1. 1. Chemical elements are joined together to form biological compounds

Question 1

carbs contain 3 elements

Answer 1

carbon

hydrogen

oxygen

Question 2

monosaccharide

Answer 2

The simplest sugars, consist of a single monomer

General formula (CH2O)n

All carbohydrates contain the elements carbon, hydrogen and oxygen.

Question 3

two isomers of glucose (a monosaccharide)
1. alpha

Answer 3

Question 4

two isomers of glucose (a monosaccharide)
2. beta

Answer 4

Question 5

difference of hydroxyl group alpha vs beta glucose

Answer 5

Question 6

difference of hydroxyl group alpha vs beta glucose

Answer 6

The only difference in the alpha (α) and beta (β) ring isomers is the position of the OH group on carbon atom 1.

To remember which ring form is which, use ABBA:

Alpha OH Below – Beta OH Above

Question 7

glucose

Answer 7

Glucose is a polar molecule – hydrogen bonds can form between the Oδ- on C2 of one glucose molecule and C3δ+ of the next glucose molecule in the chain. As a result, the amylose molecule coils up to form a helix.

This makes starch a compact molecule that is less soluble in water - an ideal properties for storage of glucose.

Also, because starch is insoluble it does not affect the water potential of the cell in which it is stored. This means that starch is osmotically stable.

Question 8

alpha glucose function

Answer 8

function
- energy storage (found in starch)
- energy source (easily broken down in cellular respiration, providing ATP)

Question 9

beta glucose function

Answer 9

function
-structural component in plants, found in cellulose, beta links create long, straight chains which are rigid
-fiber in diet, in cellulose, aids digestion

Question 10

EDITTTT glucose in nature

Answer 10

36% α glucose
-more reactive as more hydroxyl groups on bottom
-delta charge on O and H
-charge is unevely distributed on molecule

64% β glucose

Question 11

classification of monosaccharides

Answer 11

3 carbons Triose

5 carbons, pentose eg ribose, deoxyribose

6 carbons, hexose eg glucose

Question 12

eg of monosaccharide

Answer 12

glucose

fructose

galactose

Question 13

structural isomers

Answer 13

Molecules with the same molecular formula but with different arrangements of their atoms are called structural isomers.

Question 14

fructose vs glucose vs galactose

Answer 14

1. Glucose: The -OH group on carbon 4 is on the right side in the Fischer projection.
   
   2. Galactose: The -OH group on carbon 4 is on the left side in the Fischer projection.

Question 15

all types of carbs diagram

Answer 15

Question 16

glycosidic bonds

And their roles

Answer 16

type of covalent bond, forms between two monosaccharides,

formed by condensation

two types
-Alpha Glycosidic Bond
- Beta Glycosidic Bond

roles
-allow molecules to store energy efficiently
-create rigid structures, essential for plant cell walls
-breakdown via hydrolysis releases monosaccharides, used for energy production in cellular respiration

Question 17

naming glycosidic bonds

Answer 17

Question 18

glucose

fructose

galactose

Answer 18

isomers

C6H12O6

same molecular formula

different structural formula

Question 19

disaccharide

Answer 19

class of carbohydrates made up of two monosaccharide subunits

general molecular formula is C 12 H 22 O 11 .

formed by a condensation reaction (i.e., loss of water)

The bond that holds them together is called a glycosidic bond.

Question 20

hydrolysis reaction.

Answer 20

The glycosidic bond can be broken by the chemical insertion of water – this reforms the OH groups and is called a hydrolysis reaction.

Question 21

eg of disaccharide

Answer 21

sucrose = α glucose + fructose

maltose = α glucose + α glucose

lactose = α or β glucose + galactose

Question 22

condensastion reaction of two monosaccharides

Answer 22

Question 23

condensation reaction of two molecules of alpha glucose

Answer 23

Question 24

polysaccharide

Answer 24

Polysaccharides are complex carbohydrates. They are large molecules, or polymers, consisting of chains of monosaccharides linked together by glycosidic bonds.

formed by condensation reactions, to form chains

Question 25

2 functions of polysaccharides

Answer 25

Some polysaccharides have metabolic functions and others have structural functions in cells and organisms.

