8. DNA+ Protein synthesis Flashcards
how many genes are found in mitochondrial DNA?
37
which enzymes twist and close the ends of a double-twisted DNA?
topoisomerase I and topoisomerase II
how is prokaryotic DNA put inside since they have no histones?
through supercoils
DNA-polymerase III (poly III)
the function of nucleases
enzymes that clave (split/divide) phosphodiester bonds in a nucleic acid
the function of endonucleases
cleave internal phosphodiester bonds
the function of exonucleases
remove nucleotides from the 5’ or the 3’ end
does helicase require ATP?
yes
what is the replicative helicase in E. coli called?
dnaB protein
which RNA is unstable?
mRNA
role of topoisomerase
untwists the helix form of DNA
role of helicase
recognizes the origin of replication and breaks hydrogen bonds by using ATP
what is the point where replication starts called?
replication fork
leading strand
3’ to 5’
lagging strand
5’ to 3’
SSB proteins
single-stranded binding proteins
role of SSB proteins
bind to the untwisted strands to keep them separated
in which phase are chromosomes most dense and in the shortest form?
metaphase, where chromatin is fully condensed
which form of chromatin is more dense and compacted?
heterochromatin
where are TELOMERS found?
at the ends of eukaryotic chromosomal DNA
what are telomeres?
special nucleotide sequences, with noncoding genes
functions of telomeres
- act as a buffer zone to postpone (not prevent) gene erosion at the ends of the DNA
- prevent the STAGGERED ENDS of daughter DNA molecules from activating transduction pathways, which can lead to the cell’s self-destruction
which enzyme keeps DNA from supercoiling during replication?
topoisomerase
At which end does PRIMASE synthesize PRIMERS?
at the 3’ end
which enzyme takes away primers?
exonuclease
In which direction does DNA-polymerase III run?
always 5’ to 3’
(moves along the old template strand in the 3’ to 5’ direction)
role of DNA ligase?
joins together Okazaki fragments of the lagging strand
which enzyme replaces RNA nucleotides of the primers with DNA nucleotides?
DNA polymerase I
which type of polymerases do prokaryotic cells contain?
DNA polymerase I
DNA polymerase III
which type of polymerases do eukaryotic cells contain?
DNA polymerase I
DNA polymerase III
alpha polymerase
delta polymerase
epsilon polymerase
stems
base-paired portions in RNA molecules
loops
unpaired portions in RNA molecules
which DNA strand is transcribed?
3’-5’
which enzyme unwinds DNA and transcribes the material to RNA?
RNA polymerase II
what is the condition that must be fulfilled so that RNA polymerase II can start its work?
A transcription factor must attach to the promoter
TATA box
important promoter DNA sequence
what is used in prokaryotes instead of a transcription factor?
a SIGMA factor
in what direction does mRNA elongate?
in the 5’-3’ direction
termination (transcription) in eukaryotes
RNA polymerase II transcribes a sequence on the DNA called POLYADENYLATION SIGNAL SEQUENCE that signals a polyadenylation sequence in the pre-RNA.
Then, proteins bind to it and cut free the mRNA free from RNA polymerase II
polyadenylation sequence of the mRNA is:
AAUAAA
termination (transcription) in prokaryotes
- transcription proceeds through a terminator sequence on the DNA
- The transcribed terminator serves as a signal causing RNA-polymerase to detach from DNA.
- The second step can be Rho-dependent or Rho-independent
what is added in the 5’ end of the RNA?
methylated guanine
functions of the 5’ capping?
- protects mRNA from ribonucleases in the cytoplasm
- recognises ribosomal units
- helps mRNA attach to the large subunit
what is added in the 3’ end of the RNA?
poly (A) tail
functions of the 3’ tailing?
- stabilizes mRNA
- interacts with proteins in the nuclear membrane to allow exit of mRNA from the nucleus
which molecule does the splicing of pre-mRNA?
SPLICEOSOME
what does spliceosome consist of?
snRNA and a large complex of proteins
the nucleotide sequence of the tRNA where the aa binds?
CCA
where does the specificity of a codon recognition lie?
in the tRNA, not the aa
which enzyme catalyzes the attachment of the aa to the tRNA?
aminoacyl- tRNA synthetase
aminoacylation
the process which attaches aa to the tRNA and requires ATP
is base-pairing between tRNA and mRNA complementary?
no
in which site does the first tRNA go?
the P site
in which site does the first release factor bind to the STOP codon (RF1)?
the A site
what does RF1 do to the peptide chain?
instead of an aa, it adds 1 molecule of water which breaks the bond between the tRNA in the P site and the completed polypeptide, which then leaves through the tunnel of the ribosomal large subunit.
silent mutations
changes in the base of the codon, but the new codon still codes for the same aa
missense mutations
changes in the base of the codon, which results in a different aa
may have little effect
nonsense mutations
changes a normal codon to a STOP codon
which enzymes cut bonds between aa?
proteases
proteolysis
destruction of unfunctional proteins, carried out by PROTEASOMES
where are proteasomes found?
in the nucleus and the cytosol
promoter
a site where RNA-polymerase can bind to DNA and begin transcription
Operator
on/off switch that controls whether RNA-polymerase has access to transcribe a gene or not
repressor
a specific protein produced by a regulatory gene, which binds to the operator
is the binding of the repressor to the operator reversible?
yes
allosteric proteins
has 2 shapes, one active and one inactive
what changes do histones undergo to make the genes accessible by enzymes?
acetylation- COCH3
methylation- CH3
phosphorylation- (PO3)2-
are transcription factors general or specific?
there are two types
general and
specific
