Cell Structure and Function Basics
The Cell Structure and Function second half of the AP Biology curriculum’s Unit 2 Curriculum concentrates on how subcellular structures maintain cell viability and energy collection. This standard divides cellular organelles into two broad functional categories: those that maintain and build the cell, as well as those that gather and use power. Consequently, we will investigate how the endomembrane system builds a cell, as well as how chloroplasts and mitochondria work together to produce energy.
ENDURING UNDERSTANDING
Living systems are structured in a hierarchical structure with interconnected structural layers.
LEARNING OBJECTIVE
Describe the subcellular constituents and how the organelles play a critical role in cell function.
Explain how organisms acquire, store, and utilize energy by describing the structural elements of a cell.
ESSENTIAL KNOWLEDGE
Organelles and subcellular structures, as well as their relationships, aid all cellular activity.
Endoplasmic reticulum (ER) offers mechanical assistance, synthesizes proteins on membrane-bound ribosomes, and stores lipids and aids in intracellular transport.
The double-membrane of the mitochondrion divides metabolic processes into compartments.
Hydrolytic enzymes found in lysosomes play a role in intracellular digestion, organic component regeneration, as well as programmed cell death (apoptosis).
Vacuoles provide a variety of functions, including storing and releasing macromolecules and cellular debris. It helps the plants retain water to maintain the much needed turgor pressure.
The folding of the inner membrane raises the surface area, providing for the production of additional ATP.
Thylakoids and the stroma are found inside the chloroplast.
The thylakoids are arranged into grana, which are stacks of thylakoids.
The photosystems are made up of chlorophyll pigments and electron transport proteins, which are found in membranes.
The grana is where photosynthesis’ light-dependent processes take place.
Fluid that resides in between the inner chloroplast membrane and thylakoid membrane is the stroma.
The stroma is where photosynthesis’s carbon fixation (Calvin-Benson cycle) processes take place.
The Krebs cycle (citric acid cycle) processes take place in the mitochondrial matrix.
At the inner mitochondrial membrane, electron transport and ATP production take place.
Cell Structure and Function Overview
Organelles are divided into two functional areas in this section: There are organelles that preserve and restore the cell, as well as organelles that collect and disperse energy for metabolic activities. Let’s begin with the organelles, which are responsible for the maintenance and repair of cellular components.
A prokaryotic or eukaryotic creature must do an ever-changing laundry list of tasks in order to survive, develop, and reproduce. Cells must first absorb and digest an energy source before they can duplicate their DNA. This means that the cell might need to migrate and grow. It can defend itself against predators or alter its surroundings. Even additional functions are required in a multicellular organism to prepare it for reproduction.
Cell membrane
By looking at the cell membrane alone, we may begin to grasp the sorts of repair and maintenance operations that must be performed. The phospholipids that make up a cell membrane, for example, are continually breaking down. As a cell expands, they must be replaced, and many more must be formed. Furthermore, the many proteins contained inside the membrane, as well as the other molecules that cells need to identify one another, connect to surfaces, and communicate, must be made, fixed, or replaced on an almost continuous basis!
The endomembrane system, which consists of a series of membranes that create different chambers inside a cell, includes both the endoplasmic reticulum and the Golgi complex. The cytosol surrounding these chambers may have substantially distinct chemical characteristics. The rough and smooth endoplasmic reticulums are two separate parts of the endoplasmic reticulum.
Ribosomes, endoplasmic reticulum
Ribosomes coat the rough ER membrane, constantly generating fresh polypeptide chains and storing them in the several chambers created by the folded ER membrane. The protein penetrates the lumen, which is the inside of the endoplasmic reticulum (ER), in which it encounters the proper conditions to fold and operate. Several of these proteins are immediately stored in the ER membrane, which may then proliferate as transport vesicles bound to the Golgi complex or cell membrane.
The rough ER is also capable of producing phospholipids and new membranes to replenish those destroyed by transport vesicles. The proteins synthesized in the rough endoplasmic reticulum are prevented from entering the cytoplasm, where they might create issues if allowed to function. The bulk of cytosolic proteins are produced spontaneously in the cytoplasm.
Lysosomes
The immune system in your body is always fighting bacterial infections. Lysosomes are the most crucial organelles in this struggle. The white blood cells that circulate throughout your body are always on the lookout for microorganisms. When they discover one, they use a process called phagocytosis to “eat” (engulf and destroy) it. This is basically the same method used by single-celled creatures to get nourishment.
Encasing bacteria in a cellular membrane, on the other hand, just traps them in a feeding vacuole. The cell digests the substance via lysosomes. Lysosomes bind to the lipid bilayer of the food vesicle and fuse with it. As they do so, they release their acidic ingredients as well as hydrolytic enzymes into the food vacuole.
