Topic 8A - Mutations and Gene Expressions Flashcards
Why might addition mutations cause major changes to a protein, and why might it not?
(3)
Addition mutations result in frame shifts if there are one or two bases added. All triplet codes to the right will alter, therefore changing the amino acid sequence / primary structure of the protein. If there are three additions close together, only a small section is layered / potentially only the addition of one amino acid.
Describe what is meant by induced pluripotent stem cells.
- and they are unspecialise
Induced pluripotent stem cells are pluripotent stem cells formed from unipotent stem cells / somatic / body cells. (1)
They are formed by using transcription factors to stimulate. (1)
note
tightly condensed histones may make a gene hard to access due to lack of acetylation, and so is inactive / switched off.
What are silent mutations?
mutation that doesn’t cause a change in amino acid order
All types of mutations
substitution, deletion, addition, duplication, inversion, and translocation (within same or to diff chromosome)
- some of these cause a frameshift downstream of the mutation
What can cause epigenetic changes? Are they permanent?
The environment and lifestyle.
Most epigenetic markers removed during gamete formating, out some may be passed on.
Chemical tags can be removed, so aren’t permanent.
epigenetics
How chemical tags attached to DNA (and histones) that affect gene expression without altering the base sequence
What is the impact of methylation on DNA (… transcriptional factors?)?
How is gene expression impacted?
Adding methyl group allows it to bind to CpG binding site - which is a promoter region (found between C and G bases). So, the site is now not complementary to transcriptional factors :
can’t bind, so RNA polymerase can’t bind - transcription inhibited.
Adding methyl = gene switched off
Removing methyl = gene switched on
How does acetylation affect DNA?
How is gene expression impacted?
Tumour suppressor and proto - oncogenes - think about how these are impacted by methylation
Adding methyl / hypermethylated - binding site changed on gene promoter region - TF and RNA polymerase can’t bind - tumour suppressor protein not transcribed and translated.
cell division is uncontrolled, so lead to tumour growth.
Hypomethylation/ removing methyl groups
Gene mutation
change in DNA base sequence ( spontaneously) mainly during DNA replication
What do mutagenic agents do?
Increase the rate / likelihood of mutation
- may change sequence and encoded polypeptide chain then & different primary structures as different hydrogen (ionic and disulfide later on) formed as R groups interact differently > tertiary structure altered may mean non-functional protein
- mutations in genes for cell cycle may cause cancer
degenerate code
All organism’s DNA contains the same 4 type of bases and so multiple triplets can code for the same amino acid
Which mutations are least and most harmful?
Note some mutations are hereditary if gamete has it, and some mutations can cause genetic disorders or increase chance of cancer.
Least: substitution and inversion, which may only change a couple of codons, degenerate may mean no impact.
All others cause a frameshift in gene downstream : may result in incomplete triplets, stop codon earlier on, completely different protein made.
- Translocation may change phenotype
3 types of mutagenic agents
- Chemicals called base analogs can substitute for another new base during DNA replication (so mention how it can pair with the complementary base to the one its substituting !)
- some chemicals can delete /alter bases (e.g. adding a chemical group to change its structure - methyl probably an example)
Example to know : Alkylating agents add alkyl group to guanine, changes structure so not complementary - Radiation (UV) can change DNA structure - problems then arise w/ structure or during replication
- Link all of these to changing base sequences and transcription/ translation
note
only part of the totipotent DNA is expressed / translated when cells become more specialised and only some genes are expressed
Stem cells
Undifferentiated cells that continually divide to become specialised,process: differentiation
Totipotent stem cells
can mature and divide into any type of body cell - including placenta cells
These only occur for a limited time in (mammalian) embryos.
Total power
pluripotent stem cells
*
Also in embryos and can divide in unlimited numbers.
- not into placenta cells
- can be used in treating human disorders
multipotent stem cells
found in mature mammals can divide to form a limited number of different differentiated cells
unipotent stem cells
Stem cells that divide into one type of cell - must know example of cardiomycytes (circulatory/ nervous/ immune system)
Example of uni potent stem cell and why is it important that they are Unipotent.
Skin epidermal cells.
They have to divide quickly to regenerate damaged tissue - nature decreases risk of tumour development as only a few genes to transcribe (e.g. gene for haemoglobin is switched off)
What does it mean for a cell to be specialised
During their development, they only transcribe/late part of their DNA. Under certain conditions, gives may be switched off or on (read revision guide on stem cells)
bone marrow stem cells produce…
blood cells
Benefits of using stem cells in medicine?
Could save many lives - like growing organs
Could improve quality of life - eg, replace cells in eyes to cure blindness
- there may be more (such as laws against cloning or growing embryos past certain days - try exam questions)
3 main sources to obtain human stem cells
- Adult stem cells from bone marrow/ body tissue, simply done but they aren’t as flexible as embryonic stem cells as multipotent - specialise into a few.
- Embryonic stem cells at early stage using IVF (grown in lab, stem cells removed and embryo destroyed), flexible as pluripotent.
- Induced pluripotent stem cells (see other cards)
Nove to self revising : ethics of stems and iPs , revision guide and ms Estmuch
role of a tumour suppressor gene
To slow down cell division or the cycle, or to cause cell death if error during DNA replication detected
- hyper methylation of the gene stops cell destruction when needed
