5 1 1 Cellular Control

8/12/2019 5 1 1 Cellular Control

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In the table, normal digestive functioning of the pancreas associated with a particular

allele is indicated with a tick ( ) and the absence of normal functioning by a cross ( ).

!"T# allele percentage of !l

transported incomparison with normal allele

normal digestive functioning inpancreas

normal **

mutation +

mutation '

mutation - *

mutation -

mutation 5

mutation + --

mutation

mutation / +

mutation 0 -

mutation *

1ith reference to the information given in the table, e&plain why some mutant !"T#alleles allow normal digestive functioning of the pancreas and others do not.

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4. $ product manufactured using microorganisms is single cell protein (2!3).

4escribe how a protein would be synthesised in the cell of a single celled fungus.

In your answer, you should make clear the sequence of the steps in the process.

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5. 46$ is found in the nucleus of a cell.

4uring interphase 46$ replicates.

46$ is involved in the transcription stage of protein synthesis.

The following statements, Ato H, refer to events that may take place during7

46$ replication only

transcription only

both46$ replication andtranscription

neither46$ replication nortranscription.

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!omplete the table by marking the appropriate bo&es with a tick ( ) if the event takesplace or a cross ( ) if it does not take place.

46$ replication transcription

A6ucleotides line up along an e&posed46$ strand.

B The whole of the double heli& 8un9ips:.

C ;racil pairs with adenine.

D$ t#6$ triplet pairs with an e&posed

codon.

Ephosphate backbone.

GThe original 46$ molecule isunchanged after the process.

H $denine pairs with thymine.

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6. (a) 3art of the DNAbase se?uence coding for a protein is shown below.

A T G G C C T A A G T G

(i) 2tate the corresponding base se?uence of mNA.

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(ii) 6ame the process by which the 46$ code is transferred to m#6$.

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(b) The figure below is a diagram that shows the stage in protein synthesis whenamino acids are =oined in the correct se?uence to make the primary structure ofthe protein.

!"

#

$

a m i n o a c i d

(i) 6ame "to $.

The group of bases at " ........................................................................

! ............................................................................................................

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# .............................................................................................................

The group of bases at $ ........................................................................

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(ii) ;sing the information in the diagram to help you, e&plain how amino acidsbecome arranged into the correct se?uence in the primary structure of theprotein.

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(c) @istletoe is a parasitic plant that produces lectin , a ribosome>inactivatingprotein. Aectin inhibits protein synthesis in the cells of the host plant.

2uggest how lectin could inhibit protein synthesis.

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Macmillan Academy !


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%. Aiver cells damaged by hepatitis infection switch on a gene called "as, which causesthem to self>destruct. 3ioneering research has produced a strikingly successfultreatment for hepatitis in mice. The "as gene was silenced by the techni?ue of #6$interference.

#6$ molecules, ' to '- nucleotides long, were in=ected into mice with hepatitis. These?uence of this 8small interfering #6$: (si#6$) matched part of the "as gene. Bnce inthe liver cell the two strands of the si#6$ were separated so that one strand could bindto the m#6$ transcript of the "as gene. This caused the m#6$ to be destroyed byen9ymes, therefore preventing the gene product from being made.

This therapy prevented liver cell death and considerably increased the survival of micewith hepatitis.

(a) (i) 4escribe a way in which the &'n(tionof m#6$ differs from that of 46$.

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(ii) 4escribet)oways in which the *tr'(t'reof si#6$ differs from m#6$.

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(b) 4escribe how one strand of the si#6$ can bind to the m#6$ of the "as gene.

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+. The techni?ue of #6$ interference has been used to slow replication of CID (CumanImmunodeficiency Dirus) in #itro. si#6$ se?uences that match the #6$ genome of CIDcan be used to trigger destruction of this #6$, preventing CID from multiplying.

$nother approach is to use #6$ interference to silence genes for cell surface

receptors, such as the !4 and !!#5 molecules on human white blood cells. If thesegenes do not produce their protein antigens, CID cannot bind to and infect the whiteblood cells.

