At the end of this section, you can:
- Describe the structure of plant and animal eukaryotic cells
- Name the function of the plasma membrane
- Summarize the functions of the most important cell organelles
- Describe the cytoskeleton and extracellular matrix
Watch a video about oxygen in the atmosphere.
At this point it should be clear that eukaryotic cells have a more complex structure than prokaryotic cells. Organelles allow different functions to occur simultaneously in the cell. Before discussing the functions of organelles within a eukaryotic cell, let's first look at two important components of the cell: the plasma membrane and the cytoplasm.
Like prokaryotes, eukaryotic cells have a plasma membrane (Figure 3.9) composed of aPhospholipid bilayer with incorporated proteinswhich separates the cell's internal contents from its surroundings. A phospholipid is a lipid molecule composed of two fatty acid chains, a glycerol backbone and a phosphate group. The plasma membrane regulates the passage of some substances such as organic molecules, ions, and water, preventing the passage of some to maintain internal conditions while actively introducing or removing others. Other compounds passively move across the membrane.
The plasma membranes of cells specialized for absorption are folded into finger-like projections called microvilli (singular = microvilli). This fold increases the surface area of the plasma membrane. These cells are normally found in the small intestine, the organ that absorbs nutrients from digested food. This is an excellent example of how form meets function in a structure.
People with celiac disease have an immune response to gluten, a protein found in wheat, barley and rye. The immune response damages the microvilli, preventing affected individuals from absorbing nutrients. This leads to malnutrition, cramps and diarrhea. Patients with celiac disease must follow a gluten-free diet.
Cytoplasm comprises the contents of a cell between the plasma membrane and the nuclear envelope (a structure that will be discussed shortly). It consists of gel-like organelles suspended in the cytosol, cytoskeleton and various chemicals. Although the cytoplasm is 70 to 80 percent water, it has a semi-solid consistency that comes from the proteins it contains. However, proteins are not the only organic molecules found in the cytoplasm. Glucose and other simple sugars, polysaccharides, amino acids, nucleic acids, fatty acids and glycerol derivatives can also be found there. Sodium, potassium, calcium ions and many other elements are also dissolved in the cytoplasm. Many metabolic reactions, including protein synthesis, take place in the cytoplasm.
If you removed all the organelles from a cell, would only the plasma membrane and cytoplasm remain? no Inside the cytoplasm there would still be ions and organic molecules plus aprotein fiber networkThis helps maintain the cell's shape, protects specific organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and allows single-celled organisms to move independently. Collectively, this network of protein fibers is called the cytoskeleton. There are three types of fibers within the cytoskeleton: microfilaments, also known as actin filaments, intermediate filaments, and microtubules.Figure 3.10).
Microfilaments are the thinnest fibers of the cytoskeleton and are involved in the movement of cellular components, such as during cell division. You also get the structure of microvilli, the extensive folds of the plasma membrane found in cells dedicated to absorption. These components are also commonly found in muscle cells and are responsible for muscle cell contraction. Intermediate filaments are intermediate in diameter and have structural functions such as maintaining cell shape and anchoring organelles. Keratin, a compound that strengthens hair and nails, forms a kind of intermediate filament. Microtubules are the thickest fibers of the cytoskeleton. These are hollow tubes that can disintegrate and reform quickly. Microtubules guide the movement of organelles and are the structures that pull chromosomes toward their poles during cell division. They are also the structural components of flagella and cilia. In cilia and flagella, microtubules are arranged as a circle of nine double microtubules on the outside and two microtubules in the middle.
The centrosome is a region near the nucleus of animal cells that functions as a microtubule organizing center. It contains a pair of centrioles, two structures perpendicular to each other. Each centriole is a cylinder of nine microtubule triplets.
The centrosome replicates before the cell divides, and the centrioles play a role in pulling the duplicated chromosomes to opposite ends of the dividing cell. However, the exact role of centrioles in cell division is unclear, since cells that have had their centrioles removed can still divide, and plant cells that lack centrioles are capable of cell division.
flagella and cilia
Flagella (singular = flagellum) are long hair-like structures that emanate from the plasma membrane and serve to move an entire cell (e.g., sperm,euglena🇧🇷 When present, the cell has only one flagellum or a few flagella. When cilia (singular = cilia) are present, however, they are numerous and extend over the entire surface of the plasma membrane. They are short hair-like structures used to move whole cells (e.g., paramecia) or substances along the outer surface of the cell (e.g., the cilia of the cells that line the fallopian tubes that carry the egg to the uterus, or cilia that lining the cells of the uterus). airways that carry particles to the throat where the mucus gets trapped).
