biological molecules
water
a reactant in lots of chemical reactions e.g. hydrolysis
water is a solvent so substances dissolve in it- most biological reactions take place in solutions
water transports substances e.g. oxygen
water helps controls temp because of its high shc and high lhv
water is a habitat
structure
a molecule of water= 2 hydrogens and 1 oxygen atom covalently bonded
shared negative electrons are pulled towards oxygen, the other side of each hydrogen is left with a SLIGHT POSITIVE CHARGE
the unshared negative electrons on oxygen give it a slight negative charge
water is a POLAR MOLECULE
slightly negatively charged oxygen atoms attract the slightly positively charged hydrogen atoms creating HYDROGEN BONDS
properties and functions
hydrogen bonds give water a high shc
specific heat capacity= energy needed to raise the temp of 1 gram of a substance by 1 degree
hydrogen bonds ABSORB LOTS OF ENERGY
this means that water doesn't experience rapid temp changes (makes it a good habitat)
hydrogen bonds give water a high lhv
it takes a lot of energy to break hydrogen bonds between molecules
so a lot of energy is used up when it evaporates
creates a cooling effect as it takes away lots of energy when it evaporates
waters polarity makes it v cohesive
cohesion= attraction between molecules of the same type e.g. two water molecules
being polar cause water molecules to stick together / be cohesive
this helps water flow and makes it good for transporting substances, water is pulled up the xylem
waters polarity makes it a good solvent
slightly positive end of water molecule will be attracted to negative ion and the slightly negative end of water will be attracted to positive ions
this causes ions to dissolve as they are surrounded by water
e.g. ions dissolve in the water in blood and can be transported around body
less dense when solid
at low temps water freezes
water molecules are held further apart in ice than they are in liquid water because each water molecules forms 4 HYDROGEN BONDS to other water molecules making it a lattice
this causes water to float and be less dense
ice forms an insulating layer on top of water preventing water below freezing so organisms can still move
carbohydrates
monosaccharides
= the monomers that make up carbonhydrates
glucose
two types of glucose alpha and beta
glucose= hexose monosaccharide (it has 6 carbons)
function= main energy source in animals and plants
structure makes it SOLUBLE in water (not in non polar solvents) so its easy to transport
ribose
=pentose monosaccharide
all carbohydrates are made up of: carbon, oxygen and hydrogen
polysaccharides and disaccharides
monosaccharides are joined together by GLYCOSIDIC BONDS
two monosaccharides join together by a CONDENSTAION REACTION releasing one MOLECULE OF WATER- a hydrogen on one molecule and an OH on another (requires enzyme)
the reverse reaction is hydrolysis
starch
cells get energy from glucose and plants store it as starch (when its needed it breaks down starch to form glucose again)
made up of two alpha glucose polysaccharides:
amylose
a long UNBRANCHED chain of a-glucose (1 to 4)
angles of the glyosidic bonds give it a COILED STRUCTURE
makes it compact and energy dense
amylopectin
a long BRANCHED chain of a-glucose (branches are 1 to 6, others are 1 to 4
side branches allow enzymes to easily break down molecule and reach glyosidic bonds easily
allows energy to be released quickly
INSOLUBLE IN WATER- prevents water from entering cells by osmosis which would make them swell- makes it good for storage
glycogen
animal cells store glucose as glycogen
similar to amylopectin except its MORE BRANCHED - means that stored glucose can be released quickly which is important for energy release in animals (1 to 4)
its also very compact
not very soluble to water (more soluble than starch)
celluslose
made from long UNBRANCHED chains of BETA-GLUCOSE
when b-glucose molecules bond they form straight cellulose chains
the cellulose chains are linked together by HYDROGEN BONDS to form strong fibres called MICROFIBRILS
strong fibres means that cellulose provides structural support for cells
lipids
triglycerides
triglycerides are macromolecules- complex molecule with a relatively large molecular mass
contain carbon, hydrogen and oxygen
structure= one molecule of glycerol and 3 fatty acids attached to it
contain ester bonds
triglycerides are synthesized by the formation of an ester bond between each fatty acid and the glycerol molecule
each ester bond is formed by a CONDENSATION REACTION where one molecule of water is released
the process by which ester bonds are synthesized = ESTERIFICATION
ester bonds are broken down by HYDROLYSIS
Fatty acids can be saturated and unsaturated
saturated
fatty acids don't have double bonds between carbon atoms
unsaturated
have at least one double bond between carbon atoms
causes chain to kink
phospholipids
phospholipids are macromolecules
structure= one glycerol, 2 fatty acids and a phosphate group
phosphate group is hydrophilic and the fatty acids are hydrophobic
structure and functions
triglycerides
ENERGY STORAGE MOLECULES
long hydrocarbon tails of fatty acids contain lots of chemical energy- lots of energy is released when broken down (2x as much energy as carbohydrates)
INSOLUBLE- don't cause water to enter cells by osmosis which would make them swell. triglycerides bundle together as insoluble droplets (hydrophobic tails face inwards)
phospholipids
FOUND IN CELL MEMBRANES
heads are hydrophilic, tails are hydrophobic- form a double layer with heads facing outwards
centre of bilayer is hydrophobic so water-soluble substances cants easily pass through- acts as a barrier
cholesterol
small size and flattened shape- allows cholesterol to fit between phospholipid molecules in membrane
they bind to hydrophobic tails of phospholipids causing them to pack more closely together- makes membrane more rigid/ controls fluidity
proteins
