Flashcards in 6.1.1: Gene mutations Deck (28):
How can a mutation occur?
-Mutations may occur spontaneously during DNA replication before cell division.
-Certain chemicals such as tar in tobacco smoke.
-Ionising radiation such as UV light, X-rays and gamma rays, may be mutagenic.
What are mutations associated with mitotic divisions called and what are their characteristics?
-They are not passed to offspring.
-They may be associated with the development of cancerous tumors.
What types of mutations can be inherited by offspring?
Mutations associated with meiosis and gamete formation.
What are the two main classes of DNA mutation?
-Point mutation: one base pair replaces another.
-Insertion and deletion mutation: one or more nucleotides are inserted or deleted from a length of DNA. These may cause a frame shift.
What are the three types of point mutation?
All amino acids involved in protein synthesis, apart from one, have more than one base triplet code. Which amino acid doesn't?
Why is the degeneracy of the genetic code useful?
Because it reduces the effect of point mutations as they do not always cause a change to the sequence of amino acids in a protein
What is a silent mutation?
-A mutation involving a change to the base triplet where that triplet still codes for the same amino acid.
-The primary structure of the protein and therefore the secondary and tertiary structure, is not altered.
What is a missense mutation?
A change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.
How does a missense mutation have an effect on the protein produced?
-Within a gene, such a point mutation may have a significant effect on the protein produced.
-The alteration to the primary structure leads to a change in the tertiary structure of the protein, altering the shape and preventing it from carrying out its usual function.
What causes sickle cell anemia?
-A missense mutation on the sixth base triplet of the gene for the beta-polypeptide chains of the haemoglobin.
-The amino acid valine, instead of glutamic acid, is inserted at this position.
What does the mutation in siclke cell anemia cause?
It results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen.
What is a nonsense mutation?
A point mutation which alters the base triplet, so that it becomes a termination (stop) triplet.
What effect does a nonsense mutation have?
-This particularly disruptive mutation results in a truncated protein that will not function.
-This abnormal protein will most likely be degraded within the cell.
What is the genetic disease Duchenne muscular distrophy a result of?
A nonsense mutation.
Describe a how indel mutations can cause a frameshift:
-If nucleotide base pairs, not in multiples of three, are inserted in the gene or deleted from the gene all the subsequent base triplets are altered.
-This is because the code is non-overlapping and read in groups of three bases.
How is the function of a protein affected by an indel mutation?
-When the mRNA from such a mutated gene is translated , the amino acid sequence after the frameshift is severely disrupted.
-The primary sequence of the protein, and subsequently the tertiary structure is, is much altered.
-Consequently, the protein cannot carry out its normal function.
What will happen if a protein is abnormal?
It will be rapidly degraded within the cell.
What is thalassaemia?
A haemoglobin disorder, result from frameshift due to deletions of nucleotide bases.
What does the insertion and deletion of a triplet of base pairs result in?
The addition or loss of an amino acid, and not a frameshift.
What is an expanding triple nucleotide?
-Some genes contain a repeating triplet such as -CAG CAG CAG -.
-In am expanding triple nucleotide, the number of CAG triplets increases at meiosis and again from generation to generation.
What causes Huntington disease?
-Huntington disease results from an expanding triplet nucleotide repeat.
-If the number of repeating CAG sequences goes above a certain critical number, then the person with that genotype will develop the symptoms of Huntington disease later in life.
how are different alleles of a particular gene produced?
The mutation that gave rise to blue eyes arose in the human population 6000-8000 years ago. Such a mutation may be harmful in areas where the sunlight intensity is high. Why is this?
Because the lack of iris pigmentation could lead to lens cataracts.
Why can blue eyes be an advantage in temperate zones?
It could enable people to see better in less bright light.
How does high concentration of melanin benefit those living in hot climates?
By protecting them from sunburn and skin cancer.
When humans migrated to temperate regions, a paler skin would be an advantage. Why is this?
Because it enables vitamin D to be made with a lower intensity of sunlight.
-Vitamin D protects us from rickets and from heart disease and cancer.