3.8.2 Gene Expression Flashcards
Whats cell differentiation
Process how a cell develops a specialised structure to carry out a suited role
What are totipotent cells
Divide and produce any type of body cell
How are totipotent cells specialised
During development, only part of their DNA is translated into proteins, only produces proteins needed for its specialised function
When are totipotent cells present
Occur for a limited time in an early mammalian embryo
What are pluripotent stem cells
Differentiate into almost any type of cell
(All body cells except placenta cells)
Where are pluripotent stem cells found
Found in embryos
What’s a characteristic of pluripotent stem cells
Divide in unlimited numbers and can be used to treat human disorders
What are multipotent stem cells
Divide to form a limited number of different cell types
Where are multipotent stem cells found
Mature mammals
What are unipotant stem cells
Differentiate into a single type of cell
Where are unipotent stem cells found
Mature mammals
Give an example of unipotent stem cells
Cardiomyocites, heart muscle cells which divide to produce new heart tissue repairing damage to heart muscle
What are induced pluripotent stem cells, iPS cells
how are they produced
And their features
A pluripotent cell produced from a unipotent stem cell
Genetically altered to acquire characteristics of embryonic stem cells by inducing genes and protein transcriptional factors
Self renewal, divide indefinitely
Replaces embryos on research overcoming ethical issues
How can pluripotent stem cells treat human disorders
Regrow damaged tissue
What are transcriptional factors
A specific molecule causing genes to be switched on for transcription to start
These molecules move from the cytoplasm into the nucleus
What’s a steroid hormone and name one
Oestrogen
Lipid soluble molecule
What’s the role of oestrogen in initiating transcription
Lipid soluble, easily diffused through phospholipid bilayer
Oestrogen binds with a complimentary receptor of the transcriptional factor
Oestrogen changes shape of DNA binding site on transcriptional factor casing it to bind to DNA
Transcritpional factor enters the nucleus through a nuclear pore, binds to a specific base sequence on DNA
Transcriptional factor with DNA stimulates transcription of the gene
How do transcriptional factors work
Transcriptional factors move from cytoplasm to nucleus, transcriptional factor binds to a specific base sequence of DNA, after binding it causes the region of DNA to begin transcription, mRNA is produced and the information it carries is translated into a polypeptide, when a gene isn’t expressed the site on the transcriptional factor binding to DNA is inactive, no transcription nor polypeptide synthesis
What’s epigenetics
Heritable change in the gene function without changing the base sequence of DNA
Changes are caused by environmental factors like stress diet and toxins, this can inhibit transcription
What’s the epigenome
DNA is wrapped around proteins called histones forming a DNA histone complex
The DNA histone complex is covered in chemicals, these chemicals form a layer called the epigenome
Epigenome determine the shape of the DNA histone complex
How do environmental factors inhibit transcription
Chemicals forming the epigenome respond to environmental changes
Two examples of these chemical processes are increased methylation of DNA and decreased acetylation of associated histones forming
How does increased methylation of DNA inhibit transcription
A methyl group is added to cytosine bases of DNA, methylation inhibits transcription
It prevents transcriptional factors from binding to the DNA
Attracts proteins that condense the DNA histone complex, DNA is inaccessible to transcription factors
Methylation, works on me and I’m made of DNA, mutes the gene
How does decreased acetylation of associated histones inhibit transcription
Acetylation, an acetyl group from acetyl co A is transferred to a molecule
Decreased acetylation increases the +ve charges on histones, increasing their attraction to phosphate groups on DNA, stronger association between DNA and histones, not accessible by transcription factors, mRNA production isn’t initiated, gene is switched off
How can epigenetics detect and treat disease such as cancer
Altering epigenetic processes causes abnormal activation/silencing of genes, this increases the risk of mutations, which is associated with cancer
Treatments use drugs to inhibit enzymes involved with histone acetylation/DNA methylation to counteract the initial epigenetic changes
These treatments can only be used in cancerous cells or would cause cancer in healthy cells
Diagnostic tests for cancer, brain disorders and arthritis, test detects levels of DNA methylation and histone acetylation at an early stage, allows treatment to be sought earlier
Whats transcritpion and translation in basic terms
Transcritpion results in mRNA production
Translation, mRNA attaches to a ribosome and produces a protein
What does RNAi RNA interference do and explain how
Inhibits translation of mRNA from target genes in eukaryotes and some prokaryotes
- An enzyme cuts large double stranded molecules of RNA into smaller sections called small interfering RNA (siRNA)
- 1 of the 2 strands of siRNA combines with an enzyme
- siRNA guides the enzyme to an mRNA molecule, pairing up its own bases with complimentary ones on the section of mRNA
- The enzyme cuts mRNA into smaller sections
- mRNA can no longer be translated into a polypeptide as the gene is not expressed
What’s a tumor
Give some similarities and differences between benign and malignant ones
Tumour, a group of abnormal cells dividing uncontrollably
Benign
S grow large in size
D grow slowly
D form primary tumours as adhesion molecules make cells stay within tissues
D rarely reoccur after treatment
Malignant
S grow to a large size
D grow rapidly
D form secondary tumours, no adhesion molecules so spread through body called metastasis
D frequently reoccur after treatment
How do tumour suppressor genes and oncogenes result in tumours
(Normal) car driving at limit
Protoncogenes stimulate a cell to divide when growth factors attach to a protein receptor in its cell surface membrane, activates the gene for DNA replication
(Cancer) car speeding
it can mutate into an oncogene being permanently activated if the receptor protein is permanently activated even without growth factors or the oncogene codes for a growth factor produced in excessive amounts both of these stimulate excess cell division
(Normal) slowly brake
tumour suppressor genes slow down cell division, repair mistakes in DNA and promote programmed cell death (adoptosis)
(Cancer) no brake
If a tumor suppressor gene becomes mutated it is inactivated, stops inhibiting cell division cells grow out of control, these are structurally and functionally different some survive and make clones forming tumours
Oncogenes cause cancer when activated
Tumour suppressor genes cause cancer when inactivated
How does abnormal methylation of tumour suppressor genes and oncogenes lead to tumours
Increased methylation at the promoter region of tumour suppressor genes, tumour suppressor gene is inactivated, transcription at the promoter region is inhibited, tumour suppressor gene is silenced, increased cell division leading to the formation of a tumour
Reduced methylation at the promoter region of oncogenes, oncogenes are activated, transcription at the promoter region occurs, oncogenes are expressed, increased cell division forming tumours
How do increased oestrogen levels lead to the development of breast cancer
Oestrogen can activate a gene that controls cell division (protooncogenes) by binding to a receptor, promoting transcription, activates the gene (oncogene) development of breast cancer
A tumour further increases oestrogen conc, white blood cells drawn to the tumour also increase oestrogen conc both leading to greater development of the tumour