metabolic eg starch (plants) and glycogen (animals) made of a-glucose

Question 26

function of polysaccharides

Answer 26

energy storage (starch in plants, glycogen in animals)

structural (cellulose) (chitin)n

Question 27

oligosaccharides

Answer 27

short chain polysaccharides

3-10 monosacharide residues

Question 28

eg of polysaccharide

Answer 28

Starch

glycogen

cellulose

heparin

peptidoglycan

Question 29

starch

Answer 29

consists of polymers:

amylose
-polymer of α glucose, linked by 1,4 glycosidic bonds
-unbranched helical molecule
-most -OH groups are capable of forming H bonds with H2O in aqueous environments
-forms coiled molecules

amylopectin
- the bonds between glucose molecules within a branch are α-1,4 glycosidic bonds but at branching points, the bonds are α-1,6 glycosidic bonds.
-gives more ends to hydrolyse, enables faster metabolic rate

Question 30

glycogen

Answer 30

has side branches

glycosidic bonds forming between OH groups on C1 and C4 but also C1 and C6. Glycogen can form granules in cells and act as a carbohydrate/energy store.

supports higher metabolic rate of animals (as more ends avaliable to hydrolyse)

Question 31

branches in amylopectin and glycogen

Answer 31

make them better for the release of glucose. This is because there are more ‘ends’ where glycosidic bonds can be hydrolysed and glucose released, which can be used in respiration to produce ATP.

Question 32

cellulose

Answer 32

ellulose is a complex carbohydrate made of a polymer of β-glucose molecules. The β-1,4 glycosidic linkages result in the −CH2OH groups being on opposite sides of the chain of adjacent glucose molecules.

Within a cellulose chain, adjacent glucose molecules are rotated 180° relative to each other. This means that OH groups are aligned and a water molecule can be removed to form a glycosidic bond.

Therefore, hydrogen bonds do not form between glucose molecules within the same chain, but between glucose molecules in different chains.

The hydrogen bonds form cross-linkages which hold the chains together. This makes cellulose form into long threads called microfibrils.

Cellulose is completely insoluble and the microfibrils are laid down in overlapping layers in plant cell walls.

most abundant structural polysaccharide in plant cell walls

distribution of hydroxyl groups, means cross links between cellulose molecules can occur, procides support and strength

hydrogen bonds form between adjacent -OH groups on cellulose molecules

Question 33

cellulose is what type of polysaccharide

Answer 33

Cellulose is called a structural polysaccharide. It is very difficult to digest because of the very high numbers of hydrogen bonds between the chains of beta glucose. This also gives cellulose very high tensile strength; it is difficult to break when stretched. This means that cells with cellulose in their cell wall are more resistant to osmotic lysis (they are not likely to burst because cellulose stops too much water entering the cell).

Question 34

chitin

Answer 34

amino acid side chains

used for exoskeletons

Chitin is found in the cell walls of fungi and in the exoskeletons of insects. It is not a true polysaccharide as it contains the element nitrogen – it is called a heteropolysaccharide.

It has a similar structure and function as cellulose but because it contains side groups containing N, more hydrogen bonds can form. Chitin microfibrils, therefore, have greater tensile strength than those of cellulose.

The diagram shows two of the monosaccharides (N-acetyl glucosamine) found in chitin joined together by a β-glycosidic bond.

Question 35

why is cellulose less reactive than other polysaccharides

Answer 35

due to hydrigen bonds and cross linking between chains

hydroxyl groups on adjacent cellulose molecules form hydrogen bonds

strong cross links between cellulose fibers makes structure rigid

Question 36

lignin

Answer 36

polymer of sugar and amino acids

deposited between cellulose molecules to lignify tissue

Question 37

macromolecules

Answer 37

giant molecules

some are polymers

Question 38

labelled lipid

triglyceride

Answer 38

three condensation reactions, forming ester bonds

Triglycerides have key roles in respiration and energy storage due to its insolubility and high carbon to hydrogen ratio.

Question 39

lipids

Answer 39

Lipids are organic compounds made of carbon, hydrogen and oxygen. All lipids contain a high proportion of CH2 groups. Phospholipids also contain phosphorus.

All lipids have a low solubility in water but a high solubility in organic solvents (e.g., ethanol, tetrachloromethane).

long term store of energy (high energy density 9kcal per gram, hydrophobic, stored compactly)

not polymers

made of glycerol and fatty acids

too small to be macromolecules

Question 40

Triglycerides

Answer 40

molecules that form fats or oils depending on the size of the molecule. The more carbon atoms, the higher the melting point because the intermolecular forces are stronger and more energy is required to overcome them.

Each triglyceride is made from glycerol combined with three fatty acids through a condensation reaction with the release of three molecules of water.

The fatty acids bind to the glycerol by means of ester bonds.

