Aqa A-Level Biology - Topic One: Biological Molecules

Front 1

What are monomers?

Back 1

They are the smaller units from which larger molecules are made.

Front 2

What are monomers joined together by?

Back 2

A condensation reaction.

Front 3

What is a condensation reaction?

Back 3

A reaction which joins monomers by chemical bonds. It involves the elimination of a water molecule - H2O is an excess product.

Front 4

What happens when two monomers are joined?

Back 4

They form a dimer.

Front 5

What does "di" mean?

Back 5

"Di" means two, so whenever you see "di" it means two of something.

Front 6

What are polymers?

Back 6

- Long chains of repeating units of monomers.

- Molecules made from a large number of monomers joined together.

Front 7

How are polymers broken down?

Back 7

They are broken down into constituent monomers by a hydrolysis reaction.

Front 8

What does "constituent" mean?

Back 8

Being part of a whole e.g. the monomer.

Front 9

What is a hydrolysis reaction?

Back 9

Breaks a chemical bond between two molecules and involves the use of a water molecule. H2O is an added product/ reactant.

Front 10

What are some examples of monomers?

Back 10

- Amino Acids

- Nucleotides

- Monosaccharides

Front 11

How many different amino acids are there?

Back 11

There are twenty different amino acids.

Front 12

What can nucleotides either be?

Back 12

Either DNA or RNA nucleotides.

Front 13

What does "mono" mean?

Back 13

One.

Front 14

What does "poly" mean?

Back 14

Multiple.

Front 15

What does "saccharide" mean?

Back 15

Sugars.

Front 16

What polymers are the majority of the biomass that make up an organism?

Back 16

- Lipids

- Proteins

- Nucleic acid

- Carbohydrates

Front 17

What are polypeptides?

Back 17

They are the polymers of amino acids.

Front 18

How can polypeptides be modified?

Back 18

By bonding "prosthetic groups" and other polypeptides in order to form proteins.

Front 19

What are required for the biological function of some proteins?

Back 19

Cofactors that bind tightly to proteins or enzymes (a specific non-polypeptide).

Front 20

What are polynucleotides?

Back 20

The polymers of nucleotides.

Front 21

What are polynucleotides classified as being?

Back 21

There are potentially trillions of different polynucleotides but they are classified as being either:

- DNA

- mRNA

- tRNA

- rRNA

Front 22

What are the monomers in carbohydrates?

Back 22

Monosaccharides.

Front 23

What are the most common monosaccharides out of many?

Back 23

- Glucose

- Fructose

- Galactose

- Ribose

- Deoxyribose

Front 24

What are the polymers of monosaccharides?

Back 24

Polysaccharides.

Front 25

What can polysaccharides form?

Back 25

A straight or branched chain.

Front 26

What are the most common polysaccharides?

Back 26

- Cellulose

- Starch

- Glycogen

Front 27

What's the importance of carbon?

Back 27

- They are important compounds in both the

biological and the commercial world.

- They are used as a source of energy in all

organisms and a structural materials in

membranes, cell walls, and the exoskeletons of many arthropods.

Front 28

What are arthropods?

Back 28

Spiders, insects, or any other creatures with hard exteriors.

Front 29

What do all carbohydrates contain?

Back 29

The elements: Carbon (C), Hydrogen (H), and Oxygen (O) with the Hydrogen and Oxygen being present in 2:1.

Front 30

What do all monosaccharides contain?

Back 30

At least 2 hydroxyl groups (OH) and a carboxyl group (C=O).

Front 31

How are carbon atoms unusual?

Back 31

They readily form bonds with other carbon atoms allowing a sequence of carbon atoms of various lengths to be built up.

Front 32

What does carbon's unusual property allow?

Back 32

A huge number of different types and size of molecule, all based on carbon.

Front 33

What are carbon-containing molecules known as?

Back 33

Organic molecules.

Front 34

Why are carbon-containing molecules known as "organic molecules"?

Back 34

Because the variety of life that exists on earth is a consequence of living organisms being based on the versatile carbon atom.

Front 35

What is the general formula for a carbohydrate?