The table below summarises some information about the two cell surface receptorsused by CID to bind to and infect white blood cells.

cell surface receptor

!4 !!#5

type of cell with this

receptor

T lymphocyte white blood

cells which divide bymitosis

macrophage cells which

are long>lived and do notundergo mitosis

function of receptor important roles in theimmune system

limited, since E of peoplelack this receptor and showsome resistance to CID

%&periments have been carried out where,

si#6$s matching the !4 m#6$ were introduced into test tube populations of

T lymphocytesF

si#6$s matching the !!#5 m#6$ were introduced into test tube populations ofmacrophages.

In both cases CID was present but the presence of the si#6$s reduced its replication.

(i) ;se the table to suggest with reasons which of the two test tube e&perimentsshowed most reduction of CID replication.

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(ii) %&plain which receptor would be the best target for #6$ interference if theapproach was used as a therapy for humans infected with CID.

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,. $ research team was investigating the properties of a newly>discovered en9yme, theproduct of which was a valuable drug.

This en9yme had been e&tracted from cells of a marine worm, found in the 6orth$tlantic, where the temperature is always close to 5 G!. $ll the proteins of such animalsare adapted to function at low temperatures.

Three water baths were set up at 5, '* and '5 G!. Into each bath was placed a tube

containing cm-of the en9yme solution and a tube containing * cm

-of concentrated

substrate solution. Bn reaching the re?uired temperature, the en9yme and substratewere ?uickly mi&ed and kept in the water bath.

There was a lar-e e(e** o& the *'b*trate, so that substrate concentration was notalimiting factor.

2amples were taken from each tube at regular intervals and the concentration of thedrug in these samples was determined. The results are shown in "ig. .

** ) ' -

t i m e a t w h i c h s a m p l e s r e m o v e d H h o u r s

c o n c e n t r a t i o n

o f d r u g H

a r b i t r a r y u n i t s) 5 G !

' * G !

' 5 G !

,

'

,

+

)

-

5

Fi-. 1

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(a) ;sing "ig. ,

(i) describe what happened to the concentration of the drug in the tube at5 G!F

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(ii) e&plain why the concentration of the drug changed in the way you havedescribed.

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(b) 2tate onefactor, not mentioned in the a((o'nt o& the in/e*ti-ation, whichwould have been kept constant in all the tubes for the results to be valid.

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(c) 3redict ande&plain the effect of carrying out the same procedure at 5 G!.

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"ig. ' represents part of the primary and tertiary structure of the newly>discovereden9yme, including its active site. The amino acids are represented by circles, which arenumbered to show their position in the primary structure.

5 -

5 ,

5 5

5 +

a m i n o a c i d s

h y d r o g e n b o n d

h y d r o g e n b o n d

s u b s t r a t e

m o l e c u l e

d i s u l p h i d e

b o n d5 .

5 /

5 0

+ *

+ )

+ '+ - + ,

+ 5+ +

+ .

+ /

+ 0. *. ). '. -

. ,

. 5

5 ' 5 )5 *

, 0

, /

, .

, +

, 5

, ,, -, '

, )

, *

- 0

- /

- .

- +

- 5

- ,

Fi-. 2

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(d) The research team wanted to change the structure of the en9yme so that it wouldfunction at higher temperatures to produce greater yields of the drug. They useda techni?ue called *ite dire(ted m'ta-ene*i*. In this techni?ue7

single changes to the amino acid se?uence of the en9yme are planned

the gene coding for the en9yme produced by the worm is isolated

specific changes to the gene are made, in order to achieve the plannedchanges to the amino acid se?uence

the modified gene is introduced into a bacterium

the offspring of the bacterium produce the changed en9yme molecules

(i) 2uggest why it would be important that this procedure did notchange any

of the amino acids shaded grey in "ig. '.

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(ii) The amino acids numbered and ++ have side chains that link byhydrogen bonding.

2uggest why the research team might plan to replace these two aminoacids with the amino acid cysteine, which forms disulphide bonds.

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(e) %&plain why the techni?ue of site directed mutagenesis involves changingnucleotide se?uences.

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10. (a) %&plain what is meant by herita'ility.

