Chapter 1 Flashcards
Which bases are purines?
Guanine and Adenine
Which bases are pyrimidines?
Cytosine and Thymine
How many bases does one “turn” contain?
About 10 and is 34Å long
What forms of DNA exist?
B-form, aqueous and low salt conc.
A-form, high salt conc. 11bases
Z-form, 12bases
How may genes does bacteria have?
About 1000genes on 1chromsome in the circular molecule
What is supercoiling?
In bacteria, the double helix undergoes supercoiling to condense it. Supercoiling is induced by the enzyme DNA gyrase, which twists the DNA in a left-handed direction so that about 200 nucleotides are found in one supercoil. The twisting causes the DNA to condense. Extra supercoils are removed by topoisomerase I.
What are histones?
Eukaryotic DNA is wound around proteins called histones first. Histones have
a positive charge to them and this neutralizes the negatively charged phosphate backbone. DNA plus histones look like beads on a string and are called chromatin. Each bead or nucleosome has about 200 base pairs of DNA and nine histones, two H2A, two H2B, two H3, two H4, and one H1. All the histones form the “bead” except for H1, which connects the beads by holding the DNA in the linker region.
?What happens at non-expressed regions
In regions that are not expressed, the histones are condensed, preventing other proteins from accessing the DNA (this structure is called heterochromatin).
What enzyme replicates the DNA?
DNA polymerase
What are bacteriocins?
A form of toxin that bacteria secrete to kill neighboring bacteria
What bacteriocin does E.coli produce?
Colicin, that either puncture the cell membrane thus leaking the ions, or either encode nucleases that degrade DNA and RNA.
Why do these not affect the host cell?
Because the cell also creates immunity proteins that neutralize it.
What are plasmids?
Small rings of DNA that are extrachromosomal that are present in the cytoplasm.
What do plasmids do?
They contain genes that can e.g. code for colicin production.
What does diploid mean?
They have two homologous copies of each chromosome.
