biological molecules

what are monomers

the smaller units from which larger molecules are made

what are polymers

• Polymers are molecules made from a large number of monomers joined together in a chain

what are carbohydrates

molecules that contain carbon, hydrogen, and oxygen (higher proportion of oxygen than lipids)

what are the different types of carbohydrates

monosaccharides

disaccharides

polysaccharides

define a monosaccharide, give an example, and state its function

definition- made up of a single sugar unit, and all monosaccharides are reducing sugars

examples:

• ribose

• glucose- alpha and beta glucose

function- source of energy in respiration, and are the building blocks for polymers

define a disaccharide and give examples

definition- a sugar formed from 2 monosaccharides, joined by a glycosidic bond in a condensation reaction

examples:

• maltose- alpha glucose + alpha glucose (reducing sugar)

• sucrose- glucose + fructose (non-reducing sugar)

• lactose- glucose + galactose (reducing sugar)

define a polysaccharide, give an example, and state its function

definition- a polymer formed from many monosaccharides joined by glycosidic bonds in a condensation reaction

examples:

• cellulose (made from beta glucose)

• starch (made from alpha glucose in the form of amylose and amylopectin)

• glycogen (alpha glucose)

function:

energy storage:

starch- in plants

glycogen- in animals

structural- cellulose makes up the cell wall in plants

what is a condensation reaction

when monomers combine together by covalent bonds to form polymers and a water molecule is removed

what is a hydrolysis reaction

polymers are broken down into smaller subunits as covalent bonds are broken when a water molecule is added

what is the difference between reducing and non reducing sugars

the classification depends on the sugars ability to donate electrons

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

non-reducing sugars can’t donate electrons, so can’t become reduced

give examples of reducing and non-reducing sugars

reducing sugars:

• glucose

• fructose

• lactose

• galactose

non-reducing sugars:

• sucrose

what is the test for reducing sugars and non reducing sugars

sugars are soluble

place sugars in benedict’s solution (blue) and heat up solution in a water bath

reducing sugars- will donate an electron which reduces cupric ions (Cu2+) into cuprous ions (Cu1+) - this causes a colour change to brick red

non-reducing sugars- can’t donate an electron, so cupric ions (Cu2+) aren’t reduced- solution stays blue

what is an oxidation reaction

gain of oxygen

loss of hydrogen

loss of electrons

what is a reduction reaction

loss of oxygen

gain of hydrogen

gain of electrons

how are sugars named

-Sugars end in OSE

3 carbon sugar = triose sugar

4= tetrose sugar

5= pentose sugar

6= hexose

7= heptose

what is an isomer

a molecule with the same molecular formula but a different structure

what is the molecular formula for glucose

C₆H₁₂O₆

draw alpha and beta glucose

ABBA- for OH group

alpha- below (OH group is below)

beta- above (OH group is above

why are disaccharides more suitable for transport than monosaccharides

• Less Reactive – Disaccharides are more chemically stable than monosaccharides, reducing the risk of unwanted reactions during transport in plants and animals.

• Lower Osmotic Effect – They exert less osmotic pressure than monosaccharides, preventing excessive water movement that could disrupt cell balance.

• Easier Storage & Controlled Breakdown – Disaccharides can be hydrolyzed into monosaccharides when needed, allowing for controlled energy release.

• Efficient Energy Transport – In plants, sucrose (a disaccharide) is the main sugar transported in the phloem because it is stable and soluble.

how are glycosidic bonds formed

when two hydroxyl (-OH) groups on different saccharides interact to form a 1-4 glycosidic bond via a condensation reaction

1-4 because carbon 1 on one saccharide and carbon 4 on the other saccharide

results in one water molecule being removed

how are glycosidic bonds broken

hydrolysis reaction with the addition of a water molecule

compare the structure of monosaccharides and disaccharides

 

Compare the structures of monosaccharides and disaccharides

-monosaccharides are made up of 1 sugar unit e.g. Glucose and disaccharides are made up of 2 sugar units e.g. sucrose

-Disaccharides contain an alpha 1-4 glycosidic bond.

