Extended response

Question 1

How can FSH be made synthetically with recombinant DNA technology

Answer 1

• Recombinant DNA is synthetic DNA made by inserting genes from one source into a DNA molecule from a different source.
• Recombinant DNA technology are the procedures used to produce recombinant DNA, involving introducing DNA into a cell from a different type of organism or DNA that has been modified in some way
• recombinant DNA technology has enabled the manufacture of large quantities of pure protein for many medical products including insulin, growth hormone and FSH
• The first step in producing an organism with recombinant DNA is to isolate the gene of interest. This gene is then inserted into a vector and cloned. This is achieved by:
  
  • Identifying the gene responsible for producing FSH
  • Using an appropriate restriction enzyme to cut the DNA on either side of the gene
  • Using the same restriction enzyme to cut the DNA of the vector
  • Adding the desired gene to the vector
  • Using DNA ligase to join the two sections of DNA
  • The bacterium is treated so it takes up the recombinant plasmid once this is successful, the bacterium will multiply so that either the human gene or the product of the gene can be used

Question 2

what are the two types of mutations

Answer 2

• Gene mutations: changes in a single gene so that the traits normally produced by that gene are changed or destroyed
• Chromosomal mutations: A change to the structure and or number of chromosomes in an organism

Question 3

What are the two causes of mutations

Answer 3

• Induced mutations: a mutation caused by a mutagenic agent
• Spontaneous mutations: A mutation that occurs due to an error in a natural biological process (mitosis, meiosis)
  Inheritability

Question 4

Somatic mutation

Answer 4

A change occurring in a gene in a body cell. Only the individual with the mutation is affected. Each time the mutant cell divides, mutation is passed onto the daughter cell. As reproductive cells are not affected, once the individual dies, the mutation is lost, not passed on. Somatic mutations involved in many cancerous growth and maybe result of mutagenic agent.

Question 5

Germline mutation

Answer 5

A change in the hereditary material in egg or sperm that becomes incorporated into the DNA of every cell in the body of the offspring. Individual with mutation not usually affected however mutation passed on to next and subsequent generations. Eg, PKU can arise through a mutation during the formation of gametes and can be passed onto offspring

Question 6

effects of a mutation

Answer 6

• Missense mutations: Causes change in an amino acid resulting in a different protein being produced
• nonsense mutations: Results in a STOP codon, producing a shortened peptide chain unlikely to fulfil its function
• neutral mutations: Causes a change in amino acid but does not change structure of protein enough to change its function
• silent mutations: Does not change sequence of amino acids and therefore in the protein produced. Possible as most amino acids are coded for by more than one base sequence

Question 7

Point mutation

Answer 7

A change in just one of the bases of a DNA molecule. may be due to a nucleotide being:

• Inserted: a new nucleotide added to DNA strand
• Substituted: An existing nucleotide is replaced with another one, with a different base
• Deleted: a nucleotide is removed from the DNA strand

Question 8

Frameshift mutation

Answer 8

Some mutations result in a frame shift. A frame shift is a mutation involving an insertion or deletion that results in a change in the way the sequence is read. Will not occur when three bases are added or deleted. In these instances, the DNA will simply code for one more or one less amino acid but the result will be the same

Question 9

What are the five reasons for mutations affecting the largest section of DNA

Answer 9

• Duplication (or insertion): section chromosome occurs twice
• Deletion: piece of DNA is removed (e.g. cri du chat)
• Inversion: breaks occur in a chromosome and the broken piece joins back in, but the wrong way around
• Translocation: part of a chromosome breaks off and is rejoined to the wrong chromosome
• Non-disjunction: failure of a chromosome pair to separate and so one daughter to cell has an extra chromosome. Referred to as aneuploidy

Question 10

Lethal recessives

Answer 10

Most gene mutations produce a recessive allele because they prevent the gene from producing a protein that will be able to function in the body. A person could therefore have large numbers of mutations and be unaware of them. If the person reproduces with a partner who has the same recessive mutation, the recessive condition could appear in the offspring. Some recessive mutations are lethal if they are not masked by a dominant normal allele. These lethal recessives cause the death of an embryo or foetus. A lethal recessive is a recessive allele that, inherited in the homozygous condition, results in the death of the embryo, foetus or child. EG, Tay sachs

Question 11

how do lethal recessives affect a gene pool

Answer 11

People who inherit two such alleles would die before their alleles could be passed on to the next generation, so the proportion of lethal recessive alleles in the gene pool would gradually be reduced

Question 12

Tay sachs

Answer 12

It is a lethal recessive condition caused by a mutation in the gene that codes for an enzyme that is responsible for breaking down toxic substances, including fatty substances in the brain and spinal-cord. The missing enzyme results in the accumulation of fatty substances in the nervous system, which destroys the neurons. A baby with two recessive alleles for tay sachs develops normally for the first few months, and then deterioration that causes intellectual and physical disability begins. Death occurs in early childhood

Question 13

Describe gene therapy for cystic fibrosis, Type one diabetes and huntingtons disease

Answer 13

• Gene therapy aims to treat or cure genetic abnormalities by identifying faulty genes and inserting healthy ones. A vector can be used to deliver desired DNA into a cell. This DNA can be incorporated into the cell’s nucleus and undergo transcription and translation to produce the desired protein
• Unlike most conventional medicines, which treat the symptoms of a disease, gene therapy has the potential to correct the underlying cause

Question 14

Gene therapy and type one diabetes

Answer 14

• Caused by an autoimmune disease that destroys the beta cells in islets of Langerhans in the pancreas. This means that the body cannot produce insulin and therefore blood glucose levels remain high after a meal
• Gene therapy is looking at methods of making it possible for the body to produce insulin again
• One possibility is reprogramming other cells to produce insulin. In order to achieve this, the gene for insulin is introduced into a vector which is then used to ‘infect’ the desired cells such as the alpha cells in the islets of Langerhans. These cells incorporate the new DNA into their nucleus and are able to us protein

Question 15

gene therapy and Cystic fibrosis

Answer 15

• a disorder controlled by a recessive allele carried on an autosome that is incurable but can be detected during foetal development. Mucus secreting glands (particularly in the lungs and pancreas) become fibrous and produce abnormally thick mucus resulting chest infections (among other things)
• CF is a logical choice for treatment using gene therapy as it is a single gene disorder, the most severely affected organ (lungs) are easy to access to provide treatment and the disease is slow to progress
• The first experimental gene therapy treatment was given to a patient with CF where researchers modified a common cold virus to act as the vector to carry normal genes to the CFTR cells in the airways of the lung

Question 16

Gene therapy for huntingtons disease

Answer 16

• Caused by a mutation in a single gene on chromosome 4. The symptoms of this incurable genetic disorder seldom appear before the age of 40. The mutated form of a protein called huntingtin results in nerve cells in the brain being damaged, causing physical, mental and emotional changes
• Scientists experimented with a modified virus to deliver a corrective gene into brain cells that boosts a natural shield against the effects of the defective huntington protein.