The Cell. There are two distinct types of cells: eukaryotic cells and prokaryotic cells.

Transcription

1 The Cell All living things are composed of cells. The cell is smallest unit of living things that can carry out the activities necessary for life. many forms of life exist as single celled organisms such as bacteria. More complex organisms, including plants and animals, are multicellular. There are two distinct types of cells: eukaryotic cells and prokaryotic cells.

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4 Microscopy Microscopes are the most important tools of cytology, the study of cell structure Three important parameters in microscopy are magnification, contrast, and resolution. Magnification is the ratio of an object s image size to its real size. Light microscopes can magnify effectively to about 1,000 times the actual size of the specimen; Contrast, accentuates differences in parts of the sample. Improvements in light microscopy have included new methods for enhancing contrast, such as staining or labeling cell components with different color to stand out visually. Resolution is a measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two points. the light microscope cannot resolve detail finer than about 0.2 micrometer (μm), or 200 nanometers (nm), regardless of the magnification.

5 Microscopy Microscopes are the most important tools of cytology, the study of cell structure. Electron microscopes have revealed many organelles and other subcellular structures that were impossible to resolve with the light microscope. A disadvantage of electron microscopy is that the methods used to prepare the specimen kill the cells. For all microscopy techniques, in fact, specimen preparation can introduce artifacts, structural features seen in micrographs that do not exist in the living cell. But the light microscope offers advantages, especially in studying living cells. Labeling individual cellular molecules or structures with fluorescent markers has made it possible to see such structures with increasing detail. In addition, both confocal and deconvolution microscopy have sharpened images of 3-D tissues and cells. Researchers can see the distinguish subcellular structures as small as nm across.

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10 Q1. How do stains used for light microscopy compare with those used for electron microscopy? Q2. Which type of microscope would you use to study (a) the changes in shape of a living white blood cell and (b) the details of surface texture of a hair? Q3. What is the approximate size of a human red blood cell? (a) micrometer (b). 8 micrometer (c). 80 micrometer (d). 8 nanometers Q4. All of the following would require the use of electron microscopy for visualization, except a. the structure of a bacteriophage b. the matrix structure of mitochondrion c. the shape and arrangement of bacterial cells d. the pores on the nuclear membrane

11 Q1. How do stains used for light microscopy compare with those used for electron microscopy? Light microscopy is used to see individual cellular molecules or structures with different and fluorescent markers. Q2. Which type of microscope would you use to study (a) the changes in shape of a living white blood cell? (light microscopy) and (b) the details of surface texture of a hair?(electron microscopy) Q3. What is the approximate size of a human red blood cell? (a) micrometer (b). 8 micrometer (c). 80 micrometer (d). 8 nanometers Q4. All of the following would require the use of electro microscopy for visualization, except a. the structure of a bacteriophage b. the matrix structure of mitochondrion c. the shape and arrangement of bacterial cells d. the pores on the nuclear membrane

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18 The Cell All living things are composed of cells. The cell is smallest unit of living things that can carry out the activities necessary for life. many forms of life exist as single cell- organisms such as bacteria. More complex organisms, including plants and animals, are multicellular. There are two distinct types of cells: eukaryotic cells and prokaryotic cells. A eukaryotic cells contains a membrane bound structure called a nucleus and cytoplasm. Cytoplasm was filled with tiny structures called organelles (endomembrane system). Examples of the eukaryotic cells are Fungi, protists, plants, animals and humans.

19 Prokaryotic cell, which is a lot smaller than a eukaryotic cells, does not contain a nucleus and membrane-bound organelles. The DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid

20 The interior of either type of cell is called the cytoplasm; in eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane. Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are a variety of organelles of specialized form and function. These membrane-bounded structures are absent in prokaryotic cells. eukaryotic cells prokaryotic cells

21 Cell wall Chitins Cell wall is one cell structure not found in animal cells. Plants and algae have cell walls made of cellulose. The cell walls of fungi are usually made of chitins. The primary cell wall is outside the plasma membrane.

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24 Plasma membrane The cell has the plasma membrane at its outer surface. The plasma membrane is a fluid mosaics of lipids and proteins and allows some substances to cross it more easily than others (Selective Permeability), in which amphipathic proteins are embedded in the phospholipid bilayer.it is a doublelayered structure made up of phospholipids and proteins. In addition to the plasma membrane at its outer surface, a eukaryotic cell has extensive and elaborately arranged internal membranes that divide the cell into compartments the organelle. The cell s compartments provide different local environments that facilitate specific metabolic functions, so incompatible processes can go on simultaneously inside a single cell. Proteins are associated with the cell membrane. Peripheral proteins: Some of these proteins are loosely associated with the lipid bilayer. Integral proteins: They are located on the inner of the membrane. Transmembrane proteins: Their hydrophilic regions extend out of cell or into the cytoplasm, and their hydrophobic regions interact with the fatty acid tails of the membrane phospholipids.

