Chapter 11 Genetic Organization in Higher Organisms

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Chapter 11

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그림 11-1

Mitochondria

Cytoplasm (cytosol)

Endoplasmic reticulum (ER) Cell membrane

Golgi body (apparatus)

Cytoskeleton Nucleolus

Nuclear membrane Lysosome

Centrosome

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Mitochondrion

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그림 11-3 Chloroplast

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Centromere

Telomere : Greek, telos (end) + meres (part) - located at the ends of eukaryotic chromosomes

consisting of a six base pair sequence repeated about 2000 times - protects the end of chromosome from destruction

- prevents rearrangement of chromosomes

Telomere General eukaryotic chromosome structure

Chromosome arm

Replication origin

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그림 11-5

During each replication cycle the chromosomes are shortened due to loss of the RNA primer

? replication

replication

replication replication

If cells divides without telomeres, they would lose the end of the chromosome

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Telomerase

: add a few of the six base

pair to the end of chromosome , or telomere

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However, telomerase is not active in most cells.

It certainly is active in stem cells( 줄기세포 ), germ cells( 생식세포 ), hair follicles( 모낭 ) and (worryingly) in 90% of cancer cells.

Aging and Cancer

“ 복제양 돌리는 같이 태어난 다른 양들보다 텔로미어가 짧았다 !!! ”

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Haploid ( 반수체 )

: possessing only a single set of chromosomes : prokaryotes (bacteria)

Back up your files!!

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Nucleosome : DNA + histone

: 200bp DNA + 9 histones

: core particle = 140 bp + 8 histones : remaining 60bp + 9^th histone

Histones are positively charged.

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Solenoid

: 6 nucleosomes

nucleosome

Each loop has

~50 solenoids

Miniband: 18 loops

Chromatid

: 1,000,000 minibands

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상자 1

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그림 11-10

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Gene structure in Eukaryotes : exon & intron

Coding DNA Non-coding DNA

Single-celled eukaryotes: intron << exon Higher eukaryotes: intron >> exon

cf) pseudogene: defective copy of a genuine gene

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RNA Polymerase No. Genes transcribed:

I genes for large rRNAs (housekeeping)

II genes which code for proteins III genes for tRNA, 5S rRNA and

some other tiny RNAs (housekeeping)

Transcription in Eukaryotes

RNA polymerase II requires accessory proteins, called transcription factors for its activity.

Transcription factors bind to & recognize specific sequences on the DNA (promoter & enhancer)

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 Transcription apparatus ( 전사기구 )

RNA polymerase II + transcription factors + TATA box factor + other factors

upstream element

TATA box

promoter

initiator box transcription apparatus

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그림 11-13

Upstream

element TATA box Enhancer sequence

3 regions of promoter

1. Initiator box 2. TATA box

3. Upstream element

Enhancer:

- Bind to specific transcription factors &

enhance the rate of transcription

- away from the gene (upstream or downstream from the promoter)

Initiator box

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• https://courses.lumenlearning.com/wm

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Role

: regulate gene expression by controlling transcription - A protein that binds to specific DNA sequences,

thereby controlling the rate of transcription of genetic information from DNA to messenger RNA.

- Transcription factors perform this function alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase to specific genes.

Transcription Factor

(sometimes called a sequence-specific DNA-binding factor)

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4 domains

1) Binding to a specific sequence on the DNA (DNA-binding domain, DBD)

2) Binding to the RNA polymerase II complex (Trans- activating domain, TAD)

3) Getting into the nucleus where the genes are kept (nuclear

Transcription Factor

(sometimes called a sequence-specific DNA-binding factor)

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Transcription factor MyoD

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Nrf2

 전사인자의 한 종류

 Nuclear factor E2 - related factor 2

 발알물질 / 독성물지에 대한 세포방어 메커니즘에서 중요한 역할

 제 2 상해독효소 및 항산화효소의 프로모터영역에 위치한

antioxidant response element (ARE)

에 결합하여 유전자 발현

해독효소 : glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase (NQO1),

항산화효소 : heme oxygenase (HO-1)

