Section 1 Flashcards
Nucleic acids are composed of chains of ____________
nucleotides
What are the functions of DNA?
- Long-term storage molecule
- Template for DNA replication
- Coding for proteins and functional RNAs
A short nucleic acid containing 50 or fewer nucleotides is generally called an ____________
oligonucleotide
A longer nucleic acid (generally over 50 nucleotides) is called a ___________
polynucleotide
Weak forces such as _____________ and ________________ coordinate the self-assembly of nucleic acids into their 3D structure.
Watson-crick base pairing and base stacking
What are the components of a nucleotide?
- A heterocyclic base
- A five-carbon sugar called a pentose
- A phosphate group
What does heterocyclic mean?
A cyclic compound with one or more ring structures that contain atoms of at least two different elements.
Is there always an equal percentage of purines and pyrimidines in double stranded DNA?
Yes, since A always pairs with T, and C always pairs with G, according to the Watson-Crick model of DNA
What is the relationship of the number of purines and pyrimidines in DNA?
A + G = T + C
(the sum of purine residues = the
This is called Chargaff’s Rule, and is critical for information storage (maintaining nucleotide order) and replication (since it is semi-conservative)
What is the significance of Chargaff’s Rule in DNA?
Chargaff’s Rule is critical for information storage in DNA because it helps maintain the order of nucleotides and ensures that there is an equal balance of purines and pyrimidines. It is also essential for DNA replication, as it plays a role in the semi-conservative nature of DNA replication.
What is the Watson-Crick model of DNA?
The Watson-Crick model of DNA describes DNA as a double-stranded, helical molecule consisting of two sugar-phosphate backbones held together by hydrogen bonds between pairs of nitrogenous bases. The four nitrogenous bases are adenine (A), cytosine (C), guanine (G), and thymine (T). In this model, hydrogen bonding occurs between A and T, and G and C.
How are the two strands of a DNA molecule held together?
The two strands of a DNA molecule are held together via base pairing between the nitrogenous bases. Specifically, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G) through hydrogen bonds.
What type of bonds are responsible for holding the two DNA strands together?
The bonds that hold the two DNA strands together are hydrogen bonds. These are relatively weak interactions that form between the nitrogenous bases of the DNA strands.
WHy is the C-G base pair stronger than the A-T?
Because C and G share three hydrogen bonds, while A and T share only two.
The presence of an extra hydrogen bond in the C-G pair contributes to its greater stability.
What elements or groups in the nitrogenous bases are involved in forming hydrogen bonds in DNA base pairing?
Hydrogen bonds in DNA base pairing are formed due to the hydrogen-bonding capacity of the ring nitrogens, ring carbonyl groups, and the amino groups located outside the ring structure of the nitrogenous bases. These groups are involved in the interactions that lead to base pairing in DNA.
How does the strength of hydrogen bonding in DNA base pairs relate to the overall stability and structure of the DNA molecule?
The strength of hydrogen bonding in DNA base pairs is crucial for the overall stability and structure of the DNA molecule. The differential strength of these bonds contributes to the stability of the double helix and plays a fundamental role in the structural integrity of DNA, ensuring accurate replication and transmission of genetic information.
What is the overall shape of the DNA molecule?
The DNA molecule has a right-handed double helix structure.
What is the composition of the backbone of each DNA strand?
The backbone of each DNA strand is composed of alternating sugar and phosphate residues, known as the sugar-phosphate backbone. It is highly negatively charged.
Where are the nitrogenous bases of DNA located within the double helix, and what is their role?
The nitrogenous bases of DNA are positioned towards the center of the helix. They play a crucial role in hydrogen bonding with complementary bases on the opposing DNA strand, facilitating base pairing.
What is the concept of directionality in the DNA double helix?
The DNA double helix exhibits directionality, meaning each strand has opposing directionality. This directionality is based on the linkages formed by carbons at the phosphate and OH groups on the pentose sugar. The two strands run in opposite directions, with one strand having a 5’ → 3’ direction, while the other has a 3’ → 5’ direction.