Regulation of Gene Expression (A Level only) (AQA A Level Biology): Flashcards

An embryonic stem cell that can differentiate into any cell type found in an embryo, but not into extra-embryonic cells (e.g. the placenta).

A stem cell that can differentiate into a limited range of cell types, all within a specific tissue or organ system.

An adult cell that can differentiate into only one specific cell type (its own lineage), but can still self-renew.

A type of artificially created stem cell produced from adult somatic cells using appropriate protein transcription factors.

Transcription factors cause specific genes to be expressed.

This genetically reprograms the cell to behave like an embryonic stem cell, giving self-renewal and pluripotency.

Cardiomyocytes (heart muscle cells), which only form more cardiomyocytes to maintain the contraction of the heart.

True.

Multipotent stem cells are found throughout the body, e.g. in bone marrow, skin, gut, heart and brain.

False.

Pluripotent cells can form any embryonic cell type but not extra-embryonic cells like the placenta.

They mimic embryonic stem cells but without the associated ethical concerns.

Multipotent cells are more specialised than pluripotent cells but still retain the ability to self-renew.

They are very versatile and can become any tissue type.

They offer long-term potential for curative treatments.

Ethical concerns: their use involves the destruction of embryos.

Immune rejection risk and the possibility of tumour formation if division is uncontrolled.

Replacing lost dopamine-producing neurons in Parkinson's disease (or generating insulin-producing beta cells in Type 1 diabetes).

Bone marrow produces different types of blood cells.

Brain produces different types of neural and glial cells.

No embryo destruction as they are harvested from consenting adults, so there are fewer ethical issues.

They have limited differentiation potential (or are harder to isolate, or may have accumulated mutations).

Disease modelling using patient-specific cells (e.g. Alzheimer's).

Drug testing, reducing the need for animal models.

True.

Because they are made from the patient's own cells, there is no risk of immune rejection.

False.

It is very inefficient and has high costs, as only a small fraction of treated cells become pluripotent.

Adult stem cells used in bone marrow transplants need to be a close match in blood type and other body antigens to reduce rejection.

A small piece of a plant that is cut off and then grown into a new clone of the original plant.

It is composed mostly of actively dividing cells and can withstand being handled.

Many plant cells are totipotent, unlike animal cells, so any cell can produce all the cell types of a whole plant.

To ensure a sterile environment so that no fungi contaminate the experiment, which would cause fungal growth instead of explant growth.

Soak the explant in sterilising solution for 15 minutes.

Swirl it around in the solution every couple of minutes.

All the nutrients the plant needs for growth, plus a sterilant to prevent contamination.

That the explant cells can produce all the different cell types of a whole cauliflower, showing they are totipotent.

True.

The container is left on a sunny windowsill for three weeks to grow a cauliflower clone.

A small piece of plant that is cut off is called an explant, which can be grown into a clone of the original plant.

A protein that helps control transcription by either activating or repressing the transcription of a particular gene.

A section of DNA upstream of the coding region that is the binding site for proteins controlling the expression of the gene.

It binds to the promoter region at the start of a gene.

This assists RNA polymerase binding, increasing the rate of transcription.

By binding to the promoter and preventing RNA polymerase from binding, which decreases transcription.

It is a small, hydrophobic, lipid-based steroid hormone that can diffuse through the cell membrane and enter the nucleus via nuclear pores.

Oestrogen diffuses through the cell membrane and into the nucleus.

It binds an ERα receptor, causing a conformational change so the receptor detaches from its protein complex.

The receptor binds a cofactor and the promoter, stimulating RNA polymerase binding and transcription.

True.

Transcription factors move from the cytoplasm into the nucleus through nuclear pores.

False.

Up to 100 different genes are controlled by oestrogen.

A transcription factor binds to the promoter region at the start of a gene, which can either allow or prevent transcription of the gene.

Oestrogen is a steroid hormone that binds to an oestrogen (ERα) receptor within the nucleus.

The process by which genetic information is used to synthesise proteins or functional RNA molecules.

The observable characteristics of an organism, resulting from the interaction between its genotype and the environment.

Higher mRNA or protein levels usually indicate increased gene expression.

When a cell expresses a gene, RNA is produced by transcription.

Matching the RNA present to specific genes reveals which genes are being expressed in that cell.

Monozygotic twins share identical genotypes, so any phenotypic differences between them suggest an environmental influence.

The strength and direction of correlations.

Whether results show causation or only association.

Whether confounding variables have been controlled.

Genes responsible for tumour formation can be detected by analysing which genes are over-expressed in a cancer cell, helping identify drugs that block them.

True.

Genetic and environmental influences often contribute to phenotype in complex, interacting ways.

mRNA concentrations can be measured using techniques such as RT-PCR, while protein levels can be detected using methods like ELISA.

Changes in gene function without changes to the base sequence of DNA.

All of the chemical modifications to histone proteins and DNA (except base changes) in an organism.

