Cell Functions - Biology

Phagocytosis is the event of a cell engulfing particular matter from outside the cell and bringing it into the cell. Macrophages are the most prominent phagocytic cells, and help to eliminate pathogens and bacteria through phagocytosis.

Pinocytosis allows extracellular fluid to enter the cell, using invaginations on the cell membrane to create vesicles. Exocytosis involves vesicles leaving the cell, not entering. Diffusion is the passive transport of substances across the membrane and does not involve vesicles.

Exocytosis is a process by which the cell packages content and secretes it from the cell in a vesicle. Hormones, which act on cells far away from where they are produced, will travel out of the cell to reach their target tissues and organs. Vesicles of hormones will fuse with the membrane of the cell and release the hormone into the blood for transport.

DNA, RNA, and cytoplasmic constituents do not leave the cell and would not be exocytosed. Integral membrane proteins are placed in the membrane via vesicle fusion, but are not exocytosed in the process.

There are two topologically different structures inside the cell: the lumen and the cytosol. Lumen consists of the inside of the organelles and the inside of vesicles. Cytosol consists of the fluid that surrounds the organelles.

The questions states that particle A undergoes endocytosis. In endocytosis particles from outside of the cell are brought to the inside of the cell by vesicles that bud off from the cell membrane. These vesicles deliver the particles to the target organelle. The vesicles fuse with the organelle’s membrane and the particles are released into the lumen of the organelle. These particles never make contact with the cytosol side of the cell; therefore, the best answer is that particle A is destined for one of the membrane-bound organelles because it is being transported via a vesicle. This mechanism is also relevant for exocytosis. Secretory vesicles carry contents from inside the cell to the outside, without letting the contents touch the cytosol.

To answer this question you need to know the sequence of events that a protein goes through during and after synthesis.

The first step is the synthesis of protein. This occurs when mRNA is translated to protein by ribosomes. The first event is statement 2.

After its synthesis, the protein is transported to the rough endoplasmic reticulum where it is processed. This processing involves removal of unwanted amino acid sequences, such as signal sequences. The second event is statement 4.

From the rough endoplasmic reticulum the protein is transported to Golgi apparatus where it is further processed and packaged. This next event is statement 1.

The last step is the delivery of protein to the cell membrane (statement 3). Once the protein reaches the cell membrane it can either be exported to the outside (exocytosis) or become part of the membrane (integral and peripheral membrane proteins). Remember that the protein is transported by vesicles and that it never makes contact with the cytosol.

Endocytosis is the process of a cell receiving the contents of a vesicle. The vesicle will fuse with the cell membrane and release its contents into the cytoplasm for cellular use.

In contrast, exocytosis is the release of compounds from a cell via vesicle transport. Vesicles are formed at the Golgi apparatus and transported through the cytoplasm to fuse with the cell membrane, where the contents are released into the extracellular space. Transport vesicles can also be formed to contain and carry molecules away from the cell.

The plasma membrane engulfing particles to enter the cell would be an example of pinocytosis, and the conversion of light and carbon dioxide to carbohydrate and oxygen is the process of photosynthesis.

The correct answer is phagocytosis. Phagocytosis involves the engulfing of an external particle to form a phagosome (a vesicle inside the cell). This process differs from pinocytosis in that pinocyotsis refers to the engulfing of liquids from the environment. Phagocytosis is a specific form of endocytosis; thus, phagocytosis is the better answer as endocyotsis can also describe processes such as pinocytosis. Diffusion and Active Transport both do not relate to the phenomenon as no concentration gradient is in place.

Glycolysis (the process of breaking down glucose) takes place in the cytoplasm, or cytosol—the aqueous portion of the cytoplasm. It is in the cytoplasm where the enzymes required for glycolysis are found.

The citric acid cycle takes place in the mitochondrial matrix, and the electron transport chain takes place along the inner mitochondrial membrane in order to pump protons into the intermembrane space.

