OCR A A LEVEL BIOLOGY - BIOLOGICAL MOLECULES

what are hydrogen bonds

weak forces of attraction between molecules with different electronegativity values (between polar molecules)

what is the structure of water

Covalently bonded oxygen and two hydrogen atoms:

- the oxygen is delta negative

- the hydrogen is delta positive

- a polar molecule

why is ice less dense than water

when water freezes, the water molecules are held in a rigid lattice which holds the molecules further apart

why does water have a relatively high boiling point

hydrogen bonds between water molecules require extra energy to be broken

why is thermal stability in water important

water has a high specific heat capacity meaning a body of water maintains a fairly constant temperature

why is freezing in water important

ice is less dense than water so it floats which insulates the water and prevents it freezing completely this enables living organisms to survive below the ice

why is evaporation in water important

a lot of energy is needed to cause evaporation, which is used to cool the surface of living things

why is water being liquid important

it can flow and transport materials in living things

why is cohesion in water important

the attraction of water molecules produces surface tension, which creates a habitat on the surface

it also enables continuous columns of water to be pulled up the xylem

why is water being incompressible important

it can be pressurised and pumped in transport systems or used for support in hydrostatic skeletons

why is water being able to act as a reactant important

water molecules are used in a wide range of reactions such as hydrolysis and photosynthesis

why is water being able to act as a solvent important

as the molecules are polar, water can dissolve a wide range of substances by completely surrounding the ions

what is a polymer

a polymer is a long chain that comprises of similar, smaller molecules known as monomers

what is the monomer of polysaccharides

monosaccharides

what is the monomer of proteins

amino acids

what is the monomer of DNA and RNA

nucleotides

what is a hydrolysis reaction

a reaction involving the breaking of a bond in a molecule using up a water molecule

what is a condensation reaction

a reaction in which two molecules combine to form a larger molecule, and a water molecule is released

what elements are present in carbohydrates

C,H,O

what elements are present in lipids

C,H,O

what elements are present in proteins

C,H,O,N,S

what elements are present in nucleic acids

C,H,O,N,P

what is the general function of carbohydrates

they act as a source of energy, as a store of energy, and as structural units

what are the three main groups of carbohydrates

monosaccharides, disaccharides, polysaccharides

what are the properties of monosaccharides

soluble in water, insoluble in non-polar solvents and is a sweet reducing sugar

what are the two main groups of monosaccharides

pentose sugars, hexose sugars

what is the structure of alpha glucose

the OH group is below the carbon plane

what is the difference between alpha and beta glucose

the OH group on carbon one is flipped

what is the structure of beta glucose

the OH group is above the carbon plane

what bond joins two monosaccharides

glycosidic

when two monosaccharides join, what is made

a disaccharide

in what reaction do two monosaccharides join

condensation

what are the properties of disaccharides

they are soluble in water and are sweet; most are sweet reducing sugars with the exception of sucrose

how do two monosaccharides join

a hydrogen from one molecule's hydroxyl group joins to a hydroxide from another molecule's hydroxyl group and is released as water, then the remaining oxygen joins to the other molecule

which two monosaccharides join to form maltose

alpha glucose + alpha glucose

which two monosaccharides join to form sucrose

alpha glucose + fructose

which two monosaccharides join to form lactose

alpha glucose + galactose

what are the properties of polysaccharides

polysaccharides are very large, insoluble molecules

what is starch made from

amylose and amylopectin

what is the subunit in amylose

alpha glucose

what is the structure of amylose

amylose consists of a long, unbranched chain of α glucose subunits

the subunits are joined by a 1,4 glycosidic bond

what are the properties of amylose

since the hydroxyl group on carbon 2 of each subunit is hidden inside the coil, amylose is insoluble

its very compact

what are the uses of amylose

used for the storage of glucose subunits and energy in plant cells

what is the subunit in amylopectin

alpha glucose

what is structure of amylopectin

amylopectin is a long, branched chain of α glucose subunits

the subunits are joined by both 1,4 and 1,6 glycosidic bonds masking the molecule branched

what are the properties of amylopectin

its very compact

its glucose subunits are easily accessible

what are the uses of amylopectin

energy store in plants

what is the subunit in glycogen

alpha glucose

what is the structure of glycogen

glycogen is a long, branched chain of α glucose subunits

the subunits are joined by both 1,4 and 1,6 glycosidic bonds masking the molecule branched

what are the properties of glycogen

lots of branches (because more 1,6 bonds occur) meaning its glucose subunits are easily accessible, and can be removed in large quantities

