Chapter 2.2

Question 1

The key molecules that are required to build structures that enable organisms to function are

Answer 1

• Carbohydrates
• Proteins
• Lipids
• Nucleic Acids
• Water

Question 2

Carbon atoms are key to the organic compounds because:

Answer 2

Each carbon atom can form four covalent bonds – this makes the compounds very stable (as covalent bonds are so strong they require a large input of energy to break them) Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur Carbon atoms can bond to form straight chains, branched chains or rings Carbon compounds can form small single subunits (monomers) that bond with many repeating subunits to form large molecules (polymers) by a process called polymerisation

Question 3

Macromolecules

Answer 3

are very large molecules -That contain 1000 or more atoms therefore having a high molecular mass -Polymers can be macromolecules, however not all macromolecules are polymers as the subunits of polymers have to be the same repeating units

Question 4

Carbohydrates

Answer 4

-Carbohydrates are one of the main carbon-based compounds in living organisms -All molecules in this group contain C, H and O -As H and O atoms are always present in the ratio of 2:1 (eg. water H2O, which is where ‘hydrate’ comes from) they can be represented by the formula Cx (H2O)y -The three types of carbohydrates are monosaccharides, disaccharides and polysaccharides

Question 5

The Two Forms of Glucose

Answer 5

-Glucose exists in two structurally different forms

– alpha (α) glucose and beta (β) glucose and is therefore known as an isomer

—This structural variety results in different functions between carbohydrates

Question 6

types of carbohydrates

Answer 6

Question 7

Glucose

Answer 7

• The most well-known carbohydrate monomer is glucose
• Glucose has the molecular formula C6H12O6
• Glucose is the most common monosaccharide and is of central importance to most forms of life

Question 8

different types of monosaccharide

Answer 8

-There are different types of monosaccharide formed from molecules with varying numbers of carbon atom, for example:

—Trioses (3C) eg. glyceraldehyde

—Pentoses (5C) eg. ribose

—Hexoses (6C) eg. glucose

Question 9

Structure of polysaccharides table

Answer 9

polysaccharides: a-glucose : B-glucose Starch: yes : no Glycogen: yes : no Cellulose: no: yes

Question 10

monosaccharide

Answer 10

• def: single sugar monomer, all are reducing sugars
• example: glyceraldehyde, ribose, glucose
• function: source of energy in respiration, building blocks for polymers

Question 11

disaccharide

Answer 11

def: a sugar formed from two monosaccharides joined by a glyosidic bond in a condensation reaction
- examples: maltose(a-glucose + a-glucose), sucrose(a-glucose + fructose), lactose (a-glucose + B-galactose)
- Function: sugar found in germinating seeds(maltose), mammal milk sugar(lactose(, sugar stored in sugar cane (sucrose

Question 12

polysaccharide

Answer 12

• def: a polymer formed by many monosaccharides joined by glyosidic bonds in a condensation reaction
• examples: cellulose(B-glucose), Starch(a-glucose in the form of amylase and amylopectin), glycogen (a-glucose)
• function: energy storage (plants-starch-and animals-glycogen), structural - cell wall

Question 13

A covalent bond

Answer 13

is the sharing of two or more electrons between two atoms

-The electrons can be shared equally forming a nonpolar covalent bond or unequally (where an atom can be more electronegative δ) to form a polar covalent bond

Question 14

covalent bonds features

Answer 14

• Generally each atom will form a certain number of covalent bonds due to the number of free electrons in the outer orbital e.g. H = 1 bond, C = 4 bonds
• Covalent bonds are very stable as high energies are required to break the bonds
• Multiple pairs of electrons can be shared forming double bonds (e.g. unsaturated fats C=C) or triple bonds

Question 15

When two monomers are close enough that their

Answer 15

outer orbitals overlap this results in their electrons being shared and a covalent bond forming. If more monomers are added then polymerisation occurs (and / or a macromolecule forms)

Question 16

Condensation

Answer 16

• Also known as dehydration synthesis (‘to put together while losing water’)
• A condensation reaction occurs when monomers combine together by covalent bonds to form polymers (polymerisation) or macromolecules (lipids) and water is removed

Question 17

Hydrolysis

Answer 17

• Hydrolysis means ‘lyse’ (to break) and ‘hydro’ (with water)
• In the hydrolysis of polymers, covalent bonds are broken when water is added

Question 18

Reducing sugars

Answer 18

can donate electrons (the carbonyl group becomes oxidised), the sugars become the reducing agent

—Thus reducing sugars can be detected using the Benedict’s test as they reduce the soluble copper sulphate to insoluble brick-red copper oxide

