BIOL 122 1/25 Cells Cont.

What are the organelles involved in protein production and export?
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What are the organelles involved in protein production and export?
Nucleus, ribosomes, rough ER, Golgi complex, and plasma membrane
Endomembrane
The membranes of the cell form an interconnected network.
Image: Endomembrane
First step of protein synthesis: get the message from the DNA in the nucleus
- DNA is enclosed in a double-layer membrane (nuclear envelope)
- Also contains a nucleolus (little nucleus) - where rRNA and proteins make ribosomes
- Site where DNA is duplicated
- where messenger RNA (mRNA) is transcribed- mRNA can exit the nucleus through nuclear pores in the nuclear envelope and travel to where proteins are made, the cytoplasm.
Image: First step of protein synthesis: get the message from the DNA in the nucleus
Nucleus
Image: Nucleus
2nd step of protein synthesis: translate
Ribosomes in the cytoplasm- mRNA finds ribosome and joins it. Ribosomes are made in the nucleolus, but function in the cytoplasm. Ribosomes site where the message (mRNA) is translated into amino acids (to make a protein)
- if the protein is destined for export, the ribosome will attach to the mass of membrane called the rough endoplasmic reticulum
3rd step of protein synthesis: process the protein
Rough endoplasmic reticulum, a series of flattened membrane sacs embedded with ribosomes.
Proteins are processed and folded in interior of rough ER, cisternal spaces.
Membrane of ER buds off to form balls containing proteins called transport vesicles.
Smooth endoplasmic reticulum
site of lipid and carbohydrate synthesis, detoxification of drugs in liver (morphene, codiene, phenobarbital)
4th step of protein synthesis: Sort and ship the new Protein
Transport vesicles from the endoplasmic reticulum fuse with Golgi complex.
Golgi modifies, sorts, and ships proteins to their final destination.
Exocytosis
Process where vesicles fuse with outer cell membrane for final export outside cell.
Organelles with endosymbiotic origin
mitochondria and chloroplasts
both:
-have their own DNA
-are involved in the production of cellular energy (ATP)
-are thought to be descendants of endosymbiotic bacteria
Mitochondriafound in almost all Eukaryotic cells (not found in one Protist group the Archaezoa, Giardiais one example)Chloroplastsfound in all photosynthetic Eukaryotes (algae and plants)What is the function of the mitochondria?produce ATPWhat is the function of chloroplasts?photosynthesisEndosymbiotic theoryMitochondria are descendants of free-living, oxygen-using bacteria that invaded eukaryotic cells 1.4 billion years ago.Important steps in evolution of eukaryotic cells1st evol. of endomembrane system 2nd Mitochondria 3rd ChloroplastsEvolution of endomembrane system and serial endosymbiosishappened in stagesEvidence for serial endosymbiotic hypothesisa) Existence of endosymbiotic relationships now b) Molecular evidence - comparisons of ribosomal RNA- similar in base sequence c) chloroplasts and mitochondria have many similarities with modern prokaryotesChloroplasts and mitochondria have many similarities with modern prokaryotes, explainedAbout the same size as modern prokaryotes Membranes have similar enzymes and transport systems to bacteria Mitochondria and chloroplasts replicate independly (binary fission) Genome of Mitochondria and Chloroplasts have circular DNA - not associated with proteins Ribosomes are more similar to prokaryotesLysosomesArise from the Golgi apparatus. A lysosome is a membrane-bound cell organelle that contains digestive enzymes.Primary lysosomeenzymes are not activity functioningSecondary lysosomelysosome fused with damaged organelle, digestive enzymes activated, toxic chemicals isolated- after fusing with food vesicle or organelle. H+ pumped into the lysosome, causes pH to fall, enzymes activated to hydrolyze molecules.Peroxisomeorganelle with various specialized metabolic functions; produces hydrogen peroxide as a by-product, then converts it to water- Enzymes that transfer H atoms from various molecules to O2 forming hydrogen peroxide H2O2 as byproduct (later broken down).