Understanding Other Cell Structures - Biology

Recall that the central dogma of molecular biology states that the information flow within a cell involves DNA replication, transcription, and translation. DNA replication involves the formation of two identical DNA molecules from a single molecule and transcription involves synthesis of mRNA from DNA. The DNA molecules can’t leave the nucleus, therefore, both of these processes occur in the nucleus

Translation involves the synthesis of proteins from mRNA molecules. The mRNA molecules exit the nucleus after transcription (through nuclear pores) and enter the cytosol. The ribosomes in the cytosol bind to mRNA and facilitate translation; therefore, translation occurs in the cytosol.

A cell’s cytoskeleton is made up of three types of filaments: microfilaments, intermediate filaments, and microtubules. Microfilaments are made up of actin, whereas microtubules are made up of tubulin. Flagella, cilia, and the mitotic spindle of the cell are made from microtubules. The only filament given that is not made up of tubulin is microfilament.

The question states that the lumen of the organelle contains a high concentration of hydrogen ions. Recall that a high concentration of hydrogen ions results in a low pH. Lysosomes are organelles that contain degradative, hydrolytic enzymes that break down the cell’s waste products. These enzymes need a low pH to be functional, therefore, the lumen of lysosomes has a low pH (around a pH of 5). Lysosomes are known for having a high concentration of hydrogen ions to facilitate this acidic environment.

The other organelle known for sequestering hydrogen ions is the mitochondria. In mitochondria, hydrogen ions are used to create the gradient in the intermembrane space that is used to make ATP.

Atoms are the smallest functional unit of matter and are used to construct complex molecules, such as proteins. A protein is composed of numerous smaller atoms.

Ribosomes are composed of ribosomal RNA (rRNA) and proteins, but are smaller than viruses. Viruses are composed of protein coats that house genetic information coded in nucleic acids.

Mitochondria are membrane-bound organelles within the cell. These structures are smaller than the nucleus, but larger than ribosomes. While viruses must be small enough to enter the nucleus through nuclear pores, mitochondria are too large to travel much within the cell.

Cells are the basic functional unit of life. Prokaryotic cells and viruses are both significantly smaller than eukaryotic cells. Eukaryotic cells are relatively large in order to accommodate the various organelles and process that occur within them.

In order from smallest to largest, the answer is atoms, proteins, ribosomes, viruses, mitochondria, a eukaryotic cell.

Eukaryotic cells are very resourceful in every way they function. When a cell part becomes worn out or non-functional, these part is broken down and recycled by the cell via lysosomal activation. This process is known as autophagy. The biological monomers produced from the catabolic process can then be used to build new polymers and macromolecules.

Exocytosis is the process by which contents from within the cell are expelled across the membrane. This generally occurs to assist cell signaling, such as the exocytosis of neurotransmitters. Positive selection is the process by which T-lymphocytes are presented by "self" antigens. If the T-cell reacts to the "self" antigen, it is destroyed to prevent autoimmune reactions.

Lysosomes are membrane-bound organelles in the cell with a low pH internal environment. This low pH environment enables the activity of certain enzymes that reside in the lysosomes. These enzymes, known as hydrolytic enxymes, break down damaged or inactive proteins.

The incorrect answer choices largely outline processes accomplished by other organelles. The smooth endoplasmic reticulum synthesizes lipids. The Golgi apparatus and rough endoplasmic reticulum are responsible for protein modification and packaging prior to export from the cell; frequently, this will include addition of different monomers, such as a monosaccharide or lipid to adjust the protein's identity or function. Transportation of molecules through the cytoplasm is accomplished by the cytoskeleton and microtubule system.

This question requires the knowledge that several biological substrates come in enantiomer forms (think of them as your right and left hands). Effectively these molecules come in two mirror/opposite configurations. Having the right configuration or shape is crucial for enzymes to catalyze reactions due to highly shape-specific bnding sites on substrate molecules. Thus, the correct answer to this qustion is "enzymes are highly specific on shape in order to carry out a reaction." The other answer choices, except "the cell has evolved to prefer a particular enantiomer becuase it is more abundant," do not allude to this underlying concept of why cells need a particualr enantiomeritic form/shape in order to carry out a reaction and are not correct. Last, enantiomers typically appear in similar oncentrations due to equal potential energies; therefore, it is unlikely and incorrect to expect the cell to develop an evolutionary preference based upon abundance.

