BIO222 CELL BIOLOGY CH 3.pdf

Remember – All organelles are cellular structures enclosed in membranes. Structure of the 1-Nuclear envelope It also called nuclear membrane surrounds the nucleus, it is formed by two Nucleus membranes (inner and outer) that fuse to form pores. The outer membrane has...

Remember – All organelles are cellular structures enclosed in membranes. Structure of the 1-Nuclear envelope It also called nuclear membrane surrounds the nucleus, it is formed by two Nucleus membranes (inner and outer) that fuse to form pores. The outer membrane has ribosomes attached to it. 2- Nuclear pores These pores allow small water-soluble molecules to diffuse freely through the nuclear envelope, but not large molecules. Nuclear transport receptors actively transport proteins through nuclear poses 3- Nuclear Lamina A network that provide support to the nucleus. The nuclear lamina is mostly composed of lamina proteins. 4- Nucleolus is a densely stained structure found in the nucleus. It is not surrounded by a membrane. One of the most important functions of the nucleolus is the synthesis rRNA and assembly of ribosomes. 5- Chromatin is DNA-protein complex found inside the nucleus. Two types of chromatin: 1) Euchromatin 2) Heterochromatin less compact DNA form more compact (condensed) contains genes that are frequently expressed by the cell. contains DNA that are not usually transcribed. highly condensed state of chromatin lightly compacted chromatin Visible through a light microscope Undergoes transcriptions Does not undergo transcription Found in both eukaryotic and prokaryotic cells Chromatin = Genes (or DNA) + proteins (histones) Chromatin: combination of DNA and proteins that make up chromosomes Chromosome: >> In cell cycle, chromosome is a tightly coiled form of the DNA-protein complex >> In molecular biology, "chromosome" simply means "the DNA strand and associated proteins" Chromatids: identical copies of the same chromosome ("sister chromatids"), joined by the centromere During interphase, chromosomes are enclosed inside the nucleus by the nuclear envelope Nucleosomes is a specific structure formed by DNA molecules and histone proteins. It is the basic unit of eukaryotic Chromosome structure. Nucleosomes contain DNA (147 nucleotide pairs long) and different types of histone proteins 6- Ribosomes are the components of cells that make proteins from amino acids Ribosomes are found attached to the outer nuclear membrane, and also on the rough endoplasmic reticulum (RER)