UNIT 8: The control of gene expression

Fill in the blanks.
Gene mutations might arise during ___ _________.

Gene mutations might arise during DNA replication.

Name six types of gene mutations.

Six types of gene mutations include:

Addition of bases.
Deletion of bases.
Substitution of bases.
Inversion of bases.
Duplication of bases.
Translocation of bases.

Define the term inversion of bases.

Inversion of bases is when a sequence of bases is reversed.

Define the term translocation of bases.

Translocation of bases is when a sequence of bases is moved from one location in the genome to another.

Fill in the blank.
Gene mutations occur ____________.

Gene mutations occur spontaneously.

State how the mutation rate is increased.

The mutation rate is increased by mutagenic agents.

What can mutations result in?

Mutations can result in a different amino acid sequence in the encoded polypeptide.

A gene mutation changes only one triplet code.
Explain why this mutation may not result in a change to the encoded amino acid.

If a gene mutation changes only one triplet code, this mutation may not result in a change to the encoded amino acid, because the genetic code is degenerate.

Describe how some gene mutations can result in a frame shift.

Some gene mutations can result in a frame shift because the mutation changes the nature of all base triplets downstream from the mutation.

What can totipotent cells do?

Totipotent cells can divide and produce any type of body cell.

During development, describe the process that results in cell specialisation.

During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.

True or false.
Totipotent cells occur forever in early mammalian embryos.

False.
Totipotent cells occur only for a limited time in early mammalian embryos.

Where are pluripotent cells found?

Pluripotent cells are found in embryos.

Where are multipotent and unipotent cells found?

Multipotent and unipotent cells are found in mature mammals.

What can multipotent and unipotent cells do?

Multipotent and unipotent cells can divide to form a limited number of different cell types.

Fill in the blank.
Pluripotent stem cells can divide in ____ numbers.

choose from ‘limited’ and ‘unlimited’

Pluripotent stem cells can divide in unlimited numbers.

Which type of stem cells can be used in treating human disorders?

Pluripotent stem cells can be used in treating human disorders.

Give an example of a cell that is formed from a unipotent stem cell.

Cardiomyocytes are formed from unipotent stem cells.

What are iPS cells?

iPS cells are induced pluripotent stem cells.

State how induced pluripotent stem cells (iPS cells) can be produced.

Induced pluripotent stem cells (iPS cells) can be produced from adult somatic cells using appropriate protein transcription factors.

Give two advantages of the use of stem cells in treating human disorders.

One advantage of the use of stem cells in treating human disorders is that they can be used to grow organs for people needing transplants.
Another advantage is that they can replace damaged cells in the eyes of blind people, improving their quality of life.

Give an ethical issue of embryonic stem cell use.

One ethical issue of embryonic stem cell use is that it results in the destruction of an embryo, which cannot consent and has a right to a life.

How can transcription of target genes be stimulated or inhibited in eukaryotes?

In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcription factors move from the cytoplasm into the nucleus.

Describe the role of the steroid hormone, oestrogen, in initiating transcription.

The steroid hormone oestrogen binds to a transcription factor called an oestrogen receptor.
This forms an oestrogen-oestrogen receptor complex.

What happens to the oestrogen-oestrogen receptor complex after its formation?

The oestrogen-oestrogen receptor complex moves from the cytoplasm into the nucleus and binds to the promoter region of the target gene.

Define the term epigenetic control.

Epigenetic control is the control of gene expression in eukaryotes.

What does epigenetics involve?

Epigenetics involves heritable changes in gene function, without changing the base sequence of DNA.

State how epigenetics is caused.

Epigenetics is caused by changes in the environment that inhibit transcription.

Give two examples of changes in the environment that inhibit transcription.

Two examples of changes in the environment that inhibit transcription are an increased methylation of the DNA or a decreased acetylation of associated histones.

State why epigenetics is important.

Epigenetics is important in the development and treatment of disease, especially cancer.

Explain how epigenetics is important in the treatment of disease.