amino acids are monomers in proteins
dipeptide is formed when two amino acids join together
a polypeptide is formed when more than two amino acids join together
proteins are made of multiple polypeptides
structure
all amino acids have the same general structure - a carboxyl and an amine group attached to a carbon atom
each amino acid has a different variable group
amino acids are joined together by PEPTIDE BONDS
joined together by a condensation reaction and reverse is hydrolysis
protein structural levels
primary structure
= the sequence of amino acids in the polypeptide chain
different proteins have different amino acids in their primary structure
secondary structure
hydrogen bonds form between nearby amino acids in chain
cause the chain to coil into an alpha helix or a beta pleated sheet
tertiary structure
the polypeptide chain is folded and coiled further
more bonds form
polypeptide chain forms a 3D structure
other bonds which form
ionic interactions
weak attractions between negatively charged R groups and positively charged R groups on different parts of the molecule
disulfide bonds
whenever two molecules of the amino acid CYSTEINE come close together, the sulfur atom in one of the cysteine bonds to the sulfur in the other cysteine
strongest type of bond available to form
hydrophobic and hydrophilic interactions
when hydrophobic R GROUPS are close together in the protein they clump together
This means hydrophilic R groups are more likely to be pushed to the outside
effects how protein folds and coils into finals structure
hydrogen bonds
form between a slightly positively charged hydrogen atoms in some R groups and slightly negatively charged atoms in other R groups on the peptide chain
quaternary structure
proteins are made up of multiple polypeptide chains held together by bonds
the way the protein is assembled
formation of peptide bonds
globular proteins
hydrophilic R groups on the amino acid are pushed to outside of molecule
makes globular proteins SOLUBLE
haemoglobin
carries oxygen around body in red blood cells
has the haem R group which contains iron
oxygen bonds to iron
round and compact
fibrous proteins
are INSOLUBLE
e.g. collagen
forms supportive tissue in animals so needs to be strong and flexible
made of 3 polypeptide chains that are coiled into a triple helix
the chains are interlinked by strong COVALENT BONDS
minerals can bind to triple helix to increase rigidity
made of 4 polypeptide chains
tough and rope shaped
inorganic ions
an ion is an atom with a charge
ion with a positive charge= cation
ion with a negative charge= anion
an organic ion DOESNT CONTAIN CARBON
calcium
acts as a cofactor for many enzymes
involved in transmission of nerve impulses
involved in release of insulin from pancreas
sodium
regulates fluid balance in body
muscle contraction
generating nerve impulses
potassium
activates enzymes needed for photosynthesis
muscle contraction
generating nerve impulses
regulating fluid balance
hydrogen
affects pH of substances
involved in photosynthesis reactions
ammonium
absorbed from soil by plants
source of nitrogen (needed for amino acids and nucleic acids)
nitrate
important source of nitrogen (used to make amino acids and nucleic acids)
hydrogencarbonate
acts as a buffer which helps maintain blood pH
chloride
helps maintain pH of blood in gas exhange
acts as a cofactor for amylase enzyme
involved in some nerve impulses
phosphate
involved in photosynthesis and respiration reactions
needed for the synthesis of biological molecules e.g. phospholipids
hydroxide
affects PH of substances
biochemical tests for molecules
benedicts test for sugars
reducing sugars
reducing sugars= all monosaccharides and some disaccharides
1) add benedicts reagent to sample
2) heat test tube in water bath as 80 degrees for 5 minutes
if the test if positive a coloured precip will form (blue to brick red)
4) the higher the concentration the further the colour change goes
non reducing sugars
1) add dilute HCl to sample
2) place in water bath at 80 degrees for 5 minutes
3) then add sodium hydrogencarbonate
Then carry out test as you would for reducing sugar
if test is positive a coloured precip will form blue to brick red
reagent strips test for glucose
dip strip in sample
if present colour change occurs
can be compared to chart to determine concentration
used to diagnose diabetes by testing urine
iodine test for starch
add iodine solution to sample
if present solution turns blue/ black
if not present stays browny orange
biurets test for protein
1) add a few drops of sodium hydroxide solution to make sample alkaline
2) add copper sulfate solution
if present turns lilac, if not stays blue
emulsion test for lipids
1) shake test sample with ethanol for a minute
2) then pour solution into water
if present solution turns milky, if not solution stays clear
colorimetry
a colorimeter= a device that measures the strength of a coloured solution by seeing how much light passes through it
the more concentrated the colour, the higher the absorbance is
1) do a benedicts test on samples
2) remove precipitate and leave for 24 hours or centrifuge
3) use a colorimeter (with RED filter) to measure absorbance of sample remaining in tube
4) do a calibration curve of absorbance against glucose concentration
every 3rd amino acid is glycine
left handed helix
functions
source of energy
energy store
structural units
reactions
-a glucose + a glucose= maltose
-a glucose + fructose= sucrose
-b galactose + a glucose= lactose
-b glucose + b glucose= cellobiose
bundles of microfibrils form macrofibrils which are very strong
microfibrils run in different directions to add more strength
prevents cells from bursting when turgid
functions
energy source= triglycerides can be broken down in respiration to produce energy
energy store
insulation
buoyancy= less dense than water
protection for organs
provides membrane stability, is partially permeable
its a steroid alcohol