OCR A-Level Biology Cell Structure Notes PDF

OCR (A) Biology A-level Topic 2.1: Cell Structure Notes www.pmt.education All living organisms are made of cells, there are several different types of cells, some of them sharing some common features. Human are made up of eukaryotic cells. All eukaryotic cells contain a nucleu...

OCR (A) Biology A-level Topic 2.1: Cell Structure Notes www.pmt.education All living organisms are made of cells, there are several different types of cells, some of them sharing some common features. Human are made up of eukaryotic cells. All eukaryotic cells contain a nucleus and membrane bound organelles. A more detailed structure of cells called the ultrastructure can be obtained by using a microscope. Ultrastructure of eukaryotic cells: Nucleus is surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus. The nucleus also contains chromatin and a nucleolus which is the site of ribosome production Rough endoplasmic reticulum which is a series of flattened sacs enclosed by a membrane with ribosomes on the surface. RER folds and processes proteins made on the ribosomes. Smooth endoplasmic reticulum is a system of membrane bound sacs. SER produces and processes lipids. Golgi apparatus is a series of fluid filled, flattened & curved sacs with vesicles surrounding the edges. Golgi apparatus processes and packages proteins and lipids. It also produces lysosomes. Mitochondria are usually oval shaped, bound by a double membrane called the envelope. The inner membrane is folded to form projections called cristae with matrix on the inside containing all the enzymes needed for respiration. www.pmt.education  Centrioles are hollow cylinders containing a ring of microtubules arranged at right angles to each other. Centrioles are involved in cell division. Ribosomes are composed of two sub units and are the site of protein production Lysosome is a vesicle containing digestive enzymes bound by a single membrane The cytoskeleton of the cell plays an important role in providing mechanical strength as well as aiding transport within cells and enabling cell movement. Protein transport: Proteins are produced on the ribosomes Proteins which are produced on the surface on RER are folded and processed in the RER The proteins are then transported from the RER to the Golgi apparatus in vesicles They are then modified in the Golgi apparatus Golgi apparatus packages proteins into vesicles to be transported around the cells o where they’re required. Some of the proteins such as extracellular enzymes leave the cell by exocytosis. Prokaryotic cells: Cell wall –Rigid outer covering made of peptidoglycan Capsule – Protective slimy layer which helps the cell to retain moisture and adhere to surfaces Plasmid –Circular piece of DNA Flagellum- a tail like structure which rotates to move the cell Pili- Hair-like structures which attach to other bacterial cells Ribosomes- Site of protein production www.pmt.education