Study "AS Biology Cambridge DNA and protein synthesis", a flashcard deck on FORKSAI.
Define the term 'polynucleotide strand' in the context of DNA structure.
A polynucleotide strand is a polymer made up of repeating monomer units called nucleotides. In DNA, two such strands run in opposite directions, forming a double helix.
Describe the components that make up a single nucleotide.
Each nucleotide is composed of three main parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base. These components are essential for forming the DNA structure.
Explain the concept of 'antiparallel' strands in a DNA molecule.
Antiparallel refers to the orientation of the two polynucleotide strands in DNA. They run in opposite directions, meaning that the 5' end of one strand aligns with the 3' end of the other, and vice versa.
Describe how hydrogen bonds contribute to the stability of the DNA double helix.
Hydrogen bonds form between complementary nitrogenous bases on opposite strands of the DNA molecule. These weak bonds collectively hold the two polynucleotide strands together, maintaining the double helix structure.
Explain the complementary base pairing rule in DNA.
The complementary base pairing rule states that adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). This specific pairing ensures the consistent width of the DNA double helix and is crucial for replication.
Distinguish between purine and pyrimidine bases, providing examples from DNA.
Purine bases have a double-ring structure and include adenine and guanine. Pyrimidine bases have a single-ring structure and include thymine and cytosine. In DNA, a purine always pairs with a pyrimidine.
Describe the structure and function of the sugar-phosphate backbone in DNA.
The sugar-phosphate backbone forms the structural framework of each DNA strand. It consists of alternating deoxyribose sugars and phosphate groups linked by phosphodiester bonds, providing stability and protecting the nitrogenous bases.
Define a phosphodiester bond and explain where it is found in a DNA strand.
A phosphodiester bond is a covalent bond that links the phosphate group of one nucleotide (at its 5' end) to the carbon 3 of the deoxyribose sugar of an adjacent nucleotide (at its 3' end). These bonds form the sugar-phosphate backbone.
Explain the significance of a complete turn of the double helix occurring every 10 base pairs.
The consistent helical structure of DNA, with a complete turn every 10 base pairs, is a fundamental characteristic. This regular coiling contributes to the molecule's stability and its ability to be efficiently packaged within the cell.
Outline the first step in the semi-conservative replication of DNA.
The first step in semi-conservative replication is the unwinding of the DNA double helix. This process exposes the individual strands, making them accessible for replication.