Gene regulation

Gene regulation

NUCLEUS

CYTOPLASM

R. S. Winning, 2003

Gene regulation

Transcription: regulated by activators (transcription factors)and repressors (rare in eukaryotes)

Examples: heat shock transcription factor

always present; becomes active when temperature changes

steroid hormones bind directly to TF to activate it

peptide hormones bind to cell membrane and initiate series of reactions within the cell to activate TF

Gene regulation

transcription: regulated by activators (transcription factors)and repressors (rare in eukaryotes)

RNA processing: different exons may be used within one gene,producing different protein products

Gene regulation

transcription: regulated by activators (transcription factors)and repressors (rare in eukaryotes)

RNA processing: different exons may be used within one gene,producing different protein products

mRNA longevity: mRNA translates as long as it is intact‘lifespan’ encoded in the 3' UTR sequence AUUUA signals early degradation

Gene regulation

transcription: regulated by activators (transcription factors)and repressors (rare in eukaryotes)

RNA processing: different exons may be used within one gene,producing different protein products

mRNA longevity: mRNA translates as long as it is intact‘lifespan’ encoded in the 3' UTR sequence AUUUA signals early degradation

translation: mRNA may exist without being translated (not well understood)

potential phenotypic effects of mutation:morphological trait – change in color, size nutritional or biochemical variation – loss of ability to synthesize a protein - synthesis of different versions of a proteinchange in behavior – e.g., fruitflies - lose ability to recognize mate gender

changes in gene regulation - gene turned off, or onlethality – loss of essential function

Mutation

Mutation

Spontaneous mutations – errors in translation, ~ every 106 bases

repaired during translation by DNA polymerase ‘checking’

Induced mutations – due to mutagens

Single base substitutionstransitions - purine to purine, or pyrimidine to pyrimidinetransversions - purine with a pyrimidine or vice versa.

Point mutations

Single base substitutionstransitions - purine to purine, or pyrimidine to pyrimidinetransversions - purine with a pyrimidine or vice versa.

The fat cat ate the hot dog.

The fat car ate the hot dog.

The fat cat ate the hot hog.

small change in meaning,still readable

Point mutations

no change (synonymous or silent mutations)single amino acid change (missense mutation)

frameshift mutations insertions deletions

Point mutations

frameshift mutations insertions

deletions

The fat cat ate the hot dog.

The fma tca tat eth eho tdo g.

Thf atc ata tet heh otd og

includes change in stop codon:The fat cat ate the hot dog how why fry hot cat the…

profound change

Point mutations

Mutation

changes in larger segments of genome

- tandem duplicationsaddition of duplicate CAG sequences results in Huntington’s chorea

- ploidy, aneuploidy

ploidy = number of chromosome sets in cellhaploid – 1 (gametes)diploid − 2 (most cells)triploid – 3 (sterile)tetraploid – 4 ....etc.

Xenopus tropicalis 2N = 20 diploidXenopus laevis 2N = 36 tetraploidXenopus muelleri 2N = 72 octaploidXenopus ruwensoriensis 2N = 108 dodecaploid

ploidy = number of chromosome sets in cellhaploid – 1 (gametes)diploid − 2 (most cells)triploid – 3 (sterile)tetraploid – 4 ....etc.

plants tend to have more ploidy levels – can overcome sterility with vegetative reproduction

higher ploidy -> larger cells, more ‘product’- yeast- wheats

autopolyploidy vs. allopolyploidy

euploidy = correct number of chromosome sets in cellpolyploidy

aneuploidy = incomplete set of chromosomes usually due to non-disjunction during meiosis

Down’s syndrome (trisomy 21)Patau’s syndrome (trisomy 13)Turner’s syndrome (monosomy of X chromosome)Klinefelter syndrome (trisomy of sex chromosomes, XXY)

euploidy = correct number of chromosome sets in cellpolyploidy

aneuploidy = incomplete set of chromosomes usually due to non-disjunction during meiosis

Down’s syndrome (trisomy 21)Patau’s syndrome (trisomy 13)Turner’s syndrome (monosomy of X chromosome)Klinefelter syndrome (trisomy of sex chromosomes, XXY)

which is likely to have more severe effects, monosomy or trisomy?

Inversions – part of chromosome is flipped by 180

Translocations – non-homologous chromosomes exchange material (not always symmetrically)

euploidy = correct number of chromosome sets in cellpolyploidy

aneuploidy = incomplete set of chromosomes usually due to non-disjunction during meiosis

Down’s syndrome (trisomy 21)Patau’s syndrome (trisomy 13)Turner’s syndrome (monosomy of X chromosome)Klinefelter syndrome (trisomy of sex chromosomes, XXY)

loss/variation/rearrangement of portions of chromosome Cri-du-chat syndrome (loss of part of arm of chromosome 5)

Mutation

Somatic cell mutations – affect only individual

Gametic (germline) cell mutations – heritable

(e.g., cancer is largely unimportant evolutionarily)