med micro test #2 chapter 5 reading
The turnover number
(the maximum number of substrate molecules an enzyme molecule converts to product each second) is generally between 1 and 10,000 and can be as high as 500,000
Cofactors
-------- may help catalyze a reaction by forming a bridge between an enzyme and its substrate. For example, magnesium (Mg2+) is required by many phosphorylating enzymes (enzymes that transfer a phosphate group from ATP to another substrate). The Mg2+ can form a link between the enzyme and the ATP molecule. Most trace elements required by living cells are probably used in some such way to activate cellular enzymes.
true
A certain compound can be a substrate for several different enzymes that catalyze different reactions, so the fate of a compound depends on the enzyme that acts on it. At least four different enzymes can act on glucose 6-phosphate, a molecule important in cell metabolism, and each reaction will yield a different product.
six classes
All enzymes can be grouped into ------- according to the type of chemical reaction they catalyze (Table 5.1). Enzymes within each of the major classes are named according to the more specific types of reactions they assist.
level of energy
Also, each chemical reaction requires a specific
True
Although microbial metabolism can cause disease and food spoilage, many pathways are beneficial rather than pathogenic
apoenzyme and cofactor
Although some enzymes consist entirely of proteins, most consist of both a protein portion, called an apoenzyme, and a nonprotein component, called a cofactor.
biochemical reactions at a temperature that is compatible with the normal functioning of the cell.
An enzyme's ability to accelerate a reaction without the need for an increase in temperature is crucial to living systems because a significant temperature increase would destroy cellular proteins. The crucial function of enzymes, therefore, is to speed up
catabolism
An example of --------- occurs when cells break down sugars into carbon dioxide and water
Catabolism
An example of ------------------- occurs when cells break down sugars into carbon dioxide and water.
dehydration synthesis reactions, endergonic
Anabolic processes often involve ------------- (reactions that release water), and they are _________ (consume more energy than they produce)
holoenzyme
Apoenzymes are inactive by themselves; they must be activated by cofactors. Together, the apoenzyme and cofactor form a --------, or whole, active enzyme (Figure 5.4). If the cofactor is removed, the apoenzyme will not function.
substrate
As catalysts, each enzyme acts on a specific substance, called the enzyme's
lowering their activation energy
As catalysts, enzymes typically accelerate chemical reactions by
increasing the number of AB molecules that attain sufficient activation energy to react
As catalysts, enzymes typically accelerate chemical reactions by lowering their activation energy (Figure 5.2). The enzyme therefore speeds up the reaction by
True
As you will see later, dehydrogenase and oxidase enzymes have even more specific names, such as lactate dehydrogenase and cytochrome oxidase, depending on the specific substrates on which they act.
energy balancing act
Because chemical reactions either release or require energy, metabolism can be viewed as an
metabolic pathways
Before we discuss how cells produce energy, let's first consider the principal properties of a group of proteins involved in almost all biologically important chemical reactions: enzymes. A cell's ___________ (sequences of chemical reactions) are determined by its enzymes, which are in turn determined by the cell's genetic makeup.
catabolic reactions
Beverages and food: Various bacteria and yeasts (such as Saccharomyces cerevisiae, shown at right) carry out _________________________ called fermentation. Beer, wine, and foods such as cheeses, yogurt, pickles, sauerkraut, and soy sauce tap microbial metabolism as a crucial part of production.
properly oriented toward each other
But even if colliding particles possess the minimum energy needed for reaction, no reaction will take place unless the particles are
True
By causing the molecules to move faster, heat increases both the frequency of collisions and the number of molecules that attain activation energy. The number of collisions also increases when pressure is increased or when the reactants are more concentrated (because the distance between molecules is thereby decreased). In living systems, enzymes increase the reaction rate without raising the temperature.