-Disaccharides require a condensation reaction to be formed, which releases a water molecule

-Both soluble in water

-Monosaccharides such as glucose can be used straight away for respiration, however disaccharides have to be broken down/digested before they can be used in respiration

why don’t plants and animals store glucose as glucose

glucose is soluble in water which could lead to the osmosis effect as it can decrease the water potential off cells causing water to be drawn in

need to store as starch or glycogen because they are compact molecules and are insoluble in water

describe the structure and function of starch

monomer- alpha glucose

used for storage of carbohydrates in plants

form- grains

two forms- amylose and amylopectin

amylose:

• straight chain as it’s only made up of 1-4 glycosidic bonds

• helix shape allows it to be more compact (can store more glucose in a certain area)

• more resistant to digestion as it’s not branched (smaller surface area for hydrolysis- increases rate of hydrolysis)

amylopectin:

• branched chain as it has 1-4 and 1-6 glycosidic bonds

• more easily and quickly digested because it’s branched so larger SA for hydrolysis

describe the structure and function of glycogen

monomer- alpha glucose

used for storage of carbohydrates in animals and fungi

form- granules in the liver and muscle cells

glycogen contains 1-4 and 1-6 glycosidic bonds

glycogen is more branched (higher proportion of 1-6 glycosidic bonds than amylopectin so it’s more compact- animals can store more glucose than plants

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

describe the structure and function of cellulose

monomer- beta glucose, joined together by 1-4 glycosidic bonds

has straight and unbranched chains which form hydrogen bonds between adjacent layers (because beta glucose has an -OH group on either side of the molecule

hydrogen bonds are weak individually but strong together

hydrogen bonds between layers creates microfibrils which in turn create fibres that provide the cell wall with immense strength- prevents the cell from bursting when there is high tutor pressure

strengthened walls provide support to the plant

what is the test for starch

add a few drops of iodine to the solution (orange/brown)

if starch is present then there will be a colour change to blue/black

what is a lipid

macromolecules which contain carbon, hydrogen, and oxygen (lower proportion of oxygen than carbohydrates)

They are non-polar (molecules isn’t charged) and hydrophobic/insoluble in water

But they will dissolve in organic solvents such as ethanol

there are two different groups of lipids (triglycerides and phospholipids)

which stores more energy, carbohydrates or lipids

lipids store twice the energy than carbohydrates do, of the same mass

describe the structure of triglycerides

made up of 1 glycerol and 3x fatty acids which are joined by 3x ester bonds- formed via condensation reactions

describe the structure of fatty acids

they are made up of a hydrocarbon chain with a carboxyl group at one end (COOH) and a methyl group at the other end (CH3)

the hydrocarbon tail is known as the R group (chains of hydrogen atoms bonded to carbon atoms which are typically 2-20 carbon atoms long)

how can fatty acids vary

the length of the hydrocarbon chain (R group)

or they can either be saturated or unsaturated

what is a saturated fatty acid

the chain has no carbon-carbon double bonds because each carbon atom in the hydrocarbon chain has 4 strong covalent bonds

what is the general formula for saturated fatty acids

Cn H2n O2

what is an unsaturated fatty acid

where the hydrocarbon chain has at least one carbon-carbon double bond

what are the two types of unsaturated fatty acids

monounsaturated- where there is a single carbon-carbon double bond present in the hydrocarbon chain

polyunsaturated- where there is more than one carbon-carbon double bond present in the hydrocarbon chain

describe the bonding present in triglycerides

an ester bond forms between a hydroxyl group (-OH) on the glycerol molecule and a carboxyl group (-COOH) on the fatty acid molecule

a H from the glycerol combines with an OH from the fatty acid to make water

ester bonds are formed via condensation reactions where a water molecule is released

three fatty acids join to one glycerol molecule- so three water molecules are released

how does the melting point differ between fats and oils

fats are more saturated than oils

the carbon-carbon double bond results in a kink in the hydrocarbon tail

the kink pushes carbon molecules further apart from each other which makes the fatty acid more fluid- so it has a lower melting point

what are the different functions of triglycerides

energy storage

insulation

buoyancy

protection

how is the structure of triglycerides suited for energy storage

the hydrocarbon tails contain many carbon-hydrogen bonds which release energy when they are oxidised and broken which can be used to produce ATP

