molecular genetics Flashcards
what are the differences between RNA and DNA
RNA (ribonucleic acid)
- single stranded
- uracil instead of thymine
DNA (deoxyribonucleic acid)
- double stranded
- thymine instead of uracil
what are the nitrogenous bases? which are pyrimidines and purines?
pyrimidines (single ring)
- thymine (DNA) [uracil in RNA]
- cytosine
purines (double ring)
- adenine
- guanine
what makes up a nucleotide?
Pi - sugar [ribose; 5C sugar, deoxyribose; ribose minus one oxegyn] - nitrogenous base [AUCG, ATCG]
how does DNA condense in eukaryotes?
- DNA gets wrapped around histones (protein)
- Organize histone packets into a nucleosome
- nucleosomes are looped
2 of those make a metaphase chromosome
how does DNA condense in prokaryotes?
super coiling
topoisomerase
relieves tension/prevents DNA from breaking (also known as gyrase)
helicase
cuts H-bonds (unzips DNA)
SSBP
(single strand binding proteins)
keep H-bonds from re arranging
DNA polymerase III
synthesizes new DNA strands
BUT
- cannot start on its own
- can only add new nucleotides to free 3 end
- only synthesized in 5 to 3 end direction (new strand goes 5 to 3)
primase
lays down RNA primer 5 to 3 for DNA polymeraise to start
what are telomeres? and what do they do?
protects eukaryotic genes from losing important DNA when primers are removed
telomerase: can restore telomeres BUT as you age telomerase is less active
DNA polymerase I and II
excises primers and replace with nuceotides + proofread and excise typos
ligase
makes phosopdiester bonds between DNA fragments (okazaki fragements)
what it the difference in the synthesis of the leading and lagging strands
the leading strand is synthesized continuously whereas the lagging strand is synthesized in okazaki fragments since DNA poly can only work off a free
what is more harmful a base pair substitution and a frameshift mutation? and why?
frameshift mutation because an addition or deletion of a base affect all the codons after
what are the three kinds of base pair substitutions?
base pair substitution: A instead of C (for example)
- nonsense: STOP codon
- missense: differents AA
- silent: no change (redundant codon)
what is a gene
section of DNA that codes for a protein
central dogma of biology???
gene – trancribed to — mRNA — translated to —protein (sequence of AA)
what enzyme is responsible for transcription?
RNA polymerase: reads the template strand from 3 - 5 so that mRNA runs 5 - 3
what direction do the coding and template strands run
template (anti sense): 3 - 5
coding (sense): 5 - 3
what does tRNA do
tRNA brings AA to the ribosome, it has anticodons specific to the AAs needed
in eukaryotes what needs to happen to the mRNA before entering the cytoplasm
mRNA modification:
- cap and tailing: GGGG cap and poly A tail
- splicing: SnRNPs exise the introns (non coding region)
- alternative splicing: introns are not always introns, regulated with regulatory proteins
why do eukaryotes need to do mRNA modification
because the mRNA starts to degrade in the cytoplasm and must be protected from that with the caps
splicing so that the ribosome creates the right protein
explain translation
- mRNA settles into P (peptide) site of the ribosome
- tRNA brings AA to A site (acceptor)
- ribosome makes peptide bond
- ribosome shifts (3 codons over)
- process repeats until stop codon)
exit site of the ribosome: tRNA id removed/leaves to get other AAs
