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Flashcards in 15. Control of gene expression Deck (15)
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What effect would a substitution mutation in an intron have on the protein produced?

-Intron non coding/ only exons coding
-So not translated/no change in mRNA produced/ no effect on protein/ amino acids produced
-Prevents changes/ splicing
-So faulty mRNA formed
-Get different amino acid sequence


What is a transcription factor?

-A protein that moves from the cytoplasm to the DNA
-Binds to a specific gene/ promoter/ RNA polymerase
-Leads to/ blocks(pre)mRNA production/ blocks binding of RNA polymerase (to DNA)/ allows RNA polymerase to work


CREB leads to the formation of a protein that removes electrons and protons from reduced NAD in the mitochondrion.
Huntington’s disease (HD) causes the death of neurones. People with HD produce a substance called huntingtin. Some scientists have suggested that binding of huntingtin to CREB may lead to the death of neurones.

Suggest how binding of huntingtin to CREB may lead to the death of neurones

-Binding to CREB prevents transcription/ mRNA formation
-Binding of huntingtin prevents production/ translation of protein (that removes electrons and protons from NAD)
-Fewer electrons to electron transport chain/ ETC stops
-Fewer protons for proton gradient
-Not enough ATP produced/ energy supplied to keep cells alive/ anaerobic respiration not enough to keep cells alive.


The scientists used the polymerase chain reaction (PCR) to produce copies of the
cDNA (complimentary DNA). They added a DNA probe for allele A to the cDNA copies. This DNA probe
had a dye attached to it. This dye glows with a green light only when the DNA probe
is attached to its target cDNA.

Explain why this DNA probe will only detect allele A

-Probe complimentary to DNA of allele A
-Binds by forming base pairs/ hydrogen bonds
-So only this DNA labelled/ has green dye/ gives out green light


How can cells be specialised?

They only have certain genes expressed which make them adapted for their function
-Some genes permanently expressed (eg those for respiration)
-Some genes permanently switched off/ not expressed
-Some genes switched on and off as they are needed


What is a totipotent cell?

A cell that can mature into any body cell


What are the two ways in which a gene can be prevented from being expressed?

-Preventing transcription (therefore preventing the production of mRNA)
-Breaking down mRNA before its genetic code can be translated


What are the totipotent cells that exist in mature animals called?

Adult stem cells


What are stem cells and where are (adult) stem cells found?

-They are differentiated dividing cells and need to constantly be replaced
-Found in:
>Inner lining of small intestine
>Bone marrow


How can plants be cloned using in vitro development?

-Most plant cells are totipotent so taking a cell, for example, from a carrot root, under the right conditions and chemical stimulation a whole new carrot plant can be grown that is a clone of the first plant.


Describe how oestrogen can switch on a gene.

-Oestrogen diffuses across the phospholipid bilayer as it is lipid soluble
-Once in the cytoplasm it combines with a receptor site on the transcription factor because they are complementary shapes to one another
-Oestrogen binding changes the shape of the receptor molecule
-This causes the inhibitor on the DNA binding site of the transcriptional factor to be released
-Transcription factor enters the nucleus via a nuclear pore and combines with the DNA
-Combination of the T.F with DNA stimulates transcription to occur


How does small interfering RNA affect gene expression? (Start with the formation of siRNA)

-Enzyme cuts large double stranded molecules of RNA into smaller ones (siRNA)
-One of the strands of the siRNA combines with an enzyme
-siRNA complementary base pairs to an mRNA molecule
-Enzyme cuts mRNA molecule into smaller sections
-This means the mRNA can no longer be translated into a polypeptide
-Gene is not expressed


Give two potential scientific and medical uses of siRNA

-Use siRNA to block genes that cause genetic diseases to prevent the disease
-Used to identify the role of genes in a biological pathway- add siRNA to cells to block a certain gene and the effects, or lack of, could determine the role of the gene


(2 marks)
Papaya plants reproduce sexually by means of seeds. Papaya plants grown from
seeds are very variable in their yield. Explain why.

1. Meiosis;
2. Independent assortment / crossing over;
3. (Fusion of) genetically different gametes / random


(2 marks)
Describe and explain how expression of the target gene is affected by siRNA.

1. No longer able to make specific protein / cannot make
whole protein / mRNA cannot be translated;
2. Because mRNA has been cut into pieces;

1. Reference to transcribes negates this point.
2. Do not accept mRNA destroyed / do not accept
gene not expressed.
Reference to target gene broken down negates this