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Topic 1: biological molecules - Coggle Diagram
Topic 1: biological molecules
Monomers and Polymers
Monomers
are small units which are the components of larger molecules, examples include
monosaccharides
such as
glucose, amino acids
and
Nucleotides
. **Polymers are molecules made from many monomers joined together.
Monomers are joined by a chemical bond in a
condensation reaction
whereby a water molecule is eliminated.
Hydrolysis
is the opposite of a condensation reaction and is when water is added to break a chemical bond between two molecules.
Lipids
Lipids
are biological molecules made of carbon, hydrogen and oxygen which are only soluble in
organic solvents
such as alcohols. The main lipid types are
triglycerides
and
phospholipids
.
Triglyceride
Triglycerides
are lipids made of one molecule of glycerol and
three fatty acids
joined by
ester bonds
in condensation reactions. There are many different types of fatty acids which vary in chain length, presence and number of double bonds.
Structure related to properties
High ratio
of energy storing
carbon-hydrogen bonds
to
carbon atoms
and therefore they are an
excellent energy store
.
A
low mass to energy ratio
meaning that they are a good storage molecule, with a lot of energy being stored in a small volume. This is beneficial for animals as it is less mass to move around.
Being
large and non-polar
lipids are
insoluble
in water and therefore their storage does not affect the water potential of cells.
A
high ratio
of
hydrogen-oxygen atoms
means that triglycerides
release water
when they are
oxidised
and therefore provide an important source of water for organisms to live in dry environments.
Saturated + unsaturated
Saturated lipids
such as those found in animal fats -
don't contain any carbon-carbon double bonds
.
Unsaturated lipids
which can be found in
plants
- unsaturated lipids
contain carbon-carbon double bonds.
Molecule bends and kinks. As a result unsaturated fats cannot pack together as tightly and are therefore liquid at room temperature.
Phospholipids
In
phospholipids
, one of the fatty acids of a triglyceride is substituted by a phosphate containing group. Phosphate heads are
hydrophilic
and tails are
hydrophobic
and as a result phospholipids form
micelles
when they are in contact with water. The molecule is therefore polar.
Phospholipids structure related to their properties
In an aqueous environment being polar means a
bilayer
can be formed.
The hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane.
Their structure allows them to form
glycolipids
with carbohydrates which are important on the cell surface membrane for
cell recognition
.
Emulsion test
An emulsion test can be used to test for the
presence of lipids
Take a completely grease free test tube and add 2cm3 of the sample to be tested and 5cm3 of ethanol.
Shake the test tube thoroughly to dissolve all the lipid in the solution.
Add 5cm3 of water and shake gently.
A cloudy-white colour indicates the presence of a lipid.
As a control repeat the experiment using water as the sample, the final solution should remain clear.
Carbohydrates
Carbohydrates
are molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides. A single monomer is called a
monosaccharide
with a pair of monomers being called a
disaccharide
. Combining many monosaccharides results in the formation of a
polysaccharide
. These are all joined together with a
glycosidic bond
formed in
condensation reaction
.
Monosaccharides
Glucose
is a monosaccharide containing 6 carbon atoms in each molecule, and is the main
substrate for respiration
and therefore of great importance. It has two isomers- alpha and beta glucose.
Common monosaccharides include glucose, galactose and fructose. These are typically sweet-tasting, soluble substances which have the general formula
(CH2O)n
where n can any number from 3 to seven.
Disaccharides
Two monosaccharides can join together in a condensation reaction to form a
disaccharide
.In this process a molecule of water is produced.
Examples of some common disaccharides and how they are formed are shown below:
Maltose
is a disaccharide formed by condensation of
two glucose molecules
.
Sucrose
is a disaccharide formed by condensation of
glucose + fructose
Lactose
is a disaccharide formed by condensation of
glucose + galactose
.
Polysaccharides
Polysaccharides
are formed from many glucose units joined together:
Glycogen
and
starch
which are both formed by the condensation of
alpha glucose
.
Cellulose
is formed by the condensation of
beta glucose
.
Glycogen
Glycogen
is the main energy storage molecule in animals and is formed from many molecules of
alpha glucose
joined together by
1,4 and 1,6 glycosidic bonds
. It has a
large number of side branches
meaning that energy can be released quickly as enzymes can act simultaneously on these branches. Moreover, it is a relatively
large but compact
molecule thus maximising the amount of energy it can store. Finally being insoluble means it will not affect the water potential of cells and cannot diffuse out of cells.
