cytoplasma Flashcards
(14 cards)
the cytoplasm
The cytoplasm is everything inside the cell except for the nucleus.
You can think of the cytoplasm as the factory of the cell because it is the site of most cellular activities.
The cytoplasm has three main components:
Cytosol – the jelly-like fluid that fills the space.
Inclusions – stored nutrients or pigments.
Organelles – specialized structures that perform specific functions (like mitochondria, ribosomes, etc.).
cytosol
Cytosol is about 70 to 80 percent water, but it also contains other substances dissolved in it, such as nutrients, ions, proteins, and enzymes.
You can think of cytosol like a soup — the water is the broth, and the nutrients and solutes are the ingredients dissolved in it.
inclusions
Inclusions are substances stored in the cytoplasm, and they are not always present in every cell.
They can be nutrients, pigments, molecules, or waste products.
Inclusions depend on the specific function of the cell, so different types of cells may have different inclusions.
Fat cells (adipocytes) have lipid droplets.
Liver and muscle cells store glycogen.
Skin and hair cells have pigments like melanin (which gives color).
Secretory cells may store mucus or other substances to be released later.
Think of inclusions like the stuff in a pantry — items that the cell keeps on hand, depending on its needs. They are not directly made by the nucleus, but are influenced by the instructions the nucleus provides.
The organelles (or″gah-nelz′; “little organs”) are specialized cellular compartments (Figure 3.4) that are the metabolic machinery of the cell. Each type of organelle is specialized to carry out a specific function for the cell as a whole, much like the organs carry out specialized functions for the whole body
the relationship between the nucleous and the organalles.
The nucleus acts like the control center of the cell. It contains the cell’s DNA, which carries all the instructions needed for the cell to function, grow, and divide. It doesn’t directly carry out all the tasks; instead, it directs or instructs the organelles on what to do. For example, the nucleus contains genes (sections of DNA) that code for proteins, and it sends out signals to the ribosomes (organelles that make proteins) to begin making the specific proteins needed at a given time.
The organelles are the workers that follow the instructions from the nucleus. Once the nucleus tells them what proteins to make, the ribosomes will make the proteins. If those proteins need to be modified or packaged, the Golgi apparatus will handle that. Other organelles, like the mitochondria, provide the energy needed for all of these processes.
Many organelles are bounded by a membrane similar to the plasma membrane. These membrane boundaries allow organelles to maintain an internal environment quite different from that of the surrounding cytosol. This compartmentalization is crucial to their ability to perform their specialized functions for the cell. Let’s consider what goes on in each of these workshops of our cellular factory.
mitchondria
Mitochondria (singular: mitochondrion) are small, bean-shaped or sausage-like organelles that constantly change shape and lengthen inside living cells. They have a double membrane — the outer one is smooth, while the inner one has folded structures called cristae. Inside the mitochondria, enzymes in the fluid and on the cristae use oxygen to break down food molecules like glucose. These food molecules first come from the digestive system, where they are broken down into smaller units like glucose, fatty acids, and amino acids. These small molecules enter the cells from the bloodstream, and once inside, the mitochondria take them in, along with oxygen, to release energy. This energy is partly lost as heat, which helps maintain body temperature, but much of it is used to create ATP, the main energy source cells use to do their work—such as moving, building, or dividing. Because mitochondria produce most of the ATP needed for these activities, they are known as the “powerhouses” of the cell. Cells that require a lot of energy, like muscle and liver cells, contain many mitochondria, while less active cells, like an unfertilized egg, have fewer.
the diffrence between mitchondria,protien and nucleous
Nucleus = The control center
Contains DNA, which has instructions for making proteins.
Sends out those instructions so the cell knows what to do.
🔹 Proteins = The workers
Build stuff, carry things, speed up chemical reactions, and respond to signals.
They do the jobs the nucleus instructs.
🔹 Mitochondria = The powerhouse
Make ATP, the energy currency of the cell.
ATP powers the proteins so they can actually do their work.
ribosomes
Ribosomes (ri′bo-sōmz) are tiny, bilobed, dark bodies made of proteins and one variety of RNA called ribosomal RNA. Ribosomes are the actual sites of protein synthesis in the cell. Ribosomes that float freely in the cytoplasm manufacture proteins that function inside the cell, while others attach to membranes such as the rough ER, which produces proteins that function outside the cell or on the exterior cell surface.
endoplasmic reticulum (ER)
The endoplasmic reticulum (ER) is a network of fluid-filled tubes or canals that winds through the cytoplasm and is connected to the nuclear envelope. It acts like a mini circulatory system inside the cell, helping to transport substances, mainly proteins, from one part of the cell to another. The ER makes up about half of the cell’s total membranes. There are two types: rough ER, which has ribosomes and helps with protein production, and smooth ER, which doesn’t have ribosomes and helps with making lipids and detoxifying chemicals. Depending on the cell’s job, it might have a lot of one type or both.
The rough endoplasmic reticulum is so called because it is studded with ribosomes. Because essentially all of the building materials of cellular membranes are formed either in it or on it, you can think of the rough ER as the cell’s membrane factory. The proteins made on its ribosomes migrate into the rough ER tunnels, where they fold into their functional three-dimensional shapes. These proteins are then dispatched to other areas of the cell in small “sacs” of membrane called transport vesicles (Figure 3.5) that carry substances around the cell. Rough ER is especially abundant in cells that make (synthesize) and export (secrete) proteins—for example, pancreatic cells, which produce digestive enzymes to be delivered to the small intestine. The enzymes that catalyze the synthesis of membrane lipids reside on the external (cytoplasmic) face of the rough ER, where the needed building blocks are readily available.
