Genetics Flashcards
Gene Mutation
change to order or number of nucleotides in a base sequence of a gene
Causes of genetic mutations
- spontaneously during DNA replication
- high energy ionising radiation
- carcinogenic chemicals
Suggest types of substitution genetic mutations and explain what is meant by each
nonsense - codes for stop codon preventing production of polypeptide
mis-sense - codes for different amino acid = non functional protein
silent - codes for same amino acid since genetic code is degenerate
Describe impact of insertion or deletion mutations
- frame shift
- change nature of all base triplets downstream of mutation
- different sequence of amino acids coded for
Suggest ways in which the body responded to mutated cells
- apoptosis
- attacked by immune response of white blood cells
Chromosome Mutation
change to number or structure of chromosomes
Suggest types of chromosomal mutations
duplication - extra copies
deletion - whole sections lost
inversion - sequence breaks off and rejoins in reverse order
translocation - fragments break and join onto another chromosome
Explain in detail how a genetic mutation can lead to a non functional protein
- base sequence of DNA changes
- different codon in mRNA
- different anticodon so different tRNA attaches to ribosome
- different primary structure
- changes in bonding / tertiary structure
- shape of polypeptide affects function
Germline Mutation
mutations in cells that give rise to gametes so mutation is passed onto offspring
Cell Specialisation
cell only translates part of its DNA to develop structures specific to its role
Totipotency
ability of cells to differentiate into any type of body cell
Sources of stem cells
- embryo
- umbilical cord/placenta
- adult stem cell tissue
Totipotent
cells that can differentiate into any cell type (embryonic stem cells)
Pluripotent
cells that can differentiate into several cell types (embryonic cells in inner mass of blastocyst)
Multipotent
cells that can differentiate into a limited number of specialised cells (bone marrow cells)
Unipotent
cells that can only differentiate into a single type of cell (cardiomyocytes)
Induced Pluripotent Stem Cells (iPS)
made from adult somatic cells genetically reprogrammed to turn on genes that would be otherwise switched off using protein transcription factors
Advantages of induced pluripotent stem cells
- capable of self renewal so there is an endless supply
- alternative embryonic stem cells have ethical considerations
Arguments FOR embryonic stem cell research
- provide cures for people with debilitating diseases
- embryos left over from IVF are often discarded
Arguments AGAINST embryonic stem cell research
- destroying a potential life / unethical to produce blastocyst for research
- alternatives exist such as adult and induced pluripotent stem cells
Cancer
when cells from tumour have spread to other parts of boy/ metastasis occurred
Tumour
mass of abnormal cell growth
Benign tumour
- surrounded by a capsule and held together by adhesion molecules
- lacks the ability to invade neighbouring tissue or metastasize so localised effects
- slow growth
- removed with surgery/rarely reoccurs
Malignant tumour
- tumour that invades surrounding tissues in finger-like projections
- metastasises
- rapid uncontrolled growth
Compare benign and malignant tumours
- normal vs larger/darker nucleus
- specialised vs unspecialised cells
- form adhesion molecules so remain within tissue they arise vs spread via metastasis forming secondary tumours
- surrounded by capsule so localised effects vs grow in finger-like projections into surrounding tissue
- slow vs rapid growth
- remove via surgery + rarely reoccur vs radio/chemotherapy + reoccurring
Suggest how a tumour metastases
- angiogenesis occurs where tumour develops blood and lymphatic vessels
- tumour cells squeeze into vessels
- spread via blood and lymph
Proto-oncogenes
genes whose products accelerate MITOSIS when activated by growth factors
Oncogenes
- mutated proto-oncogenes
- permanently switched on resulting in uncontrolled cell division
- cause cancer growth
Tumour suppressor genes
genes whose products slow down MITOSIS by repairing DNA or causing apoptosis
Suggest how oncogenes cause uncontrolled cell division
- products stimulate cell division even in absence of growth factors
- code for excessive amounts of growth factors
Two-Hit Hypothesis
- cancer results from accumulated mutations
- mutations in both alleles to inactivate tumour suppressor genes
