2.2 biological molecules

calcium

chemical symbol: Ca2+

role in organisms: Nerve impulse transmission, stomatal opening

sodium

chemical symbol: Na+

role in organisms: Nerve impulse transmission, kidney function

potassium

chemical symbol: K+

role in organisms: production of nitrate bacteria

hydrogen

chemical symbol: H+

role in organisms: nerve impulse transmission, muscle contraction

ammonium

chemical symbol: NH4+

role in organisms: catalysis of reactions, pH determination

nitrate

chemical symbol: NO3-

role in organisms: catalysis of reactions, pH determination

hydrogen carbonate

chemical symbol: HCO3-

role in organisms: cell membrane formation, ATP and nucleic acid formation, bone formation

chloride

chemical symbol: Cl-

role in organisms: balance positive charge of sodium and potassium ions in cells

phosphate

chemical symbol: PO₄³⁻

role in organisms: nitrogen supply to plants for formation of amino acids

hydroxide

chemical symbol: OH-

role in organisms: maintenance of blood pH

chemical formula for ammonia

NH3

six most abundant elements in biological molecules

O, C, H, N, S, P

why is water polar?

because there is an uneven distribution of the electrons within the molecule. Oxygen has a slightly negative charge and hydrogen has a slightly positive charge.

what is the angle between the two hydrogen atoms in a water molecule?

104.5

high latent heat of vaporisation (explanation and importance)

Explanation: a relatively large amount of energy is needed for water molecules to evaporate.

importance: water can help to cool down living things and keep their temperature stable

high specific heat capacity

the amount of heat energy required to raise the temperature of 1kg of water by 1 degree Celsius

high specific heat capacity (explanation and importance)

explanation: the movement of water molecules are restricted because of the H bonds between them. Lots of thermal energy is needed to continually increase the KE of water molecules to break these bonds

importance: living things need a stable temp for enzyme-controlled reactions. Aquatic organisms need a stable environment

surface tension (explanation and importance)

explanation: H bonds cause water molecules at the surface to be more attracted to water molecules beneath rather than air molecules above

importance: organisms such as pond skaters can ‘walk on water‘

ice is less dense than liquid water (explanation and importance)

explanation: ice is less dense than water due to its crystalline structure

importance: floating ice on lakes and oceans insulates the water below it, meaning it is less likely to freeze and kill the organisms in it. Other organisms live on floating ice

metabolic (explanation and importance)

explanation: water is a reactant in many metabolic reactions

importance: water can be used to hydrolyse molecules in reactions such as photosynthesis

solvent (explanation and importance)

explanation: the tiny charges on water molecules mean they are attracted to and surround other molecules that have charges on them

importance: molecules and ions can move around and react in water (e.g. cytoplasm have over 70% water). molecules and ions can be transported around living things whilst dissolved in water.

cohesion (explanation and importance)

explanation: H bonds mean water molecules ‘stick‘ to each other

importance: transpiration requires water molecules to stick together in tall columns to move up the xylem and towards the leaves

liquid at room temperature (explanation and importance)

explanation: H bonds between water molecules make it more difficult for them to escape to become a gas

importance: habitat (rivers, lakes), major component of tissues in living organisms, reaction medium for chemical reactions, effective transport medium (e.g. in blood)

general formula for carbohydrates

(CH₂O)_n

pentose sugars

monosaccharides containing 5 carbon atoms

difference between alpha and beta glucose

alpha glucose has OH below the C₁ atom, beta glucose has OH above C₁

two important pentose molecules and why?

the structural isomers ribose and deoxyribose. These are important because they are constituents of RNA and DNA (forming its backbone)

difference between ribose and deoxyribose

ribose has one H atom and one -OH group attached to C₂, whereas deoxyribose has 2 H atoms and no -OH group.

dipole

a molecule that has a partially positive charge and a partially negative charge

hydrogen bonding

the attraction between a partially positive charged hydrogen atom and a highly electronegative atom

enthalpy of vaporisation

the amount of energy that must be added to a liquid substance to transform the quantity of that substance into a gas

enthalpy of fusion

the amount of energy that must be applied to a solid substance in order to trigger a change in its physical state and convert it into a liquid

cohesion

the attraction between the same type of molecule

adhesion

the attraction between unlike molecules

why does ice float in water?

