2.3 - Nucleic Acids Flashcards
Describe the structure of DNA.
Double helix, polynucleotide, macromolecule.
How is DNA organised in cells?
In eukaryotes - in the nucleus, wound around histone proteins, held as chromosomes.
Mitochondria and chloroplasts have prokaryote like plasmids, single, double stranded loop of DNA.
In prokaryotes - free in the cytoplasm, single, double stranded loop, no histones, naked DNA.
Plasmids free in cytoplasm.
What are nucleotides?
Monomers of DNA and RNA.
State the roles of nucleotides.
Phosphorylated nucleotides contain more than one phosphate group, e.g. adenosine di/triphosphate - the universal energy currency.
Regulation of biochemical pathways, e.g. cAMP.
Component of coenzymes, e.g. NAD - electron/proton carrier in respiration.
What components make up a nucleotide?
Deoxyribose (DNA), ribose (RNA).
Pentose sugar and phosphate group joined by a phosphodiester bond in a condensation reaction.
An organic nitrogenous base joined to the pentose sugar by a covalent bond formed in a condensation reaction.
What are the nitrogenous bases?
Adenine, Thymine, Uracil, Cytosine, Guanine.
Name the purines and describe their structure.
Guanine and adenine. Double nitrogenous ring.
Name the pyrimidines and describe their structure.
Cytosine, thymine and uracil (uracil replaces thymine in RNA). Single nitrogenous ring.
What is the base pair rule?
A pyrimidine always pairs with a purine. A always pairs with T (or U in RNA). C always pairs with G. A and T form two hydrogen bonds. C and G form three hydrogen bonds.
DNA strands are antiparallel - what does this mean?
The sugar phosphate backbones of each strand in DNA run in opposite directions.
The 5th carbon of the pentose is attached to the phosphate group This is the 5’ end of the molecule.
The third carbon on the pentose ring is free to bond with the 5th carbon of the next nucleotide.
This is the 3’ end of the molecule.
Nucleotides are added 5’ to 3’.
How is DNA structure related to its function, storing genetic information?
Long - can hold lots of information.
Coiled - compact so can store a lot of information in a small space.
Sugar phosphate backbone - strong bonds make DNA stable.
Many hydrogen bonds between complementary bases - give stability but easily broken to allow enzymes access for replication and transcription.
Code is universal.
Why is DNA described as universal?
DNA is the same in all living organisms.
What is the structure of mRNA?
Ribose sugar and phosphate backbone.
Organic nitrogenous bases, U replaces T.
Single stranded.
What are the 3 main types of RNA?
Messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA).
Compare and contrast DNA and mRNA.
DNA: long molecule; found in the nucleus; pentose sugar is deoxyribose; adenine, thymine, cytosine and guanine; double stranded, replicates to produce two identical molecules - semiconservative replication.
mRNA: shorter molecule; found in the nucleus and cytoplasm; pentose sugar is ribose; adenine, cytosine and guanine, uracil replaces thymine; single stranded; does not replicate, exists only for polypeptide synthesis then destroyed.