Download CHAPTER 7 – COENZYMES AND VITAMINS CHAPTER SUMMARY

CHAPTER 7 – COENZYMES AND VITAMINS
CHAPTER SUMMARY
Introduction
1. True or false? (circle one) The catalytic repertoire of an organism is limited to the amino
acid side chains in an active site.
2. What can be used to convert inactive apoenzymes to active holoenzymes?
3. What type of essential ion is loosely bound? Tightly bound?
4. What type of coenzyme is loosely bound? Tightly bound?
7.1
5. Metal-activated enzymes either _______________ added metal ions, or are
_______________ by the addition of metal ions.
6. Metalloenzymes contain _______________ bound metal ions at their active sites.
7. Some metal ions _______________ bonds by attracting electrons. Others undergo
reversible _______________ and _______________ by transferring electrons.
7.2
8. Coenzymes are categorized into _______________ (which are actually substrates in
enzyme-catalyzed reactions) and _______________ __________ (which remain bound to
the enzyme during the reaction). They both supply _______________ groups that are not
available on the side chains of amino acid residues.
9. Most species in the Kingdoms prokaryotes, protists, fungi, and plants are capable of
_______________ their coenzymes from simple precursors. _______________ have lost
this ability, and need to ingest nutrients called _______________ from plants,
microorganisms, and some from meat.
10. A nutritional–deficiency _______________ results when a vitamin is deficient or absent
in the diet of an animal (see table 7.1 on page 194).
11. Why are water-soluble vitamins required daily?
12. What happens when lipid vitamins are ingested excessively?
13. Draw the structure of the simplest vitamin, the antiscurvy agent.
7.3
14. Several nucleoside triphosphates are coenzymes, including the most abundant, _____.
15. What four groups can ATP donate?
16. ATP plays a central role in _______________ as a high-__________ cofactor.
17. ATP is the source of a number of other metabolite coenzymes, including
_______________, which is required for the conversion of norepinephrine to
epinephrine.
18. The most common nucleotide-sugar coenzyme is _______________, which can donate
its glycosyl group. This releases UDP, which can regenerate the coenzyme above after a
phosphoryl group transfer from ATP and a reaction with glucose 1-phosphate.
7.4
19. The nicotinamide coenzymes __________ and __________ were the first to be
recognized. Nicotinic acid (or __________) and nicotinamide are essential precursors of
these coenzymes.
20. NAD+ and NADP+ play a role in many __________ reactions in which they assist in the
transfer of _______________ to and from metabolites.
21. NADH and NADPH are the __________ forms of the coenzymes, and are said to have
__________ power (or are biological __________ agents). In mitochondria, the
oxidation of NADH is coupled to the synthesis of _____, and most NADPH is used as a
reducing agent in _______________ reactions.
7.5
22. The coenzymes _____ and _____ are derived from _______________ (vitamin B2).
Bacteria, protists, fungi, plants and some animals synthesize riboflavin, but mammals
obtain riboflavin from __________.
23. FAD and FMN are prosthetic groups for many _______________, called flavoenzymes
or flavoproteins. FAD and FMN are reduced to __________ and __________, and can
participate in one or two electron transfers, an important aspect of many electron transfer
systems.
7.6
24. The oxidation of fuel molecules, and the biosynthesis of some carbohydrates and lipids
depend on _______________. It is involved in __________-group transfer reactions in
which the __________ group covalently binds the acyl groups to form
_______________. A good example is _______________, an energy-rich compound
that is involved in the metabolism of carbohydrates, fatty acids, and amino acids.
7.7
25. Vitamin B1 (or _______________) is an essential vitamin in mammals, and a deficiency
leads to _______________.
26. The coenzyme is _______________ _______________ (TPP), which is required by
about a half dozen _______________, is involved in the oxidative _______________ of
-keto acids (other than pyruvate), and is a prosthetic group for _______________. The
reactive center is the _______________ ring.
