Cellular Control Flashcards

Question

DRD4

Answer 1

Gene that codes for a dopamine receptor molecule

Answer 2

Chemical or biochemical reaction that releases energy

Answer 3

Specialised sex cells In many organisms the gametes are haploid and are produced by meio

Answer 4

Eukaryotic cell or organism having only one set of chromosomes. Denoted by n

Answer 5

The concept that both genotype frequencies and gene frequencies will stay constant from generation to generation, within a large interbreeding population where mating is random, there is no mutation and no selection or migration

Answer 6

The number of time that a normal body cell divides before undergoing apoptosis. The number of divisions is about 50

Answer 7

Cell or individual having only one allele for a particular gene

Answer 8

Eukaryotic cell or organism that has two different alleles for a specific gene

Answer 9

Genes that control the development of the body plan of an organism

Answer 10

These direct development of individual body segments. They are master genes that control other regulatory genes

Answer 11

Eukaryotic cell or organism that has two identical alleles for a specific gene

Answer 12

Groups of homeobox genes. More complex organisms have more Hox clusters. This is probably due to a mutation that duplicated the Hox clusters

Answer 13

Where two alleles interact to control the expression of one characteristic, one is epistatic and one is hypostatic. Where a recessive allele at the first locus prevents the expression of another allele at a second locus, the alleles at the first locus are epistatic and the alleles at the second locus are hypostatic

Answer 14

Reductive division. The chromosome number is halved. It involves two divisions. It produces cells that are genetically different from each other and from the parent cell

Answer 15

Characteristic coded for by one gene

Answer 16

A monophyletic group is one that includes an ancestral organism and all of its descendant species

Answer 17

Structural change to genetic material - either to a gene or a chromosome

Answer 18

Disorderly, often accidental cell death

Answer 19

A unit consisting of genes that work together under the control of an operator gene An example is the lac operon, which consists of two structural genes and an operator gene Operon a were first found in prokaryotes but were later found in eukaryotes

Answer 20

Group of organisms that share evolutionary ancestry

Answer 21

Characteristic coded for by many genes. Polygenic characteristics are more influenced by environmental factors than monogenic characteristics

Answer 22

Eukaryotic organisms or cells with more than two sets of chromosomes

Answer 23

Short, single stranded sequences of DNA, around 10 bases in length. They are needed, in sequences reaction and polymerase chain reactions, to bind to a section of DNA because the DNA polymerase enzymes cannot bind directly to single-stranded DNA fragments

Answer 24

Gene that can undergo mutations to become an oncogene, which induces tumour formation (cancer)

Answer 25

How common an allele is in a population

Answer 26

A measure the amount of variation of all the alleles in the population

Answer 27

Alleles within an individual

Answer 28

Change in allele frequency Can reduce genetic variation

Answer 29

Gradual change in antigen structure on a pathogen

Answer 30

Dramatic change in antigen structure Can lead to new strains - Pandemic

Answer 31

When humans choose the characteristic to breed for. Only allow the individuals closest to the intended outcome to breed. Repeat for a number of generations. Reduces genetic variation. Leads to inbreeding, which reduces fitness (survivability + reproductive success) for most species

Answer 32

- Discontinuous | - Continuous (Only ones where enough of the variation is genetic - heritability is high) rather than environmental

Answer 33

Competing selection - Selection pressures

Answer 34

Non-sex linked chromosome

Answer 35

Chromatin condenses and supercoils Homologous pairs forms a bivalent Crossing over occurs between non-sister chromatids Nuclear envelope disintegrates Nucleolus disappears A spindle forms

Answer 36

Bivalents line up across spindle equator They are attached by the centromere to the spindle fibres Bivalents are randomly assorted with each member of the homologous pair at opposite poles

Answer 37

Homologous chromosomes in bivalents are pulled by the spindle fibres to opposite poles Centromeres don’t divide Chiasmata separate and lengths of chromatid that have crossed over remain with the chromatid

Answer 38

Two new nuclear envelopes form around each set of chromosomes at each pole Cytokinesis occurs

Answer 39

Nuclear envelope reforms and breaks fown Nuceolus disappears Chromosomes condense Spindles form

Answer 40

Chromosomes move to the spindle equator They attach to the spindle fibres by their centromeres Chromatids of each chromosomes are randomly assorted

