biochemical reaction chemistry

the importance of enzymes

Enzymes are proteins that increase the rate of chemical reactions by reducing the amount of activation energy needed for reactants to start reacting. Enzymes are synthesized in the cells that need them, based on instructions encoded in the cells DNA. Enzymes arent changed or used up in the reactions they catalyze, so they can be used to speed up the same reaction over and over again. Enzymes are highly specific for certain chemical reactions, so they are very effective. A reaction that would take years to occur without its enzyme might occur in a split second with the enzyme. Enzymes are also very efficient, so waste products rarely form.

photosynthesis and cellular respiration

Some of the most important biochemical reactions are the reactions involved in photosynthesis and cellular respira- tion. Together, these two processes provide energy to almost all of Earths organisms. The two processes are closely related, as you can see in the Figure 1.1. In photosynthesis, light energy from the sun is converted to stored chemical energy in glucose. In cellular respiration, stored energy is released from glucose and stored in smaller amounts that cells can use. A: In photosynthesis, carbon dioxide (CO2 ) and water (H2 O) are the reactants. They combine using energy from light to produce oxygen (O2 ) and glucose (C6 H12 O6 ). Oxygen and glucose, in turn, are the reactants in cellular respiration. They combine to produce carbon dioxide, water, and energy.


chemical reactions in living things

Chemical reactions that take place inside living things are called biochemical reactions (bio- means life). Its not just for energy that living things depend on biochemical reactions. Every function and structure of a living organism depends on thousands of biochemical reactions taking place in each cell. The sum of all these biochemical reactions is called metabolism.

catabolic and anabolic reactions

Biochemical reactions of metabolism can be divided into two general categories: catabolic reactions and anabolic reactions. Catabolic reactions involve breaking bonds. Larger molecules are broken down to smaller ones. For example, complex carbohydrates are broken down to simple sugars. Catabolic reactions release energy, so they are exothermic. Anabolic reactions involve forming bonds. Smaller molecules are combined to form larger ones. For example, simple sugars are combined to form complex carbohydrates. Anabolic reactions require energy, so they are endothermic. Q: Imagine! Each of the trillions of cells in your body is continuously performing thousands of catabolic and anabolic reactions. Thats an amazing number of biochemical reactionsfar more than the number of reactions that might take place in a lab or factory. How can so many biochemical reactions take place simultaneously in our cells? A: So many reactions can occur because biochemical reactions are amazingly fast. Q: In a lab or factory, reactants can be heated to very high temperatures or placed under great pressure so they will react very quickly. These ways of speeding up chemical reactions cant occur inside the delicate cells of living things. So how do cells speed up biochemical reactions? A: The answer is enzymes.

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catabolic reactions are chemical reactions in living things that

a) release energy.

b) are endothermic.

c) break bonds.

-->  d) two of the above

anabolic reactions are chemical reactions in living things that

-->  a) form larger molecules.

b) are exothermic.

c) release energy.

d) two of the above

the reactants of photosynthesis are oxygen and water.

a. true

-->  b. false

photosynthesis is an anabolic reaction.

-->  a. true

b. false

cellular respiration is a catabolic reaction.

-->  a. true

b. false

diagram questions

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