Starch
Starch
stores energy in plants and is a mixture of two polysaccharides called
amylose and amylopectin
Amylose
- amylose is an
unbranched chain
of glucose molecules joined by
1,4 and 1,6 glyosidic bonds
, and as a result is
coiled
and thus a very
compact
molecule storing a lot of energy.
Amylopectin
is
branched
and is made up of glucose molecules joined by
1,4 and 1,6 glyosidic bonds
. Due to the presence of many
side branches
these can be acted upon simultaneously by many enzymes and thus broken down to release its energy.
Some key properties of starch that make it suitable are that; its insoluble so will not affect cell water potential, it is compact so a lot of energy can be stored in a small space and when it is hydrolysed the released alpha glucose can be transported easily.
Cellulose
Component of cell walls in plants and is composed of long, unbranched chains of
beta glucose
which are joined by glyosidic bonds.
Microfibrils
are strong threads which are made of long cellulose chains running parallel to another that are joined together by
hydrogen bonds
forming strong cross linkages. Cellulose is important in stopping the cell wall from bursting under osmotic pressure. Thus means that cells stay turgid and rigid, helping to maximise the surface area of plants for photosynthesis.
Biochemical test - Benedict's reagent
Benedict's reagent
can be used to test for the presence of
reducing sugars
. All monosaccharides and some disaccharides are reducing sugars. These are therefore sugars that can donate an electron to the Benedict's reagent. Benedict's reagent is an alkaline solution of Copper(II) sulfate. When a reducing sugar is added to this and heated it forms an insoluble red precipitate (copper (I) oxide).
Add 2cm3 of the food sample to be tested (liquid).
Add 2cm3 of Benedict's Reagent.
Heat the mixture gently in a water bath for five minutes. If the solution turns
brick red
then a reducing sugar is present.
Although some disaccharides are reducing sugars, other disaccharides and polysaccharides are
non-reducing
; therefore, Benedict's Test has to be altered to test for these.
Repeat the first experiment if no change from
blue to brick red
then a reducing sugar is not present.
2cm3 of sample added to 2cm3 of
dilute hydrochloric acid
is added.
Place the test tube in a water bath for 5 minutes. HCL will hydrolyse the disaccharides into monosaccharides.
Some
sodium hydrogencarbonate
is added in order to neutralise the test tube, Benedicts will not work in acidic conditions.
Retest using the benedicts solution.
If a non-reducing sugar is present in the sample then a colour change from
blue
to
brick red
will occur.
Biochemical test - Iodine test
A chemical test for starch is
iodine/potassium iodide
. If the solution turns from
orange
to
Blue/black
then starch is present.
Proteins
Amino acids
are the monomers from which proteins are made. Amino acids contain an amino group (COOH) and a
variable R group
which is a carbon-containing chain.
There are 20 amino acids, each determined by their different R groups. Amino acids are joined by peptide bonds formed in condensation reactions. In this reaction, molecules of water are formed.
Structure of proteins
Structure of proteins
is determined by the order and number of amino acids, bonding present and the shape of protein:
Primary structure
of a protein is the order and number of amino acids in a protein. This primary structure contains the initial sequence of amino acids and will therefore determine the proteins function in the end.
Secondary structure
is the shape that the chain of amino acid chains -
either alpha helix
or
beta pleated sheet
. The hydrogen in the -NH has a slightly positive charge whilst the oxygen in the -C=O has a slightly negative charge. As a result weak hydrogen bonds can form leading to alpha helices or beta pleated sheets.
Tertiary structure
of a protein is the 3D shape of the protein and is formed from further twisting and folding. A number of different bonds maintain the structure, these are:
Disulphide bridges
- interactions between the sulfur in the R group of the amino acid
cysteine
these are strong and not easily broken.
Ionic bonds
- form between the carboxyl and amino groups that are not involved in the peptide bond. They are easily broken by pH and are weaker than disulphide bridges.
Hydrogen bonds
- numerous and easily broken
Biuret test - the test for proteins
Can be used to test for the presence of a
peptide bonds
in a protein and can therefore detect proteins in food:
Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.
Add a few drops of very dilute copper sulfate solution and mix gently.
A purple colouration indicates the presence of a peptide bond and hence a protein. Remain blue if negative.
Structure of DNA and RNA
Structure
Nucleotides
consist of a
pentose sugar
, an
organic base
and a
Phosphate group
.
