An in-depth informative booklet explaining the key biological molecules including their biochemical tests, outline of practicals for the unit, a useful set of summary questions and specification.
,Introduction
The key Biological molecules are carbohydrates, proteins, lipids and nucleic acids. The
chemical elements that can be found in these molecules are carbon, hydrogen, oxygen and
nitrogen. Some also contain phosphorous or sulphur.
Metabolism is the sum total of all the biochemical reactions taking place in the cells of an
organism. The reactions may involve breaking larger molecules into smaller ones (catabolic
reactions) or joining smaller molecules into larger ones (anabolic reactions).
Monomers single small molecules.
Polymers a large molecule made up of many similar monomers covalently bonded together.
Biological molecule Monomers Polymers
Carbohydrates Monosaccharides Polysaccharides
Proteins Amino acids Polypeptides and
proteins
Nucleic acids Nucleotides DNA & RNA
Condensation reaction – the chemical reaction that combines biological monomers
• A new covalent bond is formed
• A water molecule is released
• A larger molecule is formed by joining smaller molecules
Hydrolysis reaction - splitting larger molecules to smaller ones – the reverse of a
condensation reaction
• A covalent bond is broken
• A molecule of water is used
• Smaller molecules are formed
2
,Water
Life began in water and the tissues of mammal are 60-70% water and for plants it is 90% water.
Cytoplasm, blood plasma, tissue fluid and lymph all contain water.
Properties of Water
Water has many unusual properties.
Water is a very small dipolar
molecule made up of two hydrogen
atoms covalently bonded to one
oxygen atom. The electrons in water
are not shared evenly between the
hydrogen and oxygen atom. The
larger oxygen atom pulls the
electrons closer towards it and
becomes slightly negatively
charged (δ - ), whereas the smaller
hydrogen atom becomes slightly
positively charged (δ + ). These
slight charges attract one another
and form a weak interaction called
the hydrogen bond. These are
continually broken and reformed.
Hydrogen bonds are found in water and other biological compounds such as carbohydrates and proteins.
Hydrogen bonds in water many water molecules polar (charged) and give it unusual properties.
Biological importance of water
1. Metabolic role – many metabolic reactions
involve condensation and hydrolysis reactions
requiring water such as joining amino acids
together by peptide bonds by condensation
reactions forming polypeptides; splitting
disaccharides to monosaccharides by hydrolysis
reactions.
2. High Latent heat of Vaporisation- the
evaporation of water requires a lot of energy to
break the hydrogen bonds. When water
evaporates from a surface it ‘removes’ the heat
and has a cooling effect e.g. sweating and
transpiration.
3. Liquid with relatively high boiling point – the
continual making and breaking of hydrogen bonds
in water means that it is a liquid not a gas and it is
difficult for water molecules to escape the liquid which means that the boiling point is much higher that
other similar sized molecules.
3
, 4. Low density of ice - As the water is cooled and the molecules slow down, more hydrogen bonds form
holding the water molecules to form a crystalline structure which is less dense than liquid water. This
means that ice floats on water and insulates the organisms that live beneath it.
5. High specific Heat Capacity- Thermostability- the hydrogen bonds in water prevent the movement of
the water molecules so relatively large amounts of energy is required to increase the temperature of the
water. Water therefore has a high specific heat capacity. This means that large bodies of water are
thermostable even when there are large external fluctuations of temperature.
6. Cohesion- Hydrogen bonds cause water molecules to stick
together. This results in surface tension at the surface of water.
This can allows some organisms to ‘walk on water’ e.g. pond
skaters. Water can be transported up the xylem in the transpiration
stream as cohesion between water molecules makes long thin
columns of water difficult to break. Adhesion is when water
molecules stick to other surfaces, for example, the wall of the xylem.
7. Solvent - the polarity of water allows it to be a really good solvent.
Any polar molecules like ions will dissolve well in water. The
negative ions will be attracted to the positive end of the water
molecule and the positive ions to the negative end. Water molecules
tend to cluster around any charged parts of solute molecules. This
allows metabolic reactions such as photosynthesis and respiration to
take place in solution in the cytoplasm.
8. Transport Medium- since water is a good solvent and remains
liquid over a wide range of temperatures means that water is a good
transport medium e.g. plasma in blood, mineral ions in the xylem.
9. Transparent – As water is transparent, aquatic organisms, such as
algae and seaweed, are able to photosynthesise as the sunlight
passes through the water.
4
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller kmomoniat. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £9.99. You're not tied to anything after your purchase.
