4. Additional Conformations of DNA

C-value paradox

no correlation between the amount of DNA and the apparent complexity of organisms

c

Dna/ haploid cell

prokaryotic organisms contain

only non-repetitive dna

absolute content of non-repetitive dna increases with

genome size, plateaus at ~ 3 × 10^9 bp

better def of biological complexity

size of functional and non-repetitive section of a genome

hypothesis

increase in size of the unique part of a genome is due to positive feedback mechanisms during evolution

denaturation of circular dna

1. in vivo, nicking occurs naturally during dna replication

2. can be induced experimentally by using an enzyme

primary structure of dna

sugar-phosphate chain with purine and pyrimidine bases as side chains

secondary structure of dna

double helical structure (h bonnding) stacking interactions, phosphate backbone outside

tertiary or higher order structure

dsDNA (both circular and linear) makes complexes with proteins - super coil

supercoils reduce stress on dna by

twisting/untwisting the double helix

topological isomers

dna differing only in their states of supercoiling, a circular dna without any superhelical turn is known as relaxed molecule

dna helix becomes topographically linearized

locally uncoiled during replication and transcription

mrna

specifies order of aa during protein synthesis

trna

during translation mrna info is interpreted by trna

rrna

combined with proteins aids trna in translation

small RNAs

variety of regulatory functions

Rnas with enzymatic functions

ribozymes (splicing, and peptide bond formation during protein synthesis)

rna can be single or double stranded

linear or circular

unlike dna, rna can exhibit

different conformations

RNA 2’OH group prevents formation of B-helix

a-helix formed

G:U additional non-watson and crick base pairing possible in rna

enhances potential for self-complementarity in rna

tertiary atructure in RNA

formed thorugh interactions of secondary structures: lack of constraint by long-range regular helices means rna has high degree of rotational freedom in backbone of its non-base-paired regions → capable of folding into complex tertiary structures

formation of unconventional ___ in rna

triple base pairing is possibile

pseudoknots can form due to base-pairing between

sequences that are not adjacent t

telomerase rna

has pseudokntos

additional conformations in tertiary structure in rna

1. a-minor motif

2. tetraloop motif

3. ribose zipper motif

4. kink-turn motif

5. kissing hairpin loop motif

proteins that are membrane bound or are destined for secreation

synthesized by ribosomes assoicated with the membranes of the er

the er associated with ribosomes is

termed rough er