2c: Biological molecules Flashcards
Which chemical elements are present in carbohydrates, proteins and lipids?
All contain carbon, hydrogen and oxygen. All proteins also contain nitrogen and some also contain sulphur.
Describe the structure of carbohydrates and name the basic units from which they are formed.
Carbohydrates are made up of basic units called simple sugars. These sugars are sometimes form a ring-shaped molecule. An example of a simple sugar is glucose. Simple sugars can link together to form more complex carbohydrates. This may be as a pair, like in sucrose, or in larger molecules with many sugars bonded together. These larger molecules are known as polysaccharides and examples include starch and glycogen.
Describe the structure of proteins and name the basic units from which they are formed.
Proteins are molecules made up of long chains of amino acids. There are 20 different kinds of amino acids and they are joined together in any order to form the huge variety of proteins found in living organisms. Examples of proteins include structural proteins in muscle that allow them to contract and enzymes which control cell reactions.
Describe the structure of lipids and name the basic units from which they are formed.
Lipids, also known as fats and oils, are made from basic units called fatty acids and glycerol. Three fatty acids and one glycerol make a lipid. Different types of fatty acids are found in different lipids. Lipids are important in forming the cell membranes and many other molecules which are essential such as hormones.
Describe the test for glucose
Glucose (and other reducing sugars) can be detected using Benedict’s reagent. Benedict’s solution, which is a pale blue colour, is added to your sample. It is then heated to approx. 95 C. If the colour changes from blue to either green, yellow, orange or red, it is a positive test for glucose. Green means little glucose is present, while red means there is a high concentration of glucose.
Describe the test for starch
Starch can be detected using an iodine or potassium iodide solution. When the iodine is dropped onto the sample, if starch is present it will change from brown to dark blue or black. This happens, regardless of the amount of starch present.
Explain the term biological catalyst
A substance that speeds up a metabolic reaction and does not take part in the reactions itself. Without these, metabolic reactions would not happen fast enough to keep an organism alive.
Explain the role of enzymes as biological catalysts.
Enzymes, in their role as biological catalysts, control the rate of reaction for all metabolic reactions which occur in living cells. Each enzyme is specific, meaning it only works with one (or a few very similar) substance. These substances are known as substrates.
Explain the effect of temperature on the functioning of enzymes.
Enzymes work best at a particular temperature. This is known as the optimum temperature and is not the same for all enzymes. At temperatures below the optimum, the rate of reaction will be slower because the molecules have less energy and move more slowly. At temperatures that are higher than the optimum, the increased energy causes some of the bonds holding the enzyme together to break, causing the enzyme to change shape and no longer function. This is known as denaturation.
Explain how temperature can cause a change in shape of the active site
If temperature exceeds the optimum, the kinetic energy in each of the atoms within the enzyme becomes higher, leading to these particles to vibrate more. This vibration leads to a change in shape of the active site, whereby it no longer fits the substrate. The rate of reaction slows rapidly and eventually stops as the enzyme is denatured. This is irreversible.
Describe the structure of an enzyme
Enzymes are globular (rounded) proteins. Somewhere on there surface is a region with a very particular 3D shape. This is known as the active site and it is specifically shaped to match the substrate for that enzyme. Any change to the shape of the active site could render the enzyme useless (denatured).
Explain how pH can cause a change in shape of the active site.
Enzymes function at an optimum pH. This may be quite acidic in some cases (like the enzymes that work in the stomach) but in most cases is close to or at a neutral pH of 7. If an enzyme is in a solution, or environment with a pH that is different from its optimum, the interactions between the amino acids in the enzyme will be affected because some of these interactions are dependent upon the pH they are in. This will result in a change of shape in the enzyme and in particular the active site, leading to the enzyme becoming denatured.
Describe an experiment to investigate the effect of temperature on enzyme activity.
CORMMSS
C - Use temperatures ranging from 10-50 degrees C with intervals of 10
O - Strips of exposed negative film; same surface area, same brand, same time since exposure
R - Repeat by using 3 strips at each temperature
M - Measure time taken for film to clear completely
M - Record time in seconds
S - Control Variables: concentration of protease solution, volume of protease solution, same photo taken for each strip ( same amount of black exposure).
