BIOL1020 Week 6 : Gene Regulation in Prokaryotes and Eukaryotes

Pathogenic Bacteria

Produces disease, infectious

Mutualistic Bacteria

A relationship in which both species benefit, e.g. bacteria in the gut that aids in digestion in both humans and animals

Saprophyte Bacteria

A bacterium that establishes a symbiosis with plants

Bacterial Transcription

Regulated by ONE RNA polymerase

Eukaryotic Transcription

Regulated by 3-5 different types of RNA polymerase

Operon

Unit of genetic function. All the genes within an operon can be switched ‘on’ or ‘off’ by regulatory proteins

Consists of a promoter region (DNA sequence where RNA binds and transcription are initiated) an operator (on-off switch) and genes for proteins that work together

Gene Expression in a Eukaryote

7 different points during the Central Dogma of Molecular Biology at which gene expression can be regulated

1) Chromatin Remodelling

2) Transcriptional Regulation

3) RNA Splicing

4) RNA Localisation

5) RNA Degradation

6) Translational Regulation

7) Protein Folding/Post-translational Modification

Chromatin Remodelling

Rearrangement of chromatin, from a condensed state to a transcriptionally accessible state

Transcriptional Regulation

The means in which a cell regulates the conversion of DNA to RNA thereby orchestrating gene activity

RNA Splicing

The removal of certain sequences of the RNA, referred to as the intervening sequences, or introns

RNA Localisation

RNA molecules are localised to specific subcellular regions through interactions between RNA regulatory elements and RNA binding proteins

RNA Degradation

Counterbalances the rate of transcription and also serves to rapidly eliminate transcripts when they are no longer necessary

Translational Regulation

Control of the levels of protein synthesised from its mRNA, governs the efficiency of mRNA’s

Post-translational Regulation

Control of the levels of active protein. Can be performed either by reversible or irreversible events

Virus

Obligate, intracellular parasite. Possess the properties of both living and non-living organisms

Contain nucleic acids as genetic information and reproduce to produce progeny like living organisms

However, they need to employ host cell’s replicative and metabolic pathways as they do not have their own ribosomes or ability to produce energy

Can only replicate in living cells, outside cells they are inert macromolecules. These properties belong to non-living organisms

Viruses are very small and require a host to survive. Viruses that infect bacteria are called bacteriophages

2 Main Types of Viruses

1) Viruses with DNA (split into single stranded DNA and double stranded DNA)

2) Viruses with RNA (double stranded RNA and positive or negative sense single stranded RNA)

Virus Life Cycle

7 Main Steps

1) Attachment (binding onto receptors on the surface of the cell)

2) Penetration (crossing of the plasma membrane by the virus)

3) Uncoating (the breakdown or removal of the capsid, causing the release of the virus into the genome)

4) Transcription/Translation (viral genetic information is presented to the host cell’s protein synthesis machinery)

5) Genome Replication (genome-length progeny DNA is synthesised by the nucleus)

6) Assembly (Protein-Protein interactions between viral structural and non-structural proteins and the coordinated action of host factors)

7) Release (the virus particles are released via cell lysis of the infected cell)

Virus Lytic Cycle

The impatient, aggressive cycle

Virus infects the host cell and remains separate from the host DNA. They undergo the regular virus life cycle.

When the viruses are released from the host cell, the process KILLS the host cell (lysis)

Virus Lysogenic Cycle

The dormant, passive cycle

Virus infects the host cell and incorporates its own DNA with host DNA. As host cell replicates, the virus DNA is passed into daughter cells.
Under stressful conditions, host cell will excise the virus DNA from host DNA. The virus will then enter the lytic cycle. This process keeps the host cell ALIVE until it enters the lytic cycle

Virus : RNA-dependant RNA polymerase

Breaks the Central Dogma of Biology (DNA > RNA > Protein)

Single stranded positive sense RNA viruses need to replicate by transcribing positive sense RNA into negative sense RNA using this enzyme, which can be used as a template for more positive sense RNA.

They break the Central Dogma of Biology as they can go horizontally and vertically

Virus : Reverse Transcriptase

Breaks the Central Dogma of Biology (DNA > RNA > Protein)

Positive sense RNA uses RNA-dependant DNA polymerase to create complementary DNA, in order to be incorporated into host genome.

They break the central dogma of biology by going backwards (RNA > DNA) instead of (DNA > RNA)