20 gene expression Flashcards
what is a mutation?
any change to quantity or structure of DNA in an organism
what is a gene mutation?
change to nucleotide bases or rearrangement of the bases
what are the three possible consequences of a substitution mutation?
nonsense: formation of stop codon so production of polypeptide coded for by that section of DNA would stop, different, non-functioning protein
missense: formation of codon for different amino acid, structure of polypeptide differ in single amino acid, not function properly
silent: formation of different codon but codes for same amino acid, no effect
consequence of deletion mutation
frame shift, so gene read in wrong groups so triplets will be different and code for different amino acids
other types of gene mutation
addition of bases: frame shift to the right, no frame shift if three bases added
duplication of bases: produces frame shift to right
inversion of bases: base sequence of portion is reversed
translocation of bases: abnormal phenotype, development of cancer and reduced fertility
what are causes of mutations?
mutation rate can be increased by mutagenic agents
high energy ionising radiation: disrupt structure of DNA (x-rays and UV light)
chemicals: benzopyrene of tobacco smoke, alter structure of DNA or interfere with transcription
what are totipotent cells?
cells such as fertilised eggs that can mature into any body cell
how are genes prevented from expressing themselves?
preventing transcription (production of mRNA) preventing translation
why can’t specialised cells develop into any other cell?
once matured they lose their nuclei which contains genes so can’t develop into other cells
what are stem cells?
the few cells in mature mammals with the ability to differentiate into other cells
what are sources for stem cells in mammals
embryonic stem cells
umbilical cord blood stem cells
placental stem cells
adult stem cells
different types of stem cells
totipotent: early embryo, differentiate into any type of cell
pluripotent: found in more developed embryos, differentiate into almost any type of cell (embryonic and fetal stem cells)
multipotent: adults, differentiate into limited number of cells, e.g. stem cells in bone marro can produce any type of blood cell (adult and umbilical cord blood)
unipotent: differentiate into single type of cell, made in adult tissue
what are induced pluripotent stem cells?
type of pluripotent cells produced from unipotent cells, body cells genetically altered in lab so acquire characteristics of embryonic stem cells
uses genes and transcriptional factors within cell to express themselves, shows adult cells contain same genetic information in embryos
self-renewal: can divide indefinitely to provide limitless supply, overcome ethical issues surround use of embryonic cells
controlling transcription normally
for transcription to begin, gene switched on by transcriptional factors which have a site that binds to specific base sequence of DNA in nucleus
when binded, causes region of DNA to begin process of transcription, mRNA produced which is translated to polypeptide
when gene not expressed, the site on transcriptional factor that binds to DNA not active
how do hormones like oestrogen control transcription
oestrogen lipid soluble so diffused through phospholipid bilayer
binds with complementary site on receptor of transcriptional factor
causes oestrogen to change shape of DNA binding site on transcriptional factor which can now bind to specific base sequence on DNA (activated)
what is epigenetics?
environmental factors that cause heritable changes in gene function without changing base sequence of DNA
what is the epigenome?
chemical tags that form second layer that covers DNA and histones
what is the function of the epigenome?
determines shape of DNA-histone complex, tightly packed or unwrapped
flexible because chemical tags respond to environmental changes, stress and diet can cause chemical tags to adjust
structure of DNA-histone complex (chromatin)
when association of histones with DNA is weak, complex is less condensed so accessible by transcription factors
when association is stronger, complex is more condensed so not accessible by transcription factors
condensation inhibits transcription
decreased acetylation
increases positive charge on histones so increases attraction to phosphate groups of DNA
association between histones and DNA is stronger so DNA not accessible to transcription factors
increased methylation
methyl group added to cytosine base of DNA, inhibits transcription:
preventing binding of transcriptional factors to DNA
attracting proteins that condense DNA-histone complex so inaccessible to transcription factors
increased methylation
methyl group added to cytosine base of DNA, inhibits transcription:
preventing binding of transcriptional factors to DNA
attracting proteins that condense DNA-histone complex so inaccessible to transcription factors
how can epigenetic therapy be used to treat diseases?
drugs used to inhibit enzymes involved in either histone acetylation or DNA methylation
must be specifically targeted to cancer cells
RNA interference
translation can be inhibited by breaking down mRNA
enzyme cuts RNA into smaller sections called small interfering RNA
one of two siRNA strands combines with enzyme, siRNA guides enzyme to an mRNA molecule by pairing up complementary bases
enzyme cuts mRNA into smaller sections so can’t be translated
