Biological molecules

Question 1

Describe the structure of water?

Answer 1

• Water is a polar molecule due to a slightly negatively charged oxygen and slightly positively charge hydrogen
• H2O molecules are held together by covalent bonds
• water is held together by hydrogen bonds which are between an oxygen and hydrogen atom on corresponding water molecules

Question 2

What are the properties of water?

Answer 2

• it’s a metabolite in condensation and hydrogen reactions
• solvent which metabolic reactions occur
• high specific heat capacity limiting temp fluctuations acting as a buffer
• large latent heat of vaporisation acting as a buffer
• strong cohesion between molecules resulting in high surface tension
• higher density than ice meaning ice floats creating an insulating layer
• incompressible providing good support

Question 3

Describe the structure of carbohydrates?

Answer 3

Molecules consist only of carbon, hydrogen and oxygen. They are made of single subunits called saccharides joined by condensation reactions forming glycosidic bonds.

Question 4

Describe the structure of glucose and the difference between it’s two isomers?

Answer 4

Glucose is a monosaccharide containing six carbon atoms in each molecule and is the main substrate for respiration.

Alpha glucose has it’s OH group on the bottom of carbon atom one whereas beta glucose has it’s OH group on the top.

Question 5

Describe the structure of the three disaccharides?

Answer 5

Maltose is formed of two glucose molecules.
Sucrose is formed of fructose and glucose.
Lactose is formed of glucose and galactose.

Question 6

Describe the structure and function of glycogen?

Answer 6

Glycogen is the main energy storage molecule in animals.

It’s formed of many alpha glucose molecules joined by 1,4 and 1,6 glycosidic bonds. It has a large number of side branches meaning glucose and therefore energy can be rapidly released. It’s a large but compact molecule maximising energy storage.

Question 7

Describe the structure and function of starch?

Answer 7

Starch stores energy in plants and is made up of amylose and amylopectin.

Amylose is an unbranched chain of glucose molecules joined by 1,4 glycosidic bonds. It is therefore coiled and a very compact molecule meaning it can store lot’s of energy.

Amylopectin is branched and made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds. Due to many side branches it’s rapidly digested by enzymes releasing energy quickly.

Question 8

Describe the structure and function of cellulose?

Answer 8

Cellulose is a component of plant cell walls. It provides the plant with structural support.

It’s composed of long unbranched chains of beta glucose joined by glycosidic bonds.

Question 9

Describe the structure of lipids?

Answer 9

Lipids are biological molecules only soluble in organic solvents. They are made up of carbon, hydrogen and oxygen.

Question 10

Describe the difference between saturated and unsaturated lipids?

Answer 10

Saturated lipids are found in animal fats, don’t contain any double bonds. and are solid at room temperature.

Whereas unsaturated lipids are found in plants and contain carbon double bonds meaning they have a lower melting point due to weaker intermolecular bonds and are liquid at room temperature.

Question 11

Describe the structure and function of triglycerides?

Answer 11

Triglycerides are made of one glycerol and three fatty acids joined by ester bonds formed in condensation reactions. They are used as energy reserves in plant and animal cells.

Question 12

What are inorganic ions and give an example?

Answer 12

They occur in solutions in the cytoplasm and the body fluid of organism in varying concentrations.

• hydrogen ions
• iron ions
• sodium ions
• phosphate ions

Question 13

Describe the structure of proteins?

Answer 13

They are made up of the monomer amino acid. Amino acids are made up of an amino group, carboxylic acid group and a variable R group (defines the 20 different amino acids). Amino acids are joined by peptide bonds.

Question 14

Describe the structural level of proteins?

Answer 14

• primary structure is the order and sequence of amino acids in a protein
• secondary structure is the shape the amino acid chains take due to hydrogen bonding (alpha helix or beta pleated sheet)
• tertiary structure is the further coiling or folding of alpha helix’s and beta pleated sheets creating the 3D shape that is fibrous or globular
• quaternary structure is the arrangement of multiple polypeptide chains

Question 15

What bonds are present in each structural level of proteins?

Answer 15

• primary contain peptide bonds
• secondary contain hydrogen bonds
• tertiary contain disulfide bonds, hydrogen bonds, ionic bonds, and hydrophobic interactions
• quaternary contain hydrogen bonds

Question 16

What’s the difference between fibrous and globular proteins?

Answer 16

Fibrous proteins are long strands of polypeptide chains. They are structural and generally water insoluble.

Whereas globular proteins are roughly circular, functional and generally water soluble.

Question 17

Give an example of a fibrous protein?

Answer 17

Collagen is a fibrous protein formed from three polypeptide chains closely held together by hydrogen bonds. Collagen is a strong protein and forms the structure of bones, cartilage and connective tissue (main component of tendons).

Question 18

Give an example of a globular protein?

Answer 18

Haemoglobin is a globular protein with a quaternary structure of 4 polypeptide chains. The prosthetic haem group contains iron which combines with oxygen to form oxyhemoglobin. Each haemoglobin can carry 4 oxygen.