Smooth Endoplasmic Reticulum (Smooth ER): Unlike the rough ER, the smooth ER doesn’t have ribosomes (those are the things that make proteins). So, it doesn’t play a direct role in protein synthesis. Instead, it does other important jobs:
Lipid metabolism: This means it helps with the creation and breakdown of lipids (fats). This includes cholesterol (important for cell membranes) and phospholipids (which make up the cell membrane).
Detoxification: The smooth ER helps to break down and detoxify harmful substances like drugs and pesticides.
Liver cells are full of smooth ER because the liver is responsible for detoxifying the body (breaking down harmful substances).
Cells that produce steroid-based hormones (like testosterone in male testes) also have a lot of smooth ER because it helps synthesize these types of hormones.
So, in summary: The smooth ER doesn’t make proteins, but it is essential for lipid production, detoxifying harmful substances, and making hormones like testosterone. It works alongside the rough ER but handles different jobs related to fats and detoxification.
Golgi (gol′je) apparatus
The Golgi apparatus appears as a stack of flattened, membrane-bound sacs surrounded by many small vesicles. It’s usually located near the endoplasmic reticulum and acts as the cell’s “traffic director” for proteins. Its main job is to modify, package, and ship proteins that are sent from the rough ER through transport vesicles.
As proteins marked for export build up in the Golgi, the sacs swell. Eventually, the swollen ends pinch off to form secretory vesicles—tiny sacs filled with protein. These vesicles travel to the plasma membrane, fuse with it, and release their contents outside the cell. This is how substances like mucus and digestive enzymes (from pancreatic cells) are secreted.
In addition to exporting materials, the Golgi also packages proteins and phospholipids that are sent to the plasma membrane or other cell membranes inside the cell. It also creates lysosomes by packaging digestive enzymes into membrane-bound sacs that stay inside the cell.
Lysosomes
Lysosomes (li′so-sōmz; “breakdown bodies”), which appear in different sizes, are membranous “bags” containing powerful digestive enzymes. Because lysosomal enzymes are capable of digesting worn-out or nonusable cell structures and most foreign substances that enter the cell, lysosomes function as cellular “stomachs.” Lysosomes are especially abundant in white blood cells called phagocytes, the cells that dispose of bacteria and cell debris. As we mentioned, the enzymes they contain are formed by ribosomes on the rough ER and packaged by the Golgi apparatus.
The lysosomal membrane is ordinarily quite stable, but it becomes fragile when the cell is injured or deprived of oxygen and when excessive amounts of vitamin A are present. When lysosomes rupture, the cell self-digests.
Peroxisomes (per-ok′sih-sōmz)
Peroxisomes (per-ok′sih-sōmz) are membranous sacs containing powerful oxidase (ok′sĭ-dāz) enzymes that use molecular oxygen to detoxify a number of harmful or poisonous substances, including alcohol and formaldehyde. However, their most important function is to “disarm” dangerous free radicals. Free radicals are highly reactive chemicals with unpaired electrons that can damage the structure of proteins and nucleic acids. Free radicals are normal by-products of cellular metabolism, but if allowed to accumulate, they can have devastating effects on cells. Peroxisomes convert free radicals to hydrogen peroxide , a function indicated in their naming (peroxisomes = peroxide bodies). The enzyme catalase (kat′ah-lās) then converts excess hydrogen peroxide to water. Peroxisomes are especially numerous in liver and kidney cells, which are very active in detoxification.
Although peroxisomes look like small lysosomes (see Figure 3.4), they do not arise by budding from the Golgi apparatus. Instead, one way they replicate themselves is by simply pinching in half, like mitochondria, but most peroxisomes appear to bud directly from the ER.
Cytoskeleton
An elaborate network of protein structures extends throughout the cytoplasm. This network, or cytoskeleton, acts as a cell’s “bones and muscles” by furnishing an internal framework that determines cell shape, supports other organelles, and provides the machinery for intracellular transport and various types of cellular movements. From its smallest to its largest elements, the cytoskeleton is made up of microfilaments, intermediate filaments, and microtubules (Figure 3.7). Although there is some overlap in roles, generally speaking microfilaments (such as actin) are most involved in cell motility and in producing changes in cell shape. (You could say that cells move when they get their act(in) together.) The strong, stable, ropelike intermediate filaments are made up of fibrous subunits. They help form desmosomes (see Figure 3.2) and provide internal guy wires to resist pulling forces on the cell. The tubelike microtubules are made up of repeating subunits of the protein tubulin. They determine the overall shape of a cell and the distribution of organelles. They are very important during cell division Section 3.3b.
Centrioles
The paired centrioles (sen′tre-ōlz), collectively called the centrosome, lie close to the nucleus (see Figure 3.4). They are rod-shaped bodies that lie at right angles to each other; internally they are made up of a pinwheel array of nine triplets of fine microtubules. Centrioles are best known for their role in generating microtubules and also for directing the formation of the mitotic spindle during cell division (look ahead to Figure 3.15).
