enzymes are like this. They pass out into the gut, where they catalyse the
breakdown of food molecules.
Different enzymes
Different enzymes catalyse different digestion reactions.
Enzymes and their reactions catalysed
enzyme reaction catalysed
amylase starch sugars
proteas proteins amino acids
lipase lipids fatty acids +
Amylase is an example of a carbohydrase.…read more

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Overall, this means that:
Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine.
Proteases catalyse the breakdown of proteins into amino acids in the stomach and small
Lipases catalyse the breakdown of fats and oils into fatty acids and glycerol in the small
Other substances in digestion
You should recall that different enzymes work best at different pH values. The digestive
enzymes are a good example of this.
Enzymes in the stomach
The stomach produces hydrochloric acid.…read more

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Enzymes in industry
Enzyme names
The names of the different types of enzymes usually end in the letters -ase. Three of the
most common enzymes with their chemical actions are:
lipase - breaks down fats
protease - breaks down proteins
carbohydrase - breaks down carbohydrates
Enzyme uses
Enzymes allow certain industrial processes to be carried out at normal temperatures and
pressures, thereby reducing the amount of energy and expensive equipment needed.
Enzymes are also used in the home, for example, in 'biological' detergents.…read more


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