D2.2 Gene expression

What is the genotype of an organism?

The genotype of an organism is all its genetic information.

What is the phenotype of an organism?

The phenotype is all aspects of the structures and functions of the organism—the totality of its characteristics.

What is gene expression?

Gene expression is the process of turning the genotype into the phenotype.

What happens during transcription?

Genes within the genotype are selected and are used in the production of RNA.

How does DNA determine the base sequence of RNA?

Through complementary base pairing.

What is the role of messenger RNA (mRNA)?

mRNA is transported to ribosomes in the cytoplasm for protein synthesis.

What happens during translation?

mRNA is used in the production of polypeptides.

What does the base sequence of an mRNA molecule determine?

The amino acid sequence of a polypeptide.

Where does translation occur?

On ribosomes.

What are proteins composed of?

One or more polypeptides, sometimes with additional non-polypeptide components.

What is one function of proteins in an organism?

Proteins may form part of the structure of the organism.

How do enzymes impact phenotype?

Enzymes affect phenotype by catalyzing reactions.

What is an example of an enzyme impacting phenotype?

The ability to digest lactose is due to the enzyme lactase.

Is gene expression an on/off process?

No, it can vary in intensity and be assessed by measuring protein or gene product quantities.

What does selective transcription of RNA require?

It requires RNA polymerase binding to a promoter sequence.

What is a promoter?

A sequence close to a gene where RNA polymerase binds.

What is a common feature of promoters in eukaryotes?

The TATA box, a short base sequence (TATAAAA).

What is the function of a general transcription factor?

It binds to the TATA box, indicating where transcription should begin.

What determines which genes are selected for transcription?

DNA-binding proteins locate and attach to specific DNA base sequences.

Where do DNA-binding proteins usually bind?

In the major groove of the DNA molecule.

What are transcription factors?

DNA-binding proteins that regulate the transcription of a gene.

Where do transcription factors bind?

Upstream of the gene they regulate.

What are enhancers?

Sequences to which activators bind to increase the rate of transcription.

What are silencers?

Sequences to which repressors bind to decrease the rate of transcription.

What mechanism regulates gene expression after transcription?

Control of mRNA degradation.

What is a poly-A tail?

A long sequence of adenine nucleotides added to the 3′ end of mRNA.

How does the poly-A tail affect mRNA?

It increases stability but is shortened over time, influencing degradation.

How is mRNA degradation regulated?

The rate of shortening of the poly-A tail varies and is influenced by chemical signals like hormones.

What is an example of hormonal regulation of mRNA stability?

Oestrogen increases the stability of vitellogenin mRNA in egg-laying animals.

What is epigenesis?

The concept that organisms develop from undifferentiated cells into structures and functions.

What determines cell differentiation?

The activation of certain genes and silencing of others.

What are epigenetic tags?

Chemical modifications to DNA or associated proteins that influence gene activation or silencing.

Do epigenetic modifications affect the genotype?

No, they only influence the phenotype.

What is a genome?

The whole genetic information of a cell, including coding and non-coding sequences.

What is a transcriptome?

The entire set of mRNAs transcribed in a cell.

How does the transcriptome vary?

It changes over time within a cell and between cells in an organism.

What is a proteome?

The entire set of proteins produced by a cell.

How is the proteome determined?

By the transcriptome, but protein quantities are not directly proportional to mRNA quantities.

What is methylation of DNA?

The substitution of a hydrogen with a methyl group (–CH3) in a base.

Which DNA base is commonly methylated?

Cytosine is often converted to methylcytosine.

What is the impact of cytosine methylation in the promoter of a gene?

It represses transcription and gene expression.

What is a nucleosome?

A structure of DNA wound around eight histones.

What is the role of histone tails?

They influence DNA packing and regulate gene expression.

What are examples of epigenetic tags on histones?

Addition of methyl, acetyl, or phosphate groups.

What is the epigenome?

The sum of all epigenetic tags in a cell or organism.

How is the epigenome maintained during mitosis?

It is passed to daughter cells during cell division.

What is transgenerational epigenetic inheritance?

The passing of epigenetic tags from parent to offspring.

What is reprogramming of the epigenome?

The process of erasing epigenetic tags before gametes fuse to form a zygote.

What is genomic imprinting?

A type of non-Mendelian inheritance where epigenetic tags influence gene expression.

What is Angelman syndrome?

A condition caused by the silencing of a gene from one parent, allowing a recessive allele to be expressed.

How does air pollution impact the epigenome?

It decreases DNA methylation, influencing immune system regulation.

What are the effects of air pollution during pregnancy?

It changes methylation in specific genes, affecting development and early life.

What happens during the production of sperm and eggs?

Approximately 99% of epigenetic tags are removed.

What is Mendelian inheritance?

Inheritance where dominant alleles mask recessive alleles.

How does genomic imprinting differ from Mendelian inheritance?

In genomic imprinting, one allele is silenced, so the organism behaves as if haploid for that gene.

What causes differences in cub size between lions and tigers?

