20.Gene Expression Flashcards
(33 cards)
How does oestrogen affect gene transcription
- lipid soluble molecule, diffuses through phospholipid cs membrane
- once in cytoplasm, oestrogen bind with site on receptor molecule of transcription factor
- by binding to site, oestrogen changes shape of DNA binding site on transcription factor
- transcription factor can now enter nucleus through nuclear pore and bind to specific base sequence on DNA
- RNA polymerase can now bind and transcribe
Why do some gene mutations not result in changed amino acid sequence
Degenerate
Multiple codons encode for same amino acid some some base substitution may not change amino acid coded for
What are the types of gene mutation
Addition of bases Duplication of bases Inversion of bases Translocation of bases Base substitution Deletion of bases
What is epigenetics
Environmental factors that can alter gene expression and make heritable changes without altering base sequence of DNA
What is epigenome
DNA and histones and chemical tags
Determines the shape of DNA histone complex and keeps inactive genes tightly packed arrangement therefore cannot be read-known as epigenetic silencing
What is base substitution
- where a single nucleotide in a section of DNA molecule is replaced by another nucleotide that has a different base
- three possible consequences:may form stop codon final protein will be significantly different, different amino acid protein differ in shape not function properly, same amino different codon same protein shape
what is base deletion
loss of a single nucleotide base, creates a frame shift therefore all bases move to left by one letter, meaning rest of codons are now read differently, polypeptide will be different leading to non-functional protein
what is addition of bases
extra base is inserted into sequence, creating frame shift to right, whole sequence of triplets is altered, polypeptide different from one produced by non-mutant gene
what is duplication of bases
one or more bases are repeated creating frame shift to the right
what is inversion of bases
group of bases become separated from DNA sequence and rejoin in reverse order but in same place, affecting the amino acid coded for
what is translocation
combination of addition and deletion, group of bases separated from DNA sequence and are inserted into sequence of another chromosome, often have significant effect on gene expression
what are the causes of gene mutations
- spontaneous during DNA replication and is permanent
- basic mutation rate increased by mutagenic factors
what are some mutagenic factors
Ionising radiation; alpha beta particles and x-rays and UV light disrupt structure of DNA
- chemicals such has nitrogen dioxide alter structure of DNA or interfere with transcription
- benzopyrene inactivates tumour suppressor gene TP53 leading to cancer
how can mutagenic factors cause damage
- benzopyrene adds large group to guanine so unable to pair with cytosine, DNA polymerase inserts any other bases
- ionising radiation produce high reactive agents called free radicals in cells, alter shape of bases, DNA polymerase no longer act on them
what is totipotency
cells which can mature into any cell, from a fertilised egg
how are genes prevented from expressing themselves?
preventing transcription and so preventing the production of mRNA or preventing translation
how do cells lose their totipotency
when they mature and differentiate into specialised cells
what are stem cells
undifferentiated dividing cells taht occur in adult animal tissues and need to be constantly replaced so they self renew
where do stem cells originate from
- embryonic stem cells
- umbilical cord blood stem cells
- placental stem cells
- adult stem cells (specific to particular tissue or organ within which they produce the cells to maintain and repair the tissues throughout organism life)
what are the types of stem cells
totipotent-early stages of emryo/zygote differentiate into any specialised cell
pluripotent-in embryos eg embryonic stem cells can differentiate into almost any type of specialised cells
multipotent-adults, differentiate into limited number of specialised cells
unipotent-only differentiate into single type of specialised cell
what are induced pluripotent stem cells
type of pluripotent stem cell derived from unipotent stem cells, unipotent cell can be any body cell and is genetically altered in a lab to make them acquire the characteristics of embryonic stem cells, the genetic altering includes turning on genes which retain same genetic information that was in embryonic stem cells
pluripotent cells in treating human disorders
regrow tissues skin grafts skeletal muscle cells nerve cells skin cells
what is chromatin
DNA-histone complex
effect of RNA intereference on gene expression
small double stranded sections of siRNA
- enzyme buts large double stranded molecule of RNA into smaller sections called siRNA
- one of two strands of siRNA combines with an enzyme
- siRNA molecule guides enzyme to mRNA by pairing up its bases with complimentary ones on section of mRNA
- enzyme cuts mRNA into smaller sections
- mRNA no longer capable of being translated into polypeptide
- gene not expressed and been blocked
