Definition of a Gene & Mutations Flashcards
Gene
- definition
Inherited unit of information specifying phenotype at gross level
Morphological characteristics
Molecular level through particular products (proteins, RNAs)
Genes are inherited units of information which specify a phenotype at the gross level
By causing the expression of a specific gene or protein-/RNA-coding
They are not the only aspect of the human genome (only around 1% of bases are protein-coding)
Genes are inherited units of information which specify a phenotype at the gross level
By causing the expression of a specific gene or protein-/RNA-coding
They are not the only aspect of the human genome (only around 1% of bases are protein-coding)
Mutations can be …. or ….
spontaneous
induced
Spontaeous mutations are due….
chemical properties of nucleic acids or problems during replication or cell division
Give examples of spontaneous mutation
Spontaneous
Chemical properties of nucleic acids -deaminationchangescytosinetouracil,depurinationremoves a whole base
Problems during replication or cell division - an incorrect base can be added and not removed if not recognised by backtracking of DNA polymerase, or a repeat region can be extended as a result ofpolymerase slipping
Give examples of induced mutation
Induced
Radiation-UVexpose can causedimerization of thymine(covalent linkage), this changes the structure of DNA, affecting replication
Chemicals
Name the 3 possible consequences of mutations
Consequences
Missense- change in codon =change in amino acid
Nonsense- prematurestopcodon = shortened protein may have altered function or regulation
Frame shift- insertion or deletion not in a multiple of three
Mutations - State harmless variants
Single nucleotide polymorphisms(SNPs) - 1 in 300 nucleotides is polymorphic (multiple variants), these have no significant effect on the phenotype
disease-causing mutation
. give an example based on a gene … cancer
Mutations in proteins that are involved ingene repairincrease the susceptibility tofurther mutations(leading to cancer) - e.g. BRCA1/2 are involved in repairing double strand breaks and mutations in them can lead to familial breast and ovarian cancer
Different types of mutation and their consequences
Substitution mutations can be:
Synonymous (codon makes same AA), so it is silent and has no effect
Non-synonymous: either missense (changes the AA), nonsense (codes for a stop codon), affects splicing which can have various effects
Deletion mutations can be
A deletion of a multiple of 3, no frame shift but may affect the function and stability of the protein coded for
Not a multiple of 3, will cause a frame shift, may cause: premature termination of the gene sequence, gain or loss of function of the protein formed
Large deletion is partial or whole gene deletion which causes large level loss of function, or even expression
Insertion mutations can be
A multiple of 3, no frame shift, but may affect function/stability of the protein
Not a multiple of 3, causes a frame shift which may cause premature termination, loss/gain of function
Large insertion- partial/whole gene duplication, may affect function of protein or increase rate of a certain process because there are more of the protein, for example
Mutations can either be harmless or disease-causin
but generally, disease-causing mutations can occur in repair complexes, e.g. BRCA1/2
Harmless gene mutations can occur with single nucleotide polymorphisms where there is no significant phenotype, but these mutations play a role in gene linkage analysis and can help with genome comparisons/ relatives
Induced mutations are due to radiation or chemicals:
Exposure to UV can cause dimerization of thymine, where 2 thymines are covalently linked which affects the structure of DNA during replication
It creates a kink in the DNA which can stop or alter enzyme action, and lead to more mutations or miscoding
Spontaneous are due to chemical properties of nucleic acids or problems during replication or cell division
Deamination of cytosine forms uracil and deamination of 5-methyl-cytosine forms thymine
Changes base pairs, can impact AA sequence and therefore protein folding
Impact depends on the position of mutation in a codon
Also, uracil not normally present in DNA- it’s an RNA base
Depurination of adenine or guanine causes loss of that base
Means frame shift in 1 newly formed DNA strand after DNA replication
Many consequences in gene coding abilities as all codons after the mutation are affected
Mistakes can occur during the replication process
Certain areas of DNA are more prone to mutations/ sequence changes
Normally, wrongly incorporated nucleotides are recognised and corrected, but not always
Slippages of DNA polymerase can result in mutations/ repeated areas
Especially occurs in satellite regions of DNA (areas of DNA with lots of repeated units, the number of repeat units occurs and is not easily recognised)
