Week 2 Molecular Genetics Flashcards
What is a gene?
A functional and physical unit of heredity made of DNA that usually codes for a protein.
What is the structure of DNA?
DNA is a double helix made of two antiparallel strands held by hydrogen bonds between complementary bases.
Which bases pair in DNA and how?
A pairs with T (2 H bonds), G pairs with C (3 H bonds). Purines pair with pyrimidines.
What is a nucleotide made of?
A sugar, a phosphate group, and a nitrogenous base.
What is the difference between purines and pyrimidines?
Purines have two rings (A and G); Pyrimidines have one ring (C, T, U).
How is DNA packaged in eukaryotic cells?
DNA wraps around histone proteins forming nucleosomes, which are further packed into chromatin and chromosomes.
What is DNA supercoiling?
Over- or under-winding of DNA to compact the molecule, especially in prokaryotes.
What is semiconservative replication?
Each new DNA molecule consists of one original strand and one newly synthesized strand.
What enzyme synthesizes new DNA strands?
DNA polymerase.
In which direction does DNA polymerase synthesize DNA?
5’ to 3’ direction.
What is the function of DNA helicase?
Unwinds the DNA double helix at the replication fork.
What problem does topoisomerase solve?
Relieves tension from supercoiling ahead of the replication fork by nicking and rejoining DNA strands.
What is the role of RNA primase?
Synthesizes short RNA primers to initiate DNA synthesis.
What are Okazaki fragments?
Short DNA fragments synthesized on the lagging strand during replication.
How are Okazaki fragments joined?
By DNA ligase, which seals the nicks between fragments.
What is the replisome?
A multi-protein complex that carries out DNA replication, including helicase, primase, and DNA polymerase.
What happens at the origin of replication?
DnaA initiator protein melts the DNA to start replication.
How is telomerase involved in DNA replication?
It extends the 3’ end of the DNA to allow complete replication of linear chromosome ends in eukaryotes.
