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Nucleotides and nucleic acids Biology A level for OCR revision notes
OCR A Biology Module 2 (Foundations in Biology) Notes
BIOLOGY AS SUPERNOTES
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Biology
Foundations in Biology
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Enzymes
often named for
Enzymes are
they are involved
the reaction
in. Most names for enzymes
end in 'ase! Some names
indicate function too.
E.g. Phosphorylasescatalyse rest
the
molecules
4.1 enzyme action
Enzymes are biological catalysts. They are globular proteins that interact with the substrate molecules, causing them to react at a much faster rate without
the need for harsh environmental conditions.
The role of enzymes in reaction
1. The chemical reactions required for growth are anabolic (building up) reactions which are all catalysed by enzymes.
2. Catabolic (breaking up) reactions of large organic molecules release energy in metabolic pathways. These reactions are catalyses by enzymes
3. Digestion is catalysed by enzymes.
4. Metabolism can only happen as a result of the control imposed by enzymes. Metabolism is the sum of all of the different reactions and pathways
happening in a cell or an organism.
5. Temperature, pressure and PH may all have an effect on the rate of reaction. Enzymes can only increase the rate of reaction up to a certain point called
the Vmax (maximum initial velocity and rate of the enzyme-catalysed reaction).
The substrate
should be described
to have a complem
-entary shape to
Mechanisms of enzyme action: the enzyme's active
site, not the sam
shape 2
The specificity of an enzyme refers to the fact that each enzyme catalyses one biochemical reaction.
The activation energy is the energy needed to be supplied for a reaction to start.
Enzymes help the molecules collide successfully, reducing the activation energy required. There are two hypothesis for how enzymes do this: the lock and key
=
hypothesis and the induced fit hypothesis.
Lock and key hypothesis
The active site of the enzyme is an area within the tertiary structure of the enzyme that has a shape
complementary to the shape of a specific substrate molecule.
The lock and key hypothesis states that only a specific substrate will ‘fit' the active side of an enzyme.
An enzyme-substrate complex forms when a substrate is bound to the active site. The substrate(s) react and the
product(s) are formed in an enzyme -product complex and are then released. The active site remains unchanged.
The R group within the active site will also interact with the substrate to form temporary bonds, these put a
strain on the bonds within the substrate which also helps the reaction along.
Induced fit hypothesis:
This is a recent evidence suggesting that the shape of the active site actually changes shape slightly as the
substrate enters. The initial interaction between an enzyme and a substrate is relatively week but these week
interactions induce rapid change in the tertiary structure of the enzyme that strengthen binding. This can
weaken a bond or bonds in the substrate and therefore lowering the activation energy for the reaction
Intracellular enzymes : enzymes that act within cells. For example, catalase enzyme ensures that toxic hydrogen peroxide is broken down to oxygen and water
quickly, therefore preventing its accumulation, found in both plant and animal cells.
Extracellular enzymes: enzymes mat work outside the cell that made them.
• enzymes are released from cells to break down large nutrient molecules into smaller molecules in the process of digestion because they cannot enter the cell
directly through the cell-surface membrane as polymers.
Single-celled organisms release enzymes into their immediate environments. They break down larger molecules into smaller ones (e.g. Proteins into amino
acids) to be absorbed by the cells.
Examples of extracellular enzymes involved in digestion are amylase (for starch) and trypsin (for protein).
Digestion of starch:
It begins in the mouth and continues in the small intestine. Starch is digested in two steps involving two enzymes (different
reactions)
1. Starch polymers partially broken down into maltose, a disaccharide, by amylase. Amylase is produced into salivary glands and
the pancreas, it is released in saliva into the mouth and in the pancreatic juice into the small intestine.
2. Maltose is broken down into glucose, a monosaccharide, by Maltase which is present in the small intestine.
Glucose is small enough to be absorbed by the cell lining, into the digestive system and into the bloodstream.
Digestion of proteins:
Trypsin is a protease, digests proteins into smaller peptides which can be then broken down into amino acids by other proteases. Trypsin is produced in the
pancreas and released into the small intestine with pancreatic juice. The amino acids produced are absorbed by the cell lining the digestive system and then
absorbed into the bloodstream.
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