Biological Molecules

Haemoglobin

A globular protein that carries oxygen in red blood cells. Known as a conjugated proteins as it has a non-profit group attached (protetic group-haem group). Each of the 4 polypeptide chain has a haem group. The haem group contains iron which binds to the oxygen.

Monomer

A molecule that can be bonded to other identical molecules to form a polymer. A single unit.

Polymer

A substance which has a molecular structure built up from a large number of similar units bonded together, formed of many monomers.

Hydrogen Bond

A weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom in the other.

Test for proteins

Add a few drops of sodium hydroxide solution to your test solution. Then add some copper(II) sulfate solution. If protein is present the solution turns purple. If there is no protein then the solution stays blue.

Test for starch

Add iodine dissolved in potassium iodide solution to the test sample. If starch is present the sample will change from a browny-orange to a dark, blue-black colour. If no starch it will remain browny-orange.

Disaccharide

Any of a class of sugars whose molecules contain two monosaccharide residues. They are soluble in water. Three common examples are sucrose, lactose, and maltose.

Phospholipids

Are found in the cell membranes of all eukaryotes and prokaryotes. They make up the phospholipid bilayer. Properties: phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer. Water soluble substances cannot easily pass through the bilayer. The membrane acts as a barrier to these substances.

Ester Bond

At least one -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group.

Test for glucose

Dip test strips in a test solution and if the colour changes then glucose is present.

Polar

Electrons are usually distributed equally throughout the molecule's outer shells, called the orbitals. However, when the electrons do not have an equal distribution in the orbital, you have a polar molecule

Test for non-reducing sugars

If the reducing sugars test come negative you first have to break down the monosaccharides. Get a new samples of the test solution and add dilute hydrochloric acid and carefully heat it in the water bath. Then neutralise it with sodium hydrogencarbonate. The carry out a Benedict's test as you would for a reducing sugar. If the test is positive it will form a coloured precipitate. If negative it will stay blue which means no sugar is present.

Covalent Bond

Is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms.

Condensation

Is a chemical reaction in which two molecules or monomers combine to form a larger molecule (polymer), together with the loss of a small molecule (eg. water).

Biuret Test

Is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper(II) ion forms violet-colored coordination complexes in an alkaline solution.

Polysaccharide

Is a long-chain carbohydrate made up of smaller carbohydrates called monosaccharides that's typically used by our bodies for energy or to help with cellular structure. Each monosaccharide is connected together via glycosidic bonds. Examples include starch, cellulose, or glycogen.

Glycosidic Bond

Is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.

Hydrolysis

It is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both substance and water molecule to split into two parts. It is a reaction involving the breaking of a bond in a molecule using water. The reaction mainly occurs between an ion and water molecules.

Water

It is an unusually good solvent for a large variety of substances, and is an essential component of all organisms, being necessary for most biological processes. It is less dense as ice than in liquid form therefore ice floats.

Elastin

It's a fibrous protein found in elastic connective tissue (e.g. skin, large blood vessels and some large ligaments). It is elastic so allows tissues to return to their original shape after stretching.

Keratin

It's a fibrous protein found in the external structure of animals (e.g. skin, hair, nails, feathers, horns). It can be either flexible or hand and tough.

Insulin

It's a globular protein and a hormone secreted by the pancreas. It hepls to regulse blold glucose levels. It is soluble meaning it can be transported in the blood to tissues. It's made up of 2 polypeptide chains held together by disulfide bonds.

Amylase

It's globular protein and is an enzyme (mose enzymes are globular) that catalysis the breakdown of starch in the digestive system. It is made of a single chain of amino acids. It's secondary structure contains a-helix and b-pleated sheet sections.

Collagen

Its a fibrous protein found in animal connectuve tissues (e.g. bone, skin, muscle) and is a very strong molecule. Minerals can bind to the protein to increase rigidity

Testing the concentration of a glucose solution

Make up about 5 glucose solutions with different known concentrations using a serial dilution technique. Conduct a Benedict's test on the solutions and have a control of water. Remove any precipitate and then use the colorimeter with a red filter to measure absorbance of the Benedict's solution remaining in each tube. The lower the absorbance the higher the glucose concentration.