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28 Organelles in eukaryotic cells A eukaryotic cells are like a biological factories. It contains different kinds of organelles, each organelle has its own special task.

29 The nucleus in eukaryotic cell The nucleus is the control center of the eukaryotic cell. The nucleus is surrounded by a selectively permeable nuclear envelope that separates the contents of the nucleus from the cytoplasm. The nucleus contains chromosomes and nucleolus Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of histone proteins and one molecule of deoxyribonucleic acid (DNA). The nuclear envelope is the double lipid bilayer membrane which surrounds the genetic material (chromosomes) and nucleolus. The nuclear envelope contains protein complexes (nuclear pore complexes) to allow for the transport of molecules (mrna etc.). Nucleolus the largest structure in the nucleus. it primarily serves as the site of ribosome synthesis. Newly transcribed rrna is made, bound to ribosomal proteins to form ribosomes. Nucleolus is not a membrane-bound structure.

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31 Ribosome Ribosomes Ribosomes are composed RNAs and proteins. they are the protein factories found within all living cells, that serves as the site of biological protein synthesis (translation). Ribosomes link amino acids together to produce proteins in the order specified by messenger RNA (mrna) molecules. Ribosome proteins consist of two major components: the small ribosomal subunit, which reads the mrna, and the large subunit, which joins amino acids to form a polypeptide chain. The transfer ribonucleic acid (trna) is a type of RNA molecule that helps decode a mrna sequence by bring the amino acids to Ribosomes. Ribosomes can be either free floating in the cells or attached to endoplasmic reticulum (ER).

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33 Endoplasmic reticulum The Endoplasmic reticulum (ER) is a network of membrane-enclosed tubules and sacs (cisternae) that extends from the nuclear membrane throughout the cytoplasm in eukaryotic cells. there are two distinct types of ER that perform different functions within the cell. The rough ER, which is covered by ribosomes on its outer surface, functions in protein synthesis and processing. That is why it contains ribosomes. The smooth ER is not associated with ribosomes and is involved in 1. lipid metabolism. Assists in synthesis of lipids, steroids such as sex hormones. 2. detoxifies drugs and poisons from the body. 3. Store Ca ions in muscle cells to facilitate normal muscle contractions.

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39 Golgi apparatus The Golgi is composed of flattened membraneenclosed sacs (cisternae) and associated vesicles. A striking feature of the Golgi apparatus is its distinct polarity in both structure and function. Proteins from the ER enter at its cis face (entry face), which is convex and usually oriented toward the nucleus. They are then transported through the Golgi and exit from its concave trans face (exit face). As they pass through the Golgi, proteins are modified and sorted for transport to their eventual destinations within the cell. Golgi complex, After leaving the ER, many transport vesicles travel to the Golgi apparatus. We can think of the Golgi as a warehouse for receiving, sorting, shipping, and even some manufacturing. Here, products of the ER, such as proteins, are modified and stored and then sent to other destinations: lysosomes, the plasma membrane, or secretion. In addition, glycolipids are synthesized within the Golgi. In plant cells, the Golgi apparatus further serves as the site at which the complex polysaccharides of the cell wall are synthesized. The Golgi apparatus is thus involved in processing the broad range of cellular constituents that travel along the secretory pathway.

40 Lysosomes Lysosomes are membrane-enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers proteins, nucleic acids, carbohydrates, and lipids. PH in the lysosome is around 5. Lysosomes function as the digestive system of the cell, serving both to degrade material taken up from outside the cell and to digest obsolete components of the cell itself. In their simplest form, lysosomes are visualized as dense spherical vacuoles, but they can display considerable variation in size and shape as a result of differences in the materials that have been taken up for digestion. Lysosomes thus represent morphologically diverse organelles defined by the common function of degrading intracellular material. Plant cells do not have lysosomes

