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Strand 1 - Coggle Diagram
Strand 1
CARBOHYDRATES
monomers ~ single unit or molecule, these can be linked to form polymers, they're formed by polymerisation
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monosaccharides: (CH2O)n is the general formula, (6C), glucose, galactose and fructose are three examples
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Benedict's test
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Leave the test tube in a hot (80⁰C) water bath for about 5 minutes, or until the colour of the mixture does not change.
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To prepare a control, repeat steps 3-5 using 2 cm3 of distilled water instead of sample solution.
common disaccharides ~ sucrose, lactose and maltose
disaccharides are formed from condensation reactions, the bond that forms between the 2 monosaccharides is called a glycosidic bond
non - reducing sugar ~ sucrose, reducing sugar ~ maltose, lactose
Negative Benedict's
Add dilute hydrochloric acid, then neutralise. The acid will break down the non-reducing sugars into monosaccharides. After adding acid, neutralise the solution with sodium hydrogencarbonate.
Heat and observe colour change. We can then do the Benedict’s test, as we did above for reducing sugars. If there are non-reducing sugars in the sample, we will observe a colour change similar to the one we see with reducing sugars (blue to green to yellow to orange to brick red).
PROTEINS
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100 amino acids have been identified and approximately 20 of these occur naturally in proteins. The fact that the same 20 amino acids occur in all living organisms provides indirect evidence for evolution.
Every amino acid has a central carbon attached to four different chemical groups.Amino group (NH2) is a basic group which the amino part of the amino acid is derived. Carboxyl group (COOH) an acidic group which gives the amino acid the acid part of its name. Hydrogen atom (H). R (side) group a variety of different chemical groups. Each amino acid has a different R group. These 20 different amino acids differ only in their R group.
Amino acid monomers can combine to form a dipeptide through a condensation reaction (joins two molecules together with the formation of a chemical bond and involves the elimination of a water molecule).
The water is made by combining an OH from the carboxyl group of one amino acid with a hydrogen from the amino group of another amino acid. The two amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.
In a similar way a glycosidic bond of a disaccharide can be broken by the addition of a water molecule (hydrolysis) so the peptide bond of a dipepide can also be broken by hydrolysis to give its two constituent amino acids.
Proteins can be joined together in a process called polymerisation. The resulting chain of many hundreds of amino acids is called a polypeptide. The sequence of amino acids in a polypeptide chain forms the primary structure of any protein.
This sequence is determined by DNA. As polypeptides have many of the 20 naturally occurring amino acids joined in different sequences, it follows that there's an almost limitless number of possible combinations, and therefore types, of primary protein structure.
It is the primary structure of a protein that determines its ultimate shape and hence its function. A change in just a single amino acid in this primary sequence can lead to a change in shape of the protein and may stop it from carrying out its function.
Secondary structure for proteins: the linked amino acids that make up a polypeptide possess both NH and C O groups on either side of every peptide bond. The hydrogen of the NH group has an overall positive charge, whilst the oxygen of the C O group has an overall negative charge. These two groups therefore readily form weak bonds called hydrogen bonds. This causes the long polypeptide chain to be twisted into a 3D shape such as the coil known as an alpha helix.
The alpha helices of the secondary protein structure can be twisted and folded even more to give the complex and specific 3D structure of each protein. This is known as the tertiary structure. This structure is maintained by a number of different bonds. Where the bonds occur depends on the primary structure of the protein. These bonds include: disulphide bridges, which are fairly strong and therefore not easily broken, ionic bonds, which are formed between any carboxyl and amino acid groups that aren't involved in the forming of peptide bonds. They are weaker than disulphide bonds and are easily broken by changes in pH. Hydrogen bonds, which are numerous but easily broken.
It is the 3D structure of a protein that is important as it makes each protein distinctive and allows it to recognise, and be recognised by, other molecules. It can then interact with them in a very specific way.
Large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. There also may be non protein (prosthetic) groups associated with the molecules. Such as the iron containing haem group in haemoglobin. Although, the 3D structure is important to how a protein functions, it is the sequence of amino acids (primary structure) that determines the 3D shape in the first place.
The most reliable test for proteins is the Biuret test which detects peptide bonds. Place a sample of solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature. Add a few drops of very dilute (0.05%) copper(II) sulfate solution and mix gently. A purple colouration indicates the presence of peptide bonds and hence a protein. If no protein is present the solution remains blue.
LIPIDS
Lipids are a varied group of compounds including fats, oils and waxes.
They all contain the elements H, C, O.
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Lipids are biological molecules that are insoluble in water but soluble in organic solvents like ethanol.
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One of the fatty acid molecules is replaced by a phosphate molecule. A hydrophilic head; interacts with water but not fat. A hydrophobic tail; orients away from water but mixes with fat.
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Phosphate group ~ head is polar and hydrophilic. Fatty acid tails are non polar and hydrophobic. Form micelles/bilayers when wet.