Cellular Biology - AP Biology

ATP synthase is an enzyme that facilitates the generation of energy (ATP) in cells. It uses the proton gradient created by the electron transport chain to create ATP through oxidative phosphorylation. ATP synthase is an integral membrane protein in the inner membrane of mitochondria. Recall that all membranes are mostly made up of phospholipids (a type of lipid).

When electrons go through the electron transport chain, the protons in the matrix of the mitochondrion are pumped into the intermembrane space (the space between inner and outer membranes). This creates a proton gradient that is used by ATP synthase to create ATP through oxidative phosphorylation, not substrate-level phosphorylation. Remember that substrate-level phosphorylation is used by glycolysis and the Krebs cycle to generate ATP.

When electrons travel down the series of molecules in the electron transport chain they go from molecules of low electron affinity to molecules high electron affinity. The next molecule in the series must have higher affinity so that it can pull the electron away from its predecessor.

ATP synthase, the enzyme responsible for ATP production on the inner mitochondrial membrane, depends on the proton gradient produced by the electron transport chain (ETC). If the proton gradient is disrupted, not as many ATP can be produced.

NADH and FADH2 are essential to the function of the electron transport chain as electron donors, and are produced during glycolysis and the Krebs cycle to facilitate this process. Electron donation from these compounds is what fuels the formation of the proton gradient, while decreases in these compounds can cause uncoupling.

The Golgi apparatus is derived from the endoplasmic reticulum and consists of a series of flattened sacs. The function of the Golgi apparatus is to package and transport proteins to the cell surface within vesicles, which pinch off from the Golgi. These vesicles then interface with the cell membrane, releasing their contents into the extracellular space or integrating membrane proteins into the cell membrane.

The Golgi apparatus is not involved in differentiation between the smooth and rough endoplasmic reticulum. This difference comes from the presence of ribosomes, which are embedded in the surface of the rough endoplasmic reticulum, but absent from the smooth endoplasmic reticulum. The rough endoplasmic reticulum is responsible for synthesizing and modifying proteins that are destined for the Golgi apparatus for packaging. The smooth endoplasmic reticulum helps eliminate toxins from the cell.

Each of these answers correctly describes characteristics of mitochondria. Mitochondria are semi-autonomous: they are capable of synthesizing some of their own proteins with DNA and ribosomes. The proteins are then embedded in the inner mitochondrial membrane, and function in the electron transport chain. Mitochondria have two membranes, an inner membrane and an outer membrane. Mitochondria are the sites of cellular respiration and ATP production, often called the "powerhouse" of the cell. After glycolysis, pyruvate is transported to the mitochondrial matrix for the Krebs cycle and electron transport chain. Mitochondria are not involved in the endomembrane system; they are separate organelles.

The smooth endoplasmic reticulum contains enzymes responsible for the metabolism of small chemical molecules such as alcohol, pharmaceutical drugs, and environmental contaminants. Expansion of the smooth endoplasmic reticulum can occur under conditions of new and continued exposure to a given chemical or stimulus as an adaptation to metabolize and eliminate the drug or chemical.

Smooth endoplasmic reticulum is particularly abundant in hepatocytes, or liver cells. Blood absorbs nutrients and ingested toxins from the small intestine and immediately travels to the liver through the portal vein. Hepatocytes then filter and metabolize the absorbed toxins before they can circulate through the body.

Mitochondria and chloroplasts are organelles within eukaryotic and plant cells, respectively. All eukaryotic organisms contain mitochondria, but only photoautotrophs will contain chloroplasts. The function of these organelles is to produce energy for the cell to survive and function. Mitochondria produce energy through respiration and chloroplasts produce energy through photosynthesis. These organelles have their own DNA to express their own set of genes and have ribosomes to make the proteins necessary to make energy for the cell. The proteins for the electron transport chain, for example, are transcribed and translated within the mitochondrial matrix before being implanted in the inner mitochondrial membrane.