triglycerides are also hydrophobic so when they are stored, they don’t affect the water potential and lead to osmosis

the oxidation of carbon-hydrogen double bonds releases large numbers of water molecules during cellular respiration (useful for desert animals as they can retain this water when there is a limited supply of water to drink)

how is the structure of triglycerides suited for insulation

triglycerides help make up the myelin sheath which surrounds nerve cells and acts as an electrical conductor which helps to speed to the transmission of nerve impulses/action potentials

triglycerides also conduct heat as they form a layer of tissue just below the skin with can act as insulation to reduce heat loss

how is the structure of triglycerides suited for buoyancy

the low density of fat tissue can increase the ability of animals to float more easily

how are triglycerides suited for protection

fats can be stored around organs to help protect them from damage and impact

why are triglycerides energy reserves

they store more energy than carbohydrates per gram due to their hydrocarbon chains containing less oxygen than carbohydrates

describe the structure of a phospholipid

made up of:

• 2 fatty acids (non-polar) forms hydrophobic tail

• one glycerol

• one phosphate ion (polar)- forms hydrophilic head

2x ester bonds between fatty acids and glycerol

1x ester bond between glycerol and the phosphate ion

overall 3x water molecules are released

how do phospholipids form a bilayer

phospholipids make up the cell membrane- allows the cell membrane to act as a barrier and control what substances enter and leave the cell

the ‘hydrophobic tails’ orientate themselves inwards away from the water forming the hydrophobic core

the ‘hydrophilic heads’ form hydrogen bonds with water

how does the composition of phospholipids contribute to the fluidity of the cell membrane

if the phospholipid bilayer has mainly saturated fatty acids then it will be less fluid (less carbon-carbon double bonds)

if the phospholipid bilayer has mainly unsaturated fats then it will be more fluid (more carbon-carbon double bonds)

what is the test for lipids

add the lipid sample to the test tube- if food sample is solid it should be ground up first

add ethanol to the test tube and shake to mix it

then add the firs mixture to a different test tube with water in it

Results:

• if lipids are present then a layer of milky/cloudy emulsion will form at the top of the test tube

• if no lipids present then the solution will remain clear

what are proteins

they are polymers made of repeating monomers called amino acids

the type, number, and order of amino acids will determine the shape of the protein and therefore its function aswell

describe the structure of an amino acid

they have a central carbon atom which is bonded to:

• an amino group (-NH2)

• a carboxyl group (-COOH) - an acidic group

• a hydrogen atom

• an R group

what is the R group in an amino acid

the part of an amino acid that differs- 20 different amino acids

the R group of the amino acid depicts it’s properties

what are the bonds present in proteins

peptide bonds

how are peptide bonds formed between amino acids

formed via a condensation reaction

a hydroxyl (-OH) is lost from the carboxyl group of one amino acid and a hydrogen atom is lost from the amino group of another amino acid

water is released

what is a dipeptide

consist of two amino acids

formed via one condensation reaction

what is a polypeptide

the sequence of at least more than two amino acids joined together by peptide bonds that are formed through condensation reactions

draw hydrolysis and condensation reactions to show how dipeptides and amino acids swap between each other

describe how chromatography works

• Chromatography is a technique that can be used to separate a mixture into its individual components

• Chromatography relies on differences in the solubility of the different chemicals (called ‘solutes’) within a mixture

• All chromatography techniques use two phases:

  • The mobile phase

  • The stationary phase

• The components in the mixture separate as the mobile phase travels over the stationary phase

• Differences in the solubility of each component in the mobile phase which affects how far each component can travel

• Those components with higher solubility will travel further than the others

• This is because they spend more time in the mobile phase and are thus carried further up the paper than the less soluble components

what is the mobile phase in paper chromatography

• The mobile phase is the liquid that carries the sample through the chromatography system.

• It moves through or over the stationary phase, carrying the components of the mixture with it.

• Different compounds in the sample travel at different speeds depending on how strongly they interact with the mobile phase versus the stationary phase.

e.g. water or ethanol

what is the stationary phase in paper chromatography

• The stationary phase is the material that stays fixed inside the chromatography system. e.g. the paper

• It provides a surface for the components of the sample to interact with, leading to separation.

