Nucleic acids

nucleotide

monomer unit of nucleic acids

composed of organic base, pentose sugar and phosphate

polynucleotide

many nucleotides joined by phosphodiester bonds

ribosomes formed from?

RNA and protein

how is the chain held together?

phosphate group of each nucleotide is linked to the sugar of the next by phosphodiester bonds- this forms the sugar phosphate backbone

what is the structure of DNA?

deoxyribose- pentose sugar

nitrogen containing organic base- adenine, guanine, cytosine or thymine

phosphate group

what does DNA consist of?

two polynucleotide chains or strands, one running in the opposite way to the other (anti-parallel), twisting to form a double helix

how are the bases in each strand held together?

by hydrogen bonding

how many hydrogen bonds do the complementary bases form with each other?

adenine- two bonds with guanine

cytosine- three bonds with guanine

how can an analysis of a piece of DNA tell you if it was single stranded?

not equal proportions for A&T and C&G

not equal proportions of purines and pyrimidines

which bases are purines and which bases are pyrimidines?

purines- adenine and guanine

pyrimidines- thymine and cystosine

how does the structure of DNA relate to its function?

sugar phosphate backbone/double helix- provides strength + stability

double stranded- replication occurs semi-conservatively (both strands can act as templates)

complementary base pairing- allows accurate replication

weak hydrogen bonds- DNA strands separate easily for replication

sugar phosphate backbone- protects internal bases

helix- compact

specific base sequence- allows info to be stored

many hydrogen bonds- stable/strong molecule

what is the structure of RNA?

short

single stranded polynucleotide

pentose sugar; ribose

nitrogenouse organic base- adenine, cytosine, guanine or uracil

phosphate group

what are the three types of RNA?

mRNA

tRNA

rRNA

What is the process of semi conservative replication?

DNA helicase unwinds DNA strand, breaking hydrogen bonds

both strands can act as a template

free floating nucleotides attach to the exposed bases by complementary base pairing

DNA polymerase joins adjacent nucleotides, forming phosphodiester bonds

each new DNA molecule consists of one old strand and one newly synthesised strand

what are the three different models of DNA replication?

conservative- entirely new molecule synthesised from DNA template

semi conservative model- each new molecule consists of one newly synthesised strand and one template strand

dispersive model- new molecules are made of segments of new and old DNA

how was it tested?

DNA molecules prepared using heavier 15N and then induced to replicate in presence of lighter 14N

what happened after the first division?

DNA molecules found to have a mix of 15N and 14N, disproving the conservative model

what happened after the second division?

some molecules of DNA were found to consist solely of 14N, disproving the dispersive model