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(b) #ice plants may have, in addition to a main stem, a number of side shoots (tillers)growing from ground level. These tillers may also branch. The ability to growtillers is controlled by a single gene with two alleles, Tt.3lants with the genotypetthave a single grain>bearing stem and no tillers.

%&plain why the heritability of rice tiller growth is likely to be high.

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(c) $llele Tcodes for a protein which regulates transcription. %&pression of allele Tallows stimulation of mitosis in the buds which become tillers.

$llele thas a 8stop: triplet within its 46$ se?uence as well as at its end.

(i) 2tate what is meant by a 8stop: triplet.

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(ii) 4escribe the effect of the 8stop: triplet )ithinthe 46$ se?uence of allele t.

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(iii) 2uggest how the protein encoded by allele Tmay regulate transcription.

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(d) The number of tillers per plant and the number of times each tiller branched wererecorded for wild type TTplants and for ttplants which had been given a copy ofallele Tby genetic engineering.

The results are shown below.

**

) *

' *

- *

) ' - , 5

k e y 7 w i l d t y p e p l a n t sT T

g e n e t i c a l l y m o d i f i e d

t t I T p l a n t s

n u m b e r o f

t i l l e r s

p e r p l a n t

n u m b e r o f b r a n c h e s p e r t i l l e r

(i) 1ith reference to the figure above, compare the effect of the two ricegenotypes on tiller growth.

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(ii) 2uggest why the e&pression of allele Tmay be changed when it istransferred by genetic engineering into rice plants with the genotype tt.

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11. 1hen eaten by insects such as the larvae known as earworms, celery plants producethe chemical signal =asmonate ("). This stimulates insecticide production. Insecticidebegins to build up in the leaves after ' hours and reaches ma&imum concentrationafter to 5 days.

Cowever, earworms become resistant to this insecticide by switching on a gene in thegut lining that codes for an en9yme (E) to break it down.

6ewly hatched earworms were divided into four groups7

note&posed to "but fed on celery leaves containing insecticide note&posed to "but fed on celery leaves with noinsecticide

e&posed to " and fed on celery leaves containing insecticide e&posed to "and fed on celery leaves with noinsecticide.

The earworms continued to feed on these diets until they pupated.

The percentage mortality of the different groups of earworms and the relative

e&pression of the gene coding for en9yme Eare shown below. In the table, a tick ()indicates the presence of insecticide in the celery leaf diet and a cross ( ) indicates itsabsence.

group of earwormspresence of insecticide

in celery leaf dietrelative e&pression of gene

coding for en9yme E mortality H E

note&posed to ".* /+.

*.* 5.+

e&posed to " +.5 /.-

5.5 +.

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;sing the information given, e&plain the differences in percentage mortality of thedifferent groups of earworms.

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Macmillan Academy 1"


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12. #ead the passage below and answer the ?uestions which follow.

DNA /a((ine*

@ice and monkeys have been successfully immunised against several importantinfectious diseases using e&perimental 46$ vaccines, in the form of plasmids.3lasmids are small circular 46$ molecules.

4uring the 00*s, researchers found that mouse muscle and other mouse tissues wereable to absorb plasmids which had been in=ected into the animals. $ny genes that werepart of this plasmid 46$ were transcribed and translated. The resulting proteins weretransferred to the plasma membranes (cell surface membranes) of the mouse musclecells. The proteins were e&posed on the muscle plasma membranes together withreceptor molecules that allow the immune system to recognise cells as self or non>self.3roteins that are presented at the cell surface in this way stimulate the lymphocytes of

the immune system very effectively.

This discovery allows plasmid 46$ to be used as a vaccine, even though the 46$does not itself act as an antigen. @ost vaccines contain proteins, or fragments ofproteins, that are e&tracted from the surface of pathogens. It is a comple& and costlyprocedure to purify these protein antigens.

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The figure below shows a simplified diagram of a 46$ vaccine. This plasmid codes fortwo antigens, Aand B.

J

p r o m o t e r s e ? u e n c e

s e ? u e n c e c o d i n g f o r a n t i g e n A

s e ? u e n c e c o d i n g f o r a n t i g e n B

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(a) 2tate threeways in which the structure of plasmid 46$ differs from the structureof a protein molecule.