Suggest why individuals who inherit a mutated tumour suppressor gene are more likely to develop cancer
- mutated tumour suppressor genes are recessive in nature so both must be mutated
- most people will develop at least one mutation in their lifetime
- individuals who inherit mutated tumour suppressor genes are more likely to have both copies mutated
Suggest why risk of developing cancer increases with age
- mutations are slow
- more likely to acquire mutations over time
Describe how radiotherapy works
targets high energy radiation at cancer cells creating mutations in DNA until cell is no longer viable
Describe how chemotherapy works
damages DNA of cells as they divide so cells dividing quickly are more sensitive
Transcription Factors
- proteins that bind to DNA
- regulate gene expression
- by promoting or suppressing transcription of gene
Operon
group of closely linked genes that produce a single mRNA in transcription (consisting of both regulatory and functional DNA)
Regulatory Sequence
sequence of bases capable of increasing or decreasing the expression of specific genes
Describe how transcription factors activate gene expression
- TF activated and move into nucleus via nuclear pores
- bind to regulatory regions on DNA called promoters by complementarity of shape
- RNA polymerase stimulated to bind to promoter region and begin transcription
Describe how elevated oestrogen levels promotes progression of some breast cancers
- (steroid hormone) lipid soluble so diffuses through plasma membrane
- binds to ER-α receptor in inhibitor-transcription complex
- induces change in shape which activates TF to enter nucleus from cytoplasm
- TF stimulate transcription of oncogenes
Suggest what is meant by RNAi
- RNA inference
- inhibits translation of target genes
- by destroying mRNA before it can be translated into a polypeptide
Describe how RNAi inhibits gene expression and suggest reasons gene might still be expressed
- RISC activated by unwinding siRNA complex and single strand of siRNA remains attached
- single stranded siRNA is complementary to gene
- siRNA binds to mRNA
- mRNA cut using enzymes found in RISC
- mRNA destroyed so cannot be translated
- more mRNA than siRNA
- not all mRNA destroyed
Suggest how siRNA can act as oncogene/tumour suppressor gene
- oncogene by preventing translation of tumour suppressor gene
- tumour suppressor gene by preventing translation of oncogene
Epigenetics
- heritable changes to gene function
- without changing base sequence of DNA (genotype)
- caused by changes in environment
Epigenome
all epigenetic tags added to genome which regulate gene expression
Describe how the epigenome regulates gene expression
- epigenetic tags determine the shape of DNA-histone complex
- by methylation and acetylation
- determine whether transcription factors can bind to DNA base sequence
Suggest how the epigenome is flexible what factors affect it
epigenetic tags respond to environmental changes
- diet
- stress
- physical activity
- exposure to toxins
Heterochromatin
- DNA-histone complex condensed
- no access by transcription factors
- decreased acetylation
- increased methylation
Euchromatin
- DNA-histone complex less condensed
- access by transcription factors
- increased acetylation
- decreased methylation
Imprinted Genes
genes whose expression is determined by heritable epigenetic tags from the parent that contributed them
Describe how increased methylation of DNA inhibits transcription
- addition of methyl group to cytosine base on DNA
- prevents binding of TFs hence RNA polymerase
- attracts proteins which induce de-acetylation of histone so inaccessible to TFs
Describe how increased histone acetylation of DNA promotes transcription
- addition of acetyl group to lysine (amino acid) found at the end of DNA-histone complex
- histone more negatively charged
- repels phosphate groups on DNA
- less affinity/loose bonds so accessible to TFs
Suggest characteristic features of stem cells
- undifferentiated
- replace themselves continually
Suggest why cancer is more likely to be treated successfully if diagnosed early
- smaller tumours/ fewer cancer cells
- tumour has not metastasised
Suggest why organisms regulate gene expression
- not all cells require all genes
- more efficient and less wasteful to only synthesise substances cell requires
Explain why cells in our body have different functions but all contain the same genes
- not all genes expressed
- some genes are methylated to prevent transcription of them
Suggest why inactivation of tumour suppressor genes results in cancer
no control over mitosis