Triglycerides are broken down in a hydrolysis reaction with the chemical insertion of three molecules of water.

Question 41

The diagram shows how triglycerides are formed and are broken down.

Answer 41

Question 42

fatty acids diagram

Answer 42

R group can be saturated or unsaturated

Question 43

glycerol diagram

Answer 43

Question 44

condensation glycérol and fatty acids

Answer 44

Question 45

phospholipid

Answer 45

hydrophillic head - allows exchange of substances between cell and environment

hydrophobic tail

fat and water soluble, can form lipid bilayer, crucial for role in cell membranes

Question 46

function of a phospholipid

Answer 46

The different properties of the phosphate heads and the fatty acids affect how easily different molecules can cross a cell membrane (see Unit 1.3: Cell membranes and transport).

If phospholipids are poured into water, the molecules arrange themselves in a single layer. But in cell membranes, phospholipids form a bilayer.

The hydrophilic phosphate groups are attracted to water molecules in the cytoplasm and outside the cell.

The hydrophobic tails are repelled by water molecules and ‘hide’ from water in the cytoplasm and outside the cell.

Question 47

what affects fluidity of membrane

Answer 47

The different properties of the phosphate heads and the fatty acids affect how easily different molecules can cross a cell membrane (see Unit 1.3: Cell membranes and transport).

If phospholipids are poured into water, the molecules arrange themselves in a single layer. But in cell membranes, phospholipids form a bilayer.

The hydrophilic phosphate groups are attracted to water molecules in the cytoplasm and outside the cell.

The hydrophobic tails are repelled by water molecules and ‘hide’ from water in the cytoplasm and outside the cell.

Question 48

difference between phospholipid and triglyceride

Answer 48

triglyceride - 3 fatty acids, and no phosphate

phospholipid - 2 fatty acids and a phosphate group

Question 49

elements in aminoacids

Answer 49

N
C
H
O

Question 50

amino acids

Answer 50

essential - obtained in diet

non-essential - synthesised

Question 51

zwitterion

Answer 51

Question 52

condensation réaction of amino acids

Answer 52

Question 53

condensation réaction of amino acids

Answer 53

Question 54

hydrogen bonding

Answer 54

weak

Question 55

ionic bonding

Answer 55

between R groups

Question 56

disulphide bridge

Answer 56

amino acids oxidise to form disulphide bridge

Question 57

hydrophobic interactions

Answer 57

non-covalent bonds

between water and hydrophobes

Question 58

protein

Answer 58

Proteins are polymers made up of about 20 naturally occurring subunits called amino acids.

Each amino acid has a central carbon atom with four different functional groups attached:

the amino/-NH2 group, which has basic properties and can gain a H+ in acidic conditions to form an -NH3+group

the carboxylic acid/-COOH group, which has acidic properties and can lose a H+ in alkaline conditions to form a -COO- group

an atom of hydrogen, H

a variable group, R.

Question 59

IMPORTANT: you don’t have to learn these but it’s useful to realise how the R group can change the property of an amino acid and protein.

A highly important R group is found in the amino acid cysteine where R = -CH2-SH2

The -SH group of one cysteine can form a covalent bond with the -SH group of another cysteine. This bond is called a disulfide bridge and plays an important role in maintaining the 3D structure of proteins.

Answer 59

Question 60

primary structure of proteins

Answer 60

sequence of amino acids in a polypeptide chain determined by DNA coding

based on:

which amino acids are present
the number of each type of amino acid present
the sequence of amino acids in the polypeptide chain.

Question 61

secondary structure of proteins

alpha

Answer 61

Secondary structure - interactions with peptide backbone forms beta pleated sheets and alpha helices

Alpha helices - have a helical structure, formed by hydrogen bonds between layers of the helix, creating a spiral shape (hydrogen bonds stabilise the helical structure)

Question 62

Proteins with a secondary structure play important structural roles in organisms.

Answer 62

The alpha helix gives rise to fibrous proteins where several strands of alpha helices can be coiled together to give a rope-like arrangement. These are insoluble in water and have a structural function in organisms.
E.g., α-keratin in wool
collagen in skin and blood vessels.
Beta pleated sheets form layers of protein.
E.g., fibroin in silk.

