5. Dideoxynucleosides are employed in the course of the Sanger process of DNA sequencing. Dideocynucleosides are used because
a) They stop the synthesis of DNA strands
b) They are fluoresce
c) They are radioactive
d) They move quicly during gel electrophoresis
e) They stabilize small double-standed DNA fragments
MY ANSWER: a
6. Gel Electrophoresis sperates fragments of DNA using
a) a sieving medium through which DNA fragments are moved by gravitational forces
b) repulsion of charged DNA molecules by the electrically charged gel beads
c) a sieving medium through which DNA molecules are moved by electrical forces
d) movement through a sieving medium by positively charged DNA molecules attracted by ultracentrifugation
MY ANSWER: c
7. A fragment of DNA is called recombinant if
a) when separated by heat, it will anneal on cooling
b) it is acted upon by spliceosomes and parts of it are existed
c) it has been amplified using the polymerase chain reaction
d) it has been reverse transcribed from RNA
e)it contains DNA sequences from more than one source
8. The recognition sites of fie restriction endonucleases are shown below. Which would make cuts in the following DNA fragment? You will need to draw in the complementary DNA strand before attempting this question.
5’-GCAAGCTTGCTGCAGAATTACCCGGA-3’
Recognition Sites:
EcoRI 5’-GAATTC-3’
3’-CTTAAG-5’
SmaI 5’-GGGCCC-3’
3’-CCCGGG-5’
AluI 5’-AGCT-3’
3’-TCGA-5’
HindIII 5’-AAGCTT-3’
3’-TTCGAA-5’
a) HindIII and Smal
b) EcoRI and AluI
c) EcoRI and SalI
d) EcoRI and HindIII
e) AluI and HindIII
MY ANSWER : b
5. To determine why dideoxynucleosides are employed in the Sanger process of DNA sequencing, let's break down the options:
a) They stop the synthesis of DNA strands - This is correct. Dideoxynucleosides lack a 3' OH group, which is required for DNA synthesis. When they are incorporated into growing DNA strands during the Sanger sequencing reaction, they terminate the chain extension, allowing the identification of the bases in the DNA sequence.
b) They are fluoresce - This is not a correct reason. While fluorescence is often used in DNA sequencing, it is not the specific reason why dideoxynucleosides are used.
c) They are radioactive - This is not a correct reason. Radioactivity is not employed in the Sanger sequencing process.
d) They move quickly during gel electrophoresis - This is not a correct reason. The movement of dideoxynucleosides during gel electrophoresis is not a specific factor in their use in the Sanger sequencing process.
e) They stabilize small double-stranded DNA fragments - This is not a correct reason. Dideoxynucleosides do not specifically stabilize small double-stranded DNA fragments in the Sanger sequencing process.
Therefore, the correct option is a) They stop the synthesis of DNA strands.
6. To determine how gel electrophoresis separates fragments of DNA, let's break down the options:
a) A sieving medium through which DNA fragments are moved by gravitational forces - This is not a correct reason. Gel electrophoresis uses an electric field, not gravitational forces, to move DNA fragments through the gel.
b) Repulsion of charged DNA molecules by the electrically charged gel beads - This is not a correct reason. The gel beads themselves are not typically electrically charged. The electric field created during gel electrophoresis causes the DNA molecules, which also carry a negative charge, to move through the gel.
c) A sieving medium through which DNA molecules are moved by electrical forces - This is correct. The gel matrix acts as a sieving medium that slows down the movement of DNA molecules as they migrate based on their size and charge under the influence of the electric field.
d) Movement through a sieving medium by positively charged DNA molecules attracted by ultracentrifugation - This is not a correct reason. Ultracentrifugation is not involved in gel electrophoresis.
Therefore, the correct option is c) A sieving medium through which DNA molecules are moved by electrical forces.
7. To determine the definition of a recombinant DNA fragment, let's go through the options:
a) When separated by heat, it will anneal on cooling - This is not the definition of a recombinant DNA fragment. Annealing refers to the process of complementary DNA strands coming together, but it does not define a recombinant fragment.
b) It is acted upon by spliceosomes and parts of it are excised - This is not the definition of a recombinant DNA fragment. Spliceosomes are involved in RNA splicing, not DNA recombination.
c) It has been amplified using the polymerase chain reaction - This is not the definition of a recombinant DNA fragment. Amplification using the polymerase chain reaction (PCR) does not determine if a fragment is recombinant.
d) It has been reverse transcribed from RNA - This is not the definition of a recombinant DNA fragment. Reverse transcription refers to the process of synthesizing DNA from an RNA template, but it does not define a recombinant fragment.
e) It contains DNA sequences from more than one source - This is correct. A recombinant DNA fragment is one that contains DNA sequences from different sources, typically achieved through genetic engineering techniques.
Therefore, the correct option is e) It contains DNA sequences from more than one source.
8. To determine which restriction endonucleases would make cuts in the given DNA fragment, let's analyze the recognition sites:
The DNA fragment is: 5’-GCAAGCTTGCTGCAGAATTACCCGGA-3’
The recognition sites are:
- EcoRI: 5’-GAATTC-3’ (complementary: 3’-CTTAAG-5’)
- SmaI: 5’-GGGCCC-3’ (complementary: 3’-CCCGGG-5’)
- AluI: 5’-AGCT-3’ (complementary: 3’-TCGA-5’)
- HindIII: 5’-AAGCTT-3’ (complementary: 3’-TTCGAA-5’)
By comparing the recognition sites to the DNA fragment, we can identify which restriction endonucleases would make cuts in the DNA fragment.
From the given recognition sites, only EcoRI (complementary: 3’-CTTAAG-5’) and AluI (complementary: 3’-TCGA-5’) have matching sequences present in the DNA fragment.
Therefore, the correct option is b) EcoRI and AluI.