The atomic number of 19 is the same as the number of protons. The first orbit has the maximum two electrons, and the second orbit has the maximum eight electrons. That makes ten electrons in the first two orbits, leaving only four for the third, outermost orbit.
The more hydroxide ions there are, the stronger the base is. Isotopes also have different atomic This is true whether an atom fills its outer shell by sharing, gaining, or losing electrons. This statement is false because only RNA contains uracil. Being such large molecules, proteins need to be built from complex molecules to begin with.
Remember that glucose must become pyruvic acid before it enters the Krebs cycle. Two net mole- cules of ATP come from glycolysis, two molecules come from the Krebs cycle, and the electron transport chain churns out Breaking things down is a catabolic reaction, but building them up is anabolic.
So anaerobic is the opposite. The Krebs cycle and the electron transport chain. You need to turn the coal into electricity, and cells need to turn the glucose into ATP. A Fats are metabolized primarily during d. Every living thing has cells, but not all living things have the same kinds of cells.
Plant cells have fibrous cell walls; animal cells do not, making do instead with a semipermeable cell mem- brane, which sometimes is called a plasma membrane or the plasmalemma. This semipermeability, or selective permeability, is a result of a double layer bilayer of phospho- lipid molecules interspersed with protein molecules. The outer surface of each layer is made up of tightly packed hydrophilic or water-loving polar heads. Inside, between the two layers, you find hydrophobic or water-fearing nonpolar tails consisting of fatty acid chains.
Cholesterol molecules between the phosphate layers give the otherwise elastic membrane stability and make it less permeable to water-soluble substances.
Both cytoplasm and the matrix, the material in which cells lie, are primarily water. The polar heads electrostatically attract polarized water molecules while the nonpolar tails lie between the layers, shielded from water and creating a dry middle layer.
Lipid-soluble molecules can pass through this layer, but water-soluble molecules such as amino acids, sugars, and proteins cannot. Although it can spontaneously repair minor tears, severe damage to the membrane will cause the cell to disintegrate.
The membrane is picky about which molecules it lets in or out. When equilibrium is reached, diffusion continues, but the flow is equal in both directions. Diffusion is a natural phenomenon that behaves in much the same way as Brownian motion; both phenomena are based on the fact that all molecules possess kinetic energy.
They move randomly at high speeds, colliding with one another, changing directions, and moving away from areas of greatest concentration to areas of lower concentration. The rate of movement depends on the size and temperature of the molecule; the smaller and warmer the molecule is, the faster it moves.
The unassisted diffusion of very small or lipid-soluble particles is called simple diffusion. The assisted process is known as facilitated diffusion. Embedded with the hydrophilic heads in the outer layer are protein molecules called channel proteins that create diffusion-friendly openings for the molecules to diffuse through. Solutions are composed of two parts: a solvent and a solute. The solvent is the liquid in which a substance is dissolved; water is called the universal solvent because more materials dissolve in it than in any other liquid.
A solute is the substance dis- solved in the solvent. Typically, a cell contains a roughly 1 percent saline solu- tion — in other words, 1 percent salt solute and 99 percent water solvent. Water is a polar molecule that will not pass through the lipid bilayer; however, it is small enough to move through the pores of most cell membranes. The membrane allows the solvent water to move through but keeps out the particles dissolved in the water.
Transport by osmosis is affected by the concentration of solute the number of particles in the water. One molecule or one ion of solute displaces one molecule of water. Osmolarity is the term used to describe the concentration of solute par- ticles per liter.
As water diffuses into a cell, hydrostatic pressure builds within the cell. Eventually, the pressure within the cell becomes equal to, and is bal- anced by, the osmotic pressure outside. So the membrane of a human cell placed in 10 percent saline solu- tion 10 percent salt and 90 percent water would let water flow out of the cell from higher concentration inside to lower concentration outside , therefore shrinking it. Embedded with the hydrophilic heads in the outer layer of the membrane are protein mole- cules able to detect and move compounds through the membrane.
These carrier or transport proteins interact with the passenger molecules and use the ATP-sup- plied energy to move them against the gradient. The carrier molecules combine with the transport molecules — most importantly amino acids and ions — to pump them against their concentration gradients.
In addition, there are secondary active transport processes that are similar to diffusion but instead use imbalances in electrostatic forces to move molecules across the membrane. Fill in the blanks to complete the following sentences: The lipid bilayer structure of the cell membrane is made possible because phospholipid molecules contain two distinct regions: The 1. Because it has both polar and non- polar regions, a phospholipid is classified as a n 3.
