from DNA to proteins Flashcards
what does bp stand for
base pairs
what does kDa stand for
KiloDaltons
1000 atomic mass units
one Dalton is the mass of an H atom, or 1/12 of a C atom
what does S stand for
Svedberg unit
refers to the mass and shape of cellular organelles
generally, high S means a larger mass
S values are not additive
eg bacterial ribosome (70S) consists of 50S and 30S subunits
compare strands in DNA and RNA
DNA is double-stranded with a complementary chain
RNA is single-stranded and any double stranding is usually with itself
what are the 3 types of RNA
mRNA
tRNA
rRNA
when do most mRNA species accumulate
following cell stimulation
how is mRNA printed
as a long linear transcript
it is then processed to the mature form in proximity of the nuclear membrane
structure of mRNA
has a 5”CAP and a 3” Poly Atail
what are 80S ribosomes composed of
4 main types of rRNA combined with proteins
have a 60S and a 40S subunit
what does tRNA do
carries amino acids to ribisomes
checks that they are incorporated in the right position
each tRNA only carries one amino acid
how many tRNA types are there
at least 20
are tRNA molecules big
no they are very small
what happens at tRNA anticodon
a triplet sequence pairs with mRNA
specific amino acid with a specific triplet codon
what does tRNA have at its 3’ end
an amino acid corresponding to the codon on mRNA which the anticodon of tRNA can base pair with
what is the structure of a tRNA molecule
distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover
anticodon on one end
amino acid attachment side on one end
has a D loop, T loop and variable loop
what initiates gene expression
Proteins called transcription factors (proteins which bind to promoter regions) find their way to specific sequences on the 5’ of the 1st exon (region call the promoter)
Promoter has a specific sequence of nucleotides - they do not code for proteins but instead act as binding sites - found at the 5’ end.
a “transcription complex” forms around the TATA box 5’ of 1st exon
helix opens, DNA strand sepeation
RNA Pol II starts building mRNA
outline process of transcription
- Topoisomerase unwinds the
double helix by relieving the supercoils. - DNA helicase separates the DNA apart exposing the nucleotides.
- SSB’s coat the single DNA strands to prevent DNA re- annealing
- Free mRNA nucleotides line up next to their complementary bases on the template strand/ antisense strand of DNA ( U-T & C-G).
- RNA polymerase (specifically RNA polymerase 2) joins
the mRNA nucleotides (catalysing phosphodiester bonds between them) to form and antiparallel mRNA strand ( with a 5’CAP head and a 3’Poly A tail) - starting at a promoter (specific sequence that RNA polymerase binds to - initiation of transcription. Transcription is stopped at the stop codon)
outline process of translation
- mRNA leaves the nucleus and attaches to an 80s ribosome
- At ribosome the mRNA (bases on mRNA are read in 3 - codon) sequence is used as a template to bind to complementary tRNA molecules at their anticodon (3 bases complementary to codon on mRNA). Ribosome reads mRNA codon by codon, one codon will code for a particular amino acid. This amino acid is brought by a specific tRNA molecule (carried on it 3’ end) since tRNA molecules are attached to specific amino acids. BASES ARE READ 5’ TO 3’
- Enzymes remove amino acid from tRNA and amino acids are linked together by a peptide bond (created by a condensation reaction), creating a polypeptide chain - a protein
what is the start codon
AUG
what are 3 stop codons
UGA
UAG
UAA
where is mRNA made
in the nucleus
how do ribosomes recognise mRNA
from its CAP on the 5’ end
what are the regions of a gene
exons
introns
promoter region
what are exons
they contain the coding sequence
what are promoter regions
what RNA polymerase recognises and where it starts
what is the mRNA primary transcript
the single-stranded RNA product synthesized by transcription of DNA, and processed to make mRNAs, tRNAs, and rRNAs. The primary transcripts designated to be mRNAs are modified in preparation for translation.
how does mRNA go from primary to mature
Non-coding (introns) are removed and exonic regions are joined
what does exon shuffling allow
new proteins to be made e.g the immune system.
so it enabled huge variants of antibodies etc. to be produced
what are the features of the genetic code (3)
- degenerate, but ambiguous
- almost universal
- non overlapping and without punctuation
what does it mean when the genetic code is degenerate but ambiguous
Many amino acids specified by more than one codon, but each codon specifies only one amino acid
what does it mean when the genetic code is almost universal
All organisms use the same code - fewer than 10 exceptions
what does it mean when the genetic code is non overlapping
Codons do not overlap. Each nucleotide is only read once
how is gene expression turned off
when repressors are activated
what are repressors
inhibitors of RNA polymerase binding
how do repressors turn of gene expression
- enzymes no longer activated
- transcription and processing proteins required for RNA transcription and or processing are no longer produced
what is silencing genes
DNA can be chemically altered to the methylated form i.e turned on or off (silenced)
* In a macrophage, where immunoglobulins are not produced, but still has normal DNA, the gene for producing immunoglobulins will be in the heterochromatin (can remember as h = hiding i.e. not active) state -
since its not needed to be synthesised thus in the heterochromatin state no transcription of these gene can occur
* Whereas in a B cell, that needs to produce immunoglobulins, that gene will be in the euchromatin state - so it can be transcripted and thus immunoglobulins (proteins) can be synthesised
