8A mutations or gene expressions

• What are mutations?

  a change in the primary base sequence in amino acids which can in turn result in an altered polypeptide that the gene codes for.
• What are the types of gene mutations?

  insertion, deletion, substitution, inversion.
• What are insertion gene mutations?

  a nucleotide with a new base is randomly inserted into the DNA sequence. This causes all base pairs to slightly change.
• What are deletion gene mutations?

  a nucleotide and therefore its base is randomly deleted from the sequence. This causes all bases to slightly change.
• What are substitution gene mutations?

  a base in the dna sequence is randomly swapped. This only causes the swapped triplets to change.
• What are inversion gene mutations?

  usually occurs during crossing over in meiosis where the dna of a single gene is inverted 180 degrees. This affects multiple amino acids.
• What are the three types of substitution gene mutation?

  silent - mutation does not alter the amino acid sequence because the two codons code for the same amino acid (degenerate).

  
  

  Missense - mutation alters a single amino acid in the polypeptide chain.

  
  

  Nonsense - mutation creates a premature stop codon causing the polypeptide chain to be incomplete.
• What is the effect of mutations?

  Change the primary base sequence but usually do not change the polypeptide as the genetic code is degenerate.

  
  

  However some mutations cause a frame shift where every codon after the mutation is changed which usually results in a non functional polypeptide.
• What is the rate of mutations?

  Around 1 mutation per 100,000 genes.
• What increases the rate of mutations?

  mutagenic agents
• What are mutagenic agents?

  Factors that increase the rate of gene mutation if exposed to them e.g.

  
  

  High energy ionisation radiation such as alpha, beta, or gamma.

  
  

  Chemicals such as NO2 or benzopyrene from tobacco smoke.
• Do mutations affect the polypeptide?

  Rarely, and if so usually only slightly, however some mutations cause significantly different polypeptides usually affecting the shape.

  
  

  If the active site has changed shape, the protein may no longer be able to perform its function.
• What do we call mutations that occur after fertilisation?

  Acquired mutations
• What will happen if an acquired mutations occurs in genes that control the rate of cell division?

  Uncontrolled cell division
• What is the result of uncontrolled cell division?

  Tumour
• What is a tumour?

  mass of abnormally growing cells
• When does a tumour become cancerous?

  When it changes from benign to malignant and starts invading and destroying surrounding tissue.
• What are the two types of genes which control cell division?

  Tumour suppressor genes and proto-oncogenes
• What causes cancer?

  Mutations in either tumour suppressor genes and proto-oncogenes
• How do mutations in tumour suppressor genes cause tumours?

  Mutations in the dna sequence of the gene cause the protein that is usually produced to not be produced anymore.

  
  

  The protein is responsible for controlling cell division by stoping the dividing or causing them to self destruct (apoptosis).

  
  

  Without this protein, the cells divide uncontrollably which causes a tumour.
• How do mutations in proto onco genes cause tumours?

  A mutation in the dna of a proto-oncogene causes it to become an oncogene.

  
  

  Oncogenes are overreactive as they produce more of the protein that stimulates cell division than protooncogenes.

  
  

  This causes uncontrollable cell division which leads to a tumour.
• What is the difference between benign and malignant tumours


  Malignant tumours are cancers. They usually grow rapidly and invade and destroy surrounding tissues.

  Cells can break off the tumours and spread to other parts of the body in the bloodstream or lymphatic system.

  
  

  Benign tumours are not cancerous. They usually grow slower than malignant tumours and are often covered in fibrous tissue that stops cells invading other tissues. Benign tumours are often harmless, but they can cause blockages and put pressure on organs. Some benign tumours can become malignant.
• How do tumour cells differ to normal cells?

  They have an irregular shape.

  
  

  The nucleus is larger and darker than in normal cells.

  
  

  Sometimes the cells have more than one nucleus.

  
  

  They don't produce all the proteins needed to function correctly.

  
  

  They have different antigens on their surface.

  
  

  They don't respond to growth regulating processes.

  
  

  They divide (by mitosis) more frequently than normal cells.
• how does oestrogen cause cancer?


  Increased exposure to estrogen over an extended period of time is thought to increase a woman's risk of developing breast cancer.

  
  

  The exact reasons behind this aren't fully understood, but there are a few theories as to how estrogen can contribute to the development of some breast cancers:

  
  

  Oestrogen can stimulate certain breast cells to divide and replicate. The fact that more cell divisions are taking place naturally increases the chance of mutations occurring, and so increases the chance of cells becoming cancerous.

  
  

  This ability to stimulate division could also mean that if cells do become cancerous, their rapid replication could be further assisted by estrogen, helping tumours to form quickly.

  
  

  Other research suggests that estrogen is actually able to introduce mutations directly into the DNA of certain breast cells, again increasing the chance of these cells becoming cancerous.
• What is a stem cell?

  A cell that can divide by mitosis an unlimited number of times.
• What is differentiation?

  The process of a cell produced from stem cells becoming specialised.
• What is potency?

  The ability of a stem cell to differentiate into a specialised cell
• What are the three types of potency?

  Totipotency, pluripotency, multipotency.
• What are totipotent stem cells?

  Cells that can divide to produce cells that can differentiate into any type of body cell.
• What are totipotent cells also known as?

  Embryonic stem cells
• Where are totipotent cells found?

  early mammalian embryos in the first few cell divisions of the embryo.
• What are pluripotent stem cells?

  stem cells with the ability to differentiate to many, but not all tissues types.
• What are multipotent stem cells?

  Stem cells with the ability to differentiate into few types of cells.
• What are unipotent stem cells?

  Stem cells with the ability to differentiate into one type of cell
• Why do stem cells become specialised?

  during development only certain genes are transcribed, translated, and therefore expressed.
• What are cardiomyocytes? And what is unipotent cells role in regenerating them?

  Cardiomyocytes are heart muscle cells that make up heart tissue.

  
  

  It was thought that they couldn't regenerate themselves which is a problem if the heart becomes damaged.

  
  

  However research suggests that old or damaged cardiomyocytes are replaced by a small supply of unipotent stem cells.

  
  

  It is in discussion weather this process is continuous and how quickly it occurs.
• What is the use of embryonic stem cells?

  Due to their ability to differentiate into multiple types of cells, stem cells can be used in therapy.
• What human disorders do stem cell therapies treat?

  Disease of the blood and immune system.

  
  

  Bone marrow transplant.
• What are the benefits to stem cell therapy?

  Can save life's e.g. making new organs for those needing transplants.

  
  

  Can improve quality of life e.g. replace eye cells in blind people.
• What are the three main sources for human stem cells.

  Adult stem cells, embryonic cells, IPs cells