Lesson starter

1
Lesson starter

• Why does thrombin catalyse fibrinogen into
  fibrin, but not any other reaction?
• Enzymes are specific to a particular substrate.
  The shape of the active site of the enzyme and
  the shape of the substrate are complementary to
  each other.

2
Giving blood

• Learning objectives
• describe the conditions in which blood for
  transfusion is stored
• describe and explain the effects of changing pH
  and changing temperature on enzyme activity, with
  reference
• explain the role of co-factors in enzyme
  activity, with reference to the removal of
  calcium ions in blood stored for transfusion

3
The effect of temperature on enzyme activity

• Enzymes are proteins that speed up chemical
  reactions in our cells.
• Enzymes work best at their optimum temperature.
  The optimum temperature for the human body is
   37C.
• As the temperature increases, so does the rate of
  chemical reaction.
• This is because heat energy causes more
  collisions, with more energy, between the enzyme
  molecules and other molecules.
• However, if the temperature gets too high, the
  enzyme is denatured and stops working.

4
The effect of temperature on enzyme activity
5
Storing blood

• Blood clotting results from the activities of
  enzymes.
• As enzymes are globular proteins, they are
  affected by temperature.
• Blood must be stored at low temperature to
  prevent enzyme activity taking place
• It is also important that other blood proteins,
  such as haemoglobin, are not allowed to denature.
• Freezing blood would result in the formation of
  ice crystals inside the blood cells. These would
  damage the cell membranes so that the cells would
  be destroyed when the blood was thawed out.
• For this reason, blood is stored at 4oC

6
The effect of pH on enzyme activity

• pH is a measure of how acid or alkaline a
  solution is.
• The more hydrogen ions there are in solution, the
  more acidic it is.
• The tertiary structure of globular proteins, such
  as enzymes are held together by weak hydrogen
  bonds.
• Hydrogen bonds relay on positive and negative
  charges.
• If a solution such as blood plasma has lots of H
  ions in it, it will become more acidic and
  therefore alter the shape of the protein by
  breaking the hydrogen bonds.
• This will cause the shape of the protein to
  change and become denatured

7
The effect of pH on enzyme activity

• If the pH of stored blood changes, not only would
  enzymes denature, but blood proteins would also
  become denatured.
• A buffer solution is added to stored blood to
  stop this from happening.
• A buffer solution keeps the pH of the blood the
  same

8
Enzyme cofactors

• Cofactors are inorganic molecules that help a
  substrate and enzyme combine so that a reaction
  can take place.
• Calcium is a cofactor that is needed to help
  blood clotting and is found in blood plasma
• Calcium ions are also present in platelets and
  released from damaged platelets.
• For this reason, it is very important that
  calcium ions are removed when blood is stored to
  stop blood clots forming.
• Sodium citrate can be added to remove calcium ions

9
Exam questions
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)