Protein-Making Organelles

Protein Making Organelles

Inside a cell, there are basically two types of organellestructures within a cell that perform specialized functions.. Some participate in making proteinsLarge molecules made of amino acids with various functions in the body., while others don’t.  The protein-making organelles are called the endomembrane system. They are similar to a factory or an assembly line inside the cell.  To make a protein, the cell must extract the recipe from storage. Then, it interprets the recipe, assembles the protein subunits, folds the protein, and finally ships it.  A protein in the process of moving from one organelle to another will do so in a vesicle.

The Nucleus

So, let’s zoom in and look at the components of a eukaryotic animal cell.  This is like zooming in on your body. You are looking at your liverA large organ that produces bile, detoxifies blood, and stores nutrients. that detoxifies your blood. Your brain controlsVariables that remain constant to ensure a fair test. your voluntary and involuntary muscles, among other things. Your digestive system breaks down moleculesGroups of atoms bonded together..  Whenever we start looking at these little components called organelles, we usually look at the nucleusThe control center of the cell that contains DNA and directs cellular activities. first. 

The nucleus houses the DNA of the cell.  DNA comes in many forms, chromatinDNA and associated proteins in a loose, uncondensed form inside the nucleus., chromosomes, and other smaller divisions, but it’s all found in the nucleus.  The nucleus is double wrapped with what is called a nuclear envelopeA double membrane that surrounds the nucleus and separates it from the cytoplasm..  It’s similar to a plasma membraneThe outer boundary of a cell that controls what enters and exits.. However, it has only these openings or pores. It lacks other substances, like the proteins and cholesterolA lipid molecule that is a key component of cell membranes and a precursor for bile acids and steroi.  Only specific molecules can go into and out of the nucleus. These include nucleotidesThe building blocks of nucleic acids. of DNA, nucleotides of RNA, mRNA, and tRNAs. Each of these will be explained.

Red blood cellsThe basic structural and functional units of life. have no nucleus.  They threw it up or exocytozed it long ago to make more room for oxygen.  White blood cells, on the other hand, have a huge nucleus that grows during your lifetime.  The nucleus is making memories much like your brain makes memories.  Your brain rearranges neuronsThe functional cells of the nervous system that transmit signals. to convert short-term to long-term memoryThe ability to store and recall information..  White blood cells make DNA to remember the invader and how to fight it.  After you got vaccines for measles, mumps, rubella, and chicken pox, white blood cells created a record of how to fight these invaders.

Genetic Material

The DNA holds the instructions for life. It holds the recipes of proteins. These proteins carry out most of the functions of life.  It’s like the recipe book, and you are the collection of recipes it can make.  DNA can be found in many states that have particular names.  This is like calling a human “infant” or “adolescent” or “geriatric.”  When DNA is tightly coiled, we can see the DNA in the nucleus in 46 little chromosomes.  Now, some of these chromosomes are 9 feet long, but only a few angstroms in diameter.  An angstrom is small.  So small it’s named after someone!  In each chromosome we can see DNA wrapped around tons of these proteins called histones.  Eight histones wrapped with DNA is called a nucleosome.  Nucleosomes are then coiled up into a structure called the supercoilThe coiling of chromatin into highly condensed chromosomes..  Seriously.  Supercoil.  But, as stupid as the name is, the supercoils coil repeatedly. They form a pattern like a big long telephone cord from the 1980s. Eventually, they condense into chromosomes.  When a cell is about to divide or is in the process of dividing, we can see chromosomes.  When a cell is just kinda chilling out making proteins and living, we can’t see the DNA.  It’s all dispersed and in a spaghetti-like state called chromatin.

Ribosomes

The recipes or instructions for proteins are locked up in the nucleus. However, the machinery for making them is in the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol.. This is the gooey substance of the cell that’s inside the cell membrane but outside the nuclear envelope.  You have to think of the nucleus like the reserve materials in a library.  Reserve materials can be used in the library, but they can’t be removed. This includes things like encyclopedias and dictionaries.  You can copy the information in the reserve materials. This way, you get the information out of the library. However, you can’t remove the books. 

The copy is called mRNA, which you can see here in the bottom right corner as the pink ribbon.  It is being read by the ribosome and the ribosome is making the polypeptide according to the instructions.  We go into this process in much more detail in later modules.  Ribosomes can be free floating in the cytoplasm. They can also be bound to this internal network called the endoplasmic reticulum.  Free ribosomesSmall structures responsible for protein synthesis, either free-floating or attached to the rough ER usually make proteins for insertion into the cell’s membrane. Bound ribosomes usually make proteins to be shipped from the cell and used elsewhere.

Cells with lots and lots of ribosomes are usually cells that make lots of proteins.  Melanocytes make melaninA brown-black pigment made by melanocytes in the stratum basal and given to keratinocytes as melanos, pancreatic cells make digestive enzymesProteins that speed up chemical reactions in the body. and these cells have lots of ribosomes.

Endoplasmic Reticulum

What is the endoplasmic reticulum other than what looks like a maze of tubules?  Let’s so some root word exercises here and dissect this name.  Endo…you know what it means, it mean inside.  Plasmic, well, we must be referring to something that is inside the plasmaThe liquid component of blood. membrane.  Reticulum is a work that means network or netting, and that’s what this organelle looks like.  We consider the rough and the smooth endoplasmic reticulumA membrane network involved in lipid synthesis, detoxification, and calcium storage. or ER as separate organelles even though they look alike and are attached

RER and SER

The smooth ER is a lipid making organelle.  It’s main role is in detoxification.  It makes lipidsOrganic molecules including fats, oils, and steroids. that surround toxins, allowing their removal. 

Your liver cells, called hepatocytesLiver cells responsible for detoxification, metabolism, and bile production., filter toxins from your blood and tend to have lots of smooth ER.  Alcoholics with a tolerance to alcohol have tons of smooth ER in their hepatocytes trying to eliminate all the alcohol.  Cirrhosis of the liver can result from this overabundance of smooth ER in cells.  The rough ER has many jobs, but most have to do with the building of a protein.  The rough ER plays a role in folding the polypeptide chain. It can also make a little bubble of phospholipids, called a transport vesicle. This vesicle contains the protein so that it can be transported to the next organelle in the process of making and shipping a protein.  But the main difference between these organelles is that the smooth ER gets all the girls.

The Golgi ????

The Golgi apparatus has been called many different things. It includes the Golgi body and the Golgi complex. However, it’s all the same organelle.  I like this organelle because it looks like stacked pita bread. You can see this effect if you cut it and look at it from the side.  Think of this organelle like a conveyor belt.  A protein, contained in a vesicle from the rough ER, enters on the receiving side. It then gets labeled for its final destination. Finally, it is released out the other side in a new transport vesicle.  The Golgi makes vesicles for other reasons, too.  Some vesicles, not containing proteins, leave the Golgi and get inserted into the lipid bilayer for repair.  Some of them turn into our next organelle, lysosomes.