biology module 2 biological molecules

Properties of Water

Water is of great biological importance and is the medium in which all metabolic reactions take place in cells.

Water Composition

Water is composed of atoms of hydrogen and oxygen, with one atom of oxygen combining with two atoms of hydrogen by sharing electrons (covalent bonding).

Dipole

This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole.

Polar Molecule

When a molecule has one end that is negatively charged and one end that is positively charged, it is called a polar molecule.

Hydrogen Bonds

Hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules.

Solvent

As water is a polar molecule, many ions and covalently bonded polar substances will dissolve in it, allowing chemical reactions to occur within cells.

High Specific Heat Capacity

The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of that substance by 1°C.

Water's Specific Heat Capacity

Water's specific heat capacity is 4200 J/kg°C, meaning a relatively large amount of energy is required to raise its temperature.

Universal Solvent

Due to its polarity, water is considered a universal solvent.

High Latent Heat of Vaporisation

Water has a relatively high latent heat of vaporisation, which contributes to its thermal stability.

Density of Water

Water is less dense when solid (ice floats on water) and can act as a habitat for animals such as polar bears.

Surface Tension

Water has high surface tension and cohesion due to hydrogen bonding.

Transport Medium

Water acts as a transport medium for metabolites, allowing efficient transport of substances within cells.

Covalent Bonding

Covalent bonding in water results in an asymmetrical shape and uneven sharing of electrons.

Metabolites

Metabolites can be transported efficiently in water, except for non-polar molecules which are hydrophobic.

Chemical Reactivity

Dissolved solutes in water are more chemically reactive when they are free to move about.

Hydrogen Bond Strength

Hydrogen bonds are weak when few are present but form a strong structure when there are large numbers.

Biological Importance of Water

Water has many essential roles in living organisms due to its properties.

Metabolic Reactions

All metabolic reactions take place in cells within the medium of water.

Water Habitat

71% of the Earth's surface is covered in water, making it a major habitat for organisms.

Thermal Energy

It takes a lot of thermal energy to break and build hydrogen bonds in water, stabilizing its temperature.

Diffusion in Prokaryotic Cells

Prokaryotic cells exchange substances, such as nutrients and waste products, with their surroundings via the process of diffusion.

Stable habitats

Provides suitable stable habitats in aquatic environments such as in lakes and the ocean.

Constant temperature maintenance

Water is able to maintain a constant temperature as it can absorb a lot of heat without big temperature fluctuations.

Enzyme activity

Maintaining temperatures that are optimal for enzyme activity in both prokaryotes and eukaryotes.

Heat transfer in blood plasma

Water in blood plasma is vital in transferring heat around the body, helping to maintain a fairly constant temperature.

Heat absorption in active regions

As blood passes through more active ('warmer') regions of the body, heat energy is absorbed but the temperature remains fairly constant.

Tissue fluid regulation

Water in tissue fluid plays an important regulatory role in maintaining a constant body temperature.

Latent heat of vaporisation

A large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate.

Cooling effect of evaporation

Only a little water is required to evaporate for the organism to lose a great amount of heat, providing a cooling effect.

Transpiration

An example of cooling effect for living organisms, such as transpiration from leaves or evaporation of water in sweat on the skin.

Cohesion

Hydrogen bonds between water molecules allow for strong cohesion between water molecules.

Xylem water movement

Cohesion allows columns of water to move through the xylem of plants and through blood vessels in animals.

Surface tension

Hydrogen bonds create surface tension where a body of water meets the air, allowing insects such as pond skaters to float.

Adhesion

Water's ability to hydrogen bond to other molecules, such as cellulose, known as adhesion.

Transpiration in xylem

Adhesion enables water to move up the xylem due to transpiration.

Monomers

Monomers are the smaller units from which larger molecules are made.

Polymers

Polymers are molecules made from a large number of monomers joined together in a chain.

Polymerisation

The process by which small single subunits (monomers) bond with many repeating subunits to form large molecules (polymers).

Macromolecules

Very large molecules that contain 1000 or more atoms and have a high molecular mass.

Covalent bond

A covalent bond is the sharing of two or more electrons between two atoms.

Nonpolar covalent bond

Electrons are shared equally forming a nonpolar covalent bond.

Polar covalent bond

Electrons are shared unequally to form a polar covalent bond.

Covalent bond stability

Covalent bonds are very stable as high energies are required to break the bonds.

Double bonds

Multiple pairs of electrons can be shared forming double bonds (e.g. unsaturated fats C=C).

Triple bonds

Multiple pairs of electrons can be shared forming triple bonds.

Polymerisation

Occurs when more monomers are added, leading to the formation of macromolecules.

Condensation

Also known as dehydration synthesis, it is a reaction where monomers combine by covalent bonds to form polymers and water is removed.

Hydrolysis

A reaction where covalent bonds in polymers are broken when water is added.

