A1.2 Nucleic Acids Flashcards
DNA and RNA
genetic material of life, used as a blueprint for production of building blocks
DNA - double helical structure
Nucleotide
Phosphate sugar + 5 carbon sugar + nitrogenous base
DNA is made up of nucleotides to form a polymer
Nucleoside = sugar + base
Pyramidines and Purines
Pyramidines (single ring) - Cytosine, Uracil, Thymine
Purine (double ring) - Adenine, Guanine
Phosphodiester bond
Phosphodiester bond formed between OH group in the ribose sugar of nucleotide 1 and phosphate group of nucleotide 2 in the polymer (DNA)
DNA
- complementary base pairing using hydrogen bonding (weak) between bases
- strands bonded in antiparallel way
- palindromic sequence (reads the same backwards and forwards)
role of complementary base pairing
- ensures regular arrangement
- geometry with double helix allows an exact copy to be made in replication
1 turn of DNA has approximately 10 base pairs
RNA vs DNA
Both are nucleic acids, both are carrying a code (blueprint of life), required to build molecules, sugar (pentose), phosphate group, nitrogenous base, covalent bonds within molecules.
RNA:
1) single stranded
2) OH at 2’
3) uracil
4) short strands
5) found in cytoplasm usually with ribosomes
6) rRNA, tRNA, mRNA
DNA:
1) double stranded
2) H at 2’
3) thymine
4) long strands
5) nucleus, mitochondria, chloroplast and nucleoid and plasmid in prokaryotes
6) double or single stranded DNA, mitochondrial or plasmid DNA
genetic information
stored in the base sequence of one of two strands of a DNA molecule
any seuquence of bases is possible
directionality of RNA and DNA
linking between 3rd and 5th carbon
directionality is 5’ to 3’ direction
each strand has 5’ end with a terminal phosphate and a 3’ with a terminal hydroxyl group
in replication, DNA nucleotides can only be added to 3’ end of growing polymer because 5’ is already bonded to phosphate group
Nucleosome
DNA double helix
DNA wrapped around histone protein (nucleosome)
nucleosome coiled into chromatin fiber
chromatin
DNA double strand coils around histone protein to form nucleosome - supercoiling makes DNA denser so it takes up less space in nucleus.
Histone
Core composed of 8 histone proteins (positively charged)
Each octamer consists of two copies of different types of histones (H2A, H2B, H3, H4)
Nucleosomes linked by addition histone protein (H1)
Linker DNA connects one nucleosome to the next.
histone postive charge, DNA negative charge
DNA wraps around histone 1.6 times
Supercoiling
1) nucleosome helps supercoil and package DNA into smaller volume to fit in cell, results in compact structure (efficient storage)
2) helps protect DNA (less exposed to radiation, chemicals, etc), allow chromosomes to be mobile during mitosis and meiosis
3) helps control gene expression and DNA replication - for a gene to be transcribed it must be uncoiled