—Examples: glucose, fructose, maltose

Question 19

Non-reducing sugars

Answer 19

cannot donate electrons, therefore they cannot be oxidised

-To be detected non-reducing sugars must first be hydrolysed to break the disaccharide into its two monosaccharides before a Benedict’s test can be carried out

—-Example: sucrose

Question 20

why does the body form the Glycosidic Bond between monosaccharides

Answer 20

• To make monosaccharides more suitable for transport, storage and to have less influence on a cell’s osmolarity, they are bonded together to form disaccharides and polysaccharides
• Disaccharides and polysaccharides are formed when two hydroxyl (-OH) groups (on different saccharides) interact to form a strong covalent bond called the glycosidic bond (the oxygen link that holds the two molecules together)
• Every glycosidic bond results in one water molecule being removed, thus glycosidic bonds are formed by condensation

Question 21

The formation of a glycosidic bond by condensation between two monosaccharides (glucose) to form a disaccharide (maltose)

Answer 21

• Each glycosidic bond is catalysed by enzymes specific to which OH groups are interacting
• As there are many different monosaccharides this results in different types of glycosidic bonds forming (e.g maltose has a α-1,4 glycosidic bond and sucrose has a α-1,2 glycosidic bond)

Question 22

The formation of a glycosidic bond by condensation between α-glucose and β-fructose to form a disaccharide (sucrose)

Answer 22

Question 23

Types of Glycosidic Bonds Table

Answer 23

Question 24

Breaking the Glycosidic Bond

Answer 24

• The glycosidic bond is broken when water is added in a hydrolysis (meaning ‘hydro’ – with water and ‘lyse’ – to break) reaction
• Disaccharides and polysaccharides are broken down in hydrolysis reactions -Hydrolytic reactions are catalysed by enzymes, these are different to those present in condensation reactions
• Examples of hydrolytic reactions include the digestion of food in the alimentary tract and the breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiratio

Question 25

Sucrose result in a Benedict’s test.

Answer 25

Sucrose is a non-reducing sugar which gives a negative result in a Benedict’s test. When sucrose is heated with hydrochloric acid this provides the water that hydrolyses the glycosidic bond resulting in two monosaccharides that will produce a positive Benedict’s test

Question 26

Cellulose form of sugar

Answer 26

is a polysaccharide

Question 27

what are Polysaccharides

Answer 27

are macromolecules that are polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction to form chains.

Question 28

chains formed through condensation reactions

Answer 28

--Branched or unbranched ---Folded (making the molecule compact which is ideal for storage, eg. starch and glycogen) ---Straight (making the molecules suitable to construct cellular structures, eg. cellulose) or coiled **--Polysaccharides are insoluble in water**

Question 29

Cellulose – structure

Answer 29

- Is a polymer consisting of long chains of β-glucose joined together by 1,4 glycosidic bonds - As β-glucose is an isomer of α-glucose to form the 1,4 glycosidic bonds consecutive β-glucose molecules must be rotated 180° to each other

Question 30

what gives cellulose strenght

Answer 30

Due to the inversion of the β-glucose molecules many hydrogen bonds form between the long chains giving cellulose it’s strength

Question 31

Cellulose – function

Answer 31

- Cellulose is the main structural component of cell walls due to its strength which is a result of the many hydrogen bonds found between the parallel chains of microfibrils - The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure - The cellulose fibres and other molecules (eg. lignin) found in the cell wall form a matrix which increases the strength of the cell walls -The strengthened cell walls provides support to the plant - Cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane - As few organisms have the enzyme (cellulase) to hydrolyse cellulose it is a source of fibre

Question 32

Triglycerides:Lipids

Answer 32

-Macromolecules which contain carbon, hydrogen and oxygen atoms. --However, unlike carbohydrates lipids contain a lower proportion of oxygen -Non-polar and hydrophobic (Insoluble in water) -Different types: ---Fats and Oils (composed mainly of triglycerides) ---Phospholipids ---Steroids and waxes (considered lipids as they are hydrophobic thus insoluble in water)

Question 33

Triglycerides: def

Answer 33

Are non-polar, hydrophobic molecules - The monomers are glycerol and fatty acids - Fatty acids contain a methyl group at one end of a hydrocarbon chain (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a carboxyl group

Question 34

how are Triglycerides formed

Answer 34

are formed by esterification - An ester bond forms when the hydroxyl group of the glycerol bonds with the carboxyl group of the fatty acid - For each ester bond formed a water molecule is released - Therefore, for one triglyceride to form three water molecules are released