The endomembrane system (Endo= inside) is aGroup of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins🇧🇷 It includes the nuclear envelope, lysosomes, vesicles, endoplasmic reticulum, and the Golgi apparatus, which we will discuss shortly. Although not technicallyinsideIn the cell, the plasma membrane is part of the endomembrane system because, as you will see, it interacts with the other endomembrane organelles.
Normally, the nucleus is the most prominent organelle in a cell. The core (plural = cores)houses the cell's DNAin the form of chromatin and controls the synthesis of ribosomes and proteins. Let's take a closer look (Figure 3.11).
The nuclear envelope is adouble membrane structurewhich forms the outermost part of the nucleus (Figure 3.11🇧🇷 Both the inner and outer membranes of the nuclear envelope are phospholipid bilayers.
The nuclear envelope is punctuated withcoupleswhich control the passage of ions, molecules, and RNA between the nucleoplasm and the cytoplasm.
To understand chromatin, it's helpful to first look at chromosomes. Chromosomes are structures within the cell nucleus composed of DNA, genetic material, and proteins. This combination of DNA and protein is called chromatin. In eukaryotes, chromosomes are linear structures. Each species has a specific number of chromosomes in the nucleus of its body cells. For example, the chromosome number in humans is 46, while the chromosome number in fruit flies is eight.
Chromosomes are only visible and distinguishable from one another when the cell is preparing to divide. When the cell is in the growth and maintenance phase of its life cycle, the chromosomes resemble a bundle of tangled and uncoiled threads.
We already know that the nucleus controls the synthesis of ribosomes, but how does it do this? Some chromosomes have stretches of DNA that code for ribosomal RNA. A dark-colored area inside the nucleus called theNucleolus (plural = Nucleolus)), ribosomal RNA aggregates with associated proteins to assemble ribosomal subunits, which are then transported through nuclear pores into the cytoplasm.
or endoplasmic reticulum
The endoplasmic reticulum (ER) is a series of interconnected membranous tubules that work together to modify proteins and synthesize lipids. However, these two functions are performed in separate areas of the endoplasmic reticulum: the rough endoplasmic reticulum and the smooth endoplasmic reticulum, respectively.
The hollow part of the ER tubules is called the lumen or cisternal space. The ER membrane, which is a phospholipid bilayer embedded in proteins, is continuous with the nuclear envelope.
That onerough endoplasmic reticulum (RER)it is so named because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewed through an electron microscope.
Ribosomes synthesize proteins while attached to the ER, resulting in the transfer of their newly synthesized proteins into the lumen of the ER, where they undergo modifications such as folding or the addition of sugars. The RER also produces phospholipids for cell membranes.
If the modified phospholipids or proteins are not destined to remain in the RER, they are packaged into vesicles and transported out of the RER by membrane budding. Because the RER is involved in modifying proteins secreted by the cell, it is abundant in cells that secrete proteins, such as the liver.
That onesmooth endoplasmic reticulum (SER)it is continuous with the RER but has few or no ribosomes on its cytoplasmic surface. SER functions include synthesis of carbohydrates, lipids (including phospholipids), and steroid hormones; Detoxification of drugs and toxins; alcohol metabolism; and storage of calcium ions.
the golgi apparatus
We already mentioned that vesicles can sprout from the ER, but where do vesicles go? Before reaching their final destination, the lipids or proteins in the transport vesicles must be sorted, packaged, and labeled to get them to the right place. That oneSelection, labeling, packaging and distribution of lipids and proteinsoccur in the Golgi apparatus (also called the Golgi body), a series of flattened membrane sacs.
The Golgi apparatus has a receiving surface close to the endoplasmic reticulum and a releasing surface on the opposite side of the ER towards the cell membrane. Transport vesicles that form from the ER travel to the receptor surface, fuse with it, and empty their contents into the lumen of the Golgi apparatus. As proteins and lipids travel through the Golgi, they undergo other changes. The most common modification is the addition of short chains of sugar molecules. The newly modified proteins and lipids are then tagged with small groups of molecules so they can be targeted to their correct destinations.