Question 63

secondary structure of proteins

beta

Answer 63

Beta pleated sheets are parallel or antiparallel depending on direction of polypeptide chain

Question 64

secondary structure of proteins

Answer 64

Hydrogen bonds are crucial for the formations of secondary proteins

Question 65

tertiary structure of proteins

Answer 65

Tertiary structure - influenced by interactions of the side chains, inc hydrophobic and hydrogen bonds

depends on the properties of the R groups.

inc
ionic
covalent
hydrogen
hydrophobic interactions

Question 66

tertiary structure folding

Answer 66

The additional folding of the protein gives rise to a compact, globular, three-dimensional shape that makes the protein soluble in water – charged groups on the outside and hydrophobic groups on the inside. The tertiary structure gives globular proteins a specific 3D shape which gives the protein its function.

Many globular proteins have a metabolic function in organisms:

enzymes – active sites to bind to a substrate
antibodies – sites for binding to antigens
hormones – sites for binding to specific receptors.

Question 67

label the bonds

Answer 67

Question 68

ionic bonds

Answer 68

Ionic bonds are formed from charged variable groups and can interact with water, which helps a protein to dissolve.

Question 69

covalent bonds in disulphide bridge

Answer 69

Covalent bonds are formed from variable groups containing sulfur atoms – two of these can bond together to form a disulfide bridge. As they are covalent bonds, disulfide bridges are strong and more difficult to break. A higher temperature or more extreme pH would be needed to break these bonds.

Question 70

hydrogen bonds

Answer 70

Additional hydrogen bonds can also form between polar variable groups.

Question 71

hydrophobic interactions

Answer 71

Hydrophobic interactions take place when the variable groups are non-polar. They are repelled by water and are usually found on the inside of the protein as far away from water as possible; a protein rich in non-polar side groups will be less soluble in water.

Question 72

quarternary structure of proteins

Answer 72

Quaternary structure - involves arrangement of multiple polypeptide chains

These are fibrous proteins which have a structural role in the body.

polypeptide chains held together by:
-disulphide bridges eg insulin, haemoglobin
-hydrogen bonds eg collagen, silk These are fibrous proteins which have a structural role in the body.

Question 73

denaturation of proteins

Answer 73

breaking down of weak bonds

covalend bonds between amino acids

hydrogen bonds

active site changes shape, interactions can’t occur

BUT peptide bonds not broken

secondary and tertiary structures not destoryed
primary structure destroyed - proteins can refold

Question 74

renaturation of proteins

Answer 74

hydroken bonds reformed

if primary structure disrupted, can’t occur

Question 75

factors affecting denaturation

Answer 75

change in pH

increase in temp

heavy metals

ionising radiation

Question 76

carbs and triglycerides

Answer 76

long term energy store

Question 77

Adenine Triphosphate

Answer 77

ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular process

Question 78

nucleotide of ATP

Answer 78

Question 79

hydrolysis of ATP

Answer 79

breaks last covalent bond between phosphate groups

releases chemical energy

energy used for: active transport, muscle contraction, formation of large molecules

Question 80

uses of ATP

Answer 80

muscle contraction
active transport
DNA replication
cell divison

Question 81

nucleotide

Answer 81

Question 82

nucleotide

Answer 82

Question 83

polynucleotide

Answer 83

Question 84

While ions are all charged, molecules can have:

Answer 84

no charge – non-polar

or a slight charge – polar.

Question 85

ions, non-polar and polar behaviour

Answer 85

Ions and polar compounds attract oppositely charged particles and play important roles in the structure of molecules.

Non-polar compounds do not dissolve in water but will dissolve in lipids (fats/oils) – they are said to be lipid-soluble.

Question 86

ions

Answer 86

Question 87

Organic compounds

Answer 87

Organic compounds always contain the elements carbon and hydrogen, and many contain oxygen and/or nitrogen.

Question 88

Inorganic compounds

Answer 88

also contain carbon, hydrogen, oxygen and nitrogen, but can be made without the involvement of living organisms.

Question 89

water properties

Answer 89

Water is a polar molecule – it has no overall charge, but the hydrogen atoms have a partial positive charge and the oxygen atoms have a partial negative charge.

A water molecule is usually drawn using solid lines for the bonds between the hydrogen and oxygen atoms.

The partial charges are shown as δ+, delta positive and δ−, delta negative.

Because of their polarity, water molecules attract each other by forming hydrogen bonds. This is usually represented by a series of vertical lines as shown in the diagram.

Question 90

water properties 2

Answer 90

Question 91

water diagram

Answer 91

Question 92

why is water known as a universal solvent

Answer 92

Because of their polarity, water molecules are attracted to other water molecules and charged particles. This helps charged particles dissolve in water.

For this reason, water is sometimes referred to as the universal solvent as a large number of substances can dissolve in water.

