Chapter 3 review BIOL

Study Outline

An Introduction to Cells

Contemporary cell theory incorporates several basic concepts: (1) Cells are the building blocks of all plants and animals; (2) cells are produced by the division of preexisting cells; (3) cells are the smallest units that perform all vital physiological functions; and (4) each cell maintains homeostasis at the cellular level. (Spotlight Figure 3–1)

Cytology, the study of cellular structure and function, is part of cell biology.

The human body contains two types of cells: sex cells (sperm and oocytes) and somatic cells (all other cells). (Spotlight Figure 3–1)

3-1 The plasma membrane separates the cell from its surrounding environment and performs various functions

A typical cell is surrounded by extracellular fluid—specifically, the interstitial fluid of the tissue. The cell’s outer boundary is the plasma membrane (cell membrane).

The plasma membrane’s functions include physical isolation, regulation of exchange with the environment, sensitivity to the environment, and structural support. (Figure 3–2)

The plasma membrane is a phospholipid bilayer, which contains other lipids, proteins, and carbohydrates.

Integral proteins are part of the membrane itself; peripheral proteins are attached to, but can separate from, the membrane.

Membrane proteins can act as anchors (anchoring proteins), identifiers (recognition proteins), enzymes, receptors (receptor proteins), carriers (carrier proteins), or channels.

The carbohydrate portions of proteoglycans, glycoproteins, and glycolipids form the glycocalyx on the outer cell surface. Functions include lubrication and protection, anchoring and locomotion, specificity in binding, and recognition.

3-2 Organelles within the cytoplasm perform particular functions

The cytoplasm contains the fluid cytosol and the organelles suspended in the cytosol.

Cytosol (intracellular fluid) differs from extracellular fluid in composition and in the presence of inclusions.

Nonmembranous organelles are not completely enclosed by membranes, and all of their components are in direct contact with the cytosol. They include the cytoskeleton, microvilli, centrioles, cilia, ribosomes, and proteasomes. (Spotlight Figure 3–1)

Membranous organelles are surrounded by phospholipid membranes that isolate them from the cytosol. They include the endoplasmic reticulum, the Golgi apparatus, lysosomes, peroxisomes, mitochondria, and nucleus. (Spotlight Figure 3–1)

The cytoskeleton gives the cytoplasm strength and flexibility. All cells have three cytoskeletal components: microfilaments (typically made of actin), intermediate filaments, and microtubules (made of tubulin). Muscle cells also have thick filaments (made of myosin). (Figure 3–3)

Microvilli are small, nonmotile projections of the plasma membrane that increase the surface area exposed to the extracellular environment. (Figure 3–3)

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The centrosome is a region of the cytoplasm near the nucleus. It is the microtubule organizing center surrounding the paired centrioles. Centrioles direct the movement of chromosomes during cell division. (Figure 3–4)

A single, nonmotile primary cilium is sensitive to environmental stimuli. Multiple motile cilia, each anchored by a basal body, beat rhythmically to move fluids or secretions across the cell surface. (Figure 3–4)

Ribosomes, responsible for manufacturing proteins, are composed of a small and a large ribosomal subunit, both of which contain ribosomal RNA (rRNA). Free ribosomes are in the cytoplasm, and fixed ribosomes are attached to the endoplasmic reticulum. (Spotlight Figure 3–1)

Proteasomes remove and break down damaged or abnormal proteins that have been tagged with ubiquitin.

The endoplasmic reticulum (ER) is a network of intracellular membranes that function in synthesis, storage, transport, and detoxification. The ER forms hollow tubes, flattened sheets, and chambers called cisternae. Smooth endoplasmic reticulum (SER) is involved in lipid synthesis; rough endoplasmic reticulum (RER) contains ribosomes on its outer surface and forms transport vesicles. (Figure 3–5; Spotlight Figure 3–7)

The Golgi apparatus, or Golgi complex, forms secretory vesicles and new plasma membrane components, and packages lysosomes. Secretions exit the cell by exocytosis. (Figure 3–6; Spotlight Figure 3–7)

Lysosomes, vesicles filled with digestive enzymes, are responsible for the autolysis of injured cells. (Figures 3–6, 3–8; Spotlight Figure 3–7)

Peroxisomes carry enzymes that neutralize potentially dangerous free radicals.

Membrane flow, or membrane trafficking, refers to the continuous movement and recycling of the membrane among the ER, vesicles, the Golgi apparatus, and the plasma membrane.

Mitochondria are responsible for ATP production through aerobic metabolism. The matrix, or fluid contents of a mitochondrion, lies inside the cristae, or folds of an inner membrane. (Figure 3–9)

3-3 The nucleus contains DNA and enzymes essential for controlling cellular activities

The nucleus is the control center of cellular operations. It is surrounded by a nuclear envelope (a double membrane with a perinuclear space), through which it communicates with the cytosol by way of nuclear pores. (Spotlight Figure 3–1; Figure 3–10)

The nucleus contains a supportive nuclear matrix; one or more nucleoli typically are present.