Finally, the modified and tagged proteins are packaged into vesicles that bud on the opposite side of the Golgi. While some of these vesicles, transport vesicles, deposit their contents elsewhere in the cell where they are used, others, secretory vesicles, fuse with the plasma membrane and release their contents outside the cell.
The amount of Golgi in different cell types again shows that form follows function within cells. Cells with high secretory activity (such as salivary gland cells that secrete digestive enzymes or immune system cells that secrete antibodies) have large Golgi numbers.
In plant cells, the Golgi plays an additional role in the synthesis of polysaccharides, some of which are incorporated into the cell wall and some of which are used elsewhere in the cell.
In animal cells, lysosomes are those of the cell"garbage disposal".Digestive enzymes in lysosomes help break down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles. In unicellular eukaryotes, lysosomes are important for the digestion of ingested food and theRecycling of Organelles🇧🇷 These enzymes are active at a much lower (more acidic) pH than those found in the cytoplasm. Many reactions that occur in the cytoplasm could not occur at low pH, so the advantage of compartmentalizing the eukaryotic cell into organelles is obvious.
Lysosomes also use their hydrolytic enzymes to destroy disease-causing organisms that may invade the cell. A good example of this occurs in a group of white blood cells called macrophages, which are part of your body's immune system. In a process known as phagocytosis, a section of the macrophage's plasma membrane invaginates (folds) and engulfs a pathogen. The inverted section containing the pathogen then detaches from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome. Lysosome hydrolytic enzymes then destroy the pathogen (Figure 3.15).
vesicles and vacuoles
Vesicles and vacuoles are membrane-enclosed sacs used for storage and transport. Vacuoles are slightly larger than vesicles, and the membrane of a vacuole does not fuse with the membranes of other cellular components. Vesicles can fuse with other membranes within the cellular system. Furthermore, enzymes in plant vacuoles can break down macromolecules.
Because shecisIs the Golgi face not facing the plasma membrane?
<!– Because that face gets chemicals from the ER, which is in the middle of the cell. 🇧🇷
Ribosomes are the cellular structures responsible for thisprotein synthesis🇧🇷 When viewed through an electron microscope, free ribosomes appear as clusters or small individual dots floating freely in the cytoplasm. Ribosomes can be attached to the cytoplasmic side of the plasma membrane or to the cytoplasmic side of the endoplasmic reticulum. Electron microscopy has shown that ribosomes are composed of large and small subunits. Ribosomes are enzyme complexes responsible for protein synthesis.
Because protein synthesis is essential for all cells, ribosomes are found in virtually all cells, although they are smaller in prokaryotic cells. They are particularly abundant in immature red blood cells for the synthesis of haemoglobin, which functions in carrying oxygen around the body.
Mitochondria (singular = mitochondria) are often referred to as the"Power Plants" or "Power Factories"of a cell because they are responsible for the production of adenosine triphosphate (ATP), the cell's main energy-carrying molecule. That oneATP formationof glucose breakdown is called cellular respiration. Mitochondria are oval, double-membrane organelles (Figure 3.17) that have their own ribosomes and DNA. Each membrane is a phospholipid bilayer embedded in proteins. The inner layer has folds called cristae that increase the surface area of the inner membrane. The area surrounded by the folds is called the mitochondrial matrix. Crests and matrix have distinct roles in cellular respiration.
In keeping with our topic on shape-tracking function, it's important to note that muscle cells have a very high concentration of mitochondria because muscle cells require a lot of energy to contract.
Peroxisomes are small, round organelles surrounded by individual membranes. They carry out oxidation reactions that break down fatty acids and amino acids. They also detoxify many toxins that can enter the body. Alcohol is detoxified by peroxisomes in liver cells. A byproduct of these oxidation reactions is hydrogen peroxide, H2Ö2, which is contained in peroxisomes to prevent the chemical from damaging cellular components outside the organelle. Hydrogen peroxide is safely broken down into water and oxygen by peroxisomal enzymes.
Despite their fundamental similarities, there are some notable differences between animal and plant cells (cf.Table 3.1🇧🇷 Animal cells have centrioles, centrosomes (discussed under cytoskeleton), and lysosomes, whereas plant cells do not. Plant cells have a cell wall, chloroplasts, plasmodesmata and plastids used for storage, and a large central vacuole, whereas animal cells do not.
the cell wall
NoFigure 3.8b, the diagram of a plant cell, you can see a structure outside the plasma membrane called the cell wall. The cell wall is a rigid shell that protects the cell, provides structural support, and gives the cell shape. Fungal and protist cells also have cell walls.