The movement of water molecules through a semipermeable membrane is known as a. Diffusion b. Filtration c. Osmosis d. Active transport 5. A solution having a greater concentration of water than exists in the cell is said to be a. Hypertonic b. Hypotonic c. Isotonic d. Heterotonic 6. Swell and burst b. Shrink c. Carry more oxygen d.
Aggregate 7. The cell membrane does not function a. In selective transport of materials into and out of the cell b. As a barrier protecting the cell c. In the production of energy d. On average, it accounts for about 10 percent of the total volume of the cell, and it holds a complete set of genes.
The outermost part of this organelle is the nuclear envelope, which is composed of a double-membrane barrier, each membrane of which is made up of a phospholipid bilayer. Between the two membranes is a fluid-filled space called the perinuclear cis- terna.
The two layers fuse to form a selectively permeable barrier, but large pores allow relatively free movement of molecules and ions, including large protein mole- cules. Intermediate filaments lining the surface of the nuclear envelope make up the nuclear lamina, which functions in the disassembly and reassembly of the nuclear membrane during mitosis and binds the membrane to the endoplasmic reticulum. The nucleus also contains nucleoplasm, a clear viscous material that forms the matrix in which the organelles of the nucleus are embedded.
DNA is packaged inside the nucleus in structures called chromatin, or chromatin networks. During cell division, the chromatin contracts, forming chromosomes. The most prominent subnuclear body is the nucleolus, a small spherical body that stores RNA molecules and produces ribosomes, which are exported to the cytoplasm where they translate messenger RNA mRNA.
The following is an example question about the nucleus: Q. The only cellular organelle found A. The correct answer is nucleolus. Lamina b. Envelope c. Nucleolus d. Chromosome 8. The fluid-filled space within the nuclear envelope is called the a.
Perinuclear cisterna b. Ribosome c. Mitochondrion d. Golgi appartus 9. DNA is packaged within a. Chromatins b. Chromosomes c. Ribosomes d. The nucleolus a. Packages DNA b. Enables large molecule transport c. Forms a membrane around the nucleus d. Assembles ribosomes Looking Inside: Organelles and Their Functions Molecules that pass muster with the cell membrane enter the cytoplasm, a mixture of macromolecules such as proteins and RNA and small organic molecules such as glu- cose, ions, and water.
The fluid part of the cytoplasm, called the cytosol, has a dif- fering consistency based on changes in temperature, molecular concentrations, pH, pressure, and agitation. Within the cytoplasm lies a network of fibrous proteins collectively referred to as the cytoskeleton. They provide structural support and have a role in cell and organelle movement as well as in cell division.
They average about 10 nanometers wide and consist of interlocking proteins, including keratin, that chiefly are involved in maintaining cell integrity and resist- ing pulling forces on the cell. Like microfilaments, these components of cilia, flagella, and centrioles provide structural support and have a role in cell and organelle movement as well as in cell division. Each organelle has different responsibilities for producing materials used elsewhere in the cell or body.
In multicellular animals, including humans, cilia move materials over the surface of the cell. Composed of membrane-bound canals and cavities that extend from the nuclear membrane to the cell membrane, the ER is the site of lipid and pro- tein synthesis. The two types of ER are rough, which is dotted with ribosomes on the outer surface; and smooth, which has no ribosomes on the surface.
Located near the nucleus, it functions in the storage, modification, and packaging of pro- teins for secretion to various destinations within the cell. It destroys foreign particles in the cell and helps to remove nonfunctioning structures from the cell. The inward-folding crevices of the inner membrane are called cristae. The mito- chondrion provides critical functions in cell respiration, including oxidizing breaking down food molecules and releasing energy that is stored in ATP mole- cules in the mitochondrion.
This energy is used to accelerate chemical reactions in the cell, which we cover in Chapter 1. Composed of 60 percent RNA and 40 percent protein, they translate the genetic information on RNA mole- cules to synthesize, or produce, a protein molecule.
In animal cells, food vacuoles are membranous sacs formed when food masses are pinched-off from the cell membrane and passed into the cytoplasm of the cell.
Vacuoles also help to remove structural debris, isolate harmful materi- als, and export unwanted substances from the cell. Answer these practice questions about cell organelles: This cigar-shaped organelle produces energy through aerobic respiration.
Golgi apparatus b. Mitochondrion c. Lysosome d. The most abundant protein in human cells is a. Actin b. Tubulin c. Albumen d. Cytoplasm Which organelle gets to take out the cellular trash? Vacuole d. Endoplasmic reticulum The very small organelle responsible for protein synthesis making proteins is the a. Ribosome b. Lysosome c.
