DNA Structure and Arrangement Flashcards
(23 cards)
Describe the double-helix structure of DNA.
DNA is composed of two polynucleotide chains coiled around each other in a double helix.
What are the three components of a nucleotide?
Phosphate group, deoxyribose sugar, and a nitrogenous base (Adenine, Thymine, Guanine, or Cytosine).
State the complementary base pairing rules for DNA.
Adenine (A) pairs with Thymine (T) via two hydrogen bonds, and Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
How is eukaryotic DNA arranged?
Linear DNA organized into chromosomes, where DNA wraps around histone proteins to form nucleosomes, which coil into chromatin.
How does prokaryotic DNA arrangement differ from eukaryotic DNA?
Prokaryotic DNA is circular and found in the nucleoid region, is more compact, and lacks introns.
What are plasmids in the context of prokaryotic DNA arrangement?
Additional circular DNA molecules that may carry accessory genes.
Describe the orientation of DNA strands.
They run in opposite directions: one from 5’ to 3’ and the complementary strand from 3’ to 5’.
Why is the antiparallel arrangement of DNA critical?
It is critical for enzymatic processes like replication and transcription, ensuring enzymes like DNA polymerase synthesize new strands correctly.
What type of process is DNA replication?
A semi-conservative process, where each new DNA molecule consists of one old (template) strand and one newly synthesized strand.
What is the ‘origin of replication’?
A specific sequence where replication begins.
What is the role of helicase in DNA replication?
It unwinds the DNA, creating a replication fork.
What is the role of single-strand binding proteins (SSBs)?
They prevent the unwound DNA strands from re-pairing.
How does DNA polymerase add nucleotides during replication?
It adds nucleotides complementary to the template strand.
Differentiate between the leading and lagging strands during DNA replication.
The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously as Okazaki fragments away from the replication fork.
What are Okazaki fragments?
Short DNA segments synthesized on the lagging strand due to the antiparallel nature of DNA, which are later joined by DNA ligase.
Why are Okazaki fragments necessary?
Because DNA polymerase can only add nucleotides in the 5’ to 3’ direction.
What is the role of RNA primer in DNA replication?
DNA polymerase cannot initiate synthesis on its own and requires an RNA primer, laid down by primase, to provide a free 3’-OH group for nucleotide addition.
What happens to RNA primers after synthesis?
They are later removed and replaced with DNA.
What are telomeres?
Protective, repetitive DNA sequences at chromosome ends that prevent loss of genetic information.
What is the ‘problem of replication’ at chromosome ends?
The lagging strand cannot be fully replicated, leaving a short gap at the chromosome end, leading to progressive shortening without intervention.
What is the function of telomerase?
An enzyme that extends telomeres by adding repetitive sequences, containing an RNA template to guide elongation.
In which cells is telomerase typically active?
Germ cells, stem cells, and some cancer cells.
What is the clinical relevance of telomerase dysfunction?
Telomerase dysfunction is associated with aging and certain diseases; its reactivation in somatic cells can lead to uncontrolled growth, as seen in cancer.