Answer 41

Centromeres divide and the chromatids are pulled to opposite poles by the spindle fibres The chromatids randomly segregate

Answer 42

Nuclear envelopes reform around the haploid nuclei The two cells then divide into four haploid cells in animals In plants a tetrad of four haploid cells is formed

Answer 43

There is no significant difference between the observed and the expected result

Answer 44

Adenine, Thymine, Guanine, and Cytosine

Answer 45

Adenine, Uracil, Cytosine, and Guanine

Answer 46

Adenine — Thymine Cytosine — Guanine

Answer 47

The order of bases in a gene

Answer 48

The nucleus

Answer 49

mRNA carries the genetic code from the DNA in the nucleus to the cytoplasm, where it is used to make a protein during translation

Answer 50

tRNA carries the amino acids that are used to make proteins to the ribosomes during translation

Answer 51

Transcription and translation

Answer 52

The nucleus

Answer 53

At the ribosomes in the cytoplasm

Answer 54

When it reaches a stop codon

Answer 55

If the four nucleotide bases were arranged in pairs, the maximum number of different combinations would be 4^2, which is 16. This is not enough to code for the 20 amino acids involved in protein synthesis, plus some stop codes

Answer 56

Each amino acid has more than one triplet base code. | This helps reduce the effect of point mutations

Answer 57

Prokaryotes, as the mRNA does not have to exit a nucleus and the DNA in prokaryotes is naked - there are no histone proteins

Answer 58

21 - one for each of the 20 amino acids and a stop

Answer 59

A change in the amount of, or arrangement of, the genetic material in a cell

Answer 60

All amino acids, except methionine, have more than one triplet of bases coding for them.some have as many as six. So some point mutations will not change the amino acid that is added to the polypeptide at that position

Answer 61

It contains large amounts of vitamin A. Retinoic acid is a derivative of vitamin A and too much retanoic acid, particularly in the early stages of pregnancy when the body plan is being organised, can interfere with the normal expression of homeobox genes and causes birth defects.

Answer 62

A morphagen is a substance that governs the pattern of tissue development by activating homeobox genes

Answer 63

Transcription factors are some of the polypeptides expressed by homeobox genes, which bind to other genes further along the DNA from the homeobox genes, and switch them on. They regulate the expression of other genes and so influence the development of the embryo

Answer 64

They determine the embryo's polarity - which end is the head and which is the tail

Answer 65

They specify the polarity of each body segment

Answer 66

If the proton gradient cannot be built up across the inner membrane then there will be less chemiosmosis and less formation of ATP. The cell will not be able to carry out active transport or bulk transport and cannot maintain its metabolism - particularly anabolic reactions such as protein synthesis

Answer 67

Because the hydrolytic enzymes are enclosed in vesicles and these are ingested by phagocytes

Answer 68

Ineffective lymphocytes would have no receptors on their cell surface membranes and could not recognise antigens

Answer 69

Harmful T lymphocytes would have receptor on their cell surface membranes, with shapes complementary to self antigens, causing autoimmunity - the immune system attacking your own tissues

Answer 70

A homologous pair of chromosomes, each consisting of two sister chromatids, paired up for meiosis

Answer 71

Because gamete production by meiosis and fertilisation increases diversity. During meiosis there is crossing over, Independant assortment of chromosomes and chromatids. Fertilisation combines genetic material from two unrelated organisms

Answer 72

12:3:1 or 13:3

Answer 73

Size of population Randomness of mating Mutation Competition Selection

Answer 74

Because both alleles contribute to the phenotype, the genotype of all frequencies of all phenotypes are known

Answer 75

Predators Diseases/Pathogens Food availability Mate availability

Answer 76

Temperature Water availability Soil type Habitat availability Shelter

Answer 77

The characteristics selected as useful for humans may make the animal less adapted to its natural environment

Answer 78

If there is a genetic defect in the family's gene pool, the chances of two individuals, both carriers, mating and producing an affected individual are increased

Answer 79

If one person in the original small group of settlers carried a recessive allele, it could be passed on to his offspring and grandchildren. Cousins may marry so two carriers may mate. The frequency of this allele will increase within the population. This is know as the founder affect

Answer 80

Because bacteria do not reproduce sexually, the biological concept is not appropriate. Their biochemistry, morphology, ecological niche, can all be studied and analysed