The nucleus controls the cell by directing the synthesis of specific proteins, using information stored in chromosomes, which consist of DNA bound to histones. In nondividing cells, DNA and associated proteins form a tangle of filaments called chromatin. (Figure 3–11)

The cell’s information storage system, the genetic code, is called a triplet code because a sequence of three nitrogenous bases specifies the identity of a single amino acid. Each gene contains all the DNA triplets needed to produce a specific polypeptide chain.

3-4 DNA controls protein synthesis, cell structure, and cell function

As gene activation begins, RNA polymerase must bind to the gene.

Transcription is the production of RNA from a DNA template. After transcription, a strand of messenger RNA (mRNA) carries instructions from the nucleus to the cytoplasm. (Figure 3–12)

During translation, a functional polypeptide is constructed using the information contained in the sequence of codons along an mRNA strand. The mRNA codons correspond to DNA triplets. The sequence of codons determines the sequence of amino acids in the polypeptide.

During translation, complementary base pairing of anticodons to mRNA codons occurs, and transfer RNA (tRNA) molecules bring amino acids to the ribosomal complex. Translation includes three phases: initiation, elongation, and termination. (Spotlight Figure 3–13; Table 3–1)

Through protein synthesis, the DNA of the nucleus controls the synthesis of enzymes and structural proteins that provide short- and long-term homeostatic adjustments affecting the cell’s biochemical and physical characteristics.

3-5 Diffusion is a passive transport mechanism that assists membrane passage of solutes and water

The permeability of a barrier such as the plasma membrane is an indication of the barrier’s effectiveness. Nothing can pass through an impermeable barrier; anything can pass through a freely permeable barrier. Plasma membranes are selectively permeable.

Diffusion is the net movement of a substance from an area of higher concentration to an area of lower concentration. Diffusion occurs until the concentration gradient is eliminated. (Figures 3–14, 3–15)

Most lipid-soluble materials, water, and gases freely diffuse across the phospholipid bilayer of the plasma membrane. Small water-soluble molecules and ions rely on channel-mediated diffusion through a passageway within a transmembrane protein. Leak channels are passive channels that allow ions across the plasma membrane.

Osmosis is the net flow of water across a selectively permeable membrane in response to differences in solute concentration. Osmotic pressure of a solution is the force of water movement into that solution resulting from its solute concentration. Hydrostatic pressure can oppose osmotic pressure. (Figure 3–16)

Tonicity describes the effects of osmotic solutions on cells. A solution that does not cause an osmotic flow is isotonic. A solution that causes water to flow into a cell is hypotonic and can lead to hemolysis of red blood cells. A solution that causes water to flow out of a cell is hypertonic and can lead to crenation. (Figure 3–17)

3-6 Carrier-mediated and vesicular transport assist membrane passage of specific substances

Carrier-mediated transport involves the binding and transporting of specific ions by integral proteins. Symport (cotransport) moves two substances in the same direction; antiport (countertransport) moves them in opposite directions.

In facilitated diffusion, compounds are transported across a membrane after binding to a receptor site within the channel of a carrier protein. (Figsure 3–18)

Active transport mechanisms consume ATP and are not dependent on concentration gradients. Some ion pumps are exchange pumps. Secondary active transport may involve symport (cotransport) or antiport (countertransport). (Figures 3–19, 3–20)

In vesicular transport, materials move into or out of the cell in membranous vesicles. Movement into the cell is accomplished through endocytosis, an active process that can take three forms: receptor-mediated endocytosis (by means of clathrin-coated vesicles), pinocytosis, or phagocytosis (using pseudopodia). The ejection of materials from the cytoplasm is accomplished by exocytosis. (Figure 3–21; Spotlight Figure 3–22)

3-7 The membrane potential of a cell results from the unequal distribution of positive and negative charges across the plasma membrane

The potential difference, measured in volts, between the two sides of a plasma membrane is a membrane potential. The membrane potential in an unstimulated, or undisturbed, cell is the cell’s resting membrane potential.

3-8 Stages of the cell life cycle include interphase, mitosis, and cytokinesis

Cell division is the reproduction of cells. Apoptosis is the genetically controlled death of cells. Mitosis is the nuclear division of somatic cells. Sex cells are produced by meiosis. (Spotlight Figure 3–23)

Somatic cells spend most of their time in interphase, which includes the G1, S (DNA replication), and G2 phases. (Spotlight Figures 3–23, 3–24)

Mitosis proceeds in four stages: prophase, metaphase, anaphase, and telophase. (Spotlight Figure 3–23)

During cytokinesis, the cytoplasm is divided to form two daughter cells and cell division ends. (Spotlight Figure 3–23)

In general, the longer the life expectancy of a cell type, the slower the mitotic rate. Stem cells undergo frequent mitosis to replace other, more specialized cells.