The components of
DNA
nucleotide are
deoxyribose sugar, a phosphate group and of the nitrogen-containing organic bases
adenine, cytosine, guanine or thymine.
The components of an
RNA
nucleotide are
ribose sugar, a phosphate group and one of the nitrogen-containing organic bases
adenine, cytosine, guanine or uracil.
Nucleotides join together by
phosphodiester bonds
formed in
condensation reactions
. The result is a dinucleotide, which join to form polynucleotides. The bond forms between the deoxyribose sugar of one nucleotide and the phosphate group of another.
A DNA molecule is a
double helix
composed of two polynucleotides joined together by
hydrogen bonds
between complementary bases, whereas
RNA is a relatively short polynucleotide chain
.
Why DNA is stable
The
phosphodiester backbone
protects the more chemically reactive nitrogen-containing organic bases inside the double helix.
Hydrogen bonds form bridges
between the phosphodiester uprights. As there are
three hydrogen bonds between guanine and cytosine
, rather than
two fro adenine and thymine
, a higher proportion of C-G pairings makes DNA more stable.
Function
Both
DNA
and
RNA
carry information. DNA holds genetic information, whereas RNA transfers this genetic information from DNA to
ribosomes
for
protein synthesis
DNA replication
The semi-conservative replication
of DNA ensures genetic continuity between generations of cells meaning that genetic information is passed on from one generation to the next.
An enzyme,
DNA helicase
, causes the two strands of DNA to separate breaking the
Hydrogen bonds
between the complementary bases.
One of the strands is used as the
template
and
complementary base pairing occurs
between the template strand and free nucleotides.
Once activated nucleotides are bound the enzyme
DNA polymerase
joins them together by forming
phosphodiester bonds
.
ATP
Adenosine triphosphate
is a nucleotide derivative and consists of
ribose, adenine and three phosphate groups
.
Properties
ATP is an
immediate source of energy
and is more desirable to use than glucose as ATP can ve broken down in a single step to release a manageable quantity of energy.
ATP isn't stored
in large quantities as it can easily be reformed from ADP.
ATP is used in a variety of different ways, these include,
metabolic processes, movement, active transport, secretion and activation of molecules
.
ATP breakdown
Energy is released when ATP is hydrolysed
to form
ADP and a phosphate molecule
. This process is catalysed by
ATP hydrolase
.
The energy comes from the bonds between the phosphate molecules. These bonds are very
unstable
and thus have a
low activation energy
. Breaking them is therefore quick and releases a lot of energy.
The
inorganic phosphate
can be used to phosphorylate other compounds, as a result making them more reactive.
ATP condensation
condensation of ADP and an inorganic phosphate
catalysed by
ATP synthase
produces ATP during photosynthesis and respiration.
Water
Properties
Water is a
polar molecule
due to the
uneven distribution of charge
within the molecule - the hydrogen atoms are more positive than the oxygen atom causing one end of the molecule to be more positive than the other. As a result hydrogen bonding between many water molecules can occur allowing them to stick together.
It is a
metabolite
in metabolic reactions such as
condensation and hydrolysis
which are used in forming and breaking chemical bonds.
It is a
solvent
allowing gases to readily diffuse as well as enzymes and waste products e.g ammonia and urea.
It has a
high specific heat capacity
. This is because water molecules stick together with hydrogen bonds meaning that a lot of energy is required to break these bonds. This helps to
minimise temperature fluctuations
in living things therefore it acts as a
buffer
.
Hydrogen bonding means that it requires a lot of energy to evaporate 1 gram of water. Therefore, water has a
large latent heat of vaporisation
, meaning evaporation of water provides a
cooling effect
with little water loss e.g sweating.
Strong cohesion
between molecules enables effective transport of water in tubes like the xylem. The
strong cohesion supports columns of water
, as result of strong cohesion
the surface tension at the water-air boundary is high
.
Inorganic ions
Inorganic ions
occur in solution in the cytoplasm and body fluid of organisms, some in high concentrations and others in very low concentrations.
Hydrogen ions
which
determine the PH
of substances such as blood -
the higher the concentration of hydrogen ions the lower the PH
.
Iron ions are a component of haemoglobin
which is an oxygen carrying molecule in red blood cells.
Sodium ions
are
involved in co-transport of glucose and amino acids
.
Phosphate ions
are a
component of DNA and ATP