Section 8 Flashcards
Give two characteristic features of stem cells
They will keep dividing so they can replace themselfes
They start off undifferentated then can differentate into other cell types
Describe the 3 new types of mutation
Duplication - doubling a base
Inversion - a section of a base sequence is inverted
Translocation - moving a section of base sequence to another part of the DNA
What is a totipotent cell?
Can differentiate into any body cell
Only present into mammalian embryos for a short time
During development they translate only part of their DNA resluting in cell specialisation
What is a pluripotent cell?
Found in embryos
Can differentiate into many different cell types (not embryonic) and can be used to treat human disorders
What is a multipotent cell?
can differentiate into many cell types within the same system
What is a unipotent cell and give an example
can only differentiate into one cell type e.g cardiomycetes in the heart
What are induced pluripotent cells?
produced from somatic cells using transcription factors
What are the advanatges of using induced pluripotent cells for genetic engenering?
Not taken from embryos and no risk of rejection as the cell is taken from the host body
What is potency?
a measure of how many types of specialised cells a stem cell can make
What is the difference between adult and embryonic stem cells?
Adult - can only differentate into cells within their type (e.g blood cells differentiating into different types of blood cell)
Embryonic - can differentiate into any cell type
What is epigenetics?
the process which enviromental factors cause heritable changes in gene function without changing the base sequence of DNA
What is a nucleosome?
When DNA is wrapped around histones
What is the epigenome?
Chemical tags on the nucleosome creating the shape of the DNA histone complex
What does RNA polymerase do?
binds RNA nucleotides together in phosphodiester bonds and catalyses the condensation reactions
What is a promoter?
a sequence of bases on the DNA strand where RNA polymerase binds to start transcription
What is a transcription factor?
Proteins that help RNA polymerase bind to DNA
They activate RNA polymerase and bind to the promoter
Made in the cytoplasm and travels to the nucleus
What is RNA interference?
the process of targeting mRNA using small RNA molecules so its not translated, genes are silenced so protein isn’t made
What is SiRNA?
Small interfering RNA, short double stranded, has to be fully complimentary to mRNA for hydrolysis by binding to the mRNA within RISC
What is miRNA?
mirco RNA, hair pin loop of RNA, not fully complimentary to mRNA so can bind to several mRNA for hydrolysis - binds to RISC by complimentary base pairing
What is RISC and what does it do?
An enzyme which which forms RNA induced silencing complexs
Breakes siNRA into seperate strands, one attaches and the other is discarded
The complex binds to mRNA casuing RISC to cut mRNA in two
What does RNA hydrolase/ nuclease do?
breaks down mRNA into nucelotides so can’t be translated
What is histone acetylation?
Amino acids at the tails of histones can be chemically modified by adding acetyl groups
This causes the DNA to become less condensed giving easier acsess to transcription factors leading to more transcription (the genes become more active)
Removal of acetyl groups (deacetylation) from histones will inactivate genes
What is DNA methylation?
Cytosine bases in DNA can be methylated making it so transcription factors can’t bind and transcription is inhibited
Describe what happens in RNA interference
Small interfering RNA (SiRNA) binds to a protein called RISC and it breaks the double stranded SiRNA into seperate strands
One strand binds to RISC and the other is discarded
The RISC RNA complex binds to mRNA molecules in the cytoplasm by complimentary base pairing
This binding causes RISC to cut the mRNA in two so it can no longer be used in translation
What are the applications of SiRNA?
Can be used to silence genes
SiRNA is made in the lab complimentary to the gene wanted to be silenced
This can then identify gene functions, genetically modify plantsby getting rid of unwanted genes, silencing cancer genes
How is RNA interference used in the body?
Defence against viral attack
Describe the action of Oestrogen in translation
Steriod hormones enter the cell by diffusing across the membrane - they can do this because they are lipid soluble
Inside the cell the hormone binds to a receptor protein
The hormone - receptor complex enters the nucleus
Where it binds to the promotor region of a specific gene and acts as a transcription factor
And stimulates RNA polymerase to start transcription
Which produces the mRNA which is then translated to make the protein encoded by the gene
How can altered DNA lead to cancer?
DNA is altered by mutation which changes the base sequence of a gene that controlls cell division
This gene could be an oncogene or a tumor supressor gene
An oncogene codes for a protein which stimulates cell division so mitosis is uncontrolled
If a tumore supressor gene mutates a non functional protein is made so mitosis becomes uncontrolled which leads to a malignant tumor forming
What are oncogenes?
