Topic 8- The control of gene expression Flashcards
What is a gene mutation
A change in the base sequence of DNA that can arise spontaneously during DNA replication
What is a mutagenic agent
A factor that increaes rate of mutation
Explain how any type of mutation can lead to the production of a non coding protein/enzyme
-Changes sequence of base triplets in DNA so changes sequence of codons on mRNA
-Changes sequence of amino acids in the enclosed polypeptide.
-Changes position of hydrogen/ionic/disulphide bonds
-So tertiary structure is changed in protein
-Enzymes active site no longer complementary to substrate, so E-S complex cannot form
What is a substitution mutation?
A base/nucleotide is replaced by a different base/nucleotide in DNA.
What is an addition mutation?
One or more bases/nucleotides are added to the DNA base sequence.
What is a deletion mutation?
One or more bases/nucleotides are lost from the DNA base sequence.
What is a duplication mutation?
A sequence of DNA bases/nucleotides is repeated/copied.
What is an inversion mutation?
A sequence of bases/nucleotides detaches from the DNA sequence, then rejoins at the same position in the reverse order.
What is a translocation mutation?
A sequence of DNA bases/nucleotides detaches and is inserted at a different location within the same or a different chromosome.
Explain why not all gene mutations affect the order of amino acids
Some substitutions change only 1 triplet/codon which could still code for the same amino acid as the genetic code is degenerate so can be coded for by more than one triplet
-Some occur in introns which do not code for amino acids
GIve examples of mutagenic agents
High energy ionising radiation - a&b particles as well as UV and X ray which can disrupt the structure of DNA
Chemicals- Such as nitrogen dioxide that may directly alter DNA structure or interfere with transcription. OR benzopyrene
Explain why a change in amino acid sequence is not always harmful
-May not change tertiary structure of the protein (poistions of H/I/D) dont change
-May positively change the properties of the protein, giving the organsim a selective advantage.
Explain what is meant by a frameshift
-When a gene mutation changes the number of nuclotides bases by any numer not divisible by 3
-This shifts the way the genetic code is read, so all DNA triplets/mRNA codons downstream from the mutation change
-The sequence of amino acids encoded changes accordingly and the effects on the encoded polypeptide are significant.
What are stem cells
Undifferentiated or specialised cells capable of dividing by mitosis to replace themselves indefinently and can differentiate into other types of specialsed cells
Explain how stem cells can be used in the treatement of human disorders giving an example of diabeties and blood caner
-Transplanted into patients to divide in ulimited numbers the differentiated into required healthy cells to replace faulty/damaged cells
-Potential treatement of Type 1 diabeties by creating healthy islet cells that produce insulin
-Bone marrow in patient can be destroyed so no fulty cells are produced then tranplant bone marrow stem cells rom healthy peson and they can divide and differentiate into healthy cells
How do stem cells become specialised during development?
Stimuli lead to activation of some genes due to transcription factors. mRNA is transcribed from these genes and translated to form proteins, which modify cells permanently and determine cell structure/function.
What are totipotent cells?
Totipotent cells occur for a limited time in early mammalian embryos. They can divide and differentiate into any type of body cell, including extra-embryonic cells like the placenta.
What are pluripotent cells?
Pluripotent cells are found in mammalian embryos after the first few cell divisions. They can divide and differentiate into most cell types, but not placental cells.
What are multipotent cells?
Multipotent cells are found in mature mammals and can divide AND differentiate into a limited number of cell types.
Can you give an example of multipotent cells?
An example of multipotent cells is those in bone marrow, which can divide and differentiate into different types of blood cells.
Example: multipotent cells in bone marrow can divide and differentiate into different types of blood cell.
What are unipotent cells?
Unipotent cells are found in mature mammals and can divide and differentiate into just one cell type.
Can you give an example of unipotent cells?
An example of unipotent cells is those in the heart, which can divide and differentiate into cardiomyocytes (cardiac muscle cells).