Paternal imprinting favors larger cubs; maternal imprinting favors smaller cubs.

What are dizygotic twins?

Fraternal twins that arise when two eggs are fertilized.

What are monozygotic twins?

Identical twins that develop from a separated early embryo.

What do studies of monozygotic twins reveal?

They show the relative impact of genes and the environment on phenotype.

What regulates lactose metabolism in E. coli?

The presence or absence of lactose regulates gene expression through negative feedback.

How does lactose regulate gene expression in E. coli?

It deactivates a repressor protein, allowing lactose metabolism genes to be expressed.

What happens once lactose is metabolized in E. coli?

The repressor protein is reactivated and blocks further expression of lactose metabolism genes.

Why is gene regulation critical in multicellular organisms?

It allows for cellular differentiation and development.

What is an example of hormonal regulation of gene expression?

Oestrogen binds to receptors in the endometrium, activating target genes.

What does oestrogen regulate in the uterine cycle?

It makes the endometrium more responsive to progesterone during the luteal phase.

What is the role of the promoter in transcription?

The promoter is a DNA sequence near a gene that binds RNA polymerase to initiate transcription.

What is the TATA box?

A TATA box is a short DNA sequence (TATAAAA) in eukaryotic promoters where a general transcription factor binds to indicate the transcription start site.

What are transcription factors?

Transcription factors are DNA-binding proteins that regulate transcription by attaching to specific DNA sequences.

What is the difference between enhancers and silencers?

Enhancers increase the rate of transcription by binding activators, while silencers decrease transcription by binding repressors.

What happens to mRNA after transcription is complete?

A poly-A tail is added to the 3′ end of mRNA, increasing stability and regulating degradation.

How does mRNA degradation influence protein production?

The length of the poly-A tail determines how long mRNA persists, impacting how much protein is produced.

What are epigenetic tags?

Epigenetic tags are chemical modifications, such as methylation, that influence gene expression without altering the DNA sequence.

What is methylation of DNA?

Methylation of DNA is the addition of a methyl group (–CH3) to a base, commonly cytosine, affecting gene expression.

What is the function of histones?

Histones are proteins that DNA wraps around, forming nucleosomes, and they regulate DNA packing and gene expression.

What is acetylation of histones?

Acetylation of histones adds acetyl groups to histone tails, making DNA more accessible for transcription.

What is the epigenome?

The epigenome is the sum of all epigenetic tags in a cell or organism, influencing gene expression and phenotype.

What happens during epigenetic reprogramming?

During epigenetic reprogramming, most epigenetic tags are erased in gametes, but some may persist into the next generation.

What is transgenerational epigenetic inheritance?

It is the transmission of epigenetic tags from one generation to the next, potentially affecting gene expression.

What is genomic imprinting?

Genomic imprinting is when one parent’s allele of a gene is silenced, affecting inheritance and expression patterns.

How does genomic imprinting differ from Mendelian inheritance?

In genomic imprinting, only one parent's allele is expressed, unlike Mendelian inheritance, where both alleles contribute.

What is Angelman syndrome?

Angelman syndrome is a condition caused by genomic imprinting, where the paternal allele is silenced, revealing a recessive condition.

What are dizygotic twins?

Dizygotic (fraternal) twins result from two separate eggs being fertilized, sharing about 50% of their genetic material.

What are monozygotic twins?

Monozygotic (identical) twins arise when a single embryo splits, creating two individuals with identical genetic material.

How can environmental factors impact monozygotic twins?

Environmental differences can lead to variations in gene expression and phenotypic traits in monozygotic twins.

What regulates lactose metabolism in Escherichia coli?

Lactose presence deactivates a repressor protein, allowing genes for lactose metabolism to be expressed.

What is negative feedback in lactose metabolism?

Negative feedback occurs when lactose breakdown reactivates the repressor protein, shutting off lactose metabolism genes.

How does eukaryotic gene regulation affect differentiation?

Eukaryotic gene regulation ensures specific genes are expressed, enabling cellular differentiation and development.

What role do hormones play in gene expression?

Hormones like oestrogen bind to receptors and target gene promoters, influencing transcription and cell function.

What is the function of oestrogen in the endometrium?

Oestrogen promotes the expression of the progesterone receptor gene, enhancing endometrial responsiveness during the luteal phase.

What is a transcriptome?

A transcriptome is the entire set of mRNAs transcribed in a cell, reflecting gene expression at a given time.

What is a proteome?

A proteome is the entire set of proteins produced by a cell, based on the transcriptome and regulated gene expression.

What is the relationship between the transcriptome and proteome?

The proteome is derived from the transcriptome but is influenced by regulation of translation and protein stability.

How does air pollution affect the epigenome?

Air pollution decreases DNA methylation, affecting immune system proteins and increasing risks of inflammation and diseases.

What is the significance of epigenetic tags in development?

Epigenetic tags guide gene activation and silencing, enabling differentiation and the formation of specialized tissues.

How do methylation and acetylation impact chromatin?

Methylation and acetylation modify histones, influencing DNA accessibility and transcription regulation.