Cell Biology and Geometry Quiz

The kinetochore is a protein complex that attaches chromosomes to microtubules during cell division. It binds to the centromere, the constricted region of the chromosome where sister chromatids are joined.

Myelin is a fatty substance that wraps around axons, providing insulation. This insulation helps to prevent the diffusion of the electrical signal along the axon, improving the efficiency of nerve impulse transmission.

All cells are defined by the presence of cytosol, a fluid that contains biomolecules such as proteins, lipids, and nucleic acids. This fluid provides a medium for essential cellular processes and houses organelles.

The Anaphase Promoting Complex/Cyclosome (APC/C) is a protein complex that controls the progression of the cell cycle. It triggers the degradation of cyclin proteins and activates the separase enzyme, ultimately leading to the separation of sister chromatids during anaphase.

The cross sections represent a cuboid, a 3D shape with six rectangular faces.

In the EM picture, 1 represents the osteoclast, 2 represents the osteocyte, and 3 represents the bone matrix.

The G1 phase is the first phase of the cell cycle after division. During this phase, the cell grows, synthesizes new proteins, and makes new organelles. DNA synthesis does not occur in this phase.

S/Cdk is a cyclin-dependent kinase complex that triggers the initiation of DNA replication during the S phase of the cell cycle.

Multicellular organisms belong to the Eukaryotic domain. This domain encompasses all organisms that contain a nucleus and other membrane-bound organelles within their cells.

The organelle indicated by number 1 is a mitochondrion. These organelles are responsible for cellular respiration, the process of converting nutrients into energy.

Cyclins are proteins involved in regulating the cell cycle. They are degraded at the end of the M phase, specifically at the metaphase/anaphase transition (Checkpoint 3 in the picture). This degradation is crucial for the progression of the cell cycle.

The striped pattern observed in collagen fibers under the electron microscope is caused by the staggered arrangement of tropocollagen molecules. These individual molecules assemble into a larger fiber, creating the characteristic banding pattern.

The TED talk by Professor Clevers highlighted two advantages of stem cell therapy: 1. Transplantation of organ parts: Stem cells can be used to regenerate specific tissues, allowing for partial organ transplantation. 2. Autologous transplantation: Stem cells can be derived from the patient themselves, reducing the risk of rejection.

Ordered from largest to smallest: nucleus, mitochondrion, ribosome, water molecule.

Electron microscopes use a beam of electrons to create images, while light microscopes use a beam of light. Therefore, electron microscopes contain components not found in light microscopes, such as electron guns and electromagnetic lenses.

Desmosomes are cell junctions that provide strong adhesion between cells. They are characterized by the presence of cadherins, proteins that bind to intermediate filaments.

GTP hydrolysis plays a crucial role in tubulin polymerization. GTP is bound to tubulin dimers, and its hydrolysis drives the assembly of microtubules. The GTP-bound form promotes polymerization, while the GDP-bound form promotes depolymerization.

Integrin molecules are transmembrane proteins that act as cell adhesion receptors. They bind to the extracellular matrix (ECM), specifically connecting actin filaments to components like collagen.

When a G-protein binds to an activated receptor, the receptor undergoes conformational changes that activate the G-protein. This activation involves the exchange of GDP for GTP on the G-protein.

The length of an actin filament is determined by the number of actin monomers that are added or removed from the filament ends. Actin monomers bind to the plus end of the filament, driving its growth, while they can also detach from the minus end, leading to shrinkage.

The Signal Recognition Particle (SRP) is a protein-RNA complex that recognizes and binds to signal sequences on newly synthesized proteins destined for the endoplasmic reticulum (ER). The SRP then interacts with a receptor on the ER membrane, facilitating the targeting and translocation of the protein across the ER.

Protein disulfide isomerase (PDI) is an enzyme that catalyzes the formation and breakage of disulfide bonds in proteins. It is retained in the endoplasmic reticulum (ER) by a C-terminal KDEL signal sequence. This signal sequence allows for the retrieval of PDI from the Golgi apparatus back to the ER.

Pinocytosis is a type of endocytosis where the cell takes in small amounts of extracellular fluid. The cell membrane invaginates, forming a vesicle that encloses the fluid and brings it into the cell.

Mannose-6-phosphate is a targeting signal used for directing newly synthesized lysosomal enzymes to their appropriate destination. It is added to the lysosomal enzymes in the Golgi apparatus, allowing them to be sorted and packaged into transport vesicles destined for lysosomes.

The majority of mitochondrial proteins are synthesized in the cytoplasm, not in the nucleus. These proteins have specific signal sequences that allow them to be imported into the mitochondrial matrix.