cell nucleus, import & export, control of gene expression

8/10/2019 Cell Nucleus, Import & Export, Control of Gene Expression

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Cell Nucleus:

The nucleus

Membrane bound structure conntaining genetic

material

It controls & manages cell activity

Function:

1.

Nuclear envelope :

- Separate genetic material from

cytoplasm & preventing them

from coming out from cytoplasm

- Attached to ER (Endoplasmic

reticulumn)

2.

Nucleoplasm:- Fluid inside nucleous

- Maintain the DNA

- Place where solute fo nucleus is dissolved

- Maintain the shape of nucleus

3. Nuclear matrix:

- Maintain DNA material

- Anchor of transcription & replication & splicing

- Portein containing fibrilar network

4.

Nucleolus:

-

rRNA synthesis

- assembling ribosome

5. Nuclear pore complez

- Help in transportation of imported & exported goods

The transporting of material


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Importing

o Import enzymes DNA Polymerase

(replication), RNA polymerase

(transcription), ligase, etc.

o Transported into the nucleus by the help of

importin (import protein) and NLS (nuclear

localization signal)

o PROCESS:

1) The imported goods CARGO bind

to NLS and importin SHUTTLE BUS (as nuclear filament only recognize importin)

with the help of Ran-GTP

2) The CARGO, NLS, and importin are tranported from cytoplasm to the nucleus

(out in)

3) Importin and NLS leaves the CARGOinside and comes out from the nucleus into

the cytoplasm to pick another imported goods

4)

Ran-GTPRan-GDP

Exporting

o

Export goods ions, mRNA, tRNA, rRNA (ribosome)

o Transported out from the nucleus by the help of exportin (export protein) and in some

cases also with the help of NES (nuclear export signal)

o PROCESS:

1) Exportin (as nuclear filament only recognize exportin) SHUTTLE BUS enter the

nucleus through the pores picking (binding) up (with) the exported goods CARGO


a.

If the CARGO is mRNAit has to be changed into RNP

(Ribonucleoprotein) and bind to NES (nuclear export signal) and exportin


b.

If the CARGO is rRNAit has to be changed into RNP

(Ribonucleoprotein) and bind to exportin with the help of Ran-GTP


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c. If the CARGO is tRNAit has to be changed into RNP

(Ribonucleoprotein) and exportin-t with the help of Ran-GTP

2) The CARGO(if RNA in the form of RNP), exportin or exportin-t, and/or NES are

tranported from nucleus into the cytoplasm (in out)

3) Exportin or exportin-t and/or NES leaves the CARGOoutside and comes in from

the cytoplasm to nucleus to pic another exported goods

4)

Ran-GTPRan-GDP


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The Chromosome & Telomere

Centromere

Determine if theres a correct number of

chromosome

Contain recognition site for protein used in cell

divisionMT (Microtubular protein)

o MT ensure that chromosome separate in

the right directon and place during cell

fivision


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Telomere

Function:

1) Determining shelf life of chromosome

2)

Work like 5 capprevent hanging part

of chromosome to attach to another

chromosome

3)

Make sure one chromosome did not

form any complex with another

chromosomeit is dangerous and

make chromosoem cannot be

segregated properly during cell division

Problem during replicationduring replication, DNA polymerase work from 5-3, synthesis of the

lagging (hanging) strand occurs through back-stitching mechanism that produce short fragment

of DNA, however no enough room for RNA primer to start the fragment of 3 end and the gap that

supposed to be filled by DNA polymerase after RNA primer is removed, therefore it is recognize as

a borken piece of DNA.

Enzyme Telomerase containing RNA-reverse transcriptase which is an enzyme containign RNA

sequence with DNA polymerase activity

IMPORTANTif not elongated, telomere too short, cell dies

HOW IT WORKS?

1) Part of RNA sequence hybridize with the single strand overhang on the DNA strand, leaving

a single stranded overhanging RNA sequence

2) DNA poly. Function of telomerase synthesize the DNA strand complementary to the RNA

strand in telomerase and translocate to the end of the newly synthesize stand3) RNA primase synthesize Rna primer near the 3 end

4) DNA poly. Fills the vacant region


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Control of Gene Expression:

Prokaryotes

Prokaryotes are simple organism so they control their gene expression selectively depending oncondition

TRANSCRIPTION

Operonsets of gene that can be controlled

2 TYPES:

1. Lac Operon

- it is negatively controlled operon (normally off but on when appropiate inducer is

present)

- when RNA polymerase come cannot do their job (transcription) due to repressor

(OFF)

- RNA polymerase can work if inducer (lactose) is present

o HOW: lactose change the structure of repressor thereby removing the

repressor & produce Beta-Galactosidae (enzyme) (ON)- 3 Types:

o Lac Z & Acodes for beta-galactosidae

o Lac Ylactose Permease

2.

