biological molecules

What is the test used when testing for proteins?

Biuret test

describe the Biuret test?

• the test solution needs to be alkaline, so first you add a few drops of sodium hydroxide solution.

• then you add some copper (II) solution.

what colour change would be an indicator that a protein is present?

change from blue to purple.

What is the test used for testing for lipids?

The emulsion test

describe the test used to test for lipids?

• shake the test substance for about a minute with ethanol.

• then pour the solution into water.

What would indicate a positive result for the emulsion test?

The solution will turn milky.

What is the test used when testing for starch?

The iodine test

Describe the iodine test when testing for starch?

• Add iodine dissolved in potassium iodide solution to the test sample.

• Watch for the colour change.

what would indicate a positive test result in the iodine test?

a colour change from brown/orange to blue.

What is the test used when testing for sugars?

The benedict’s test.

what are lipids?

they are macromolecules, and they all contain the elements carbon, hydrogen and oxygen.

what are the three types of lipids?

Triglycerides, Phospholipids and Cholesterol.

describe the structure of a triglyceride.

they have one molecule of glycerol attached to three fatty acid tails.

how are triglycerides formed?

• condensation reaction between one molecule of glycerol and three molecules of fatty acid.

• ester bonds form between the molecule of glycerol and the fatty acids chains.

how many ester bonds does one triglyceride have?

three

how are the ester bonds formed?

each ester bond is formed by a condensation reaction between the carboxyl groups of the fatty acids and the three hydroxyl groups on the molecule of glycerol.

what is the name for the process where triglycerides are synthesised?

esterification

describe the structure of the fatty acids?

• they have long tails made of hydrocarbons with 4-36 carbon atoms.

• the tails are hydrophobic (repel water).

what are the two types of fatty acids?

saturated and unsaturated

describe saturated fatty acids.

they do not have any double bonds between their carbon atoms in their hydrocarbon tails. the fatty acid is ‘saturated’ with hydrogen.

describe unsaturated fatty acids.

they have at least one double bond between carbon atoms, which causes the chain to kink.

describe the structure of a phospholipid?

contains a phosphate group (hydrophilic), glycerol, and two fatty acid tails (hydrophobic).

describe the structure of cholesterol?

it has a hydrocarbon ring structure attached to a hydrocarbon tail. the ring structure has a polar hydroxyl group (OH) attached to it.

what are the function of triglycerides?

• mainly used as energy storage

• energy source for respiration

• thermal insulation

how are triglycerides good for energy storage?

the long hydrocarbon tails of the fatty acids contain lots of chemical energy - a load of energy is released when they are broken down.

what is the function of phospholipids?

they are found in the cell membranes of all eukaryotes and prokaryotes. they make up the phospholipid bilayer.

how are phospholipids good in the bilayer?

their heads are hydrophilic and their tails are hydrophobic, so they form a double layer with the heads facing outwards and the tails facing in. this makes the centre of the bilayer hydrophobic, so water-soluble substances can’t easily pass through.

what is the function of cholesterol in the cell membrane?

they help strengthen the cell membrane and regulate fluidity by interacting with the phospholipid bilayer.

how is cholesterol good at its function?

it has a small size and flattened shape - which allows cholesterol to fit in between the phospholipid molecules in the membrane. they bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together, this helps the membrane be more rigid and less fluid.

how much does water make up of the cell contents?

80%

what are some of the functions of water?

• it is a reactant in important chemical reactions (e.g. hydrolysis)

• it is a solvent, meaning some substances dissolve in it and most chemical reactions take place in the solution.

• it transports substances (e.g. glucose and oxygen around plants and animals).

• it helps with temperature control as it has a high specific heat capacity and high latent heat of evaporation.

