?

Log in

No account? Create an account

Previous Entry | Next Entry

Organ Systems I, Organelles


RIBOSOME

The ribosome is made of proteins that are transcribed from the DNA and folded into the ribosomal component parts in the nucleolus. The two subunits are known as 60s and 40s. The 60s subunit is made of 50 proteins and 3 types of rRNA. The 40s is made of 30 proteins and 1 rRNA. The s refers to the Svedberg unit, which is based on sedimentation during centirfugation.

If a ribosome is floating free in the cytoplasm ("free polysomes") the proteins it makes are designed for the nucleus, peroxisomes and mitochondrial membranes. If it's attached to the ER then it's making secretory and membrane proteins.

ENDOPLASMIC RETICULUM

The ER comprises more than 50% of the total membrane in eukaryotic cells. There are two kinds: rough and smooth.

ROUGH ER (is the site of N-linked glycosylation)

The ribosomes (which make it rough) are attached to the cytosolic side. It has cisternae---wiggles and squiggles. The ribosomes are cranking out proteins, and the rER adds stuff to make glycoproteins. It does N-linked glycosylation....transfers preformed mannose rich oligosaccharides to the asparagine side chains. The glycosylation pattern allows us to trace a protein through the intracellular compartments back to its origin.

More on N-linked glycosylation--on the insertion of membrane proteins into the ER membrane: When N is linked on the inside of the original membrane, the transport bud has the N inside. When the exosome merges with the next membrane, the N is outside, and the C end is on the inside.
Type I protein - cross membrane 1 time, N-terminus in lumen
Type II - cross membrane 1 time, C-terminus in lumen
Type III - crosses membrane several times

SMOOTH ER

Detox happens here, via hydroxylation reactions (esp in the liver). Water insoluble compounds such as steroids, alcohol, drugs and insecticides are toxic at high concentrations, and by adding a hydroxyl group (using cytochrome P450) you can make these lipids water soluble so they can be excreted. Conjugation reactions also happen here, which adds other polar groups (such as sulfate or glucaronic acid) to toxic water insoluble molecules. Also glycogen degradation and gluconeogenesis happens here, this is the Krebs cycle happening in the smooth ER.

Lipoproteins are assembled in the smooth ER, as well as lypolysis.

The smooth ER is the same thing as the sarcoplasmic reticulum in striated (skeletal and cardiac) muscle. It's involved in sequestration and release of calcium ions, which control muscle contraction. When Ca+ is released it diffuses to adjacent myofibrils, binds to toponin C, and kicks off a contraction.

GOLGI APPARATUS

The golgi is comprised of stacks of disc shape cisternae, from which vesicles bud off. The cis side faces the rER, the trans side faces the cell membrane. There are different enzymes in different parts of the stack.

The golgi functions to sort new proteins and lipids, do n-linked glycosylation (same as the rER) as well as modifying glycosylations that came from the rER, and is the only site where o-linked glycosylation happens. O-linkied oligosaccrharides are attached to the hydroxy group on the side chain of serine, theonine or hydroxylysine. More functions of the golgi include packing, concentration and storage of secretory granules or veiscles.

Diseases associated with malfunctions of the golgi include I-cell disease, in which hydolase enzyme are sent to the wrong destination where they are secreted instead of going to the lysosome where they belong. It results in clusion bodies--glycoconjugates in lysosomes. Another disease of golgi origin is hyperproinsulinemia. Normally pro-insulin is cleaved to insulin in the sER, but lacking the petidase that cleaves pro-insulin leaves too much of it in the system. This results in clinical manifestations as seen with NIDDM (type 2 diabetes mellitus).

LYSOSOMES

L's are the garbage disposal of the cell. They are small, membrane bound vesicles that bud off the golgi. They degrade cellular material (including DNA, RNA, lipids, clycoconjugates, proteins and peptides, dephosphorylators) with some 60+ hydrolytic enzymes. These enzymes function at a low pH of around 5.0, which makes them harmless in the cytoplasm. They also do something called "recall endocytosis" in which a lysosome fuses with an endosome, degrading extracellular material as well. And it will also help the cell keep house via autophagy--will consume degraded organelles.

ENDOSOMES/EXOSOMES

Endosomes bud into the cell via the plamsa membrane, exosomes bud off the golgi and go out of the cell. Just another means of transport in and out of the cell.

PEROXISOMES

Peroxisomes contain oxidative enzymes such as catalase, D-amino acid oxidase and uric acid oxidase. They make H2O2 thus the name, by transferring hydrogen from organic substrates to oxygen. They also take H2O2 apart to H2O and O2 (via a catalase). They oxidize urate, D amino acids (we have L form, D's are from bacteria), and very long fatty acid chains. They beta-oxidize fatty acid chains longer than 24 carbons.

There are lots of diseases associated with deficiencies of this system. Accumulation of bile precursors, failure to oxidize long fatty acid chains, and a list of other diseases the names of which I'm not worried about just yet.

MITOCHONDRIA

Similar in (small) size and (cigar) shape to bacteria, AND they reproduce by dividing! They vary in number based on cell type and metabolic activity. The liver has lots of them, 700-1000 per cell, each with a half life of around 10 days. So in a month we have each completely replaced our liver mitochondria!! This organelle uses pyruvate to make ATP.

The outer membrane around a mitochondria has porins--an integral membrane protein that allows molecules less than 10KD to pass right through. The inner membrane is impermeable to most small ions (Na+, K+, H+) and small molecules (ATP, ADP, pyruvate), and contains a lipid called cardiolipin. The inner membrane has folds called cristae to increase its surface area, and there are more folds when there is more metabolic activity.

The space between the two membranes contains enzymes that use ATP to phosphorylate other nucleotides. The space inside the inner membrane contains a matrix with dehydrogenases, DS DNA genome, RNA, ribosomes and intramitochondrial graules containing calcium and magnesium. Are these things stored here ?

Profile

moon
liveonearth
liveonearth

Latest Month

April 2019
S M T W T F S
 123456
78910111213
14151617181920
21222324252627
282930    

Tags

Powered by LiveJournal.com
Designed by chasethestars