because water is less dense in solid form. as water freezes, more hydrogen bonds are formed between the molecules that are now arranged in fixed, hexagonal patterns. The larger space between the water molecules makes the ice less dense.

the bond formed between two glucose molecules

alpha 1,4 glycosidic

hydrolysis reaction

a reaction in which the chemical bond between two molecules is broken, resulting in water being formed

condensation reaction

a reaction which joins monomers by chemical bonds and it involves the elimination of a water molecule

maltose monosaccharide(s)

alpha glucose

lactose monosaccharide(s)

galactose and alpha glucose

sucrose monosaccharide(s)

alpha glucose and fructose

glycogen being highly branched

stored glucose can be released easily from the ends or glucose can be added on easily. Glucose can be released quickly when required

glycogen being a compact molecule

large amounts of glycogen and therefore energy can be stored in a small space

glycogen being insoluble

does not affect the water potential of cells that it is stored in

glycogen being metabolically inactive

stable energy store

properties of amylose

• helix shape

• compact

• soluble

• small- takes up less space when stored

• H bond is situated inside of the coil- helps keep it in shape

properties of amylopectin

• insoluble

• many branches mean bonds can be easily broken and reformed to release energy

bond that make the branches of amylopectin

alpha 1,6 glycosidic

how do macrofibrils provide the cell wall with more strength?

they run in all directions criss-crossing the wall in all directions

structure of cellulose

Cellulose is a long chain of beta-glucose. Beta-glucose molecules are linked by glycosidic bonds to form linear cellulose chains that are unbranched.

which polysaccharides are found in plants

amylose, amylopectin, cellulose

which polysaccharide is found in humans?

glycogen

where are amylose and amylopectin stored?

in starch grains

where is glycogen found?

in the liver

where is cellulose found?

in the cell wall

which polysaccharides are a form of starch?

amylose and amylopectin

what is the monomer of amylopectin, amylose and glycogen?

alpha glucose

what is the monomer of cellulose?

beta glucose

which polysaccharides are branched?

glycogen and amylopectin

which polysaccharides are branched?

amylopectin and glycogen

which polysaccharides are spiralled?

amylose and amylopectin

which polysaccharides have hydrogen bonds holding its shape?

amylose, amylopectin, cellulose

explain how two nitrogen molecules form a triple covalent bond to produce N₂

share 6 electrons between 2 nitrogen atoms to form a full outer shell

molecular formula of maltose

C₁₂H₂₂O₁₁

roles of carbohydrates

• energy supply for cells

• energy storage - sugars can be stored as complex carbohydrates

• structural components - cellulose and chitin are used in cell walls

• cellular recognition - Glycoproteins help cells identify each other and communicate

• Building blocks for biological molecules - Deoxyribose and ribose can be used to make nucleic acids

monosaccharide

• carbohydrates made of one subunit

• examples: glucose, fructose, galactose (all hexose sugars)

disaccharide

• carbohydrates made of two subunits (two mmonosaccharides)

• examples: maltose, lactose, sucrose

polysaccharide

• carbohydrates made of more than two subunits

• examples: starch, glycogen, cellulose

properties and uses of glucose

• soluble - The hydroxyl groups can form hydrogen bonds with water, so it can be transported around organisms.

• Its bonds store lots of energy - This energy is released when the bonds are broken

what happens when two monosaccharides join?

a hydroxyl group (OH) of one monosaccharide reacts with a hydroxyl group (OH) of another monosaccharide. This forms a glycosidic bond, and a water molecule (H₂O) is released.

starch

a polysaccharide used by plants to store excess glucose. It is made up of many alpha-glucose monomers joined via glycosidic bonds to form chains.

Starch being insoluble

It does not affect the water potential, so water does not enter cells by osmosis. 

starch being large

It cannot diffuse out of cells.

starch having many side branches

These allow enzymes to hydrolyse the glycosidic bonds easily to rapidly release glucose. 

starch being coiled

This makes it compact so that a lot of glucose can be stored in a small space. 

structure of cellulose

• made of long chains of beta glucose, which are joined via glycosidic bonds.

• Every other beta-glucose molecule is flipped upside down

Why does every other beta-glucose molecule need to be flipped?

When they are lined up next to each other, the hydroxyl groups on C₁ and C₂ are too far from each other to react. So, inverting every other beta-glucose brings them close enough to react.