Trp Operon

- it is posititvely controlled operon (normally on but off when appropiate inducer is

present)

Control of GeneExpression

Transcription

Lac Operon

Trp Operon

Translation Riboswitch


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- RNA polymerase can do their job (transcription) due to the absence of repressor

(ON)

- If repressor + corepressor (Tyrptophan) bind to promotor side RNA polymerase

cannot work (OFF)

TRANSLATION

Prokaryotes control its translation process by stopping it using RIBOSWITCH

HOW:

1.

translation process has produce enough amount of protein

2. metabolites are producedbyproduct that is produced when the target concentration of

protein needed for the cell is already reached (Ex: glucosamine)

3. metabolites attach to mRNAstop translation process by becoming an obstcle for the

ribosome


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- If CpG region is

methylated

Transcription is turn

off, CpG is off

- Big problem is when

non-methylated cpG

region attached to

promotor site in

ocncogeneif non

methylated

transcription is on

unregulated division

(Cancer)

2) HISTONE (Acetylation, deacetylation of lysine)

- Happen in lysine in histone

- Acetylated lysine = ON

o Enzymeacetylase

Acetyl attahced to lysine in histone histone will be less denseeasier

for RNA polymerase to read and do transcription

- Deacetylated lysine = OFF

o Acetyl did not attach to lysine in histone histone wil be dense hard

for RNA polymerase to read and transcription is prevented

Factors affecting the process

o

Activator- Transcription factor that bind in actovator site to help initiate transcription

o Repressor

- Preventing/inhibiting transcription

- 3 ways:

Masking BlockingDisplacing

1. masking the effect of TF (Transcription factor)

2.

blocking the TATA box

3. displacingkicking the presence activator, inhibiting transcription

- binding site of repressor (part of DNA sequence)

1.

Enhancer


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Can be located anwhere in the DNA sequence as long as it is in the

sequence Enhancerdid not carry codon which can product protein therefore

after transcripted to pre-mRNA it is removed & become part of intron

2. Silencer

2. PROCESSING LEVEL (pre-mRNA mRNA)SPLICING

Occur in splicing processo 1 Genedifferent result same location

EX: Pepatocykinin (skin cell) several protein (alpha, beta, gamma)

o 1 Genediferent result different location

EX: Calcitonin genecalcitonin (thyroid), CGRP (brain)

3. TRANSLATIONAL LEVEL

Once mRNA in cytoplasm no guarantee that the RNA will be translation

Make sure right mRNA is translated in right amount

3 ways:

1) Cytoplasmic localization

-

Happen during fetus (oocyte) development

- Its location determine the function of mRNA being translatied & how much mRNA

is being translated

2)

Selective inhibition of mRNA translation

- Eukaryoic can postpone translation depending on the situation

o EX: mRNA in cytoplasm of oocyte dormant until fertilization mRNA

translated into many regulatory protein

- The process (translation)can be prevented by inhibitory protein (disturb

translation process) & miRNA

o EX: human cell is subjected o stress protein kinase (hormone related to

the effectstress hormone) is activatedphosphoylate eIF2-GTP

block protein synthesis

3) Maintaining the life span of mRNA

- Stability of mRNA depends on 3 end UTR (Untranslated Region) which contain

sequence for binding site of protein stabilization (CCUCC)

o WHY?

Determine the length of poly-A-taillonger tail longer mRNA

more protein produced

If 3 UTR is mutatedmrNA is destabilized

4.

POST-TRANSLATIONAL CONTROL Cell can control how long a specific protein can survive

Protein stability is controlled by amino acid in N (amino) terminus, containing NH2


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Protein destroyed by enzyme, PROTEASOME

o Proteasomefound in nucleus & cytosol, destoy protein that is slected & marked for

destruction (i.e. abnormal, not needed, excessive, depending on condition)

Amino Acid in N-Terminus

o if arginine & lysine present in N-terminus short lived

o if it is phosphorylated recognize for destruction by proteasome

o if contain degronshort lived

cell nucleus, import & export, control of gene expression

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