Gene Expression Flashcards
(21 cards)
Control of Degradation of mRNA
mRNA’s life depends on the poly-A tail added to the 3’ end of the mRNA during post transcriptional modification
The shorter the poly-A tail, the less likely the mRNA will be translated and the more likely it will be degraded
The stability of mRNA molecules can be regulated by RNA-binding proteins, which can stabilize the tail to extend its lifespan. However, others recruit enzymes which degrade the tail and lead to faster breakdown
Hormones and other chemical signals can influence mRNA degradation rates aswell
Lac Operon
A length of DNA that codes for the enzyme which is responsible for the transport and metabolism of lactose in the bacterium
Estrogen and Steroid Hormones
Diffuse through the plasma membrane into the cytoplasm due to it being hydrophobic
Bind to the receptor of the transcription factor in the cytoplasm of the target cell to form a receptor-hormone complex
This causes a slight change in the DNA binding site and activates the transcription factor
The receptor-hormone complex enters the nucleus through the nuclear pores and binds to the DNA which initiates transcription
Epigenesis
Changing gene expression patterns without altering the DNA
Histone Modification
Histones have tails that determine how tightly the DNA is packaged. DNA methylation has a positive charge, which with the negative charge of the tail, makes DNA more coiled and therefore reduces transcription
When acetyl group is added, due to its negative charge, it repels the DNA and it becomes less tightly coiled and opens up the nucleosome therefore increasing transcription
Epigenetic Tags
Chemical modifications to the DNA and histones which regulate gene expression
These modifications change the phenotype without changing the genotype which affects how cells read the genes
Epigenesis is essential for normal development and is associated with aging and various diseases including cancer
Importance of RNA Degradation
Allows for quicker adjustments to changing cellular needs
Allows for precise control over protein synthesis
Degraded mRNA’s can be recycled, thus reducing the need for constant synthesis of new transcripts
Monozygotic and Dizygotic
Dizygotic (Fraternal): When two eggs are released during ovulation, they are both fertilized
Monozygotic (Identical): When one egg splits into two and both zygotes develop into separate individuals
Reprogramming
The erasing of all pre-existing epigenetic tags before gametes fuse to produce a zygote, which ensures that the early embryo can form every type of cell in the body
Some epigenetics do not get removed, and is known as transgenerational epigenetic inheritance, with the genes themselves being imprinted genes which allow for phenotypic change in offspring which can be easily reversed
Consequences of Imprinted Genes
In genomic imprinting, the allele of a gene inherited from one parent is silenced and the other one is expressed
Methylation Inheritance
Methylation can be inherited and can vary over an organism’s lifetime and by environmental factors
Monozygotic Twin Studies
Can be used to determine the contribution of genetics and the environment to phenotypic variation by comparing DNA methylation patterns
DNA methylation patterns will differ between twins and continue to change due to different environmental exposure, and can be used to identify genes that are involved in the development of diseases that are present in one twin
In the Presence of Lactose
Lactose is directly converted to allolactose, which binds to repressor protein and distorts its shape to prevent it from binding to the operator region of the DNA, thus allowing transcription of genes
Effect of Air Pollution on Gene Expression (Example of Environmental Effects on Gene Expression)
Exposure to air pollution decreases DNA methylation which results in greater expression of proteins
These changes in gene expression can lead to increased inflammation in the body, higher susceptibility to diseases such as asthma, and disrupted cell growth and repair, thus increasing the risk of cancer
In the Absence of Lactose
Repressor protein binds to operator region which inhibits transcription which stops production of enzymes
Sperm and Egg Development
Maternal genes are usually silenced in sperm development and paternal genes are usually silenced in egg development
Gene Expression
The process of turning genotype into phenotype
Genome, Transcriptome and Proteome
Genome is all the genetic information in a cell or organism, and provides the starting point for gene expression
Transcriptome is the entire set of RNAs transcribed in a cell, and varies based off cellular needs
Proteome is the entire set of proteins produced by a cell, and is based on the transcriptome as proteins are synthesized from mRNA. Proteins constantly turn over due to synthesis, degradation and post-transcriptional modification
Transcription Factors
DNA-binding proteins that regulate transcription of a gene
DNA Methylation
The substitution of a hydrogen with a methyl group in a Cytosine base of the promotor region
The methyl group is an epigenetic tag that affects how tightly the DNA is packed
DNA methylation causes DNA to remain tightly packed which silences the gene by inhibiting the binding of transcription factors thus repressing gene transcription
Lions and Tigers
In lions paternal imprinting favors larger offspring while maternal favors smaller offspring
When a male lion and female tiger reproduce they make a liger - the biggest of the cat species
When a female lion and male tiger reproduce they make a tigon - a cat that is about the same size as its parents
