mutations (m&m, dna genomics 1 and 2)

Question 1

what are gene mutations

Answer 1

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

Question 2

what is subsitution mutation

Answer 2

replacement of one nucleotide by another, resulting in one codon changed

Question 3

what is inversion mutation

Answer 3

a segment of nucleotides separates from the allele and rejoins at the original position but is inverted, resulting in 1 or more codons changed

Question 4

major effects of subsitution/inversion mutation on proteins

Answer 4

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

Question 5

minor effects of subsitution/inversion mutation on proteins

Answer 5

same amino acid is synthesised
properties of new amino acid is chemically similar
affected amino acid found is not found in critical location

Question 6

what is insertion mutation

Answer 6

one or several nucleotides are inserted into a sequence

Question 7

what is a deletion mutation

Answer 7

one or several nucleotides are removed from a sequence

Question 8

major effects of insertion/deletion mutation on protein

Answer 8

ribosomes begin to read incorrect triplets from the point of insertion/deletion, producing a nonfunctional protein

Question 9

minor effects of a deletion/insertion mutation

Answer 9

number of nucleotides deleted/inserted are a multiple of 3, changes primary sequence but will not result in a frame shift

Question 10

outcomes of frame-shift mutation

Answer 10

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

Question 11

outcome of silent mutation

Answer 11

point mutation that does not change the amino acid sequence in a polypeptide = synthesising the same polypeptide

Question 12

outcome of missense mutation

Answer 12

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

Question 13

outcome of nonsense mutaion

Answer 13

point mutation that results in a premature stop codon, causing the polypeptide to be truncated and nonfunctional

Question 14

what is the mutation that occurs in sickle cell anemia

Answer 14

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

Question 15

effects of change from glutamate to valine

Answer 15

charged and hydrophilic glutamate replaced by nonpolar hydrophobic valine

Question 16

effects on HbS in low oxygen concentrations

Answer 16

1. at lowoxygen concentrations, HbS will lose the oxygen and undergo a conformation change which will cause the hydrophobic patches on HbS to stick out
2. 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

Question 17

effects on HbS in high oxygen concentrations

Answer 17

1. oxygen will bind to HbS again
2. HbS returns to original conformation and red blood cells return to their original biconcave shape
3. polymerisation of HbS and sickling of red blood cells are reversible

Question 18

effects of sickle cell anemia disease on the body

Answer 18

1. 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
2. sickle shaped RBCs lodge in small blood vessels and interfere with blood circulation

Question 19

chromosome aberrations due to chromosome structure

Answer 19

1. 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

Question 20

effects of chromosomal aberrations due to deletions/duplications

Answer 20

phenotypic abnormalities due to the reduced or additional genes

Question 21

effects of chromosomal aberrations due inversion/translocation

Answer 21

result in disease: although amount of genetic material remains the same, expression of gene can be affected by its location

Question 22

chromosomal aberrations due to chromosomal number

Answer 22

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

Question 23

non-disjunction in meiosis l

Answer 23

1. during meiosis l: homologous chromosomes do not move properly to opposite poles so all cells will be mutated

Question 24

nondisjunction happening in meiosis ll

Answer 24

during meiosis ll: sister chromatids do not separate properly to opposite poles so only 2/4 cells will be mutated)
3.

Question 25

effects of chromosomal aberration due to chromosome number

Answer 25

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

Question 26

describe trisomy 21

Answer 26

results from non disjunction in meiosis l
has an extra chromosome 21 , so there are 3 copies
each body cell has 47 chromosomes