AQA A level biology paper 1

what are the four types of biological molecules?

carbhydrates, lipids, proteins and nucleic acids

what elements are found in carbohydrates?

carbon, hydrogen, and oxygen

what elements are found in lipids?

carbon, hydrogen, and oxygen

what elements are found in proteins?

carbon, hydrogen, oxygen, and nitrogen

what elements are found in nucleic acids?

carbon, hydrogen, oxygen, nitrogen, and phosphorus

what is a monomer?

is a smaller unit that combines to make a polymer

what is a polymer?

is a large molecule made up of many repeating units of monomers joined together by chemical bonds

what is the process by which monomers join to form a polymer?

polymerisation

what type of reaction synthesises most polymers?

by condensation reaction

what type of reaction breaks down most polymers?

by hydrolysis reaction

what is a condensation reaction?

a reaction where monomers join together and release a water molecule

what is a hydrolysis reaction?

a reaction where a water molecule is added to break a chemical bond between 2 molecules

what is the ratio of hydrogen to oxygen atoms in a carbohydrate?

the ratio of hydrogen to oxygen is 2:1

what is the general formula for a carbohydrate?

Cn(H20)n

what is the main role of carbohydrates in living organisms?

provide an energy supply for cells

what is the role of glycoproteins in cellular recognition?

help cells identigy each other and communicate

which carboydrates can be used to make nucleic acids?

deoxyribose and ribose

what are the three types of carbohydrates?

monosaccharides, disaccharides and polysaccharides

what is the difference between a monosaccharide and a disaccharide?

a monosaccharide is made up of one subunit, whereas a disaccharide is made up of 2 subunits

name 3 examples of monosaccharides?

glucose, fructose and galactose

what is the main function of disaccharides?

used for transport

what is the main function of polysaccharides?

used for storage

what are monosaccharides?

the simplest form of carbohydrates, also known as simple sugars

what is the general formula for monosaccharides?

(CH2O)n

what is the difference between pentose and hexose sugars?

pentose have 5 carbon atoms whereas hexose have 6 carbon atoms

what is the formula for glucose?

C6H12O6

what are the names of the two glucose isomers?

alpha-glucose and beta-glucose

what is the difference between alpha-glucose and beta-glucose?

the orientation of the hydroxyl group on carbon 1

what is the primary energy source in animals and plants?

glucose

why is glucose a good energy source?

it is soluble and its bonds store lots of energy

what are disaccharides?

carbohydrates formed when two monosaccharides join together

name three examples of disaccharides

maltose, sucrose and lactose

name the monosaccharides found in maltose, sucrose and lactose

maltose = glucose and glucose

sucrose = glucose and fructose

lactose = glucose and galactose

how are disaccharides formed?

formed via condensation reactions so the hydroxyl group reacts with another this forms a glycosidic bond and releases a water molecule

how are disaccharides broken down?

are broken down via hydrolysis reactions so a water molecule is added to break the glycosidic bond to release the monosaccharides

what are polysaccharides?

complex carbohyrates made up of many monosaccharides joined by glycosidic bonds

name three examples of polysaccharides?

starch, glycogen and cellulose

what is the function of starch in plants?

to store excess glucose and release it to supply energy when needed

what are the characteristics of starch that make it a good energy store?

insoluble, large, many side branches, coiled, hydrolysis releases alpha-glucose monomers

what is the function of glycogen in animals?

to excess glucose and release it to supply energy when needed

what is the structure of glycogen?

glycogen consists of highly branched chains of alpha-glucose monomers joined by glycosidic bonds

what are the characteristics of glycogen that make it good as an energy store?

insoluble, compact, more highly branched than starch, large, hydrolysis releases alpha-glucose monomers

what is cellulose?

a polysaccharide that forms the structural component of plant cell walls

what is the function of cellulose?

to provide strength and rigidity to plant cells

describe the structure of cellulose?

is made of beta glucose joined by 1-4 glycosidic bonds everyother beta-glucose monomer is inverted by 180 degrees

what are the good characteristics of cellulose that make it good at forming new cell walls?

made of long straight and unbranched chains, hydrogen bonds between chains and made of micorfibrils

what are the two categories of sugars that can be tested for?

reducing sugars and non reducing sugars

which sugars are classified as reducing sugars?

monosaccharides and some disaccharides like maltose and lactose

which sugars are classified as non-reducing sugars?

some disaccharides such as sucrose and all polysaccharides

how can you test for reducing sugars?

add bendicts reagent to the sample, heat the mixture in a water bath if reducing sugars are present the mixture will change from a blue solution to a brick red precipitate

what does a blue colour indicate in the reducing sugar test?

no reducing sugar is present

what does an orange colour indicate in the reducing sugar test?

a medium concentration of reducing sugar

what are the quantitative methods to determine reducing sugar concentration?

using a colorimeter or filtering and weighting the precipitate

what is the first step to test for non-reducing sugars?