hydrolytic, exergonic
Catabolic reactions are generally ____________ (reactions which use water and in which chemical bonds are broken), and they are __________ (produce more energy than they consume)
the energy needed for anabolic reactions
Catabolic reactions provide
anabolic reactions
Catabolic reactions provide building blocks for anabolic reactions and furnish the energy needed to drive__________, this coupling of energy-requiring and energy-releasing reactions is made possible through the molecule adenosine triphosphate (ATP)
collide
Chemical reactions occur when chemical bonds are formed or broken. For reactions to take place, atoms, ions, or molecules must _______
nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+)
Coenzymes may assist the enzyme by accepting atoms removed from the substrate or by donating atoms required by the substrate. Some coenzymes act as electron carriers, removing electrons from the substrate and donating them to other molecules in subsequent reactions. Many coenzymes are derived from vitamins (Table 5.2). Two of the most important coenzymes in cellular metabolism are
Microbial Metabolism
Drugs: The pharmaceutical industry uses a variety of bacteria and fungi in the production of antibiotics, such as penicillin, (derived from the Penicillium fungus, shown on the right). Bacitracin, erythromycin, and other treatments such as vaccines, vitamins, and enzymes are also derived from
Products
During enzymatic reactions, substrates are transformed into new substances called
true
Enzymes are extremely efficient. Under optimum conditions, they can catalyze reactions at rates 108 to 1010 times (up to 10 billion times) higher than those of comparable reactions without enzymes
True
Enzymes are subject to various cellular controls. Two primary types are the control of enzyme synthesis (see Chapter 8) and the control of enzyme activity (how much enzyme is present versus how active it is).
Substrates
Enzymes catalyze reactions for specific molecules called
Key Concepts
Enzymes facilitate metabolic reactions. ATP is used by microbes and other cells to manage energy needs. Catabolic reactions couple with ATP synthesis. Anabolic reactions couple with ATP breakdown.
lock fits with its key
Enzymes have specificity for particular substrates. For example, a specific enzyme may be able to hydrolyze a peptide bond only between two specific amino acids. Other enzymes can hydrolyze starch but not cellulose; even though both starch and cellulose are polysaccharides composed of glucose subunits, the orientations of the subunits in the two polysaccharides differ. Each of the thousands of known enzymes have this specificity because the three-dimensional shape of the specific amino acids of the active site fits the substrate somewhat as a
dehydrogenases
Enzymes in the oxidoreductase class that remove hydrogen (H) from a substrate are called ---------
Cofactors
Enzymes, which are generally proteins may need other nonprotein molecules called ______________ to work
anabolic processes
Examples of ___________ are the formation of proteins from amino acids, nucleic acids from nucleotides, and polysaccharides from simple sugars. These biosynthetic reactions generate the materials for cell growth.
Oxidoreductases
For example, the class called __________ is involved with oxidation-reduction reactions
True
For example, the enzyme DNA polymerase I, which participates in the synthesis of DNA, has a turnover number of 15, whereas the enzyme lactate dehydrogenase, which removes hydrogen atoms from lactic acid, has a turnover number of 1000.
Turning ATP Into Energy. Whenever a cell needs energy, it breaks the beta-gamma phosphate bond to create adenosine diphosphate (ADP) and a free phosphate molecule. ... Cells get energy in the form of ATP through a process called respiration, a series of chemical reactions oxidizing six-carbon glucose to form carbon dioxide
How does ATP provide the energy for synthesis?
Adenosine Triphosphate (ATP)
However, without energy, certain reactions will never occur, even if enzymes are present. ______________ is a molecule that cells use to manage energy needs.
catabolic reactions provide building blocks for anabolic reactions and furnish the energy need to drive anabolic reactions. this coupling of energy-requiring and energy-releasing reactions is made possible through the molecule ATP. ATP stores energy derived from catabolic reactions and releases it later to drive anabolic reactions and perform other cellular work.
Identify the role of ATP as an intermediate between catabolism and anabolism. p. 112
Break those same bonds and use the released energy to fuel other reactions
If a reaction results in excess energy some can be captured in the form of ATP bonds. A cell can then
Enzymes
In living cells, _______ serve as biological catalysts
catabolism. the breakdown of complex organic compounds into simpler ones.
