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Flashcards in Biological Molecules Deck (34)
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What chemical elements are present in carbohydrates?

carbon, hydrogen and oxygen


What chemical elements are present in proteins?

carbon, hydrogen, oxygen, nitrogen (sometimes sulfur)


What chemical elements are present in lipids (fats and oils)?

carbon, hydrogen, oxygen


Describe the structure of carbohydrates as large molecules made up from smaller basic units

- Simple sugars formed from carbon hydrogen and oxygen atoms, sometimes arranged in a ring shaped molecule.
- One example of a simple sugar is glucose (monosaccharide)
- Simple sugar molecules can link together to form larger molecules (disaccharides eg sucrose, polysaccharides eg starch and glycogen, long chains of glucose molecules)


Describe the structure of proteins as large molecules made up from smaller basic units

- Long chains of amino acids linked together
- Over 20 different types of amino acid
- They can be joined together in different orders to make hundreds of thousands of different types of protein


Describe the structure of lipids as large molecules made up from smaller basic units

- fatty acids and glycerol
- most common type of lipid in body is called a 'triglyceride'
- made of two different sub units called 1x glycerol and 3x fatty acids


What are food tests for carbohydrates detecting?

Presence of starch and glucose


Testing for starch solutions and results:

- Iodine
- Negative = yellow/ brown
- Positive = blue/ black


Testing for glucose solutions and results:

- Benedicts solution
- needs to be heated above 80 degrees
- negative = stays blue
- slightly positive = green or yellow
- positive = orange or brick red


Testing for protein solutions and results:

- Biuret solution
- negative = blue
- positive = lilac/ purple


Testing for fat solutions and results:

- ethanol
- negative = colourless
- positive = white emulsion


Define reagent:

A chemical that indicates the presence of a substance, usually by changing colour.


What may be necessary when adding a reagent to a food sample which changes colour depending on what biological molecules are present?

Sometimes it may be necessary to crush the food or add water to the food before adding the reagent.


How to carry out test for starch?

- place food on dropping tile
- drop iodine solution onto food


How to carry out test for glucose?

- add the food to a test tube
- add Benedict solution
- put water bath at 85 degrees then leave for 5-10 mins


How to carry out test for protein?

- add the food to a test tube
- add a few drops of Biuret's solution


How to carry out test for fats?

- add food to a test tube
- add a few drops of ethanol, put bung + shake
- pour solution into test tube containing water


Why does a cloudy layer form for fats?

Fats don't dissolve in water but do in ethanol


Which two chemicals are found in Biuret reagent?

sodium hydroxide (NaOH) and hydrated copper(II) sulfate


Practical to show how enzymes work

- Visking tubing acts like the walls of the intestine.
- It is a 'partially permeable membrane', so only small molecules can fit through its small holes
- The enzyme amylase can break down long starch molecules into small glucose molecules
- They can then pass through the intestine wall and into the blood to go to all body cells and be used for respiration
- Pour starch and amylase solution into risking tubing in a boiling tube
- After 25 minutes the water in the test tube can be tested for glucose using iodine
- Should be positive as amylase breaks down starch into glucose


What are enzymes?

- biological catalysts
- speed up chemical reactions in cells


Synthetic reactions vs Breakdown reactions

- synthetic = large molecules built up from small
- eg making glycogen from glucose

- breakdown = large molecules to smaller ones
- eg making glucose from glycogen


Enzymes are proteins?

Yes, they are made up of long chains of amino acids which are folded into specific shapes


The lock and key hypothesis
(see diagram)

the substrate fits into the enzyme molecule
the products of the reaction are released at the end, leaving the enzyme free to be used again


Properties of enzymes

- work very rapidly
- only needed in small amounts
- they are specific, will only catalyse one reaction


Why are enzymes specific?

Due to specific active site, meaning they can only lock together with a substrate that has a specific shape and matches


Why is the reaction low at low temperatures?

Molecules have low kinetic energy and so move slowly, this means the enzyme and substrate are less likely to collide
Less successful collisions = less enzyme substrate complex will form and no product will be made


What is the temperature at which the rate of an enzyme-controlled reaction is the fastest?

The 'optimum temperature'


Why does rate of reaction increase with temperature?

- As the temperatures increase the substrate and enzyme molecules gain kinetic energy and move more.
- This means the enzyme and substrate are more likely to collide.
- More collisions means more enzyme-substrate complexes, and more product formed.
- Therefore there is a higher rate of reaction.


What happens to the enzymes at high temperatures? How does this affect the rate of reaction?

- At very high temperatures the enzyme is damaged and the active site change shape, this is called denaturing.
- When the enzyme is denatured the substrate no longer fits in the active site and no product is formed.
- Denaturing is irreversible, so once the enzyme is boiled it will never work again even if it is cooled down.