Tonofibrils are groups of keratin tonofilaments (intermediate filaments) most commonly found in the epithelial tissues, not endocrine tissues, and which play an important structural role in cell makeup.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

A phosphatase removes a phosphate group from its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Ubiquitin ligases add ubiquitin to their ligands. The addition of ubiquitin acts as a signal that a protein has become ineffective and is ready for degradation. When multiple ubiquitin residues have been added to a protein molecule, it is transported to the lysosome in the cell to be digested.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

Several different types of proteins can change the structure of a ligand, such as isomerases.

A cell must exchange molecules and ions with its surroundings. This process is controlled by the selective permeability of the plasma membrane. Passive transport requires no energy from the cell; molecules like water can diffuse into and out of the cell through the phospholipid bilayer freely by way of osmosis. Other molecules and ions, like sodium, are actively transported across the phospholipid bilayer. This requires ATP created by the cell. Active transport moves solutes against their concentration gradients, which is why it requires energy.

Glycolysis (the process of breaking down glucose) takes place in the cytoplasm, or cytosol—the aqueous portion of the cytoplasm. It is in the cytoplasm where the enzymes required for glycolysis are found.

The citric acid cycle takes place in the mitochondrial matrix, and the electron transport chain takes place along the inner mitochondrial membrane in order to pump protons into the intermembrane space.

Tonofibrils are groups of keratin tonofilaments (intermediate filaments) most commonly found in the epithelial tissues, not endocrine tissues, and which play an important structural role in cell makeup.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

A phosphatase removes a phosphate group from its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Ubiquitin ligases add ubiquitin to their ligands. The addition of ubiquitin acts as a signal that a protein has become ineffective and is ready for degradation. When multiple ubiquitin residues have been added to a protein molecule, it is transported to the lysosome in the cell to be digested.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

Several different types of proteins can change the structure of a ligand, such as isomerases.

A cell must exchange molecules and ions with its surroundings. This process is controlled by the selective permeability of the plasma membrane. Passive transport requires no energy from the cell; molecules like water can diffuse into and out of the cell through the phospholipid bilayer freely by way of osmosis. Other molecules and ions, like sodium, are actively transported across the phospholipid bilayer. This requires ATP created by the cell. Active transport moves solutes against their concentration gradients, which is why it requires energy.

The citric acid cycle is the process by which acetyl-CoA (a two-carbon molecule) is completely broken down to carbon dioxide and energy. Acetyl-CoA loses its CoA and is attached to oxaloacetate (OAA) to produce citrate, which is converted to isocitrate. From there the following occurs:

• Isocitrate (6C) is converted to -ketoglutarate (5C), 1 CO2, and 1 NADH
• -ketoglutarate (5C) is converted to succinyl-CoA (4C), 1 CO2, and 1 NADH
• Succinyl-CoA (4C) is converted to succinate (4C) and 1 GTP (similar to ATP)
• Succinate (4C) is converted to fumarate (4C) and 1 FADH2
• Fumarate (4C) is converted to malate (4C)
• Malate (4C) is converted to OAA (4C) and 1 NADH

The net result is 3 NADH, 2 CO2, 1 FADH2, and 1 GTP (similar to ATP) per round. Since one glucose molecule produces two pyruvate molecules, which produce two Acetyl-CoA, the cycle occurs twice per glucose molecule.

Glycolysis is the first step in extracting energy from a sugar molecule. It converts a 6-carbon sugar molecule, such as glucose, into two three-carbon pyruvate molecules. It does not require oxygen, and is the first step in both aerobic and anaerobic respiration. Glycolysis produces two net ATP per sugar molecule.

If oxygen is present, the pyruvate molecules are broken down into acetyl-CoA and translocated into the mitochondria, where they undergo the Krebs cycle in the mitochondrial matrix. The Krebs cycle products NADH and FADH2, which are used to make ATP in the electron transport chain, which uses oxygen and hydrogen ions to create water. The electron transport chain creates an additional 34 ATP per original sugar molecule.

If oxygen is not present, pyruvate from glycolysis can be converted to lactic acid through fermentation, which regenerates the NAD+ required for more glycolysis cycles. The Krebs cycle and electron transport chain cannot function in anaerobic conditions (no oxygen).