Mr G bio 5 mutations and gene expression Flashcards
what are stem cells?
unspecialised cells that can develop into other types of cell.
stem cells keep dividing to produce more stem cells, which then differentiate to become specialised
where are stem cells found?
-embryos
-adult tissues
what are the two types of stem cells in embryos?
totipotent and pluripotent
what is a totipotent stem cell (in embryos)?
can differentiate into any type of body cell in an organism (including placental cells) only present in mammals in the first few divisions of an embryo
what is a pluripotent stem cell?
can mature into any type of body cell but have lost the ability to develop into placental cells
what are the two types of stem cells found in adult mammals?
multipotent and unipotent
what is a multipotent stem cell?
can differentiate into a few diff types of cell
what is a unipotent stem cell?
can only differentiate into one type of cell
how are stem cells able to become specialised?
become specialised because they all contain the same genes but during development not all are transcribed and translated (expressed). under one set of conditions, certain genes are expressed and others are switched off
how do stem cells become specialised?
genes that are expressed get transcribes into mRNA which is then translated into proteins. the proteins modify the cell and changes to the cell produced by these proteins cause the cell to become specialised (difficult to reverse)
what are cardiomyocytes?
heart cells which cant divide to replicate themselves
how are cardiomyocytes replaces after heart attack or after they become worn with age?
small supply of unipotent stem cells in the heart which can replace old or damaged cardiomyocytes
give an example of existing an stem cell therapy (stems cells in medicine)
-bone marrow transplants (bone marrow contain stem cells that can become specialised into any type of blood cell)
how and what type of stem cell are sourced from adult tissues?
from body tissues of an adult through a simple but painful procedure. multipotent so can only differentiate into a limited no. of specialised cells
how and what type of stem cell is sourced from an embryo?
-taken from embryos at early stage of development
-embryos creates in lab (in vitro fertilisation)
-at 4-5 days old, stem cells removed and embryo destroyed
-stem cells can divide an unlimited no. of times and are pluripotent
what is the name for a multipotent stem cell being turned into a pluripotent stem cell?
induced pluripotent stem cell
how are induced pluripotent stem cells formed?
adult cells are made to express a series of protein transcription factors that are normally associates with pluripotent stem cells. protein transcription factors cause the adult body cells to express genes that are associated with pluripotency
how can a virus be used to form an induced pluripotent stem cell?
protein transcription factors can be introduces to adult cells by infecting then with a modified virus, which contains genes coding for the protein transcription factor with its genetic material. virus infects cell which incorporates the PTF genes into the cell DNA which is then expressed producing PTF
what are the ethical considerations surrounding stem cells?
-obtaining stem cells from an embryo results in the destruction of an embryo- destroying a potential life
-could take stem cells from unfertilised egg that had been stimulated to divide
-some people say only adult stem cells should be used but arent as useful as mulitpotent
what are the benefits of stem cell therapy?
-could save many lives
-if IPS are used then possible to make new tissues or organs for people which are genetically identical (less chance of rejection)
-improve quality of life for people
what is the risk of stem cell therapy?
stem cells may divide out of control leading to a tumour
what is a mutation?
change to the base sequence of DNA.
what are the 6 types of mutation?
substitution, addition, deletion, duplication, inversion, translocation
what is a duplication mutation?
one or more bases are repeated
what is an inversion mutation?
sequence of bases is reversed
what is a translocation mutation?
sequence of bases is moves from one location in the genome to another.
could be movement within same chromosome or to diff chromosomes
what effect do mutations have?
causes the DNA base sequence to alter, altering the amino acid sequence in the polypeptide. this may change the final tertiary structure of the protein changing H/ionic/disulphide bonds formed, altering its function. some can increase the likelihood of developing certain cancers
how can some mutations cause a genetic disorder?
if a gamete containing a mutation for a type of cancer or a genetic disorder is fertilised, the mutations will be present in the foetus- hereditary mutations- passed from parent onto offspring
why dont all mutations affect the order of amino acids in the protein?
the degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet
what is a frameshift mutation?
some mutations have a huge effect on the DNA base sequence of a gene
additions, duplications and deletions always change amino acid sequence and the no. of bases in the DNA code which causes a frameshift in base triplets that are downstream
what is a mutagenic agent and give an example
things that increase the rate of mutation e.g. UV radiation, some chemicals
how can mutagenic agents increase the rate of mutation by acting as a base?
chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA
how can mutagenic agents increase the rate of mutation by altering bases?
some chemicals can delete or alter bases
how can mutagenic agents increase the rate of mutations by changing the structure of DNA?
some types of radiation can change the structure of DNA which causes problems during DNA replication
what is a transcription factor?
a protein molecule that controls the transcription of genes as not all genes in a cell are expressed and because diff genes are expressed, diff proteins are made which modify the cell
how do transcription factors work?
