1. introduction
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Transcript of 1. introduction
Biological molecules
Carbon based life forms are made form molecules using carbon atoms
A carbon atom has 6 protons6 neutrons and 6 electrons
This gives 4 electrons in the outer shell so a carbon atom will make 4 covalent bonds to have a stable 8 electrons
Here carbon (blue) has made a covalent bond with each of 4 hydrogens (red)This makes a molecule called methane with a chemical formula of CH4
Methane is a 3-dimensional structure like this:
Which can be drawn like this: Or more simply like this:
Carbon can share an electron with another carbon, forming a covalent bond
Notice that there are now only 3 hydrogen atoms on each carbon CH3CH3 or C2H6
This is ethene
By forming covalent bonds between carbon atoms long carbon chains can be built
Notice that each carbon makes 4 bonds so the terminal carbons have 3 hydrogens, the central ones have 2
Other atoms like oxygen and nitrogen can also form covalent bonds with carbon
Oxygen requires 2 more electrons to form a stable shell so often forms a double bond, sharing 2 electrons with carbon which also shares 2 electrons
Double BondsThese can form between 2 carbons or between other atoms
Each carbon still has 4 bonds, but there are 2 bonds between the carbonsSo there is only space for 2 hydrogen atoms to attach to each carbonThis is EthyleneCH2CH2 or C2H4
There can even be a triple bond between carbon molecules
Notice that sometimes we simply draw a line without showing Hydrogen on the end – it is implied
Double Bonds can form between carbon and other
moleculesOr as part of a ring structure
Functional groupsThe order in which atoms attach to a carbon chain will determine the properties
of the molecule
Aldehyde group - CHO
This attaches to a carbon chain
This is a carbonyl group
Aldehydes often smell aromaticAcetone and some vitamins are aldehydes
Keto group - CO
A central carbon bonds to oxygenThis is another carbonyl group
Hydroxyl group - OH
This attaches to a carbon
Molecules with this group are called alcohols
Hydroxyl groups are important in making bonds by condensation
Molecules are named according to the position of the hydroxyl group
Hydroxyl is terminal
Hydroxyl is in the middle
Carboxyl group - COOH
These are called acidsThe hydrogen will dissociate and become a proton (H+) in solution – making the solution acidic
The oxygen left becomes positively charged giving the molecule an overall charge
Charged molecules are called polar molecules
Saturated Carbon chains have no double bonds
Unsaturated carbon chains have one or more double bonds and therefore fewer hydrogen
molecules
OPTICAL ISOMERISMThis may occur when 2 molecules have the same
molecular formula but different arrangements in space, forming mirror images.
If a central carbon has FOUR DIFFERENT groups attaches it will be asymmetrical, and may exist in two different forms.
The central black carbon has 4 different groups attachedBy rearranging these we can form isomers which are mirror images
Like a left and a right hand
This is important in biology because molecules must fit into enzymesIf the shape is wrong it would be like trying to put your left hand into a right-hand glove
Isomers change the angle of plane-polarised light;Bending it either right or leftThey are named accordingly
Molecules are actually based on the properties of the isomers of glyceraldehyde
D = rightL = left