7.6.1 Transcription factors and hormones switching genes on and off Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

The 20 questions

1. What is the role of a transcription factor?

   • Joining two polypeptide chains together to form a functional quaternary protein in the cytoplasm
   • Breaking down messenger RNA once translation of the protein has been completed in the ribosome
   • Carrying amino acids to ribosomes so that they can be joined into a growing polypeptide chain
   • Binding to specific DNA sequences and controlling whether a gene is transcribed into messenger RNA

2. Which molecule is produced when a gene is transcribed?

   • Phospholipid, a molecule with a hydrophilic head and two hydrophobic tails that forms membranes
   • Glycogen, a branched polymer of glucose that is stored mainly in the liver and the muscles
   • Messenger RNA (mRNA), a single-stranded copy of the gene sequence used to direct protein synthesis
   • Haemoglobin, a protein made of four polypeptide chains that carries oxygen in red blood cells

3. Why are steroid hormones able to act on the nucleus of a cell?

   • They are lipid-soluble and can diffuse through the cell-surface membrane into the cytoplasm and nucleus
   • They are digested before reaching the cell, so only their breakdown products can enter the nucleus
   • They are large, polar molecules that cannot cross membranes, so they must act on receptors inside the nucleus directly
   • They bind to ribosomes in the cytoplasm only, and the ribosomes then carry the hormone to the nucleus

4. Where are the receptors for steroid hormones usually located?

   • In the extracellular fluid as free proteins that carry the hormone to target cells around the body
   • Inside the cell, in the cytoplasm or nucleus, where they can bind the hormone and act on DNA
   • On the surface of lysosomes only, where they break down the hormone after it enters the cell
   • On the outer surface of the cell-surface membrane only, where they bind hormones arriving in the blood

5. Why do non-steroid hormones such as adrenaline usually act through second messengers rather than entering the cell?

   • They are polar and cannot cross the lipid bilayer, so they bind to surface receptors that start a signalling cascade
   • They are broken down immediately in the blood, so they never reach the cell and act only on the blood vessels
   • They bind only to the ribosome, which then produces the second messenger to carry the signal into the cell
   • They are lipid-soluble and diffuse into the nucleus, where they then trigger the release of second messengers

6. A steroid hormone-receptor complex binds to a DNA sequence. What is the most likely effect?

   • The complex is destroyed on contact with the DNA, so the gene is switched off permanently in the cell
   • It stops translation in the cytoplasm immediately, although the mRNA levels in the nucleus remain unchanged
   • It prevents any mRNA being made in the cell at all, which stops all protein synthesis in the cytoplasm
   • It alters the rate of transcription of a target gene, increasing or decreasing the amount of mRNA made

7. Which sequence correctly shows how a steroid hormone changes gene expression?

   • Hormone binds a ribosome, then mRNA is made, then the hormone is excreted by the kidneys in the urine
   • Hormone is digested in the cell, then amino acids bind DNA directly, then transcription stops at the promoter
   • Hormone diffuses through the membrane, binds an intracellular receptor, the complex binds DNA, and transcription changes
   • Hormone binds a surface receptor, then DNA is replicated, then the protein is hydrolysed by enzymes in the cytoplasm

8. Which statement describes the effect of a transcription factor on a gene that it switches off?

   • It breaks the gene's DNA into fragments, which are then removed from the nucleus by the cell
   • It increases the transcription rate of the gene above its normal level, producing more mRNA
   • It makes the gene produce a different amino acid sequence in the protein that is then made by the ribosome
   • It binds DNA and blocks or reduces transcription of that gene, so less mRNA and protein are made

9. A cell is exposed to a steroid hormone that causes a 4-fold increase in the mRNA for a particular protein. Which explanation best fits this result?

   • The hormone-receptor complex increased transcription of the gene encoding that protein
   • The hormone removed the nuclear envelope, which allowed the mRNA to leak out into the cytoplasm of the cell
   • The hormone destroyed the ribosomes in the cell, so the mRNA builds up because it cannot be translated
   • The hormone blocked translation of all mRNA, so the mRNA levels rise even though protein production falls

10. Which hormone is a steroid that acts as a transcription factor in many target cells?

    • Insulin, a polypeptide hormone that binds surface receptors and lowers blood glucose after a meal
    • Oestrogen, a steroid hormone that enters cells and binds intracellular receptors to regulate gene transcription
    • Adrenaline, a catecholamine released in stress that acts through surface receptors and second messengers
    • Glucagon, a polypeptide hormone released by the pancreas that raises blood glucose through the liver