Epigenetics is important in the treatment of disease because these changes are reversible.
Drugs are designed to counteract these changes.

What does RNA interference (RNAi) do?

RNA interference (RNAi) inhibits the translation of the mRNA produced from target genes in eukaryotes and some prokaryotes.

Give the two types of RNAi.

The two types of RNAi are siRNA and miRNA.

What is a tumour?

A tumour is a mass of abnormal cells caused by uncontrolled cell division.

Give the main characteristics of benign tumours.

The main characteristics of benign tumours involve being covered in a fibrous tissue that stops cells from invading other tissues.
They grow slower than malignant tumours and are non-cancerous, but can put pressure on organs or cause blockages.

Give the main characteristics of malignant tumours.

The main characteristics of malignant tumours involve a rapid growth.
They invade and destroy surrounding tissues as cells can break off the tumours and spread to other parts of the body by the bloodstream or lymphatic system.

What is the role of a tumour suppressor gene?

A tumour suppressor gene slows cell division by producing proteins that stop cells from dividing or causing them to self-destruct, known as apoptosis.

What is the role of a proto-oncogene?

A proto-oncogene stimulates cell division by producing proteins.

Describe how abnormal methylation of tumour suppressor genes can lead to the development of tumours.

Abnormal methylation of tumour suppressor genes can lead to the development of tumours because these genes are not transcribed.
This results in uncontrollable cell division.

Describe how abnormal methylation of proto-oncogenes can lead to the development of tumours.

Abnormal methylation of proto-oncogenes can lead to the development of tumours because too little methylation causes them to act as oncogenes.
This increases the production of proteins that stimulate cell division, resulting in uncontrollable cell division.

State a factor that can contribute to the development of some breast cancers.

Increased oestrogen concentrations can contribute to the development of some breast cancers.

Describe how oestrogen can contribute to the development of some breast cancers.

Oestrogen can contribute to the development of some breast cancers because it stimulates certain breast cells to divide. This increases the chance of mutations, which can lead to cancerous cells forming. These cancerous cells will grow faster because of the oestrogen.

What have sequencing projects done?

Sequencing projects have read the genomes of a wide range of organisms, including humans.

What does determining the genome of simpler organisms allow?

Determining the genome of simpler organisms allows the sequences of the proteins that derive from the genetic code (the proteome) of the organism to be determined.

Give an application for determining the proteome of an organism.

One application for determining the proteome of an organism is the identification of potential antigens for use in vaccine production.

Explain why knowledge of the genome cannot easily be translated into the proteome in complex organisms.

In complex organisms, knowledge of the genome cannot easily be translated into the proteome because of the presence of non-coding DNA and of regulatory genes.

Fill in the blanks.
Sequencing methods are ____________ _______ and have become ________.

Sequencing methods are continuously updated and have become automated.

What does recombinant DNA technology involve?

Recombinant DNA technology involves the transfer of DNA fragments from one organism, or species, to another.

Suggest why the transferred DNA can be translated within cells of the recipient (transgenic) organism.

The transferred DNA can be translated within cells of the recipient (transgenic) organism because the genetic code, transcription mechanisms, and translation mechanisms are universal.

Give three methods used to produce fragments of DNA.

One method used to produce fragments of DNA is the conversion of mRNA to complementary DNA (cDNA), using reverse transcriptase.
Another method is using restriction enzymes to cut a fragment containing the desired gene from DNA.
A third method is creating the gene in a ‘gene machine’.

Suggest why mRNA is used to make a strand of cDNA instead of DNA.

mRNA is used to make a strand of cDNA instead of DNA because there are many mRNA molecules, as opposed to two DNA molecules.
This makes mRNA easier to obtain.

Describe the first step in the method using restriction enzymes.

In the first step in the method using restriction enzymes, the DNA sample is incubated with a specific restriction endonuclease.
The active site of the restriction endonuclease binds to the recognition sequence because the shapes are complementary.

Describe the second step in the method using restriction enzymes.

