DNA Structure Flashcards
What is DNA, and how is it classified?
DNA (Deoxyribonucleic Acid) is a polynucleotide made up of many nucleotides bonded together in a long chain. It contains the genetic instructions for the development and functioning of all known living organisms.
What are nucleotides, and what are their components?
Nucleotides are the monomers of DNA, each consisting of:
A deoxyribose sugar (a 5-carbon pentose sugar).
A phosphate group.
A nitrogenous base (adenine, thymine, cytosine, or guanine).
What type of bonds connect nucleotides in a DNA strand? What do they form between?
Nucleotides in a DNA strand are connected by phosphodiester bonds. These covalent bonds form between the phosphate group of one nucleotide and the 3’ carbon of the sugar in the next nucleotide.
What is the sugar-phosphate backbone in DNA?
The sugar-phosphate backbone is the structural framework of DNA. It consists of alternating deoxyribose sugars and phosphate groups linked by phosphodiester bonds.
What does it mean when DNA strands are described as antiparallel?
The two DNA strands run in opposite directions:
- One strand runs 5’ to 3’ (phosphate to hydroxyl group).
- The other strand runs 3’ to 5’ (hydroxyl group to phosphate).
- This orientation is crucial for the complementary base pairing and the stability of the double helix.
How are the ends of a DNA strand defined?
The 5’ end of a DNA strand has a free phosphate group attached to the 5’ carbon of the sugar.
The 3’ end has a free hydroxyl group (-OH) attached to the 3’ carbon of the sugar.
What are the two types of nitrogenous bases in DNA?
Purines: Larger, double-ring bases including Adenine (A) and Guanine (G).
Pyrimidines: Smaller, single-ring bases including Thymine (T) and Cytosine (C).
What is complementary base pairing?
Complementary base pairing occurs between specific bases:
Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
This ensures the stability and fidelity of the DNA molecule.
How does Chargaff’s rule relate to complementary base pairing? What does this reflect?
Chargaff’s rule states that:
The amount of Adenine (A) equals the amount of Thymine (T).
The amount of Guanine (G) equals the amount of Cytosine (C).
This reflects the 1:1 ratio of complementary base pairs in DNA.
How are nitrogenous bases positioned within the DNA molecule?
The nitrogenous bases project inward from the sugar-phosphate backbone and form hydrogen bonds with complementary bases on the opposite strand. This creates the rungs of the DNA double helix.
What role do hydrogen bonds play in DNA structure?
Hydrogen bonds hold the two DNA strands together.
They provide stability while allowing the strands to separate during processes like replication and transcription.
How many hydrogen bonds are formed between each base pair?
Adenine (A) and Thymine (T): Two hydrogen bonds.
Guanine (G) and Cytosine (C): Three hydrogen bonds.
Why is DNA described as a double helix?
DNA is a three-dimensional structure in which two antiparallel strands twist around each other to form a spiral. This double helix shape is stabilized by hydrogen bonds and the sugar-phosphate backbone.
What are the key features of the DNA double helix?
Antiparallel strands.
Complementary base pairs held together by hydrogen bonds.
A sugar-phosphate backbone on the outside.
A uniform width due to purine-pyrimidine pairing.
What components of DNA must you be able to identify in a diagram?
Sugar-phosphate backbone.
Nucleotides.
Complementary base pairs.
Phosphodiester bonds.
Hydrogen bonds.