Centriole d. Vesicle Which organelle has ribosomes attached to it? Smooth agranular endoplasmic reticulum b. Golgi apparatus c. Rough granular endoplasmic reticulum d. Nucleus Which organelle contains secretory materials? Which of the following can change the consistency of cytoplasm? Changes in acidity or alkalinity b. Temperature c. Pressure d. All of the above Structures found inside the nucleus include the a. Mitochondria b. Lysosomes c. Chromatin network d.
Use the terms that follow to identify the cell structures and organelles shown in Figure Centrioles b. Cilia c. Cytoplasm d. Golgi apparatus e. Lysosome f. Mitochondrion g. Nucleolus h. Nucleus i. Plasma cell membrane j. Ribosomes k. Rough endoplasmic reticulum l. Smooth endoplasmic reticulum m. Vacuoles n. Match the organelles with their descriptions.
Long, whip-like organelle for locomotion Fluid-like interior of the cell that may become a semisolid, or colloid Membranous sacs containing digestive enzymes Powerhouse of the cell The mRNA moves through nuclear pores to the rough endoplasmic reticulum ER , where ribosomes translate the message one codon of three nucleotides, or base pairs, at a time.
The ribosome uses transfer RNA, or tRNA, to fetch each required amino acid and then link them together through peptide bonds, also known as amide bonds, to form proteins see Figure for details. Proteins are chains of amino acids usually very long chains of at least acids. Enzymes, used to catalyze reactions, also are chains of amino acids and therefore also are categorized as proteins. Polypeptides, or simply peptides, are shorter chains of amino acids used to bond larger protein molecules, but they also can be regarded as proteins.
Both antibodies and hormones also are pro- teins, along with almost everything else in the body — hair, muscle, cartilage, and so on. Even the four basic blood types — A, B, AB, and O — are differentiated by the pro- teins found in each. There, ribosomes Molecules called Hormones b. Enzymes c. Antibodies d. Which of the following comes first in the protein-synthesis process?
Transfer RNA b. Transcription c. Peptide bonds d. Translation Blood cells b. Protein molecules d. DNA A codon is a sequence of three a. Nucleotides b. Base pieces Cycling Along: Grow, Rest, Divide, Die The cell life cycle, usually referred to simply as the cell cycle or the CDC cell division cycle , extends from the beginning of one cell division to the beginning of the next division. The human body produces new cells every day to replace those that are damaged or worn out.
We cover this phase in detail in Chapter 3. New cells are produced for growth and to replace the billions of cells that stop function- ing in the adult human body every day. Some cells, like blood and skin cells, are contin- ually dividing because they have very short life cycles, sometimes only hours. Other cells, such as specialized muscle cells and certain nerve cells, may never divide at all. Human cells can live a. A few hours b. A few days c. Indefinitely d.
The cell cycle is measured a. By the number of times a cell divides b. From the beginning to the end of one cell division c. From the beginning of one cell division to the beginning of the next d. Because it has both polar and nonpolar regions, a phospholipid is classified as a n 3. Why not diffusion? Because diffusion has to do with the passive transport of substances other than water.
The prefix hypo refers to under or below normal. The prefix hyper refers to excess, or above normal. Someone who has been out in the cold too long suffers hypothermia — literally insuffi- cient heat. So a solution, or tonic, with very few particles would be hypotonic.
With more water outside the cell than inside, the membrane would allow osmosis to continue past the breaking point. The nuclear lamina, or intermediate filaments, link the ER with the nucleus. None of the other answer options contains a full package of DNA. None of the other options are involved in cellular respiration or energy production l The most abundant protein in human cells is a.
Cells pull out the vacuoles. Protein synthe- sis. Get it? Rough granular endoplasmic reticulum. This is a good example of using previous questions to answer later ones.
Golgi apparatus. All of the above. In addi- tion, molecular concentration and agitation also can change cytoplasmic consistency. Cytoplasm; Vesicle formation; Nucleolus; Nucleus; Vacuoles; Rough endoplasmic reticulum; Golgi apparatus; Plasma cell membrane; Cilia; Mitochondrion; Ribosomes; Smooth endoplasmic reticulum; Lysosome; Centriole H Mitochondrion: d. Powerhouse of the cell I Nucleolus: e.
Long, whip-like organelle for locomotion K Cytoplasm: b. Fluid-like interior of the cell that may become a semisolid, or colloid L Lysosomes: c. Proteins come in myriad shapes, sizes, and functions.