Answer 81

It focuses on evolution, rather than on similarities between species It places great importance on using objective and quantitative analysis It uses DNA and RNA sequencing It uses computer programmes and the data obtained from nucleic acid sequencing to generate cladograms that represent the evolutionary tree of life It makes no distinction between extinct and extant species and both may be included in cladograms

Answer 82

The phylogenetic (cladistic) system, as we can't deduce anything about their sexual reproduction and ability to produce fertile offspring, but we can deduce information about morphology, genes, and ecological niche

Answer 83

The sequence of the bases on a gene is a code with instructions for the construction of proteins. It has a number of characteristics: It is a triplet code- three bases code of an amino acid It is a degenerate code- All amino acids bar one have more than one code Some codes don’t code for amino acids but are ‘stop’ codons- they indicate the end of the polypeptide chain It is widespread but not universal- Codons generally always code for the same amino acid in every organism, but this is not always the case.

Answer 84

1. Free RNA nucleotides are activated, two extra phosphoryl groups are added to make ATP, GTP, CTP and UTP. 2. The gene to be transcribed unwinds and unzips. To do this the length of DNA that makes up the gene dips into the nucleolus & the hydrogen bonds between the nucleotide bases break. 3. Activated RNA nucleotides binds, using Hydrogen Bonds, with their complementary exposed bases on the template strand. This is catalysed by RNA polymerase 4. The two extra phosphoryl are released, releasing energy for bonding two adjacent nucleotides The mRNA produced is complementary to the nucleotide base sequence on the template strand of DNA and therefore is a copy of the base sequence on the coding strand of DNA 5. The mRNA is released from the DNA and passes out of the nucleus through a pore in the nuclear envelope to a ribosome

Answer 85

1. A molecule of mRNA binds to a ribosome. Two codons are attached to the small subunit of the ribosome and exposed to the large subunit. The first exposed mRNA codon is always AUG. Using ATP energy and an enzyme, a tRNA molecule with the amino acid methionine and the anticodon UAC forms hydrogen bonds with this codon 2. A seconds tRNA molecule, bearing a different amino acid, binds to the second exposed condon with its complementary anticodon 3. A peptide bonds forms between the two adjacent amino acids. This is catalysed by an enzyme in the small ribosomal sub unit 4. The ribosome now moves along the mRNA reading the next codon. A third tRNA brings another amino acid and a peptide bonds forms between it and the dipeptide. The first tRNA leaves and is able to collect and bring another of its amino acids. 5. The polypeptide chain grows until a stop codon is reached, for which there are no corresponding tRNAs and the polypeptide chain is complete

Answer 86

The sequence of nucleotides in DNA molecules

Answer 87

Beneficial The mutation changes the sequence of amino acids and therefore the phenotype, but this gives the organism an advantageous characteristic E.g. Paler skin in more temperate climates absorbs more vitamin D Neutral It is a mutation in a non-coding region of the DNA It is a silent mutation- although the base triplet has changed, it still codes for the same amino acid and so the protein is unchanged. Harmful The mutation changes the sequence of amino acids and therefore the phenotype, and the resulting characteristic is harmful E.g. paler skin in a hotter climate burns more easily

Answer 88

Altering their three-dimensional structure

Answer 89

1. The regulator gene is expressed and the repressor protein is synthesised. It has two binding sites. One binds to lactose and one that binds to the operator region 2. In binding to the operator region, it covers part of the promoter region where RNA polymerase normally attaches 3. RNA polymerase cannot bind to the promoter region so the structural genes cannot be transcribed into mRNA 4. Without mRNA the genes cannot be translated and the enzymes cannot be synthesised

Answer 90

1. Lactose binds to the other site on the repressor protein, causing the molecule to change shape. This prevents the other binding site from binding to the operator region. The repressor dissociates from the operator region 2. The leaves the promoter region unblocked. RNA polymerase can now bind to it and initiate the transcription of mRNA. 3. The operator- repressor- inducer system acts as a molecular switch. It allows synthesis of the structural genes 4. As a result, the bacteria can now use the lactose permease enzyme to take up lactose from the medium into their cells. They can then convert it to glucose and galactose using the β-galactosidase enzyme. These sugars can then be used for respiration

Answer 91

E. coli grown in a culture medium with no lactose can be placed in a growth medium with lactose. At first they cannot metabolise the lactose because they only have tiny amounts of the enzymes needed to catalyse the reaction. A few minutes after the lactose is added, E. coli increases the rate of synthesis of these enzymes by about 1000 times, so lactose must trigger the production of them - it is the inducer.