• it is a habitat, it becomes less dense when it is frozen meaning many organisms can survive and reproduce in it.

what is the structure of water?

one atom of oxygen (O) joined to two atoms of hydrogen (H2) by shared electrons.

are the hydrogen atoms on a water molecule positive or negative?

positive

is the oxygen atom on a water molecule positive or negative?

negative

how is water a polar molecule?

one side (oxygen) has a slight negative charge, however the other side (hydrogen atoms) have a slight positive charge due to the shared electrons being drawn to the negative oxygen atom.

what is the attraction between water molecules?

hydrogen bonding

what are some of the properties of water?

• high specific heat capacity

• high latent heat of evaporation

• very cohesive

• lower density than when solid

• good solvent

• high surface tension

what are the benefits of water having a high specific heat capacity?

it takes a lot of energy to heat it up, so water doesn't experience rapid temperature changes, which is one of the properties that make it a good habitat.

what are the benefits of water having a high latent heat of evaporation?

it takes a lot of energy to break the hydrogen bonds between water molecules, this is good for living organisms as it means that water is great for cooling things.

what are the benefits of water being very cohesive?

helps water to flow, making it great for transporting substance. also helps water travel up plants stems in the transpiration stream.

what are the benefits of water having a lower density when solid?

• makes a lattice shape which is why ice floats.

• useful for living organisms because in cold temperatures, ice forms an insulating layer on the top of water which can act as a habitat for some organisms.

• also, the water below doesn't freeze. so organisms that live in water (like fish) do not freeze and can still move around.

why is water an important solvent for organisms?

its a polar universal solvent so dissolves and transports charged particles involved in intra/extracellular reactions.

what are the three types of carbohydrates?

monosaccharides, disaccharides, polysaccharides

what are three examples of monosaccharides?

glucose, fructose, galactose

what are three examples of disaccharides?

sucrose, lactose, maltose

what are three examples of polysaccharides?

starch, glycogen, cellulose

describe the structure of a hexose monosaccharide?

6 carbons in a ring structure, with one molecule of a carbohydrate.

what is the chemical formula for a hexose monosaccharide?

C6 H12 06

what are some examples of hexose monosaccharides?

alpha-glucose, beta-glucose, galactose and fructose.

describe the structure of a pentose monosaccharide?

5 carbon atoms in a ring structure, with one molecule of a carbohydrate.

what is the chemical formula for a pentose monosaccharide?

C5 H10 O5

what are some examples of pentose monosaccharides?

ribose and deoxyribose

how is ribose different from deoxyribose?

ribose has a hydroxyl group attached to its 2' carbon and deoxyribose has a hydrogen attached to its 2' carbon.

what is a disaccharide?

two monosaccharides joined together

which monosaccharides make up sucrose?

glucose and fructose

which monosaccharides make up lactose?

glucose and galactose

which monosaccharides make up maltose?

glucose and glucose

what is a polysaccharide?

when three or more monosaccharides are joined together

what are the two forms of glucose?

alpha glucose and beta glucose

what type of bonds join monosaccharides together?

glycosidic bonds

what is a condensation reaction?

when two molecules bond through the loss of a water molecule.

what is a hydrolysis reaction?

a reaction in which a bond is broken by the addition of a water molecule

what are the two polysaccharides that make up starch?

amylose and amylopectin

what is the function of starch?

energy storage in plants

what is the structure of amylose?

• long, UN-BRANCHED chain of alpha-glucose

• angles of glycosidic bonds give it a coiled structure

• compact molecule, so good for storage

what is the structure of amylopectin?

• long, BRANCHED chain of alpha-glucose

• its side chains allow the enzymes to break down the molecule and get to the glycosidic bonds easily.

what is the function of glycogen?

energy storage in animals, they store excess glucose as glycogen.

what is the structure of glycogen?

• BRANCHED coils of alpha-glucose

• contains 1-4 and 1-6 glyosidic bonds

• more branches than amylopectin

• very compact molecule

what is the function of cellulose?

it is the structural component of plant cell walls.

what is the structure of cellulose?