carry out the test for reducing sugars

how can you test for non reducing sugars?

carry out the test for reducing sugars, add the sample to some dilute hydrochloric acid, heat the mixture in a water bath then neutralise the mixture by adding sodium hydrogencarbonate solution and retest the sample using the test for reducing sugars

how can you test for starch?

add iodine solution to the sample and if starch is present the solution will turn from orange to blue-black

are lipids considered polymers?

no they are not made up of long chains so arent polymers

what are the roles of lipids?

energy supply, structural components, waterproofing, insulation and protection

what are phospholipids used for?

used in cell membranes as structural components

what are most lipids made up of?

made of fatty acids combined with an alcohol, usually glycerol

describe the structure of a fatty acid

a fatty acid consists of a carboxyl group (COOH) attached to a hydrocarbon chain (R group)

what is a saturated fatty acid?

has a hydrocarbon chain saturated with hydrogen with no carbon-carbon double bonds

what is an unsaturated fatty acid?

has a hydrocarbon chain with at least one carbon-carbon double bond, causing the chain to kink

what is the difference between monounsaturated and polyunsaturated fatty acids?

monounsaturated fatty acids have 1 carbon-carbon double bond, while polyunsaturated fatty acids have two or more carbon-carbon double bonds

how can you test for lipids?

place sample in a test tube, add ethanol, shake and add distilled water and a milky white emulsion forms if lipids are present

what is the primary function of triglycerides?

used to store energy in animals, plants and some bacteria

what is the structure of a triglyceride?

consists of a glycerol molecule attached to three fatty acid tails

what characteristics of triglycerides that make them good stores of energy?

long hydrocarbon tails, low mass to energy ratio, insoluble and high ratio of hydrogen to oxygen atoms

how are triglycerides synthesised?

via condensation reactions the OH groups on the glycerol and on 3 fatty acids react to release 3 water molecules and form 3 ester bonds

how are triglycerides broken down?

via hydrolysis reactions the addition of three molecules of water breaks the ester bonds to separate the glycerol and fatty acids

what are the components of a phospholipid?

consist of glycerol, phosphate and 2 fatty acid tails

why are phospholipids described as being polar?

the head is hydrophilic and the fatty acid tails are hydrophobic

how do phospholipids arrange themselves in water?

into a double layer (bilayer) with hydrophillic heads facing out and hydrophobic tails facing in

what are the similarities between triglycerides and phospholipids?

both contain glycerol, fatty acid tails and ester bonds, insoluble in water and contain carbon, hydrogen and oxygen

what are the differences between triglycerides and phospholipids?

phospholipids contain phosphate, phospholipids contain 2 fatty acids but triglycerides contain 3 fatty acids, phospholipids are polar but triglycerides arent, phospholipids form bilayers in water, triglycerides dont

what are proteins made up of?

amino acids

what names are given to the monomers, dimers and polymers of proteins?

monomers = amino acids, dimers = dipeptides, polymers = polypeptides

what are the roles of proteins?

enzymes, antibodies, transport, structural components, hormones, muscle contraction

what is the general structure of an amino acid?

a central carbon atom, an amino group, a carboxyl group, a hydrogen atom and an R group

what determines the properties of an amino acid?

the R group

what type of bond joins amino acids together?

peptide bonds

what is a dipeptide?

two amino acids joined by a peptide bond

how are dipeptides synthesised?

via condensation reactions, the OH in the carboxyl group reacts with the hydrogen in the amino group and releases water and forms a peptide bond

how are dipeptides broken down?

via hydrolysis reactions, a water molecule is added which breaks the peptide bond to release the two amino acids

which test can identify proteins?

the biuret test

what does the biuret test detect?

the presence of peptide bonds

how is the biuret test carried out?

place the food sample in a test tube, add an equal volume of biuret solution, if proteins are present the solution will turn from blue to purple

what colour does a blue colour indicate in the biuret test?

no proteins are present

what are the four main levels of protein structure?

primary, secondary, tertiary and quaternary

what holds the primary structure of a protein together?

peptide bonds

what type of bonds are involved in the secondary structure of a protein?

hydrogen bonds

what are the two possible shapes formed by a protein’s secondary structure?

alpha helix and beta pleated sheet

what hold the tertiary structure of a protein together?

hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic and interactions

what are the weak interactions between polar and non polar R groups called?

hydrophobic interactions

what is the quaternary structure of a protein?

two or more polypeptide chains held together by bonds

what are the bonds involved in the quaternary structure?

hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic and interactions

what are non protein groups added to the quaternary structure called?

prosthetic groups

do all proteins have a quaternary structure?

no only some

what is the primary structure of a protein?

the unique sequence of amino acids in the polypeptide chain

what is the secondary structure of a protein?

is the folding of the polypeptide chain into an alpha helix or beta pleated sheet