Genu expressionDNS 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. One or more sigma factors initiate transcription of a gene by enabling binding of RNA polymerase to promoter DNA.

2. 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.

3. RNA polymerase adds matching RNA nucleotides that are paired with complementary DNA nucleotides of one DNA strand.

4. RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form an RNA strand.

5. Hydrogen bonds of the untwisted RNA + DNA helix break, freeing the newly synthesized RNA strand.

6. 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

7-methylguanosine 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.

SplicingSplicing 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 RNA-protein complex called the spliceosome, but some RNA molecules are also capable of catalyzing their own splicing (see ribozymes).

http://en.wikipedia.org/

EditingmRNA 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).

http://www.youtube.com/watch?v=NJxobgkPEAo

Ribosomes

Žurnāls "Nature " 9/27/2001

Ribosomas pārvietošanās virziens

Initiation

• Initiation factors.

• Additional information:

http://www.rpi.edu/dept/bcp/molbiochem/MBWeb/mb2/part1/translate.htm

1stage:

2stage :

3stage :

Translation

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

signalpeptide

Ribosome

Ribosome

mRNA

mRNA

receptor peptidase

translocator

ER and N-linked glycosylation

LUMEN

CYTOSOL

OLIGOSACCHARIDE

POLYPEPTIDE

glucose

mannose

dolichol dolichol dolichol

ER LUMENCYTOSOL

glucose

mannose

N-acetylglucosamine

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

http://www.youtube.com/watch?v=teV62zrm2P0

Leading strandLagging strand

Okazakifragment

RNA

DNA helicase

Topoisomerase

http://www.stmary.ws/highschool/science/APBIO/Heredity/DNA_replication.htm