3.8.2.2 - GENE EXPRESSION Flashcards
(22 cards)
one method of transferring RNAi molecules into cells involves combining these molecules with a lipid.
suggest why this increases uptake of RNAi molecules into cells (1)
- phospholipid bilayer
- no need for channel/carrier protein for uptake
testosterone is a steroid hormone that belongs to a group of male sex hormones called androgens.
steroid hormones are hydrophobic.
explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane. (2)
- lipid soluble
- can diffuse through phospholipid bilayer
testosterone is a steroid hormone that belongs to a group of male sex hormones called androgens.
in the cytoplasm, testosterone binds to a specific androgen receptor (AR). an AR is a protein.
suggest and explain why testosterone binds to a specific AR (2)
- has a specific tertiary structure
- structures are complementary
testosterone is a steroid hormone that belongs to a group of male sex hormones called androgens. in the cytoplasm, testosterone binds to a specific androgen receptor (AR). an AR is a protein.
the binding of testosterone to an AR changes the shape of the AR. this AR molecule now enters the nucleus and stimulates gene expression.
suggest how the AR could stimulate gene expression (2)
- AR is a transcription factor
- binds to promoter region on DNA
- stimulates RNA polymerase
suggest how transcription factors can reprogramme cells to form iPS cells (2)
- attach to promoter region
- inhibit/stimulate transcription/RNA polymerase
scientists investigated the role of a protein called CENP-W in mitosis. their method involved cell fractionation and ultracentrifugation.
the scientists began by lysing (breaking open) cells and organelles using a detergent that dissolves lipids in water.
suggest how the detergent releases CENP-W from cells (2)
- cell membranes made from phospholipid
- detergent dissolves membranes/phospholipids
scientists investigated the role of a protein called CENP-W in mitosis. their method involved cell fractionation and ultracentrifugation.
the scientists began by lysing (breaking open) cells and organelles using a detergent that dissolves lipids in water.
explain how ultracentrifugation separates CENP-W from other molecules (2)
- spin supernatant at high speed
- molecules separate depending on density/size
define what is meant by epigenetics (2)
- heritable changes in gene function
- without changes to the base sequence of DNA
explain how increased methylation could lead to cancer (3)
- methyl groups added to tumour suppressor gene
- transcription of tumour suppressor genes is inhibited
- leading to uncontrolled cell division
HIV particles have a specific protein on their surface that binds to a receptor on the plasma membrane of a human cell and allows HIV to enter. this HIV protein is found on the surface of human cells after they have become infected with HIV.
scientists made siRNA to inhibit expression of a specific HIV gene inside a human cell. they attached this siRNA to a carrier molecule.
the flow chart shows what happens when the carrier molecule reaches a human cell infected with HIV.
carrier with siRNA attached binds to HIV protein on plasma membrane of infected cell –> allows carrier with siRNA to enter human cell –> siRNA binds to mRNA transcribed from HIV gene –> mRNA from HIV gene not transcribed
the siRNA would only affect gene expression in cells infected with HIV. suggest two reasons why (4)
- only infected cells have HIV protein on surface
- so carrier only attaches to these cells OR siRNA complementary to one mRNA
- only infected cells contain mRNA of HIV
oestrogen is a hormone that affects transcription. it forms a complex with a receptor in the cytoplasm of target cells.
explain how an activated oestrogen receptor affects the target cell (2)
- binds to promoter region which stimulates RNA polymerase
- increases transcription
oestrogen only affects target cells. explain why oestrogen does not affect other cells in the body (1)
other cells do not have oestrogen receptors
plants transport sucrose from leaves to other tissues for growth and storage. SUT1 is a sucrose co-transporter protein. scientists investigated whether the cells of tobacco plant leaves used SUT1 to transport sucrose to other tissues.
to study the role of SUT1 in tobacco plants, scientists reduced the expression of the SUT1 gene.
when the SUT1 gene is transcribed, the SUT1 mRNA produced is called ‘sense’ SUT1 mRNA. the scientists genetically modified plants by inserting an extra gene so that this also allowed the production of ‘antisense’ SUT1 mRNA.
the scientists had two types of tobacco plants:
• type A – plants that were genetically modified
• type B – plants that were not genetically modified.
suggest how the production of ‘antisense’ SUT1 mRNA in type A plants would reduce the expression of the SUT1 gene. (4).
- antisense mRNA is complementary to ‘sense’ mRNA
- antisense mRNA would base pair to the sense mRNA
- ribosomes would not be able to bind
- so less production of SUT1 protein
suggest two reasons why people had the drug injected into the cerebrospinal fluid bathing the brain rather than taking a pill containing the drug (2)
1.so drug will directly reach the brain
2. so it is not digested by enzymes
suggest and explain one way epigenetica may affect the age when symptoms of Huntington’s disease start (2)
ONE PAIR:
- increased methylation of DNA
- inhibits transcription
OR
- decreased acetylation of his tones
- inhibits transcription
some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. this stimulates the cancer cells to divide.
scientists have produced a monoclonal antibody that stops this stimulation.
use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour (3)
- antibody has specific tertiary structure
- complementary shape to receptor protein
- prevents GF binding to receptor
sometimes, a mutagenic agent causes DNA to break. an enzyme called ATM binds to the broken DNA. this leads to the activation of a protein coded for by a tumour suppressor gene. the effect of ATM binding is to stop cell division until DNA is repaired. a mutation could result in a person having non-functional forms of the gene that produces ATM.
what can you predict about the possible effects of having a non-functional form of ATM? (3)
- ATM will not bind to (broken) DNA
- DNA not repaired/cell still has broken DNA
- cell division continues/tumour forms
- tumour suppressor (gene) not effective/activated
- may have no effect in diploid / heterozygous
- which will still have a functional ATM/ATM gene
the signal proteins secreted into the air by a plant being attacked by a pathogen act as stimuli leading to the expression of genes for defensive enzymes in other plants.
suggest how they lead to the expression of these genes (3)
- bind to receptor on target plant
- acts as a transcription factor
- stimulates transcription of genes
suggest and explain the advantage to tomato plants of transmitting signal proteins through mycorrhizal networks, rather than releasing them intro the air (2)
- direct plant-to-plant transmission
- so localised response/faster response
suggest how the growth of new blood vessels into damaged heart tissues could increase the rate of repair of tissues (3)
- greater blood supply
- bringing more oxygen/glucose for respiration
- brings more amino acids for protein synthesis
- for cell repair/division/mitosis
this siRNA would only affect gene expression in cells infected with HIV.
suggest two reason why (4)
- only infected cells have HIV protein on surface
- so siRNA can only enter these cells
OR
- siRNA base sequence complementary to one mRNA
- only binds to this mRNA
mikanolide is a drug that inhibits the enzyme DNA polymerase.
explain why this drug may be effective against some types of cancer (2)
- prevents/slows DNA replication
- new strand not formed