In living cells, the enzyme-regulated chemical reactions that release energy are generally the ones involved in
Energy
In other words Catabolic and Anabolic pathways are linked by
Metal Ions
Inorganic cofactors include
coenzyme
Ions of iron, zinc, magnesium, or calcium are examples of cofactors. If the cofactor is an organic molecule, it is called a -------
activation energy
Let's assume that molecules of substance AB (the reactant) are to be converted to molecules of substances A and B (the products). In a given population of molecules of substance AB, at a specific temperature, some molecules possess relatively little energy; the majority of the population possesses an average amount of energy; and a small portion of the population has high energy. If only the high-energy AB molecules are able to react and be converted to A and B molecules, then only relatively few molecules at any one time possess enough energy to react in a collision. The collision energy required for a chemical reaction is its ________ which is the amount of energy needed to disrupt the stable electronic configuration of any specific molecule so that the electrons can be rearranged
cellular environment
Many enzymes exist in the cell in both active and inactive forms. The rate at which enzymes switch between these two forms is determined by the
true
Molecules move more slowly at lower temperatures than at higher temperatures and so may not have enough energy to cause a chemical reaction. For enzymatic reactions, however, elevation beyond a certain temperature (the optimal temperature) drastically reduces the rate of reaction (Figure 5.5a)
anabolic (energy-requiring) reactions.
NADP+ is primarily involved in -----------
True
Nitrogen cycle: Nitrogen is a key component in proteins, DNA and RNA, and plant chlorophyll. But without microbes, there would be little nitrogen available for most life forms. Certain bacteria (such as these Rhizobium, above, within a soybean root nodule, shown at right) in the soil convert nitrogen from the atmosphere into forms that other life forms can use.
raise its temperature
One way to increase the reaction rate of a substance is to
FAD, NAD+, and NADP+
Organic cofactors, or coenzymes include the electron carries
Catabolic
Pathways break down macromolecules into simple component parts, releasing energy in the process
Anabolic
Pathways build up macromolecules by combining simplier molecules using energy in the process
the velocities of the colliding particles, their energy, and their specific chemical configurations
Several factors determine whether a collision will cause a chemical reaction
temperature, pH, substrate concentration, and the presence or absence of inhibitors.
Several factors influence the activity of an enzyme. Among the more important are temperature, pH, substrate concentration, and the presence or absence of inhibitors.
catalysts
Substances that can speed up a chemical reaction without being permanently altered themselves are called
all atoms, ions, and molecules are continuously moving and colliding with one another. The energy transferred by the particles in the collision can disrupt their electron structures enough to break chemical bonds or form new bonds
The basis of the collision theory is that
catabolic reactions
The chemical reaction that produces energy in microorganisms
the anabolic reactions
The chemical reaction that uses energy in microorganisms
catabolic, anabolic
The chemistry of metabolism can seem overwhelming at first, with pathways, or sets of many coordinated reactions, working together toward common goals. But the basic rules of metabolism are actually quite simple. Pathways can be categorized into two general types
anabolism
The enzyme-regulated energy-requiring reactions are mostly involved in _________ the building of complex organic molecules from simpler ones.
anabolism
The enzyme-regulated energy-requiring reactions are mostly involved in _________, the building of complex organic molecules from simpler ones
True
The flavin coenzymes, such as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), contain derivatives of the B vitamin riboflavin and are also electron carriers. Another important coenzyme, coenzyme A (CoA), contains a derivative of pantothenic acid, another B vitamin. This coenzyme plays an important role in the synthesis and breakdown of fats and in a series of oxidizing reactions called the Krebs cycle. We will come across all of these coenzymes in our discussion of metabolism later in the chapter.
The surface of the substrate contacts a specific region of the surface of the enzyme molecule, called the active site. A temporary intermediate compound forms, called an enzyme-substrate complex. The enzyme orients the substrate into a position that increases the probability of reaction, which enables the collisions to be more effective. The substrate molecule is transformed by the rearrangement of existing atoms, the breakdown of the substrate molecule, or in combination with another substrate molecule. The transformed substrate molecules—the products of the reaction—are released from the enzyme molecule because they no longer fit in the active site of the enzyme. The unchanged enzyme is now free to react with other substrate molecules.