The bacteria within the cell are digested by hydration processes that break down all the polymers. The ingredients which the cell may regenerate leak from the feeding vacuole into the cytoplasm. Certain types of debris are returned to the circulation, in which they are eliminated by the kidneys and liver. The cell will subsequently use the Golgi complex to create new lysosomes in preparation for its subsequent encounter with a bacterial cell.
Vacuoles
Vacuoles are another component of the endomembrane system, as they perform a range of storage roles in different species. A vacuole’s membrane is filled with unique proteins that allow certain molecules to enter the vacuole. This removes the compounds from the cytoplasm, allowing the cytoplasm’s chemistry to stay stable and dependable. Because no new molecules are generated in the vacuole, its chemistry is not important. There are two different sorts of vacuoles to consider.
Many freshwater species have contractile vacuoles. Hypotonic creatures exist in freshwater environments. This means they must keep a higher solute concentration inside the cell than in the surrounding space. As a result of the gradient, water repeatedly attempts to enter the cell. The contractile vacuole absorbs this water and afterwards pushes it out of the cell during periodic intervals. This allows the cell to maintain pH and water content despite the constant influx of water.
Plants use vacuoles as well, although for a different purpose. A big central vacuole in plant cells is filled with water. This vacuole forces cell walls outward, causing them to push against adjacent cell walls. The numerous vacuoles inside a plant work together to form a solid structure that helps the plant withstand gravity, wind, and various external factors.
Whenever a plant is starved of water, the vacuoles progressively empty, causing the plant to become floppy and finally perish. Though this is the principal activity of the central vacuole, plants also employ it to store a number of chemicals. Some plants, for example, contain poisons in their vacuoles that might harm herbivores or insects that eat them.
Whereas the endomembrane system is specialized for the maintenance and repair of a growing cell, other organelles are responsible for collecting, storing, and using the energy required to fuel the endomembrane system’s many reactions. Chloroplasts and mitochondria are the organelles in question. Both of these organelles possess a double-membrane system since they evolved from symbiotic bacteria billions of years ago.
The inner membranes of these organelles are very convoluted in order to increase the quantity of surface area required to carry out essential metabolic operations. Cristae comprise the folds in the inner membrane of mitochondria that contain the electron transport chain, which assists in the transfer of energy from glucose bonds towards ATP bonds. The inner membrane of chloroplasts is folded into a huge number of thylakoids. Each chloroplast contains a huge number of grana. They are disc-shaped formations piled into units known as grana. The photosystems of thylakoids are a complex of electron transport chains that gather solar power and use it to produce glucose molecules.
Both organelles provide power in one form or another for almost all creatures on the planet.
Chloroplasts are found in abundance in plant cells, where they make sugar via the complicated process of photosynthesis. These processes originate in the membrane of thylakoids. The thylakoids are densely packed together to maximize the amount of sunlight that can be captured, and they take up the majority of the interior space inside the chloroplast. In the realm of photosystems, however, the genuine magic happens.
The photosystems consist of a series of proteins found in the thylakoid membrane. These photosystems gather energy by means of the pigment molecule chlorophyll, as detailed in subsequent portions of the AP Biology curriculum. After that, utilize the energy to break apart a water molecule. An electron transport chain as well as ATP synthase transform the released energy into NADH and ATP, both of which may be used to power other operations.
The Calvin cycle takes place in the stroma of the chloroplast, where these molecules are transported. This process, commonly referred to as carbon fixation, utilizes the power of ATP and NADH to construct sugar molecules from tiny carbon dioxide molecules
This is virtually the polar opposite of what occurs in mitochondria, as we’ll discover!
Chloroplasts produce glucose, which may be consumed in the cell where it was produced or transferred to other parts of the plant. Despite the fact that animals do not produce glucose, herbivores devour plants for the glucose-based energy they contain, while carnivores devour herbivores for the same reason. The initial stage in obtaining this energy is the breakdown of 6-carbon glucose in the cell’s cytoplasm. This process is referred to as glycolysis. The mitochondrial matrix may then be filled with a smaller 3-carbon molecule.
After that, this molecule participates in the Krebs cycle (often referred to as the citric acid cycle). This method is nearly identical to photosynthesis’s Calvin cycle, but backwards! To make a 6-carbon molecule, the 3-carbon molecule is combined with another 3-carbon molecule. The molecule is progressively ripped apart by a series of biological processes, liberating carbon dioxide and generating NADH, FADH, and a trace quantity of ATP.
These electron transporters (NADH and FADH) make their passage to the inner membrane-located mitochondrial electron transport chain. These electron transporters deposit all electrons and power initially into membrane-bound proteins. These proteins use the energy to push hydrogen into the space between both the inner and outer membranes of mitochondria, known as the intermembrane space.
The hydrogen gradient generated by ATP synthase is then used by the enzyme to build many more ATP molecules. These ATP molecules may be transferred from the mitochondria to fuel activities throughout the cell, from the production of novel DNA molecules prior to cellular division to the production of fresh lipids in the smooth endoplasmic reticulum!
