Biology 12

Chapter 2 Enzymes and Energy • MHR 61

COMMUNICATING

30.Earth is an open system for energy but a closed
system for matter. Explain what this means in
terms of cell processes.

31.In the ATP cycle, the breakdown of glucose is
coupled to the buildup of ATP. Use words and
diagrams to describe this process in terms of
stored energy, free energy, and thermal energy.

32.Energy flows through living things, but matter
is cycled. Explain how enzymes demonstrate
efficient use of matter in the cell.

33.Make a flip-book animation to show the
induced fit of a substrate on an enzyme’s
active site.

34.Enzymes are generally substrate-specific.
However, some enzymes can catalyze the
reactions of a family of substrates. Use
diagrams to show how an enzyme could be
specific to two substrates that are similar yet
different in structure.

35.Make a diagram of a polypeptide chain of five
amino acids to explain how R-groups:
(a)interact with a substrate, and

(b)are affected by a decrease in pH.

36.This diagram shows the metabolic pathway

used by eukaryotic cells to break down

proteins. Ubiquitin is a polypeptide chain that

joins to certain proteins. Existing enzymes can

break down the protein when ubiquitin is

connected.

(a)How is this pathway energy-efficient?

(b)Ubiquitin prepares the protein for the

enzyme. How does adding ubiquitin change

the protein?

ubiquitin

polypeptide

added

protein

to be

degraded

protein-ubiquitin

complex

enzymes break

protein into

fragments

ubiquitin

polypeptide

released

protein

fragment

protein

fragment

MAKING CONNECTIONS

37.Is a cell a closed system or an open system?
Justify your response.

38.About 95 percent of the electric energy
supplied to an incandescent light bulb is lost
as waste thermal energy. If this were a
biological reaction, how would an enzyme
affect the use of energy?

39.Glucose is one of the products of
photosynthesis. Glucose can also be produced
artificially, but in this case both optical isomers
are produced (that is, left-handed and right-
handed glucose). Explain how biological
enzymes produce only one isomer.

40.Milk is heated when it is pasteurized. The

pasteurization process involves heating milk to

kill bacteria without denaturing the milk itself.

In Canada, milk is heated to 72.8°C for 16 s

and then cooled rapidly to 4°C. Ultra High

Temperature (UHT) milk products can be

heated to 135°C for a shorter period of time,

usually 2–5 s. How is each process beneficial

to the producer and the consumer?