Back 35

Cx(H2O)n

Front 36

What numbers can "n" be in a carbohydrate?

Back 36

Any number from 3 to 7.

Front 37

What is the chemical formula for glucose?

Back 37

C6H12O6

Front 38

What is the chemical formula for ribose?

Back 38

C5H10O5

Front 39

What is the chemical formula for glyceraldehyde?

Back 39

C3H6O3

Front 40

What is it called when n=3?

Back 40

A triose sugar.

Front 41

What is it called when n=5?

Back 41

A pentose sugar.

Front 42

What is it called when n=6?

Back 42

A hexose sugar.

Front 43

What is the basic monomer unit in carbohydrates?

Back 43

A sugar.

Front 44

What is glucose?

Back 44

- A hexose sugar

- The C6H12O6 atoms form a ring.

- There are two forms of glucose (isomers): α

(alpha) glucose and β (beta) glucose.

Front 45

What is an isomer?

Back 45

Molecules with the same molecular formula, but have different arrangements of their atoms.

Front 46

Draw the structure of an "α" (alpha) glucose?

Back 46

Front 47

Draw the structure of a "β" (beta) glucose?

Back 47

Front 48

Draw the structure of a complex "α" alpha glucose?

Back 48

Front 49

Draw the structure of a complex "β" beta glucose?

Back 49

Front 50

What is a reducing sugar?

Back 50

A sugar that can donate (or reduce) electrons to another chemical, in this case it's Benedict's reagent.

Front 51

Give three examples of a reducing sugar?

Back 51

- Glucose

- Fructose

- Galactose

Front 52

Describe the test for reducing sugars?

Back 52

1.) Put a test tube containing 2cm^3 of glucose into a water bath for 2 mins with 10 drops of Benedict's solution.

2.) Observe the colour changes to compare.

3.) Add 2cm^3 of each food sample to a

labelled test tube. If it's not already a liquid, mix 1cm of food with 2cm^3 of water.

4.) Heat the mixture in a water bath for 5 mins.

5.) Observe the colour change to see which

solutions contain a reducing sugar.

Front 53

How does the test for reducing sugars work?

Back 53

- Benedict's reagent is a blue alkaline solution of copper (II) sulfate.

- When a reducing sugar is heated with Benedict's reagent, it forms an insoluble red

precipitate of copper (I) oxide.

- This happens because all monosaccharides and some disaccharides (e.g. maltose) are

reducing sugars - this means they donate

electrons to reduce another chemical, in this case Benedict's reagent.

Front 54

What does "no colour change (blue)" indicate in a reducing sugars test?

Back 54

No non-reducing sugars present.

Front 55

What does a "green colour change" indicate in the reducing sugars test?

Back 55

Trace amounts of non-reducing sugars present.

Front 56

What does a "yellow colour change" indicate in the reducing sugars test?

Back 56

Low amounts of reducing sugars present.

Front 57

What does a "orange colour change" indicate in the reducing sugars test?

Back 57

Moderate amounts of reducing sugars present.

Front 58

What does a "brick-red colour change" indicate in the reducing sugars test?

Back 58

Large amounts of non-reducing sugars present.

Front 59

What type of reaction are carbohydrates joined by?

Back 59

A condensation reaction.

Front 60

What type of bond are carbohydrates joined by?

Back 60

A glycosidic bond.

Front 61

What is a glycosidic bond?

Back 61

A type of covalent bond that joins a carbohydrate (sugar) molecule to another group.

Front 62

What is the disaccharide maltose made of?

Back 62

Glucose + Glucose

Front 63

What is the disaccharide sucrose (table sugar) made of?

Back 63

Glucose + Fructose

Front 64

What is the disaccharide lactose (milk sugar) made of?

Back 64

Glucose + Galactose

Front 65

What type of glycosidic bond is between maltose?

Back 65

A 1-4 glycosidic bond (bond forms between

carbon-1 on one molecule and carbon-4 on the other).

Front 66

What type of glycosidic bond is between sucrose?

Back 66

A 1-2 glycosidic bond.

Front 67

What is the test for non-reducing sugars called?

Back 67

The Benedict's with acid test.

Front 68

Describe the test for non-reducing sugars?

