Gene Expression & Technology (8)

Question 1

Embryonic stem cells are a type of which cells used to treat diseases?

Answer 1

Pluripotent cells

Question 2

Types of adult specialised stem cells (2)

Answer 2

1. Multipotent; can differentiate into cells like bone marrow forming blood cells
2. Unipotent; only form one type of specialised cell e.g skin cells

Question 3

Why are pluripotent stem cells more useful than embryonic stem cells?

Answer 3

Pluripotent cells can be induced from other body cells

Question 4

Which type of stem cell has the most potential to differentiate into any other type of cell?

Answer 4

Totipotent (found in early stages of the embryo)

Question 5

What type of stem cell can differentiate into the MOST types of cell?

Answer 5

Pluripotent (found in embryos and in foetuses, induced pluripotent stem cells can be created from adult cells by switching on specific genes)

Question 6

What is the term for how a stem cell can turn into a type of cell?

Answer 6

(low/high) Differential potential

Question 7

State what is meant by the terms totipotent and pluripotent

Answer 7

Totipotent = all cell types
Pluripotent = some cell types

Question 8

Explain how cells produced from stem cells can have the same genes yet be of different types

Answer 8

• Not all genes activated / switched on;
• Correct reference to factors/mechanisms for gene switching;
• E.g reference to promoters / transcription factors

Question 9

Describe the mechanism by which a signal protein causes the synthesis of mRNA

Answer 9

• signal protein {binds to / joins to / interacts with / activates;
• receptor on surtace membrane;
• messenger molecule moves from cytoplasm and enters nucleus;
• {produces / activates} transcription factor;
• binds to promoter region;
• RNA polymerase transcribes target gene

Question 10

Describe how DNA is replicated in a cell (5)

Answer 10

1. DNA strands separate / hydrogen bonds break;
2. Parent strand acts as a template for semi-conservative replication;
   • Nucleotides line up by complementary base pairing (A-T);
   • DNA polymerase joins adjacent nucleotides on the developing strand via condensation forming a phosphodiester bond;
   • 5’ to 3’ anti parallel direction;
   • Formed by semi-conservative replication

Question 11

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment

Answer 11

1. Requires DNA fragment, TAQ DNA polymerase, (free-floating) nucleotides and primers;
2. Heat to 95c to break hydrogen bonds between strands;
3. Reduce temperature (40-65c) so primers bind to DNA strands;
4. Increase temperature (70-75c) so DNA polymerase joins nucleotides (REPEAT METHOD)

Question 12

Why is the DNA heated to 95c during PCR? (2)

Answer 12

• Produce single stranded DNA
• Breaks weak hydrogen bonds between strands

Question 13

Why do you add primers during PCR? (3)

Answer 13

• Attaches to/complementary to start of gene / end of fragment;
• Replication of base sequence from here;
• Prevents strands annealing

Question 14

Explain why base pairs is a suitable unit for measuring the length of a piece of DNA

Answer 14

• DNA = two chains of A-T/C-G (purine with pyramide pairs);
• Bases are a constant distance apart (in sugar phosphate backbone);
• Each base pair is the same length

Question 15

Name one mutagenic agent

Answer 15

• High energy radiation / ionising radiation: alpha, beta, x-rays

• Chemicals: benzene, ethanol

• Carcinogens e.g mustard gas, tar, phenols

Question 16

A deletion mutation occurs in gene 1
Describe how a deletion mutation alters the structure of a gene

Answer 16

• Removal of one or more bases/nucleotides;
• Frame shift from point of mutation to base sequence change.

Question 17

Describe the main stages in the copying, cutting and separation of the DNA

Answer 17

• Heat DNA to 95c;
• strands separate (H bonds broken);
• Cool (65c) so primers bind to DNA;
• Add DNA polymerase and free-floating nucleotides;
• use RESTRICTION ENDONUCLEASES enzymes to cut DNA at specific base sequence (breaks phosphodiester bonds);
• Use if electric current and agar gel (gel electrophoresis);
• Shorter fragments move further (to + electrode)

Question 18

Describe a plasmid

Answer 18

Circular DNA, separate from bacterial DNA, contains only a few genes.

Question 19

Describe the polymerase chain reaction

Answer 19

• Heat DNA (95c);
• Breaks H bonds / separates strands;
• Add primers and free-floating nucleotides;
• Cool (65c);
• To allow binding of primers;
• TAQ DNA polymerase (heat stable);
• Repeat cycle many times

Question 20

Suggest one reason why DNA replication stops in the polymerase chain reaction

Answer 20

• Limited number of primers/nucleotides/ used up;
• TAQ DNA polymerase (eventually) denatures

Question 21

Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once (2)

Answer 21

• enzymes only cut DNA at specific base sequence/recognition site;
• sequence of bases/recognition site occur ONCE in plasmid and many times in human DNA;

Question 22

Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use (3)

Answer 22

• Use of fermenters;
• Provides nutrients plus suitable conditions for optimum growth;
• Reproduction of bacteria (by nuclear fission);
• Insulin accumulates and is extracted.

Question 23

Explain what is meant by a vector

Answer 23

1. Carrier;
2. (of foreign) DNA/gene;
3. Into host cell

Question 24

Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected

Answer 24

1. Isolate TARGET gene/mRNA from another organism;
2. Using restriction endonucleases enzymes to produce STICKY ends;
3. Use DNA ligand to join target gene to plasmid;
4. Include marker gene;
5. Example of marker e.g antibiotic resistance;
6. Add plasmid to bacteria to grow colonies (by binary fission);
   7? Replica plate onto medium where marker gene is expressed;
7. Bacteria not killed have antibiotic resistance gene AND TARGET GENE;
8. Bacteria expressing the marker gene have the target gene also.

Question 25

mRNA may be described as a polymer. Explain why (1)

Answer 25

Made up of many similar monomer nucleotides

Question 26

What is a DNA probe?

Answer 26

• (Short) single strand of DNA
• Bases complementary with target gene/DNA/allele

Question 27

Name three techniques used by scientists to compare DNA sequences (3)

Answer 27

• Polymerase Chain Reaction
• DNA Fingerprinting
• Gel Electrophoresis

Question 28

Explain how oestrogen enables RNA polymerase to transcribe its target gene

Answer 28

• Oestrogen diffuses through cell membrane;
• attaches to ERa receptor;
• ERa receptor changes shape;
• ERa receptor leaves protein complex which inhibited its action;
• oestrogen receptor binds to promoter region;
• enables RNA polymerase to transcribe target gene

Question 29

Define Epigenetics (1)

Answer 29

Heritable phenotype changes (to a gene function) that do not involve alterations in the DNA sequence/mutation