Answer 92

Homeotic genes are similar in plants, animals and fungi. These genes control the development of body plans and are expressed in specific patterns and in particular stages of development depending on when they are activated. The homeobox is a sequence of DNA that codes for a region of 60 amino acids, and the resulting protein is found in most, if not all, eukaryotes. The region binds to DNA so that they can regulate transcription. In animals the homeobox is common in genes concerned with the control of developmental events, such as segmentation, the establishment of the anterior-posterior axis and the activation of genes coding for body parts such as limbs

Answer 93

Apoptosis is an integral part of plant and animal tissue development. It is a series of biochemical events that leads to an orderly and tidy cell death, in contrast to cell necrosis, which leads to the release of harmful hydrolytic enzymes. Apoptosis ensures that the rate of cells produced by mitosis is the same as the rate of cells dying, so the number of cells remains constant. Not enough apoptosis leads to cancer. Apoptosis causes the digits (toes and fingers) to separate from each other during development. 1. Enzymes break down the cell cytoskeleton 2. The cytoplasm becomes dense with organelles tightly packed 3. The cell surface membrane changes and blebs form 4. The Chromatin condenses and the nuclear envelope breaks. DNA breaks into fragments 5. The cell breaks down into vesicles that are taken up by phagocytosis. The cellular debris is disposed of so that it does not damage other cells or tissue.

Answer 94

1. The chromatin condenses and supercoils 2. The chromosomes come together in their homologous pairs to form a bivalent. Each member of the pair has the same genes at the same loci. Each pair consists of one maternal and one paternal chromosome 3. The non sister chromatids wrap around each other and attach at points called chiasmata 4. They may cross over and swap sections of chromatids with each other 5. The nucleolus disappears and the nuclear envelope breaks down 6. A spindle forms

Answer 95

1. Bivalents line up across the equator of the spindle, attached to spindle fibres at the centromeres 2. The bivalents are arranged randomly (random assortment) with each member of the homologous pair facing opposite poles

Answer 96

1. The homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles 2. The centromeres do not divide 3. The chiasmata separate and the lengths of chromatid that have been crossed over remain with the chromatid to which they have become newly attached

Answer 97

Telophase I 1. In most animal cells two new nuclear envelopes form- one around each set of chromosomes at each pole and the cell divides by cytokenesis. There is a brief interphase and the chromosomes uncoil 2. In most plant cells the cell goes straight from Anaphase I to Meiosis II

Answer 98

This occurs at right angles to Meiosis I Prophase II 1. If a nuclear envelope has reformed, it breaks down again 2. The nucleolus disappears, chromosomes condense and spindles form Metaphase II 1.The chromosomes arrange themselves on the equator of the spindle. They are attached to spindle fibres at the centromeres 2. The chromatids of each chromosome are randomly assorted Anaphase II 1. The centromeres divide and the chromatids are pulled to opposite poles by the spindle fibres. The chromatids randomly segregate Telophase II 1. Nuclear envelopes reform around the haploid daughter nuclei 2. In animals, the two cells now divide to give four daughter cells 3. In plants, a tetrad of four haploid cells if formed

Answer 99

Meiosis: Crossing over ‘shuffles’ alleles Random distribution and subsequent segregation of maternal and paternal chromosomes in the homologous pairs during meiosis I leads to genetic reassortment Random distribution and segregation of the chromatids at meiosis II leads to genetic reassortment Random mutations Fertilisation Randomly combining two sets of chromosomes, one from each of two genetically unrelated individuals

Answer 100

Epistasis is the interaction of different gene loci so that one gene locus makes or suppresses the expression of another gene locus. Recessive Epistasis The homozygous presence of a recessive allele prevents the expression of another allele at a second locus E.g. flower colour in Salvia: The alleles for purple (B) and pink (b) can only be expressed in the presence of the allele A. When the genotype is aa-- the phenotype is white Dominant Epistasis A dominant allele at one gene locus masks the expression of alleles at the second gene locus E.g. feather colour in poultry: If the dominant allele A is present, the chickens will be white; even if the dominant allele of the second gene, B/b is present. The genotype must be aaB- for any colour to be expressed