Whereas the main component of prokaryotic cell walls is peptidoglycan, the main organic molecule in plant cell walls is cellulose, a polysaccharide composed of long, straight chains of glucose units. When nutrition information refers to fiber, it refers to the cellulose content of the food.
Like mitochondria, chloroplasts have their own DNA and ribosomes. Chloroplasts are involved in photosynthesis and are found in eukaryotic cells such as plants and algae. Photosynthesis uses carbon dioxide, water, and light energy to produce glucose and oxygen. This is the main difference between plants and animals: plants (autotrophs) are able to produce their own food such as glucose, while animals (heterotrophs) depend on other organisms for their organic compounds or food source.
Like mitochondria, chloroplasts have outer and inner membranes, but within the space bounded by the inner membrane of a chloroplast is a series of interconnected, stacked membranous sacs called thylakoids (Figure 3.18🇧🇷 Each stack of thylakoids is called a granum (plural = grana). The fluid enclosed by the inner membrane and surrounding the grana is called the stroma.
Chloroplasts contain a green pigment called chlorophyll that captures energy from sunlight for photosynthesis. Like plant cells, photosynthetic protists also have chloroplasts. Some bacteria also perform photosynthesis but lack chloroplasts. Its photosynthetic pigments reside in the thylakoid membrane within the cell itself.
evolution in action
Endossimbiosis:We mentioned that both mitochondria and chloroplasts contain DNA and ribosomes. Have you ever wondered why? Strong evidence points to endosymbiosis as an explanation.
Symbiosis is a relationship in which organisms from two different species live in close association, often exhibiting specific adaptations to each other. endosymbiosis (Endo-= inside) is a relationship in which one organism lives in the other. Endosymbiotic relationships are abundant in nature. The microbes that produce vitamin K live in the human gut. This relationship is beneficial for us because we cannot synthesize vitamin K. It is also beneficial for microbes as they are protected from other organisms and given a stable habitat and abundant food by living in the colon.
Scientists have long established that bacteria, mitochondria and chloroplasts are similar in size. We also know that mitochondria and chloroplasts have DNA and ribosomes like bacteria, and are similar to the types found in bacteria. Scientists believe that when host cells absorb, but do not destroy, aerobic bacteria and cyanobacteria, the host cells and bacteria form a mutually beneficial endosymbiotic relationship. Through evolution, these ingested bacteria became more specialized in their functions, with aerobic bacteria becoming mitochondria and photosynthetic bacteria becoming chloroplasts.
The central vacuoles
Earlier, we mentioned vacuoles as essential components of plant cells. if you look atFigure 3.8b, you will see that every plant cell has a large central vacuole that occupies most of the cell. The central vacuole plays a key role in regulating the cell's water concentration under varying environmental conditions. In plant cells, the fluid in the central vacuole provides the turgor pressure, which is the external pressure caused by the fluid in the cell. Have you ever noticed that a plant wilts if you forget to water it for a few days? This is because when the water concentration in the soil becomes less than the water concentration in the plant, water from the central vacuoles and the cytoplasm enters the soil. As the central vacuole shrinks, it leaves the cell wall unsupported. This loss of support for a plant's cell walls results in a wilted appearance. In addition, this liquid has a very bitter taste, which discourages consumption by insects and animals. The central vacuole also serves to store proteins in developing sperm cells.
Most animal cells release materials into the extracellular space. The main components of these materials are glycoproteins and collagen protein. Collectively, these materials are referred to as the extracellular matrix (Figure 3.19🇧🇷 The extracellular matrix not only holds cells together to form a tissue, it also allows cells within the tissue to communicate with each other.
Blood clotting is an example of the role of the extracellular matrix in cell communication. When the cells lining a blood vessel are damaged, they reveal a protein receptor called tissue factor. When tissue factor binds to another factor in the extracellular matrix, it causes platelets to adhere to the damaged blood vessel wall, stimulates adjacent smooth muscle cells in the blood vessel to contract (thus narrowing the blood vessel), and initiates a series of of steps that stimulate platelets to produce clotting factors.
Cells can also communicate with each other through direct contact called intercellular connections. There are some differences in the way plant and animal cells do this. Plasmodesmata (singular = plasmodesma) are junctions between plant cells, whereas junctions of animal cells include tight and gap junctions and desmosomes.