U Which of the following comes first in the protein synthesis process? Remember that you have to transcribe before you can translate. V tRNA is used to gather b. Simple as that. W A codon is a sequence of three a. It takes three to round up a single amino acid.
X Human cells can live d. Cell life cycles can vary widely. Y The cell cycle is measured c. Your cells already do that. That one cell divides and divides and divides , eventually becoming an entire complex being. Their younger, more functional neighbors divide to take up the slack.
Only single-celled organisms do. Although cell division breaks down into several stages, there are no pauses from one step to another. Cell division as a whole is called mitosis because most of the changes occur during that process. But mitosis and cytokinesis do end together. Keep in mind: Cells are living things, so they mature, reproduce, and die. In this chapter, we review the cell cycle as mitosis also is known , and you get plenty of practice figuring out what happens when and why.
The Mitotic Process It may look like cells are living out their useful lives simply doing whatever specialized jobs they do best, but in truth mitosis is a continuous process. It begins when the new cells are done forming and ends when the cell prepares to divide. Interphase is divided into subphases, each of which lasts anywhere from a few hours for those cells that divide frequently to days or years for those cells that divide less frequently nerve cells, for example, can spend decades in interphase.
The two centrioles that have formed from the centrosome push apart to opposite ends of the nucleus. Using protein filaments, they form poles and a mitotic spindle between them as well as asters or astral rays which radiate from the poles into the cytoplasm.
At the same time, the chromatin threads or chromonemata shorten and coil, forming visible chromosomes. The chromosomes divide into chro- matids that remain attached at an area called the centromere, which produces micro- tubules called kinetochore fibers. These interact with the spindle to assure that each daughter cell ultimately has a full set of chromosomes.
The chromatids start to migrate toward the equatorial plane, an imaginary line between the poles. The nucleus itself is gone. The chromatids line up exactly along the center line of the cell or the equatorial plane , attaching to the mitotic spindle by the centromere.
The centromere also is attached by microtubules to opposite poles of the cell. Packing up to move out: Anaphase In anaphase, the centromeres split, separating the duplicate chromatids and forming two chromosomes. The spindles attached to the divided centromeres shorten, pulling the chromosomes toward the opposite poles. The cell begins to elongate. In late anaphase, as the chromosomes approach the poles, a slight furrow develops in the cytoplasm, showing where cytokinesis will eventually take place.
The spindles and asters of early mitosis disappear, and each newly forming cell begins to synthesize its own structure. New nuclear membranes enclose the separated chromosomes. The coiled chromo- somes unwind, becoming chromonemata once again. The furrow intended to divide the newly formed sister nuclei at last gets to finish the job. It migrates inward until it cleaves the single, altered cell into two new cells. Each new cell is smaller and contains less cytoplasm than the mother cell, but the daughter cells are genetically identical to each other and to the original mother cell.
Try this warm-up question on cell division: Q. Cell division takes place to A. The correct answer is all of the above. In addition, single-cell a. Repair injuries organisms use cell division for b. Replace nonfunctioning cells asexual reproduction. Grow the organism d. All of the above 1. Cells are dormant during interphase. True b.
False 2. The G1 subphase of interphase is a. The period of DNA synthesis b. The most active phase c. The phase between S and G2 d. Part of cell division 3. DNA is duplicated during which subphase? The nuclear membrane, or envelope, disappears during a.
Telophase b. Metaphase c. Prophase d. Interphase 5. Which of the following happens in prophase? The chromatids align on the equatorial plane. The chromosomes divide into chromatids. The nucleus reappears. The chromosomes move to opposite poles. Which of the following is true for metaphase? The nuclear membrane appears. The chromosomes move to the poles. During metaphase, each chromosome consists of two duplicate chromatids. False 8. Identify an event that does not happen during anaphase.
Early cytokinesis occurs with slight furrowing. The cell goes through subphase G1. Spindles shorten. The centromeres split. Genetically identical chromosomes are pulled toward opposite poles during a. Anaphase d. Interphase Which event does not occur during telophase? The chromosomes uncoil. The chromosomes reach the poles. The chromosomes become more distinct. The nuclear membrane reforms. What structures disappear during telophase? Spindles and asters b.
Nuclear membranes c. Nucleolei d. Which is the correct order of mitosis? Prophase, interphase, metaphase, telophase, anaphase b. Interphase, prophase, metaphase, anaphase, telophase c. At Medicos Library, we believe in quality and speed which are a part of our core philosophy and promise to our viewers.
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