Chapter 20 - Gene expression Flashcards
state the 3 possible outcomes of a base substitution
- formation of a stop codon which prematurely ends the addition of amino acids
- formation of a codon which codes for a different amino acid
- codon for the same amino acid known as a silent mutation
what is caused by the deletion of bases
frame shift
why might a deletion at the end of the sequence have less of an impact on the final polypeptide sequence than a deletion at the start?
deletion at the beginning will change all subsequent codons
how is addition of bases similar to deletion of bases?
can also cause a frame shift but to the right
what is duplication of bases
when one or more bases are repeated, causing a frame shift to the right
what is inversion of bases?
when a group of bases become separated form the DNA strand and rejoin in inverse order, only effects the amino acids of this portion
what is translocation of bases?
when a group of bases become detached from the sequence at one chromosome and become inserted into a different chromosome, often has severe effects on phenotype
what are the two main causes of gene mutations?
- high ionising radiation such as alpha and beta particles or x-rays
- chemicals such as nitrogen dioxide can directly interfere with transcription and the structure of DNA
what are the causes of mutations known as?
mutagenic agents
why must cells become specialised or differentiated in multicellular organisms
no single cell structure could carry out all functions required for survival
how are cells able to become specialised in multicellular organisms if they all contain the same genes?
only certain genes are expressed in each cell or ‘switched on’
what is totipotency
any cell, such as a fertilised egg, which can mature into any body cell
how are genes prevented from expressing themselves (2)
- preventing transcription and therefore preventing the production of mRNA
- preventing translation
what are stem cells
undifferentiated dividing cells which occur in adult animal
what are embryonic stem cells?
come from embryos in the early stages of developement that can differentiate into any type of cell
what are umbilical cord blood stem cells
cells derived from umbilical cord blood, similar to adult stem cells
what are placental stem cells?
cells found in the placenta which develop into specific types of cells
what are adult stem cells
found in the body cells of a fetus through to the adult, specific to a particular tissue or organ
what are totipotent stem cells
found in an early embryo and can differentiate into any type of cell, zygotes are totipotent
pluripotent stem cells
found in embryos and can differentiate into almost any type of cell
multipotent stem cells
found in adults and can differentiate to a limited number of specialised cells
unipotent stem cells
can only differentiate into a single type of cell, derived from multipotent stem cells and are found in adult tissue
what are induced pluripotent stem cells
unipotent stem cells whcih have been genetically altered in a lab to create pluripotent stem cells, similar to embryonic stem cells in function, also able to possibly divide infinately
how might iPS cells be used to treat humans?
e.g. skin grafts
outline the process by which transcriptional factors control transcription (3)
- each transcriptional factor has a specific site that binds to a specific base sequence on the DNA
- when it binds it causes the region of DNA to begin transcription
- when a gene is not being expressed, the the site on the transcriptional factor is not active
outline the process by which oestrogen can activate transcriptional factors (4)
- lipid soluble so diffuses across phospholipid bilayer
- oestrogen then binds to a receptor on the transcriptional factor
- this causes the transcriptional factor to change in shape and therefore be able to bind to the DNA
- begins process of transcription
what are epigenetics
explanations of how environmental influences can alter the genetic inheritance of an organisms offspring
what is the epigenome
the accumulation of the chemical tags, or signals, over a lifetime. the chemical tags form a layer surrounding the DNA-histone complex which determine the shape of the DNA-histone complex and, thus, transcription
what is the effect on transcription of decreased acetylation?
- deacetylation increases the positive charges on histones therefore increasing there attraction to the phosphate groups of DNA
- this causes the association between the DNA and histones to become stronger and the DNA less accessible to transcription
- therefore the gene becomes switched off
what is the effect of increased methylation?
- methyl group added to cytosine
- attracts proteins that condense the DNA-histone complex and thus prevent transcription
- preventing the binding of transcriptional factors
what is epigenetic therapy
use drugs to inhibit or counteract changes to histone acetylation or DNA methylation
outline the process by which siRNA interferes with gene expression
- enzyme cuts double stranded RNA into smaller sections (siRNA)
- one of the two strands of siRNA combines with an enzyme
- siRNA guides enzyme to mRNA
- enzyme cuts mRNA into smaller sections
- mRNA no longer able to carry out translation
state 5 main features of a malignant tumour
- grows to large size
- grow rapidly
- large and dark nucleus (much DNA)
- cells become de-differentiated (unspecialised)
- cells do not produce adhesion molecules
- tumours not surrounded by capsule so grow finger-like projections
- often have systemic effects
- more likely to be life threatening
- removal usually involves radiotherapy and or chemotherapy aswell as surgery
- more frequently reoccur after treatment
what are oncogenes
mutations of proto-oncogenes that are permanently active (cells divide constantly)
what are tumour suppressor genes?
slow down cell division, repair mistakes in DNA and ‘tell’ cells when to die
what is the process by which hypermethylation can lead to cancer? (3)
- hypermethylation occurs in specific region of tumour suppressor genes which leads to the tumour suppressor genes being inactivated
- transcription of promoter regions of tumour suppressor genes is inhibited meaning it is silenced
- its inactivation leads to increased cell division and the formation of a tumour
what is the effect of oestrogen concentrations on breast cancer?
after menopause,oestrogen production in breast tissues is increased. once a tumour develops, oestrogen concentrations increase further and white blood cells which are attracted further increase oestrogen concentration, leading to further development of the tumour
what is WGS sequencing
whole genome shotgun sequencing, when the DNA is cut into many small pieces for easy sequencing then using computer algorithms to assemble it
what are SNP’s
single nucleotide polymorphisms, single base variations which cause disease and stuff
what is the proteome
all the proteins produced by a genome
why is determining the proteome of prokaryotes relatively easy?
- most have only 1 circular piece of DNA wich is not associated with histones
- no non-coding portions of DNA
how much of human DNA is thought to be coding?
around 1.5%