In general, the plasma membranes of neighboring plant cells cannot touch each other over long distances because they are separated by the cell walls that surround each cell. Plasmodesmata are numerous channels that run between the cell walls of neighboring plant cells, connecting their cytoplasm and allowing the transport of signaling molecules and nutrients from one cell to another.Figure 3.20one).
A tight junction is a tight seal between two adjacent animal cells (Figure 3.20b🇧🇷 Proteins hold cells tightly together. This strong adhesion prevents materials from leaking between cells. Tight junctions are normally found in the epithelial tissue that lines internal organs and cavities and makes up most of the skin. For example, the tight junctions of the epithelial cells that line the urinary bladder prevent urine from leaking into the extracellular space.
Also found only in animal cells are desmosomes, which act as soldering points between neighboring epithelial cells.Figure 3.20c🇧🇷 They hold cells in extending organs and tissues, such as skin, heart, and muscle, together in a sheet-like formation.
Gap junctions in animal cells are like plasmodesmata in plant cells in that they are channels between adjacent cells that allow the transport of ions, nutrients, and other substances that allow cells to communicate.Figure 3.20d🇧🇷 However, gap junctions and plasmodesmata differ structurally.
Present in prokaryotes?
Present in animal cells?
Present in plant cells?
|plasma membrane||Separates the cell from the external environment; controls the passage of organic molecules, ions, water, oxygen, and waste products into and out of the cell||E||E||E|
|Cytoplasm||Gives structure to the cell; site of many metabolic reactions; Medium in which organelles are located||E||E||E|
|Kern||Cellular organelle that houses DNA and controls ribosome and protein synthesis||not||E||E|
|mitochondria||ATP production/cellular respiration||not||E||E|
|Peroxissoma||Oxidizes and breaks down fatty acids and amino acids and detoxifies toxins||not||E||E|
|vesicles and vacuoles||storage and transport; digestive function in plant cells||not||E||E|
|centrossimo||Unspecified role in cell division in animal cells; Microtubule organizing center in animal cells||not||E||not|
|lysosome||digestion of macromolecules; recycling of spent organelles||not||E||not|
|cell wall||Protection, structural support and maintenance of cell shape||Yes, mostly peptidoglycan in bacteria but not in archaea||not||Yes, mainly cellulose|
|Endoplasmatisches Retikulum||Modifies proteins and synthesizes lipids||not||E||E|
|Golgi Apparat||Modifies, sorts, labels, packages and distributes lipids and proteins||not||E||E|
|Zitoskeleton||Maintains cell shape, secures organelles in specific positions, allows movement of cytoplasm and vesicles within the cell, and allows single-celled organisms to move independently||E||E||E|
|flagella||Cellular Locomotion||Any||Any||No, except some plant sperm.|
|eyelashes||Cell locomotion, movement of particles along the extracellular surface of the plasma membrane, and filtration||not||Any||not|
Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membranes connected organelles that allow the compartmentalization of functions. The plasma membrane is a phospholipid bilayer embedded in proteins. The nucleolus within the cell nucleus is the site for ribosome assembly. Ribosomes are located in the cytoplasm or are attached to the cytoplasmic side of the plasma membrane or the endoplasmic reticulum. They carry out protein synthesis. Mitochondria carry out cellular respiration and produce ATP. Peroxisomes break down fatty acids, amino acids and some toxins. Vesicles and vacuoles are storage and transport compartments. In plant cells, vacuoles also help break down macromolecules.
Animal cells also have a centrosome and lysosomes. The centrosome has two bodies, the centrioles, with an unknown role in cell division. Lysosomes are the digestive organelles of animal cells.
Plant cells have a cell wall, chloroplasts and a central vacuole. The plant cell wall, whose main component is cellulose, protects the cell, provides structural support, and gives the cell shape. Photosynthesis takes place in chloroplasts. The central vacuole expands and enlarges the cell without the need to produce more cytoplasm.
The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and plasma membrane. These cellular components work together to modify, package, label, and transport lipids and membrane proteins.
The cytoskeleton consists of three different types of protein elements. Microfilaments provide rigidity and shape to the cell and facilitate cell movement. Intermediate filaments carry the tension and anchor the nucleus and other organelles in place. Microtubules help the cell resist compression, serve as cues for motor proteins that move vesicles around the cell, and pull replicated chromosomes to opposite ends of a dividing cell. They are also the structural elements of centrioles, flagella and cilia.
