3.4: DNA replication
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Outline the function of a helicase.
Helicase is a type of enzyme that separates two annealed strands of nucleic acids, e.g. separate the two strands of DNA in DNA replication or in transcription or the two strands in a RNA-DNA hybrid.
Outline the function of DNA polymerase.
DNA polymerase is a type of enzyme used in the formation of DNA strand by catalyzing polymerisation of deoxyribose-nucleotides. It causes free nucleotides to be added to the DNA strand.
What happens at each stage of DNA replication?
- 1. DNA double helix
- 2. DNA double helix unwinds.
- 3. Double helix unzips and two strands separate, catalysed by the enzyme helicase.
- 4. Free nucleotides from the cytoplasm join at the free sites as the helix unwinds. Adenine always pairs with thymine, gunanine pairs with cytosine to maintain the sequence of nucleotides.
- 5. DNA polymerase catalyses the formation of bonds to join the nucleotides to the DNA strand.
- 6. Two identical strands of DNA are formed from the original strand.
Explain the importance of the conservation of the base sequence during replication.
The conservation of the base sequence is highly important in the process of DNA replication. The production of two identical strands which have the same code as the original strand ensures genetic information will continue and the cells of the organism will be able to carry out the correct processes for normal functioning. Mistakes in the form of mutation can occur.
Identify when DNA replication occurs.
DNA replication occurs before mitosis occurs. It is part of the process of cell reproduction needed for growth and replacement of cells/tissues.
Identify some locations where DNA replication occurs.
DNA replication occurs in tissues that are growing or require cell replacement, e.g. in animals - germinal layers of the skin, bone marrow, digestive tract; and in plants - root tip, shoot tip, camblum.
Why is DNA replication is semi-conservative.
DNA replication is semi-conservative as both strands formed from the original consist of one 'old ' strand and one 'new' strand.
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