Back 68

1.) Add 2cm^3 of each food sample to a labelled test tube. If it's not

already a liquid, mix 1cm of food with 2cm^3 of water.

2.) Place the test tube in the water bath for 5 mins with 10 drops of Benedict's reagent. If it stays blue it means that it is not a reducing sugar.

3.) Add a fresh 2cm^3 of food sample to 10 drops of hydrochloric acid in a test tube (to split up the disaccharide). Place the test tube into a gently boiling water bath for 5 mins.

4.) Add sodium hydrogen carbonate to the test tube until it stops fizzing to neutralise the acid (Benedict's doesn't stop working in acidic

conditions). Test with pH paper to check that the solution is neutral.

5.) Retest the solution bu adding 10 drops of Benedict's reagent and heating in a water bath for 5 mins.

6.) If a non-reducing sugar is present it will turn orange/brown.

Front 69

Describe the test for starch?

Back 69

1.) Add iodine solution to food.

2.) Foods containing starch will turn a black/blue colour

Front 70

Describe the structure of starch?

Back 70

- Polymer of a-glucose monomers joined

together by glycosidic bonds.

- The role of starch is energy storage.

- Found in only plants in form of small grains.

- Large & insoluble.

- Compact because helical/ coiled.

- Branched with more ends (a 1-6).

Front 71

Describe amylose?

Back 71

- A helix shape (20% of it is starch).

- A-glucose joined together by 1-4 glycosidic bonds.

- Very compact.

Front 72

Describe amylopectin?

Back 72

- Branched starch (80% of it is starch).

- A-glucose molecules joined by A 1-4 glycosidic bonds with A 1-6 branches every 20-30 monomers.

Front 73

Describe the structure of glycogen (animal)?

Back 73

- A-glucose monomers.

- Found as granules in animal cells only (mainly muscle or liver cells) and bacteria as an energy source.

- It has 1-4 and 1-6 glycosidic bonds.

- Amount stored small as fat is main energy store.

- Very similar structure to starch but has shorter chains and is more branched therefore it can be hydrolysed more quickly to a-glucose monomers.

- Large molecule made up of many monomers.

- Compact because branched (1-6 glycosidic bonds).

- Large and therefore insoluble.

- Many branches with lots of ends.

Front 74

Describe the structure of cellulose (plants)?

Back 74

- Contains hydrogen bonds.

- Mainly structural component of plant cell walls offering support and rigidity.

- Made up of B-glucose and 1-4 glycosidic bonds.

- Straight chain, unbranched, long, B-glucose chains.

- Parallel chains join together to form microfibrils which form fibrils.

- Very strong, keeps plant cells turgid & supports them.

- Permeable to numerous substances e.g. carbon dioxide.

- Parallel.

- Many weak H-bonds between adjacent chains.

- Microfibrils formed, group together to form fibrils.

Front 75

What are the characteristics of lipids?

Back 75

- Lipids are organic molecules.

- Triglycerides - good source of energy.

- Phospholipids - have a structural role in cell membranes.

- Lipids made up of mainly C,H, with some O.

- Lipids are non-polar molecules so are insoluble in water but soluble in organic solvents.

Front 76

What are the roles of lipids?

Back 76

1.) Energy source - They provide more than twice the amount of energy as carbohydrates - about 38 kJ/g.

2.) Heat insulation - in mammals, adipose tissue underneath the skin helps reduce heat loss.

3.) Protection - adipose tissue around delicate organs such as the kidneys acts as a cushion against impacts.

4.) Insulation - under the skin & around the nerve cells (myelin sheath)

5.) Waterproofing - Insects, plants, & animals (oil secretion)

Front 77

What are triglycerides?

Back 77

They are fats and oils.

Front 78

What type of molecule is a triglyceride?

Back 78

A macromolecule (not a polymer, no repeating subunits).

Front 79

How are triglycerides formed?

Back 79

Water is eliminated from the 3 COOH bonds (tri) and ester bonds are bonded together (formed between the carboxyl group of the fatty acid & hydroxyl group (OH) of the glycerol).

Front 80

Draw the bonding in a triglyceride?

