Cell Biology 17Cell Biology 17- Organelle 1- Organelle 1stst

Cell Biology 17Cell Biology 17- Organelle 1- Organelle 1stst

Sung Youn Lee, PhD. StudentSung Youn Lee, PhD. StudentVeterinary collage, Room 320Veterinary collage, Room 32002 450 3719, 016 293 605902 450 3719, 016 293 6059

leevet@paran.comleevet@paran.com

The cell nucleus

Nuclear envelope• Nearly all of the cellular DNA in the nucleus in eukaryotic cell.• Bilayer :

– Inner membrane : contact with a meshwork of intermediate filament, the nuclear lamina

– Outer membrane : contiguous with the membrane of the endoplasmic reticulum (ER)

– Periplasmic space : between the inner and outer membranes• Components :

– DNA– RNA– Nuclear proteins (structural proteins, DNA and RNA polymerase, RNA-pro

cessing proteins, histones, and gene regulatory proteins) are synthesized in the cytoplasm on free ribosomes and are brought into the nuclear compartment.

• Nuclear pore : continues

Nuclear pore• Ions and small molecules (9nm diameter (<60kDa))

can pass through it. ==> prevent bulk exchage• 60kDa < nuclear protein ==> selective transport ac

ross the nuclear membrane, receptor mediated process

• Ex1, nucleoplasmin, 165-kDa, in frog oocyte nuclei– EM labeled with gold particle– COOH-terminal region (signal peptide)– ATP dependent

• Multistep pathway – GTP mediated

Structural protein of nuclear lamina &

matrix• 10nm filament --> square latticework• Lamin A• Lamin B – membrane-binding sequence, isoprenyl gro

up which allows membrane lipid attachment• Lamin C• Gene, alternative splicing (A,C) and distinct gene (B)• The biochemical function of the nuclear matrix is uncl

ear. – heterogenous nuclear RNA(hnRNA) are enriched in nuclear matrix --> RNAs don’t diffuse within nucleoplasm and they are bound to nuclear matrix as they are spliced to be mature form

1-condensation of chromosome2-breakdown of nuclear envelope

Lamin kinase-->Lamin A,B,C phosphorylate-->depolymerisation of nuclear lamina

Lamin B remains associated with nuclear envelopeLamin A & C are dispersed within theprometaphase cell.

Genome• Nucleus contains almost all of the genetic informa

tion of the cell in the form of DNA.• The total genetic information stored within the chr

omosome --> genome• 3 functional domains

– Origin : point of initiation– Kinetochore : attachment for mitotic spindle– Telomere : maintenance of chromosomal structure, CG r

epeats enriched• Chromatin : DNA + Protein (histone+nonhistone pr

otein)

Right handed corner= sex chromosome

Chromosomal protein

• Histone protein – only in eukaryotic cell– The most abundant protein– rich (+) charge arginine & lysine, so can bind to (-) char

ged DNA– 5 types histones ; H1, H2A, H2B, H3 and H4 --> nucle

osomal histones ; formation of nucleosome• Nonhistone protein

– Structural protein (HMG), regulatory protein (Fos, Myc), Enzymes (RNA & DNA polymerase)

Chromatin• Heterochromatin

– Highly condense– Transcriptionally inactive – Little heterochromatin is present in transcriptionally acti

ve cell (spermatozoa). – Lacated periphery and around nucleolus

• Euchromatin– More extended dispersed conformation– Transcriptionally active– Providing RNA molecules

Nucleolus• Dense nuclear organelle• Function ; Production of ribosomal subunits• 4 distinct regions

– Pale-staining fibrillar center / Dense fibrillar core or center(ribosomal gene transcription) / Granular region (assemble rRNAs with proteins) / Nuclear matrix

• The size and shape of nucleolus is dependent on its activity. – Cell, that synthesizing large amount of proteins, has the nuc

leolus may occupy up to 25% of the total nuclear volume.

Organelles involved in macromolecular

synthesis and turnover

Ribosomes• Ribosomes serve as catalysts of protein synthesis.• Small subunit (40S) and Large subunit (60S) form an

80S ribosome.• Membrane bound or free• Proteins synthesized at membrane bound ribosome

s ; integral transmembrane proteins, ER, Golgi complex, endosomal, lysosomal and secretory proteins

• Proteins synthesized at free ribosomes ; cytosolic proteins, peropheral membrane proteins, some nucleus proteins, mitochondria and peroxisomes.

Protein targeting1. Most transmembrane proteins and membrane lipids are sy

nthesized within the ER.2. The targeting of membrane proteins to specific sites such

as the ER, Golgi, lysosomes, or plasma membrane requires specific signal sequence within newly synthesized protein.

3. Default pathway : -ER associated ribosome ; ER --> Golgi --> secretory vesicles --> cell su

rface-free ribosome ; ribosome --> cytosol

4. To avoid a constantly increasing plasma membrane surface area, membrane is recycled by endocytosis.

Protein targeting• Pulse-Chase experiment

Radioactive amino acid [3H]leucine

pulse chase

Endoplasmic reticulum

• RER and SER• Except skeletal muscle, SER is continuous with the

RER. SER is referred to as the transitional elements. (buds off, vesicle, to Golgi apparatus)

• 50% of the total cellular membrane• Function

– Protein synthesis ; RER– Lipid synthesis ; RER and SER, phospholipids steroids, trigl

yceride– Detoxification ; cytochrome P450 electron transfer chain

Signal peptides

BIP ; binding proteinIn ER lumen, BIP binds to unfold protein andcatalyst protein folding

16~30 amino acids

Signal peptidase

Integral membrane protein

• Simple case(A); 20-30 hydrophobic amino acids in its NH2 terminal and it is not cleaved by signal peptidase / -COOH terminal is on the lumen

• Slightly more complicated case(B,C) ; two mechanism– Cleaved peptide on lumen– Similar to the mechanism of peptide into lumen

Into lumen – 內로 유도만함Intergral – 內 外

GlycosylationN-linked O-linked

Sugar bind Asn-NH2 Serine-OHThreonine-OH

Where? ER Golgi apparatusHow? 14-sugar and One-by-one

trime

Long-chain unsaturated hydrocarbon

Glycosylphosphatidyl-inositol anchors

Thank you for your attention ~Thank you for your attention ~