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(b) (i) 4efine the term anti(en, as used in the passage.

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(ii) 2uggest why proteins presented at the cell surface are able to stimulate animmune response more effectively than proteins dissolved or suspended inthe blood or tissue fluids.

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(c) (i) %&plain why a promoter se?uence is needed as part of the plasmid if thevaccine is to work.

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(ii) 2uggest why it may be desirable to include nucleotide se?uences codingfor more than one antigen in a 46$ vaccine.

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(iii) 2e?uences of nucleotides, labelled J on the figure, code for groups ofamino acids at the beginning of each polypeptide. These amino acidse?uences direct the newly synthesised polypeptides to the Jolgiapparatus of the muscle cell.

%&plain how this makes the vaccine effective.

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(d) 2uggest threereasons why researchers may be more concerned about thepotential risks of 46$ vaccines as compared with protein>based vaccines.

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13. (a) !ats with either black or white fur are common in producing alleles are present in thegenotype. The recessive allele, a, has no effect on fur colour.

Jenes AaandBbare not linked and neither is on the K chromosome.

(i) 2tate the fur colour of cats with the following genotypes7

AaBB ...................................................................................................

aaBB ....................................................................................................

Aabb .....................................................................................................

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(ii) 2tate the name given to this type of gene interaction.

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(iii) 2uggest how one gene may inhibit the action of another.

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(b) Two white cats produced a litter of kittens with three different coat colours7 white,black and brown.

(i) 2tate onepossible genotype for ea(hof the two white parents and e&plain

the reasons for your choice.

Lou may use the space below for rough work, if needed.

genotypes of parents ............................................................................

e&planation ............................................................................................

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(ii) 2tate the ratio of phenotypes this pair of cats would be e&pected to producein time, when the fur colour of several litters of kittens could be recorded.

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14. #esearch is taking place to see if chemicals can be added to toothpaste that block thee&pression of the genes responsible for the synthesis of the sticky gel and thereforestop pla?ue forming.

NA inter&eren(e is one method used to block the e&pression of genes.

This uses #6$ molecules that are complementary to the messenger #6$ of the gene.

(i) %&plain how #6$ interference affects the e&pression of a gene.

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(ii) ;nfortunately, adding complementary #6$ to toothpaste has not provedsuccessful in controlling pla?ue. 2uggest why.

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15. The bacterium Escherichia coli uses glucose as a respiratory substrate. In the absenceof glucose, E. coli can use lactose.

%&plain how lactose induces the en9yme system involved in its uptake and metabolism.

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16. @uscle fibres may become torn and damaged.

4amaged muscle fibres have an increased messenger #6$ (m#6$) concentrationand a higher rate of o&ygen consumption, at re*t, than undamaged muscle fibres.

%&plain these observations7

increased m)*A concentration+

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hi(her rate of oy(en consumption.

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1%. (a) #epeating nucleotide se?uences are common in the genomes of eukaryotes, fore&ample in the centromeres and in the regions, called introns, which appear tointerrupt the genes. #epeating se?uences have been referred to as 8=unk 46$:.

2uggest why the term 8=unk 46$: is misleading.

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(b) 2ome species of plant are able to grow on soils that contain very little phosphate,while other species, for e&ample stinging nettles, can only grow well in soils thatare rich in phosphate. %ach nucleotide in a 46$ molecule includes a phosphategroup.

If much of the non>coding 46$ can be correctly regarded as functionless 8=unk:,there may be a correlation between the percentage of 46$ that is non>codingand the minimum concentration of phosphate ions needed for healthy growth.

4raw a straight line graph, using the a&es in the figure below, to show thecorrelation that you would predict.

p e r c e n t a g eo f 4 6 $ t h a ti s n o n > c o d i n g

m i n i m u m c o n c e n t r a t i o n o f p h o s p h a t e i o n s n e e d e df o r h e a l t h y g r o w i n g

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(c) 6ame a substance other than DNA that is found in cells and has one or morephosphate groups as part of its chemical structure.

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1+. $n en9yme, such as amylase, has a specific ->dimensional shape.

%&plain how 46$ structure determines the specific shape of en9ymes.

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5 1 1 Cellular Control

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