Back 80

Front 81

What is a monounsaturated molecule?

Back 81

Where it only has one double bond.

Front 82

What is a polyunsaturated molecule?

Back 82

Multiple double bonds.

Front 83

Describe unsaturated fatty acids?

Back 83

Unsaturated fatty acids have a double bond (C=C). They have a low melting point and so tend to have a low melting point and so tend to be

liquid at normal temperatures (double bond gives curved shape)

Front 84

Describe saturated fatty acids?

Back 84

They have no double bonds and therefore is a straight molecule.

Front 85

Describe the structure of triglycerides?

Back 85

- High ratio of energy-storing bonds.

- Low mass to energy ratio therefore energy is stored in small volumes and so it has a light mass.

- Non-polar therefore insoluble.

- High ratio of H2O means important source of water - desert animals.

Front 86

What does a phospholipid have?

Back 86

- Hydrophobic fatty acid tails

- Hydrophilic phosphate heads

Front 87

Give some examples of other lipids?

Back 87

- Steroids

- Hormones

- Cholesterol

- Waxes

Front 88

How many hydrocarbon chains does a

phospholipid have?

Back 88

Two.

Front 89

Draw the structure of a phospholipid?

Back 89

Front 90

Describe the structure of a phospholipid?

Back 90

- Has a hydrophilic head, as the phosphate group has a negative charge and therefore attracts water.

- Has a hydrophobic tail, as the fatty acids have no charge and therefore repel water.

Front 91

Describe the emulsion test?

Back 91

- Add ethanol and water by shaking (mix).

- A cloudy white emulsion will form if lipids are present.

Front 92

What is each protein made up of?

Back 92

Amino acid subunits.

Front 93

How many different amino acids are there?

Back 93

20, but each have the same amine group (NH2) and carboxyl group (COOH) but a different

variable (R) group that can make them positively or negatively charged, hydrophobic, or sulphur-containing.

Front 94

How do two amino acids react together?

Back 94

Through condensation reactions, where the amine group from one and the carboxyl group from another form a peptide bond.

Front 95

What are two amino acids bonded together called?

Back 95

A dipeptide.

Front 96

What are multiple amino acids joined together called?

Back 96

A polypeptide.

Front 97

What kind of bond is formed between amino acids?

Back 97

Peptide bonds.

Front 98

Describe test for protein?

Back 98

1.) Add equal volumes of sample solution and Biuret reagent (sodium hydroxide).

2.) Observe the colour change.

3.) Lilac/ Purple indicates presence of protein.

Front 99

What is the primary structure of proteins?

Back 99

- It is the sequence of amino acids in the

polypeptide chain.

- Determined by DNA, different combinations of bases code for different amino acids.

- Determines ultimate shape & function.

- Changing a single amino acid may lead to change in the shape of the protein, therefore may stop it carrying out its function.

Front 100

What is the secondary structure of proteins?

Back 100

- Alpha (structured as alpha helix):

* Contains weak hydrogen bonds

* Forms multiple hydrogen bonds between them making the coil shape.

* The H of the -NH has a positive charge.

* The O of the -C-O as a negative charge

* Therefore causes polypeptide charge to be twisted into a 3D shape, known as a-helix.

- Beta (B) pleated sheets:

* Hydrogen bonds hold adjacent primary chains.

Front 101

What is the tertiary structure of proteins?

Back 101

- The overall three-dimensional shape of a polypeptide chain. Structure is maintained by different bonds.

- Every protein has a unique structure responsible for its properties and function.

- 3D shape of the protein is important - determines function, allows it to recognise, and be recognised by other molecules.

- All three types of bond: Disulfide, Hydrogen, Ionic - which contribute

towards the maintenance of this structure.

Front 102

What is the quaternary structure of proteins?

Back 102

- Almost all working proteins are composed of more than one

polypeptide chain, the arrangement of the different chains is called the quaternary structure. There are huge variety of structures but some are:

1.) Haemoglobin consists of four chains arranged in a tetrahedral

(pyramid) structure.

2.) Antibodies compromise four chains arranged in a Y shape.

3.) Collagen consists of 3 chains in a triple helix structure.