In the second step in the method using restriction enzymes, the restriction endonuclease hydrolyses the phosphodiester bonds between nucleotides.
The cut may leave sticky ends at each end of the fragment.

Describe the first step in the method using a ‘gene machine’.

In the first step in the method using a ‘gene machine’, a sequence of bases is designed.
Nucleotides are added step by step in the correct order in a cycle of processes that add protective groups. These ensure the nucleotides are joined at the correct points, preventing branching.

Describe the second step in the method using a ‘gene machine’.

In the second step in the method using a ‘gene machine’, short sections of DNA called oligonucleotides are produced.
These are combined to produce longer DNA fragments.

How can fragments of DNA be amplified?

Fragments of DNA can be amplified by in vitro and in vivo techniques.

Give an example of an in vitro method to amplify DNA fragments.

One example of an in vitro method to amplify DNA fragments is the polymerase chain reaction (PCR).

Describe the first step in the polymerase chain reaction.

In the first step in the polymerase chain reaction, a mixture containing a DNA sample, free nucleotides, primers, and DNA polymerase is heated to 95°C break the hydrogen bonds between DNA strands.

Describe the second step in the polymerase chain reaction.

In the second step in the polymerase chain reaction, the temperature is reduced so the primers can bind to the DNA strands.
The temperature is increased to allow DNA polymerase to join the nucleotides together to form two new complementary strands of DNA fragments.

Describe the third step in the polymerase chain reaction.

In the third step in the polymerase chain reaction, the mixture is heated to 95°C again and all four strands act as templates.
Each PCR cycle doubles the amount of DNA.

Give an example of an in vivo method to amplify DNA fragments.

One example of an in vivo method to amplify DNA fragments is using a culture of transformed host cells.

Describe the first step in the method using a culture of transformed host cells.

In the first step in the method using a culture of transformed host cells, promoter and terminator regions are added to the fragments of DNA.

Describe the second step in the method using a culture of transformed host cells.

In the second step in the method using a culture of transformed host cells, the fragments of DNA are inserted into vectors.
The vector DNA is cut open using the same restriction endonuclease, so the sticky ends of the vector are complementary to the sticky ends of the DNA fragment containing the gene.
DNA ligase joins the two sticky ends together.

Describe the third step in the method using a culture of transformed host cells.

In the third step in the method using a culture of transformed host cells, the host cells are transformed using the vectors with the recombinant DNA.

Describe the fourth step in the method using a culture of transformed host cells.

In the fourth step in the method using a culture of transformed host cells, marker genes are used to detect genetically modified (GM) cells or organisms.
Identified transformed cells continue to grow, producing many copies of the cloned gene.

Explain two advantages of using recombinant DNA technology in agriculture.

One advantage of using recombinant DNA technology in agriculture is higher yields or more nutritious crops. This reduces the risk of famine and malnutrition.
Another advantage is pest resistance, reducing costs and any environmental problems with using pesticides.

Explain one advantage of using recombinant DNA technology in industry.

One advantage of using recombinant DNA technology in industry is that enzymes used can be produced in large quantities, reducing costs.

Explain one advantage of using recombinant DNA technology in medicine.

One advantage of using recombinant DNA technology in medicine is making drugs and vaccines quickly, cheaply and in large quantities.

Explain three disadvantages of using recombinant DNA technology in agriculture.

One disadvantage of using recombinant DNA technology in agriculture is monoculture, which reduces biodiversity.
Another disadvantage is an uncontrolled spread of recombinant DNA to wild plants, which could affect weeds.
A third disadvantage is contamination of organic crops by wind-blown seeds – no longer organic.

Explain one disadvantage of using recombinant DNA technology in industry.

One disadvantage of using recombinant DNA technology in industry is globalisation.
As the use of this technology increases, biotech companies may force smaller companies out of business.

Explain one disadvantage of using recombinant DNA technology in medicine.

One disadvantage of using recombinant DNA technology in medicine is the creation of designer babies, which is unethical.

Describe two issues with ownership surrounding recombinant DNA technology.

