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Flashcards in 2.4* Deck (234)
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What is a active site?

Indented area on the surface of an enzyme molecule, with a shape that is complimentary tot he shape of a substrate molecule.


What is catalyst?

Chemical that speeds up the rate of a reaction and remains unchanged and reusable at the end of the reaction.


What is the meaning of extracellular?

Outside the cell.


What is the meaning of intracellular?

Inside the cell.
(enzymes catalyse a wide range of intracellular as well as extracellular reactions)


What is the meaning of metabolic/metabolism?

The chemical reactions that take place inside living cells or organisms.


What is the meaning of product?

A molecule produced from substrate molecules, by an enzyme catalysed reaction.


What is the meaning of substrate?

A molecule that is altered by an enzyme catalysed reaction?


Why are enzymes called biological catalysts?

Enzymes are called biological catalysts because they speed up metabolic reactions in living organisms. Their actions affect both structure and function within cells, tissues and organs.


Give examples of how enzymes effect both structure and function within cells?

Catalysts speed up chemical reactions and remain unchanged at the end of the reaction, able to be used again.
A small amount of catalysts can catalyse the conversion of a large number of substrate molecules into product molecules.
The number of reactions that an enzyme molecule can catalyse per second is known as its turnover number.


Why are enzymes better than chemical catalysts, regarding energy usage?

Whereas chemical catalysts usually need very high temperatures increased pressures and extremes of PH, enzymes speed up metabolic reactions by up to 10 to the power of 12 times at lower temperatures, often at neutral PH and at normal pressures. Hence, as biological catalysts, they re able to function in conditions that sustain life.


Why are enzymes better than chemical catalysts, concerning economy?

Enzymes are also more specific than chemicals catalysts. They do not produce unwanted by-products and rarely make mistakes. The cells in which they are made and/or act can also regulate their production and activity to fit the needs of the cell or organism at the time.


What may prevent an enzyme from functioning apart from heat and PH?

For enzymes to catalyse some reactions, they may need help from co-factors.
The instruction fro making enzymes are encoded in genes. If the gene has a mutation that alters the sequence of amino acids in a protien, then this may alter the enzyme tertiary structure and prevent it from functioning.


What causes a metabolic disorder?

If an enzyme that catalyses a metabolic reaction is deficient, then a metabolic disorder results.


What do enzymes catalyse that may cause the 'Stone man syndrome'

Enzymes also catalyse the formation of the organisms structural component, such as collagen in bone, cartilage, blood-vessel walls, joints and connective tissue. Some genetic disorders cause malformations of connective tissue and can be very harmful, such as 'stone man syndrome'.


Describe PKU.

Many metabolic disorders are caused by deficient or non-functioning enzymes, for example if the active site is misshapen. The genetic disorder phenylketonuria, PKU, results when the enzyme phenylalanine hydroxylase does not function and cannot convert the essential amino acid, phenylalanine, to another amino acid, tyrosine. As a result, sufferers cannot make melanin (which is made from tyrosine), and the accumulation of phenylaline in their blood impairs brain development leading to severe mental impairment.


How do we treat PKU?

Because this enzyme deficiency is so severe, all new born babies are screened for PKU, so that if the result is positive their diet can be adjusted to include only very small amounts of phenylalanine, to prevent the irreversible brain damage.


Describe the active site of an enzyme.

Enzymes are large molecules with a specific areas, an indentation or cleft on the surface of the molecule, called the active site. This consists of just a few - often about 6 to 10 - amino acids.
The active site is part of the enzyme molecule, not part of the substrate molecule.


Why is each type of enzyme specific in its function?

So, each type of an enzyme is highly specific in its function, as it can only catalyse a reaction involving the particular type of substrate molecule that fits into its active site.


What is crucial to make an enzymes shape complimentary to the shape of the substrate molecule?

The tertiary structure of the active site is crucial, as its shape is complimentary to the shape of the substrate molecule.


What be altered by changes in temperature and PH?

The shape of the enzymes active site, and hence its ability to catalyse a reactions, can be altered by changes in temperature and PH, as these affect the bonds that hold proteins in their tertiary structure.


Why might the same enzyme complex be known by different names?

Most enzymes catalyse a reaction in either direction depending on the cells needs. Hence ATPase can catalyse the formation of ATP or the hydrolysis of ATP. Sometimes an enzyme catalyses two reactions, because it is really a large enzyme complex and has more than one active site. So, the same enzyme complex may be known by different names.


How many metabolic reactions go on inside your body?

In any cell, and within its organelles, there may be up to 1000 metabolic reactions going on at the same time, each being catalysed by a different enzyme. Some of these reactions are part of a metabolic pathways.


What is each metabolic pathway in a living cell?

Each metabolic pathway in a living cell is one of a series of consecutive reactions, every step catalysed by a specific enzyme that produces a specific production.


Metabolic pathways:
What acts as substrates?

The various reactants and intermediates act as substrates for specific enzymes.


Metabolic pathways:
What are the reactants, intermediates and products known as?

The reactants, intermediates and products are known as metabolites.


Metabolic pathways:
Where is energy released?

In some metabolic pathways, described as catabolic, metabolites are broken down to smaller molecules and release energy.


Metabolic pathways:
When is energy used?

In other metabolic pathways, described as anabolic, energy is used to synthesise larger molecules from smaller ones.


Metabolic pathways:
Give some examples of complex metabolic pathways.

Respiration and photosynthesis are examples of complex metabolic pathways, with many enzymes involved.
(diagram of enzyme at the top of page 101)


Where is catalase found?

In nearly all living organisms.


Why is catalase important?

It is a very important enzyme, as it protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide, a potentially harmful by-product of many metabolic reactions, to water and oxygen.