AS OCR Biology Unit 2

Differences between the structure of glycogen and collagen

 Glycogen                                                                               Collagen

Carbohydrate (made of monosaccharide’s)                            Protein ( made of amino acids)

Branched molecule                                                                 Unbranched molecule

Glycosidic bond                                                                      Peptide bond

No cross links                                                                         Cross links between chains

Identical units                                                                          Different amino acid units

One chain per molecule                                                          Three chains per molecule

Properties of collagen (in ligaments) that make it suitable for holfing the bones together at joints:

• Insoluble
• Flexible
• Strong
• Does not stretch

State what the term glycoprotein means

• protein/polypeptide with a carbohydrate chain

Name a shape formed by the coiling of the primary structure of a protein

• alpha helix

Name a shape formed by the folding of the primary structure of a protein

• beta pleated sheets

Explain why cholesterol must be carried by the blood by proteins while glucose does not need any transport protein.

• Cholesterol is insoluble in water
• Cholesterol has a hydrophobic nature
• However, glucose is soluble

State what a gene codes for

• a sequence of amino acids

State the role of RNA (mRNA)

• they take RNA (transcribed gene codes) to ribosomes and allow the assembly of proteins (protein synthesis).
• they transfer gene codes for ribosomes where amino acids are assembled to create proteins.

Suggest how changing the sequence of DNA nucleotides could affect the final product the DNA codes for.

• Each sequence of DNA nucleotides consists of amino acids,
• this would affect the final product as the amino acids assemble in different orders.
• different sequences of amino acids can affect the final product, e.g. protein, enzyme.

DNA is found in the nucleus. The molecule is twisted into a double helix in which each of the strands are anti-parallel. It has two sugar-phosphate backbones attached to one another by complementary bases. These bases pair in the centre of the molecule by means of hydrogen bonds.

Three ways in which the structure of DNA differs from RNA.

Feature                         DNA                                    RNA

Number of strands        2                                          1

Bases present              GCAT                                  GCAU

Sugar present              deoxyribose                          ribose 

Biochemical tests

Substance              heat biuret reagent benedicts reagent dilute acid  result is blu/blac

lipid                           x               x                            x                  x                yes

protein                      x              yes                          x                  x                  x

starch                       x                x                            x                  x                  x  

reducing sugar        yes             x                           yes                x                  x

non- reducing s       yes             x                           yes               yes               x

To test for a non-reducing sugar you boil with dilute acid and then carry out the same test for a reducing sugar.

Amino acids contain carboxyl, R group and amine group. In cysteine

• Carboxyl = C=0, C-OH
• R group = CH2-SH
• Amine group = N-H, N-H

Describe how a second amino acid would bond to cysteine in forming the primary structure of a protein.

• A H from one amine group of an amino acid would combine with OH from a Carboxyl group of another amino acid.
• A peptide bond is formed between these amino acids. This continues with many amino acids on the surface of the ribosome.
• Water is lost in the reaction and covalent bond formed, the primary structure is formed.

Describe how R groups can interact to determine the tertiary structure of a protein.

• Some R groups can attract/ repel (ionic bonds form between oppositely charged R groups)
• Disulfide bridges form between the amino acids,
• Hydrogen bonds form

Name the bond that joins the two molecules to form a disaccharide.

• glycosidic bond

What is marker assisted selection?

• A section of DNA is used as a marker to recognise the desired characteristics.
• Once offspring have been produced from selective parents, DNA is checked.
• allows selection at a very early stage.
• e.g. tomatoes bred with improved disease resistance.

A balanced diet is one which provides an adequate intake of energy and nutrients for the maintenance of our body. If energy intake exceeds energy usage over a period of time, an individual can become obese. The deficiancy disease anaemia can be caused by a lack of the mineral iron in the diet. As a result of this deficiency, the body is unable to produce sufficient amounts of the protein haemoglobin in red blood cells.

BMI = mass in kg/(height in m)2

Factors that may prevent the BMI from being completely correct.

• Doesn't account for pregnancy
• Doesn't distinguish between men and women
• Does not measure actual fat (doesn't take into account muscle)

Two diseases associated with obesity

Type 2 diseases and CHD

Explain what is meant by the term activation energy

• Energy required for a reaction to take place. Enzymes reduce energy required 

Describe how the lock and key model can be used to explain how an enzyme breaks down a substrate molecule.

• the substrate, or 'key' fits into the enzyme 'lock' creating an enzyme-substrate complex.
• the enzyme has a specifcally shaped active site.
• this induces a reaction when the substrate fits into the enzyme

Describe how the induced fit model differs from the lock and key model of enzyme action

• that the changes in shape of enzyme occur as the substrate binds to the active site.