1. Carbohydrates
  2. Making and using serial dilutions
  3. Starch-iodine solution sensitivity
  4. Heating and cooling starch suspension
  5. Testing carbohydrates with Benedict’s reagen
  6. Testing glucose with potassium manganate
  7. Respiration: Yeast


Biochemistry 01: Carbohydrates:

A very simple look at modelling carbohydrates. Glucose, sucrose, maltose, fructose and lactose. Monosaccharide (single sugars) and disaccharides (two monomer sugars joined) suffix -OSE for carbohydrate suffix -ASE for enzymes. Starch structure and other similar polymers.

Biochemistry 02: simple carbohydrates:

Sweets modelling sugars. Glucose Fructose Sucrose Maltose. Starch is amylose and amylopectin. Condensation and hydrolysis reactions.

Biochemistry 03: maltose digestion:

Maltose hydrolysis to break glycosidic bonds to produce the two glucose sugars. And the reverse reaction known as condensation.

Biochemistry 04: simple lipid models:

Further consideration of condensation and hydrolysis reaction in lipids this time. Fatty acids produced make the pH more acidic so we are able to monitor that change in a rate of reaction,

Making and using serial dilutions

Making and using serial dilutions 01:

An introduction to coloured solutions and serial dilutions. For example, making up a factor of 10 dilution. The colours help to show the dilution effect. Then use the range made up try to identify ‘unknown’ samples.

Making and using serial dilutions 02:

Making solutions, typically, the range of solutions you might need for osmosis experiments. Consider adding a small extra challenge with the sort of equipment you might offer for the task and then evaluate the effectiveness.

Making and using serial dilutions 03:

Making a serial dilution by diluting your stock concentration by a factor of 10. Checking you have the ‘right equipment’ for the task. Make sure you actually use the correct equipment carefully rather that the ‘slap dash’ method shown here. Be aware of poor technique introducing potential contamination.

Starch-iodine solution sensitivity

Starch-iodine solution sensitivity 01:

Preparing the final sample in our dilution range. We are going to look at how sensitive our iodine solution is in the detection of starch. At what concentration of starch will the ‘blue-black’ colour not be visible? Dilute the starch samples by a factor of 10 (i.e. each one is 10 times weaker) then add drops of iodine solution. Look for the blue-black colours to judge the limits of the sensitivity. Is there a point when there isn’t enough starch present for the iodine solution to detect? Adding iodine solution to our starch dilution range. Your iodine solution concentration is something to consider. You could easily give ‘arbitrary scores’ for blue-black reaction colours; a sort of eye-colorimeter.

Starch-iodine solution sensitivity 02:

Contamination problems caused by poor washing techniques. Even a few drops in the wrong place can wreck the results. There can be discussion points around ”just how small a contamination might be to invalidate results”.

Heating and cooling starch suspension

Heating and cooling starch suspension:

Starch forms a blue-black colour with iodine solution. What happens to the starch structure and colour complex when the temperature is increased? You might use beads and ribbon to model the starch structure and explain the colour changes. In this case the starch is mainly amylose.

Testing carbohydrates with Benedict’s reagent

Testing carbohydrates with Benedict’s reagent 01:

Testing for reducing and non-reducing sugars. This preliminary work is a ‘bucket chemistry’ approach to become familiar with the techniques and perhaps some limitations for you to work around. It is not meant as a technique guide for learners! In certain cases, you might need to know the constituents of your solutions. So, a negative result might be just as useful as a positive one. Also be aware that some are sources of starch are contaminated with reducing sugar.

Testing carbohydrates with Benedict’s reagent 02:

The non-reducing sugar test. Add acid to the sucrose and try the starch too. We are looking for hydrolysis reactions to break glycosidic bonds to reveal the constituent monosaccharides of glucose and fructose. Compare the colours and maybe the copper oxide precipitate formed. Adding excess Benedict’s to see a positive result for non-reducing sugar.

Testing carbohydrates with Benedict’s reagent 03:

Look at the results after 24 hours. There are different quantities of copper oxide precipitates produced. That mass will indicate the relative amounts of reducing sugar.

Testing glucose with potassium manganate

Testing glucose with potassium manganate 01:

Trying to determine glucose concentration. Ideas of how you might set up the experiment.

Testing glucose with potassium manganate 02:

The pink colour will decolourise after a certain time with different glucose concentrations. How you might decide on repeat readings to plot. Calibration curves used to identify unknowns.

Testing glucose with potassium manganate 03:

Using larger volumes of reagents should you see fit. Judging end-points is a perennial problem.

Respiration: Yeast

Yeast respiration and carbon dioxide:

Yeast respiration and detecting carbon dioxide. The old favourite balloon inflation idea. Investigating the variables that could affect the enzymes involved in yeast respiration. Detecting carbon dioxide from fermenting yeast alginate beads. More ideas to follow.

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