The general sequence of events in enzyme action is as follows (Figure 5.3a).
-ase
The names of enzymes usually end in
temperature increases
The rate of most chemical reactions increases as the
denaturation, the loss of its characteristic three-dimensional structure (tertiary configuration)
The rate of reaction declines beyond the optimal temperature because of the enzyme's
heat
The role of ATP in coupling anabolic and catabolic reactions is shown in Figure 5.1. Only part of the energy released in catabolism is actually available for cellular functions because part of the energy is lost to the environment as ______. Because the cell must use energy to maintain life, it has a continuous need for new external sources of energy.
The substrate contacts the active site on the enzyme to form 2 an enzyme-substrate complex. 3 The substrate is then transformed into products, 4 the products are released, and 5 the enzyme is recovered unchanged. In the example shown, the transformation into products involves a breakdown of the substrate into two products. Other transformations may occur, however. (b) Left: A molecular model of the enzyme in step 1 of part (a). The active site of the enzyme can be seen here as a groove on the surface of the protein. Right: As the enzyme and substrate meet in step 2 of part (a), the enzyme changes shape slightly to fit together more tightly with the substrate.
The substrate contacts the active site on
flexible, and they change shape somewhat as they meet to fit together more tightly. The substrate is usually much smaller than the enzyme, and relatively few of the enzyme's amino acids make up the active site
The unique configuration of each enzyme enables it to "find" the correct substrate from among the diverse molecules in a cell. However, the active site and substrate are
Anabolism
These reactions are called anabolic, or biosynthetic, reactions
catabolism
These reactions are called catabolic, or degradative, reactions
enzymes and the molecule adenosine triphosphate (ATP).
Two key players in metabolism are
more probable that their collision will cause a reaction.
Up to a point, the higher the particles' velocities, the
ATP -> ADP + P + energy
What is the chemical equation for releasing energy?
True
When complex molecules are split apart (catabolism), wsome energy is transferred to and trapped in ATP. -when simple molecules are combined to form complex molecules (anabolism) ; ATP PROVIDES ENERGY FOR SYNTHESIS
adenosine diphosphate (ADP)
When the terminal phosphate group is split from ATP, ______________ is formed, and energy is released to drive anabolic reactions.
?
Why does a chemical reaction require increased activation energy without an enzyme as a biological catalyst?
an adenine, a ribose, and three phosphate groups.
a molecule of ATP consists of
ATP breakdown
anabolic reactions are coupled to
ATP synthesis
anabolic reactions are coupled to ATP breakdown, and catabolic reactions are coupled to
True
anabolic reactions are coupled to ATP breakdown, and catabolic reactions are coupled to ATP synthesis
Substrate
and each catalyzes only one reaction. For example, sucrose (table sugar) is the substrate of the enzyme sucrase, which catalyzes the hydrolysis of sucrose to glucose and fructose.
maintains the life of a cell
chemical composition of a living cell is constantly changing: some molecules are broken down while others are being synthesized. This balanced flow of chemicals and energy
collision theory
explains how chemical reactions occur and how certain factors affect the rates of those reactions
between 35°C and 40°C
he optimal temperature for most disease-producing bacteria in the human body is
Metabolism
is the buildup and breakdown of nutrients within a cell. These chemical reactions provide energy and create substances that sustain life.
those that release energy and those that require energy.
metabolism can be divided into two classes of chemical reactions:
ADP + P + energy -> ATP
reaction for the synthesis of ATP
ATP
stores energy derived from catabolic reactions and releases it later to drive anabolic reactions and perform other cellular work.
reaction rate
the frequency of collisions containing sufficient energy to bring about a reaction
Metabolism
the sum of all chemical reactions within a living organism
oxidases
those that add electrons to molecular oxygen (O2) are called -------
catabolic (energy-yielding) reactions
wo of the most important coenzymes in cellular metabolism are nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+). Both compounds contain derivatives of the B vitamin niacin (nicotinic acid), and both function as electron carriers. Whereas NAD+ is primarily involved in
