Differential Gene Expression and Regulation Flashcards
What does differential gene expression allow?
different cells to have different functions
How many chromosomes do all human cells have?
22 pairs of autosomal and 1 pair of sex
Which cell types have gene amplification, gene loss and gene rearrangement?
some immune cells and tumour cells
What can differentiated cells do in many types of plants?
de-differentiate so that a single cell can form a clone of progeny cells that later give rise to an entire plant
What are the 4 conclusions of differential gene expression?
- not all genes are expressed in any single cell
- different sets of genes are expressed in different types of cells
- the same gene may be expressed at different levels in different types of cells
- the same gene may be expressed at different levels in the same cell but under different circumstances
How can differential mRNA expression be shown?
by transcriptomic analyses (heat map)
How can differential protein expression be shown?
2D gel electrophoresis analyses
How can the same protein have different isoforms?
post-translational modifications
What are housekeeping genes?
genes that are expressed in all types of cells for basic cellular structures and functions
What are tissue-specific genes?
genes that are expressed in one or a few tissues to give the cell its specific phenotype
What does RNA-seq do?
- generate a large number of short sequence tags that can be mapped to the genome and counted for quantitative analyses of RNA expression
- provide information on the transcription start site, intron/exon junction and differential RNA splicing
What are 4 the steps of RNA-seq?
- isolate RNA
- convert RNA to cDNA
- prepare the sequence library
- sequence the RNA on an NGS platform
What are characteristics of cell differentiation?
- cells become different through the synthesis of different sets of mRNAs and proteins
- each type of cell synthesises a few characteristic and specialised proteins at high abundance
- cell differentiation is usually stable and irreversible
What does the final level of a protein in a cell depend on?
- efficiency of each step
- rates of degradation of the RNA and protein molecules
What must happen in eukaryotes before mRNA can be translated?
- 2 ends of the RNA are modified
- introns are removed by splicing
- resulting mRNA is transported from the nucleus to the cytoplasm
What are the 5 levels of gene expression regulation?
- pre-transcriptional control
- transcriptional control
- post-transcriptional control
- translational control
- post-translational control
What are the 5 main pre-transcriptional controls?
- chromatin structure
- DNA methylation
- DNA amplification
- gene loss
- DNA rearrangement
What is the net result of chromatin remodelling?
each DNA molecule has been packaged into a mitotic chromosome that is 10,000x shorter than its fully extended length
What is heterochromatin?
a highly condensed form of DNA that mostly consists of repetitive DNA sequences and non-coding RNA transcripts (transcriptionally inactive)
What is euchromatin?
the opposite of heterochromatin made up of nucleosomes which each contain a segment of DNA wound around eight histone proteins (transcriptionally active)
What is DNA methylation?
the covalent addition of a methyl group at position 5 of cytosine to form 5-methyl C (CMe)
Where does DNA methylation occur in humans and other mammals?
at cytosines next to guanines linked by phosphate CpG sites
What does increased DNA methylation do to gene expression?
decrease it
Why are specific genes sometimes amplified?
to meet the high demand of gene product
Give examples of genes that undergo amplification
- xenopus ribosomal NRA genes
- drosophila polytene chromosomes
- certain drug resistant genes
- tumour oncogenes
Where does gene loss most commonly occur?
red blood cells and cornified cells in the skin, hair and nails
When does gene loss occur?
after the required proteins are expressed and ceases transcription
What are the 2 genes that display DNA rearrangement?
antibody gene and TCR gene