Question 93

letter R

Answer 93

The carbon chain in fatty acids is often represented by the letter R, a variable group containing a chain of between 4 and 24 carbon atoms.

Question 94

state of lipid at room temp

Answer 94

Lipids with long hydrocarbon chain fatty acids are more likely to be solid at room temperature – these are fats.

Those with short hydrocarbon chains form oils which are liquid at room temperature.

This is because there are weak forces of attraction between the fatty acid chains – the longer the carbon chain, the greater the force of attraction, so the higher the melting point. Some examples of different fatty acids and their melting points are shown below.

Question 95

Functions of triglycerides

Answer 95

Triglycerides are efficient energy storage molecules. They are more efficient than carbohydrates:

1 g fat provides about 38 kJ energy
1 g carbohydrate provides about 17 kJ energy.
Because of this, fats and oils are the preferred energy storage molecule in animals and many seeds (lipids store twice as much energy per gram than carbohydrates).

Triglycerides are also good thermal insulators and provide mechanical protection for delicate organs.

Because fats are less dense than water, they are used to provide buoyancy for many aquatic animals.

Some animals spread oil onto their fur or feathers because this makes them waterproof. This is because fats are hydrophobic and repel water.

Question 96

Saturated fatty acids

Answer 96

They can also be saturated, with only single bonds between carbon atoms. They contain the maximum number of hydrogen atoms.

Lipids containing only saturated fatty acids generally form fats at room temperature. This is because the fatty acid tails are straight and can pack closely together. Stronger forces of attraction can form which means more energy is needed to break the bonds and melt the fat – the melting point is higher.

Question 97

Unsaturated fatty acids

Answer 97

Fatty acids can also be unsaturated, with one or more double bonds between carbon atoms.

They do not contain the maximum number of hydrogen atoms. For each carbon-carbon double bond, the fatty acid will contain two fewer hydrogen atoms.

Lipids containing unsaturated fatty acids are usually oils at room temperature.

The double bonds make the fatty acid tails less straight (they kink) so they cannot pack as closely together.

The forces of attraction between the fatty acids are weaker, so less energy is needed to break the bonds and melt the fat – they have a lower melting point.

Question 98

A high intake of fat by humans, notably saturated fats, is a contributory factor in heart disease.

Answer 98

It raises the low-density lipoprotein (LDL) cholesterol level, which increases the incidence of atheromas in coronary arteries (and in other arteries).

This leads to blockages and eventually, heart disease.

Question 99

POLYUNSATURATED FAT

Answer 99

An essential fat that we must get from food because our bodies cannot produce it. It lowers LDL (bad cholesterol). Found in: most cooking oils, pumpkin seeds, pine nuts, sesame seeds, fatty fish. Also known as: omega-3 and omega-6 fatty acids.

Question 100

MONOUNSATURATED FAT

Answer 100

Considered a healthy fat: it lowers LDL (bad cholesterol) and maintains HDL (good cholesterol). Found in: olive oil, avocado and avocado oil, most nuts and nut butters.

Question 101

SATURATED FAT

Answer 101

Increases total cholesterol and LDL (bad cholesterol). Best to consume in moderation. Found in: red meat, whole milk, cheese, coconut, butter, processed meat, many baked goods, and deep fried foods.

Question 102

TRANS FAT

Answer 102

A by-product of processing healthier fats to give them a longer shelf life. Raises your LDL (bad cholesterol) and lowers your HDL (good cholesterol). Intake should be limited. Also known as: partially hydrogenated oil

Question 103

Amino acids can polymerise through a condensation reaction to give

Answer 103

dipeptides and polypeptides.

Question 104

linkage between 2 amino acids

Answer 104

The linkage between two amino acids is called the peptide bond. Peptide bonds form between the carboxyl group of one amino acid and the amino group of another.

Question 105

Answer 105

Question 106

Answer 106

Question 107

two different dipeptides can be formed from two different amino acids

Answer 107

This means that the dipeptides can have different properties because of the arrangement of the amino acids on either side of the peptide bond.

Question 108

how do different R groups affect amino acids

Answer 108

This can affect the charges on the amino acid and therefore the properties of the dipeptide. This is also shown in the diagram.

Question 109

polypeptide

Answer 109

a series of peptide bonds holding amino acids together - form a chain

Question 110

how does order of aminoacids affect molecule (polypeptide)

Answer 110

The sequence or order of amino acids in a polypeptide affects the organisation of the molecule as it is processed to form a functional protein.