Structure Of DNA Flashcards
What are the basic components of a nucleotide in DNA?
A nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, guanine, or cytosine).
What is the structure of DNA?
DNA consists of two polynucleotide strands forming a double helix.
How do the nitrogenous bases pair in DNA?
Adenine pairs with thymine (A-T) via two hydrogen bonds, and guanine pairs with cytosine (G-C) via three hydrogen bonds.
What is the significance of major and minor grooves in DNA?
Major and minor grooves provide accessible sites for protein binding and drug interactions.
What role do alkylating agents play in cancer therapy?
Alkylating agents introduce modifications to DNA that prevent replication and transcription.
Fill in the blank: DNA is stabilized by _______ interactions and _______ bonds.
base-stacking; hydrogen
What is the primary structure of DNA?
The primary structure consists of a double helix formed by two antiparallel strands of nucleotides.
What are nitrogen mustards and how do they affect DNA?
Nitrogen mustards are alkylating agents that form aziridinium ions, causing cross-linking in DNA.
True or False: The B-DNA form has about 10 base pairs per turn.
True
What is supercoiling in DNA?
Supercoiling is the tertiary structure that allows DNA to be compacted for fitting within the cell nucleus.
What is the impact of alkylation on DNA structure?
Alkylation can lead to base mispairing, cross-linking, and DNA strand breaks.
What differentiates A-DNA from B-DNA?
A-DNA is more compact and dehydrated, while B-DNA is the most common form with accessible grooves.
What is the function of metal ions like Mg²⁺ in DNA?
Metal ions neutralize the negative charge of the phosphate backbone, enhancing stability.
Fill in the blank: The sugar-phosphate backbone of DNA is linked by _______ bonds.
phosphodiester
What are intercalating agents?
Intercalating agents are molecules that insert between DNA bases, potentially distorting its structure.
What is the role of transcription factors in DNA?
Transcription factors bind to major and minor grooves to regulate gene expression.
What is the mechanism of action of cisplatin?
Cisplatin forms adducts with the N7 position of guanine, leading to DNA bending and cross-linking.
True or False: DNA’s structure is not affected by environmental factors.
False
What are the three structural variants of DNA?
B-DNA, A-DNA, and Z-DNA.
What is the significance of hydrogen bonding in DNA stability?
Hydrogen bonding between base pairs ensures the structural stability of the DNA double helix.
What are the nucleophilic sites targeted by alkylating agents?
N7 of guanine, N3 of adenine, and O6 of guanine.
What happens during DNA fragmentation?
DNA fragmentation can occur through hydrolytic reactions or repair enzyme actions on alkylated DNA.
What is the structure of DNA?
DNA consists of two antiparallel polynucleotide strands coiled into a double helix
The strands run in opposite directions: 5’ to 3’ and 3’ to 5’.
Which bases pair together in DNA and how many hydrogen bonds do they form?
Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds, and Guanine (G) pairs with Cytosine (C) via 3 hydrogen bonds
This complementary base pairing is crucial for the stability of the DNA double helix.
What are the major and minor grooves in DNA?
Grooves created by the helical structure of DNA that allow interaction with proteins and molecules
The major groove and minor groove are lined with hydrogen bond donors and acceptors.
What is a nucleoside?
A nucleoside consists of a nitrogenous base attached to a deoxyribose sugar
Purines include adenine and guanine; pyrimidines include cytosine and thymine.
What is a nucleotide?
A nucleotide is formed when one or more phosphate groups attach to a nucleoside
Nucleotides are the building blocks of DNA linked by phosphodiester bonds.
What determines the genetic information encoded in DNA?
The sequence of nucleotides along a DNA strand
The order of bases forms the genetic code.
What are the nucleophilic sites in DNA?
Mainly nitrogen and oxygen atoms in the bases
Nitrogen atoms involved in the nucleoside bonds are not available for reactions with electrophiles.
What types of interactions govern nucleophile-electrophile attraction?
Electrostatic control and orbital control
These interactions influence the reactivity and bonding between nucleophiles and electrophiles.
What is electrostatic control?
Attractive forces between oppositely charged particles
Involves the attraction between a negatively charged nucleophile and a positively charged electrophile.
What is orbital control?
Overlap of molecular orbitals between a nucleophile and an electrophile
Facilitates the transfer of electrons and forms covalent bonds.
What is the primary target for alkylating agents in DNA?
The N7 position of guanine
Other targets include nitrogen atoms in adenine, cytosine, and O6 of guanine.
What impact does alkylation have on DNA?
Alkylation modifies DNA structure, disrupts hydrogen bonding, and leads to incorrect base pairing
This can prevent DNA replication and transcription.
What are the consequences of DNA alkylation?
Inhibition of DNA functions, DNA cross-linking, and increased cytotoxicity
Cross-linking can stabilize DNA abnormally, blocking essential cellular processes.
What is the mechanism of DNA alkylation by nitrogen mustards?
Formation of an aziridinium ion that reacts with nucleophilic sites on DNA
This disrupts the DNA double helix and prevents proper cellular function.
Why are bifunctional alkylating agents more cytotoxic than monofunctional ones?
They can form multiple cross-links in DNA
There is a strong correlation between interstrand cross-linking and cytotoxic effect.
What therapeutic implications do alkylating agents have?
Used in cancer chemotherapy to damage DNA and inhibit cancer cell proliferation
However, they can also affect normal cells, leading to side effects.
True or False: The electrostatic attraction is influenced by the strength of the charges involved.
True
Stronger charges result in stronger electrostatic attraction.
Fill in the blank: The aziridinium ion is a _______ intermediate in DNA alkylation.
reactive
It is key to the alkylation process.