4.) Actin consists of hundreds of globular chains arranged in a long

double helix.

5.) The enzyme ATP synthase is composed of the 22 chains forming a rotating motor.

Front 103

What type of proteins are enzymes?

Back 103

Globular proteins.

Front 104

What are enzymes?

Back 104

Biological catalysts.

Front 105

What do enzymes do?

Back 105

They increase the rate of reactions by a factor of between 10^6 to 10^12 times.

Front 106

Describe the reaction mechanism?

Back 106

E + S -> ES (enzyme-substrate) complex -> EP (enzyme-product) complex -> E + P

Front 107

Describe enzyme structure?

Back 107

- The region on the surface of the enzyme that the substrate binds to is called the "active site" and an "enzyme-substrate complex" is formed.

- An enzyme is specific to its substrate.

- It is the "enzyme-substrate complex" that lowers the activation

energy for two reasons:

* If two substrates molecules need to be joined - being attached to the

enzymes hold them close together, reducing any repulsion so that they can bond more easily.

* It is a breakdown reaction, fitting into an active site puts a strain on bonds in the substrate, so the substrate molecules break up easily.

Front 108

Describe and explain the induced fit model?

Back 108

1.) The active site forms as the enzyme and substrate interact.

2.) A change in the environment of enzyme causes them to interact.

3.) When the substrate binds to the enzymes active site it "induces" a change of shape so that the substrate and enzyme become fully complementary

4.) The enzyme is flexible & can mound itself around the substrate.

5.) As it changes shape, the enzyme puts a strain on the substrate, distorts bonds, and eventually breaks them.

Front 109

Describe a successful enzyme-substrate reaction?

Back 109

- Enzyme bonding with substrates is a highly specific process.

- Governed only by random collision of molecules as result of kinetic

energy from heat.

- In order for reaction to take place enzyme & substrate must have

successful reaction.

- If successful reaction happens enzyme-substrate complex formed and

reaction can occur so enzyme is free to catalyse next reaction.

Front 110

What are two ways we can see how quickly the enzyme-involved reaction is catalysed?

Back 110

1.) The formation of a product over time.

2.) Disappearance of a substrate over time.

Front 111

Where are enzymes made and where may they act?

Back 111

Inside living cells but may act inside the cell

(intracellular) or outside the cell (extracellular) e.g. the digestive enzymes of the alimentary canal.

Front 112

What are environmental conditions that can change the 3D structure of the enzyme molecule?

Back 112

- Temperature

- pH

- Substrate concentration

- Enzyme concentration

Bonds are broken and hence the configuration of the active site is altered, the enzyme is said to be denatured.

Front 113

What are inhibitors?

Back 113

Substances that reduce or completely stop the action of an enzyme.

Front 114

Describe a competitive inhibitor?

Back 114

- Where inhibition acts on the enzyme's active site.

- The substrate & inhibitor are chemically very similar in shape.

- The inhibitor can bind to the active site.

- When the inhibitor binds to the active site it blocks the substrate from entering the active site.

- This blockage reduces the rate of reaction.

BUT

- If the substance concentration is increased it occupies more active sites than the inhibitor. Therefore the substrate out-competes the

inhibitor for the active site. The rate of reaction will increase again.

Front 115

Describe a non-competitive inhibitor?

Back 115

- Where inhibition acts on another region of the enzyme molecule (non-competitive).

- The substrate and the inhibitor are chemically different in molecular structure.

- The inhibitor can bind to another region (allosteric site) of the enzyme molecule.

- The bonding of the inhibitor with the enzyme causes structural changes to the active site which causes the active site to change shape.

- The substrate cannot bind to the active site therefore the rate of

reaction decreases.

- Because the substrate and inhibitor are not competing for the same active site increasing the concentration of the substrate will have no

effect on the inhibitor.

Front 116

Describe control of metabolic pathways?

Back 116

- Reactions of the metabolic pathway are

catalysed at each step by enzymes.

- Enzymes are often attached to the membranes of organelles inside the cell in a highly structured way with a precise sequence.

- The cell maintains optimum conditions for the correct functioning of the enzymes.