{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Review Sheet 4- The Cell Anatomy and Division

Review Sheet 4- The Cell Anatomy and Division - p CYTOLOGY...

Info iconThis preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 6
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 8
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 10
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 12
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Background image of page 14
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: p CYTOLOGY Cytology is the study of the structure and function of cells. This exercise is designed to study cells by con— structing a cell model and by making general observations with the light Iriicroscope. Due to low magnifications ob— tained with the light Irticroscope. many cell structtlrcs can only be observed using the high magnifications of the elec— tron microscope. Photographs are included to enhance and test your ob— servations made with the light microscope. Photographs made through a microscope are called micrographs. If the light microscope was used. the resulting photograph is called a photolnicrograph. The electron microscope produces an electron micrograph. It is important to keep in mind that there are many struc— turally and physiologically different cells ofthe body. Since it is impossible to find a typical cell for study. a cell model must be constructed. To construct and study the "gener— alized or typical" cell. it is divided into four major parts: (1 J plasma membrane,(2) cytoplasm,(3} organelles, and (4) inclusions. Observe Figure 4.1 and acell model. Identify the com— ponents of a "generalized" cell. Cilia Microvilli 'l‘ightjunction Mitochondria Smooth endo— plasmic reticulum Centrosome Centriole Desmosomc Golgi apparatus Vesicle Gapjunction Figure 4.1 Structure of a "generalized" cell. Cytology 37 1. Define cytology. 2. What are the four major parts ofthe "generalized" cell‘? PLASMA MEMBRANE The plasma membrane is the limiting membrane which forms the cell boundary. It separates the watery en— vironments of the cytoplasm {intracellular fluid} and the external environment {extracellular fluid). It consists of a phospholipid framework. Other lipid molecules (such as cholesterol and glycolipids) and proteins (such as glyco- proteins) are embedded in the phospholipid framework. A structural model of the plasma membrane is illustrated in Figure 4.2. 3. What does the framework of the plasma membrane consist of? 4. Name three types of molecules that are found etnbed— ded in the phospholipid framework ofthe plasma mem— brane. Rough endo— plasmic reticulum Ribosomes 0 Nuclear membrane 0 a i i '9 ’fi’zll’” Nuclear pore if -- gig I Nucleolus Chromatin Cytoplasm asma membrane. molecular structure [see Figure 4.2} 38 Cytology Extracellular fluid Cholesterol \ Phospholipid bilayer Phospholipid Nonpolar tails l Polar head ' Peripheral protein Transmembrane Glycolipid Integral proteins channel Figure 4.2 Intracellular fluid Molecular structural model of the plasma membrane MOLECULAR STRUCTURE PROTEIN MOLECULES LIPID MOLECULES The lipids include phospholipids. cholesterol. and glycolipids (Figure 4.2). The most abundant lipids are the phospholipids. The phospholipids are a group of lipids that have a polar (charged) “head” region that contains phosphorus attached to a nonpolar (uncharged) “tail” re— gion that contains a pair of fatty acids. Fundamental mem- brane structure (framework) is produced by the phos- pholipids being arranged in two layers (bilayer). The polar “heads” of each layer interact with the water environ— ments and are described as hydrophilic (water loving). The nonpolar “tails” of each layer face each other to form the interior of the membrane. They are described as hydro- phobic (water fearing). Lipid molecules with attached carbohydrates are called glycolipids. Glycolipids are located in the outer phos- pholipid layer. Their lipid portion is associated with the lipid portion of the outer phospholipid layer. and the car— bohydrate chains project away from the membrane into the extracellular environment. Cholesterol is distributed in both layers of the phos— pholipid bilayer. Its hydrocarbon ring structure is loeated between the fatty acid “tails” of the phospholipids, 5. Name three types of lipid molecules of the plasma membrane. 6. Which part of the phospholiptd molecule is hydrophilic? 7’. Which part ofthe phospholipid molecule is hydropho— bic? 8. How are the phospholipids arranged to form the frame— work of the plasma membrane? 