Eukaryotic Cells
1.A) Two main forms of cells exist: eukaryotic cells and prokaryotic cells. Prokaryotic cells are smaller and do not have membrane-bound nucleus or membrane- bound organelles, but do have: plasma membrane, cytosol and cytoplasm, and ribosomes. Prokaryotes contain much less DNA than eukaryotes and have circular chromosomes. Eukaryotic cells have information processing organelles, such as the nucleus which houses most of the cell’s DNA, and ribosomes which use information from DNA to produce proteins. In prokaryotes gene regulation begins during transcription. Transcription begins when RNA polymerase binds to the promoter. RNA polymerase then begins to separate the two DNA strands and initiates copying. Once this has occurred, a terminator sequence signals the end of the gene. The terminator sequence gets transcribed, RNA polymerase detaches, and mRNA is released. Translation in prokaryotes is coupled with translation. The moment a stretch of RNA is synthesized by RNA polymerase, ribosomes attach to it to make a protein. In eukaryotic cells, initiation begins when transcription factors bind to the promoter, followed by RNA polymerase II and TX factors. DNA strands separate and RNA polymerase II begins copying. After this, a polyadenylation signal sequence signals the end of the gene. The polyadenylation signal is transcribed, pre-mRNA is cleaved and released, and RNA II polymerase continues transcribing until it falls off. Eukaryotic cells continue to modify pre-mRNAs after transcription. Modifications to the ends of mRNA are made by the addition of guanine to the 5’ cap and a poly-A-tail to the 3’ cap. Following this RNA splicing occurs. Here noncoding regions (introns) of mRNA are removed and coding regions (exons) are joined. After this has taken place, the mRNA travels to the cytoplasm and mRNA degradation occurs, and translation begins. The genetic material forming the mitochondrial genome is similar in structure to that of the prokaryotic genetic material.