Chapter 2.2 Flashcards
The key molecules that are required to build structures that enable organisms to function are
- Carbohydrates
- Proteins
- Lipids
- Nucleic Acids
- Water
Carbon atoms are key to the organic compounds because:
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
Macromolecules
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
Carbohydrates
-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
The Two Forms of Glucose
-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
types of carbohydrates
Glucose
- 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
different types of monosaccharide
-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
Structure of polysaccharides table
polysaccharides: a-glucose : B-glucose Starch: yes : no Glycogen: yes : no Cellulose: no: yes
monosaccharide
- def: single sugar monomer, all are reducing sugars
- example: glyceraldehyde, ribose, glucose
- function: source of energy in respiration, building blocks for polymers
disaccharide
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
polysaccharide
- 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
A covalent bond
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
covalent bonds features
- 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
When two monomers are close enough that their
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)
Condensation
- 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
Hydrolysis
- Hydrolysis means ‘lyse’ (to break) and ‘hydro’ (with water)
- In the hydrolysis of polymers, covalent bonds are broken when water is added
Reducing sugars
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
Non-reducing sugars
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
why does the body form the Glycosidic Bond between monosaccharides
- 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
The formation of a glycosidic bond by condensation between two monosaccharides (glucose) to form a disaccharide (maltose)
- 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)
The formation of a glycosidic bond by condensation between α-glucose and β-fructose to form a disaccharide (sucrose)
Types of Glycosidic Bonds Table
Breaking the Glycosidic Bond
- 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
Sucrose result in a Benedict’s test.
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
Cellulose form of sugar
is a polysaccharide
what are Polysaccharides
are macromolecules that are polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction to form chains.
chains formed through condensation reactions
–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
Cellulose – structure
- 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
what gives cellulose strenght
Due to the inversion of the β-glucose molecules many hydrogen bonds form between the long chains giving cellulose it’s strength
Cellulose – function
- 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
Triglycerides:Lipids
-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)
Triglycerides: def
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
how are Triglycerides formed
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
Unsaturated fatty acids can be? two forms
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
Fatty acids can vary in two ways
- 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)
Triglycerides Function: Energy storage
- 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
Triglycerides Function: Insulation
- 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)
Triglycerides Function: Buoyancy
The low density of fat tissue increases the ability of animals to float more easily
Triglycerides Function: Protection
The adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage
plants store triglycerides
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
mammals store triglycerides
Mammals store triglycerides as oil droplets in adipose tissue to help them survive when food is scarce (e.g. hibernating bears)
Phospholipids Structure
- 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)
are amphipathic
(they have both hydrophobic and hydrophilic parts)
-As a result of having hydrophobic and hydrophilic parts phospholipid molecules form monolayers or bilayers in water
vital Role of Phospholipids
- 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
Starch and glycogen are used for storage
Because they are polysaccharides
-Compact as well as insoluble meaning no osmotic effect
Starch
storage in plants, It is stored as granules i plastids (eg chloroplasts)
-starch is constructed from two different polysaccharides
-amylose and amylopectin
Glycogen storage
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
-amylose (10-30% starch) structure
- 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
-amylopectin(70-100% starch) structure
- 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
Summary of Storage Polysaccharides Table
Phospholipids v Triglycerides Table