9. Where do the carbohydrate chains of the glycolipid project? Protein membrane molecules may be named integral or peripheral according to their location (Figure 4.2). In- tegral proteins are located within the phospholipid bi- layer. They may be located in either the outer or inner phospholipid layer or. they may penetrate both layers as transmembrane proteins. Peripheral proteins are located at the phospholipid membrane surface either associated with integral proteins or lipids. Glycoprotcins are proteins with attached carbohy- drate chains. The carbohydrate chains project away from the membrane into the extracellular environment. The plasma membrane is not a homogeneous structure with the same organization and chemical components over its entire surface. For example. a cell that forms the lining of the intestine has several different membrane surfaces: an exposed surface that functions in absorption of digestive end products. membrane surfaces that attach the cell to neighboring cells, and a basal surface that functions in the removal of substances from the cell. It). What two names may be applied to protein molecules according to their location? I 1. Where are integral proteins located? 12. Where are peripheral proteins located? 13. Where do the carbohydrate chains of the glycoprotcin project? FUNCTIONS OF THE PLASMA MEMBRANE The molecular structure of the plasma membrane de— termines its functions. Membrane functions include the maintenance ofa physical boundary, the transport of mate— rials into and out of the cell. providing receptor sites. and cell identity markers. The phospholipid framework allows simple diffusion ofsubstances that are nonpolar and lipid soluble. Substances which are polar and are not lipid soluble have limited diffu- sion ability through the phospholipid bilayer. Membrane proteins participate in a variety of mem- brane functions. Transmembrane protein channels allow the passage either by passive or active transport (require ATP) of small molecules and ions. Transmembrane pro- tein carrier molecules allow a type of transport called fa- cilitated diffusion. This type of transport is passive and uses carrier molecules with specific receptor sites to trans— port specific substances across the membrane. Glycopro— teins embedded in the outer phospholipid layer have vari— ous functions such as receptors and cell identify markers. Peripheral proteins may serve as attachment sites to pro— duce cell structure, and as enzymes to mediate chemical reactions. 14. What are four functions of the plasma membrane? IS. What type ofsubstances easily diffuse through the phos— pholipid framework? 16. What is the function of transmembrane protein chan— nels'.’ 17. What is the function of transmembrane protein carri— ers? 18. What is a function of glycoproteins'.’ MODIFICATIONS OF THE PLASMA MEMBRANE Some cells of the body, such as blood and sperm. are not attached to other cells. However, many cells are at— tached one to another by membranejunctions. Membrane junctions (Figure 4.3) are direct membrane to membrane interactions and include (1) gap junctions. (2) desmo— somes. (3) tight junctions. Gapjunction Tightjunction ' I Desmosome ' ' '.'. l: Plasma membranes of Extracellular space- adjacent cells Figure 4.3 Three types of membi‘anejunctions. GAP JUNCTION A gap junction (Figure 4.3) is a membrane junction formed by an interaction of adjacent cell membrane proteins which produces a channel between the two cells. The channel allows the passage of small molecules and ions from cell to cell. This type of membrane junction is found in tissues such as cardiac muscle that conduct electrical activity by the passage of ions from cell to cell. ' Cytology 39 DESMOSOME A desmosome (Figure 4.3) is a membrane junction formed by thin intercellular filament proteins that are associated with thickened inner membrane layers and cytoskeletal filaments of adjacent cells. The membranes of the cells do not touch but are held together by the inter- cellular proteins. This type of membranejunction produces great mechanical strength and is located in areas such as the skin where strong cell adhesion is required. TIGHT JUNCTION A tight junction (Figure 4.3) is a membrane junc- tion formed by the connection of proteins of the plasma membranes ofadjacent cells. The connection of the Incin— branes prevents the diffusion of substances through the intercellular space. This type ofjunetion is located in areas such as the lining of the urinary bladder where diffusion of water and ions across the lining membrane is restricted. MICROVILLI Microvilli are plasma membrane projections (Fig- ure 4.4). A cell which functions in the absorption of ma— terials often has its surface membrane modified into mi— crovilli. Increasing the amount ofplasma membrane (sur- face area) increases the transport capability of the cell. Microvilli Figure 4.4 Microvilli. 19. How is a gap junction formed? 20. What is the function of a gap junction‘.j '21. How is a desn‘tosontc formed? 22. What is the function of a destnosome? 23. How is a tight junction formed? 24. What is the function of a tight junction‘.J 25. How are microvilli formed? 26. What is the function of microvilli? 40 Cytology CYTOPLASM Cytoplasm is the substance between the plasma membrane and the nucleus. Its lluid component is called the cytosol. It is mostly water with a variety of inorganic and organic substances from ions to complex proteins. Sus— pended in the cytosol are organelles and inclusions. ()r- ganelles arc the "little organs" {functional components) of the cell. They may or may not be membrane bound. Inclu- sions are chemical substances in the cytoplasm. They are not functional units but are used in the functioning of the cell. Inclusions include glycogen. lipid droplets. and he— moglobin. 