In this summary, all the lectures of the course Cell Physiology and Genetics, which is given at Wageningen University, are elaborated extensively. This summary therefore provides a complete overview of the theory to be studied and thus this summary is an ideal preparation for the exam of this cours...
Summary lectures Cell Physiology and Genetics
Lectures Introduction to genetics
Different sub-disciplines from the discipline genetics:
- Molecular genetics
- Microbial genetics
- Population genetics
- Plant & Animal genetics
- Mendelian genetics: sub-discipline of genetics which is concerned with how genes are passed on
from parents to offspring.
- Cyto-genetics: sub-discipline of genetics which is concerned with the structure and function of cells
and in particular with the location of chromosomes inside the cell and the behaviour of the
chromosomes during mitosis and meiosis.
Model organisms which are frequently used in genetics:
- Escherichia coli (bacterium)
- Mus musculus (House mouse)
- Caenorhabditis elegans (nematode)
- Sacharromyces cerevisiae (Baker’s yeast)
- Drosophila melanogaster (Fruit fly)
- Arabidopsis thaliana (Thale-cress plant)
Gene: part of the DNA-sequence which codes for one or more proteins.
Gene = unit of inheritance
One gene has:
- One Open Reading Frame (ORF)
- Different mRNAs after transcription due to alternative splicing
Due to DNA-polymorphisms different forms of a gene exist in populations -> alleles
Gene structure:
- Regulatory elements/proximal control elements: DNA-sequences to which transcription factors can
bind.
- Promoter: DNA-sequence to which RNA-polymerase II (which is responsible for transcription) can
bind.
- Open Reading Frame (ORF): the DNA-sequence which is transcribed into mRNA by the RNA-
polymerase during transcription.
Each eukaryotic cell contains each chromosome twice (one chromosome inherited from father, one
chromosome inherited from mother) -> homologous chromosomes: 2 chromosomes which form a
pair inside the cell.
,Each chromosome of pair of homologous chromosomes contains the gene for a specific trait -> for
each gene there are 2 alleles (one inherited from father, one inherited from
mother)
Allele: a different form of a gene. -> alleles can be:
- Dominant -> denoted with capital letter
- Recessive -> denoted with small letter
Locus: a specific place on a chromosome where an allele is located.
Due to DNA-polymorphisms different forms of a gene exist in populations -> alleles
Organisms can be:
- Homozygote: an individual which possesses 2 identical alleles at a locus.
- Heterozygote: an individual which possesses 2 different alleles at a locus.
Phenotype/traits: the appearance or manifestation of characteristics of an organism . -> determined
by:
- Genotype: all genetic information an organism possesses.
- Environmental influences
Biological information flow:
1. Transcription: process in which the DNA of the gene is
transcribed to pre-mRNA.
2. Splicing/RNA-processing: process in which the introns are cut
out of the pre-mRNA and in which the remaining exons are linked
together by the spliceosome to form the mRNA.
3. Translation: process in which ribosomes synthesize proteins by
linking amino acids based on the triplets/codons of the mRNA.
Alternative splicing: splicing/RNA-processing which occurs in another alternative way so that a
different protein is produced based on the same gene. -> due to this process multiple different
proteins can be produced based on just one gene!
,Regulation of gene expression:
Transcriptional control:
1. Transcription factors: proteins which bind to
regulatory elements in the DNA to control
transcription.
- Activators: transcription factors which activate
transcription and enhance the transcription rate by
binding to enhancers.
- Repressors: transcription factors which deactivate
transcription and slow down the transcription rate
by binding to silencers.
- Basal/general transcription factors: transcription
factors which position RNA-polymerase at the start
of the protein-coding region of the gene and send it
on its way to start transcription when signals from
activators order to do so.
- Coactivators: transcription factors which pass on
the signals from activators and repressors to the
basal transcription factors.
2. Regulatory elements in DNA:
- Enhancer: DNA-sequence to which activators bind.
- Silencer: DNA-sequence to which repressors bind.
- Insulator: DNA-sequence which prevents binding
of activators and repressors which are meant for one gene to bind to enhancers and silencers which
are meant for another gene.
2 types of gene regulation by regulatory elements in DNA:
1. Cis regulation/effect: a change in the promoter of the gene or in
the gene itself causes a change in expression of the gene.
2. Trans regulation/effect: a change in another gene than the gene
itself causes a change in the expression of the gene.
, Translational control:
1. RNA-degradation:
When mRNA leaves the nucleus 2 situations can occur:
A. mRNA is stabilized -> no RNA-degradation by exosome
B. mRNA is NOT stabilized or destabilized-> RNA-degradation by exosome
2. RNA interference (RNAi): small RNAs bind to mRNA so that this mRNA is stabilized to prevent RNA-
degradation, destabilized to make RNA-degradation possible, prevented from being translated into
protein or activated to be translated into protein.
3. Increasing or decreasing translation rate.
Post-translational control:
1. Reversible:
- Addition of chemical groups to protein
- Addition of polypeptides to protein
- Addition of complex molecules to protein
2. Irreversible:
- Amino acid modification
- Cleavage of protein
Histons: proteins around which DNA is wrapped.
Nucleosome: a histon with DNA wrapped around it.
Chromatin: a lot of nucleosomes together. -> chromosomes are composed out of chromatin.
2 types of chromatin:
1. Euchromatin: chromatin which is less condensed because the nucleosomes are less densely
packed upon each other -> transcriptionally active + most genes are present here
2. Heterochromatin: chromatin which is tightly condensed because the nucleosomes are very densely
packed upon each other -> transcriptionally inactive + few genes are present here (repeat sequences
present here)
Epigenetics: sub-discipline of genetics in which reversible changes in gene function which are NOT
caused by change in DNA-sequence are studied.
Epigenetic variation between organisms can be due to variation in:
1. Chromatin structure
2. Chromatin remodeling/histon modification: process in which histone modifier proteins modify
histons by attaching chemical groups to them.
- Methylation: methyl groups attached to histons by histone modifier proteins.
- Acetylation: acetyl groups attached to histons by histone modifier proteins.
- Phosphorylation: phosphate groups attached to histons by histone modifier proteins.
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