topic 2.6- structure of DNA and RNA Flashcards
what are nucleic acids?
polymers of nucleotides (eg DNA/RNA)
what do nucleotides consist of?
- a pentose sugar (5 C)
- a phosphate group (acidic, negatively charged part)
- a base (contains nitrogen and has 1/2 rings of atoms)
describe the structure of DNA
a double helix made of two antiparallel strands of nucleotides linked by H bonding between complementary base pairs
how are nucleotides in DNA linked?
by phosphodiester bonds between the sugar base of one nucleotide and the phosphate group of the adjacent nucleotide
what are the two strands in DNA described as?
antiparallel- they run in opposite directions,
- one strand in the direction 5’ to 3’
- one strand in the direction 3’ to 5’
adenine always pairs with …. why?
thymine; adenine can only make 2 H bonds and thymine only needs 2 H bonds to be stable
cytosine pairs with… why?
guanine; both make 3 hydrogen bonds
purines
adenine and guanine (2 rings)
pyrimidines
cytosine and thymine
(1) are used by the cell to package the DNA into structures called (2)
- histones
- nucleosomes
what does a nucleosome consist of?
- a central core of eight histone proteins (2 copies of 4 different types of histones) with DNA coiled around them.
- an additional histone protein molecule, H1, binds DNA to the core particle
what do nucleosomes do?
they help to supercoil DNA
give and explain 3 differences between DNA and RNA
- DNA contains deoxyribose sugar; in RNA it is ribose
- in DNA, there are two polymers of nucleotides, making it double stranded; in RNA, there is only one polymer of nucleotides, making it single stranded
- DNA bases are adenine, cytosine, guanine and thymine; RNA bases are adenine, cytosine, guanine and uracil
draw a diagram of DNA and RNA
elsewhere
