1. nucleic acid, mutation, chromatin and gene expression

what is the function of nucleic acids

primary information-carrying molecules in cells

what are the two main classes of nucleic acids

deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

where is DNA located

in the nucleus

where is RNA located

synthesized in the nucleus and translocated in the cytoplasm

what is the basic structure of nucleic acids

long chainlike molecules composed of nucleotides

what is a nucleotide

building block of nucleic acids

what are the 3 components of nucleotides

nitrogenous base, pentose sugar (5 carbon), and phosphate groupw

what is a nucleoside

a nucleotide with out the phosphate

• base and sugar

what divides nucleic acids into DNA and RNA

pentose sugar

what pentose makes up RNA

ribose sugar

• OH (hydroxyl) on the 2 position

• normal sugar

what pentose makes up DNA

deoxyribose sugar

• lacks one O (deoxy) on the 2 position

• modified sugar

which nucleic acid is less stable

RNA is less stable than DNA

what are the two nitrogenous bases

purines and pyrimidines

what makes up purines

adenine and guanine

• “pure as gold”

• pair of fused rings

what makes up pyrimidines

cytosine, uracil, and thymine

• “cut the pyramids”

• single ring

the _____ in DNA is replaced by the ____ in RNA

• thymine

• uracil

what are the nitrogenous base pairings in DNA

• A with T

• C with G

what are the nitrogenous base pairings in RNA

• A with U

• C with G

what are nitrogenous bases attached to

sugar molecule

• attach in place of the -OH on the 1’ C in the sugar ring

bases attach to the sugar by _____

glycosidic bond

phosphate groups make nucleic acids _____

negatively charged

phosphate groups contains one or two _____

negatively charged O atoms

• negative charge helps in binding of proteins to DNA and allows DNA to remain straight when denatured because negative charges repel themselves

what makes up the backbone of nucleic acids

sugars and phosphates

• phosphate groups link the 3” C of the first sugar to the 5” carbon of the next sugar

what is a phosphodiester bond

phosphate forms two ester bonds

• bonds between sugars

what imparts directionality of nucleic acids

phosphodiester bonds

what are the two ends of nucleic acids

5’ and 3’

5’ end bears _____

a free phosphate group

3’ end bears _____

a free hydroxyl group (OH)

• where nucleotides are added

what kind of strand is RNA

single stranded

what kind of strand is DNA

double stranded

• antiparallel strands (opposite directions)

• orientation of the sugar molecules is opposite in the two strands

what is a double helix

• makes up DNA

• two linear strands that run opposite to each other and twist together

• connected through hydrogen bonds between pairs of nucleotides

the twisting of the DNA double helix and the geometry of the bases creates a _____ and a _____ that run along the length of DNA

• wider gap: major groove

• narrower gap: minor groove

bonds present in DNA

• hydrogen: between nitrogenous bases (weakest)

• glycosidic: between sugar and base

• phosphodiester: between sugar and phosphate

what is DNA supercoiling

over- or under- wiring of a DNA strand

what is positive supercoiling

more coiling, more compaction

what is negative supercoiling

unwinding, relaxed DNA

what is DNA supercoiling for

essential for several biological processes including DNA compaction, DNA metabolism, and likely gene expression

what do topoisomerases do

monitor and adjust DNA supercoiling

• create temp strand breaks

• solve topological problems of DNA by uncoiling and resealing

• facilitate protein interactions with DNA

• prevent excessive supercoiling

what are the two major types of topoisomerases

• type 1 topoisomerase: make a single break in one strand

• type 2 topoisomerase: make a break in both DNA strands

how does topoisomerase 1 work

makes a break in one of the DNA strands, wind or unwinds the DNA, and reseals the break

how does topoisomerase 2 work

• binds to the gate (G) duplex

• G duplex - topo 2 complex binds with transported (T) duplex

• ATP binds and promotes formation of the topological complex

• Mg²⁺-dependent cleavage of the G duplex

• T duplex passes through the gap

• G duplex is re-ligated and the bound ATP is hydrolyzed

what do topoisomerase inhibitors do

prevent repair and promotes cell death

what are the types of topoisomerase inhibitors

anti-cancer and anti-bacterial

mitochondria have _____

their own circular DNA

• each mitochondrion has several copies of the same circular DNA molecule

• about 5% of the mitochondrial proteins are encoded by the mitochondrial DNA

what are the major types of RNA

• mRNA: messenger

• rRNA: ribosomal

• tRNA: transfer

what is mRNA

• synthesized from a DNA template by transcription

• serves as intermediary between DNA and protein

• codes for proteins

• carries the message from the DNA (genetic info)

what is rRNA

• stable RNA molecules

• 60% of ribosome’s mass

• ensures the proper alignment of mRNA, tRNA, and ribosome during protein synthesis

what is tRNA

• stable RNA with extensive intramolecular base pairing

• contains an amino acid binding site and an mRNA binding site

• carries the correct amino acid to the site of protein synthesis in the ribosome