BIOL 122 1/25 Cells Cont.

What are the organelles involved in protein production and export?
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- 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
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
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).