41 Fig (a). Fatty acid oxidation in peroxisomes Peroxisome lysosome Fig (b). Peroxisomes and lysosomes are two brothers and work together to break down the waste products in the cell Peroxisomes Peroxisomes are organelles and found in both plant and animal cells perform the specialized functions. In animal, they are common in the liver and kidney cells. They contain catalase catalyzes the following chemical reactions and detoxify various substances (Fig). Peroxisomes contain at least 50 different enzymes, which are involved in a variety of biochemical pathways in different types of cells. Peroxisomes originally were defined as organelles that carry out oxidation reactions leading to the production of hydrogen peroxide (H2O2). Because hydrogen peroxide is harmful to the cell, peroxisomes also contain the enzyme catalase, which decomposes hydrogen peroxide either by converting it to water or by using it to oxidize another organic compound. A variety of substrates are broken down by such oxidative reactions in peroxisomes, including uric acid, amino acids, and fatty acids. The oxidation of fatty acids is a particularly important example, since it provides a major source of metabolic energy. In animal cells, fatty acids are oxidized in both peroxisomes and mitochondria, but in yeasts and plants fatty acid oxidation is restricted to peroxisomes.

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45 Vacuole A vacuole is a membrane bound organelle which is present in all plant and fungal cells and some protists, animal and bacterial cells. Vac uoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution. Plant cells contain a large vacuole. D

46 The Plant H+-ATPase has a ph optimum of 6.6, it is well below the physiological ph of the plant cell cytoplasm (usually around ). Thus, when ever protons start accumulating in the cytoplasm, the activity of the H+-ATPase increases, resulting in the expulsion of the excess H+ from the cell. Endosomal V-ATPase (vesicular H + -ATPase) is a ph-sensor regulating the degradative pathway. According to our model, V-ATPase is responsible for: (i) the generation of a ph gradient between vesicular membranes; (ii) sensing of intravesicular ph; and (iii) transmitting this information to the cytosolic side of the membrane. In plants, the V-ATPase is an active component of the vacuole, which in situations such as citrus fruits can reach ph values as low as 2.2, although other proton pumps may be involved in helping to maintain such a low ph.

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49 Confocal Microscopy of the eukaryotic cytoskeleton. Actin filaments are shown in red, microtubules are show in green that supports cell shape and function. Cytoskeleton The cytoskeleton can be referred to as a complex network of interlinking microfilaments and microtubules that extend throughout the cytoplasm, from the nucleus to the plasma membrane. Microtubules are hollow cylinders, they form the centrioles (Fig 5), cilia and flagella(fig 6). Tubulin participate in cellular division and movement. Microfilaments are composed of linear polymers of G- actin proteins. They also act as tracks for the movement of myosin molecules in muscle contraction. Intermediate filaments support cell shape and fix organelles in place. Structure Movement 6 5

50 Eukaryotic Cytoskeleton The cytoskeleton can be referred to as a complex network of interlinking microfilaments and microtubules that extend throughout the cytoplasm, from the nucleus to the plasma membrane. Microtubules are hollow cylinders, they form the centrioles, cilia and flagella. Tubulin participate in cellular division and movement. Microfilaments are composed of linear polymers of G-actin proteins. They also act as tracks for the movement of myosin molecules in muscle contraction. Intermediate filaments support cell shape and fix organelles in place. Movement

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52 Centrioles Centrioles are small, paired, cylindrical structures that are found within microtubule organizing centers (MTOCs). When a cell is ready to divide, the centrioles produce microtubules, which pull the replicated chromosomes apart and move them to opposite ends of the cell. Centrioles are common in animal cells, they are not found in plant cells Spindle fibers and centrioles consist of nine triplets of microtubules arranged in circle

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54 Cytokinesis Plant cells Vesicles originating from Golgi bodies migrate to the plane between the two newly forming nuclei. The division of the cytoplasm takes placed by cell plate formation Cell plate formation starts at the center of cell and grows outward. Animal cells Microfilaments form a ring inside the plasma membrane between the two newly forming nuclei. The division of the cytoplasm takes place by cleavage Cleavage starts at periphery and then moves inward.

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58 Mitochondria Mitochondria are the powerhouses of the cell. Mitochondria are the site of cellular respiration. All cells have many mitochondria. A very active cell could have 2500 of them. Mitochondria have an outer double membrane and an inner series of membranes called cristae. They contain enzymes that converting the energy from organic molecules into energy molecule-adenosine triphosphate (ATP). Mitochondria are involved in other tasks, such as signaling, cellular differentiation, and cell death. The mitochondrion has its own independent DNA that shows substantial similarity to bacterial DNA. The mitochondrion has its own independent ribosomes. 18 C

59 Chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. chloroplasts have an outer double membrane Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide gas to produce food for the plant. They have an outer double membrane, their own independent DNA that shows substantial similarity to bacterial DNA. They have their own independent ribosomes.

