BIOLOGICAL MOLECULES Summarized Notes

*Note that, Monosaccharides and disaccharides are sugars; they are reducing sugars for Benedict's reagent, except for the disaccharide sucrose which is non-reducing*

3. Starch, glycogen and cellulose (polysaccharides)
Very large, complex molecules are made when many thousands of simple sugar molecules join in a long chain, as shown in the figure below, Examples of these large, complex molecules are starch, which is found inside plant cells, and glycogen, which is found in the liver and muscle cells of animals. Cellulose, which forms the cell wall in plants, is also a complex sugar molecule. Most of these complex carbohydrates are insoluble, do not have a sweet taste and are insoluble in water.

*Note that,  Polysaccharides are not considered Sugars and don't have a sweet taste. Excess polysaccharides are stored in the liver and muscles*

The Role Of Carbohydrates In Living Organisms
Glucose is used as the main source of energy for cells when it is oxidised during cell respiration. Carbohydrates are transported around the body via the bloodstream in the form of glucose. Glucose is the building block for making larger carbohydrate molecules, Such as disaccharides and polysaccharides. It is also the starting molecule for building many other molecules, such as amino acids and fatty acids. Glycogen is the form or carbohydrate stored in animal tissues as an energy reserve. Starch is stored in plant tissues. Glycogen can be readily broken down to glucose as needed. In humans, for example, glycogen is stored in the liver and muscle cells, and broken down into glucose when the glucose level in the body drops. In plants, starch is stored as energy reserve in parts such as seeds and tubers. Cellulose, which is also made of carbohydrate molecules, is the main material that makes up the cell walls of plant cells. It supports the walls and keeps them rigid.

Proteins
Foods from animals, such as meat, fish, eggs, milk and cheese, contain a lot of protein. Many plant foods are also good sources of protein, especially grains and other seeds. Fiqure below shows some foods that are a good source of protein.
Protein molecules usually Contain:
• Carbon (C)
• Hydrogen (H)
• Oxygen (O)
• Nitrogen (N)
Protein molecules sometimes contain:
• Sulphur (S)
• Phosphorus (P)

Protein molecules are made of long chains of smaller molecules called amino acids, as shown in the figure below. A short chain of amino acids is called a polypeptide. A chain of polypeptides is called a protein. There are about 20 different amino acids and they can be joined in any sequence to make different protein molecules. Millions of different proteins are made as a result of changes in the sequence of amino acids

*Note that,  Protein molecules and starch molecules are both made of long chains of small molecules linked together*

Peptide bonds
When two amino acid subunits combine, the carboxyl group of one amino acid reacts with the amino group of the other amino acid in a condensation reaction. The bond that is formed is a peptide bond. The peptide bonds that hold amino acids together can be broken down by hydrolysis. The figure below shows the formation of a peptide bond that joins amino acids. 

*You do not need to learn the detailed molecular structure of amino acids or proteins, but you should have the general idea that amino acids are linked by peptide bonds*

You can see on the left side of Figure above that a molecule of water is removed in the condensation reaction when two amino acids Combine to form a dipeptide. The peptide bond shown above now links two amino acids. Long chains of amino acids held together by peptide other by peptide bonds are called polypeptides. The figure below shows how amino acid subunits join to form part of a polypeptide chain

*Note that Proteins are only used to provide energy if a person does not have enough fat and carbohydrates*

Uses Of Proteins
Proteins are used for making:
• new cells for growth and repair of damaged cells, for example, cell membranes and cytoplasm contain a lot of protein
• antibodies that fight bacteria and viruses inside the body, *Enzymes hormones and haemoglobin are all proteins*

Fats
Many people think that fats are bad for you. A high cholestrol diet can have a negative effect on your health, especially the heart. But everyone needs some fat in their diet. You get fats from meat, cheese, eggs, milk, butter, and cooking oil. Some of these are shown in the figure below

Fats are made of glycerol and fatty acids, the word fats includes fats and oils. They are very similar chemically, but different in appearance. Fats are usualy solids (usually produced by animals), and oils are liquids (usually produced by plants) at room temperature. Both fats and oils are insoluble in water. Fats and oils contain only three kinds of atoms:
• carbon (C)
• hydrogen (H)
• oxygen (O)
*Note that These are the same atoms found in carbohydrates*

A molecule of fat is made up of tour molecules - one molecule of glycerol joined three long molecules of fatty acids, as shown in the figure below. It is classified as a triglyceride, because of the presence of tri (three) fatty acids.

