Revision:Human Biochemistry - C (Higher)

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C.7 Enzymes

C.7.1 Characteristics

• most of the proteins in the organism are enzymes. They act as catalysts for biochemical reactions in the body.

• an enzyme's activity depends on its tertiary and quaternary structure- different enzymes catalyse different reactions depending on their structure because substrates bind to the enzyme's active site during the reaction. this active site is only present in tertiary and quaternary structures. The properties and positions of the R-groups exposed at the active site determine which substrates will bind to the enzyme.

• some enzymes do not bind to substrates unless their active sites don't contain additional ions or molecules.

• CO-FACTOR: a substance held to the protein by other bonds eg ions Ca2⁺

• CO-ENZYMES: non protein organic molecules eg vitamins

C.7.2 SUBSTRATE CONCENTRATION

• a single enzyme can process only a limited amount of substrate in a given time, when substrate concentration increases, reaction rate increases. When all the enzymes are bound to substrates, the rate depends on the enzymes' rate of processing the substrates. The reaction rate eventually reaches a maximum limit.

C.7.3 V_max and Michelis Constant (K_max)

• the rate is expressed as the number of reactions catalyzed by a given enzyme molecule per unit time.

• in a graph of substrate concentration vs rate of reaction, the graph rises in a curved fashion, with a decreasing slope. V_max is recognized as being the point in which the graph continues in a horizontal line, parallel to the x-axis.

• the K_max is the substrate concentration at which the reaction rate is 1/2 V_max. this is a measure of how readily the enzyme-substrate binding occurs. when K_max is low, the reaction proceeds at a rapid rate even at low substrate concentrations

• K_max is recognized on a graph by finding the 1/2 V_max rate on the y-axis and drawing a perpendicular down to the x-axis. The perpendicular will reveal the concentration at K_max.

C.7.4 I guess this is part of what I did in C.7.4

C.7.5 Active Site

• It is a cluster of chemical groupings formed as a part of the enzyme's folding pattern. the properties of the R-groups exposed at the active site determine which substrates will bind.

• when enzymes and substrates combine, they change shape: the active site is a flexible pert of the enzyme, which increases the surface area between the substrate and enzyme.

C.7.6 Inhibition

• COMPETITIVE: compounds that are similar to the substrate, which compete with the substrate by binding to the active site. This decreases the reaction rate because the enzyme cannot bind to the substrate.

• NON-COMPETITIVE: ?

C.7.7 Effects on Enzyme Activity

• HEAVY METAL IONS:?

• TEMPERATURE: when temp rises, molecules move faster, colliding harder and more often, therefore they are more likely to react than at lower temp. When the temp increase is too high (above 60°C), the enzymes will be denatured permanently, and will no longer function-their 3-D structure will be destroyed. At low temp reactions proceed slowly, and at very low temperatures (below 0°C) the enzymes are denatured. They normally function at body temperature -37°C

• pH-enzymes are electrically charged because R-groups may ionize when they dissolve in water. The pH therefore determines the changes in the enzyme. Enzymes will function only at given pH's depending on their electrical charge. Most enzymes function best at neutral pH's.

C.7.8 BIOTECHNOLOGY

C.8

C.9 Metal Ions in Biological Systems

C.9.1 Roles in the Body/Chemical Properties

• Sodium and Potassium are vital the the functioning of nerves and muscles.

• Calcium is necessary for muscular activity

• Calcium and phosphorus are needed for bone formation (see p643 bio book)

C.9.2 Ion Concentration Across Cell Membrane

• Active transport-moves substances either with or against their electrochemical gradients, and requires energy. A source of energy may be Na⁺ of H⁺ concentration on the two sides of the membrane

• Sodium/Potassium Pumps- it uses energy from ATP to transfer sodium ions out of the cell and potassium ions inside. This pump is responsible for the electrical potential across plasma membranes. In the membrane, 3 sodium ions are moved for every two potassium ions that move in. The cell becomes more negative compared with the outside. when the tendency of K⁺ leaving the cell balances its tendency to enter it, the membrane potential is reached. K⁺ movement ceases.

• this type of pump controls the water content of the cell. It also drives the transport of sugars and amino acids. This process controls: the ability of nerves to conduct electricity, kidneys to form urine, muscles to contract, absorption of food in digestive tract.

C.9.3 Copper Ions in Electron Transport

• the electron transport system accepts hydrogen atoms and passes their electrons from one member of the chain to the next.

• cytochromes-electron carrier molecule consisting of a protein and a porphyrin ring, containing a copper ion

Iron Ions in Oxygen Carriers:

• haemoglobin-respiratory pigment that carries oxygen in the blood

• contain a heme group with an iron atom a its center. The iron atom binds to the oxygen. When O binds to Fe, the hemoglobin is oxygenated and appears bright red. Without the iron center, oxygen wouldn't bind to hemoglobin, and oxygen couldn't be carried through the blood stream and to the cells in the body.

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