Question 35

Unsaturated fatty acids can be? two forms

Answer 35

mono or poly-unsaturated - If H atoms are on the same side of the double bond they are cis-fatty acids and are metabolised by enzymes - If H atoms are on opposite sides of the double bond they are trans-fatty acids and cannot form enzyme-substrate complexes, therefore, are not metabolised. - They are linked with coronary heart disease

Question 36

Fatty acids can vary in two ways

Answer 36

- Length of the hydrocarbon chain - The fatty acid may be saturated (mainly in animal fat) or unsaturated (mainly vegetable oils, although there are exceptions e.g. coconut and palm oil)

Question 37

Triglycerides Function: Energy storage

Answer 37

- The long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced) - So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP - Triglycerides therefore store more energy per gram than carbohydrates and proteins (37kJ compared to 17kJ) As triglycerides are hydrophobic they do not cause osmotic water uptake in cells so more can be stored - The oxidation of the carbon-hydrogen bonds releases large numbers of water molecules (metabolic water) during cellular respiration

Question 38

Triglycerides Function: Insulation

Answer 38

- Triglycerides are part of the composition of the myelin sheath that surrounds nerve fibres, This provides insulation which increases the speed of transmission of nerve impulses - Triglycerides compose part of the adipose tissue layer below the skin which acts as insulation against heat loss (eg. blubber of whales)

Question 39

Triglycerides Function: Buoyancy

Answer 39

The low density of fat tissue increases the ability of animals to float more easily

Question 40

Triglycerides Function: Protection

Answer 40

The adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage

Question 41

plants store triglycerides

Answer 41

Plants store triglycerides, in the form of oils, in their seeds and fruits. -If extracted from seeds and fruits these are generally liquid at room temperature due to the presence of double bonds which add kinks to the fatty acid chains altering their properties

Question 42

mammals store triglycerides

Answer 42

Mammals store triglycerides as oil droplets in adipose tissue to help them survive when food is scarce (e.g. hibernating bears)

Question 43

Phospholipids Structure

Answer 43

- Phospholipids are a type of lipid, therefore they are formed from the monomer glycerol and fatty acids - Unlike triglycerides, there are only two fatty acids bonded to a glycerol molecule in a phospholipid as one has been **replaced by a phosphate ion (PO43-)** - As the phosphate is polar it is soluble in water (hydrophilic) - The fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic)

Question 44

are amphipathic

Answer 44

(they have both hydrophobic and hydrophilic parts) -As a result of having hydrophobic and hydrophilic parts phospholipid molecules form monolayers or bilayers in water

Question 45

vital Role of Phospholipids

Answer 45

- The main component (building block) of cell membranes - Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when a phospholipid bilayer forms, This acts as a barrier to water-soluble molecules - The hydrophilic phosphate heads form H-bonds with water allowing the cell membrane to be used to **compartmentalise** - This enables the cells to organise specific roles into organelles helping with efficiency - **Composition of phospholipids contributes to the fluidity** of the cell membrane - Phospholipids control membrane protein orientation : Weak hydrophobic interactions between the phospholipids and membrane proteins hold the proteins within the membrane but still allow movement within the layer

Question 46

Starch and glycogen are used for storage

Answer 46

Because they are polysaccharides -Compact as well as insoluble meaning no osmotic effect

Question 47

Starch

Answer 47

storage in plants, It is stored as granules i plastids (eg chloroplasts) -starch is constructed from two different polysaccharides **-amylose and amylopectin**

Question 48

Glycogen storage

Answer 48

in animas and fungi, It is highly branded and not coiled - liver and muscles cells have a high concentration of glycogen, present as visible granules, as the cellular respiration rate is high in these cells - glycogen is more branded than amylopectin making it more compact which helps animals store more - the branching enables more free ends where glucose molecules can either be added or removed allowing for condensation and hydrolysis reactions to occur more rapidly - this the storage and release of glucose can suit the demands of the cell

Question 49

-amylose (10-30% starch) structure

Answer 49

- is double helix shaped chain with 1,4 glycosidic bonds between a-glucose molecules - the **helix shape enable** it to be **more compact and thus more resistant to digestion**

Question 50

-amylopectin(70-100% starch) structure

Answer 50

- **1,4** glycosidic bonds between a-glucose molecules but also **1,6** glycosidic bonds from between glucose molecules creating a branched molecule - the branches result in many **terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage**

Question 51

Summary of Storage Polysaccharides Table

Answer 51

Question 52

Phospholipids v Triglycerides Table

Answer 52