Addition of acetyl groups to histone proteins.

Addition of methyl groups to DNA.

Changes in the environment, such as smoking, stress, exercise and diet.

Internal signalling from the body's cells.

Acetyl groups added to lysine remove positive charges, so DNA wraps less tightly.

RNA polymerase and transcription factors bind more easily, so gene expression is switched on.

Methyl groups are added to cytosine bases.

This suppresses transcription, as methylated bases attract proteins that bind and inhibit transcription.

The gene and promoter regions are hidden from transcription factors and RNA polymerase, so transcription cannot occur.

True.

Deacetylation makes DNA wrap more tightly around histones, which inhibits transcription.

False.

Epigenetics involves changes in gene function without changing the DNA base sequence.

The addition of methyl groups to DNA suppresses transcription, whereas the addition of acetyl groups to histones switches gene expression on.

To reverse epigenetic changes in order to restore normal gene expression.

Unlike mutations, epigenetic changes are reversible.

Changes in DNA methylation and histone acetylation cause tumour suppressor genes to be silenced and oncogenes to be activated, deregulating the cell cycle.

It enables the genes to be expressed again.

The proteins produced can regulate the cell cycle and stop tumours forming.

The DNA wraps more tightly, silencing the oncogenes.

Faulty cells can then undergo apoptosis rather than replicating.

They inhibit enzymes (DNA methyltransferases) that add methyl groups, aiming to reactivate silenced tumour suppressor genes.

They prevent histone deacetylation, keeping chromatin open and increasing expression of beneficial genes (e.g. those inducing apoptosis).

True.

Epigenetic therapies are explored for neurological diseases (e.g. Alzheimer's), autoimmune and metabolic conditions.

Because epigenetic changes are reversible, drugs can reverse them by removing acetyl and methyl tags to restore normal gene expression.

A form of post-transcriptional gene silencing, occurring in the cytoplasm, that is sequence-specific.

Small, double-stranded RNA molecules that bind to complementary mRNA from target genes, leading to its breakdown.

siRNA binds to the target mRNA by complementary base pairing.

An associated protein complex cuts the mRNA into fragments, so it cannot be translated.

Double-stranded RNA (dsRNA) is produced by RNA-dependent RNA polymerases.

dsRNA is hydrolysed into fragments about 23 nucleotides long, called siRNAs.

Separating the strands (using ATP) exposes the nucleotide bases so they can pair with bases on an mRNA molecule.

The fragments are broken down into RNA nucleotides by enzymes, so no functional protein is produced.

siRNAs can target oncogenes that have been over-expressed.

This reduces the proteins that cause or maintain cancerous growth.

False.

RNA interference is a post-transcriptional process that occurs in the cytoplasm.

True.

siRNA binds the target mRNA via complementary base pairing, localising it to the protein complex for hydrolysis.

Small interfering RNAs bind to mRNA through complementary base pairing, causing it to be cut up so it cannot be translated.

A group of abnormal cells that forms a lump or growth, which can start in any cell of the body.

They grow rapidly, then invade and destroy surrounding tissues.

When cells break off a malignant tumour and spread to other parts of the body via the bloodstream or lymphatic system.

Grows slowly.

Does not invade other tissues or metastasise.

Does not usually grow back when removed.

By damaging the organ they are in, causing blockages or obstructions, or damaging other organs by exerting pressure.

To supply the tumour with nutrients, growth factors and oxygen.

UV or X-ray exposure and tobacco from cigarettes (also asbestos or processed meat).

False.

Benign tumours do not metastasise or invade other tissues, unlike malignant tumours.

True.

Malignant tumours can still grow back after surgical removal.

Malignant tumours are cancerous, whereas benign tumours are non-cancerous and grow slowly.

From uncontrolled mitosis due to mutations in genes that regulate the cell cycle, forming a tumour.

A normal gene that codes for proteins which stimulate cell growth and differentiation.

A mutation (often caused by a carcinogen) causes the constant activation of proteins that stimulate cell growth and division, speeding up the cell cycle.

They encode proteins that repair DNA, slow the cell cycle at checkpoints, and signal apoptosis if damage is irreparable.

Mutation or epigenetic silencing stops the protein being made.

The brake on cell division is removed, so tumour formation can occur.

Methylation silences the gene, as transcription factors cannot bind.

Tumour suppressor proteins are not made, so tumour formation occurs.

The gene becomes accessible, transcription factors bind and protein synthesis is activated.

The gene behaves like an oncogene, even without a mutation.

It is a competitive inhibitor that binds the ERα receptor.

This prevents gene activation, as the receptor cannot bind the promoter, inhibiting tumour growth.

True.

BRCA-1 is a tumour suppressor gene mainly expressed in breast tissue; its protein repairs DNA or triggers apoptosis.

A mutated proto-oncogene becomes an oncogene, which permanently stimulates cell division, while silencing of a tumour suppressor gene removes the brake on division.