Cell theory consists of three statements: all organisms considered to be alive are made of cells, the cell is the simplest unit of a living thing, and all cells arise from other live cells. Thus, the idea that cells arise spontaneously is not part of cell theory.

Ribosomes are composed of protein and ribosomal RNA (rRNA). They are made up of 2 subunits—one small and one large.

Ribosomes are found in all cell types and in all three domains. Recall the central dogma of biology: DNA RNA protein. Thus, all cells synthesize proteins using ribosomes. Also, note that although prokaryotes have ribosomes, ribosomes are never membrane-bound. Thus it still holds true that prokaryotes do not have any membrane-bound organelles.

Glycoproteins are proteins that have been modified by the addition of chains of carbohydrates of varying length. Glycosylation of proteins happens in the endoplasmic reticulum and the Golgi apparatus. Phospholipids are not proteins and are thus not synthesized in the endoplasmic reticulum, rather, they are synthesized in the cytosol. mRNA is the nucleic acid product of transcription, which occurs in the cytosol in eukaryotes, and in the cytosol in prokaryotes. Lumen is the term which means "an opening," e.g., the lumen of a blood vessel is the space where the blood flows, the lumen of the endoplasmic reticulum is the space inside the organelle itself.

One of the functions of the liver is to detoxify certain substances such as alcohol, lactic acid, and drugs. Since the smooth endoplasmic reticulum plays an important role in detoxification, liver cells contain extensive smooth endoplasmic reticula. The process of forming glycoproteins is carried out by the rough endoplasmic reticulum, and to some extent, the Golgi apparatus.

The golgi apparatus collects, packages and distributes proteins to the locations where they are used. Proteins are always synthesized on ribosomes, which can either be floating in the cytosol, or on the rough endoplasmic reticulum. The smooth endoplasmic reticulum's functions include synthesis of lipids, and detoxification of substances. Lysosomes contain hydrolytic enzymes which break down macromolecules.

Lysosomes are membrane-bound organelles that contain digestive enzymes which break down all four types of macromolecules. The mitochondria is responsible for synthesis of the majority of the cell's energy in the form of ATP. The cytoskeleton maintains cell shape and provides a "freeway" for transporting substances within the cell. Flagella are proteinaceous structures that aid in cell motility.

Hydrogen peroxide is an example of a reactive oxygen species, made as a byproduct of metabolism. Peroxisomes use the enzyme catalase to catalyze the following reaction: . Hydrogen peroxide can be toxic to a cell if it builds up, thus converting it to harmless substances like water and oxygen gas is an important metabolic function of peroxisomes. Also, note that the breakdown of fatty acids (beta oxidation) occurs in both peroxisomes and mitochondria. Proteins, carbohydrates, and nucleic acids are broken down by the lysosome.

The plant central vacuole is a membrane bound organelle containing water and other enzymes. The central vacuole functions as a storage space in the center of the plant cell, and is responsible for many functions including digestion, isolating harmful materials, maintaining internal hydrostatic pressure (turgor), storage of water and small molecules, cell rigidity, and more. Aerobic respiration occurs in the mitochondria, where:

The tail, terminal disc, and most mitochondria are found near the rear of the sperm cell (in order to facilitate movement). The acrosome is a cap-like organelle (derived from the Golgi apparatus) that develops over the anterior half of the head in the sperm cells of many animals. The acrosome contains digestive enzymes which allows the break down of the outer membrane of the ovum (zona pellucida). In short, the acrosome is located at the head of the sperm cell and allows penetration of the egg cell.

Lysosomes serve as the "clean-up" crew in the cell, digesting excess proteins and lipids in the cell and breaking them down into smaller molecules. Lysosomes do not produce messenger RNA, which is produced in transcription byDNA. Ribosomes synthesize proteins, and the Golgi Apparatus sorts and ships proteins.

The flagellum (plural flagella) is the whip-like structure on the end of a human sperm cell that propels it forward. Cilia are the hair-like structures on membranes on cells that aid in movement. Smooth endoplasmic reticulum (ER) is the organelle involved in synthesizing lipids and detoxifying substances. Cytoplasm is the jelly-like substance throughout the cell.