One issue with ownership surrounding recombinant DNA technology is whether the donor or the researcher owns the genetic material.
Another issue is farmers being sued for breaching patent laws when non-GM crops are contaminated by GM crops.

What does gene therapy involve?

Gene therapy involves altering the mutated alleles inside cells to treat genetic disorders and cancer.

Name the technology used in gene therapy.

Recombinant DNA technology is used in gene therapy.

What are labelled DNA probes and DNA hybridisation used for?

Labelled DNA probes and DNA hybridisation are used to locate specific alleles of genes.

Explain why a DNA probe will hybridise with the target DNA molecule.

A DNA probe will hybridise with the target DNA molecule because the base sequence on the DNA probe is complementary to the base sequence on the target DNA molecule.

Suggest why DNA probes are labelled.

DNA probes are labelled so they can be detected.

Give two examples of labels for DNA probes, and how each is detected.

One example of a label for DNA probes is a radioactive label, detected using X-ray film.
Another example is a fluorescent label, detected using UV light.

Describe the first step in using a labelled DNA probe to locate specific alleles of genes.

In the first step in using a labelled DNA probe to locate specific alleles of genes, the DNA is extracted and amplified by PCR.
Restriction enzymes are used to cut DNA at specific base sequences on either side of the gene.

Describe the second step in using a labelled DNA probe to locate specific alleles of genes.

In the second step in using a labelled DNA probe to locate specific alleles of genes, the DNA fragments are separated using gel electrophoresis and then treated to form single strands with exposed bases.
The labelled DNA probe is added which hybridises with target alleles.
The DNA probe is then detected.

Labelled DNA probes be used to screen patients for which three things?

Labelled DNA probes can be used to screen patients for heritable conditions, drug responses or health risks.

Describe how the information from screening patients is used in genetic counselling.

The information from screening patients is used in genetic counselling to identify if someone is the carrier.
They can identify the type of mutated allele and the most effective treatment.

Describe how the information from screening patients is used in personalised medicine.

The information from screening patients is used in personalised medicine to identify the most effective treatments, based on drug responses and health risks.

An organism’s genome contains many VNTRs.
What are VNTRs?

VNTRs are variable number tandem repeats, repeated base sequences that do not code for proteins.

Fill in the blank.
The probability of two individuals having the same VNTRs is very __.

The probability of two individuals having the same VNTRs is very low.

What does genetic fingerprinting analyse?

Genetic fingerprinting analyses DNA fragments that have been cloned by PCR.

In genetic fingerprinting, suggest why a fluorescvent tag is added to the DNA fragments.

In genetic fingerprinting, a fluorescent tag is added to the DNA fragments so they are visible under UV light.

Describe the first step in gel electrophoresis.

In the first step in gel electrophoresis, the DNA mixture is placed into a well in a slab of gel and covered in a buffer solution that conducts electricity.
An electrical current is passed through the gel.

Describe the second step in gel electrophoresis.

In the second step in gel electrophoresis, DNA fragments move towards the positive electrode because they are negatively charged.
The DNA fragments separate according to size because small DNA fragments move faster and travel further through the gel.

Describe the third step in gel electrophoresis.

In the third step in gel electrophoresis, the DNA fragments are viewed as bands under UV light.
Two genetic fingerprints can be compared to see if they have the same number of nucleotides and hence the same number of VNTRs.

Give two uses of genetic fingerprinting.

Genetic fingerprinting is used to determine genetic relationships and to determine the genetic variability within a population.

Describe a use of genetic fingerprinting in the fields of forensic science.

One use of genetic fingerprinting in the fields of forensic science is comparing samples of DNA collected from crime scenes to samples of DNA from possible suspects.

Describe a use of genetic fingerprinting in medical diagnosis.

One use of genetic fingerprinting in medical diagnosis is to diagnose genetic disorders and cancer.

Describe a use of genetic fingerprinting in animal and plant breeding.

One use of genetic fingerprinting in animal and plant breeding is identify how closely-related individuals are to prevent inbreeding.