storing and using DNA Flashcards
Describe the double-helical structure of DNA.
Where is it stored?
DNA is made up of polymers of nucleic acids.
Nucleic acids are made up of a phosphate group and 2’-deoxyribose sugar and a base (A-T, C-G)
The backbone is made up of phosphate and sugar. The two strands are held together by hydrogen bonds between the bases.
A-G are purines- flat and double ring
C-T-U are pyrimidines- single ring, flat.
Bases bind to the carbons 3 and 5 on the pentose sugar.
One strand will run from 3’ and the other from 5’.
DNA is contained in the nucleus- in chromosome- in chromatin.
Chromatin is condensed-heterochromatin- or extended- euchromatin.
Chromatin is most packaged up during metaphase.
Extragenic DNA- uncoding repeted sequences of DNA.
-Tandem: mainly found in telomere and centromere
a. satellite: 14-500 bp in 20-100kb
b.microsatellite: 15-100bp in 1-5 kb
-Interspred: makes up 45% of genome
a. short inter spread nuclear elements- found in ALU elements
b.long inter spread nuclear elements-Found in L1 elements
Describe the process by which DNA is replicated
Chromatin must be unravelled and histones removed:
-histones enzymatically modified
-histones displaced by chromatin remodelling complex.
DNA in the nucleus is unravelled by breaking the hydrogen bonds between the strands.
DNA polymerase forms new bonds between the DNA strand and free nucleotides according to complementarity.
The polymerase can only add nucleotides from the 3’ side of DNA. So DNA is copied from the 5’ to 3’ side- bi-directional.
Two new copies are formed- one old chain, one new one- Semi-conservative.
Describe how a base-sequence of DNA is transcribed into a base-sequence in RNA.
RNA polymerase forms singles strands of pre-mana from the DNA chains.
The pre-mRNA is sliced to remove non- coding sections of the sequence (introns).
Alternative splicing allows the exons to be rearranged in a variety of ways so that many different sequences can be formed.
Describe in outline the post-transcriptional processing of RNA.
Translation:
The mRNA is then transported into the cytoplasm.
tRNA in the cytoplasm binds to amino acids according to complementarity between the anti-codon on the tRNA and codon on the amino acid.
The rRNA (which codes for ribosomes) is also transported to the cytoplasm.
DNA is degenerate: Each sequence of 3 bases codes for an aminoacid. As there are 4 bases there are 64 different combinations but only 20 amino acids.
Methionine only has one codon sequence. It is the start signal for many amino acid chains.
Describe the translation of mRNA.
The amino acids are transported to the mRNA and new bonds are formed between two adjacent amino acids due to the ribosomes.
When the ribosome reaches a stop codon on the mRNA it detaches and the polymer is completed.
