mutations (m&m, dna genomics 1 and 2) Flashcards
what are gene mutations
alterations in the sequence of nucleotides which may change the sequence of amino acids in a polypeptide chain
may change the 3d shape and hence the function of the protein and subsequently affect the phenotype of the organism
can result in new alleles
what is subsitution mutation
replacement of one nucleotide by another, resulting in one codon changed
what is inversion mutation
a segment of nucleotides separates from the allele and rejoins at the original position but is inverted, resulting in 1 or more codons changed
major effects of subsitution/inversion mutation on proteins
if new amino acid is synthesised
properties of new amino acid is chemically different
affected amino acid found in critical location such as active site
minor effects of subsitution/inversion mutation on proteins
same amino acid is synthesised
properties of new amino acid is chemically similar
affected amino acid found is not found in critical location
what is insertion mutation
one or several nucleotides are inserted into a sequence
what is a deletion mutation
one or several nucleotides are removed from a sequence
major effects of insertion/deletion mutation on protein
ribosomes begin to read incorrect triplets from the point of insertion/deletion, producing a nonfunctional protein
minor effects of a deletion/insertion mutation
number of nucleotides deleted/inserted are a multiple of 3, changes primary sequence but will not result in a frame shift
outcomes of frame-shift mutation
insertion/deletion of a number of nucleotide that is not divisible by 3, disrupting the reading frame, making the ribosomes read the incorrect triplets from the point of insertion/deletion, producing a completely different and nonfunctional polypeptide
outcome of silent mutation
point mutation that does not change the amino acid sequence in a polypeptide = synthesising the same polypeptide
outcome of missense mutation
point mutation that results in a codon that codes for a different amino acid
conservative mutation: new amino acid has similar biochemical properties
non-conservative mutation: new amino acid has different biochemical properties
outcome of nonsense mutaion
point mutation that results in a premature stop codon, causing the polypeptide to be truncated and nonfunctional
what is the mutation that occurs in sickle cell anemia
point mutation
change in DNA: CTC to CAC
change in mRNA: GAG to GUG
change in amino acid: glutamate to valine
beta globin chain of haemoglobin affected
HbS formed instead of HbA
effects of change from glutamate to valine
charged and hydrophilic glutamate replaced by nonpolar hydrophobic valine
effects on HbS in low oxygen concentrations
- at lowoxygen concentrations, HbS will lose the oxygen and undergo a conformation change which will cause the hydrophobic patches on HbS to stick out
- hydrophobic areas of different HbS molecules will stick together and this polymerisation of HbS results in the formation of abnormal rigid rod like fibres which will distort shape of biconcave red blood cell and make it sickle shaped
effects on HbS in high oxygen concentrations
- oxygen will bind to HbS again
- HbS returns to original conformation and red blood cells return to their original biconcave shape
- polymerisation of HbS and sickling of red blood cells are reversible
effects of sickle cell anemia disease on the body
- sickle shaped red blood cells are more fragile and break easily, resulting in shortage of red blood cells and poor oxygen transport, which causes anemia, lack of energy and heart failure
- sickle shaped RBCs lodge in small blood vessels and interfere with blood circulation
chromosome aberrations due to chromosome structure
- deletion: removes a chromosomal segment
duplication: repeats a chromosomal segment
inversion: reverses a segment within a chromosome
translocation: moves a segment from one chromosome to another chromosome which is non-homologous
effects of chromosomal aberrations due to deletions/duplications
phenotypic abnormalities due to the reduced or additional genes
effects of chromosomal aberrations due inversion/translocation
result in disease: although amount of genetic material remains the same, expression of gene can be affected by its location
chromosomal aberrations due to chromosomal number
aneuploidy: genetic disorder whre cell does not have a chromsome number that a multiple of the haploid number - either extra or fewer
trisomic: 2n+1
monosomic: 2n-1
non-disjunction in meiosis l
- during meiosis l: homologous chromosomes do not move properly to opposite poles so all cells will be mutated
nondisjunction happening in meiosis ll
during meiosis ll: sister chromatids do not separate properly to opposite poles so only 2/4 cells will be mutated)
3.
effects of chromosomal aberration due to chromosome number
one gamete will receive 2 same type of chromosome and another gamete receives no copy
if abnormal gamete fuses with normal gamete during fertilisation, zygote will have abnormal number of chromosomes
mitosis transmits anomaly to all embryonic cells
describe trisomy 21
results from non disjunction in meiosis l
has an extra chromosome 21 , so there are 3 copies
each body cell has 47 chromosomes
