Writing Linking Paragraphs to help learn vocabulary.
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Look over all your vocabulary! Don’t just start with the first word and end with the last
Identify an overarching word or theme (or create one) to introduce the topic
Create groups of words to describe key ideas
If you can’t “link everything” (or if you have too many words) begin a new paragraph.
Check off words as you go.
Create sentences that “help you to study” by defining a word or action or linking words
together.
Chemical reactions are required in all living things. These chemical reactions are collectively called
metabolism. Whether a reaction is exothermic or endothermic, some type of energy input is usually
required to start a reaction. The energy required to start a reaction is called activation energy. When
chemical reactions break things down (like digestion), they are catabolic reactions. When chemical
reactions build things up, the reactions are called anabolic. Some anabolic reactions (like
photosynthesis) put molecules together. The products of photosynthesis end up having more energy
(stored in their bonds) than the reactants. These types of reactions are called endothermic (or
endergonic). Other reactions (such as cellular respiration) break apart the products of photosynthesis
and release energy. These types of reactions of exothermic (exergonic) and their products have less
energy than their reactants.
The reactions in our body need to occur at a very rapid rate. But molecules move around “randomly”
which means that their chance that a reaction between two molecules will occur is low. Catalysts are
molecules that speed up the rate of a reaction. Enzymes are catalysts that are found within living
organisms. Enzymes increase the likelihood that a reaction will occur. Enzymes do this by “positioning”
the substrate so that the reaction can easily take place. Because of this we say that enzymes “lower”
the activation energy needed for the reaction (see the diagram below)
In the diagram to the left, the substrate fits into the active site of an enzyme. The active site is the area
on the enzyme that helps the substrate to complete its’ reaction.
Once the substrate is in the active site, the entire molecule
(enzyme and substrate) is called the enzyme-substrate complex.
Enzymes exhibit substrate specificity . This means that an enzyme
can only be used for a specific substrate (like sucrose, or starch, or
triglycerides). This in turn means that either the active site must
have a specific shape that exactly matches the substrate (lock and
key model) or that the active site “wraps around” the right
substrate (induced fit model) to allow the reaction to occur.
An enzyme’s action (how well it speeds up a reaction) can be impacted by temperature, pH, the amount
of substrate or the amount of the enzyme. When an enzyme is exposed to a temperature that is above
it’s optimal temperature (the temperature at which it works best), an enzyme will quickly lose its
functionality because the protein denatures (loses its 3D shape) and the rate of reaction will decrease or
go quickly to zero. This can also occur if the pH is outside the correct range (either too high or too low).
If the condition (heat or pH) is quickly corrected, the protein may be able to renature and become active
again. If you increase enzyme concentration and keep the substrate level constant, the reaction rate
will increase. If you fix the enzyme concentration, and increase substrate concentration, you will see a
leveling off of the reaction rate. The pictures below show examples of the effect of heat, pH, substrate
concentration, and enzyme concentration.
Three different enzymes
Which might be found in a cold water shrimp?
Which might be found in a mammal?
might be found in a Yellowstone geyser?
Enzyme found in the stomach?Which
Enzyme found in small intestine
a. The effect of substrate concentration on the rate of a
reaction catalyzed by a FIXED amount of enzyme.
b. The effect of enzyme concentration on a CONSTANT
level of substrate (that means as it is converted to product, the
substrate is replaced.
And today, I finally learned why I take one-a-day vitamins (with minerals). It seems that both vitamins
(co-enzymes) and minerals (co-factors) attach to enzymes and increase the chance that the substrate
will bind to the enzyme (this means I need less enzyme, but achieve the same result). I also found out
that some molecules (like drugs or poisons) can inhibit (shut down or suppress enzymes). This is GREAT
if a drug (like an antibiotic) is suppressing enzymes in the bacteria that is making me sick. This is not so
great if something like cyanide is eaten (inhibiting cellular respiration) because I will die.
My own body can also produce molecules that suppress enzymes. Many times what inhibits is the
product that is being made. This is called “feedback inhibition”
Finally, all of these molecules inhibit in one of two ways. Competitive inhibition means that the
inhibitory molecule competes with substrate for the active site. Non-competitive inhibition means that
the inhibitory molecules bind to a site other than the active site. In this case it chances the shape of the
protein (and the active site) so that the active site doesn’t work.