Mutated proto oncogenes (dominant)
They mutate so it is permanently active and cell division is uncontrolled
It may code for a growth factor receptor that is permanently active or a growth factor which is produced excessively
What are proto oncogenes?
They code for proteins which are involved in stimulating a cell to divide in response to a growth factor
What does a growth factor do?
Binds to a cell surface receptor
A series of events occur which lead to the activation of genes controlling DNA replication and cell division
What is a tumor supressor gene?
Recessive gene
Slows down cell division
Repairs mistakes
Regulates apoptosis
What happens when tumor supressor genes mutate?
If the gene is switched off by mutation the cell can divide uncontrollably
Fill in the gaps
Increased methylation of DNA _____ genes and ______ transcription
If tumor supressor genes are incativates cell division is ______
Decreased methyation of DNA ______ genes and ______ transcription
Proto oncogenes become _______
If oncogenes are activated cell division is _______
inactivates
prevents
increased
activates
stimulates
oncogenes
increased
How do restriction endonucleases work?
They cut double stranded DNA molecules at a specific recognition site
Makes a staggered cut breaking phosphodiester bonds making sticky ends (unpaired bases at the end)
What does DNA ligase do?
Joins fragments of DNA together by their sticky ends creating a recombinant piece of DNA
Reforms phosphodiester bonds
How does reverse transcriptase make DNA using mRNA as a template?
Reverse transcriptase makes a strand of complimentary DNA from the mRNA
mRNA is degraded
A strand of complimentary DNA is made by DNA polymerase
Describe how a gene machine works
The desired DNA sequence is put into a computer
The computer designs short overlapping sequences of bases called oligonucleotides
A machine supplied with chemical reagents make the sequences in the right order
Chemicals are added to make sure the nucleotides join at the right points
The short sequences are joined to make longer sequences
Describe gene cloning using plasmids
A desired gene is isolated from the human cell
Human DNA and plasmid are treated with the same restriction enzyme to make identical sticky ends
Mix DNAs together and add DNA ligase
Add new DNA into bacteria culture
What are the conditions for bacteria to take up new DNA?
Calcium chloride treatment and heat shock
Give two examples of marker genes and how they work
The new DNA has antibiotic resistance so ones without will die if treated
The new DNA has the GFP gene added to it and under UV it glows green
Describe how the polymerase chain reaction happens
Strand separation
- Heat to 93degC
- this separates the strands and H bonds are broken
Primer binding
- Add primers and cool to 55degC
- Primers are made in the gene machiene and are short sequences of single stranded DNA complimentary to the ends of the DNA being amplified
Strand synthesis
- Add heat stable DNA polymerase and free nucleotides and heat to 72degC
-Complimentary strands of DNA are made by DNA polymerase
- 2 new strands made from one
- the cycle is repeated by changing the temp
What is the point of PCR?
produces larger numbers of identical copies of double stranded DNA
Very small amount of DNA can be used
What are the uses of PCR?
To copy small amounts in forensic smaples so it can be used in genetic finger printing
Genetic screening
Detection of bacteria of viruses when present in small numbers
What is the problem with PRC?
Very sensitive - the wrong DNA may be copied if the sample is contaminated
Describe the process of genetic profiling
Use PCR to amplify the DNA
DNA is cut into fragments using restriction endonucleases
The fragments are seperated using gel electrophoresis which seperates fragments according to size and charge
DNA transfererd to a filter sheet and made into single strands
A probe is added which is radioactive so it can be detected
This identifies VNTRs within DNA fragments
A pattern of bands is formed that is unique to every individual
What is a gene probe?
A short sequence of single stranded DNA with a label e.g radioactive isotopes or fluroescent
What are VNTRs?
Variable number tandem repeates
Aka mini satellites
Short sequences of bases that repeate themselves over and over again
They differe in people by the number of repeates and the types of them
What are some uses of genetic modification?
GM organisms to produce human proteins/ drugs for medical use (insulin)
GM plants for more yeild, more nutrition, make their own pesticides, toleratant of extreme conditions
What are some risks/ ethical issues around genetic modification?
effects biodiversity and food chains if pests are killed
antibiotic resistance
using viruses as vectors may cause disease
might switch on/ off other genes
designer babies
playing God
animal rights
