Enzymes Flashcards
what are enzymes?
enzymes are biological catalysts. They are globular proteins that interact with substrate molecules causing them to react at much faster rates without the ned for harsh environmental conditions.
-without enzymes many of the processes necessary to life would not be possible.
what are the chemical reactions required for growth?
the chemical reactions required fro growth are anabolic (building up) reactions and they are all catalysed by enzymes
how is energy released from large organic molecules (glucose)?
in metabolic pathways consisting of many catabolic (breaking down) reactions.
what are catabolic reactions catalysed by?
enzymes
what is the difference between anabolic and catabolic reactions?
anabolic = building up reactions catabolic= breaking down reactions
what is metabolism?
the sum of all of the different reactions and reaction pathways happening in a cell or an organism, and it can only happen as a result of the control and order imposed by enzymes
what are some factors which may have an effect on the rate of chemical reactions?
- temperature
- pressure
- pH
up to what point can enzymes increase the rate of a reaction?
up to a certain pint called the Vmax
what is the Vmax?
maximum initial velocity or rate of the enzyme- catalysed reaction
what is the specificity of an enzyme?
many different enzymes are produced by living organisms, as each enzyme catalyses one biochemical reaction, of which there are thousands in any given cell
what is the activation energy?
the minimum amount of energy that much be supplied for most reactions to start
what happens if the activation energy is very high?
it prevents reactions from happening under normal conditions
what is an ‘active site’?
an area within the tertiary structure of the enzyme which ahs a shape that is complementary to the shape of a specific substrate molecule
what is the lock and key hypothesis?
in the same way that only the right key will fit into a lock, only a specific substrate will ‘fit’ the active site of an enzyme.
how do enzymes work according to the lock and key hypothesis?
- when the substrate is bound to the active site an enzyme- substrate complex is formed.
- the substrate or substrates then react and the product or products are formed in an enzyme- product complex.
- the product(s) are then released, leaving the enzyme unchanged and able to take part in subsequent reactions
- the substrate is held in such a way by the enzyme that the right atom- groups are close enough to react.
- The R-groups within the active site of the enzyme will also interact with the substrate, forming temporary bonds. these put strain on the bonds within the substrate, which also helps the reaction along.
what is the induced fit hypothesis?
enzyme action suggesting that the active site of the enzyme actually changes shape slightly as the substrate enters.
how does the induced fit hypothesis work?
- the initial interaction between the enzyme and the substrate is relatively weak but these weak interactions rapidly induce changes in the enzymes tertiary structure that strengthen binding, putting strain on the substrate molecules.
- this can weaken a particular bond or bonds in the substrate, therefore lowering the activation energy for this reaction
what are some examples of reactions that require enzymes?
the synthesis of polymers from monomers, fro example making polysaccharides from glucose, requires enzymes
what are intracellular enzymes?
enzymes that act within cells are called intracellular enzymes
how does catalase break down catalase?
- H2O2 is a toxic product of many metabolic pathways.
- The enzyme catalase ensures hydrogen peroxide is broken down to oxygen and water quickly. therefore preventing its accumulation.
where is catalase and hydrogen peroxide found?
in both plants and animals
what form are nutrients required for reactions found in?
often in the form of polymers such as proteins and polysaccharides
why can’t nutrients in the form of polymers directly enter through the cell surface membrane?
- these large molecules cannot enter cells directly through the cell-surface membrane.
- they need to be broken down into smaller components first
how do larger nutrients enter the cell surface membrane?
enzymes are released from cells to break down these large nutrient molecules into smaller molecules in the process of digestion
what are extracellular enzymes?
they work outside the cell that made them
where do single celled organisms release enzymes?
- single celled organisms such as bacteria and yeast, release enzymes into their immediate environment.
- The enzymes break down larger molecules, such as proteins, and the smaller molecules produced, such as amino acids and glucose, are then absorbed by the cells
how are nutrients used as substrates?
- many multicellular organisms eat food to gain nutrients.
