Genu expression
DNS replication
Topic 4
Genu expression
Gene expression is the process by which
information from a gene is used in the
synthesis of a functional gene product.
These products are often proteins, but in
non-protein coding genes such as
ribosomal RNA (rRNA), transfer RNA
(tRNA) or small nuclear RNA (snRNA)
genes, the product is a functional RNA.
http://en.wikipedia.org/
Role of RNA and protein synthesis in a
cell
Transcription
Transcription is the first step of gene expression, in
which a particular segment of DNA is copied into
RNA by the enzyme, RNA polymerase.
During transcription, a DNA sequence is read by an
RNA polymerase, which produces a
complementary, antiparallel RNA strand.
•
http://www.youtube.com/watch?v=WsofH466lqk
http://en.wikipedia.org/
1.
2.
3.
4.
5.
6.
One or more sigma factors initiate transcription of a gene
by enabling binding of RNA polymerase to promoter
DNA.
RNA polymerase moves a transcription bubble, like the
slider of a zipper, which splits the double helix DNA
molecule into two strands of unpaired DNA nucleotides,
by breaking the hydrogen bonds between
complementary DNA nucleotides.
RNA polymerase adds matching RNA nucleotides that
are paired with complementary DNA nucleotides of one
DNA strand.
RNA sugar-phosphate backbone forms with assistance
from RNA polymerase to form an RNA strand.
Hydrogen bonds of the untwisted RNA + DNA helix
break, freeing the newly synthesized RNA strand.
If the cell has a nucleus, the RNA is further processed
(addition of a 3'UTR poly-A tail and a 5'UTR cap) and
exits to the cytoplasm through the nuclear pore complex.
http://en.wikipedia.org/
Actin
Nuclear myosin
Transcription
factor
Polymerase I
The result of transcription is messenger RNA
(mRNA), which will then be used to create
that protein via the process of translation.
The transcribed gene may encode for either
non-coding RNA genes (such as
microRNA, lincRNA, etc.) or ribosomal
RNA (rRNA) or transfer RNA (tRNA),
other components of the protein-assembly
process, or other ribozymes.
http://en.wikipedia.org/
Eukaryotic pre-mRNA processing
5' cap addition
5' cap A 5' cap (also termed an RNA cap, an RNA 7methylguanosine cap, or an RNA m7G cap) is a modified
guanine nucleotide that has been added to the "front" or 5'
end of a eukaryotic messenger RNA shortly after the start of
transcription. Its presence is critical for recognition by the
ribosome and protection from RNases.
Splicing
Splicing is the process by which pre-mRNA is modified to
remove stretches of non-coding sequences called introns; the
stretches that remain include protein-coding sequences and
are called exons. Splicing is usually performed by an RNAprotein complex called the spliceosome, but some RNA
molecules are also capable of catalyzing their own splicing
(see ribozymes).
http://en.wikipedia.org/
Editing
mRNA can be edited, changing the nucleotide composition of that
mRNA. An example in humans is the apolipoprotein B mRNA,
which is edited in some tissues, but not others. The editing creates
an early stop codon, which, upon translation, produces a shorter
protein.
Polyadenylation
Polyadenylation is the covalent linkage of a polyadenylyl moiety to a
messenger RNA molecule. In eukaryotic organisms all messenger
RNA (mRNA) molecules are polyadenylated at the 3' end. The
poly(A) tail and the protein bound to it aid in protecting mRNA
from degradation by exonucleases.
Polyadenylation occurs during and immediately after transcription of
DNA into RNA. After transcription has been terminated, the
mRNA chain is cleaved through the action of an endonuclease
complex associated with RNA polymerase. After the mRNA has
been cleaved, around 250 adenosine residues are added to the free
3' end at the cleavage site. This reaction is catalyzed by
polyadenylate polymerase.
http://en.wikipedia.org/
http://en.wikipedia.org/
RNA processing and splicing
http://www.youtube.com/watch?v=YjWuVrzvZYA
http://www.youtube.com/watch?v=FVuAwBGw_pQ
miRNA can
change
translation
Ribosomes
• Free ribosomes
• Free ribosomes can move about anywhere in the cytosol, but are
excluded from the cell nucleus and other organelles. Proteins that are
formed from free ribosomes are released into the cytosol and used
within the cell. Since the cytosol contains high concentrations of
glutathione and is, therefore, a reducing environment, proteins
containing disulfide bonds, which are formed from oxidized cysteine
residues, cannot be produced in this compartment.