27'. Where is the cytoplasm located? 28. What is cytosol'.’ 29. What are organelles? 30. What are inclusions? ORGAN ELLES The organelles ("little organs") are a variety of struc- tures that perform various cellular functions. Most or- ganelles are too small to be easily studied with the light microscope. Cellular studies with the electron microscope have provided the details for the structural identification of the organelles. NUCLEUS The nucleus (Figure 4.5) consists of three major components: (1) a nuclear membrane, (2) chromatin, and (3) nucleoli. Chromatin H“ Double nuclear membrane Nucleolus Figure 4.5 Nucleus. The nucleus is the control center of the Cell because it contains the genetic material, deoxyribonucleic acid (DNA). that directs cell activity. Many cells contain a single nucleus that is generally spherical. Other nuclear shapes include lobes and indentations as seen in the various white blood cells. Some cells may have more than one nucleus. from two nuclei tbinucleate) to many (multinueleate). Mature red blood cells are the only body cells that do not have ntl— clei [anucleate). The nucleus is extruded as the cell moves from the bone marrow into the circulation pathway. NUCLEAR MEMBRANE The nuclear membrane (Figure 4.5) is composed of two layers, an inner and outer phospholipid layer. Small openings (nuclear pores) are distributed throughout the membrane. Nuclear pores make the membrane selectively permeable. DNA is restricted to the nucleus whereas other substances such as nucleotides. small proteins. and RNA molecules tnove freely across the membrane. CHROMA’I‘IN Chromatin [Figure 4.5) is composed of DNA and associated proteins called histones and appears as threads distributed throughout the nucleus. Portions of the DNA and histones become arranged into organizational structures called nucleosomes. A nucleosome consists of eight asso— ciated histone proteins wrapped with a portion of the DNA molecule. Inactivation of genes is partially controlled by the selective wrapping of portions of the DNA. During mitosis the chromatin is further condensed into structures called chromosomes. This packaging of the DNA into chro— mosomes facilitates its distribution to daughter cells. NUCLEOLI The nucleus may have a single nucleolus (Figure 4.5) or many nucleoli. They appear as dark-stained nuclear regions and are associated with chromatin that is active in the synthesis of ribosomal RNA. At these regions the ri— bosomal RNA is combined with proteins to make the sub— units of ribosomes. The ribosomal subunits leave the nucleus and enter the cytoplasm where they assemble into ribosomes. Since ribosomes are the sites ol'protein synthesis. cells that are active in protein synthesis usually have several nucleoli. 3 |. What is the function of the nucleus? 32. What are three major components of the nucleus? 33. What is the function of nuclear pores? 34. What is the composition of chromatin'.’ 35. What are chromosomes? 36. What is the function of nucleoli? MITOCHONDRIA A mitochondrion (Figure 4.6) is a rod-shaped or- ganelle located in the cytoplasm. Outer membrane Cristae Inner membrane Matrix Figure 4.6 Mitochondrion r) The mitochondrion is bounded by a double membrane. The outer membrane surrounds the mitochondrion forming its outennost boundary. The inner membrane folds deeply into the mitochondrion's interior forming sheltlilte partitions called cristae. The substance within the interior is called the matrix. Mitochondria function as the “powerhouses of the cell.” Aerobic respiration. which generates most of the cell's energy-rich molecules (ATP), occurs within the mitochondria. 37", What are cristae? 38. What is the Function of mitochondria? RIBOSOMES A ribosome (Figure 4.7) is a very small organelle that consists of a large and a small subunit, The subunits are composed of a ribonucleic acid (RNA) called ribosomal ri— bonucleic acid {rRNA} and proteins. The rRNA originates by transcription from DNA in the nucleolus. It is then com— bincd with proteins to form the subunits which leave the nucleus by way of the nuclear pores. Ribosomes are found either attached (Figure 4.7) to membrane channels called the endoplasmic reticulum or are free (Figure 4.7) in the cytoplasm. Endoplasmic reticulutn Attached ribosomes? . " o a I ‘ 0 Free ribosomes <. a g I Q . 1. . Q hlgure 4.7 . Ribosomes If the ribosomes are attached to the endoplasmic reticu— lum, the manufactured proteins accutnulate in the interior ofthe endoplasmic reticulum. Free ribosomes produce pro— teins that become a part of the cytoplasm. Ribosomes are described functionally as the sites of protein synthesis. They receive protein coding informa— tion transcribed from DNA in the form of another type of ribonucleic acid (RNA) called messenger ribonucleic acid (mRNA). The coding information (mRNA) is then trans— lated with the assembly of amino acids to form proteins. 39. Where does rRNA originate? 40. What are the two possible locations for ribosomes? 