Cell organelles Flashcards
What is one theory on how the membrane developed?
The DNA was stuck to the cell membrane. Eventually, the membrane invaginated and form a vesicle. Extra membrane layering may have been a primative ER.
What are the evolutionary benefits of having membrane bound organelles (4)?
- Surface area
- Directed protein flow
- Compartmentalization
- cell waste breakdown
How much membrane is cell membrane vs organelle membrane?
2 to 98%
How much of the cell is cytosol vs membrane bound?
50/50
What are the two classifications of organelles?
Membrane- golgi, ER, mitochondria, lysosome, perioxosomes, vesicles
Macromolecular- ribosomes, proteosomes
Where are mitochondria found in the cell?
Often found in areas with the highest energy demands. They are often associated with MTs
Describe how mitochondria make energy.
The CAC occurs inside the matrix and takes Acetyl-CoA from cytosol and turns it into CO2 and the energy carriers FADH2 and NADH. NADH and FADH2 go to the intracellular membrane where they donate electrons to a series of 3 protein complexes, which pump H from the matrix into the intramembrane space (against the diffusion gradient). As the H ions return to the matrix, they pass the membrane through ATP synthase, spinning it. ATP synthase turns the kinetic energy provided by the H into ATP. It can produce as much as 100 ATP/sec.
What is unique about mitochondria as an organelle?
It contains its own DNA/ribosomes/ribosomal proteins. The copies of DNA vary widely and are inherited maternally. Most malfunctions of mitochondria occur b/c of a problem with mtDNA.
What is MERRF?
ragged red fibers- occurs b/c of mtDNA mutation to tRNA lysine.
Describe the composition of ribosomes.
Two subunits, one large and one small, each made up of a combination of protein and rRNA. The large catalyzes the new peptide bonds whereas the small is the framework for the mRNA.
Describe how translation occurs.
Ribosomes have 4 bindings spots- 1 for mRNA and 3 for peptides (A,P,E). mRNA in the A site has codon “read” and matched with appropriate tRNA. P spot AA has its carboxyl end bound to amino end of new A spot AA. Large subunit translocates relative to small, moving the two AA into the E and P spots. Small subunit translates 3 bases. tRNA in E slot is removed and new tRNA enters the A spot.
In what direction is mRNA translated?
5’ to 3’
In what direction are AA read?
N terminal to C terminal
How is where a protein is made related to where it will eventually go?
Membrane bound proteins or proteins that will be exocytosed are made in ribosomes associated with the rER. Cytosolic proteins are made by free ribosomes.
What are polyribosomes?
Found both in free and membrane ribosomes, they are a collection of ribosomes working on the same mRNA.
What is the importance of the difference between eukaryotic and prokaryotic ribosomes?
Prokarytoic subunits are smaller, and because they are different from eukaryotic ribosomes, they can be selectively targeted therapeutically.
What are chaperone proteins?
They assist in the folding of new proteins.
What are proteasomes?
They degrade damaged or incorrectly folded proteins tagged with ubiquitin.
What is the significance of ubiquitin?
Ubiquitin marks things for destruction by proteasomes. The proteasome cap recognizes the ubiquitin, and ATP is used to denature the protein and draw it into the proteasomes active site.
Where does the ER originate?
Its lumen is continuous with that of the nuclear envelope
What are the purposes of the smooth and rough ERs?
Smooth ER
synthesize phosphlipids, glycolipids, cholesterol (steroids and lipids)
break down cytochrome p450
Ca sequestration
Rough ER
protein sorting and synthesis
How do the contents of the ER move throughout it?
Diffusion and vesicle transport.
What are the defining features of the Golgi?
Cis (close to nucleus) and trans (away from nucleus) face
What are the three ways out of the golgi?
Receptor mediated secretory vesicle transport
Recemptor mediated endosome/lysosme
Constitutive vesicle release
What are peroxisomes?
Oxidize substrates- forms h202 and breaks it down
beta oxidation of fatty acids
abundant in liver and kidneys
important for myelin sheath formation and ethanol breakdown
Why did organelles develop?
It was necessary to increase the surface area of membrane relative to the overall size of the cell
