Gene Expression & Technology (8) Flashcards
Embryonic stem cells are a type of which cells used to treat diseases?
Pluripotent cells
Types of adult specialised stem cells (2)
- Multipotent; can differentiate into cells like bone marrow forming blood cells
- Unipotent; only form one type of specialised cell e.g skin cells
Why are pluripotent stem cells more useful than embryonic stem cells?
Pluripotent cells can be induced from other body cells
Which type of stem cell has the most potential to differentiate into any other type of cell?
Totipotent (found in early stages of the embryo)
What type of stem cell can differentiate into the MOST types of cell?
Pluripotent (found in embryos and in foetuses, induced pluripotent stem cells can be created from adult cells by switching on specific genes)
What is the term for how a stem cell can turn into a type of cell?
(low/high) Differential potential
State what is meant by the terms totipotent and pluripotent
Totipotent = all cell types
Pluripotent = some cell types
Explain how cells produced from stem cells can have the same genes yet be of different types
• Not all genes activated / switched on;
• Correct reference to factors/mechanisms for gene switching;
• E.g reference to promoters / transcription factors
Describe the mechanism by which a signal protein causes the synthesis of mRNA
• 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
Describe how DNA is replicated in a cell (5)
- DNA strands separate / hydrogen bonds break;
- 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
Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment
- Requires DNA fragment, TAQ DNA polymerase, (free-floating) nucleotides and primers;
- Heat to 95c to break hydrogen bonds between strands;
- Reduce temperature (40-65c) so primers bind to DNA strands;
- Increase temperature (70-75c) so DNA polymerase joins nucleotides (REPEAT METHOD)
Why is the DNA heated to 95c during PCR? (2)
• Produce single stranded DNA
• Breaks weak hydrogen bonds between strands
Why do you add primers during PCR? (3)
• Attaches to/complementary to start of gene / end of fragment;
• Replication of base sequence from here;
• Prevents strands annealing
Explain why base pairs is a suitable unit for measuring the length of a piece of DNA
• 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
Name one mutagenic agent
• High energy radiation / ionising radiation: alpha, beta, x-rays
• Chemicals: benzene, ethanol
• Carcinogens e.g mustard gas, tar, phenols
A deletion mutation occurs in gene 1
Describe how a deletion mutation alters the structure of a gene
• Removal of one or more bases/nucleotides;
• Frame shift from point of mutation to base sequence change.
Describe the main stages in the copying, cutting and separation of the DNA
• 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)
Describe a plasmid
Circular DNA, separate from bacterial DNA, contains only a few genes.
Describe the polymerase chain reaction
• 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
Suggest one reason why DNA replication stops in the polymerase chain reaction
• Limited number of primers/nucleotides/ used up;
• TAQ DNA polymerase (eventually) denatures
Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once (2)
• 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;
Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use (3)
• Use of fermenters;
• Provides nutrients plus suitable conditions for optimum growth;
• Reproduction of bacteria (by nuclear fission);
• Insulin accumulates and is extracted.
Explain what is meant by a vector
- Carrier;
- (of foreign) DNA/gene;
- Into host cell
Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected
- Isolate TARGET gene/mRNA from another organism;
- Using restriction endonucleases enzymes to produce STICKY ends;
- Use DNA ligand to join target gene to plasmid;
- Include marker gene;
- Example of marker e.g antibiotic resistance;
- Add plasmid to bacteria to grow colonies (by binary fission);
7? Replica plate onto medium where marker gene is expressed; - Bacteria not killed have antibiotic resistance gene AND TARGET GENE;
- Bacteria expressing the marker gene have the target gene also.
mRNA may be described as a polymer. Explain why (1)
Made up of many similar monomer nucleotides
What is a DNA probe?
• (Short) single strand of DNA
• Bases complementary with target gene/DNA/allele
Name three techniques used by scientists to compare DNA sequences (3)
• Polymerase Chain Reaction
• DNA Fingerprinting
• Gel Electrophoresis
Explain how oestrogen enables RNA polymerase to transcribe its target gene
• 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
Define Epigenetics (1)
Heritable phenotype changes (to a gene function) that do not involve alterations in the DNA sequence/mutation
