Gene Regulation and Expression

Gene Regulation in Eukaryotes

Methylation of histone tails and DNA

Methyl is expressed as (-CH₃) and is attached to the molecule. In histone tails, tyrosine, an amino acid, gets the methyl group. In DNA, cytosine, a nitrogenous base, receives the methyl group.

Methylation usually causes more packing of chromatin, leading to less or reduced transcription. It is sometimes referred to as a “silence gene” due to its effect

on transcription.

Acetylation of Histone Tails

Histone tails contain lysine. Acetylation is expressed as (-CH₂CH₃).

Acetylation usually causes less packing of chromatine which leads to an increase in transcription.

Genomic Imprinting and Epigenetics

Genomic Imprinting is defined as epigenetic influences that occur at critical periods, usually during embryonic development or when gametes form.

Epigenetics is defined as environmental factors or outside influences that affect gene expression but don’t alter the DNA sequence. These traits are heritable and can be passed down through generations. They can be reversed, usually by chemical means.

ncRNA (non-coding RNA)

There are two types of ncRNA: siRNA and miRNA.

siRNA: small interfering RNA

miRNA: microRNA

Both of them block translation or will degrade proteins that have already been produced.

The difference between them is the precursor RNA they are formed from.

RNAi - RNA Interference

RNAi is a biotech technique to silence gene expression

3 Main Factors that Activate Oncogenes

1. Translocation of a gene - gene moves location

2. Amplification of a gene - multiple copies of the same gene are produced over and over again, leading to more cell division

3. Point Mutations - occurs in the gene or the control element

Virus Composition

The genome of a virus could be single-stranded RNA/DNA or double-stranded RNA/DNA.

Capsids are the outer protein coat that protects the genome made of capsomeres. Think of the capsid as the roof and the capsomeres as the shingles of the roof.

Some proteins will have glycoproteins on the surface or envelopes made from the host cell membrane.

The genome and capsids are the main parts of a virus.

Zoonotic Transmission

Animal-to-human transmission of viruses and bacteria.

Lytic vs Lysogenic Viruses

Lytic - the host cell bursts and is immediately infectious.

Lysogenic - do not immediately kill the host and are triggered to enter the lytic cycle by different kinds of stressors, like AP Biology. Lysogenic viruses are initially dormant and incorporate themselves into the host genome.

Retroviruses

ex: HIV

Uses reverse transcriptase for replication

Normal, Viral Replication: DNA —> Transcription —> RNA

Retrovirus Replication: RNA —> Reverse Transcriptase —> DNA

Viroid vs Prion

Viroid —> Naked RNA —> Infects plants

Prion —> Misfolded brain proteins —> infects humans and mammals —> Virtually indestructible (heat, antibiotics, medicine, Goku)

Biotech

Restriction enzymes - molecular scissors that cut a specific recognition sequence. An example of this is in the packet.

CRISPR - gene editor

PCR - polymerase chain reaction that will amplify (make copies of) DNA sequences, but not entire genomes.

Gel electrophoresis - separates DNA fragments by size. Longer fragments travel slower than smaller fragments.

Transformation - bacterial uptake of plasmids/small DNA

Operons

Operons are prokaryotic gene regulation and not eukaryotic.

Know the components and how operons work.

Lac operon and TRP operon are examples of negative gene regulation. Negative gene regulation means regulation that has mechanisms that inhibit gene expression. Molecules will bind to repressors or operators and block the transcription of genes involved in specific metabolic pathways, reducing the production of proteins when they are not needed.

Cap Lac operon is an example of positive gene regulation. Activator will bind to a specific site on the DNA and increase the possibility of transcription occurring leading to the production of proteins when conditions are favorable.

Review

p53 pathways - tumor suppression

RAS pathways - g-protein in a cell division pathway

Bacteria has a circular genome and can contain plasmids, which are pieces of extra DNA. There are two types of plasmids, R plasmid and F plasmid. R plasmid centers around antibiotic resistance and F plasmid centers fertility.

Review the Ways to Get Recombinant DNA in Bacteria lab and the stickleback gene activity.