11. What is meant by 'gene expression' in this context?

    • The loss of a gene from the genome, which happens when a region of DNA is deleted during cell division
    • The process by which a gene is copied and translated to make a functional product, such as a protein
    • The breakdown of a protein into amino acids, which happens when the protein is no longer needed in the cell
    • The movement of ions across the membrane, which is driven by the sodium-potassium pump in the axon

12. Why does a steroid hormone need a receptor to produce a response?

    • The receptor is specific to the hormone shape, so only target cells that have it respond to the hormone
    • The receptor provides the energy for transcription, which would not occur if the receptor were absent from the cell
    • Receptors make the cell membrane impermeable, which prevents the hormone from leaving the cell after it arrives
    • Receptors break down the hormone into smaller molecules, which is needed before it can enter the cell nucleus

13. A student states that all transcription factors are hormones. Which evaluation is correct?

    • Incorrect, because transcription factors are lipids that bind to the cell wall and control the release of the nucleus
    • Incorrect, because transcription factors are proteins that bind DNA, and only some of them are activated by hormones
    • Correct, because hormones are the only molecules that are able to bind DNA and so control transcription
    • Correct, because all transcription factors are steroid hormones that are produced by glands and circulate in the blood

14. Which statement explains why a steroid hormone affects many different cells differently?

    • Each hormone molecule has a different structure in each cell, so the responses differ between the cells
    • Every cell contains identical receptors and genes, so the responses to the same hormone are always the same
    • Different cells express different genes and so respond to the same hormone in different ways
    • Steroid hormones only act on red blood cells, which explains why their effects are limited to the blood

15. A steroid hormone binds its receptor at a concentration of 2 nmol per dm^3 and a gene's transcription rate rises as concentration increases to 8 nmol per dm^3. What is the best conclusion?

    • There is a positive relationship between hormone concentration and transcription rate over this range
    • The hormone must have destroyed the gene at the higher concentration, which stopped the transcription
    • Transcription falls as hormone concentration rises, which shows that the hormone inhibits its target gene
    • Transcription is independent of hormone concentration, since the rise in hormone level has no effect on the gene

16. Which statement describes the key difference between how steroid and non-steroid hormones produce a response?

    • Non-steroid hormones always enter the nucleus directly, where they bind DNA and change transcription
    • Steroid hormones act only on the surface; non-steroid hormones act only in the nucleus of the target cell
    • Steroid hormones act by changing transcription; non-steroid hormones usually act through surface receptors and second messengers
    • There is no difference in the mechanism, since both types of hormone enter the cell and bind to DNA

17. Which feature of gene switching allows the same DNA to produce different cell types?

    • Cells use only mitochondrial DNA, which is identical in every cell and so does not create any variation
    • Every gene is switched on in every cell, so all cells of the body produce exactly the same proteins at all times
    • DNA is lost from cells during development, so cells that remain produce proteins from other sources
    • Transcription factors switch genes on or off in different cells, so different sets of proteins are made

18. A patient is prescribed a drug that blocks a steroid receptor from binding DNA. What is the expected effect on the target gene?

    • Transcription of the gene increases above normal, since the drug frees the DNA from the receptor's control
    • Translation of the gene increases with no effect on mRNA, since the drug acts only on the ribosome in the cytoplasm
    • The gene is permanently deleted from the genome, since the drug binds the receptor and damages the DNA sequence
    • Transcription of the gene is reduced because the hormone-receptor complex cannot act as a transcription factor

19. Which pair correctly matches a hormone type with its typical receptor location?

    • Steroid: intracellular receptor; non-steroid: cell-surface receptor on the membrane of the target cell
    • Both types: mitochondrial receptor, which is found in the inner membrane and binds hormones to make ATP
    • Steroid: cell-surface receptor; non-steroid: intracellular receptor in the cytoplasm of the target cell
    • Both types: ribosomal receptor, which is found in the cytoplasm and binds hormones before they reach the nucleus

20. Which molecule, when it binds an intracellular receptor, forms a complex that can act as a transcription factor?

    • Glucose, which crosses the membrane through transporters and is used in respiration rather than gene control
    • Adrenaline, a polar hormone that binds a surface receptor and cannot enter the cell
    • Insulin bound to a surface receptor only, which acts through a tyrosine kinase cascade in the cytoplasm
    • A steroid hormone such as oestrogen, which diffuses into the cell and binds an intracellular receptor

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