4t , What is the function of ribosomes? 42. Where do the proteins produced by attached ribosomes accumulate?I 43. Where do the proteins produced by the free ribosomes accumulate? 41 Cytology ENDOPLASMIC RETICULUM (ER) The endoplasmic reticulum (Figure 4.8) is structured as a network of membranes which form fluid filled chan- nels. oflTran sport vesicles Ribosomes Channels Rough ER '. . ' Smooth ER Figure 4.8 Endoplasmic reticulum (ER). The endoplasmic reticulum (ER) is distributed in the cyto- plasm and usually interconnects the nuclear and plasma membranes. Two types ot‘endoplasmic reticulum can be described depending upon the association with ribosomes. lt' ribo— somes are attached to the endoplasmic reticulum. it is called rough (granular) endoplasmic reticulum (rough ER). If ribosomes are not attached. the endoplasmic reticulum is described smooth (agranular) endoplasmic reticulum (smooth ER). Proteins produced by ribosomes on the rough ER mem— brane move into its cavity. Once in the HR cavity the pro— teins may be modified before being pinched off in a mem— branous sac called atransport vesicle. Transport vesicles move substances to the Golgi apparatus for processing. Smooth ER functions include the production and modi- fication of lipid and carbohydrate molecules such as: phospholipids. glycolipids. steroids. lipoproteins, glycogen. and fatty acids. 44. How is the endoplasmic reticulum structured? 45. Where is the endoplasmic reticulum located? 46. What two types of endoplasmic reticulum can be de— scribed depending upon the association with ribosomes? 47. What type of molecules are found within the cavity of the rough endoplasmic reticulum? 48. What is the function of transport vesicles? 49. What is the function of the smooth endoplasmic reticu— lum? 42 Cytology I GOLGI APPARATUS The Golgi apparatus (Figure 4.9), loeated near the nucleus. consists of one to many groups of flattened mem- branous sacs stacked one upon the other. Membranous sacs - Figure 4.9 Golgi apparatus It functions in the modification, concentration, and pack- aging of various molecules (proteins. lipids}. Small meni— brane sacs, called vesicles. transfer materials to and from the Golgi apparatus. Delivery of proteins is by transport vesicles that originated from the rough ER. The proteins are processed and packaged into vesicles for three pos- sible destinations: (1) secretory vesicles transport proteins to the plasma membrane for exocytosis, (2) membrane- bound vesicles deliver proteins to the plasma membrane for incorporation into the membrane. and (3) other vesicles form organelles called lysosomes and peroxisomes. 50. What is the structure of the Golgi apparatus?I Sl . What is the function of the Golgi apparatus? 52. What is delivered to the Golgi apparatus in the trans- port vesicles? 53. What are the three possible destinations for processed and packaged proteins? LYSOSOMES Lysosonles (Figure 4.10) are double membrane spheres formed by the fusion of vesicles produced by the Golgi apparatus. Hydrolytic enzymes Double membrane Figure 4.10 Lysosome They contain digestive (hydrolytic) enzymes which func- tion in the digestion of a variety of materials such as worn-out organelles, inclusions. and engulfed substances. Phagocytic white blood cells have abundant lysosomes that digest engulfed (phagocytized) bacteria. viruses, etc. 54. How are lysosomes formed? 55. What do lysosomes contain? 56. What is the function of lysosomes'? CENTROSOME AND CENTRIOLES Located near the nucleus, the centrosome (F igure 4.11) is an area of cytoplasm which contains a pair of cylin- drical structures called centrioles. Centrosomes Centrosome Centrioles ' Nondividing cell Dividing cell Figure 4.11 Centrosonle and centrioles The centrioles are positioned at right angles to each other and are composed of a group of small tubules called mi- erotubules. The centrosolne functions as an organizing center in the nondividing cell. In the dividing cell, the centrioles function by acting as the centers from which microtubules (spindle fibers) originate. Microtubules (spindle fibers) function ill the organization and movement of the chromosomes during cell division. Cells, such as nerve cells, which lack centrioles cannot divide. 57. What is the centrosome composed of? 58. What is the function of the centrosome in the nondi— viding cell‘.’ 59, What is the function of the centrosome in the dividing cell'? CILIA AND FLAGELLA Cilia and flagella (Figure 4.12) are cellular projections composed mostly of microtubules and surrounded by the plasma membrane. C'h“ Flagellum \ Pseudostratified cilialetl columnar epithelium Figure 4.” Cilia and flagellum Sperm cell Cilia are short, numerous extensions from the exposed surface of a cell. Cilia function in the movement ofmate- rials tsuch as mucus) over the surface of the cells. The airways of the respiratory tract are lined with ciliated cells (pseudostratified ciliated columnar epithelium) which move mucus away from the lungs. Flagella are long and few in number and function in the movement of the...
View Full Document

{[ snackBarMessage ]}