IBBIOHL epigenetics content

To be used with bioninja

What is gene expression

The mechanism by which genetic instructions (genotype) give rise to observable characteristics (phenotype)

What are the three main ways gene expression is moderated?

1. Regulating gene accessibility via epigenetic tags

2. Controlling the production and activity of RNA via transcription factors

3. Moderating the functional levels of RNA and protein within the cell via targeted degradation

What is the genome?

The entire set of genetic instructions for an organism

What is the transcriptome?

The genetic instructions that have been actively transcribed into RNA molecules

What is the proteome?

The totality of proteins expressed within a cell

What is DNA methylation? What does it do?

1. The incorporation of a methyl group to a DNA base in order to change the activity of a DNA segment without changing the base sequence

2. It reduces transcription by inactivating it

What does adding an acetyl group (acetylation) to a histone protein do?

Neutralises the positively charged histone tails which makes DNA less tightly coiled and increases transcription

What happens when you add a methyl group to the tail (methylation) of a histone protein?

It maintains the positive charge which makes DNA more coiled and reduces transcription

What is chromatin?

Individual nucleosomes linked together, the unravelled form of a eukaryotic chromosome

Define heterochromatin

DNA that is supercoiled and not accessible for transcription

Define euchromatin

DNA that is loosely packed and accessible for transcription

What external conditions can affect genetic expression?

Air pollution generally decreases DNA methylation

Define epigenesis

The development of a complex multicellular organism from a zygote to death

Why do reproductive cells undergo epigenetic tag removal to return the gametes to a genetic 'blank slate’?

To ensure the embryo can form every type of cell in the body by resetting the epigenome

What are imprinted genes?

Genes that retain their epigenetic tags during gamete production that allow for phenotypic changes to be potentially passed on to offspring

What is the consequence of inheriting imprinted genes?

1. Imprinted genes have higher rates of mutation as methylated DNA is susceptible to deamination

2. Higher rates of evolution as imprinted genes have only one active copy, making them more vulnerable to selective pressures

What is the role of transcription factors in gene expression?

They regulate gene expression in eukaryotes as RNA polymerase cannot initiate transcription without them

What effect do Activator Regulatory Proteins have?

They bind to enhancer sites and increase the rate of transcription

What effect do Repressor Regulatory Proteins have?

they bind to silencer sequences and decrease the rate of transcription

What are some internal factors impacting the pattern of gene expression

Hormones and inducer molecules (lactose)

How does controlling the degradation of mRNA affect translation regulation?

The longevity of the mRNA transcripts will determine the expression levels of a gene through translation, so the degradation of mRNA transcripts will alter the transcriptome

How does controlling the digestion of protein affect gene expression post-translation?

Proteins broken down by proteasomes will alter the proteome of the cell

Explain the Lac Operon and how it works

1: the metabolism of lactose in bacteria is controlled by a group of genes called the lac operon

2: Transcription of the lac operon is normally inhibited by a depressor protein which binds to a silencer sequence called the operator

3: When lactose levels are high, lactose binds to the depressor and inactivities it which allows transcription to proceed