- most prominent feature of a eukaryotic cell
- it includes:
- the nuclear envelope - double membrane that surrounds the nucleus. Continuous with the endoplasmic reticulum. Often has ribosomes on its surface. Controls entry and exit of materials from and to the nucleus. Contains reactions inside the nucleus.
- Nuclear pores - allows the passage of large molecules like messenger RNA (mRNA) out of the nucleus. Around 3000 pores in each nucleus. Diameter of 40-100 nm.
- Nucleoplasm - the material that makes up the majority of the nucleus.
- Chromatin - The DNA found within the nucleoplasm. It is the "diffuse" form that chromosomes take up when the cell is not dividing.
- Nucleolus - The small spherical body within the nucleoplasm which manufactures ribosomal RNA (rRNA) and assembles the ribosomes.
- control centre of the cell, produces mRNA therefore begins protein synthesis.
- keeps the genetic material of the cell in the form of DNA or chromosomes.
- manufactures rRNA and ribosomes.
Mitochondria are rod shaped and 1-10 μm in length. They are made up of:
- Double Membrane - surrounds the organelle. Outer one: controls entry and exit of materials. Inner one: folded to form extensions called cristae.
- Cristae - shelf-like extensions of the inner membrane, some of which extend across the whole width of the mitochondrion. Provides a large surface area for the attachment of enzymes involved in respiration.
- The Matrix - makes up the remainder of the organelle. Semi-rigid, containing lipids, protein and traces of DNA that allows the mitochondia to control the production of their own protiens. The enzymes involved in respiration are found in the matrix.
Sites of certain stages of respiration. Responsible for the production of the energy-carrier molecule ATP from carbohydrates. the number and size of the mitochondria all increase in cells that have a high level of metabolic activity. Eg, muscle and epithelial cells (need it for active transport)
There are two types of endoplasmic reticulum (ER):
- Rough ER - has ribosomes on the outer surfaces of the membranes. FUNCTIONS:
- provides a large surface area for the synthesis of proteins and glycoproteins.
- provides a pathway for the transportation of materials, especially proteins, throughout the cell.
- Smooth ER - lacks ribosomes on its surface and is often more tubular in appearance. FUNCTIONS:
- synthesises, stores and transports lipids
- synthesises, stores and transports carbohydrates.
Cells that need to manufacture and store large quantities of carbs, lipids and proteins have extensive ER. Eg: Liver and secretory cells and epithelial cells which line the intestines.
Occurs in almost all eukaryotic cells. Similar to SER in appearance but its more compact. Proteins and lipids produced by the ER are passed through the golgi apparatus in sequence. Modifies them by usually adding a non-protein component to them. Also "labels" them allowing them to be accurately sorted and sent to their correct destinations. Once sorted they are transported in vesicles which move to the cell surface and fuse with the membrane to release their contents to the outside.
- add carbs to proteins to form glycoproteins
- produce secretory enzymes, such as secretory enzymes by the pancreas
- secrete carbs such as those used in making cell walls in plants.
- transports, modifies and stores lipids.
- forms lysosomes.
Golgi apparatus is well developed in secretory cells, such as epithelial cells that line the intestines.
Formed when the vesicles produced by Gogi apparatus contain enzymes such as proteases and lipases. Lysosomes isolate the enzymes from the rest of the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell.
- breaks down the material ingested by phagocytic cells, such as white blood cells
- releases enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell
- digests worn out organelles so that the useful chemicals they are made of can be re-used.
- completely breaks down cells after they have died (autolysis).
Especially abundant in secretory cells, such as epithelial cells and in phagocytic cells.
Small cytoplasmic granules found in all cells. May occur in the cytoplasm or be associated with the RER. Two types, depending on the cell which they are found.
- 80S type - found in eukaryotic cells (around 25nm diameter)
- 70S type - found in prokaryotic cells (slightly smaller)
They have two subunits, one large, one small. Each contain ribosomal RNA and protein. The occur in vast numbers (accounts for up to 25% dry mass of the cell)
Important in protein synthesis.
Finger-like projections of the epithelial cell that increase the surface area to allow efficient absorption.
RELATING CELL ULTRASTRUCTURE TO FUNCTION:
Each organelle has its own function. Therefore we can deduce the role of a cell by looking at the number of each organelle in contains.