The control of gene expression

Question 1

What is insertion?

Answer 1

when a nucleotide is randomly inserted into a DNA sequence
affects function of the polypeptide due to causing a frameshift
causes Huntington’s disease

Question 2

What is deletion?

Answer 2

when a nucleotide is randomly deleted in a DNA sequence
affects function of the polypeptide due to causing a frameshift
causes Cystic fibrosis

Question 3

What is substitution?

Answer 3

where a DNA nucleotide is swapped for a different one
It is:
silent - doesn’t alter amino acid sequence
missense - alters a single amino acid
nonsense - can create a premature stop codon
causes sickle-cell anaemia

Question 4

What is inversion?

Answer 4

when a single gene is cut in 2 places, inverted 180 degrees and re-joined
results in a non- functional protein
causes haemophilia A

Question 5

What is duplication?

Answer 5

where one or more nucleotides are duplicated in a DNA sequence
original gene is not gene
causes Charcot-Marie tooth disease

Question 6

What is translocation?

Answer 6

when a section of a chromosome is added to another chromosome that isn’t its homologous partner
Philadelphia chromosome that’s found in leukaemia cancer

Question 7

What is a cause of mutations?

Answer 7

chemical mutagents
ionising radiation
errors in DNA replication

Question 8

What are stem cells?

Answer 8

Stem cells are undifferentiated cells which can keep dividing to give rise to other cell types

Question 9

What is a totipotent stem cell?

Answer 9

cells that are able to differentiate into any type of cell found in body and into
extra embryonic cells such as those in the placenta.

Question 10

What are pluripotent cells?

Answer 10

cells that can form any cell type in the body, however cannot form extra embryonic cells.

Question 11

What are multipotent cells?

Answer 11

can differentiate into other cells
types but are more limited

Question 12

What are unipotent cells?

Answer 12

these cells can only differentiate
into one type of cell

Question 13

How can oestrogen alter transcription?

Answer 13

-The lipid soluble nature of oestrogen means that is can freely diffuse across the cell
membrane where is binds to a receptor molecule on a transcription factor

-The binding alters the shape of the DNA binding site on the transcription factor and makes it
able to bind to the DNA.

-The transcription factor therefore enters the nucleus via the nuclear pore where it binds to DNA. This stimulates the transcription of the gene that makes up the DNA.

Question 14

What are transcriptional factors?

Answer 14

molecules that bind to a specific site on DNA to begin the
process of transcription

Question 15

What is small interrupting RNA and what does it do?

Answer 15

silencing DNA that ‘switches off’ genes by binding onto strands and preventing transcription

Question 17

What is genomics?

Answer 17

the study of the whole set of genetic information in the form
of the DNA base sequences that occur in the cells of organisms of a particular species

Question 18

What is a genome?

Answer 18

the complete set of genetic information contained within an organism / cell

Question 19

What is a proteome?

Answer 19

the full range of proteins that the cell can produce

Question 20

Why is determining the proteome of a simple organism easy?

Answer 20

-They have just one, circular piece of DNA that is not associated with histones
-There are no non-coding portions of DNA which are typical of eukaryotic cells

Question 21

Why is determining the proteome of a complex organism difficult?

Answer 21

-There are many non-coding genes
-Many genes have a role regulating other genes
-Individuals (except identical twins) have different base sequences on their DNA, therefore mapped DNA will differ, slightly, from everyone else’s DNA

Question 22

What is the Human genome
project?

Answer 22

International research initiative with the primary goal of mapping and
sequencing the entire human genome.
It aimed to determine the order of all the nucleotide bases in human DNA, identify all the genes, and understand their functions.
The project, which began in 1990, was officially completed in
2003.

Question 23

How were the sections of the human genome cloned in the
Human Genome Project?

Answer 23

introduced into bacteria, allowing the fragments to be
cloned and amplified.
The amplified DNA was then sequenced and pieced together using computational techniques.

Question 24

What advances have been made as a result of
publishing the research of the Human Genome Project?

Answer 24

-Identification of genes linked to diseases: such as cystic fibrosis,
Huntington’s disease, and certain cancers.
-Advances in personalized medicine: Development of targeted therapies based on individual genetic profiles.
-Biotechnology advancements: Use of genomic data in drug development and agricultural improvements.
-Evolutionary insights: Understanding human evolutionary history and comparing genomes across species.

Question 25

What is recombinant DNA (rDNA)?

Answer 25

where fragments of foreign DNA are inserted into other sections of DNA

Question 26

What is genetic engineering?

Answer 26

an area of research that studies the design and construction of different biological pathways, organisms and devices, as well as the redesigning of existing natural biological systems

Question 27

Describe the steps of genetic engineering:

Answer 27

- Identification of the DNA fragment or gene - Isolation of the desired DNA fragment - Multiplication of the DNA fragment (using polymerase chain reaction - PCR) - Transfer into the organism using a vector (e.g. plasmids, viruses, liposomes) - Cloning-Identification of the cells with the new DNA fragment (by using a marker), which is then cloned

Question 28

What is needed to modify an organism?

Answer 28

Enzymes (restriction endonucleases, ligase and reverse transcriptase) Vectors - used to deliver DNA fragments into a cell (eg. plasmids, viruses and liposomes) Markers - genes that code for identifiable substances that can be tracked (eg. GFP - green fluorescent protein which fluoresces under UV light or GUS - β-glucuronidase enzyme which transforms colourless or non-fluorescent substrates into products that are coloured or fluorescent)

Question 29

What are types of GM crops?

Answer 29

-herbicide-resistant crops -disease-resistant crops -crops with increased nutritional value e.g. Golden Rice

Question 30

What are 3 methods of creating fragments of DNA?

Answer 30

-Using restriction enzymes -Reverse transcriptase -Gene machine

Question 31

What are restriction endonucleases?

Answer 31

They separate the two strands of DNA at the specific target base sequence or recognition sequence by ‘cutting’ the sugar-phosphate backbone in two ways. Either leaving ‘blunt’ or ‘sticky ends’

Question 32

Describe mRNA and reverse transcriptase

Answer 32

-Once isolated, the mRNA is then combined with a reverse transcriptase enzyme and nucleotides to create a single strand of complementary DNA (cDNA). -Reverse transcriptase enzymes are sourced from retroviruses and they catalyse the reaction that reverses transcription. The mRNA is used as a template to make the cDNA -DNA polymerase is then used to convert the single strand of cDNA into a double-stranded DNA molecule which contains the desired code for the gene. -This technique for isolating the desired gene is considered advantageous as it is easier for scientists to find the gene because specialised cells will make very specific types of mRNA

Question 33

What is the gene machine used for?

Answer 33

-If the amino acid sequence is known, it is possible to synthesise genes artificially. -Scientists use computers to generate the nucleotide sequence (rather than an mRNA template) to produce the gene. -Short fragments of DNA are first produced one nucleotide at a time, which are joined to make longer sequences of nucleotides and then inserted into vectors (eg. plasmids). This method is being used to create novel genes contained in vaccines.

Question 34

What is recombinant DNA (rDNA)?

Answer 34

is a form of DNA that has been artificially created by combining genetic material from two or more different sources. This technology is used in genetic engineering to produce transgenic/genetically modified organisms (GMOs).

Question 35

What is meant by a palindromic recognition sequence?

Answer 35

a specific sequence of DNA bases that reads the same in both directions when looking at complementary strands. These sequences are recognised by restriction enzymes, which cut the DNA at or near these sites.