These are detailed Revision Notes for Topic 2.1.2 and 2.1.3 of OCR A-Level Biology (Biological Molecules, Nucleotides and Nucleic Acids). They were written by me using a combination of the textbook and class notes. I will also be uploading the other topics and creating bundles.
Topics Included:
...
Biological Molecules
3.1 Biological elements
3.1 Biological Elements
- The major elements in biological molecules are Carbon, Hydrogen, 3.2 Water
Oxygen and Nitrogen. 3.3 Carbohydrates
- C, H and O for carbohydrates and lipids
- C, H, O, N and S for proteins 3.4 Testing for carbohydrates
- C, H, O, N and P for nucleic acids 3.5 Lipids
- Most elements found in living things will be ionised either positive
3.6 The structure of proteins
(cations) or negative (anions).
Anion Symbol Examples of Roles 3.7 Types of proteins
Nitrate ions NO3- -Nitrogen supply for plants 3.8 Nucleic acids
to make amino acids and
proteins 3.9 DNA Replication and the Genetic Code
Hydrogen carbonate ions HCO3- -Maintaining blood pH 3.10 Protein Synthesis
Chloride ions Cl- -Balance positive charges 3.11 ATP
from Na+ and K+
Phosphate ions PO43- -Cell membrane formation
-Nucleic acids and ATP Cation Symbol Examples of Roles
formation Calcium ions Ca2+ -Nerve impulse transmission
-Bone formation -Muscle contraction
Hydroxide ions OH- -Catalysis of reactions Sodium ions Na+ -Nerve impulse transmission
-pH determination -Kidney function
Potassium ions K+ -Nerve impulse transmission
-Stomatal opening
Hydrogen ions H+ -Catalysis of reactions
-pH determination
Ammonium ions NH4+ -Production of nitrate by bacteria
Iron ions Fe2+/Fe3+-Haemoglobin in blood
3.2 Water
- Water is a covalently bonded molecule.
- The oxygen is more electronegative than
hydrogen and so takes a greater share of the
electrons than hydrogen. This leaves the oxygen
slightly (delta 𝛿 -) negative and the hydrogens
slightly positive.
- Water is said to be a dipolar molecule.
- The uneven balance of charge gives water its properties.
- When multiple molecules are together the delta positive region is attracted to the delta negative region
of other molecules. This is called a hydrogen bond.
- Each molecule can make 4 hydrogen bonds. These bonds are individually weak but collectively strong.
High Specific Heat Capacity
- The energy needed to raise 1g/1kg of water by 1oC. Measured in kJkg-1oC-1 / Jg-1oC-1
- The specific heat capacity of water is 4.2 Jg-1oC-1
- Having a high specific heat capacity means it takes a lot of energy to increase the temperature and
also must lose a lot of energy to cool down.
- This means that it is thermostable and there is not a lot of temperature fluctuation. This is good for
enzymes, and it keeps a constant rate of reactions
, High Latent Heat
- It helps evaporative cooling – sweat cooling down the body.
- High latent heat also means you can lose more energy
with less water lost for this, cooling you down more
effectively and conserving water. Large heat loss for
small volume of water lost.
Cohesion and Adhesion
- Cohesion is the attraction of like molecules because of the
hydrogen bonds.
- Cohesion can be seen in water droplets.
- This means if water is taken from the end of a tub, water molecules follow behind, this allows plants to
pull water up the xylem.
- The cohesive property of water results in unique behaviour of water at the interface between water
and air. Water molecules at the surface of water are more attracted to other water molecules than
they are to molecules in the air. This uneven attraction pulls the water molecules towards the water
below the surface, so the surface of the water is placed under tension. This tension creates a ‘skin’ on
top of the water surface that is difficult to break through. This provides a habitat for pond-skaters.
- Adhesion is the attraction between non-alike molecules.
- Water displays adhesive properties when it is attracted to other polar or charged surfaces. E.g. in a
narrow glass tube.
Ice/Water
- Water is a liquid between 0oC and 100oC. This is because the hydrogen bonds between molecules are
collectively strong and so take a lot of energy to overcome.
- In ice the bond angle of water allows for an almost perfect tetrahedral arrangement of the molecules.
They line up in a more regular pattern, but the molecules are further apart.
- As there are almost as many hydrogen bonds in water as in ice and they are further apart in ice, they
are less dense.
- This means ice can float on water. This is important as ice can insulate water beneath it e.g. in a pond.
This allows aquatic life to survive better without climate temperature changes.
Solvent Abilities
- As water is a polar molecule allowing it to easily dissolve ionic and polar molecules.
- This is because the ionic compounds are attracted to the delta charges, as are other polar molecules.
3.3 Carbohydrates
- A single sugar unit is known as a monosaccharide.
- They have the general formula of Monosaccharide Hexose or Pentose Biological Significance
(CH2O)n 𝛼-glucose Hexose -Respiratory substrate
- When two monosaccharides join -Synthesis of di & poly
together, they form a disaccharide, -Found in nectar
with usually the general formula of 𝛽-glucose Hexose -As above
C12H22O11 (two hexoses – water). -Monomer of cellulose
- When two or more monosaccharides Fructose Hexose -In nectar and fruits to
join together, they form a polymer attract animals
called a polysaccharide, with the -Respiratory substrate
general formula of Cx(H2O)y. Galactose Hexose -Part of lactose
- Monosaccharides are either trioses (3 -Respiratory substrate
carbons), pentoses (5 carbons) or Ribose Pentose -In RNA – ribonucleotides
hexoses (6 carbons).
Deoxyribose Pentose -In DNA - deoxyribonucleotides
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 emilysarahjudge. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £2.99. You're not tied to anything after your purchase.
