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A level Biology: Post your doubts here!

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Syeeeer

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Assalamualaikum. Can anyone help me with this question?

Explain why, in gene technology, a promoter needs to be transferred along with the desired gene.

Mark Scheme:
1. promoter, initiates transcription/switches on gene/causes gene expression/AW;
2. ref. binding of, RNA polymerase/transcription factors;
3. otherwise gene has to be inserted near an existing promoter;
4. this is difficult to do/this may disrupt expression of existing gene;
5. in eukaryotes precise position of promoter important;
 
Afza Munir

Afza Munir

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Syeeeer said:
Assalamualaikum. Can anyone help me with this question?

Explain why, in gene technology, a promoter needs to be transferred along with the desired gene.

Mark Scheme:
1. promoter, initiates transcription/switches on gene/causes gene expression/AW;
2. ref. binding of, RNA polymerase/transcription factors;
3. otherwise gene has to be inserted near an existing promoter;
4. this is difficult to do/this may disrupt expression of existing gene;
5. in eukaryotes precise position of promoter important;
Click to expand...
In the DNA of bacteria and other prokaryotes, base sequences called promoters are
situated just before (‘upstream’ of) each gene. These identify the point at which
transcription should begin. Usually, these consist of two short six base sequences,
TATAAT, situated about 10 bases before the gene and, TTGACA, situated about 35
bases before the gene. The presence of at least one of these is usually necessary to
initiate transcription of the gene in prokaryotes.
In the case of insulin, the first successful recombinant DNA involved using the
promoter of an existing non-essential gene, for an enzyme involved in lactose
metabolism (B-galactosidase). The human insulin gene was inserted into the
existing gene. The promoter for this gene remained intact. There is also a lactosesensitive regulatory sequence that is designed to turn on the natural B-galactosidase
in the presence of lactose. The promoter, regulator and gene, are together called an
operon, in this case the lac-operon. The effect of all this is that when the genetically
engineered E coli, containing the human insulin gene in its lac-operon, was exposed
to lactose, it transcribed a polypeptide that contained the first part of the Bgalactosidase, followed by human insulin.
Now that more is known about prokaryote promoters, synthetic DNA can be made,
rather than trying to make use of natural promoters in this way.
In eukaryotes, the regulation of gene expression is considerably more complex, and
so eukaryote promoters may well not have the intended effect in prokaryotic cells.

What this means in practice, is that if a gene, such as the human insulin gene, is
transferred into prokaryote DNA without adding a prokaryotic promoter, it will not be
transcribed and hence will not be expressed.
When genes are transferred from eukaryotes to prokaryotes, it is therefore essential
that a suitable prokaryote promoter is added to the gene before it forms recombinant
DNA with the plasmid vector. The promoter initiates transcription of the gene so that
the desired product is expressed.
If eukaryote promoters are to be transferred with eukaryotic genes, into eukaryotic
cells of a different species, then care must be taken to ensure that all of the relevant
code is included, which may include short base sequences close to the start of the
gene (such as TATAAA, [TATA box] within 50 bases of the start of the gene,
promotes mRNA formation) or other sequences further away from the gene (such as
CACGTG [E box] which binds proteins needed for transcription) some of which may
cause the DNA to bend back on itself, so that the promoter is several thousand
bases before the gene.
 
S

smoothieoeek

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Can somebody help me?
During stomatal closure, why is the water potential of the guard cells higher than epidermal cells?
 
S

smoothieoeek

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Afza Munir said:
suggest three reasons why exchange between the cell and its environment is essential? :rolleyes:
Click to expand...

The cells needs to uptake CO2 for use in the Calvin cycle, and excrete O2 which is produced in the cells through photolysis, through the stomata. Cell needs to uptake water, to be used in the light dependent stage of photosynthesis. Is this ok?
 
S

Syeeeer

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Afza Munir said:
In the DNA of bacteria and other prokaryotes, base sequences called promoters are
situated just before (‘upstream’ of) each gene. These identify the point at which
transcription should begin. Usually, these consist of two short six base sequences,
TATAAT, situated about 10 bases before the gene and, TTGACA, situated about 35
bases before the gene. The presence of at least one of these is usually necessary to
initiate transcription of the gene in prokaryotes.
In the case of insulin, the first successful recombinant DNA involved using the
promoter of an existing non-essential gene, for an enzyme involved in lactose
metabolism (B-galactosidase). The human insulin gene was inserted into the
existing gene. The promoter for this gene remained intact. There is also a lactosesensitive regulatory sequence that is designed to turn on the natural B-galactosidase
in the presence of lactose. The promoter, regulator and gene, are together called an
operon, in this case the lac-operon. The effect of all this is that when the genetically
engineered E coli, containing the human insulin gene in its lac-operon, was exposed
to lactose, it transcribed a polypeptide that contained the first part of the Bgalactosidase, followed by human insulin.
Now that more is known about prokaryote promoters, synthetic DNA can be made,
rather than trying to make use of natural promoters in this way.
In eukaryotes, the regulation of gene expression is considerably more complex, and
so eukaryote promoters may well not have the intended effect in prokaryotic cells.

