3.1 biological molecules

Monomers

small units that can join together to form polymers

Polymers

large compound formed from combinations of many monomers

condensation reaction

joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

hydrolysis reaction

breaks a chemical bond between two molecules and involves the use of a water molecule

Monosaccharides

glucose, fructose, galactose

Disaccharides

Carbohydrates that are made up of two monosaccharides

maltose

glucose + glucose

Sucrose

glucose + fructose

Lactose

glucose + galactose

alpha glucose

• Monomer for starch and glycogen

• OH on bottom

beta glucose

• Monomer for cellulose and chitin

• OH on top

Polysaccharides

Carbohydrates that are made up of more than two monosaccharides

Glycogen

- An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.

Starch

• A storage polysaccharide in plants consisting entirely of glucose, insoluble so no osmotic effect

• amylose: long, unbranched chain of alpha glucose which has a coiled structure so compact

• amylopectin: long, branched chain of alpha glucose. Side branches allow it to be easily hydrolysed

Cellulose

• polysaccharide consisting of glucose monomers that reinforces plant-cell walls

• long, unbranched chains of beta glucose

• chains link together by H bonds that form microfibrils

Benedict's test for reducing sugars

1. Add benedict's reagent (blue) to sample

2. Heat in a boiling water bath

3. Positive = green / yellow / orange / red precipitate (reducing sugar present)

Benedict's test for non-reducing sugars

• If the result of a reducing sugar test is negative, a non reducing sugar may still be present. To test for these you have to break them down into monosaccharides.

1. Hydrolyse the sample (HCl) and carefully heat in a water bath that's been brought to boil.

2. Neutralise the solution using sodium hydrogencarbonate.

3. Carry out Benedict's test, if colour change occurs a non reducing sugar is present. If it remains blue neither a reducing or non reducing sugar is present.

Iodine test

Test for starch, just add iodine and turns blue-black

Triglycerides

• formed by the condensation of one molecule of glycerol and three molecules of fatty acid (hydrophobic).

• A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

• The R-group of a fatty acid may be saturated (no double bonds) or unsaturated (double bonds).

phospholipids

• a lipid consisting of a glycerol bound to two fatty acids and a phosphate group formed by the condensation reaction

• A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

• form bilayer in cell membranes

Emulsion test

Test for lipids. Mix your sample with ethanol and shake then add water and shake. If a white cloudy emulsion forms then a lipid is present.

amino acids

• monomers of proteins

• general structure of an amino acid: NH2 represents an amine group, COOH represents a carboxyl group and R represents a side chain.

• The twenty amino acids that are common in all organisms differ only in their side group.

• A condensation reaction between two amino acids forms a peptide bond.

Dipeptides

formed by the condensation of two amino acids.

Polypeptides

formed by the condensation of many amino acids.

Protein structure

• primary: sequence of amino acids

• secondary: alpha helix or beta pleated sheets, H bonds

• tertiary: 3D shape, H bonds, ionic bonds, disulphide bonds

• quaternary: multiple polypeptide chains

Biuret test

test for proteins, add biurets and turns lilac if present

Enzymes

• Catalysts for chemical reactions in living things, lowers activation energy

• proteins that have a specific active site shape that is complementary to specific substrate to form E-S complex

induced-fit model

Change in the shape of an enzyme's active site that enhances the fit between the active site and its substrate(s)

effects factors on the rate of enzyme-controlled reactions

enzyme concentration, substrate concentration, concentration of competitive and of non-competitive inhibitors, pH and temperature.

Calculating pH

pH\=-log[H+]

deoxyribonucleic acid (DNA)

• A double-stranded, helical nucleic acid molecule held together by H bonds, capable of replicating and determining the inherited structure of a cell's proteins.

• The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.

• A condensation reaction between two nucleotides forms a phosphodiester bond.

ribonucleic acid (RNA)

• a single stranded natural polymer that is present in all living cells and that plays a role in protein synthesis

• An RNA molecule is a relatively short polynucleotide chain.

• Ribosomes are formed from RNA and proteins.

• The components of an RNA nucleotide are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.

• A condensation reaction between two nucleotides forms a phosphodiester bond.

semi-conservative replication of DNA

-Ensures genetic continuity between generations of cells.

1. unwinding of the double helix due to breakage of hydrogen bonds between complementary bases in the polynucleotide strands by DNA helicase

2. attraction of new DNA nucleotides to align to exposed bases on template strands and base pairing

3. DNA polymerase catalyses condensation reaction that joins adjacent nucleotides to form sugar-phosphate backbone via phosphodiester bonds

Meselson-Stahl Experiment

Used isotope of nitrogen to change the weight of bacteria DNA N15 & N14, demonstrated that the semi-conservative model is the best description of replication after centrifugation.

ATP (adenosine triphosphate)

• nucleotide derivative and is formed from a molecule of ribose, a molecule of adenine and three phosphate groups

• energy is stored in high energy bonds between the phosphate groups and released via hydrolysis

• Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) is catalysed by the enzyme ATP hydrolase.

• The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive.

• ATP is resynthesised by the condensation of ADP and Pi. This reaction is catalysed by the enzyme ATP synthase during photosynthesis, or during respiration.

Water properties

• high heat capacity = temperature buffer

• high heat of vaporization = cooling effect

• polar = solvent so can dissolve substances so can be uptaken

• cohesive = transpiration, high surface tension

• metabolite = used in reactions

Inorganic ions

• atom that has a electric charge

• Each type of ion has a specific role, depending on its properties.

• hydrogen ions and pH

• iron ions as a component of haemoglobin

• sodium ions in the co-transport of glucose and amino acids

• phosphate ions as components of DNA and of ATP.