Uses Of Fats And Oils
Like carbohydrates, fats and oils can be used in a cell to release energy. A gram of fat or oil releases about 39 kJ of energy; twice as much energy as that released by a gram of carbohydrate. It is easier, however, for cells to release energy from carbohydrates than fats and so the cell only releases energy from fats when all the available carbohydrates have been used. Fats are used as an energy store In the body. For example whales have thick layers of blubber under their skin that act as a store of energy as well as insulation against heat loss, the figure below will help you know the location of fats on whales

Fats are also very important in the formation of cell membranes and the outer covering of nerves. Many single celled aquatic organisms produce an oil droplet to aid buoyancy. Delicate mammalian organs, such as the kidneys, which are vulnerable to knocks and bumps, have relatively thick layers of fat around them to absorb shock. Oily secretions of glands, which are found in the skin of mammals, act as a water repellent. They prevent fur and hair from becoming waterlogged when wet. Birds have a preen gland that fulfils this same function

*You will need knowledge and understanding of the practical procedures used in testing foods for what is contained within them*

The Role Of Water As A Solvent, In Digestion, Excretion And Transport
Water is possibly the most necessary substance in life as we know it, as we need it in order to survive; it also provides an environment for many species. About 70% of your body tissue is made up of water. It is the most essential part of the cytoplasm in your cells. Water acts as a solvent and transport medium in your body, and it regulates all functions, including the activity of everything it dissolves and circulates. All chemical processes, such as digestion and metabolic reactions, need water to take place. In other words, water provides a medium in which all materials react. Oxygen, glucose, mineral salts, hormones and vitamins are all transported around the body in a solution in the blood. Likewise, waste products like urine and sweat are transported and excreted from the body in a water solution. You will also learn inthe next posts about transportation that body fluids, such as blood, lymph, and tissue fluid, all contain a lot of water. Your body gains water from drinking fluids, eating wet food and from water that is produced in the body during cell respiration. You lose water by sweating, urination and exhalation, so it is essential to drink lots of fluids to replace water lost by the body. Most dieticians recommend drinking six to eight glasses of water a day, and more it you exercise or if the weather is very hot. Excess loss of water through diarrhoea, Vomiting or heavy sweating may lead to dehydration. For these reasons it is essential to replace water that is lost

How Different Sequences Of Amino Acids Give Different Shapes Of Protein Molecules
Proteins are macromolecules and have four different levels of structure known as primary, secondary, tertiary and quaternary

Primary Structure
Individual amino acids are joined together by peptide bonds created by condensation reactions catalysed by enzymes. Hydrolysis also occurs during digestion. Successive condensations form a linear chain of amino acids. This sequence of amino acids represents the primary structure of the protein, this primary structure is maintained by covalent bonds between adjacent amino acids.

Secondary Structure
The polypeptide chains may take on regular arrangements called the secondary structure of protein for example, the alpha helix. This secondary structure is maintained by hydrogen bonds between C=O and N-H groups of every peptide link. An alternative secondary structure, the B-pleated sheet, has hydrogen bonds between peptide links of adjacent polypeptide chains.

Tertiary structure
Sections of the a-helix may be folded on themselves. This supercoling of the x-helix represents the tertiary structure of the protein. This three-dimensional shape of the protein is maintained by a series of interactions between R-groups on the polypeptide chain. These interactions are very weak, so that the conformation of such globular proteims can easily be changed by local physical changes. These alterations are reversible and are essential for the biological function of these molecules.

Tertiary Structure
Several polypeptide chains (tertiary structures) may be fitted together to produce the quaternary structure of the protein. The stability of the quaternary structure is maintained by weak interactions between R-groups of adjacent polypeptides and Van der Waal's forces between subunits.

Summary For The Four Structures Of Protein

*note how the x-helix and B-chain are written, from the figures*

The Structure Of DNA (double helix, base pairs and the sequence of pairing)
DNA is a substance that belongs to a group of chemicals called nucleic acids. A nucleic acid is found in, or associated with the nucleus of cells. There are two forms of nucleic acid:
• DNA -deoxyribonucleic acid
• RNA -ribonucleic acid

A DNA molecule is made up of subunits called nucleotides. Each nucleotide is made up of three chemical groups:
• a sugar molecule called deoxyribose
• a base; there are four of these called adenine (A), thymine (T), guanine (G) and cytosine (C)
• a phosphate group represented by the letter P
The Figure Below Is A Structure Of A DNA

These three chemical groups are joined together to form a nucleotide, as shown in
the figure below

Each nucleotide is joined together to another by a backbone of sugar-phosphate
groups to form a chain of nucleotides, as shown in the figure below

Two chains of nucleotides lie side by side and are joined by hydrogen bonds between
the bases to form part of a DNA molecule, as shown in the figure below

You can see from the figure below that the DNA molecule is like a ladder. The sugar phosphate groups act as the uprights of the ladder and the bases form the rungs

The End, See You In The Next Post. Posted By Mr DeHaan Ahil.