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Sem 1 > 21. Cell Differentiation and Gene Expression > Flashcards

21. Cell Differentiation and Gene Expression Flashcards

1
Q

Describe cell differentiation (2pt)

A
  • Cell differentiation is the process through which a cell undergoes changes in gene expression and gene activity to specialise and take on specific roles in an organism.
  • Irreversible process
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2
Q

Describe what happens as we approach maturity?

A

The proportion of dividing cells fall as we approach maturity. In adults the majority of the cells are terminally differentiated which means they cannot divide any more. Only a small minority of cells are capable of cell division.

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3
Q

Describe a stem cell

A

Undifferentiated and unspecialised cells of the human body

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4
Q

Describe a totipotent stem cell

A

Can differentiate into every cell type. It has the ability to develop into a total individual.

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5
Q

Describe a pluripotent stem cell?

A

Can differentiate into all cell types except placental cells.

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6
Q

Describe a multipoint stem cell?

A

Can differentiate into a limited number of cell types e.g hemaotpoetic stem cells.

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7
Q

Describe a unipotent stem cell?

A

Can form one type of differentiated cell only e.g dermatocytes.

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8
Q

Describe Asymmetric Division? (2pts)

A
  1. State that a stem cell produces one stem cell and one differentiated stem cell.
  2. A fate regulator e.g polarity protein distributes unequally in the daughter cells.
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9
Q

Describe Symmetric division?

A

A stem cell produced two differentiated cells or two stem cells

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10
Q

Describe embryonic stem cells? (2pts)

A
  1. Pluripotent

2. Derived from a blastocyst

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11
Q

Describe adult stem cells? (5pts)

A
  1. Multipotent
  2. Typically gives rise to various types of differentiated cells within the tissue they reside in as they are tissue specific stem cells.
  3. Their function is dead cell replacement.
  4. Low number in tissues where there is a low rate of cell turnover.
  5. Abundant in tissues such as intestine epithelium and blood cells.
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12
Q

Describe adult stem cells? (5pts)

A
  1. Multipotent
  2. Typically gives rise to various types of differentiated cells within the tissue they reside in as they are tissue specific stem cells.
  3. Their function is dead cell replacement.
  4. Low number in tissues where there is a low rate of cell turnover.
  5. Abundant in tissues such as intestine epithelium and blood cells.
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13
Q

Describe stem cell niches?

A
  1. Tissue specific stem cells are maintained in an environment called stem cell niches.
  2. These consist of:
  3. Supporting ECM
  4. Neighbouring niches cells
  5. Secreted soluble signalling factors such as growth factors and cytokines.
  6. Physical parameters such as sheer stress, tissue stiffness and topography
  7. Environmental signals- metabolites, hypoxia and inflammation.
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14
Q

Describe bone marrow stem cells?

A

From foetal week 20 blood cells are produced from the bone marrow. There are two types- Hematopoetic stem cells and Mesenchymal stem cells (MSC).

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15
Q

Describe a Hematopoetic stem cell? (4pts)

A
  1. Multipotent stem cells anchored to fibro-blast like osteoblasts of the marrow of long bones
  2. Produce all blood cells and some immune system cells.
  3. Regular self renewal
  4. Can replicate indefinitely
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16
Q

Describe Mesenchymal stem cells (MSCs)? (5pts)

A
  1. Stromal cells found in the bone marrow and other organs.
  2. Poorly defined and heterogenous
  3. Do not self renew very regularly
  4. Multipotent
  5. Give rise to cartilage, bone, muscle cells and adipocytes.
17
Q

Describe Progenitor cells?

A

Progenitor cells can only divide a limited number of times and can only differentiate into one type of linage unlike stem cells which can divide indefinitely.

18
Q

How can we determine how a cell differentiates?

A

The types and number of proteins a cell generates helps to determine how a cell differentiates.

19
Q

How can we analyse the transcription profile of each cell?

A

RNA sequencing and microarrays assay allow to analyse the transcription profile of each cell.

20
Q

Describe regulatory transcription factors? (3pts)

A
  1. Transcription factors bind to regulatory regions of a gene and affect its expression by switching it on and off.
  2. Certain transcription factors are tissue specific and different transcription factors are associated with differentiation of stem cells into different tissues.
  3. Specific transcription factors ensure the genes are expressed in the right cell at the right time and at the right amount.
21
Q

Describe regulatory transcription factors? (3pts)

A
  1. Transcription factors bind to regulatory regions of a gene and affect its expression by switching it on and off.
  2. Certain transcription factors are tissue specific and different transcription factors are associated with differentiation of stem cells into different tissues.
  3. Specific transcription factors ensure the genes are expressed in the right cell at the right time and at the right amount.
22
Q

Describe transcriptional factors? (3pts)

A
  1. Different genes are activated by different transcription factors according to the binding elements in their promoters and enhancers
  2. Each cell type transcribes a different set of genes
  3. For transcription to occur RNA polymerase must have access to chromatin.
23
Q

Describe House-keeping genes?

A

Genes are transcribed in all cell types e.g basic metabolic enzymes.

24
Q

Describe Luxury genes?

A

Specialised genes expressed in only some type of cells e.g haemoglobin gene in red blood cells.

25
Q

Describe Pioneer factors? (3pts)

A
  1. Transcription factors that can bind closed chromatin, remodel it and imitate cell-fate and differentiation.
  2. Highly expressed in embryonic stem cells and needed to maintain their pluripotency.
  3. Can activate or inhibit gene expression via histone modification and DNA methylation blockage.
26
Q

Describe DNA methylation? (4pts)

A
  1. DNA methylation is the addition of a methyl group to DNA.
  2. Heritable and reversible changes in gene expression which do not involve a change in the DNA sequence.
  3. Results from external or environmental factors or as part of a development program.
  4. The DNA methylation pattern is inherited and remembered in daughter cells.
27
Q

Describe DNA methylation in Cytosine? (4pts)

A
  1. Covalent addition of the methyl group at the 5-carbon of the cytosine ring results in 5-methylctyosine(5-mC)
  2. In somatic cells, 5-mC occurs on CPG sites.
  3. During differentation unmehtylated CpG pairs can become methylated by a de nova methyltransferase.
  4. It is copied to the opposite strand by a maintenance methyltrasnferase.
28
Q

Describe the consequences of DNA methylation? (3pts)

A
  1. DNA methylation increases folding (hterochromatin) and silences transcription.
  2. DNA methylation means the gene is switched off and transcription does not occur.
  3. Developmentally regulated:
  4. In embryonic stem cells the majority of Cpg sites are unmethylated.
  5. Globin genes are expressed in the red blood cell lineage but not elsewhere. Their promoters are methylated in other cell types.
  6. In sperm genes are silenced by methylation. DNA is very heterochromatic.
29
Q

Describe Somatic cell nuclear transfer? (3pts)

A
  1. Artificial removal of the nucleus of a differentiated somatic cell and its placement in a denucleated egg cell.
  2. Introduced nucleus is reprogrammed by factors in the egg cytoplasm.
  3. The new egg behaved like a zygote (totipotent)
    - challenging and time consuming.

e.g dolly the sheep

30
Q

Describe induced pluripotent stem cells? (4pts)

A
  1. Pluripotent stem cells artificially produced from somatic cells.
  2. Can potentially produce all cells of the organism.
  3. Cells exposed to only 4 transcription factors.
  4. Induced pluripotent stem cells have many applications as they have the capacity to keep dividing and differentiating cell types ion the body. Used in gene therapy, regenerative medicine and model disease and drugs screening.

Sem 1 (37 decks)

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