7.8
27. Pyridoxal or pyridoxamine (_______________) is widely available from plants and
animals, so deficiencies in humans are rare. In the cell, it is phosphorylized by ATP to
_______________ _______________ (PLP).
28. PLP is the prosthetic group for many enzymes that catalyze reactions with amino acids,
including _______________, _______________ and side-chain _______________ or
_______________ reactions.
7.9
29. __________ is a prosthetic group for enzymes that catalyze transfers of __________
groups, and ATP-dependent _______________ reactions. It is covalently linked to the
end of a __________ residue, and participates as a carrier of CO2.
7.10
30. _______________ are the coenzyme forms of the vitamin folate, which is required in the
diet of humans. One of tetrahydrofolate’s derivatives is an important component in the
biosynthesis of _____. Another derivative is required by enzymes that catalyze
biochemical transfers of several one-carbon units.
7.11
31. _______________ (vitamin B12) is the largest B vitamin, and was the last to be isolated.
It is required as a _______________ by all animals and some bacteria and algae, and in
animals, a deficiency can lead to pernicious anemia, in which there is a decrease in the
production of __________ cells by bone marrow.
32. Adenosylcobalamin participates in several _______________ rearrangements,
methylcobalamin helps in __________ group transfers, and B12-dependent reductive
dehalogenases __________ chlorinated organic molecules (like PCBs).
7.12
33. _______________ is covalently anchored to a lysine residue of dihydrolipoamide
acyltransferases. It functions as a swinging arm that carries acyl groups between
__________ __________ in multienzyme complexes.
7.13
34. The four lipid vitamins (A, D, E and K) contain __________ and long aliphatic
__________ chains, making them highly _______________ (even though they have at
least one polar group on the molecule).
a. Vitamin A (_______________) is produced through the oxidative cleavage of
_______________, which is found in __________ and other __________
vegetables. The terminal functional group may be an __________ (retinol), an
_______________ (retinal – absorbs a photon of light which triggers a neural
impulse), or a _______________ acid (retinoic acid – a signal cmpd that binds to
receptor proteins in cells, and the complex that forms can bind to chromosomes
and can regulate gene expression during cell differentiation).
b. Vitamin D is a group of __________ vitamins. Vitamin D3 (_______________)
is formed in the skin when humans are exposed to sunlight. The active forms of
these vitamins are hormones that help control __________ utilization – they
regulate the _______________ absorption and its deposition in __________.
c. Vitamin E (_______________) scavenges __________ and __________
__________, which may prevent damage to fatty acids in membranes.
d. Vitamin K (_______________) is from plants and is required for the synthesis of
some of the proteins involved in blood _______________.
7.14
35. Ubiquinone (coenzyme ___) is lipid soluble and synthesized by almost all species. Its
long hydrophobic chain allows it to dissolve into _______________, and its function is
the transport of _______________ between membrane-embedded enzyme complexes.
36. Coenzyme Q is responsible for moving __________ from one side of the membrane to
the other through a process called the “Q Cycle”, which results in the proton gradient that
drives _____ synthesis.
37. Plastoquinone, an analog of ubiquinone, functions similarly in _______________
electron transport in chloroplasts.
7.15
38. Some proteins act as _______________ as well. They don’t catalyze reactions
themselves, but are required by certain enzymes. They participate in __________
transfer reactions or in __________ reactions (in which the transferred group is hydrogen
or an electron).
39. Examples include __________ (which contain heme prosthetic groups),
_______________ (reducing agents in the citric acid cycle and in photosynthesis), and
_____ ( a component of all fatty acid synthetases that have been tested).
7.16
40. Cytochromes are _____-containing protein coenzymes. Their __________ ions undergo
reversible one-electron reduction.
41. They are classified as ___, ___ and ___ based on their visible absorption spectra. Each of
their heme groups is slightly different, and each has a different _______________
_______________ (ability to transfer an electron to another substance). The range of
reduction potentials is an important feature of membrane-associated _______________
transport pathways, and of _______________.