central dogma of bio Flashcards
outline the central dogma
genetic info flows from
DNA –(transcription)–> RNA
–>(translation)–> proteins
where does DNA synthesis take place?
inside the nucleus of the cell
where does DNA transcription take place?
inside the nucleus of the cell (same as DNA synth)
structural features of cell nucleus
outer/inner nuclear membrane = nuclear envelope
outer continuous w ER
nuclear pores
DNA and proteins inside
nucleolus
describe the nucleolus and its purpose
25% of volume of nucleus, made of proteins and RNA
Site of ribosome synthesis:
transcribes ribosomal RNA (rRNA) and combines it with proteins to form ribosomes
describe DNA replication briefly
DNA strands unzipped
each strand acts as a template to form two complementary strands –> two identical daughter DNA double helices
DNA synthesis is catalysed by
DNA polymerase
how does DNA polymerase catalyse DNA synthesis
catalyses the stepwise addition of a base to the 3’ end of a chain
editing function - proofreads at the same time as polymerisation
nuclease clips off wrong nucleotide
DNA synthesis occurs in which direction
5’ –> 3’
bases added to 3’ end
what is the DNA daughter strand / lagging strand?
DNA synthesised only 5’-3’
daughter strand = continuously synthesised, leading
lagging strand = discontinuous Okazaki fragments, stitched together
role of DNA ligase
an enzyme that joins DNA strands together by catalysing the formation of a phosphodiester bond
joins Okazaki fragments
what is error prone replication
a strategy commonly used by viruses where nucleotides are synthesised without fidelity to mutate + evolve to avoid the host
common in RNA viruses
how can cells regulate the expression of each of its genes
by controlling the production of its RNA, and hence the amount of protein produced after translation
what is transcription
DNA –> single stranded complimentary RNA
DNA is transcribed by what enzyme?
RNA polymerase
(eukaryotic cells have three types, bacteria have 1)
how does RNA polymerase work
moves stepwise along DNA, unwinding a small portion just ahead of the active site for polymerisation
RNA chain extended in 5’-3’ direction
fast process, modest proofreading system
how is transcription initiation carried out
by RNA polymerase II
requires transcriptional activator proteins which bind to specific short sequences of DNA (eg. TATA box)
after the primary RNA transcript is produced what happens
(eukaryotic cells)
5’ capping
RNA splicing (removing introns)
3’ polyadenylation
–> produces resulting mRNA, matures as it is transported from nucleus to cytoplasm via nuclear pore complex
how is splicing of primary RNA transcript signalled and executed?
signalled by nucleotide sequences
a specific adenine nucleotide in the intron attacks the 5’ splice site, cutting backbone, covalently links, creating loop
3’ OH end of exon reacts w start of next exon, releasing intron sequence
describe alternative splicing and give an example of where it occurs
not always the same exons
–> generates a variety of transcripts from the same gene
eg. antibody reproduction
explain the main difference between bacterial and eukaryotic mRNAs
polycistronic - bacterial mRNAs contain instructions for several different proteins (ie, multiple sequence segments in one mRNA)
bacterial mRNAs 5’ and 3’ ends are unmodified
after transcription, where is mRNA located
in the cytoplasm, adjacent to the ER
mRNA function
messenger RNA
the final product of transcription
template for protein synthesis during TRANSLATION
tRNA function
transfer RNA
brings amino acids + reads genetic info during translation
rRNA
ribosomal RNA
along with proteins makes up ribosomes
catalyses translations
where are eukaryotic ribosomes assembled
in the nucleolus, where they associate with rRNAs
then exported to cytoplasm, coats ER
general structure of a ribosome
large and small subunits
A, P, E sites (amino acyl, peptidyl RNA and exit)
binding site for mRNA
how to ribosomes translate mRNA into proteins
two subunits join around mRNA 5’ end
mRNA pulled through, codons translated into amino acid sequence using tRNA to add each amino acid
structure of tRNA
a four leaf clover structure
one end is the anticodon, three consecutive nucleotides that pair w the complementary codon in an mRNA
the other end has single stranded 3’ region, attaches to matching amino acid
two loops to either side
role of tRNA synthetases
editing and proofreading to select the correct amino acid (highest affinity to active site) to attach to the 3’ end of the tRNA
after proteins are produced from translation and folded, how do they know where to go?
signal sequences
15-60 amino acids long, often removed from the finished portion once delivered
what is recombinant DNA technology
isolate + manipulate DNA segments of interest
can combine DNA of different species and produce new genes
circular double stranded plasmid DNA (cloning vector) cleaved with nuclease, DNA fragment to be cloned is ligated with DNA ligase
cell reproduces with the protein of interest.
what is the polymerase chain reaction
a simple way to selectively amplify specific DNA fragments with heat
Primer strands –> DNA synth catalysed by Taq polymerase (purified from thermophilic bacterium)
each cycle doubles amount of DNA
DNA sequencing methods
old method: four different chain terminating bases produces different sets of products, separated by electrophoresis. read bands.
Illumina dye sequencing: distinguishes base by size/ charge using reversible dye-terminators
producing cDNA
copyDNA, contains introns and exons
mature mRNA –> reverse transcriptase (viral) –> copies
back-produce double stranded cDNA
