Module 2, section 2: Biological molecules.

Describe some functions of water, and how its properties arise.

Any one of these properties;

Polar molecule, so acts as a solvent to dissolve substances in the cells.

High surface tension, so organisms can live on its surface, due to hydrogen bonds being formed between water molecules on the surface.

Water is highly cohesive, meaning it effectively flows and can stick to things. This property allows it to be pulled up xylem vessels in plants.

Its high specific heat capacity means that lots of energy is required to heat water even a little bit, meaning water acts as an unusually stable habitat. Even under significant heat, water does not increase in temperature by very much.

Water also has high latent heat of vaporisation, meaning lots of energy is required to make it evaporate. This makes water especially good in cooling mechanisms, like sweating in humans. When water evaporates away from the skin, it takes lots of excess heat with it, cooling the person down.

Water expands when it freezes, due to hydrogen bonds being held apart further in ice than in liquid water. This means it floats on water, due to reduced density. This ice layer acts as an insulating layer, protecting the life forms that live below it. Without it, ice would freeze from the bottom up, killing all aquatic life. Thus, water expanding in its solid form is of paramount importance to all organisms on earth.

What are the two isomers of glucose, and how are they distinct? How does glucose’ structure explain its properties?

Alpha glucose, has the hydrogen on the right carbon above the hydroxide group, whilst beta glucose has the hydrogen atom below the hydroxide ion.

Glucose’s glycosidic bonds contain lots of energy, making it the premier energy molecule in multicellular organisms.

What are four examples of polysaccharides, and how is their structure relevant to their specific function?

Starch is the main energy storage molecule in plants, and it has two forms. Amylose is a tightly coiled chain that acts as a storage molecule for plants. Comparatively, amylopectin is a highly branched form of starch, that allows it to be quickly released.

Glycogen is the main energy store for animals, and is a highly branched molecule that has loads of glycosidic bonds. This makes it great as an energy storage molecule, and it is also compact.

Cellulose is a polysaccharide formed from long, unbranched chains of beta glucose, that are weakly attracted to each other due to hydrogen bonds between the chains. This makes cellulose particularly effective for structural support.

What are lipids fundamentally comprised of, and what is the simplest lipid? What are their bonds called?

Lipids are made of fatty acids and glycerol, and three fatty acids and a glycerol molecule bind together to form a triglyceride. They bind using ester bonds.

What’s significant in the structure of fatty acids?

They have ‘tails’ which are really variable r-groups. These tails can be saturated or unsaturated, depending if the tails feature double bonds.

What are some functions of lipids in animals?

Triglycerides are the primary long-term storage molecule in animals, due to the long hydrocarbon tails. So, they are the most efficient respiratory substrate, twice better than carbs.

Phospholipids are found in cell membranes, and contribute to their impermeability.

Cholesterol is another lipid, and it is used to control membrane rigidity.

How are amino acids bound together?

Amino acids are combined via condensation reactions, forming dipeptides, that are bound via peptide bonds.

Describe the general structure of an amino acid.

A central carbon atom, covalently bonded to four different groups. A NH2 group, a hydrogen atom, a COOH molecule and a variable r-group that allows for different amino acids to form.

What atoms do amino acids contain?

Carbon, hydrogen, oxygen, nitrogen and sulphur.

Describe the secondary structure of protein.

Hydrogen bonds between -NH and -CO groups cause the chain to change shape.

It either coils into a alpha-helix, or folds into a beta-pleated sheet.

Describe the tertiary structure of proteins.

Further coiled polypeptide chains, furthered by ionic bonds and disulfide bonds from variable r-groups meaning structures become more complex. Hydrogen bonds also contribute to this effect.

Hydrophobic and hydrophillic interactions also inform the shape of the protein.

How about quarternary?

The manner in which polypeptide chains are bound to each other. Represents the final structure of a protein.

What are globular proteins?

Round and compact proteins, that are soluble in water, due to hydrophillic/phobic interactions.