Cell Structures - AP Biology

In eukarytoic cells, the nucleolus is located within the nucleus and is the site of ribosomal RNA synthesis

Osmosis is an example of passive transport. Osmosis does not use energy. Instead, it acts using the concentration gradient. The sodium-potassium pump, proton pump, and electrogenic pump are all examples of active transport. This means that they can pump solutes against their concentration gradients using cellular energy.

When secretory proteins are synthesized they localize to the endoplasmic reticulum (ER), specifically the rough ER, for modification. Following modification there, secretory proteins are then packaged in secretory vesicles which go on to interact with the Golgi body, and are then finally released from the the plasma membrane.

The Endosymbiotic Theory states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). The aerobic bacteria were initially free-living prokaryotes, before being ingested by anaerobic bacteria.

Microtubules are hollow rods made up of thousands tubulin protein subunits. There form long tube-like structures in the cell and are responsible for guiding the movement of organelles. Note that microtubules have other functions such as guiding chromosomes during mitosis and meiosis via the spindle fibers, which are made of microtubules.

The ribosomes are responsible for the assembly of proteins. These structures link amino acids together to form a polypeptide chain which gets folded into a functional protein. Note that ribosomes are not membrane-bound organelles.

Lysosomes are organelles responsible for programmed cell death and the site of intracellular digestion. They do not occur in plant cells. Chloroplasts occur only in plant cells. Peroxisomes, mitochondria, and golgi apparatus are found in all eukaryotic cells, which includes plants.

The nucleolus is a specialized structure within the nucleus that is the site of ribosome synthesis and assembly. The nucleolus is not directly involved in DNA replication, translation, or ATP synthesis. While the DNA of eukaryotic cells is stored in the nucleus, it is not stored in the nucleolus since this part of the nucleus is specialized for ribosome assembly.

Prokaryotes do have organelles, but not complex, membrane-bound organelles. As a result, the membrane-bound mitochondria would not be seen in prokaryotes. Remember that plants are eukaryotes, and have cell walls just like prokaryotes. In addition, prokaryotes have ribosomes as well as DNA.

The fluid mosaic model describes the mosaic structure of the cell membrane. According to this model, the cell membrane is composed of a variety of protein molecules randomly bobbing around in a sea of phospholipids. Due to phospholipid polarity, they naturally form a bilayer in accordance with their dual hydrophobic (tails) and hydrophilic (heads) natures.

Integral proteins have both a hydrophobic region and hydrophilic region. The hydrophobic region allows them to sit within the cell membrane, while their hydrophilic regions face the aqueous solutions on either side of the membrane.

An amphipathic molecule is one that has both hydrophilic and hydrophobic regions. In the case of phospholipids, the tail is hydrophobic and the head is hydrophilic.

Endocytosis occurs when the cell engulfs an external substance and takes it into the cell by the infolding of the cell membrane. Exocytosis occurs when the cell secretes a substance outside the cell.

Actin is what makes up microfilaments. Chitin is indeed in cell walls of fungi. Cellulose is the main ingredient to plant cell walls and peptidoglycan are found in the cell walls of cyanobacteria and bacteria. Also, cellulose is made of polysaccharides, therefore, this is also an incorrect answer because it is a component of the cell wall.

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.

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.

As the name implies, when activated and induced to undergo a conformational change by a ligand, ions are able to flow through the channel and into the cell. This allows the charge across the membrane tobe manipulated by the cell.