• long, UNBRANCHED chains of beta-glucose

• contains 1-4 glyosidic bonds

• beta-glucose molecules form straight cellulose chains

• cellulose chains are linked together by hydrogen bonds

when cellulose chains are joined together by hydrogen bonds, they form strong fibres called?

microfibrils

What are the monomers of proteins?

Amino acids

what is formed when two amino acids are joined together?

a dipeptide

what is formed when two or more amino acids are joined together?

a polypeptide

What is the structure of an amino acid?

Contains a Carboxyl group (-COOH), an amino group (-NH2) and a hydrogen atom attached to a carbon atom. All amino acids contain a different variable (R) group, which differs them from each other.

What type of reaction links amino acids together?

Condensation reaction

what are the bonds between amino acids called?

peptide bonds

What is the type of reaction which breaks two amino acids apart?

Hydrolysis reaction

Describe the primary structure of a protein

a sequence of amino acids in a polypeptide chain. It is held together by the peptide bonds between the amino acids.

describe the secondary structure of proteins

• the polypeptide chain doesn’t remain flat and straight.

• hydrogen bonds form between the -NH and -CO groups of the amino acids in the chain.

• this makes it coil into an alpha helix or fold into a beta pleated sheet.

Describe the tertiary structure of a protein

The coiled or folded chain of amino acids is often coiled or folded further. More bonds form between parts of the polypeptide chain such as; Ionic bonds, disulfide bonds, hydrophobic and hydrophilic interactions and hydrogen bonds.

What do the ionic bonds in the tertiary structure do?

they are attractions between negatively-charged R groups and positively charged R groups on different parts of the molecule.

What do the disulfide bonds do?

Whenever two molecules of cysteine come close together, the sulfur atom in one cysteine bonds to the sulfur atom in another cysteine.

Where is the only protein where you find disulfide bonds?

Cysteine

What do the Hydrophobic and Hydrophilic interactions do?

When Hydrophobic R groups are close together in a protein, they tend to clump together. This means that the Hydrophilic R groups are more likely to be pushed to the outside, which affects how the protein folds up into its final structure.

What do the Hydrogen bonds do?

These weak bonds form between slightly positively charged hydrogen atoms in some R groups and slightly negatively charged atoms on other R groups on the polypeptide chain.

What are some examples of proteins that have a quaternary structure?

Haemoglobin and Insulin

What is a globular protein?

Round and compact. The hydrophilic R groups tend to be pushed to the outside of the molecule. This is caused by the Hydrophobic and Hydrophilic interactions caused by the proteins tertiary structure. This makes globular proteins soluble, so they are easily transported in fluids.

what is a fibrous protein?

• fibrous proteins are tough and rope-shaped

• they are also insoluble in water and strong

• they’re structural proteins and are fairly unreactive.

What are three examples of globular proteins?

Haemoglobin, insulin and amylase.

What are three examples of fibrous proteins?

Collagen, Keratin and elastin.

Describe the structure and function of Collagen?

Collagen is found in animal connective tissues, such as bones, skin and muscle. It is a very strong molecule. Minerals can bind to the protein to increase its rigidity. E.g. in a bone.

Describe the structure of Keratin?

It is found in many of the external structures of animals, such as skin, hair, nails, feathers and horns. It can either be flexible (like skin) or hard and tough (like nails).

describe the structure of elastin?

• it is found in elastic connective tissue, such as skin, large blood vessels and some ligaments.

• it is elastic, so it allows some tissues to return back to it’s original shape after they have been stretched.

What is a conjugated protein?

A protein with a non-protein group attached (also known as a prosthetic group).

what is an example of a conjugated protein?

haemoglobin, has a prosthetic group called haem.

what are the chemical elements found in carbohydrates?

carbon, hydrogen and oxygen

what are the chemical elements found in lipids?

carbon, hydrogen and oxygen

what are the chemical elements found in proteins?

carbon, hydrogen, oxygen, nitrogen and sulphur

what are the chemical elements found in nucleic acids?

carbon, hydrogen, oxygen, nitrogen, phosphorus