Chapter 3

Discuss the consequence of too little cell division and too much cell division.

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List five factors that control when and if a cell divides.

1. The DNA at the tips of chromosomes. 2. Kinases and cyclins. 3. Cell size 4. Hormones and growth factors 5. Space availability

An adult human body consists of about ________ cells. (p. 76)

50 to 100 trillion

List the steps of apoptosis. (p. 106)

A receptor on the cell membrane receives a signal to die. Special enzymes are activated inside the cell. These enzymes lead to cell destruction. The cell changes appearance. Finally, the cell shatters. Phagocytes destroy the remains.

Distinguish between organelles and inclusions

An organelle is a structure within the cytoplasm that has a specific function. Inclusions are masses of lifeless chemicals such as pigments or glycogen.

Provide an example of apoptosis. (p. 106)

Apoptosis carves away webbing between developing fingers and toes.

Distinguish between necrosis and apoptosis. (p. 106)

Apoptosis is fast, orderly, and contained destruction. Necrosis is a disordered form of cell death associated with inflammation and injury.

Explain how apoptosis (cell death) can be a normal part of development. (p. 106)

Apoptosis is programmed cell death which sculpts organs from tissues that naturally overgrow.

State a way that cellular adhesion is essential to health; and a way that abnormal cellular adhesion harms health. (p. 81)

Cellular adhesion enables cells to aggregate to form tissues. Certain cellular adhesion molecules also assist the immune system in recognizing "self" and "non-self" cell surfaces. Abnormal cellular adhesion could indicate a potential threat to health.

Endocytosis

Cellular energy is used to move substances into or out of a cell without actually crossing the cell membrane. Different processes transport substances across the cell membrane.

______________occur simultaneously. (p. 101)

Cytokinesis and telophase

Cytoskeleton

Cytoplasm also contains abundant protein rods and tubules that form a supportive framework called the

List the parts of the nucleus and explain why each is important. (p. 89)

Describe the structure of the nucleus and the functions of its contents. The nucleus is a cellular organelle that is usually located near the center of the cell. It is a relatively large, spherical structure enclosed in a double bilayered nuclear envelope, consisting of inner and outer membranes. This allows various substances to move between the nucleus and the cytoplasm. The nucleolus is a small, dense body composed largely of RNA and protein. It assists in the production of ribosomes. Chromatin consists of loosely coiled fibers composed of DNA molecules and protein that contain information for synthesizing proteins that promote cellular life processes. These become chromosomes during cell divisions.

Which of the following is true? (p. 105)

Differentiated cells are pluripotent until they specialize

Define differentiation

Differentiation is the process by which cells develop different characteristics in structure and function.

Distinguish between hypertonic, hypotonic, and isotonic solutions.

Hypertonic refers to a solution that has a higher osmotic pressure than that of the cell. This causes the cell to shrink as water moves out of the cell. Hypotonic refers to a solution that has a lower osmotic pressure than that of the cell. This causes the cell to swell and possibly burst as water moves into it. Isotonic refers to a solution that has the same osmotic pressure as body fluids. This allows the cell size to remain unchanged as water or solutes are not being pulled in any specific direction.

Explain why interphase is not a period of rest for a cell. (p. 100)

Interphase is the stage in the life cycle of a cell where young cells grow, manufacture compounds, new organelles are made and the chromosomes, and centrioles replicated.

Describe the relationship between apoptosis and mitosis. (p. 109)

Mitosis and apoptosis are synchronized throughout development, maturation, and aging.

Explain how meiosis differs from mitosis. (p. 100)

Mitosis is the division of somatic cells resulting in two identical daughter cells containing the diploid number of chromosomes. Meiosis is the division of sex cells resulting in two, and then four, daughter cells each containing the haploid number of chromosomes

Filtration

Molecules move through membranes by diffusion because of their random movements. In other situations, the process of filtration (fil-tra′shun) forces molecules through membranes. Filtration is commonly used to separate solids from water. One method is to pour a mixture of solids and water onto filter paper in a funnel

Describe three types of differentiated cells. (p. 76)

Nerve cells are long with threadlike extensions that can be used to transmit motor or sensory information. Muscle cells are slender and rod-like which contract to move parts of the body. Epithelial cells, specifically simple squamous, are thin and flattened for gas exchange.

Distinguish between the ways that mutations in oncogenes and tumor suppressor genes cause cancer. (p. 104)

Oncogenes are versions of genes that normally control the cell cycle, but are over expressed, increasing cell division rate. Tumor suppressor genes, when removed or inactivated, lift control of the cell cycle, and uncontrolled cell division results.

Explain the general function of organelles. (p. 76)

Organelles divide the labor in a cell by partitioning off certain areas or providing specific functions, such as dismantling debris or packaging secretions.

Define osmosis

Osmosis is a special type of diffusion involving water. This is when water molecules diffuse from a region of higher water concentration to a region of lower water concentration.

Distinguish between active and passive mechanisms of movement across cell membranes.

Passive mechanisms do not require cellular energy. Active mechanisms use cellular energy.

