Posts Tagged ‘enzymes’


Thursday, October 14th, 2010

Lock and Key by B K Dewey on flickr

There are a lot of questions to answer in this topic.  It is one of my favourite aspects of biology, as an understanding of enzymes relates to nearly every branch of biology.  So, here goes….

What is an enzyme?  What is an active site?  What is enzyme specificity and what causes it?  What is the “lock and key” hypothesis? What effects do temperature, pH and substrate concentration have on enzyme activity?  What is denaturation?  How is lactose-free milk made?

What is the induced fit model of enzyme action? How do enzymes catalyze reactions?  What is the difference between competitive and non-competitive inhibition?  What are allosteric sites?  What is end-product inhibition?

Here are some useful resources. Mr Taylor’s presentationEnzymes AHL  These two clips (first and second) are good for review.  This one is pretty complicated – but I’m adding it as some of you aiming for 7s may like to look at it.

Digestion and absorption of digested foods

Thursday, April 8th, 2010
Ileum (3) by GreenFlames09 on flickr

Ileum (3) by GreenFlames09 on flickr

H2 – digestion.  We’ve done the basics, and because you ask good questions, we’ve gone further, so much of this you will have some idea about already.  You have the background, now we need to fill in the details.  Click here.

  • State that digestive juices are secreted into the alimentary canal by glands, including salivary glands, gastric glands in the stomach wall, the pancreas and the wall of the small intestine.
  • Explain the structural features of exocrine gland cells.
  • Compare the chemical composition of saliva, gastric juice and pancreatic juice.
  • Outline the control of digestive juice secretion by nerves and hormones, using the example of secretion by gastric juice.
  • Outline the role of membrane-bound enzymes on the surface of epithelial cells in the small intestine in digestion.
  • Outline the reasons for cellulose not being digested in the alimentary canal.
  • Explain why pepsin and trypsin are initially synthesized as inactive precursors and how they are subsequently activated.
  • Discuss the roles of gastric acid and Helicobacter pylori in the development of stomach ulcers and stomach cancers.
  • Explain the problem of lipid digestion in a hydrophilic medium and the role of bile in overcoming this.

 H3 – absorption of digested foods.  This is a short section, much of which we’ve covered before.  Click here. You need to be able to:-

  • Draw and label a diagram showing a transverse section of the ileum as seen under a light microscope.
  • Explain the structural features of an epithelial cell of a villus as seen in electron micrographs, including microvilli, mitochondria, pinocytotic vesicles and tight junctions.
  • Explain the mechanisms used by the ileum to absorb and transport food, including facilitated diffusion, active transport and endocytosis.
  • List the materials that are not absorbed and are egested.