Answer 101

Discontinuous variation describes qualitative differences between phenotypes - they fall into clearly distinguishable categories with no intermediates. E.g. blood type is either A, B, AB or O Continuous variation is quantitative differences between phenotypes - there is a wide range of variation within the population with no distinct catagories E.g. height

Answer 102

Discontinuous variation Different alleles at a single gene locus have large effects on the phenotype. Different gene loci have different effects on the trait Continuous variation Different alleles at the same gene locus have small effects Different gene loci have the same, often additive effect on the trait A large number of gene loci may have a combined effect on the trait

Answer 103

While an organism may have the genetic potential to achieve a certain characteristic, e.g. length of corn cob, the environment also has an influence. The corn cob may have the genetic potential to be 12cm long, but the plant may be short of water, light or certain minerals, meaning that the cob is shorter, as the environmental factors have limited the expression of the genes.

Answer 104

So that when the environment changes, there will be individuals that are better adapted, so they will survive and reproduce passing on the advantageous alleles to their offspring and allowing the species to continue

Answer 105

In unchanging conditions, stabilising selection maintains existing adaptations and so maintains existing allele frequencies. In changing conditions, directional selection alters allele frequencies. A mutation may be disadvantageous in existing conditions, and so is removed in stabilising selection, but if the conditions change, the mutation might be advantageous and selected for, meaning that selection becomes an evolutionary force

Answer 106

Genetic drift is a change in allele frequency that occurs by chance because only some of the organisms in each generation reproduce. It is particularly noticeable when a small number of individuals are separated from the rest of the large population. They form a small sample of the original population and so are unlikely to be representative of the large population’s gene pool. Genetic drift will alter the allele frequency still further.

Answer 107

If two sub-populations are separated from each other, they will evolve differently as they have different selection pressures, so different alleles will be eliminated or increased within each sub population. Eventually the sub populations will not be able to interbreed and so will be different species. The sub populations may be split by various isolating mechanisms Geographical barriers e.g. rivers or mountains Seasonal barriers e.g. climate change throughout the year Reproductive mechanisms e.g. their genitals, breeding seasons or courtship rituals may be different

Answer 108

The biological species concept A species is ‘a group of similar organisms that can interbreed and produce fertile offspring and it reproductively isolated from such other groups’ But Not all organisms reproduce sexually Members of the same species can look very different to each other Males can look different to females Isolated populations may appear to be very different from each other The phylogenetic species concept A species is ‘a group of organisms that have similar morphology, physiology, embryology and behaviour, and occupy the same ecological niche’. This classification shows the evolutionary relationships, or phylogeny. The phylogenetic linage is called a clade

Answer 109

Natural selection The organisms best adapted for their environment are more likely to survive and pass on the favourable characteristics to their offspring Artificial selection Humans select the organisms with the useful characteristics Humans allow those with useful characteristics to breed and prevent the ones without the characteristics from breeding Thus, humans have a significant impact on the evolution of these populations or species

Answer 110

Each cow’s milk yield is measured and recorded The progeny of bulls is tested to find out which bulls have produced daughters with high milk yields Only a few good-quality bulls need to be kept are the semen from one bull can be used to artificially inseminate many cows Some elite cows are given hormones so they produce many eggs The eggs are fertilized in vitro and the embryos are implanted into surrogate mothers These embryos could also be clones and divided into many more identical embryos

Answer 111

Wheat can undergo polyplody- the nuclei can contain more than one diploid set of chromosomes. Modern bread wheat is hexaploid, having 42 chromosomes in the nucleus of each cell, meaning that the cells are bigger.

Answer 112

Reproductive cloning is the production of offspring which are genetically identical to either the mother (nuclear transfer), or the other offspring (splitting embryos) Non-reproductive cloning is the use of stem cells in order to generate replacement cells, tissues or organs which may be used to treat particular diseases or conditions of humans

Answer 113

The English Elm is adapted to reproduce asexually following damage to the parent plant. New growth in the form of basal sprouts appears within two months of the destruction of the main trunk These suckers grow from meristem tissue in the trunk close to the ground where the least damage is likely to have occured

