Cellular Biology - AP Biology

During embryogenesis, the process of myogenesis forms myocytes and muscle tissue.

The sarcoplasm in muscle cells is comparable to the cytoplasm in other types of cells. The sarcoplasm is specialized in the high amount of myoglobin present. Its specialized regulation of calcium ion concentrations controls muscle contractions.

Intercalated disks are structures that connect cardiac muscle cells, allowing them to work together and communicate within the heart. Intercalated disks are made up of different types of cell junctions and are observable under the microscope. This makes cardiac muscle tissue distinguishable.

The calcium ions bind to troponin, which causes the release of the tropomyosin from actin as a result of the troponin-tropomyosin complex detaching. This makes the binding site on actin available for myosin to attach to. The sarcoplasmic reticulum stores calcium for its quick release to facilitate muscle contraction.

The nucleolus is a structure found inside the nucleus. It is responsible for the production of rRNA, and also constructs the subunits of ribosomes.

Mitochondria are responsible for ATP production, and various chaperone proteins are responsible for directing substance transport within a cell. Several classes of proteins in the nucleus are involved in mRNA transcription and post-transcription modification, but these processes do not involve the nucleolus.

Desmosomes are the primary junction that helps keep tissues that are under a lot of stress, like skin, intact. Although tight junctions typically accompany desmosomes, their primary function is to prevent substances from passing between cells. Gap junctions are used for communication between cells, and intercalated discs are only found in cardiac muscle tissue.

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.

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.

Human muscle contraction relies on the action of the motor proteins actin and myosin. Muscles contract through the sliding of myosin and actin filaments along one another.

The binding of ligands causes the activation and conformational change in the ion channel to open it. Then, ions are able to flow into the cell. After a short time, the ligand dissociates from the ion gated channel. This causes the channel to deactivate and close.

The lysosome is an organelle that is used to digest broken cellular machinery or foreign particles. It maintains an acidic environment inside by pumping hydrogen ions in, not out. This environment helps denature the things it needs to digest, and is the most effective pH for the digestive enzymes that are inside.

The other structures do not maintain acidic environments, and would need the capability of removing protons.

The rough endoplasmic reticulum is given its name due to the ribosomes present within its membrane. These ribosomes are able to translate proteins, which are then modified within the endoplasmic reticulum and sent to the Golgi apparatus.

Ribosomes are the only cellular machinery capable of translating RNA into proteins.

The Golgi apparatus is a series of flattened membrane sacs found in the cell. It receives vesicles filled with proteins from the rough endoplasmic reticulum. The Golgi apparatus is responsible for recognizing proteins based on their signal sequences and sending concentrations of similar proteins to various parts of the cell. It can also deliver proteins out of the cell using secretory vesicles. The membrane sacs of the Golgi apparatus are constantly used and regenerated to create vesicles of packaged proteins.

Local cell signaling in eukaryotic cells refers to the communication between nearby cells. This is done through direct contact between cells, namely via cell junctions and cell-cell recognition. Gap junctions are intercellular connections that allow cytoplasmic transfer in animal cells. The counterpart in plant cells is the plasmodesmata, which are channels penetrating the cell walls of cells, allowing communication. Cell-cell recognition is the ligand-receptor binding between two cells that elicits receptor cell response. Methods of local cell signaling allow nearby cells to communicate with each other and coordinate cellular responses and activities.

Phagocytosis is a form of endocytosis in which a cell takes up solid material through the invagination of the plasma membrane to form intracellular vesicles. In multicellular organisms, the process of phagocytosis is utilized in nutrient uptake, immune system response, and in cell recycling. Cells perform phagocytosis to uptake solid nutrients into the cell. The immune system uses phagocytosis to consume foreign material for eventual degradation. In the continual process of cell recycling, old and dead cell material is taken up and reused by cells.