21: Gene Expression Flashcards
Describe the Stimulation of Transcription in Eukaryotes:
- transcriptional factors are found in the cytoplasm of the cell
- these move into the nucleus
- each transcriptional factor has a site which binds to the promotor region of DNA (specific base sequence of DNA)
- binding of transcriptional factor to promotor region of DNA allows the attachment of RNA polymerase to the DNA and transcription is stimulated
- mRNA produced and subsequently translated into a protein
What is the role of RNA polymerase?
How can transcriptional factors be used to inhibit transcription?
- attachment of adjacent nucleotides together, via the formation of phosphodiester bonds
- could prevent RNA polymerase from binding to DNA, by binding themselves to the DNA
What is Oestrogen?
How does it enter the cytoplasm of the cell?
- lipid-soluble, steroid hormone released into the bloodstream
- simple diffusion in between the phospholipids
How can Oestrogen initiate Trancription?
- oestrogen enters cytoplasm via simple diffusion
- this binds to the transcriptional factor in the cytoplasm, causing the transcriptional factor to change shape
- this causes the inhibitor molecule (on transcriptional factor) to be released, exposing the DNA binding site on the transcriptional factor
- transcriptional factor now moves into the nucleus and binds to a specific sequence of bases on the promoter region, enabling RNA polymerase to bind and initiate transcription
What is the function of the inhibitor molecule?
- prevents the transcriptional factor from binding to the promotor region of the DNA, so no RNA polymerase can bind when protein synthesis isn’t needed
Describe the effect of RNAi (RNA interference) on Gene Expression:
- double stranded RNAi is coded for by special regulatory genes
- this moves into the nucleus where it becomes single stranded and associates itself with a nuclease enzyme
- this now binds to specific mRNA molecules with complementary base pairs via complementary base pairing
- this enzyme cuts the mRNA into 2
- translation of mRNA cannot occur so protein synthesis stops
What is RNAi?
When might RNAi be important in a cell?
- small double stranded sections of RNA, which inhibit gene expression at the translation stage in a process called RNA interference
- if mRNA concentration needs to be regulated, it can limit the amount of protein translated
- stops translation of viral RNA in a cell infected by virus
Give 2 applications of RNAi in research:
- prevention of a genetic condition
- could be used to identify the role of genes in a biological pathway
What are the 2 main features of stem cells?
- undifferentiated but can differentiate into specialised cells
- they can replace themselves to form more stem cells
What are the 4 main types of Stem Cell and Roles?
- totipotent cells:
- occur for a limited time in early mammalian embryos
- can differentiate to produce any type of body cell, including placental cells - pluripotent cells:
- found in embryos
- can differentiate into any type of cell, apart from placental cells - multipotent cells:
- found in many tissues of mature mammals
- can differentiate to form a limited number of different cell types e.g stem cells in bone marrow can produce any type of blood cell - unipotent cells:
- found in mature mammals
- can only differentiate into one type of cell or tissue
How do Induced Pluripotent Stem Cells (iPS) work?
- these are pluripotent stem cells produced from differentiated adult body cells
- specific transcriptional factors are used to ‘reprogramme’ the body cells
- the iPS cells are able to divide to produce new iPS cells or differentiate into any type of body cell
- these are replacements to the ethically challenging embryotic pluripotent stem cells
Describe the advantages + disadvantages of using stem cell types for production of new cells:
- pluripotent
- multipotent
Pluripotent:
- advantage: can differentiate into many different specialised cells
- disadvantage: risk of rejection as they are not the patient own cells + there are ethical issues with using embryos
Multipotent:
- advantage: no organ rejection, as cells are reimplanted from the host
- disadvantage: can only differentiate into a limited number of cell types
What type of Stem Cell are plants?
- mature plants have totipotent cells, which can differentiate into any other cell
Define Epigenetics:
What factors can affect Gene Expression?
Define Epigenome:
- involves heritable changes in gene function, without altering the base sequence of DNA
- environmental factors such as:
1. diet
2. stress
3. toxins - comprises of all the chemical tags which have been added to a persons genome
Describe the increased Acetylation of Histones:
- acetyl groups bind to histone proteins
- this causes the DNA to be less tightly wrapped around histones, which causes chromatin to be less condensed
- this increases accessibility of promotor region
- transcriptional factors can now bind to promotor region and initiate transcription
- genes are now switched on
Why does the increased Acetylation of Histones lead to less tightly wrapped DNA?
- DNA is negatively charged (due to phosphate group), so is attracted to positive charged histones
- Addition of acetyl group decreases the positive charge, so less attraction
Describe the Increased Methylation of DNA:
- methyl group are added to cytosine bases of DNA
- this leads to decreased acetylation of histones
- DNA wraps more tightly around histones, and increased condensation of chromatin occurs
- this then leads to promotor regions becoming inaccessible to transcriptional factors
- transcription is inhibited
- gene is switched off
What are non-cancerous tumours called?
How does this occur?
- benign tumour:
- a benign tumour is a mass of cells that has not spread into neighbouring tissues
- the location of the tumour is restricted to only one part of the body
- not cancerous as they do not invade surrounding tissues
What are cancerous tumours called?
How do these tumours occur?
- malignant tumours
- tumours are uncontrollably dividing cell groups that may spread/metastasise, to other parts of the body
How does Chemotherapy work?
How does Radiation-Therapy work?
- drugs killing fast-growing cancer cells
- uses ionising radiation to damage the DNA of the cancer tissue to kill the abnormal cells
Describe the normal role within a cell of:
1. Proto-Oncogene
2. Tumour Suppressor Gene
- stimulates cell division
- inhibits cell division
- repairs faulty DNA
- instructs cell death of faulty cells (apoptosis)
What happens to the Proto-Oncogene and the Tumour Suppressor Gene when mutated?
Proto-Oncogene:
- becomes an oncogene
- gene is permanently active
- cells divide continuously by mitosis
Tumour Suppressor Gene:
- tumour suppressor gene is inactivated
- cells divide continuously by mitosis
______ DNA ____________ can lead to cancer
Abnormal DNA methylation can lead to cancer
Describe how Hypermethylation (too much) of Tumour Suppressor Gene could lead to cancer:
- increased methylation
- methyl groups are added to cytosine bases in DNA
- decreased acetylation of histones
- transcription of gene is inhibited
- no translation producing any protein
- protein no longer inhibits cell division
- cell divides rapidly by mitosis
