D2.2 GENE EXPRESSION

Outline and define gene expression

1. Is the mechanism by which information in genes has effects on the phenotype 🧬

2. Information is coded in genes and genetic code 💁

3. Transcription of DNA produces mRNA, translation of mRNA at the ribosome produces proteins 🏳‍⚧️

Discuss the factors that control gene expression

1. Transcription factors ✍

2. Control of the degradation of mRNA 😥

3. Epigenetic tags - methylation of DNA, acetylation of histone proteins 🏷

4. Environmental factors - hormones, chemical environment of the cell 🌍

5. Epigenesis - development of patterns of differentiation ⭕

   • nucleosomes, introns

   • different cells/times

Compare genotype and phentotype

GENOTYPE: Information in the genes, the combination of alleles for a trait 🧬

PHENOTYPE: observable characteristics of traits 🙈

The mechanism where info in genes/genotype affects on the phenotype is gene expression 😻

Outline the role of transcription factors in gene expression

✍ TRANSCRIPTION FACTORS: proteins that bind to specific base sequences in DNA to regulate transcription of DNA / Genes into mRNA

1. Transcription factors can bind to the enhancer/silencer/promotor regions of DNA — when bound to enhancer/promotor regions, increases transcription of gene 😍

2. Regulation of transcription is the most common control of gene expressions — can be turned on/off 💡

3. The proteome/proteins produced by the cell can change according to the needs of the cell ⌛

Outline the role of the degradation of mRNA in gene expression

1. mRNA is degraded by nuclease enzymes in the cytoplasm 😥

2. Control of the degradation of mRNA is a means of regulating translation 📔

3. the addition of the 3’ poly adenosine tails prevents the degradation of mRNA → allows for translation of mRNA at the ribosome to produce proteins 🏳‍⚧️💪

4. Shortening of poly-A tail signals degradation of mRNA 🩳 😥

5. The degradation of mRNA ensures that proteins are synthesised only when needed, and mRNA is removed when done 😁

Discuss the differences between genome, transcriptome, and proteome of individaul cells

GENOME: All of the genetic information in a cell, organisms 🧬

• Unique to all individuals EXCEPT for monozygotic twins

• All cells within an organisms will have the same genome as they derived from the same cell/zygote

TRANSCRIPTOME: Range of mRNA transcripts produced within a cell/tissue at a particular time ✍

PROTEOME: All of the proteins within a cell, tissue, or organism at a particular time 💪

• varies between individuals due to differences in the genome

• varies within the organsim cells/tissues based on environmental changes, functions of the cells/tissues

Discuss the role of environmental factors on gene expression with examples!

1. Environmental factors can impact/affect gene expression, like diet, traumatic events and stress 🌍

2. Methylation of DNA promotor regions 😍

3. Methylation/acetylation of histone tails 🐒

EXPOSURE TO AIR POLLUTION: Nitrous oxides and soot have been linked to DNA methylation of genes involved in inflammation and oxidative stress 😷

DIET: High folic acid can increase methylation of genes associated with the coat colour in mice 🫑

TEMPERATURE: Warmer temperatures lead to more female births in many reptiles and turtles 😎

Discuss the role of epigenetic tags on gene expression

1. Methylation of the promotor region in the DNA regulates gene transcription/genes are silenced — prevents RNA polymerase from binding to the promotor 😍🔇

2. Methylation of histone tails can decrease/increase gene expression 🐒👆 👇

3. Acetylation of the histone tails increases gene expression 🐒👆

Outline epigenetic inheritance & removal

REMOVAL: after fertilisation 💧

1. Reprogramming of the zygote removes environmental tags/epigenetic tags from the ovum and sperm 🐳

2. This mechanism prevents epigenetic tags from the environment being passed onto the offspring 👎

INHERITANCE: Imprinting 🏷

1. Epigenetic tags can be inherited 🏷

2. Methylation of DNA or modifications of histone tails in parents can be passed onto the offspring 🐒

3. Phenotypic changes in the offspring can occur without changes to the DNA/nucleotide sequence 🙈

Discuss the effect of environmental factors of lactose in gene expression in bacteria

LAC OPERON:

1. Contains genes involved in lactose metabolism 🧬

2. The regulatory gene is transcribed into mRNA and produces a repressor protein ✍

3. This repressor protein binds to the operator and blocks the RNA polymerase from binding to the promotor — with no lactose, the gene is not transcribed 👎

4. When lactose is present, it binds to the regulatory protein, making it inactive → allows transcription for the genes that are used to produce the protein/enzyme lactase 💪

Outline the significance monozygotic twin studies

1. Monozygotic twins develop from the same cell/zygote and contain the same genetic material/genome 👬

2. Gene expression is the result of each individual’s genome and the impact of the environment 🌍

3. Monozygotic twin studies can be used to determine the relative impact of either genetics or environment on the expression of genes and a particular trait 😻

Discuss the role of epigenesis in gene expression

EPIGENESIS: The different patterns of differentiation within the cells of a multicellular organism in an undifferentiated zygote

DIFFERENTIATION: The process of expressing certain genes and not others

1. Undifferentiated cells in a zygote/morula/blastocyst can differentiate into any cell type 🧬

2. Each cell contains ALL of the genes to develop into any cell → produce any protein 💪

3. Only some genes are expressed in certain types of cells, most genes are turned off and NOT expressed 💡

FACTORS IMPACTING EPIGENESIS:

1. The chemical environment of the cell 🌍

2. Cytoplasmic gradient in an embryo 👶

3. Location of the cell/surrounding cells 📍