20: Gene expression Flashcards
gene mutation
- alteration of a base in the sequence, likely to occur during dna replication
- if different amino acid, hydrogen and ionic bonds formed in diff places, fold in diff places, diff 3d shape, nonfunctioning protein
mutagenic agents
- high energy and ionising radiaton. damage and disrupt dna
- carcinogens. chemical that interferes with structure of dna, interferes with transcription
6 types of gene mutations
- addition (frame shift)
- substitution
- deletion (frame shift)
- inversion (detach then rejoin inverted)
- translocation (section of bases detach and attach to different chromosome)
stem cells
- undifferentiated cells that can continually divide to become specialised
four types of stem cells;
- pluripotent
- multipotent
- totipotent
- unipotent
totipotent stem cell
can divide into any type of body cell. occur only for limited time in early mammalian embryos
pluripotent stem cells
- found in embryos and can become almost any type of cell
- used in research to treat human disorders
- regrow damaged cells like burnt skin cells
- issues as sometimes treatment doesnt work and can continually divide to create tumours
- ethically wrong to make a therapeutic clone of yourself
- destroy embryos
INDUCED PLURIPOTENT;
- take body cell and manipulate the dna by transcription factors
multipotent and unipotent stem cells
- found in mature mammals and can divide to form a limited number of different cell types
- multi = such as bone marrow can differentiate into limited number
- uni = differentiate into one type of cell
sources of stem cells
- embryos up to 16 days after fertilisation
- umbilical cord blood
- placenta
- adult stem cells such as bone marrow
control of gene expression
- gene expression (protein synthesis) is controlled by epigenetics
Epigenetics
the heritable change in gene function, without changing the dna base sequencd
- caused by changes in environment and can inhibit transcription
- such as diet, stress and toxins
epigenome
- single layer of chemical tags on the SNA
- impacts shape of DNA-histone complex and whether dna is tightly wound so wont be expressed or unwound
- if too tight, transcription factors cant bind
Methylation of dna - 1 chemical tag
- increased methylation of dna inhibits transcription
- when methyl groups are added to dna they attach to cyotsine base
- this prevents transcriptional factors from binding
- attracts proteins that condense the dna-histone complex
Acetylation of histone proteins - chemical tag
- decreased acetylation of associated histones proteins on dna inhibits transcription
- if acetyl groups are removed from dna, histones become more positive and are attracted more to phopshate group on dna
- makes dna and histones more strongly associated and hard for transcription factors to bind
epigenetics and cancer
- tumour suppressor genes: produce proteins to slow down cell division and cause cell death if dna copying errors r detected
- if mutation, cant produce proteins so cell division could continued and mutated cells arent destroyed. BRCA1 and BRCA2 are mutated tumour suppressor genes linked to breast cancer
- tumour suppressor genes: produce proteins to slow down cell division and cause cell death if dna copying errors r detected
- abnormal methylation: control of transcription. methylation can cause a gene to turn on or off. tumour suppressor genes can become hyperethylated,so inactivate and gene turns off. in oncogenes, they may be hypomethylated, reducing methyl groups attached so gene is permanently switched on