Biological molecules

Organic molecules

carbon, hydrogen, oxygen

Carbohydrates, proteins, lipids and nucleic acids

- respiratory substrates which provide energy
- structure on cell membranes + cell walls

- source of energy
- help to insulate organisms
- waterproofing
- form membranes and hormones

- Main component of cellular structures
- Form enzymes and chemical messengers

- Form DNA and RNA which make up genetic material
- Code for sequence of amino acids for all proteins

Smaller units from which larger molecules are made

Molecules made from repeating units joined together

Joins two monomers together with the formation of a covalent bond and involves the elimination of a molecule of water

Breaks the covenant bond between two monomers and involves the use of a water molecule

individual sugar molecules that make up disaccharides and polysaccharides

Alpha glucose, beta glucose, galactose + fructose

formed when two monosaccharides join through a condensation reaction forming a glycosidic bond between the two OH groups

Maltose, sucrose + lactose

formed when more than two monosaccharides are joined together by a condensation reaction

contains six carbon atoms

contains five carbon atoms

two or more compounds with the same formula but a different arrangement of atoms in the molecules

Different due to different arrangement of atoms

- Respiration
- Used to make glycogen + starch in plants

Building block of cellulose

Used to make lactose

Alternative to supply energy when there is a lack of glucose

Electron donor in chemical reactions + can be broken down into glucose

2 alpha glucose

Efficient energy transfer + increased energy store

Glucose + fructose

Provides energy

glucose and galactose

All monosaccharides and some disaccharides are reducing sugars- they can lose or donate electrons to other compounds

Sucrose

- Add dilute HCl and heat in water bath
- Add an alkali to neutralise
- Add excess Benedict's reagent to the sample
- Heat in the water bath above 80 degrees

- Made of 2 types of polymers: amylose + amylopectin

- Store excess glucose in plants
- hydrolysed to release glucose for respiration

- Polysaccharide formed from glucose monomers joined together by 1-4 glycosidic bonds
- Long unbranched chain forming a coiled spring shape
- Coils held together by many weak hydrogen bonds

Coils make it compact for efficient storage of glucose

- Polysaccharide formed from glucose monomers joined together by 1-4 and 1-6 glycosidic bonds
- Long branched chain

High surface area for efficient hydrolysis

- Long branched chain
- made from condensation reaction of alpha glucose bonded together by 1-4 and 1-6 glycosidic bonds

Store carbohydrates in mammals

- lots of branches to increase surface area for efficient hydrolysis
- compact molecule for storage

- 1-4 glycosidic bonds between beta glucose where every 2nd beta glucose is inverted
- Forms a straight unbranched chain

Hydrogen bonds attach each cellulose chain together to form thicker fibres called microfibrils

- Support cell wall
- Allows cells to become turgid

- Hydrogen bonds between the cellulose chain make the microfibrils very strong but still flexible to provide support

glycerol molecule + 3 fatty acid chains

Ester bonds between the 3 OH groups on the glycerol and the OH groups on the fattty acids formed by condensation reactions

A glycerol molecule, a phosphate group and two fatty acid chains

Ester bond between 2 OH groups on the glycerol and the OH group of each fatty acid chain formed by condensation reactions

Hydrophilic- attracted to water

Hydrophobic- repulsed by water

Fatty acid chains are hydrophobic making lipids insoluble in water
-> they bundle together as insoluble droplets as their tails face inwards and the glycerol heads shield them from water

- Phosphate group is hydrophilic and the fatty acid chains are hydrophobic allowing phospholipids to form bilayers which make up membranes around a cell

Energy stores- lots of energy released when the fatty acid chain is broken down

Membranes + hormones

- no double bonds
- maximum amount of hydrogen it can hold
- solid at room temperature ( high melting point)

- Double bonds between carbon atoms
- Contain fewer hydrogen atoms
- Bends and kinks in chain
- lower boiling point

A double layer formed by phospholipids with their hydrophilic heads facing outwards and their hydrophobic tails facing inwards

- Centre of the bilayer is hydrophobic so water soluble substances cannot easily pass through
- This creates a barrier and allows separation of solutions allowing different conditions to be created either side of the membrane

Amino acids (monomers)

20

Peptide bond ( -C-N-)

Dipeptide

Polypeptide

Number and sequence of amino acids which can determine the 3D shape or tertiary structure

- Hydrogen bonds between amino acids in the chain
- Chain can coil into alpha helix
- Chain can fold into beta pleated sheets

Makes the structure stable

Alpha helices

- 3D shape of the polypeptide chain
- creates a specific shape due to the sequence of amino acids

- hydrogen bonds
- ionic bonds
- disulphide bridges
- van der Waals forces

If proteins are made of more than one polypeptide chain then they are joined together to create a quaternary structure

Antibodies + haemoglobin

Between the OH group of one amino acid and the C=O group of another

Form between sulfur-containing amino acids that are near each other

Between R groups

Weak intermolecular forces that hold the tertiary structure in shape

globular + fibrous

Soluble + spherical in shape

- straight chain polypeptides
- insoluble

Straight chain polypeptides that are side by side and held together by hydrogen bonds

More resistant to physical + chemical attack

- Heat energy increases the kinetic energy of the molecule making it vibrate more
- The vibrations are strong enough to break the intermolecular forces + affect the shape of the protein

Extreme changes in pH can disrupt the ionic charges on the R groups, resulting in ionic bonds breaking

A biological catalyst that speeds up chemical reactions

Catalyse specific metabolic reactions at a cellular and extracellular level without being used up in the reaction

Proteins with a 3D structure
Specifically shaped active site that is complementary to a certain substrate

When the enzyme binds to the substrate

Lowering the activation energy of a reaction:
- hold substrates close together, reducing repulsion and allowing them to bond more easily
- put more strain on bonds of a substrate allowing them to break apart more easily

The active site is not exactly complimentary to the substrate molecule. When the substrate collides with the enzyme the active site can change shape slightly to fit around the substrate and form an ES complex

- Inc enzyme increases active sites available
- More ES complexes can form
- Rate of reaction increases until substrate concentration becomes the limiting factor

-Inc substrates inc rate of reaction
- more substrate available meaning more collisions
- more ES complexes can form
- Rate of reaction will slow as enzyme concentration becomes the limiting factor and all active sites are occupied

As temperature increases so does the rate of reaction:
- more kinetic energy so molecules move faster increasing the number of collisions and ES complexes formed

Enzyme molecule vibrates too much and the bonds which maintain the tertiary structure are broken -> active site changes shape and no more ES complexes can form as they enzyme is permanently damaged

Above and below the optimum pH pf an enzyme the H+ and OH- ions disrupt the ionic and hydrogen bonding that hold the tertiary structure in shape
-> site of the active site can change and no ES complexes can form and the enzyme is permanently denatured

Have a similar shape to the substrate so can compete with the substrate and bind to the active site and block it -> prevent ES complexes from forming

- Bind to the allosteric site
- causes the shape of the active site to change to it is no longer complimentary and ES complexes can't be formed