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.
Why is the antiparallel orientation of DNA more energetically favorable than the parallel orientation?
The antiparallel orientation of DNA is more energetically favorable due to the geometry of the component bases. In the antiparallel arrangement, the complementary base pairs align in a way that allows for proper hydrogen bonding. In a parallel orientation, the bases would not align correctly, making it less stable and less suitable for genetic information storage and replication.
What is antiparallel vs parallel?
Antiparallel: In an antiparallel arrangement, the two DNA strands run in opposite directions along the length of the helix. One strand runs in the 5’ to 3’ direction, meaning the 5’ end of one strand is paired with the 3’ end of the other strand, and vice versa. This arrangement allows for the complementary base pairs (A with T and C with G) to align properly and form hydrogen bonds.
Parallel: In a parallel orientation, both DNA strands run in the same direction along the length of the helix, such as both running from 5’ to 3’ or both running from 3’ to 5’. In this configuration, the bases on the two strands do not align correctly for proper hydrogen bonding. A parallel orientation is not found in the natural structure of DNA because it would result in an unstable and ineffective molecule for genetic information storage and replication.
How is a phosphodiester bond in nucleic acids formed?
A phosphodiester bond is created when the 5′-phosphate group of one nucleotide unit is linked to the 3′-hydroxyl group of the next nucleotide. This reaction involves the loss of water, and the linked nucleotides are now referred to as ‘residues.’
In the DNA double helix, what are the two unequal surfaces formed by the twist of the helix, and what are they called?
The twist of the DNA helix forms two unequal surfaces known as the major groove and the minor groove. The major groove is the wider groove found on the outside of the DNA strand and is primarily where the nucleotide sequence is read by DNA-binding proteins, as it is more accessible.