stem cells and epigentics

Question 1

what are the four types of stem cells and what can each one differentiate into?

Answer 1

totipotent: found in the embryo and can differentiate into ANY type of cell
pluripotent: found in embryos and fetal cells and can differentiate into ALMOST ANY type of cell
multipotent: found in mature mammals and can differentiate into a FEW types of cells
unipotent: found in mature mammals and can differentiate into ONLY ONE type of cell

Question 2

What are induced pluripotent stem cells, and how do they work?

Answer 2

They are unipotent cells that produce pluripotent cells using transcription factors.
Transcription factors are used to transcribe or inhibit genes so cells develop similar features to embryonic stem cells. These IPS cells then develop a wide range of different types of tissue cells.

Question 3

what are epigenetics?

Answer 3

heritable changes in gene functions without altering the base sequence. for example: diet , environment, stress, exposure to toxins

Question 4

name and explain two ways in which transcription is inhibited

Answer 4

increase methylation:
methyl groups attach to DNA through the CpG site. Increased methylation inhibits transcription by preventing the binding of transcription factors to the promotor region so genes are not expressed.

decrease acetylation of histones:
When histones are less acetylated, the chromatin is more condensed, which inhibits transcription as the genes are less accessible for the the transcription factors

Question 5

what are the differences between the two types tumours

Answer 5

malignant:
-fast growing
-cancerous
-dark and larger nucleus
-cells often become undifferentiated (non-specialised)

benign:
-slow growing
-non cancerous
-relatively normal nucleus
-cells remain differentiated(specialised)

Question 6

what are the two ways methylation can cause cancer

Answer 6

1. hypermethylation of tumour suppressor genes (so that these genes are not transcribed)
   -the proteins which slow down cell division are not produced, leading to rapid and uncontrollable cell division and the development of a tumour
2. hypomethylation of protooncogenes (so that these genes are continually transcribed)
   -This increases production of proteins that stimulate cell division, which leads to rapid and uncontrollable cell division, which can lead to a tumour

Question 7

what is recombinant DNA

Answer 7

involves the transfer of genes from one organism /species to another

Question 8

describe the process of using reverse transcriptase to obtain genes

Answer 8

-mRNA is extracted from required cell
-mRNA is then mixed with free DNA nucleotides and reverse transcriptase
-the free DNA nucleotides allign next to the complemtary bases on mRNA template
-reverse transcriptase then joins the DNA nucleotides together to produce a fragment of DNA which is called complimentary DNA (cDNA)
-the new DNA strands are hydrolysed so strands separate (cDNA by itself now)
-DNA polymerase is added which makes cDNA double stranded

Question 9

describe the process of using restriction endonuclease to obtain genes

Answer 9

Each type of restriction endonuclease cuts the DNA at a specific’recognition site.’’
If it cuts to produce a ‘sticky end’ they have a staggered cut, which is good as it allows different DNA fragments to join together by complementary base pair
-if it cuts to produce blunt end or straight cuts, these are less useful (as they cannot complement the base pair)

Question 10

describe the process of using gene machine to obtain genes

Answer 10

This produces fragments of DNA/genes without any pre-existing DNA or mRNA
This is a computer program that works backwards, converting the amino acid sequence of a protein back into the sequence of dna nucleotide.

Question 11

what is gene therapy?

Answer 11

its a process that uses recombinant dna to replace unhealthy or non-functioning cells with healthy, functioning cells

Question 12

suggest two reasons why its better to use mRNA rather than DNA for genetic engineering.

Answer 12

-mRNA has no introns so new DNA will have no introns
-There is more mRNA than DNA

Question 13

explain why different restriction enzymes cut plasmids at different locations

Answer 13

they have different recognition sites

Question 14

suggest why these plasmids are different sizes from one another

Answer 14

all the fragments of DNA that are cut are dfferent sizes

Question 15

suggest one advantage of using the gfp gene to be a marker

Answer 15

it only needs uv light to be seen

Question 16

explain how the binding of arabinose sugar to the protein araC changes the intensity of the green light

Answer 16

when arabinose binds to araC it can no longer bind to the promoter therefore increases transccription as more mRNA /GFP

Question 17

Ex[lain why comparing a DNA from a muscle from one mammal and sample from the bone from another mammal is valid

Answer 17

DNA is the same in both muscle and bones

Question 18

name the process which amplifies a small amount of DNA to large amounts

Answer 18

PCR

Question 19

Describe one method used to make radioactively labelled fragments visible following electrophoresis

Answer 19

-to use a nylon membrane/sheet to obtain a replica
-then place it on an x-ray or photographic film to record positions

Question 20

in gel electrophoresis, two bands are usually seen for each person tested. suggest why only one band may be seen for a person

Answer 20

that person could have 2 of the same alleles (homozygous)

Question 22

Explain why the scientist would use the same restriction endonuclease enzymes on each DNA sample

Answer 22

-to cut DNA at same recognition sites
-so can get fragments with required gene

Question 23

Explain how gel electrophoresis separates the fragments of DNA

Answer 23

-negatively charged DNA fragments move towards the positively charged terminal
-different rates of movement due to charge/size of fragment

Question 24

Explain why radioactive DNA probes are used to locate specific DNA fragments

Answer 24

DNA is invisible on gel
Radioactive probes allows detection

Question 25

Explain why it is important to wash off the surplus probe

Answer 25

To remove any unattached DNA probes

Question 26

The allele for beta-thalassaemia differs from the normal allele by only one base pair. Explain why the probe used to identify these alleles consists of a piece of DNA twenty bases in length and not just one base

Answer 26

Single bases occur many times
Sequence of 20 bases is unlikely to occur

Question 27

Describe how an isolated gene can be replicated by the pcr

Answer 27

-heat DNA to 95C
-so hydrogen bonds break and DNA strands separate
-add DNA primers and nucleotides
-and let cool to 55C to allow primers to join
-then heat back to 72C which is optimum temperature for DNA polymerase to form new strands and join nucleotides together

Question 28

Suggest two reasons why DNA replication stops in the pcr

Answer 28

-could run out of primers
-could run out of nucleotides
-DNA polymerase will eventually denature

Question 29

what enzyme is used to insert genes into plasmids

Answer 29

dna ligase

Question 30

give the name of a gentic marker and explain how it can be used to detect if the plasmid had taken up the gen for hGH

Answer 30

-bacteria will glow under fluorescent light if desired gene is there

Question 31

what is a free radical

Answer 31

an atom/atoms that has an unpaired electron so its highly unstable

Question 32

give two ways in which free radicals can form

Answer 32

-during metabolism
-pollutants
- ciggarete smokes
-external exposure to x-rays
-the immune system

Question 33

name the type of molecules which can neutralise free radicals

Answer 33

antioxidants

Question 34

when genes are introduced into plasmids, GFP genes are often added as well. Explain the reason for this

Answer 34

-its a marker gene
-allows identification of cells with new gene