Biological Molecules Flashcards
(34 cards)
1
Q
What chemical elements are present in carbohydrates?
A
carbon, hydrogen and oxygen
2
Q
What chemical elements are present in proteins?
A
carbon, hydrogen, oxygen, nitrogen (sometimes sulfur)
3
Q
What chemical elements are present in lipids (fats and oils)?
A
carbon, hydrogen, oxygen
4
Q
Describe the structure of carbohydrates as large molecules made up from smaller basic units
A
- 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)
5
Q
Describe the structure of proteins as large molecules made up from smaller basic units
A
- 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
6
Q
Describe the structure of lipids as large molecules made up from smaller basic units
A
- 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
7
Q
What are food tests for carbohydrates detecting?
A
Presence of starch and glucose
8
Q
Testing for starch solutions and results:
A
- Iodine
- Negative = yellow/ brown
- Positive = blue/ black
9
Q
Testing for glucose solutions and results:
A
- Benedicts solution
- needs to be heated above 80 degrees
- negative = stays blue
- slightly positive = green or yellow
- positive = orange or brick red
10
Q
Testing for protein solutions and results:
A
- Biuret solution
- negative = blue
- positive = lilac/ purple
11
Q
Testing for fat solutions and results:
A
- ethanol
- negative = colourless
- positive = white emulsion
12
Q
Define reagent:
A
A chemical that indicates the presence of a substance, usually by changing colour.
13
Q
What may be necessary when adding a reagent to a food sample which changes colour depending on what biological molecules are present?
A
Sometimes it may be necessary to crush the food or add water to the food before adding the reagent.
14
Q
How to carry out test for starch?
A
- place food on dropping tile
- drop iodine solution onto food
15
Q
How to carry out test for glucose?
A
- add the food to a test tube
- add Benedict solution
- put water bath at 85 degrees then leave for 5-10 mins
16
Q
How to carry out test for protein?
A
- add the food to a test tube
- add a few drops of Biuret’s solution
17
Q
How to carry out test for fats?
A
- add food to a test tube
- add a few drops of ethanol, put bung + shake
- pour solution into test tube containing water
18
Q
Why does a cloudy layer form for fats?
A
Fats don’t dissolve in water but do in ethanol
19
Q
Which two chemicals are found in Biuret reagent?
A
sodium hydroxide (NaOH) and hydrated copper(II) sulfate
20
Q
Practical to show how enzymes work
A
- 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
21
Q
What are enzymes?
A
- biological catalysts
- speed up chemical reactions in cells
22
Q
Synthetic reactions vs Breakdown reactions
A
- synthetic = large molecules built up from small
- eg making glycogen from glucose
- breakdown = large molecules to smaller ones
- eg making glucose from glycogen
23
Q
Enzymes are proteins?
A
Yes, they are made up of long chains of amino acids which are folded into specific shapes
24
Q
The lock and key hypothesis
see diagram
A
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
25
Properties of enzymes
- work very rapidly
- only needed in small amounts
- they are specific, will only catalyse one reaction
26
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
27
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
28
What is the temperature at which the rate of an enzyme-controlled reaction is the fastest?
The 'optimum temperature'
29
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.
30
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.
31
Effect of pH on enzymes
- Each enzyme requires a certain pH to work efficiently. This is called the optimum pH. Some enzymes work best in acidic conditions, others in alkaline conditions.
- Changes in pH also alter the shape of an enzyme’s active site
Enzymes are also sensitive to pH. Changing the pH of its surroundings will also change the shape of the active site of an enzyme.
Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule, positively and negatively charged amino acids will attract. This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site.
Changing the pH will affect the charges on the amino acid molecules. Amino acids that attracted each other may no longer. Again, the shape of the enzyme, along with its active site, will change.
Extremes of pH also denature enzymes. The changes are usually permanent.
Enzymes work inside and outside cells, for instance in the digestive system where cell pH is kept at 7.0 to 7.4. Cellular enzymes will work best within this pH range. Different parts of the digestive system produce different enzymes. These have different optimum pHs. The optimum pH in the stomach is produced by the secretion of hydrochloric acid.
The optimum pH in the duodenum is produced by the secretion of sodium hydrogencarbonate.
The following table gives examples of how some of the enzymes in the digestive system have different optimum pHs:
32
Practical showing effect of temperature on enzymes
(see sheets too)
Set up water baths at various temperatures (e.g. 0°C, 20°C, 40°C, 60°C and 80°C).
Add starch solution to 5 test tubes.
Add amylase solution to another 5 test tubes.
Place one starch and one amylase test tube into each water bath for 5 minutes - to allow the enzyme and substrate to reach the desired temperature.
Place 1 drop of iodine into each dimple on a spotting tile.
Add the amylase to the starch in the 0°C water bath.
Start the timer.
Every minute remove a sample of the starch-amylase solution and add it to a drop of iodine on the spotting tile.
Repeat step 8 until the iodine no longer changes colour - meaning that there is no starch present, in other words the amylase has broken all starch down.
Repeat steps 6-9 for each of the temperatures.
Record results.
Draw a graph to show the time taken for starch to be digested at different temperatures.
Results
At the optimum temperature the amylase will break down starch very quickly.
At low temperatures the amylase will break starch down slowly due to reduced kinetic energy.
At high temperatures the amylase will break starch down slowly or not at all due to denaturation of the enzyme’s active site.
Controlled variables
pH
Same volume and concentration of starch.
Same volume and concentration of amylase.
33
Practical
Set up a Bunsen burner, heatproof mat, tripod and gauze.
Place a beaker of water on the gauze and adjust the flame to keep the water at about 35°C.
Now put two drops of iodine solution into each spot of a spotting tile.
Add 2 cm3 of amylase enzyme solution to a test tube.
Place 2 cm3 of starch solution into the same tube.
Finally add 1 cm3 of pH solution to the tube. This will keep the pH constant.
Mix the solution in the test tube and place it into the beaker of water on the Bunsen burner.
Use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile.
Repeat until the iodine solution stops turning black.
Record the time this takes.
Repeat with different pH solutions.
Conclusions
The enzyme amylase breaks down starch into glucose. If the enzyme is working effectively, this will happen quickly. At pH 7 it took the shortest time before the iodine no longer changed colour. This shows that the starch was broken down more quickly at this pH. The optimum pH for amylase is therefore pH 7
Risks
Iodine solution is an irritant. If it touches skin it should be washed off.
Goggles should be worn at all times.
34
see diagrams and notes
see diagrams and notes