Describe the events of mitosis in sequence. (p. 101)

Prophase is the first stage of mitosis where the chromosomes appear scattered throughout the nucleus. The nuclear envelope dissolves and the sister chromatids are attached by the centromere. A spindle-shaped group of microtubules forms between the centrioles as they move apart. Metaphase is the second stage of mitosis. The chromosomes move along the spindle fibers and align midway between the centrioles. Spindle fibers become attached to the centromere of the chromosomes. Anaphase is where the centromere of the chromatids separate and the chromatids become individual chromosomes. These are pulled apart toward the opposite sides of the cell. Telophase is the final stage of mitosis where the chromosomes complete their migration toward the centrioles. It is much like prophase but with everything reversed. The nuclear envelope reforms and the chromosomes become invisible.

Explain how phagocytosis differs from receptor-mediated endocytosis. (p. 97)

Receptor-mediated endocytosis moves very specific kinds of particles into the cell. In this process, protein molecules exit through a portion of the cell membrane to the outer surface, where they serve as receptors for liquids. The proteins become binding sites for specific substances found in the interstitial fluid. These are then allowed to enter the cell. It would be useful in the blood-brain barrier if there were a specific receptor that could be triggered to allow substances, such as a drug, to cross the membrane.

The period of the cell cycle when DNA replicates is _________________. (Outcome 3.11)

S phase

Define selectively permeable. (p. 79)

Selectively permeable means that the cell membrane allows some substances to pass through easily, while excluding other substances.

Facilitated diffusion

Small solutes that are not lipid-soluble, such as ions of sodium, potassium, and chloride, may diffuse through specific protein channels in the membrane, described earlier. (Water molecules diffuse through similar channels, called aquaporins.) This type of movement follows the concentration gradient, and because it depends on membrane proteins it is considered a form of facilitated diffusion (fah-sil″-tāt′ed d-fu′zhun).

Describe a general function of stem cells in the body. (p. 106)

Stem cells allow for continual growth and renewal by dividing repeatedly.

Describe the structure of a cell membrane and explain how this structural organization provides the membrane's function. (p. 79)

The basic structure of the cell membrane consists of a phospholipid bilayer. It contains embedded protein molecules. It functions to keep the inner portion of the cell intact. It controls the entrance and exit of substances.

Distinguish between the cytoplasm and the cytosol of a cell. (p. 76)

The cytoplasm is composed of specialized structures called cytpolasmic organelles suspended in a liquid called cytosol. The cytoplasm surrounds the nucleus and is contained by the cell membrane.

Endoplasmic reticulum

The endoplasmic reticulum is the site of protein and lipid synthesis, and serves as a transport system. (a) A transmission electron micrograph of rough endoplasmic reticulum (ER) (28,500×). (b) Rough ER is dotted with ribosomes, whereas (c) smooth ER lacks ribosomes.

List three functions of membrane proteins. (p. 80)

The functions of membrane proteins include acting as a receptor to combine with a specific substance such as a hormone, while some form narrow passageways, or channels, through which various molecules and ions can cross the cell membrane. Others function as enzymes in signal transduction.

Explain how transcytosis combines endocytosis and exocytosis. (p. 98)

Transcytosis is the selective and rapid transport of a substance or particle from one end of a cell to the other. It also enables substances to cross barriers formed by tightly connected cells.

Active transport

When molecules or ions pass through cell membranes by diffusion or facilitated diffusion, their net movement is from regions of higher concentration to regions of lower concentration.

Explain why it is important for the cell cycle to be highly regulated.

With too infrequent mitoses, an embryo could not develop, a child could not grow, and wounds would not heal. Too frequent mitoses or those that continue unabated produce an abnormal growth, or neoplasm, which may form a disorganized mass called a tumor.

Mitochondria

are elongated, fluid-filled sacs 2-5 µm long. They often move slowly in the cytoplasm and can divide. A mitochondrion contains a small amount of DNA that encodes information for making a few types of proteins and specialized RNA.

Vesicles

are membranous sacs that store or transport substances within a cell

Ribosomes

are tiny, spherical structures composed of protein and RNA. They provide a structural support and enzymatic activity to link amino acids to form proteins

The three major parts of a cell are ______________________________. (p. 76)

b. the nucleus, cytoplasm, and the cell membrane

Golgi apparatus

is a stack of half a dozen or so flattened, membranous sacs called cisternae. This organelle refines, packages, and delivers proteins synthesized on the rough ER

Exocytosis

is essentially the reverse of endocytosis. Substances made in the cell are packaged into a vesicle, which then fuses with the cell membrane, releasing its contents outside the cell. Cells secrete some proteins by this process. Nerve cells use exocytosis to release the neurotransmitter chemicals that signal other nerve cells, muscle cells, or glands

Diffusion

is the tendency of atoms, molecules, and ions in a liquid or air solution to move from areas of higher concentration to areas of lower concentration, thus becoming more evenly distributed, or more diffuse.

Cilia

motile extensions of certain cells.

A stem cell ____________. (p. 105)

self-renews.

Peroxisomes

synthesis of bile acids used in fat digestion breakdown of lipids called very-long-chain fatty acids degradation of rare biochemicals detoxification of alcohol