Covalent Bonds

Strong bonds formed between atoms in organic molecules, requiring a large input of energy to break.

Organic Compounds

Compounds that contain the chemical elements carbon (C) and hydrogen (H).

Carbohydrates

Organic molecules containing carbon, hydrogen, and oxygen, represented by the formula C(H2O)y.

Monosaccharides

The simplest form of carbohydrates, consisting of single sugar molecules.

Disaccharides

Carbohydrates formed from two monosaccharides.

Polysaccharides

Carbohydrates that are made up of long chains of monosaccharide units.

Energy Source

Carbohydrates like glucose are used for energy release during cellular respiration.

Energy Storage

Glycogen is stored in the muscles and liver of animals as a form of energy reserve.

Structural Importance

Cellulose serves as a structural component in the cell walls of plants.

Lipids

Organic molecules containing carbon, hydrogen, and oxygen, with a lower proportion of oxygen compared to carbohydrates.

Triglycerides

A type of lipid that includes fats and oils.

Phospholipids

Lipids that are a major component of biological membranes.

Energy Yield

Lipids provide a high energy yield when respired.

Insulation

Lipids provide thermal insulation under the skin of mammals and electrical insulation around nerve cells.

Proteins

Organic molecules that contain carbon, hydrogen, and oxygen, and perform a variety of functions in the body.

Proteins

Required for cell growth, cell repair and the replacement of biological materials.

Proteins

Structurally important e.g. in muscles, collagen and elastin in the skin, collagen in bone and keratin in hair.

Proteins

Can act as carrier molecules in cell membranes, antibodies, enzymes or hormones.

Nucleic Acids

Contain the chemical elements C, H, O, N (in their bases) and P (in the form of phosphate groups).

Nucleic Acids

Have the function of carrying the genetic code in all living organisms.

Nucleic Acids

Essential in the control of all cellular processes including protein synthesis.

Monosaccharides

Sugars classified as reducing or non-reducing based on their ability to donate electrons.

Reducing Sugars

Can donate electrons; detected using Benedict's test which reduces soluble copper sulphate to insoluble brick-red copper oxide.

Examples of Reducing Sugars

Include glucose, fructose, and galactose.

Non-reducing Sugars

Cannot donate electrons; must be hydrolysed to monosaccharides before detection.

Example of Non-reducing Sugar

Sucrose.

Types of Monosaccharides

Include triodes (3C), pentoses (5C), and hexoses (6C).

Glucose

Has the molecular formula C6H12O6 and is the most common monosaccharide.

Function of Glucose

Main energy source used in respiration, releasing energy for the production of ATP.

Properties of Glucose

Soluble and can be transported in water.

Isomers of Glucose

Exist in two structurally different forms - alpha (α) glucose and beta (β) glucose.

Ribose and Deoxyribose

Important pentose sugars found in the nucleotides that make up RNA and DNA.

Difference between Ribose and Deoxyribose

Deoxyribose has lost one oxygen atom at carbon number 2.

OILRIG Mnemonic

Used to remember what happens to a molecule when electrons are lost (oxidation) or gained (reduction).

Glycosidic Bond

A strong covalent bond formed when two hydroxyl (-OH) groups on different saccharides interact.

Condensation Reaction

A reaction where two monosaccharides bond together, resulting in the removal of one water molecule.

Hydrolysis Reaction

A reaction that breaks the glycosidic bond by adding water, resulting in the formation of monosaccharides.

Disaccharide

A carbohydrate formed from two monosaccharides joined by a glycosidic bond.

Polysaccharide

A macromolecule formed by many monosaccharides joined by glycosidic bonds.

Maltose

A disaccharide formed from two glucose molecules.

Sucrose

A disaccharide formed from glucose and fructose.

Lactose

A disaccharide formed from glucose and galactose, found only in milk.

Amylose

An unbranched polysaccharide that is 10 - 30% of starch, formed by 1,4 glycosidic bonds between α-glucose molecules.

Amylopectin

A branched polysaccharide that is 70 - 90% of starch, formed by 1,4 and 1,6 glycosidic bonds between α-glucose molecules.

Glycogen

A highly branched polysaccharide found in animals, made up of α-glucose molecules with 1,4 and 1,6 glycosidic bonds.

Hydrolytic Reactions

Reactions that break down disaccharides and polysaccharides into monosaccharides.

Enzymes in Hydrolysis

Catalysts that facilitate hydrolytic reactions, different from those in condensation reactions.

Branched Polysaccharides

Polysaccharides like glycogen and amylopectin that have a branched structure.

Unbranched Polysaccharides

Polysaccharides like amylose that have a straight chain structure.

Compact Molecules

Molecules like starch and glycogen that are folded to make them ideal for storage.

Straight Molecules

Molecules like cellulose that are suitable for constructing cellular structures.