 Nrf2 K/O mice: 현저하게 낮은 수준의 제 2 상 해독효소 -> 발알물질에 취약

 Keap1 에 의해 조절

(for nuclear translocation & proteasomal degradation)



독성물질뿐만 아니라 천연항암물질에 의해서도 유도됨

(Kong et al 2001, Itoh et al 1997, Fahey et al 2002)

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Cellular membrane

Cytosol

Chemopreventive agents

Electrophiles, ROS

Nrf2

PI3K PKC MAPK

PERK ER stress

Nrf2 P

P

Degradation Nrf2

degradation degradation

Nrf2 P

degradation

Keap1 -S-S- Nrf2 -S-S-

Nrf2 pathway Nrf2 pathway

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NF-B

 전사인자의 한 종류

 Nuclear factor kappa B

 Most common NF-B is a heterodimer of p65 and p50

 COX-2 및 iNOS 등 염증매개 효소의 promoter 영역에 위치

 TNF- , IL-1, LPS, viruses, UV, oxidative stress 에 의해 유도

 Sequestered in the cytosol by IBs

 만성염증질환 및 암의 발생에 관여

 In most cells, its activation results in cell survival. 세포증식

(Baeuerle and Baltimore 1996, Siebenlist et al 1994, Karin and Ben-Neriah 2000)

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TNF

P P

IB

p50 p65

P P

IB ^p50

p65

IKK

IKK IKK

IKK

NIK

Ub Ub

IB

Proteolysis

Ubiquitination Phosphorylation

Cellular membrane

Cytosol

Nucleus

MEKK1/3 Inflammatory cytokines

Oxidative Stress, UV

TNFR

TRADD FADD

TRAF2

Ras RIP

PI3K AKT

p50 p65

P

Growth factors

p38 Chemopreventive

agents

NF- NF- B pathwayB pathway

P

IB

p50 p65

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그림 11-15

Splicing

: removal of introns

and joining exons 5’ 3’

Guanosine monophosphate (GMP)

 methylation

Poly(A) polymerase 100~200 adenines

AAUAAA primary transcript

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Guanosine monophosphate (GMP)

 methylation on guanine

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5’ Cap methylation

- mRNA capping is highly regulated and vital in the creation of stable and mature messenger RNA able to undergo translation during protein synthesis.

- Mitochondrial and chloroplast mRNA are not capped

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Poly A tail

nuclease

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snRNP “snurps”

: small nuclear ribonucleoproteins : proteins + snRNA

: U1, U2, U4, U5, U6

RNA splicing

: removal of introns : by spliceosome

Spliceosome

: macromolecular complex

which removes introns from RNA : proteins + snRNA

(small nuclear RNA)

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그림 11-19

Spliceosome recognizes both ends of the intron and binds to them.

 formation of loop

 Cutting and sticking Recognition : RNA of snRNP

Cutting and sticking: Protein of snRNP

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formation of loop Splice site

Branch site

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그림 11-21

Alternative splicing : variations in processing mRNA which allow more than on possible protein to be made from a single gene

1. alternative promoter

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Alternative splicing

2. alternative tail site selection

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그림 11-24

Alternative splicing 3. exon cassette selection

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Alternative splicing 4. trans-splicing

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그림 11-26

RNA editing

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Nuclear pore

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그림 11-28

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40S eukaryotic pre-initiation complex

Branch site

Initiator tRNA

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Regulation of gene expression

• The different cell types of a multicellular organism contain the same DNA.

• Neuron vs lymphocyte

• Cell differentiation depends on changes in gene

expression rather than on changes in the nucleotide sequence of the cell’s genome.

• examples : pancreatic β-cell – insulin hormone,

pancreactic �-cell – glucagon hormone, lymphocyte – antibodies, red blood cell – hemoglobin

• An individual cell specifies its many thousands of genes to express : differentiation

• By regulation of gene expression.

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Gene expression can be regulated at many of the steps in the pathway from DNA to RNA to protein.

(1) controlling when and how often a given gene is transcribed,

(2) controlling how an RNA transcript is spliced or otherwise processed,