A Level Biology Revision "The Endoplasmic Reticulum and Golgi Apparatus"

[Music] hi and welcome back to free science lessons by the end of this video you should be able to describe the roles of the roof on smooth endoplasmic reticulum and the Golgi apparatus in the last video we looked at the role of the nucleus and protein synthesis in the first stage of protein synthesis mRNA is produced by the gene for that protein this process is called transcription and it takes place in the nucleus the MRNA then passes through a nuclear pore into the cytoplasm the next stage is called translation and this takes place on a ribosome during translation the genetic information in the MRNA is used to synthesize the protein required now there are a couple of key ideas you need to understand about proteins firstly once a protein has been formed it then has to fall into its three-dimensional shape we'll be looking at that in detail in the videos on protein structure once a protein is folded it can then be modified further for example some proteins have carbohydrate molecules attached to them forming glycoproteins and these modifications are critically important for the function of those proteins the next idea you need to understand is that different proteins have different destinations some proteins function in the cytoplasm other proteins are sent to different organelles for example certain digestive enzymes are sent to lysosomes some proteins are inserted into the cell membrane for example receptor proteins and finally other proteins are secreted from the cell such as hormones or antibodies now how proteins are targeted at different destinations there's a very complex subject but a lot of the targeting involves the rough endoplasmic reticulum and the Golgi apparatus okay as we said before translation takes place on ribosomes ribosomes consist of two subunits each subunit contains a number of different proteins plus ribosomal RNA now in any cell a large number of ribosomes are found in the cytoplasm these ribosomes translate proteins which remain in the cytoplasm other ribosomes are found attached to the roof endoplasmic reticulum I'm showing you here a close-up of the roof endoplasmic reticulum the roof ER consists of sheets of membranes forming flattened sacs called cisterni and these cisterni contain a range of different enzymes the membranes of the cisterni are covered with ribosomes these ribosomes are where translation takes place for proteins which are secreted from the cell as well as proteins for the cell membrane and for lysosomes I'm showing you here a ribosome on a rough ER a molecule of mRNA has attached and translation is taking place the growing polypeptide chain passes through the membrane and into the Lumen of the rough ER in the Lumen the polypeptide chain now falls into its tertiary structure now the polypeptide makes its way through the rough ER and during this process the polypeptide can be modified for example carbohydrate molecules can be added to form a glycoprotein finally the polypeptide is packaged into vesicles and is transported to the Golgi apparatus the Golgi apparatus also consists of sheets of flattened socks called cisterni as the polypeptide makes its way through the Golgi apparatus it can be modified further for example additional carbohydrate molecules may be attached at some point the polypeptide will have reached its final structure and scientists now refer to it as a functional protein once the protein has completed its Journey Through the Golgi apparatus it's packaged into vesicles these vesicles can then fuse with the cell membrane and the protein can be secreted from the cell alternatively the protein can form part of the structure of the cell membrane and in some cases the protein can enter vesicles which go on to form lysosomes the final destination of any protein depends both on the amino acid sequence of the protein and how the protein was modified in the roof ER and Golgi apparatus now there are a couple of final points I want to make firstly cells that secrete large amounts of protein will have a lot of rough endoplasmic reticulum for example beta cells in the pancreas which make the hormone insulin secondly some endoplasmic reticulum is not covered with ribosomes scientists call this smooth endoplasmic reticulum the job of this smooth ER is to make and store both lipids and carbohydrates these can then pass through the Golgi apparatus while they can be modified and then transported to their final destinations for example lipids can be transported to the cell membrane to form part of the phospholipid bilayer okay so hopefully now you can describe the roles of the rough and smooth endoplasmic reticulum and the Golgi apparatus foreign [Music]

Channel: Freesciencelessons

Views: 29,634

Keywords: a level, biology, endoplasmic reticulum, Golgi apparatus

Id: 7PJGaweLeOk

Length: 5min 31sec (331 seconds)

Published: Wed Jun 07 2023