Animal cells communicate through their extracellular matrices and are connected to each other by tight junctions, desmosomes, and gap junctions. Plant cells are connected by plasmodesmata and communicate with each other.
cell wall:a rigid cell envelope made of cellulose in plants, peptidoglycan in bacteria, non-peptidoglycan compounds in archaea, and chitin in fungi that protects the cell, provides structural support, and gives the cell shape
central vacuoles:a large organelle of the plant cell that functions as a storage compartment, water reservoir, and site of breakdown of macromolecules
chloroplast:a plant cell organelle that carries out photosynthesis
eyelash:(plural: cilia) a short, hairlike structure that extends in large numbers from the plasma membrane and serves to move an entire cell or substances along the outer surface of the cell
Cytoplasm:the entire region between the plasma membrane and the nuclear envelope, consisting of organelles, the cytoskeleton, and various chemicals suspended in the gel-like cytosol
Zitoskeleton:The network of protein fibers that collectively maintain the shape of the cell, secure some organelles in specific positions, allow movement of cytoplasm and vesicles within the cell, and allow movement of single-celled organisms
Zitosol:the gel-like material of the cytoplasm in which cell structures are suspended
Desmossom:a junction between adjacent epithelial cells that forms when cadherins in the plasma membrane bind to intermediate filaments
Sistema endomembranar:the group of organelles and membranes in eukaryotic cells that work together to modify, package, and transport lipids and proteins
Endoplasmic Reticulum (ER):a series of interconnected membrane structures in eukaryotic cells that work together to modify proteins and synthesize lipids
Extracellular matrix:The material, primarily collagen, glycoproteins, and proteoglycans, secreted by animal cells that holds cells together like tissue, allows cells to communicate with each other, and provides mechanical protection and anchorage for cells in tissue
Flagellum:(plural: flagella) the long hairlike structure that extends from the plasma membrane and serves to move the cell
Point of contact:a channel between two adjacent animal cells that allows ions, nutrients, and other low-molecular-weight substances to pass between the cells, allowing the cells to communicate
Golgi apparatus:a eukaryotic organelle composed of a series of stacked membranes that sort, label, and package lipids and proteins for distribution
Lysosomes:an organelle in an animal cell that functions as the cell's digestive component; It breaks down proteins, polysaccharides, lipids, nucleic acids and even worn-out organelles
mitochondria:(singular: mitochondria) the cellular organelles responsible for conducting cellular respiration, resulting in the production of ATP, the cell's main energy-carrying molecule
atomic envelope:the double-membrane structure that forms the outermost part of the cell nucleus
Nucleolus:the dark-colored body within the nucleus responsible for assembling ribosomal subunits
Kern:the cell organelle that houses the cell's DNA and controls the synthesis of ribosomes and proteins
Peroxissoma:a small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many toxins
plasma membrane:a phospholipid bilayer with embedded (integral) or attached (peripheral) proteins that separates the cell's internal contents from its surroundings
Plasmodesma:(plural: plasmodesmata) a channel that runs between the cell walls of neighboring plant cells, connecting their cytoplasm and allowing the transport of substances from one cell to another
Ribosomes:a cellular structure that carries out protein synthesis
rough endoplasmic reticulum (RER):the region of the endoplasmic reticulum filled with ribosomes and involved in protein modification
smooth endoplasmic reticulum (SER):the endoplasmic reticulum region, which has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; Detoxifies chemicals such as pesticides, preservatives, medications, and environmental pollutants and stores calcium ions
narrow crossing:a tight seal between two adjacent animal cells created by the binding of proteins
I guarantee:a membrane-enclosed sac, slightly larger than a vesicle, that functions in cell storage and transport
Gallbladder:a small membranous sac that functions in cell storage and transport; its membrane can fuse with the plasma membrane and the membranes of the endoplasmic reticulum and Golgi apparatus
- Figure 3.11: NIGMS work modification, NIH
- Figure 3.13: Change at work by NIH; Scale data by Matt Russell
- Figure 3.14: Modification of Louisa Howard's work; Scale data by Matt Russell
- Figure 3.16: Modification of Magnus Manske's work
- Figure 3.17: Modification of Matthew Britton's work; Scale data by Matt Russell
- Figure 3.20: Modification of Mariana Ruiz Villareal's work