• Membrane-bound ribosomes
• When a ribosome begins to synthesize proteins that are needed in
some organelles, the ribosome making this protein can become
"membrane-bound". In eukaryotic cells this happens in a region of the
endoplasmic reticulum (ER) called the "rough ER". The newly
produced polypeptide chains are inserted directly into the ER by the
ribosome undertaking vectorial synthesis and are then transported to
their destinations, through the secretory pathway.
Ribosomes in the cytoplasm and polysomes
attached to the endoplasmic reticulul (ER).
Ribosomes
http://www.youtube.com/watch?v=NJxobgkPEAo
Ribosomas pārvietošanās virziens
Žurnāls "Nature " 9/27/2001
Initiation
• Initiation
factors.
• Additional
information:
http://www.rpi.edu/dept
/bcp/molbiochem/M
BWeb/mb2/part1/tra
nslate.htm
Translation
1stage:
2stage :
3stage :
4. stage:
5. stage:
6. stage:
7. stage:
How many phosphates are
necessary to produce a
sigle polypeptide (100
amino acids)
Proteins after translation
http://www.sumanasinc.com/webcontent/animations/content/lifecycleprotein.html
Proteins of the secretory pathway are translocated into the endoplasmic reticulum
(ER) lumen co-translationally through proteinaceous channels in the ER
membrane called translocons. b | In the extremely crowded, calcium-rich,
oxidizing environment of the ER lumen, resident chaperones like BiP, calnexin
and protein disulphide isomerase (PDI) serve to facilitate the proper folding of the
nascent protein by preventing its aggregation, monitoring the processing of the
highly branched glycans, and forming disulphide bonds to stabilize the folded
protein. c | Once correctly folded and modified, the protein will exit the ER
through the formation of transport vesicles and move on through the secretory
pathway. d | If the ER quality-control system deems that the protein is malfolded
or unable to fold, it will be targeted for retrotranslocation to the cytosol and
degraded by the 26S proteasome. e | Changes in the ER environment shift the
balance from normal folding to improper folding (thicker arrow), leading to the
accumulation of unfolded proteins in the ER. This activates three ER-stress
sensors — IRE1, PKR-like ER kinase (PERK) and ATF6 — which initiate the
unfolded protein response. SRP, signal-recognition particle.
Secretory proteins
Ribosome
mRNA
signalpeptide
Ribosome
mRNA
translocator
receptor
peptidase
ER and N-linked glycosylation
mannose
glucose
POLYPEPTIDE
CYTOSOL
dolichol
dolichol
dolichol
OLIGOSACCHARIDE
LUMEN
N-acetylglucosamine
mannose
glucose
CYTOSOL
ER LUMEN
ER and turnover of ER resident proteins
Golgi complex and N-linked glycosylation
Phosphorylation of lysosomal proteins
Golgi complex and proteolysis of secretory proteins
DNA synthesis
DNA replication is the process of
producing two identical copies from one
original DNA molecule. DNA is composed
of two strands and each strand of the
original DNA molecule serves as template
for the production of the complementary
strand, a process referred to as
semiconservative replication.
Replicons
DNA replication and amount of DNA
• DNA content
changes intensity of
staining
• “x” axis – DNA
content
• “y” axis – number of
cells
2n
4n
DNA replication
Topoisomerase
DNA helicase
Lagging strand
Leading strand
Okazaki
fragment
RNA
http://www.youtube.com/watch?v=teV62zrm2P0
http://www.stmary.ws/highschool/science/APBIO/Heredity/DNA_replication.htm