• Some compounds adhere to the stationary phase more strongly than others, causing them to move slower.

describe the primary structure of a protein

the sequence of amino acids in a polypeptide chain

The DNA of a cell determines the primary structure of a protein by instructing tRNA molecules to join amino acids in a specific order

peptide bonds form between amino acids via condensation reactions

the primary structure of a protein determines the structure and function of the protein

describe the secondary structure of a protein

the secondary structure of a protein is held together by hydrogen bonds that form between the carboxyl group of one amino acid and the amino group of another amino acid

these hydrogen bonds can lead to:

• α-helix

• β-pleated sheet

hydrogen bonds are individually weak but strong together

what can hydrogen bonds in the secondary structure of a protein be broken by

high temperatures and changes in pH

describe the tertiary structure of a protein

additional bonds form between the R groups of amino acids which gives the protein its 3D structure

still contains peptide bonds and hydrogen bonds between amino and carboxyl groups

the 3D structure allows proteins to have a specific function e.g. a specific shaped active site

the additional bonds include:

• hydrogen bonds between strongly polar R groups

• disulfide bonds/bridges between cystine amino acids

• ionic bonds between amino and carboxylate groups on different R groups

• weak hydrophobic interactions between non-polar R groups

describe the quaternary structure of a protein

occurs in proteins that have more than one polypeptide chain working together as a functional protein e.g. haemoglobin

each polypeptide chain is referred to as a subunit of the protein

describe ionic bonds in the tertiary structure of a protein

ionic bonds form between positively charged amino groups and negatively charged carboxyl groups on different R groups

ionic bonds are stronger than hydrogen bonds but weaker than disulfide bonds

they are easily broken by changes in pH

describe disulphide bonds in the tertiary structure of a protein

disulphide bonds are strong covalent bonds that form between two cystine R groups

this is because cystine is the only amino acid that has an available sulfur atom in its R group

these are the strongest bonds in the tertiary structure

describe hydrophobic interactions in the tertiary structure of a protein

hydrophobic interactions form between the non-polar R groups

describe the difference between hydrogen bonds in the secondary and tertiary structure of a protein

in the secondary structure of a protein hydrogen bonds only form between carboxyl and amino groups on different amino acids

whereas,

in the tertiary structure, hydrogen bonds form between strongly polar R groups (they are the most common bond in the T structure because they are able to form between a wide variety of R groups)

how do you test for proteins

biuret test

a liquid solution containing the sample is treated with sodium or potassium hydroxide to make it alkaline

a few drops of copper II sulphate is added to the sample (blue colour)

if a colour change from blue → lilac/purple is observed then protein is present

what are the problems with using biuret to test for proteins

test doesn’t work on amino acids or dipeptides- must be more than two peptide bonds present

colour change is subtle so its recommended to hold the test tube up against a white tile

what is an enzyme

an enzyme is a biological catalyst that speeds up the rate of reaction but aren’t used up in the process

they do this by lowering the activation energy for the reaction

how are enzymes specific

the shape of the enzymes active site is complimentary to its substrate

the shape of the active site is determined by the enzymes/proteins tertiary structure

• Proteins are formed from chains of amino acids held together by peptide bonds

• The order of amino acids determines the shape of an enzyme

• If the order is altered, the resulting three-dimensional shape changes

what does the term denaturation mean

when extreme heat or pH disrupts the bonds in the tertiary structure of the enzyme causing it’s 3D structure to change → changes the shape of the active site → prevents substrate from binding as it’s no longer complimentary

what is the difference between catabolic and anabolic enzyme reactions

catabolic- the breakdown of complex molecules into simpler products

single substrate is drawn into the active site and broken apart into two or more distinct molecules

anabolic- the building of more complex molecules from simpler molecules

two or more substrates are drawn into the active site, and bonds are formed between them which forms and releases a single product

define activation energy

the minimum amount of energy required for a reaction to occur

how do enzymes lower the activation energy of a reaction

they provide an alternate energy pathway

this means that reactions can take place at lower temperatures (hence why the human body’s temperature is 37.7 .C

what is collision theory

states that the enzyme and the substrate must collide at the correct orientation with sufficient energy for the reaction to occur

describe the lock and key theory