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Answer either A or B in the space below - Scottish Highers Human Biology - Question 12 - 2017
Question 12
Answer either A or B in the space below. Labelled diagrams may be used where appropriate. A Describe the structure of DNA and the process of DNA replication. OR B ... show full transcript
Worked Solution & Example Answer:Answer either A or B in the space below - Scottish Highers Human Biology - Question 12 - 2017
Step 1
Describe the structure of DNA
Answer
DNA (deoxyribonucleic acid) is a molecule composed of nucleotides containing a deoxyribose sugar, a phosphate group, and a nitrogenous base. The four bases are adenine (A), thymine (T), cytosine (C), and guanine (G). In terms of structure:
- The two strands of DNA are held together by complementary base pairing, where adenine pairs with thymine, and cytosine pairs with guanine.
- The backbone of the DNA molecule consists of a sugar-phosphate structure.
- DNA exists as a double helix formed by the two strands running in opposite directions (antiparallel) from 5' to 3' and 3' to 5'.
Step 2
Describe the process of DNA replication
Answer
The process of DNA replication involves several key steps:
- Unwinding the DNA: The double helix structure is unwound by the enzyme helicase. This creates two single strands to serve as templates.
- Primer Binding: A short RNA primer is synthesized and binds to the template strand, providing a starting point for DNA synthesis.
- DNA Polymerization: DNA polymerase adds nucleotides to the 3' end of the newly growing strand, complementary to the template strand. This occurs continuously on one strand (leading strand), while the other strand (lagging strand) is synthesized in small fragments known as Okazaki fragments.
- Joining of Fragments: The RNA primers are removed and replaced with DNA nucleotides, and the fragments are joined together by the enzyme ligase to create a continuous DNA strand.