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65 Features of prokaryotic cells such as bacteria: Cell wall Plasma membrane Cytoplasm Ribosomes Nucleoid region Bacterial chromosome Flagella and cilia Capsule Features of eukaryotic cells Cell wall (plants only) Plasma membrane Cytoplasm Ribosomes Nucleus and nucleolus Centrioles (animals only) Rough endoplasmic reticulum Smooth endoplasmic reticulum Golgi apparatus Mitochondria Chloroplasts (plants only) Lysosomes Peroxisomes Vacuole Central vacuole(plants only) Cytoskeleton Structure Plant cell Animal Cell Cell wall Yes No Mitochondria /Chloroplasts Chloroplasts &Mitochondria Centrioles No Yes Central vacuole Yes, large Lysosomes No Yes Mitochondria No or smaller

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78 Membrane transport Membrane transport refers to the collection of mechanisms that regulate the passage of solutes such as ions and small molecules through biological membranes, which are lipid bilayers that contain proteins embedded in them. The regulation of passage through the membrane is due to selective membrane permeability - a characteristic of biological membranes which allows them to separate substances of distinct chemical nature. Water molecules are polar and not lipid soluble, but they can rapidly cross a lipid bilayer through aquaporins, which are integral membrane proteins that regulate the flow of water. Transport can be either active or passive. Active transport requires energy (e.g. ATP ). passive transport requires no energy.

79 Passive transport Passive transport is the movement of molecules down a concentration gradient from until equilibrium is reached. Passive transport are diffusion and osmosis. Passive transport does not use cellular energy. There are two types of diffusion: simple diffusion and facilitated diffusion.

80 Active transport Active transport is the movement of molecules across a cell membrane from a region of their lower concentration to a region of their higher concentration in the direction against some gradient or other obstructing factor (often a concentration gradient). Active transport uses cellular energy to move them against a gradient, polar repulsion, or other resistance. Active transport is usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from ATP, it is termed primary active transport. The best sample of the active transport is a special protein called the Sodium-potassium pump. Secondary active transport involves the use of an electrochemical gradient. Examples of the active transport include the uptake of glucose in the intestines in humans. Primary active transport. Secondary active transport

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85 Endocytosis Eukaryotic cells are also able to take up macromolecules and particles from the surrounding medium by a distinct process called endocytosis. In endocytosis, the material to be internalized is surrounded by an area of plasma membrane, which then buds off inside the cell to form a vesicle containing the ingested material. The term endocytosis was include both the ingestion of large particles (such as bacteria) and the uptake of fluids or macromolecules in small vesicles. The former of these activities is known as phagocytosis (cell eating) and the latter as pinocytosis (cell drinking). A special type of endocytosis, receptor-mediated endocytosis, the macromolecules to be first bind to specific cell surface receptors. These receptors are concentrated in specialized regions of the plasma membrane, called clathrin-coated pits. These pits bud from the membrane to form small clathrin-coated vesicles containing the receptors and their bound macromolecules (ligands). The clathrin-coated vesicles then fuse with early endosomes, in which their contents are sorted for transport to lysosomes or recycling to the plasma membrane. Mammalian cells use receptor-mediated endocytosis to take cholesterol into cells. Cholesterol in the blood is usually found in lipid-protein complexes called low-density lipoproteins (LDLs). LDLs bind to specific receptor proteins on the cell surface, thereby triggering their uptake by receptor-mediated endocytosis.

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87 Exocytosis In exocytosis, materials are exported out of the cell via secretory vesicles. In this process, the Golgi complex packages macromolecules into transport vesicles that travel to and fuse with the plasma membrane. This fusion causes the vesicle to spill its contents out of the cell. Exocytosis is important in expulsion of waste materials out of the cell and in the secretion of cellular products such as digestive enzymes or hormones. The movement of macromolecules such as proteins or polysaccharides into or out of the cell is called bulk transport. Exocytosis requires the expenditure of energy (ATP).

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89 Bulk Flow Bulk flow is one-way movement of fluids brought about by pressure. The movement of blood through a blood vessel or movement of fluid in xylem vessels and phloem tubes of plans are examples of bulk flow. Transport in xylem relies upon the cohesion of water molecules to each other and adhesion to the vessel's wall via hydrogen bonding. If an air bubble forms the flow will be stopped as the column is broken and the pressure difference in the vessel cannot be transmitted; this is called an embolism. Once these embolisms are nucleated, the remaining water in the capillaries begins to turn to water vapor. Plants have physiological mechanisms to reestablish the capillary action within their cells.