insoluble

what are the uses of glycogen

an energy store in animals

what is the subunit in cellulose

beta glucose

what is the structure of cellulose

cellulose consists of a long, straight chain of β glucose subunits

the subunits are joined by a 1,4 glycosidic bond

what are the properties of cellulose

the hydroxyl group on carbon 2 is exposed, allowing hydrogen bonds to form

every second cellulose molecule is rotated 180 degrees to help form the glycosidic bond; this prevents the molecule from twisting

cellulose is strong and insoluble

what are the uses of cellulose

lots of cellulose molecules join together to form a microfibril; lots of microfibrils make up a macrofibril

plant cell wall

what are lipids

they are a large group of compounds like triglycerides, phospholipids and steroids

what is the structure of triglycerides

a triglyceride is a macromolecule containing one glycerol molecule and three fatty acid chains

what bonds are present in triglycerides, and in what reaction are these formed

ester bonds between the glycerol and the fatty acids are formed in condensation reactions

what are the properties of triglycerides

triglyceride molecules are rich in energy

what are the uses of triglycerides

storing excess energy, providing buoyancy and insulation (thermal and electrical)

what are fatty acids

long chains of carbon atoms with hydrogen atoms bonded to them

what is a saturated fatty acid

a saturated fatty acid is a fatty acid with no double bonds

what is an unsaturated fatty acid

an unsaturated fatty acid is a fatty acid with a double bond

what are the properties of saturated fatty acids

they have a high melting point so are most likely to be solid at room temperature

what are the properties of unsaturated fatty acids

they have quite a low melting point so are most likely to be liquid at room temperature

what is the structure of phospholipids

phospholipids are similar to triglycerides, but one of the fatty acid chains is replaced by a phosphate group

which end of a phospholipid is hydrophobic

fatty acid tails

which end of a phospholipid is hydrophilic

phosphate head

how do phospholipid bilayers form

phospholipids form bilayers, with the hydrophobic 'tails' in the centre and the hydrophilic 'heads' pointing outwards; this is the basis of all cell membranes

what is cholesterol

a steroid alcohol

what is the structure of cholesterol

it consists of four carbon-based rings

what is the function of cholesterol

it regulates the fluidity of the membrane, preventing it from becoming too fluid or too stiff

used to make the hormones oestrogen and testosterone, bile and vitamin D

what are proteins

long chains of amino acids folded into a specific 3D shape

what is the general structure of an amino acid

they have an amine group (NH2), a carboxyl group (COOH), a central carbon with a hydrogen attached, and a variable (R) group

what bonds form between two amino acids, and which reaction forms these bonds

peptide bonds are formed in condensation reactions

what is the primary structure of proteins

the sequence of amino acids joined by peptide bonds

what is the secondary structure of proteins

secondary structure is how the primary structure folds and coils, forming either an alpha (α) helix or a beta (β) pleated sheet. Hydrogen bonding is present.

what is the tertiary structure of proteins

tertiary structure is formed when the secondary structure is folded or coiled again to produce a 3D structure

what is the quaternary structure of proteins

when a protein is made up of more than one tertiary structure

what bonds are present in the tertiary structure of proteins

hydrogen, ionic, disulphide, hydrophobic and hydrophilic interactions

how do two amino acids join

the peptide bonds form between the amine group of one amino acid and the carboxylic acid group of another

what are the properties of globular proteins

these proteins are more water soluble and are active in metabolism; their activity relies on their 3D shape

what are the three examples of globular proteins

haemoglobin, amylase, insulin

what is the function of haemoglobin

transporting oxygen around the body

how many polypeptide chains make up haemoglobin

four:

two alpha chains

two beta chains

why is haemoglobin described as conjugated

it is conjugated as each subunit has a prothetic group, a haem group, attached containing a single iron ion (Fe2+)

what is the function of amylase

amylase is an example of an enzyme; it hydrolyses the bonds between glucose subunits in amylose

how is amylase adapted to its function

its compact globular shape contains an active site that's shape is complementary to the shape of the substrate

the active site contains at least one calcium ion that acts as a cofactor and is essential for the correct action of the enzyme

what is amylase

an enzyme

what is insulin

a hormone

what is the function of insulin

is used to stimulate the removal of excess glucose from the blood

how is insulin adapted to its function

the molecule has a specific 3D shape that is complementary to the to the shape of glycoprotein receptors in the liver

what are the three examples of fibrous proteins

collagen, keratin and elastin

what are the properties of fibrous proteins

they tend to have a regular sequence of amino acids, aren't soluble in water and form fibres that have structural functions

how many polypeptide chains does collagen have

three

what are the properties of collagen

strong, not easily stretched

what are the functions of collagen

provides strength in the arterial walls, in tendons and in bone

what are the properties of keratin

protects delicate parts of the body

how many polypeptide chains does elastin have

two

what are the functions of keratin

strong, impermeable to water