Answer 114

A small piece of tissue is taken from the plant to be cloned, usually from the shoot tip- this is called the explant The explant is placed on a nutrient growth medium Cells in the tissue divide but do not differentiate. Instead they form a mass of undifferentiated cells called a callus After a few weeks, single callus cells can be removed from the mass and placed on a growing medium containing plant hormones that encourage shoot growth After a further few weeks, the growing shoots are transferred onto a different growing medium that encourages root growth The growing plants are then transferred to a greenhouse to be acclimatised and grown further before they are planted outside

Answer 115

Advantages Very many genetically identical plants can be produced from one original plant Plants can be produced at any time of the year and air-freighted around the world Callus can be genetically engineered Disadvantages Because all of the plants are genetically identical, they are all susceptible to a newly mutated pathogen or pest, or to changing environmental conditions The process is labour intensive- it is more difficult to plant plantlets than to sow seed

Answer 116

Nuclear transfer A nucleus from an adult differentiated cell is placed in an enucleated egg cell. The egg then goes through the stages of development using the genetic information from the inserted nucleus Splitting embryos Cells from a developing embryo are separated out, with each one going on to produce a separate, genetically identical organism

Answer 117

Advantages High value animals, e.g. cows giving a high milk yield, can be cloned in high numbers Rare animals can be cloned to preserve the species Genetically modified animals- e.g. sheep that produce pharmaceutical chemicals in their milk- can be quickly reproduced Disadvantages High value animals are not necessarily produced with animal welfare in mind. Some strains of meat producing chickens jave been developed that are unable to walk As with plants, excessive genetic uniformity in a species makes it unlikely to be able to cope with, or adapt to, changes in the environment It is still unclear whether animals cloned using the nuclear material of adult cells will remain healthy in the long term

Answer 118

Grow rapidly in favourable conditions, with a generation time of as little as 30 minutes Often produce proteins or chemicals that are given out into the surrounding medium and can be harvested Can be genetically engineered to produce specific products Grow well are relatively low temperatures, much lower than those required in the chemical engineering of similar processes Can be grown anywhere in the world and are not dependent on climate Tend to generate products that are in a more pure form than those generated via chemical processes Can often be grown using nutrient materials that would otherwise be useless or even toxic to humans

Answer 119

Adsorption Enzyme molecules are mixed with the immobilising support and bind to it due to a combination of hydrophobic interactions and ionic links. Covalent bonding Enzyme molecules are covalently bonded to a support, often by covalently linking enzymes together and to an insoluble material using a cross-linking agent Entrapment Enzymes are trapped, for example in a gel bead or network of cellulose fibres. Substrate and product molecules can pass through the material to the enzyme, but the enzyme cannot pass through to the solution Membrane separation Enzymes are physically separated from the substrate mixture by a partially permeable membrane. The substrate and product molecules can pass through the membrane, but the enzymes cannot

Answer 120

Enzymes can be recovered easily and used many times The product is not contaminated by the enzyme Protection by the immobilising material means the enzyme is more stable in changing temperatures or pH Enzyme activity can be controlled more easily

Answer 121

Batch Culture Growth rate is slower because nutrient level declines with time Easy to set up and maintain If contamination occurs, only one batch is lost Less efficient- fermenter is not in operation all of the time Very useful for processes involving the production of secondary metabolites Continuous Culture Growth rate is higher as nutrients are continuously added to the fermentation tank Set up is more difficult, maintenance of required growing conditions can be difficult to achieve If contamination occurs, huge volumes of product may be lost More efficient- fermenter operates continuously Very useful for processes involving the production of primary metabolites

Answer 122

Primary metabolites are substances produced by an organism as part of its normal growth. The production of primary metabolites matches the growth in population of the organism Secondary metabolites are substances produced by an organism that are not part of its normal growth. The production of secondary metabolites usually begins after the main growth period of the organism and so does not match the growth in population of the organism

Answer 123

The growing conditions can be manipulated and controlled in order to ensure that the microorganism is growing in its optimum conditions, and so the yield can be maximised Temperature Too hot and enzymes will be denatured, too cold and growth will be slowed Type and addition of nutrient This depends on whether the product is a primary or a secondary metabolite Oxygen concentration Most organisms are grown under aerobic conditions so there must be a sufficient supply of oxygen to prevent the unwanted products of anaerobic respiration and a reduction in growth rate pH Changes in pH can reduce the activity of enzymes and therefore reduce growth rates