90 Dialysis Dialysis is the diffusion of solutes across a selectively permeable membrane. A cellophane bag is often used as an artificial membrane to separate small molecules from large molecules. Dialysis is the artificial process of eliminating waste (diffusion) and unwanted water (ultrafiltration) from the blood. Our kidneys do this naturally. Some people, however, may have failed or damaged kidneys which cannot carry out the function properly - they may need dialysis. Kidney dialysis is a life-support treatment that uses a special machine to filter harmful wastes, salt, and excess fluid from the blood. This restores the blood to a normal, healthy balance.

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92 Q7. All the following required ATP Except a. Na-K pump b. Cell absorbing oxygen c. Receptor-mediated endocytosis d. Amoeboid movement Q8. An animal cell in a hypertonic solution would a. Swell b. Swell and exhibit turgor c. Exhibit plasmolysis d. Shrink and them swell Q9. When the concentration of solutes differs on the two sides of a membrane permeable only to water a. Water will move across the membrane by osmosis b. Water will move across the membrane by active transport c. Water will move across the membrane by plasmolysis d. Solutes will move across the membrane from the region of higher concentration to the region of lower concentration

93 Q7. All the following required ATP Except a. Na-K pump b. Cell absorbing oxygen c. Receptor-mediated endocytosis d. Amoeboid movement Q8. An animal cell in a hypertonic solution would a. Swell b. Swell and exhibit turgor c. Exhibit plasmolysis d. Shrink and them swell Q9. When the concentration of solutes differs on the two sides of a membrane permeable only to water a. Water will move across the membrane by osmosis b. Water will move across the membrane by active transport c. Water will move across the membrane by plasmolysis d. Solutes will move across the membrane from the region of higher concentration to the region of lower concentration

94 Q refer to the following key, each answer in the key may be used more than once or not at all a. Active transport b. Bulk flow c. osmosis d. Facilitated diffusion Q10. Solutes will move across the membrane from the region of higher solute concentration to the region of lower solute concentration without the aid of proteins. Q11. Water will move across the membrane from the region of higher concentration of water to the region of lower concentration of water without the aid of proteins. Q12. movement of urine through the urinary tract. Q13. movement of solutes across a plasma membrane requiring the addition of energy.

95 Q14. The movement of molecules during diffusion can be described by all of the following Except a. Molecular movements are random b. Net movement of solute molecules is from a region of higher concentration to region of lower concentration c. Each molecule move independently of other molecules d. Solution molecules always move down the concentration gradient Q15. A saturated suspension of starch is enclosed in a dialysis tubing bag, a material through which only water can pass, but not starch. The bag with starch is placed into a beaker of distilled water. All the following are expected to occur Except a. There will be a net movement of water from a hypotonic region to a hypertonic region. b. There will be a net movement of solute from a hypertonic region to a hypotonic region. c. The dialysis bag with its contents will gain weight. d. No starch will be detect outside the dialysis bag. Q16. The Na-K Pump transports Na ions and K ions across the plasma membrane against their concentration gradients. This pump is not considered a co-transport because a. ATP is produced through this transporter. b. A gradient, not ATP, drives the transport of these ions c. ATP, not A gradient, drives the transport of these ions. d. co-transporters go in only one direction, but the Na-K Pump drives ions across the membrane in both directions. Q17. The resting membrane potential depends on which of the following? I. Active transport II. Selective permeability III. Differential distribution of ions across the axonal membrane a. III only b. I and II only c. II and III only d. I, II, and III

96 Q14. The movement of molecules during diffusion can be described by all of the following Except a. Molecular movements are random b. Net movement of solute molecules is from a region of higher concentration to region of lower concentration c. Each molecule move independently of other molecules d. Solution molecules always move down the concentration gradient Q15. A saturated suspension of starch is enclosed in a dialysis tubing bag, a material through which only water can pass, but not starch. The bag with starch is placed into a beaker of distilled water. All the following are expected to occur Except a. There will be a net movement of water from a hypotonic region to a hypertonic region. b. There will be a net movement of solute from a hypertonic region to a hypotonic region. c. The dialysis bag with its contents will gain weight. d. No starch will be detect outside the dialysis bag. Q16. The Na-K Pump transports Na ions and K ions across the plasma membrane against their concentration gradients. This pump is not considered a co-transport because a. ATP is produced through this transporter. b. A gradient, not ATP, drives the transport of these ions c. ATP, not A gradient, drives the transport of these ions. d. co-transporters go in only one direction, but the Na-K Pump drives ions across the membrane in both directions. Q17. The resting membrane potential depends on which of the following? I. Active transport II. Selective permeability III. Differential distribution of ions across the axonal membrane a. III only b. I and II only c. II and III only d. I, II, and III