in eukaryotes, TF moves from cytoplasm into the nucleus, then bind to specific DNA sites called promoters (found near start if their target genes), TF control expression by controlling the rate of transcritprion
what are the two types of transcription factors?
activators and repressors
what do activators do?
increase the rate of transcription- they activate RNA polymerase by helping the enzyme bind and increase transcription
what do repressors do?
decrease the rate of transcription- bind to the start of the target gene, preventing RNA polymerase from binding, stopping transcription
describe how oestrogen can affect expression of genes
binds to a transcription factor called an oestrogen receptor, forming and oestrogen-oestrogen receptor complex. complex moves from cytoplasm into nucleus where it binds to promoter region and can act as an activator or repressor
what is RNAi (RNA interference)?
where small double stranded RNA molecules stop mRNA from target genes being translated into polypeptides
what are the molecules involved in RNAi?
siRNA (small interfering RNA) and miRNA (microRNA)
how does siRNA work?
one mRNA has been transcribed it enters the cytpolasm, in the cytpolasm, double stranded siRNA associates with several proteins and unwinds, one of the single strands of siRNA is selected and the other degraded, forms a complex called an RNA- induced silencing complex, single strand of siRNA then binds to the target mRNA, the base sequence of the siRNA is complementary to the base sequence in sections of the target mRN, so binds, the proteins associated with the soRNA cut mRNA into fragments- no translation
how does miRNA in mammals work?
miRNA isnt usually fully complementary to target mRNA (less specific), one strand associated with proteins and binds to target mRNA in cytoplams, mRNA is not cut, the miRNA- protein complex physically blocks the ribosomes attaching the mRNA thus preventing translation, mRNA is degraded or stored
what is epigenetics?
a heritable change in gene function, without changes to the DNA base sequence
how does epigenetic control work?
determines whether gene is switched on or off (expressed) through attachment or removal of chemical groups to or from DNA or histone proteins.
dont alter base sequence of DNA
alter how easy it is for RNA polymerase and other proteins needed for transcription to interact and transcribe the DNA
how can epigenetic changes be inherited?
organisms inherit base sequences from their parents.
most epigenetic marks are removed between generations, but some escape the removal process
this means expression of some genes in offspring can be affected by environmental chnages that affected their parents
how does methylation of DNA control gene expression?
A methyl group is attached to the DNA coding for a gene
group always attaches at a CpG site
increased methylation of DNA changes the DNA structure so RNA polymerase cant transcribe the gene- gene not expressed
how does acetylation of histones allows controlling of gene expression?
histones can be epigenetically modified by the addition or removal of acetyl groups
when histones are acetylates, chromatin is less condensed
RNA polymerase can bind the DNA, allowing genes to be transcribed and expressed
how can a mutation lead to cancer?
if the mutation is in a gene that controls the rate of mitosis, can cause uncontrolled cell division, this can lead to a tumour and tumours that invade and destroy surrounding tissue are called cancers
what is a tumour?
mass of abnormal cells
what are the two types of genes that control cell division?
-tumour suppressor genes
-proto-oncogenes
what is a tumour suppressor gene?
normally slows cell division by producing proteins that stop cells dividing or cause self destruct (apoptosis)
what happens if a mutation occurs in a tumour suppressor gene?
the gene is inactivated. the protein isnt coded for and produced and the cells divide uncontrollably (rate of division increases) resulting in a tumour
what are proto-oncogenes?
normally stimulate cell division by producing proteins that cause cells to divide
what happens when a mutation occurs in a proto-oncogene?
the gene can become overactive. stimulated cells to divide uncontrollably (rate of division increases) resulting in a tumour. mutated proto-oncogene called an onco-gene
what is a malignant tumour?
cancerous, grow rapidly and invade and destroy surrounding tissue , cells can break off tumours + spread to other parts of the body in bloodstream or lymphatic system
what is a benign tumour?
not cancerous, grow slower than malignant and often covered in fibrous tissue that stops cells invading other tissues. often harmless but can cause pressure on organs and sometimes become malignant
how do tumour cells differ from normal cells?
-nucleus larger and darker
-irregular shape
-dont produce all proteins needed to function correctly
-different antigens on cell surface membran
-dont respons to growth regulating processes
-undergo mitosis more frequently
what happens when TSG becomes hypermethylated?
gene is not transcribed so proteins made to slow mitosis arent made, cells are able to divide by mitosis uncontrollably and tumours can develop
what happens when proto-oncogenes become hypomethylated?
causes them to act as oncogenes, increases transcription and therefore translation of proteins that increases mitosis, cells stimulated to mitose uncontrollably, forming a tumour
how can oestrogen cause breast cancer?
can stimulate breast cells to divide and replicate. more divisions taking place so more chance of mutations occurring so increased chance of cells becoming cancerous. also, of cell does become cancerous then rapid replication can be further assisted by oestrogen