What this means in practice, is that if a gene, such as the human insulin gene, is
transferred into prokaryote DNA without adding a prokaryotic promoter, it will not be
transcribed and hence will not be expressed.
When genes are transferred from eukaryotes to prokaryotes, it is therefore essential
that a suitable prokaryote promoter is added to the gene before it forms recombinant
DNA with the plasmid vector. The promoter initiates transcription of the gene so that
the desired product is expressed.
If eukaryote promoters are to be transferred with eukaryotic genes, into eukaryotic
cells of a different species, then care must be taken to ensure that all of the relevant
code is included, which may include short base sequences close to the start of the
gene (such as TATAAA, [TATA box] within 50 bases of the start of the gene,
promotes mRNA formation) or other sequences further away from the gene (such as
CACGTG [E box] which binds proteins needed for transcription) some of which may
cause the DNA to bend back on itself, so that the promoter is several thousand
bases before the gene.
Click to expand...

Thank you :)
 
Afza Munir

Afza Munir

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smoothieoeek said:
The cells needs to uptake CO2 for use in the Calvin cycle, and excrete O2 which is produced in the cells through photolysis, through the stomata. Cell needs to uptake water, to be used in the light dependent stage of photosynthesis. Is this ok?
Click to expand...
ya sure it is thanksss.!(y)
 
Afza Munir

Afza Munir

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smoothieoeek said:
Can somebody help me?
During stomatal closure, why is the water potential of the guard cells higher than epidermal cells?
Click to expand...
However, most plants do not have the aforementioned facility and must therefore open and close their stomata during the daytime in response to changing conditions, such as light intensity, humidity, and carbon dioxide concentration. It is not entirely certain how these responses work. However, the basic mechanism involves regulation of osmotic pressure.
When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity), a proton pump drives protons (H+) from the guard cells. This means that the cells' electrical potential becomes increasingly negative. The negative potential opens potassium voltage-gated channels and so an uptake of potassium ions (K+) occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. In some cases, chloride ions enter, while in other plants the organic ion malate is produced in guard cells. This increase in solute concentration lowers the water potential inside the cell, which results in the diffusion of water into the cell through osmosis. This increases the cell's volume and turgor pressure. Then, because of rings of cellulose microfibrils that prevent the width of the guard cells from swelling, and thus only allow the extra turgor pressure to elongate the guard cells, whose ends are held firmly in place by surrounding epidermal cells, the two guard cells lengthen by bowing apart from one another, creating an open pore through which gas can move.[5]
When the roots begin to sense a water shortage in the soil, abscisic acid (ABA) is released.[6] ABA binds to receptor proteins in the guard cells' plasma membrane and cytosol, which first raises the pH of the cytosol of the cells and cause the concentration of free Ca2+ to increase in the cytosol due to influx from outside the cell and release of Ca2+ from internal stores such as the endoplasmic reticulum and vacuoles.[7] This causes the chloride (Cl-) and inorganic ions to exit the cells. Second, this stops the uptake of any further K+ into the cells and, subsequently, the loss of K+. The loss of these solutes causes an increase in water potential, which results in the diffusion of water back out of the cell by osmosis. This makes the cellplasmolysed, which results in the closing of the stomatal pores. hope this helps........ :)
 
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smoothieoeek

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Afza Munir said:
However, most plants do not have the aforementioned facility and must therefore open and close their stomata during the daytime in response to changing conditions, such as light intensity, humidity, and carbon dioxide concentration. It is not entirely certain how these responses work. However, the basic mechanism involves regulation of osmotic pressure.
When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity), a proton pump drives protons (H+) from the guard cells. This means that the cells' electrical potential becomes increasingly negative. The negative potential opens potassium voltage-gated channels and so an uptake of potassium ions (K+) occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. In some cases, chloride ions enter, while in other plants the organic ion malate is produced in guard cells. This increase in solute concentration lowers the water potential inside the cell, which results in the diffusion of water into the cell through osmosis. This increases the cell's volume and turgor pressure. Then, because of rings of cellulose microfibrils that prevent the width of the guard cells from swelling, and thus only allow the extra turgor pressure to elongate the guard cells, whose ends are held firmly in place by surrounding epidermal cells, the two guard cells lengthen by bowing apart from one another, creating an open pore through which gas can move.[5]
When the roots begin to sense a water shortage in the soil, abscisic acid (ABA) is released.[6] ABA binds to receptor proteins in the guard cells' plasma membrane and cytosol, which first raises the pH of the cytosol of the cells and cause the concentration of free Ca2+ to increase in the cytosol due to influx from outside the cell and release of Ca2+ from internal stores such as the endoplasmic reticulum and vacuoles.[7] This causes the chloride (Cl-) and inorganic ions to exit the cells. Second, this stops the uptake of any further K+ into the cells and, subsequently, the loss of K+. The loss of these solutes causes an increase in water potential, which results in the diffusion of water back out of the cell by osmosis. This makes the cellplasmolysed, which results in the closing of the stomatal pores. hope this helps........ :)
Click to expand...

It does! Thanks.
 
S

smoothieoeek

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Just a question. Are we allowed to write long words in simplified notations?
Eg. Proximal convoluted tubule as PCT?
 
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