Cellular organelles Organelles = membrane bound Cytoplasm and cytosol · Cytoplasm - Cell contents within plasma membrane (except nucleus) · Cytosol (blue region) Conc aq. gel around organelles Contains large and small molecules Site of many chemical reactions nucleus mitochondrion lysosome peroxisome cytosol nuclear envelope Golgi apparatus vesicle endoplasmic reticulum (A) (B plasma membrane > Most prominent organelle - (3-10um) > Characteristic of eukaryotes > Contains the genome - Chromosomes & proteins Site of DNA and RNA synthesis Contains sub-nuclear structures · Nucleolus (very prominent) V Site of ribosome production rRNA synthesis Not membrane bound V Variable in size depending on number of ribosomes produced (can be larger if a very active cell) Membrane-bound Chromosomes DNA comes in the form of chromosomes > Not always visible > Condense and become visible as a cell is about to divide (Nuclear membranes are made of a lipid bilayer) · Hydrophilic head and hydrophobic tails Nuclear envelope > A double lipid bilayer with pores where inner and outer membranes connect > Envelope is penetrated by pores > Pores act as gates to permit RNA, proteins & other molecules to move appropriately > Provides QC Only mature mRNA leaves the nucleus Cytosol Nucleus Nuclear support (cytoskeleton) 1 Supported mechanically by networks of intermediate filaments Outside V Inside the nuclear envelope = nuclear lamina Fibrous network DNA and associated proteins (chromatin) endoplasmic reticulum nucleolus centrosome intermediate filaments microtubule nuclear lamina nuclear pore 1 um outer nuclear membrane nuclear envelope inner nuclear membrane Figure 4-9. Molecular Biology of the Cell, 4th Edition. (There are some exceptions. Some cells don't have many organelles such as the nucleus. For example, haemoglobin. Some cells contain more than one nucleus such as skeletal muscles) Endoplasmic reticulum > Massive membrane system
> Interconnecting labyrinth of branches and flattened sacs > Contains over 50% of a cell's membrane > Continuous with nuclear envelope > Central role in biosynthesis and modification of lipids and proteins e.g. adding sugar to make glycoproteins Proteins for export, some organelles or the cell surface move into the ER whilst being made 1 Ribosomes needed on ER surface = ROUGH endoplasmic reticulum > We will talk later in the course about how proteins get into the ER Further sugar modifications occur here Packed in vesicles Exit 1 Cell surface ER SORTING · phosphorylation of oligosaccharides on lysosomal proteins · removal of Man · removal of Man · addition of GlcNAc · addition of Gal · addition of NANA · sulfation of tyrosines and carbohydrates SORTING cis Golgi network Golgi apparatus Smooth ER 1 ER without ribosomes > Abundant in cells involved in lipid metabolism e.g. steroid hormone production from cholesterol Often occurs within regions of RER A Also involved in Ca2+ storage V Involved in rapid cellular responses SMOOTH ROUGH >Ribosome coated > No ribosomes > Phospholipid synthesis > Lots in hepatocytes Protein modification and secretion Lots in specialized secretory cells like plasma cells Golgi apparatus Works closely with ER > Functions to process, pack & export >