Secondary structure of proteins

Polypeptide chains don't remain flat and straight. Hydrogen bonds form between nearby amino acids in the chain. Making it coil into a a-helix or fold into a b-pleated sheet.

Test for reducing sugars

Reducing sugars include all monosaccharides and some disaccharides. To test you add Benedict's reagent to a sample and heat it in a water bath that's been bought to the boil. If the test it positive it will form a coloured precipitate. The higher the concentration of reducing sugar the further the color change goes. If the solution is brick red from blue then the concentration of reducing sugar is high.

Rf value equation

Rf= distance travelled by spot ÷ distance travelled by solvent

Test for lipids

Shake the test substance with ethanol for about a minute then pour the solution into water. If lipid is present the The solution will turn milky. The norenlipid present the more noticeable the milky colour will be. If there is no lipid present the solution wil stay clear.

Starch

Structure: a mixture of two polysaccharides of a-glucose (amylose and amylopectin). Amylose is a long unbranched chain of a-glucose. Angles of glycosidic bonds give it a collided structure, almost like a cylinder. This makes it compact, so is really good for storage because you can fit more into a small space. Amylopectin is a long branched chain of a-glucose. Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily. This means that the glucose can be released quickly. Properties: starch is insoluble in water, so it doesn't cause water to entre cells by osmosis meaning the cell swells. This makes it good for storage. Plants store excess glucose as starch

Triglycerides

Structure: long hydrocarbon tails of the fatty acids contain lots of chemical energy- a load of energy gets released when they are broken down. Because of these tails, lipids contain about twice as much energy per gram as carbohydrates. Properties: they're insoluble, so they don't cause water to enter cells by osmosis which would cause swelling. They bundle together as insoluble droplets in cells because the fatty acid aid tails are hydrophobic and the glycerol heads are hydrophilic. in animals and plants, triglycerides are mainly used as energy storage molecules. Some bacteria (eg. mycobacterium tuberculosis) use triglycerides to store both energy and carbon.

Cellulose

Structure: long unbranched chains of b-glucose. When b-glucose molecules bond they form straight cellulose chains. Cellulose chains are linked together by hydrogen bonds to form strong fibers called micro fibrils. Properties: strong fibers means cellulose provides structural support for cells (eg. cell walls).

Glycogen

Structure: very similar to amylopectin, except that it has loads more side branches coming off it. loads of branches means stored glucose can be released quickly, which is important for energy release in animals. Very compact molecule so good for storage. Properties: animal cells get energy from glucose. Animals store excess glucose as glycogen - another polysaccharide of a-glucose.

Tertiary structure of proteins

The coiled or folded chain is often further coiled or folded. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure form their final 3D structure.

Primary structure of proteins

The sequence of amino acids in the polypeptide chain. Different proteins have different sequences of amino acids. A change in 1 amino acid can change the whole structure.

Quaternary structure of proteins

The way in which many different polypeptide chains are put together (eg. haemoglobin is made of 4 polypeptide chains bonded together). For proteins made of more than 1 polypeptide chain, the quaternary structure is their final 3D structure.

Monosaccharide

They are the simplest form of carbohydrates. They consist of one sugar and are usually colorless, water-soluble, crystalline solids. They are any of the class of sugars (e.g. glucose) that cannot be hydrolysed to give a simpler sugar. Common examples include glucose (dextrose), fructose, galactose, and ribose.

Cholesterol

Type of lipid - hydrocarbon ring structure attached to a hydrocarbon tail. The ring has a polar hydroxyl group attached. In Eukaryotic cells, cholesterol molecules help strengthen the cell membrane by interacting with the bilayer. Structure: cholesterol has a small size and flattened shape - this allows it the fit between the phospholipid molecules in the membrane. They bind to the tails, causing them to pack closer together. This helps make membrane less fluid and more rigid.