Answer 124

Asepsis is the absence of unwanted microorganisms which could: Compete with the culture microorganisms for nutrients and space Reduce the yield of useful products from the culture. microorganisms Cause spoilage of the product Produce toxic chemicals Destroy the culture microorganisms and their products

Answer 125

Genomes are mapped to identify which part of the genome that they come from. Information that is already known is used, such as the location of microsatellites Samples of the genome are mechanically sheared into smaller sections of around 100,000 base pairs These sections are places in separate Bacterial Artificial Chromosomes (BACs) and transferred to E. coli cells. As the cells are grown in culture, many copies of the sections are produced- referred to as Clone Libraries Cells containing specific BACs are taking and cultured. The DNA is extracted from the cells and restriction enzymes used to cut it into smaller fragments. The use of different restriction enzymes on a number of samples gives different fragment types The fragments are separated using electrophoresis The many copies of the fragments are put in a reaction mixture containing DNA polymerase, free DNA nucleotides and primers, with some of the nucleotides containing a florescent marker. The primer anneals to the 3’ end of the template strand, allowing DNA polymerase to attach DNA polymerase adds free nucleotides If a modified nucleotide is added, the polymerase enzyme is thrown off and the reaction stops on that template strand As the reaction proceeds, many molecules of DNA are made. The fragments generally differ in size, as different numbers of nucleotides will have been added As the strands run through a machine, a laser reads the colour sequence. The sequence of colours, and therefore the sequence of bases can then be displayed

Answer 126

The identification of genes for proteins found in all or many living organisms gives clues to the relative importance of such genes to life Comparing the DNA of different species shows evolutionary relationships Modelling the effects of changing DNA can be carried out Comparing genomes from pathogenic and similar but non-pathogenic organisms can be used to identify the genes or base-pair sequences that are more important in causing the disease, so more effective drugs can be developed The DNA of individuals can be analysed to reveal the presence of alleles associated with particular diseases

Answer 127

A section of DNA, often in the form of a plasmid, which is formed by joining DNA sections from two different sources

Answer 128

The required gene is obtained A copy of the gene is placed in a vector The vector carries the gene to the recipient cell The recipient expressed the gene through protein synthesis

Answer 129

A DNA probe can be used to locate the gene on DNA fragments and the gene can be cut from a DNA fragment using a restriction enzyme Restriction enzymes cut through DNA at specific points, only where a specific base sequence occurs, normally about 10 base pairs long. The enzyme catalyses a hydrolysis reaction which breaks the sugar phosphate backbone of the DNA at different places. The gives a staggered cut which leaving some exposed bases called sticky ends

Answer 130

DNA samples are treated with restriction enzymes to cut them into fragments The DNA samples are placed into cells cut into the negative electrode end of the gel The gel is immersed in a tank of buffer solution and an electric current is passed through the solution for a fixed period of time, usually around two hours DNA is negatively charged because of its phosphoryl groups. It is attracted to the positive electrode. Shorter lengths of DNA move faster than longer lengths, so move further in the fixed time that current is passed through the gel The position of the fragments can be shown by using a dye that stains DNA molecules

Answer 131

A DNA probe is a short single-stranded section of DNA that is complementary to the section of DNA being investigated. The probe is labelled in one of two ways: Using a radioactive marker so that the location can be revealed by exposure to photographic film Using a fluorescent marker that emits a colour on exposure to UV light Copies of the probe are added to a sample of DNA fragments and will anneal to any fragment where a complementary base strand is present

Answer 132

The DNA sample is mixed with a supply of DNA nucleotides and DNA polymerase The mixture is heated to 95°C. This breaks the hydrogen bonds holding the strands together, so the samples are now single stranded Primers (short lengths of single stranded DNA) are added The temperature is reduced to 55°C to allow the primers to bind and form small sections of doubl stranded sections DNA polymerase can bind to these double-stranded sections The temperature is raised to 72°C. The enzyme extends the double stranded section by adding nucleotides to the unwound DNA When the DNA polymerase reaches the other end of the DNA, a new, double stranded DNA molecule is generated The whole process can be repeated many times so the amount of DNA increase exponentially

Answer 133

The plasmids and the fragments are both cut with the same restriction enzyme so they have complementary sticky ends The base pairs anneal and DNA ligase joins together the phosphate sugar backbones to form recombinant DNA

Answer 134

Liposomes Viral DNA e.g. bacteriophages Hybrid vectors with the propertied of both plasmids and bacteriophages

