biological molecules Flashcards
Most of the molecules in living organisms fall into three categories:
carbohydrates, proteins and lipids
These all contain..and so are described as … molecules
carbon
organic
carbohydrates
Long chains of simple sugars
Glucose is a simple sugar ( a monosaccharide)
When 2 glucose molecules join together maltose is formed (a disaccharide)
When lots of glucose molecules join together starch, glycogen or cellulose are formed (a polysaccharide)
Glycogen, cellulose and starch are all made from glucose molecules
Fats
Most fats (lipids) in the body are made up of triglycerides
Their basic unit is one glycerol and three fatty acids
The fatty acids vary in size and structure
Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)
Proteins
Long chains of amino acids
There are about 20 different amino acids
They all contain the same basic structure but the ‘R’ group is different for each one
When amino acids are joined together a protein is formed
The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins
Even a small difference in the order of the amino acids results in a different protein being formed
Protein Shape
There are thousands of different proteins in the human body and other organisms
Many of these proteins are different shapes and the shape often has an important effect on the function of the protein
For example:
Enzymes have an area in them known as the active site – this is important as this is the place where another molecule fits into the enzyme in order for a reaction to take place
If the shape of the active site does not match the shape of the molecule that fits into it, the reaction will not take place
Every enzyme has a different shaped active site
Antibodies are proteins produced by certain types of white blood cell to attach to antigens on the surface of pathogens
The shape of the antibody must match the shape of the antigen so that it can attach to it and signal it for destruction
The different sequences of amino acids cause the polypeptide chains to fold in different ways and this gives rise to the different shapes of proteins
In this way every protein has a unique 3-D shape that enables it to carry out its function
Test for Glucose (a reducing sugar)
Add Benedict’s solution into sample solution in test tube
Heat at 60 – 70 °c in water bath for 5 minutes
Take test tube out of water bath and observe the colour
A positive test will show a colour change from blue to orange or brick red
Testing for glucose using Benedict’s solution
Test for Starch
Add drops of iodine solution to the food sample
A positive test will show a colour change from brown to blue-black
Testing for starch using Iodine solution
Test for Protein
Add drops of Biuret solution to the food sample
A positive test will show a colour change from blue to violet / purple
Test for Fat
Food sample is mixed with 2cm3 of ethanol and shaken
The ethanol is added to an equal volume of cold water
A positive test will show a cloudy emulsion forming
Test for vitamin C
Add 1cm3 of DCPIP solution to a test tube
Add a small amount of food sample (as a solution)
A positive test will show the blue colour of the dye disappearing
When describing food tests in exam answers, give the …colour of the solution and the colour it changes to for a …
starting
positive result
Describing DNA structure
NA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms
It consists of two strands of DNA wound around each other in what is called a double helix
The individual units of DNA are called
nucleotides
bases of DNA
There are four different bases, Adenine (A), Cytosine (C), Thymine (T) and Guanine (G)
The bases on each strand pair up with each other, holding the two strands of DNA in the double helix
The bases always pair up in the same way:
Adenine always pairs with Thymine (A-T)
Cytosine always pairs with Guanine (C-G)
The phosphate and sugar section of the nucleotides form
the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder
It is this sequence of bases that
holds the code for the formation of proteins
importance of water
Water is important as a solvent in the following situations within organisms:
Dissolved substances can be easily transported around organisms – eg xylem and phloem of plants and dissolved food molecules in the blood
Digested food molecules are in the alimentary canal but need to be moved to cells all over the body – without water as a solvent this would not be able to happen
Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine
Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells
