Cell biology Lect. 1 B .pdf

Protoplasm u Protoplasm is the living content of the cell that is surrounded by plasma membrane. u It is a colorless material that exists throughout the cell together with the cytoplasm, nucleus and other organelles. u Protoplasm is composed of a mixture of small particles, such as ions, a...

Protoplasm u Protoplasm is the living content of the cell that is surrounded by plasma membrane. u It is a colorless material that exists throughout the cell together with the cytoplasm, nucleus and other organelles. u Protoplasm is composed of a mixture of small particles, such as ions, amino acids, monosaccharides, water, macromolecules like nucleic acids, proteins, lipids and polysaccharides. u It responds to the stimuli like heat, electric shock, chemicals and so on. Ass.Prof. Hanaa Elbadawy 1 I- Cytoplasm u Cytoplasm is semifluid gelatinous substance that fills the cell. It is made up of 80% percent water and is usually clear and colourless. u Many organelles are suspended and bound together by a lipid bilayer plasma membrane. u It constitutes dissolved nutrients, numerous salts and acids to dissolve waste products. u Further, most cellular activities such as many metabolic pathways including glycolysis and cell division occur in cytoplasm. u It helps movement of the cellular materials around the cell through a process called cytoplasmic streaming. u Cytoplasmic streaming plays an important role in cell processes since it promotes solute exchange between the cytoplasm and organelles and enables lateral transport for extensive distances. Ass.Prof. Hanaa Elbadawy cytoplasmic streaming Ass.Prof. Hanaa Elbadawy II- Cell organelles include: Nucleus u The nucleus is usually the most prominent organelle in a eukaryotic cell. u It contains molecules of DNA—extremely long polymers that encode the genetic information of the organism. u The nucleus is a membrane-bound structure that is present only in eukaryotic cells. The vital function of a nucleus is to store DNA or hereditary information required for cell division, metabolism and growth. u Nucleolus: It manufactures cell’s protein-producing structures and ribosomes. u Nucleopore: Nuclear membrane is perforated with holes called nucleopore that allows proteins and nucleic acids to pass through. u DNA also carries the genetic information in prokaryotic cells; these cells lack a distinct nucleus not because they lack DNA, but because they do not keep their DNA inside a nuclear membrane nuclear envelope Ass.Prof. Hanaa Elbadawy Mitochondria Generate Usable Energy from Food to Power the Cell u Mitochondria are present in essentially all eukaryotic cells, and they are among the most conspicuous (clear) organelles in the cytoplasm. u When seen with an electron microscope, individual mitochondria are found to be enclosed in two separate membranes, with the inner membrane formed into folds that project into the interior of the organelle. u Mitochondria are generators of chemical energy for the cell. They harness the energy from the oxidation of food molecules, such as sugars, to produce adenosine triphosphate, or ATP— GTP. ATP is the principal energy carrier in the cell while GTP has specific roles in many signaling pathways. u The mitochondrial membranes shows the smooth outer membrane (gray) and the highly convoluted inner membrane (red ). u The inner membrane contains most of the proteins responsible for cellular respiration—one of the mitochondrion’s main functions—and it is highly folded to provide a large surface area for this activity. Ass.Prof. Hanaa Elbadawy Mitochondria Generate Usable Energy Ass.Prof. Hanaa Elbadawy Plastides Ass.Prof. Hanaa Elbadawy Chloroplasts Capture Energy from Sunlight u Chloroplasts are large, green organelles that are found only in the cells of plants and algae, not in the cells of animals or fungi. u their two surrounding membranes, they possess internal stacks of membranes u containing the green pigment chlorophyll. u Chloroplasts carry out photosynthesis—trapping the energy of sunlight in their chlorophyll molecules and using this energy to drive the manufacture of energy-rich sugar molecules. u In the process, they release oxygen as a molecular by-product. Ass.Prof. Hanaa Elbadawy u Like mitochondria, chloroplasts contain their own DNA, reproduce by dividing in two. The chloroplasts, showing the inner and outer membranes, as well as the highly