The mitochondria are membrane-bound organelles involved in the process of cellular respiration. Specifically, the Krebs cycle takes place in the matrix of the mitochondria and the electron transport chain takes place along the inner mitochondrial membrane. During aerobic respiration, oxygen is used as the final electron receptor of the electron transport chain and generates water as a byproduct. Without oxygen, the mitochondria cannot perform oxidative phosphorylation, and the cell must rely on glycolysis for energy.

Lysosomes contain hydrolytic enzymes that can digest macromolecules from phagocytosis, endocytosis, and autophagy. When damage occurs to the membrane of the lysosome, these enzymes can be released and cause damage to the cell, leading to apoptosis.

Peroxisomes contain peroxidases, which help to eliminate hydrogen peroxide from the cell and prevent the creation of free radicals. The nucleus houses DNA and would be severely damaged by the introduction of hydrolytic enzymes. The plasma membrane is used to contain the cytoplasm and organelles and the endoplasmic reticulum is used to modify and package proteins.

Homeostasis is the mechanism that allows for organisms to maintain equilibrium of their internal environments. Certain variables of the internal environments are regulated such that the conditions of the organism remain stable and relatively constant. This is often accomplished via negative feedback loops and hormone regulation.

Reproduction refers to an organism's ability to generate offspring. Respiration refers to the method of gas exchange in the lungs. Synthesis refers to the generation of certain molecules. Mitosis refers to cellular division. While any of these processes could be used to affect the equilibrium state of an organism, they are all mediated by homeostatic mechanisms in order to maintain biological stability.

Centrioles are cell structures that are mainly composed of tubulin and are involved in the organization of the mitotic spindle and cytokinesis during cell division.

Cellular respiration primarily occurs on the inner mitochondrial membrane with the aid of membrane proteins. Glycolysis and gluconeogenesis occur in the cytoplasm and are facilitated by proteins. Lipids are mostly stored in bones and adipose tissue. These processes do not require intervention from the cytoskeleton or microtubules that compose the centrioles.

Nuclear lamins are fibrous proteins (intermediate filaments) that provide the structural function and the transcriptional regulation in the nucleus of a cell. Note that lamins differ from laminins, which are a protein component of basement membranes.

Euchromatin is “light” chromatin that represents DNA that is currently active for transcription. The fact that it is “light” implies that it is relatively decondensed and accessible by polymerases. Euchromatin is generally present during interphase, when most transcription and replication takes place, and is converted to heterochromatin during mitosis.

Translation occurs outside of the nucleus and uses mRNA as a template, not DNA.

Remember that NADH and FADH2 are electron carriers and do not directly create any energy. The movement of the electrons through the electron transport chain also does not create energy directly, but does create a proton gradient that is later used to create energy. The movement of protons down its proton gradient through ATP synthase does, however, generate energy. It actually generates around 30 ATP molecules per one glucose.

In both cellular respiration and photosynthesis, chemiosmosis occurs. Chemiosmosis is the process in which the creation of a proton gradient leads to the transport of proton down its concentration gradient to produce ATP. This occurs in the electron transport chain in both mitochondrias and chloroplast. In the photosynthesis it occurs when the electron is transported from photosystem II to photosystem I.

The laws of inheritance include the laws of segregation (each gamete receives only one copy of each gene from its parent), dominance (in a heterozygote individual, only the dominant allele will influence the phenotype), and independent assortment (inheritance of one gene does not influence inheritance of another gene)

The law of independent assortment states that inheritance of one gene does not influence inheritance of another gene. Thus, inheritance of seed color does not affect the inheritance of seed shape.

According to the Law of Segregation, each gamete receives one allele for each gene from each parent. During Meiosis, each parent’s two copies of each allele are separated from each other, then the gamete receives one copy of each allele from each parent (for a total of two alleles).

This is the definition of the law of independent assortment; during meiosis, the inheritance of one gene does not influence whether another, separate gene will also be inherited by that gamete.