Answer 135

Large quantities of the plasmid are mixed with bacterial cells Calcium salts are added, and the temperature of the culture is lowered to freezing before the being quickly raised to 40°C. This increases the rate at which plasmids are taken up by bacterial cells to around 0.25%

Answer 136

Genetic variation | In the case of antibiotic resistance genes, survival in the presence of these chemicals

Answer 137

Not all bacteria take up the plasmid. Some of the bacteria take up a plasmid that has not seals with a copy of the gene, but just sealed up on itself to reform the original plasmid A plasmid is used which carries genes which make any bacteria receiving them resistance to two different antibiotics. The resistance genes are known as genetic markers The plasmids are cut by an enzyme which has its resistance site in the middle of one of the resistance genes (G1), so that if the required gene is taken up, the resistance gene for one of the antibiotics does not work, but it other (G2) does The DNA is placed in the plasmids, and the plasmids in bacteria cells The bacteria are grown on an agar plate to produce a colony Some cells from the colonies are transferred onto agar that has been made from the antibiotic that remains intact, meaning that all bacteria that have taken up a plasmid will grow. Some cells are transferred onto agar that has been made from the second antibiotic. Only the bacteria which have taken up a plasmid that is not recombinant will grow. By keeping track of which colonies are which, we now know that any bacteria which grow on the agar containing the first antibiotic, but not on the agar containing the second antibiotic must have taken up the recombinant plasmid The required colonies can now be identified and be grown on a large scale

Answer 138

1. mRNA from human insulin is extracted from pancreas cells 2. Reverse transcriptase uses mRNA as a template to make single stranded cDNA, and this is made double stranded by DNA polymerase 3. A single sequence of nucleotides (GGG) is added to each end of the DNA to make sticky ends 4. Plasmids are cut open when a restriction enzyme 5. Cut plasmids have a single sequence of nucleotides (CCC) asses to each to make sticky ends 6. Plasmids and the insulin gene are mixed so that sticky ends form base pairs 7. DNA ligase links sugar-phosphate backbones of plasmid and insulin gene 8. Plasmids are mixed with bacteria in the presence of calcium ion 9. Bacteria take up plasmids and multiply to form a clone 10. Genetically engineered bacteria transcribe and translate the human gene to make insulin

Answer 139

Two genes from the Daffodil and one from the bacterium Erwina urefovora were inserted into TI plasmids and taken up by the bacterium Agrobacterium tumefaciens. This introduced the genes into rice embryos The resulting rice plants produced seeds with β-carotene in the endosperm, which is yellow. Vitamin A is produced in our bodies from β-carotene

Answer 140

Pigs have been engineered to lack the enzyme α-1,3-transferase, which is a key trigger for rejection of organs in humans The human nucleotidase enzyme has been grafted into pig cells in culture. It reduces the number of immune cell activities involved in xenotransplant rejection

Answer 141

Any therapeutic technique where the functioning allele of a particular gene is placed in the cells of an individual lacking the functioning alleles of that particular gene. Can be used to treat some recessive conditions, but not dominant conditions

Answer 142

Somatic cell gene therapy The functioning allele of the gene is introduced into target cells - ∴ techniques are needed to get the gene to the target location, or the specific cells must be removed, treated and then replaced Introduction into somatic cells means that any treatment is short-lived and has to be repeated regularly. The specialised cells containing the gene will not divide to pass on the allele There are difficulties in getting the allele into the genome in a functioning state. Genetically modified viruses have been tried, but the host becomes immune to them so cells will not accept the vector on second and subsequent treatments. Liposomes are used but these may be inefficient Genetic manipulations are restricted to the actual patient Germline cell gene therapy The functioning allele of the gene is introduced into germline cells- delivery techniques are more straightforward Introduction into germline cells means that all cells derived from the germline cells will contain a copy of the functioning allele. The offspring may also contain the allele Although more straightforward, it is considered unethical to engineer human embryos. It is not possible to know whether the allele has been successfully introduced without any unintentional changes to it which may damage the embryo Genetic manipulations could be passed on to the patient’s children

Answer 143

Religious objections Objections to tampering with an organism’s natural genotype Fears of unforeseen effects of the gene Fears of the consequences of escape into the wild Growing GM plants might damage the environment Eating GM plants might be bad for health