Entire Topic 8 Flashcards
What is a gene mutation?
What occurs when a mutation happens - start from DNA bases
A change in the DNA base sequence of a gene
- it occurs mainly in DNA replication and occur randomly
- however frequency is increased by exposure to mutagenic agents
- this can result in different amino acid sequence in primary structure
- Therefore hydrogen and ionic bonds form in different locations
- Therefore different tertiary structure and therefore different 3D shape
- therefore different function or non functioning protein
- alterations in genes can result in a mutation which causes cancer
Describe and explain the effect of:
1. Addition mutation
2. Deletion mutation
3. Substitution mutation
- Addition
One extra nucleotide is added to the sequence - therefore all the subsequent codons are altereted, aka frame shift - very harmful because altered codons could code for different amino acids resulting in a non functioning protein - Deletion
Deletion of a base sequence - causes frame shift to the left and could result in a different polypeptide chain and nonfunctioning protein - Substitution
One base is changed for a different base - results in one codon changing and because genetic code is degenerate it may code for the same amino acid and have no impact - also no impact if mutation is in introns
Describe and explain the effect of:
1. Inversion mutation
2. Duplication mutation
3. Translocation
- Inversion mutation
Section of DNA bases detatch but when they rejoin they are inverted - can result in different amino acid being coded for in this region - Duplication mutation
One particular base is doubled at least once in a sequence - causes frame shift to the right and different sequence of amino acids are coded for - Translocation
When section of bases on one chromosome detaches and attaches onto a different chromosome - alteration is substantial as it can cause significant impacts on gene epression which are expressed on the phenotype
What are stem cells?
What are these types of stem cells and where are they found:
- totipotent
- pluripotent
- multipotent
- unipotent
Undifferentiated stem cells than can continually divide and become specialised
totipotent - stem cells can divide and produce any type of cell - found in early mammalian embryos
pluripotent - found in embryos and can divide into unlimited numbers and be used to treat human disorders - cant specialise into placenta cell
multipotent - can divide and produce into a limited type of cells - found in mature animals
unipotent - can divide and produce one type of cell - found in mature animals
What are iPS and how do you produce them
- iPS - can be produced from adult somatic cells using appropiate transcription factors to overcome ethical issues
- to do this, genes that were switched off to make cell specialised are switched back on using trancriptional factors
What do transcription factors do and how do they active or deactivate genes?
Transcription factors - stimulate or inhibit transcription of target gene, where they move from the cytoplasm into the nucleus and binds to DNA
These transcription factors, which are proteins bind to different base sequences and therefore initiate
transcription of genes
Once bound, transcription begins to create a protein
How does oestrogen work to initiate transcription
- Oestrogen binds to a receptor site on transcriptional factor
- This causes a slight change in shape and makes it complementary and able to bind to DNA to initiate transcription
1.What are epigenetics?
2.What does increased methylation do and explain its steps.
3. What happens when decreased acetylation occurs?
- Epigenetics - heritable change in gene function, without changing DNA base sequence - changes are caused by environment and can inhibit transcription
- Methyl group attaches to DNA cytosine base - prevents transcription factors from binding and attracts proteins that condense DNA-histone complex - methylation prevents a section of DNA from being transcribed
3.Acetyl groups are removed from DNA then histones become more positive. This attracts histone to phosphate group on DNA
This makes DNA histones more tightly coiled and hard for transcription factors to bind
How does RNAi interfere with translation
- done through siRNA
- An enzyme cut mRNA into siRNA
- One strand of siRNA combines with enzyme RISC
- siRNA-RISC bind via complementary base pairing to another mRNA molecule
- When bound, enzyme will cut up mRNA so it cannot be translated
What are benign tumours?
What are malignant tumours
Benign:
- tumours which grow at a very large but slow rate
- noncancerous as they produce adhesive molecule sticking them together to particular tissue
- surrounded by capsule - so remain compact - impact is localized
Malignant:
- tumours which are cancerous and grow large rapidly
- Cell nucleus becomes large and cell becomes unspecialised again
- Metastasise - tumour breaks off and spreads to other tissues in the body
- Tumour grows projections into surrounding tissues and develop its own blood supply
- life threatening as even after removal it can reoccur
- What are oncogenes and how they develop tumours?
- What are Tumour Supressor genes and how do they lead to tumours?
- Oncogenes
- Mutated versions of proto-oncogenes (proteins which are involved in the start of DNA replication and mitosis cell division)
- oncogene mutations can result in this process being permanently activated to make cells divide continually - Tumour supressor genes (TSG)
- produce proteins to slow down cell division and cause cell death if DNA copying errors are detected
- mutations result in TSG not producing proteins to carry out this function
- therefore cell division continues
- mutated cells will not be identified and destroyed
- How can abnormal methylation (hyper and hypo) result in tumours?
- Abnormal methylation
- TSG could become HYPERmethylated - therefore increased methyl groups attach to the gene, therefore gene is inactivated
- Oncogenes are hypomethylated - therefore reduced methyl groups attached - gene is permanently switched on
How does oestrogen result in cancer?
- after menopause stops, fat cells in breast tissues produce oestrogen - this is linked with breast cancer in women
- There is a knock on effect: tumour results in even more oestrogen produced as more breast tissue is produced
- this may be because oestrogen can activate gene by binding to a gene which inititates transcription - if this is a proto-oncogene, result is that it is permanently turned on activating cell division
How would you use reverse transcription to create of DNA and what are its advantages?
This enzyme makes copies from mRNA
- Cell which naturally produces protein X - this cell contains large amounts of mRNA for X
- Reverse transcriptase joins DNA nucleotides with complementary bases to mRNA sequence
- Single stranded cDNA is made - this is intron free
- DNA polymerase is used to make this dna fragment double stranded - this does not contain introns
How would you use restriction endonucleases to create of DNA and what are its advantages?
Restriction endonucleases cut up DNA
- Each enzyme cuts DNA at specific location as active site is complementary in shape to recognition sequences
- Some enzymes cut at same location in double strand and create a blunt end, other enzymes cut to create staggered ends which expose DNA bases - these are called sticky ends - ability to join DNA with complementary base pairs
