Chapter 2: M9 & M8



As previously mentioned in M5, cell
membranes consist of two lipid layers with
other molecules embedded in them (Not in bed
with them.)
Some of these molecules are receptors designed
to bond with specific chemicals in order to
bring about a response inside the cell.
This function is what allows for
communication between cells. (Ergo, your
body talks to itself and this is how.)



The cell membrane,
along with the
structures embedded
within it, allows
selectivity of chemicals.
This is important for
the cell to control its
internal environment.
It is the unique selection of membrane structures found
on each type of cell which makes this possible.
Most cellular communication happens via hormones.
Cells have many receptors all over the outside of their
membranes to facilitate the receipt of hormone
messages. Each type of receptor is produced only by
certain cells and can only match one type of hormone.

A hormone is itself a
protein produced by
cells in endocrine
glands. When it binds
to a receptor protein on
the cell membrane it
can induce a change in
the shape of that
receptor which can then
cause secondary
enzymes or messages to
change conditions
within the cell.



Adrenaline is a hormone produced from the
Adrenal Glands on top of the kidneys.
When it binds to the receptors on the cell
membrane of liver cells it causes the cell to
convert glycogen into glucose which is then
released into the bloodstream.
This is then used by the other cells of your
body to produce energy for things like the
fight-or-flight response.

M8.1 Describe the induced-fit model of enzyme
substrate binding.
Enzymes are referred to as biological catalysts. A
catalyst is anything which speeds up a reaction,
therefore an enzyme is something which speeds up
reactions in cells.
 Usually enzymes are proteins.
 Their 3D shape determines the specificity.
 Substances which the enzyme binds to in a reaction
are called the substrate molecule(s). These are
specific to each enzyme.





The active site of the enzymes ( the bit which fits to the
substrate) is a groove or an imprint on the surface of the
enzyme which binds or joins to the specific substrate.
ONE SUBSTRATE, ONE ENZYME.
The binding is with weak bonds (e.g. hydrogen bonds)
and this binding may change the shape of the enzyme
and the substrate.
The substrate bonds become stressed by the change of
shape so they break easily. This leads to the
catalytic action of the
enzyme. When the
reaction is finished there
is no permanent change
to the enzyme.




The active site is capable of changing shape
because it is flexible. It brings the chemicals
together in close proximity to encourage the
reaction to occur quicker.
Enzymes can have more than 1 active site as
well. Some may have over a hundred.
The reaction they assist can happen very
quickly.
Some enzymes are estimated to process more
than 100,000 reactions in a second, per enzyme.

Temperature:



Enzyme’s temperature range is very specific: 3540 degrees. As temp. increases, molecules of
substrate collide more frequently, and interact
easily with the active site of the enzyme.
If temp raises too high (past the normal range)
the enzyme is denatured, which changes the
active site so it can’t bind with the substrate.
Low temperatures produce slow reaction rates
because with less energy there are less collisions.

Chemical Factors:

Inhibitors: chemicals which inhibit the action of
specific enzymes.
 Competitive Inhibitors: These resemble the normal
substrate and so compete for the active binding site.



Non-Competitive Inhibitors: These will bind
elsewhere on the enzyme, but stress it so that it alters
the shape of the active site elsewhere.
Examples include poisons such as arsenic and
cyanide.
Penicillin blocks the active site of an enzyme that
many bacteria use to manufacture their cells walls.
This renders them useless and they die!

pH Level:



Most enzymes in humans need an
optimum PH level of 6-8. However,
each enzyme has its own optimum
pH level which can vary depending
on its purpose.
i.e. Pepsin works in the stomach
juices which are acidic so it prefers a
pH of 2 whereas Trypsin in the
intestines prefers a pH of 8.
This is also why bleach is bad for
your hair girls.



Finally: Cofactors effect enzyme reactions, but
unlike the other things, these actually help.
These factors can either bind to the enzyme’s
active site, or to the substrate itself temporarily,
to make the process more efficient.
These “cofactors” include things like metal
atoms; copper, iron, zinc, or organic molecules
like vitamins which are also called co-enzymes.