biological molecules

molecule

a substance containing at least two elements chemically bonded together

water’s polar structure

oxygen atom pulls the electrons (from the covalent bonds between hydrogen atoms and oxygen atom) more towards itself

it has a slight/partial negative charge

therefore the hydrogen atoms become slightly/partially positively charged

cohesion

the partially positively charged hydrogen atoms are attracted to the partially negatively charged oxygen atom of each water molecule

this causes a hydrogen bond to form

the hydrogen bonds are weak individually, but when many water molecules stick to each other, the hydrogen bonds are collectively strong

this allows for water molecules to stick to each other

water as a solvent, examples

many compounds are ionic, so made of positive ions and negative ions

when added to water, they split into their ions

the positive ions are attracted to the partially negative oxygen atom, and the negative ions are attracted to the partially positive hydrogen atoms

each ion is surrounded by water molecules and the compound dissolves

water dissolves and transports many substances like hormones and ions around the body in the blood plasma

most biological reactions take place in solution - like in the cytoplasm of eukaryotes and prokaryotes

water has a high specific heat capacity

a lot of energy is needed to raise the temperature of 1 gram of water by 1°C (so lots of energy needed to break hydrogen bonds and heat the water)

so many hydrogen bonds between the water molecules can absorbs a lot of energy before being broken

this means that water is resistant to rapid changes in temperature

this makes it a stable environment for marine life, and allows body temperature to remain at a fairly stable temperature

water as a coolant

water has a high latent heat of vaporisation

so lots of energy is needed to evaporate 1 gram of water (to break hydrogen bonds and change its state from liquid to gas)

when water evaporates from the surface of the skin it takes heat energy away from the surface, cooling the organism down

water as a habitat

water has a high specific heat capacity and high latent heat of vaporisation

so does not change state or temperature easily

providing a stable environment for organisms to live in

however at low temperature water freezes into ice

water molecules are held further apart in ice, so when solid is less dense

ice as a result floats, forming an insulating layer at the surface of ponds and lakes, so water below the layer does not freeze

organisms within the water can move and survive

water as a metabolite

water is involved in many chemical reactions inside organisms

hydrolysis - water helps to break down complex molecules

condensation - releases water to join molecules together

photosynthesis - water used as a raw material

water as a transport medium

cohesion - the tendency of water molecules to stick together via hydrogen bonds

adhesion - the tendency of water molecules to stick to other polar molecules and surfaces

this helps water to flow through organisms and carry substances along with it

example: in the xylem, water travels in a continuous column

adhesion

the partial negative charge of the oxygen atom in the water molecule is attracted to a partial positive charge of another polar molecule or surface, causing capillary action and continuous fluid motion

surface tension

water molecules are attracted to other water molecules by hydrogen bonds; cohesion

above the water, there is no air, so water molecules are not attracted to the air

this causes an inward pull from the other water molecules, creating a dome shape on the surface of the water

monomer

small basic molecule, one singular unit

polymer

large molecule of many monomers joined together by covalent bonds in a repeating chain

macromolecule

any very large molecule, could be a polymer if it has a repeating chain

making polymers from monomers

condensation reaction

water is released when a polymer is formed

when the hydroxide reacts with hydrogen from the hydroxyl groups

joining two monomers together to create a polymer

breaking down polymers into monomers

hydrolysis reaction to reform the two monomers

water is added to the polymer to reform the two monomers

break down of the bond between monomers in a polymer using water

terms specific to carbohydrates

monomer - monosaccharide

polymer - polysaccharide

made of carbon, oxygen, and hydrogen atoms

monosaccharides are polar so dissolve in water

alpha glucose and beta glucose

both are hexose sugars - 6 carbon atoms in its structure

alpha and beta are structural isomers - same molecular formula but the atoms are connected differently

the OH group of carbon 1 is reversed

draw alpha glucose

c1 - H - CO - OH

c2 - H - C - OH

c3 - OH - C - H

c4 - H - C - HO

c5 - C - H (DOWN) - O (TO THE RIGHT)

c6 - CH₂OH

draw beta glucose

c1 - OH - C - H

c2 - H - C - OH

c3 - OH - C - H

c4 - H - C - HO

c5 - C - H (DOWN) - O (TO THE RIGHT)

c6 - CH₂OH

ribose and deoxyribose

pentose sugars

disaccharide formation

is made of two alpha glucose molecules

the carbon 1 and carbon 4 hydroxyl groups react to form water

oxygen in the middle holds the two monosaccharides together after the water molecule (condensation) is removed to form a disaccharide (two glucose molecules held together in a glycosidic bond)

add water to break the glycosidic bond and obtain the monosaccharide sugars

disaccharide name: maltose

formed from two alpha glucose molecules

used in starch digestion

disaccharide name: sucrose

made from alpha glucose and fructose

transported sugar in plants

disaccharide name : lactose

made from beta galactose and beta glucose

found as the sugar in milk

glycosidic bond description

are alpha when the OHs are on the same plane

are beta when the OHs are on different planes and form a curved glycosidic bond

polysaccharide

when more than two monosaccharides are joined together by a glycosidic bond created in a condensation reaction

starch (amylose) structure, type of bonding, and function

coiled structure of long unbranched alpha glucose

is compact so good for storage

forms alpha 1,4 glycosidic bonds

starch is insoluble so does not allow osmosis, so no swelling and good for storage

starch (amylopectin)

long branched chains of alpha glucose

branches allow for easy and quick release of glucose

forms alpha 1,4 and 1,6 glycosidic bonds

glycogen

made up of alpha glucose, has more side branches

is compact and good as storage molecules

forms alpha 1,4 and more 1,6 glycosidic bonds than amylopectin

stored glucose can be released quickly

glucose can be broken down quickly for energy release

cellulose

made up of long unbranched chains of beta glucose

chains linked by hydrogen bonds to form strong fibres called microfibrils - provides structural support

forms beta 1,4 glycosidic bond - each alternating beta glucose is inverted to allow a straight bond between the beta glucose molecules so the cellulose chains are straight and not coiled

high tensile strength and structural support