- although the nutrients are taken into the digestive system the large molecules still have to be digested so small molecules can be absorbed into the bloodstream
- from there they are transported around the body to be used as substrates in cellular reactions
what are some extracellular enzymes involved in digestion in humans?
amylase and tripsin
how is starch digested?
1- starch polymers are partially broken down into maltose, which is a dissacharride. The enzyme involved in this stage is called amylase. Amylase is produced by the salivary glands and the pancreas. It is released in saliva into the mouth, and in pancreatic juice into the small intestine.
2- Maltose is then broken down into glucose, which is a monosaccharide. The enzyme involved in this stage is called maltase. Maltase is present in the small intestine.
Glucose is small enough to be absorbed by the cells lining the digestive system and subsequently absorbed into the bloodstream
how are proteins digested?
trypsin is a protease, a type of enzyme that catalyses the digestion of proteins into smaller peptides, which can be broken down further into smaller peptides, which can then be broken down further into amino acids by other proteases.
Trypsin is produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins.
The amino acids that are produced by the action of proteases are absorbed by the cells lining the digestive system and then absorbed into the bloodstream.
how can factors affecting enzyme actions be investigated?
by measuring the rate of the reactions they catalyse
what is the temperature coefficient, Q10, and what does it mean?
the temp coefficient, Q10, of a reaction (or process) is a measure of how much the rate of a reaction increases with a 10 degrees rise in temp.
-For enzyme- controlled reactions this is usually taken as 2, which means that the rate of reaction doubles with a 10 degrees temp increase.
what happens to enzymes are high temps?
- as enzymes are proteins their structure is affected by temp
- at high temps the bonds holding the protein together vibrate more
- as the temp increases the vibrations increase until the bonds strain and then break
- the breaking of these bonds result in a change in the precise tertiary structure of the protein
- the enzyme has changed the shape and is said to be denatured
- when an enzyme is denatured the active site changes shape and is no longer complementary to the substrate
- the substrate can no longer fit into the active sites and the enzyme will no longer function as a catalyst
what is the optimum temp?
the optimum temp is temp at which the enzyme has the highest rate of activity
what happens to enzymes above the optimum temp?
- the enzymes denature in temps above the optimum temp, the decrease in rate of reaction is rapid
- there only neds to be a slight change in shape of an active site for it to no longer be complementary to its substrate
- this happens to all of the enzyme molecules at about the same temp so the loss of activity is relatively abrupt
what happens to the temp coefficient when an enzyme is denatured?
at this point in an enzyme- controlled reaction the temp coefficient, Q10 does’t apply any more as the enzymes have denatured
how quickly does the rate of reaction decrease when the temp is below the optimum temp?
- the decrease in the rate of reaction below the optimum temp is less rapid
- this is because the enzymes have not denatured, they are just less active
what are some examples of some extreme cold environments?
-deep oceans, high altitudes and polar regions
what are some properties of enzymes adapted to the cold environments?
- they tend to have more flexible structures, particularly at the active site, making them less stable than enzymes that work at higher temps
- smaller temp changes will denature them
what are organisms adapted to very hot environments called?
-thermophiles
what are some examples of very hot environments?
- hot springs
- deep sea hydrothermal vents
what are properties of enzymes adapted to very hot environments?
- the enzymes present in these organisms are more stable than other enzymes due to the increased number of bonds, particularly hydrogen bonds and sulfur bridges, in their tertiary structures
- the shape of these enzymes, and their active sites, are more resistant to changes as the temp rises
what extracellular reaction does amylase catalyse?
-the digestion of starch
Explain how an enzyme changes when temperature is increased
Increasing temperature gives the molecules more kinetic energy
• This gives more successful collisions
• More enzyme / substrate complexes form
• Enzymes have an optimum temperature
• Above this the hydrogen bonds that hold the tertiary structure are affected
• The 3D shape changes and the active site is distorted
• The change in shape prevents the substrate from binding
• The effect of high temperature is known as denaturing
• This is irreversible
