Cell Differentiation and Gene Expression Flashcards
What is the difference between cell differentiation and cell determination?
- Cell DIFFERENTIATION is the production of different cell types within an organism.
- Cell DETERMINATION is the stability of cell differentiation even after the end of any inducing signal (basically, the memory of differentiation). It is transmitted to the daughter cells.
What is cell lineage?
- It is the pathway of a precursor to a particular cell type.
- Cell lineages can branch, where particular precursor cells are able to produce more than one daughter cell type. Such precursor cells are called pluripotent.
What is gene expression?
- It is the whole process leading to the synthesis of the final product of a given gene, either a protein or a functional RNA like tRNA.
- It includes transcription and (for a protein) translation.
What is cell modulation?
- It is the simple, reversible change in gene expression, but no change in the cell type.
- |t is also known as adaptation.
What are the differences between cell determination and cell modulation?
Cell differentiation is a STABLE, COMPLEX change, while cell modulation is a TEMPORARY, SIMPLE change.
How do we know that all differentiated cells have a complete genome?
- We know this from cloning experiments, an example being Dolly the sheep.
- A whole differentiated (mammary epithelial) sheep cell was fused to the cytoplasm of a sheep oocyte (egg cell).
- The resulting cell proliferated to form a whole early embryo, which was implanted in the uterus of a ewe and resulted in Dolly.
- Thus we know that the differentiated cell had all the genes necessary to form a whole sheep (the entire genome).
Ewe meaning - the female of the sheep especially when mature.
Proliferated meaning - The reproduction or multiplication of similar forms, especially of cells and morbid cysts.
What is meant by the ‘programme of differentiation’?
- It is the diverse set of cell-type-specific genes that are generally activated in expression during one step in lineage, while others are repressed.
- It is largely controlled at the level of mRNA transcription.
What are DNA ‘probes’, and what is their purpose?
- They are DNA with a known sequence which is complementary to the sequence you are searching for.
- This reveals many mRNA differences between any 2 cell types.
What are the two ways in which our bodies control transcription?
- Chromatin remodelling / folding.
- Specific transcriptional regulation of individual genes.
Describe chromatin remodelling/folding.
- Our chromatin exists in two forms: euchromatin and heterochromatin.
- Euchromatin is our active form; the DNA is not compactly stored.
- Heterochromatin is our inactive form; here, the chromatin is tightly packed, interfering with transcription.
- One mechanism of increasing chromatin folding (ie. converting euchromatin to heterochromatin) is DNA methylation.
- It occurs on cytosine within a CpG pair(C phosphate G) (lietrally means CG base pair), changing it to methylcytosine.
- It is copied to the opposite strand in replication by a maintenance methyltransferase.
- This means that the methylation pattern is ‘remembered’ in daughter cells.
- Unmethylated pairs can become methylated by de novo methylation, carried out by de novo methyltransferase.
- This methylated DNA becomes highly folded.
What is the role of transcription factors in specific transcriptional regulation of individual genes?
- Transcription factors are regulators of transcription.
- They are proteins that physically fit onto a specific DNA sequence.
- They can bind to specific sequences on a gene promoter, and alter transcription of that gene (either increase or decrease).
What are household genes?
- Some genes are transcribed in all or nearly all cell types (e.g. basic metabolic enzymes).
- These are sometimes called household genes.
What are luxury genes?
- Luxury genes are tissue-specific or organ-specific, which means they are not expressed in all cells.
- They are not constantly expressed, only when their function is needed.
- Examples of luxury genes are plasmids of bacteria and genes coding for heat-shock proteins.
What are master gene regulators?
- They are a type of transcription factor.
- They regulate transcription of a whole set of lineage-specific genes (a ‘program’) for a given cell type.
- E.g. MYOD (Myogenic Differentiation) in skeletal muscle can activate a program of muscle-specific genes.
Describe the mechanism of a master gene regulator.
- Transcription of the gene for the master gene regulator occurs, creating the regulatory proteins.
- These proteins then bind to and activate the promoters of different genes coding for proteins that will differentiate the cell.
- These specialised proteins are made, and then proceed to work on the cell.