3-9 Several factors regulate the cell life cycle

A variety of hormones and growth factors can stimulate cell division and growth (Table 3–2)

3-10 Abnormal cell growth and division characterize tumors and cancers

Produced by abnormal cell growth and division, a tumor, or neoplasm, can be benign or malignant. Malignant cells may spread locally (by invasion) or to distant tissues and organs (through metastasis). The resultant illness is called cancer. Modified genes called oncogenes often cause malignancy. (Figure 3–25)

3-11 Cellular differentiation is cellular specialization as a result of gene activation or repression

Cellular differentiation, a process of cellular specialization, results from the inactivation of particular genes in different cells, producing populations of cells with limited capabilities. Specialized cells form organized collections called tissues, each of which has certain functional roles.

Contemporary cell theory: (1) Cells are building blocks; (2) cells arise from division of preexisting cells; (3) cells are the smallest units performing vital functions; (4) cells maintain homeostasis.

Cytology studies cell structure and function.

Human cells: sex cells and somatic cells.

3-1 Plasma Membrane

Separates cell from environment. Functions: physical isolation, exchange regulation, environmental sensitivity, structural support. Made of phospholipid bilayer with lipids, proteins, carbohydrates.

Proteins: integral (part of membrane) and peripheral (attached but separable).

Membrane proteins: anchors, identifiers, enzymes, receptors, carriers, channels.

Glycocalyx (proteoglycans, glycoproteins, glycolipids) functions: lubrication, protection, anchoring, locomotion, binding specificity, recognition.

3-2 Organelles

Cytoplasm contains cytosol and organelles.

Cytosol differs from extracellular fluid.

Nonmembranous organelles: cytoskeleton, microvilli, centrioles, cilia, ribosomes, proteasomes.

Membranous organelles: endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, nucleus.

Cytoskeleton: strength and flexibility; microfilaments, intermediate filaments, microtubules, thick filaments (muscle cells).

Microvilli: increase surface area.

Centrosome: microtubule organizing center with centrioles for chromosome movement during cell division.

Cilia: primary (nonmotile, sensitive to stimuli) and motile (move fluids).

Ribosomes: protein synthesis (rRNA); free and fixed.

Proteasomes: remove damaged proteins.

Endoplasmic Reticulum (ER): synthesis, storage, transport, detoxification; smooth ER (lipid synthesis), rough ER (ribosomes, transport vesicles).

Golgi Apparatus: secretory vesicles, plasma membrane components, lysosomes; exocytosis.

Lysosomes: digestive enzymes, autolysis.

Peroxisomes: neutralize free radicals.

Membrane Flow: membrane recycling among ER, vesicles, Golgi apparatus, plasma membrane.

Mitochondria: ATP production (aerobic metabolism); matrix and cristae.

3-3 Nucleus

Control center with nuclear envelope, nuclear pores, nuclear matrix, nucleoli.

Controls cell via protein synthesis using chromosomes (DNA + histones); chromatin in nondividing cells.

Genetic code: triplet code for amino acids; genes for polypeptide chains.

3-4 DNA and Protein Synthesis

RNA polymerase binds to gene to start gene activation.

Transcription: DNA to RNA; mRNA carries instructions to cytoplasm.

Translation: polypeptide construction using mRNA codons; tRNA brings amino acids to ribosomal complex (initiation, elongation, termination).

DNA controls enzyme and structural protein synthesis for homeostasis.

3-5 Membrane Transport - Diffusion

Permeability: effectiveness of barrier (impermeable to freely permeable); plasma membranes are selectively permeable.

Diffusion: movement from high to low concentration until gradient is eliminated.

Lipid-soluble materials, water, gases diffuse across phospholipid bilayer; small water-soluble molecules use channel-mediated diffusion.

Osmosis: water flow across membrane due to solute concentration differences; osmotic pressure and hydrostatic pressure.

Tonicity: effects of osmotic solutions on cells (isotonic, hypotonic/hemolysis, hypertonic/crenation).

3-6 Carrier-Mediated and Vesicular Transport

Carrier-mediated: ions bind to integral proteins; symport/cotransport (same direction), antiport/countertransport (opposite directions).

Facilitated diffusion: compounds bind to carrier protein.

Active transport: uses ATP, not dependent on concentration gradients; ion/exchange pumps; secondary active transport (symport or antiport).

Vesicular transport: materials move via vesicles; endocytosis (receptor-mediated, pinocytosis, phagocytosis) and exocytosis.

3-7 Membrane Potential

Potential difference across membrane; resting membrane potential in undisturbed cells.

3-8 Cell Life Cycle

Cell division: reproduction; apoptosis (programmed death); mitosis (somatic cells); meiosis (sex cells).

Interphase: G1, S (DNA replication), G2 phases.

Mitosis: prophase, metaphase, anaphase, telophase.

Cytokinesis: cytoplasm division into two daughter cells.

Mitotic rate varies with cell type lifespan.

3-9 Cell Life Cycle Regulation

Hormones and growth factors can stimulate cell division and growth.

3-10 Tumors and Cancers

Tumor/neoplasm: benign or malignant; malignant cells spread (metastasis), causing cancer; oncogenes.

3-11 Cellular Differentiation

Specialization via gene activation or repression, forming tissues with specific roles.