folded system of internal membranes containing the green chlorophyll molecules that absorb light energy. u Chloroplasts may be spherical, ovoid, or discoid in higher plants and stellate, cup-shaped, or spiral as in some algae. u The chloroplast is bounded by two lipoprotein membranes, an outer and an inner membrane, with an intermembrane space between them. u The inner membrane encloses a matrix, the stroma which contains small cylindrical structures called grana. Most chloroplasts contain 10-100 grana. Ass.Prof. Hanaa Elbadawy Ass.Prof. Hanaa Elbadawy u Each granum has a number of disc-shaped membranous sacs called grana lamellae or thylakoids. u The grana are interconnected by a network of anastomosing tubules called inter-grana or stroma lamellae. u Chloroplasts thus have three different membranes, the outer, the inner and the thylakoid membrane. u The inner surface of the thylakoid membrane is granular in the organization due to small spheroidal quantosomes. u The quantosomes are the photosynthetic units, and consist of two structurally distinct photosystems, PS I and PS II, containing about 250 chlorophyll molecules, helps in conversion of light energy to chemical energy ATP u In higher plants, the pigments present are chlorophyll-a, chlorophyll-b, carotene, and xanthophyll. u the two photosystems absorb different wavelengths of light. The PSII special pair absorbs best at 680 nm, while the PSI special absorbs best at 700 nm. u Note: the visible light has range between 380 to 700 nanometers. Ass.Prof. Hanaa Elbadawy chloroplast Ass.Prof. Hanaa Elbadawy  Endoplasmic reticulum (ER) u The endoplasmic reticulum produces many of the components of a eukaryotic cell. u it is specialized for protein secretion. u The ER is continuous with the membranes of the nuclear envelope. u The black particles studding the particular region of the ER shown here are ribosomes, structures that translate RNAs into proteins. Because of its appearance, ribosome-coated ER is often called “rough ER” to distinguish it from the “smooth ER,” which does not have ribosomes bound to it. Ass.Prof. Hanaa Elbadawy Ass.Prof. Hanaa Elbadawy proteins Are made on polyribosomes u The synthesis of most protein molecules takes between 20 seconds and several minutes. u But even during this short period, multiple ribosomes usually bind to each mRNA molecule being translated. u Eukaryotic ribosomes are also known as 80S ribosomes, referring to their sedimentation coefficients in Svedberg units, because they sediment faster than the prokaryotic (70S) ribosomes. Eukaryotic ribosomes have two unequal subunits, designated small subunit(40S) and large subunit (60S) according to their sedimentation coefficients. Ass.Prof. Hanaa Elbadawy  Proteins are blue, membrane lipids are yellow, and ribosomes and DNA are pink. Ass.Prof. Hanaa Elbadawy Peroxisomes u are small, membrane-enclosed vesicles that provide a safe environment for a variety of reactions in which hydrogen peroxide is used to inactivate toxic molecules. u Peroxisomes are microbodies which have enzymes for peroxide metabolism. They include : u (a) Peroxide producing oxidative enzymes like peroxidase, urate oxidase or uricase, amino acid oxidase and (b) Peroxide destroying enzymes like catalase. u Peroxisomes occur widely in animals cells, fungi, higher plants but quite common in photosynthetic cells. In mesophyll cells, peroxisomes interact with chloroplasts, and mitochondria to take part in photorespiration. u The peroxisomes have enzymes that are capable of speeding up the production and breakdown of hydrogen peroxide. u The peroxisomes are found in approximately 70-100 different locations throughout the cell, Ass.Prof. Hanaa Elbadawy Golgi Apparatus The Golgi apparatus modifies, stores and routes proteins and other chemical products to where they need to go. Exchange of materials takes place between the endoplasmic reticulum, the Golgi apparatus, the lysosomes, and the outside of the cell. https://plantcellresortandspa.weebly.com/golgi-apparatus.html Ass.Prof. Hanaa Elbadawy Some of the main functions of Lysosomes (rare in plant cells) are as follows: u Intracellular digestion:... u Removal of dead cells:... u Help in protein synthesis:... u Help in fertilization:... Ass.Prof. Hanaa Elbadawy Central Vacuole u It occupies around 30% of the cell’s volume in a mature plant cell. § Tonoplast is a membrane that surrounds central vacuole. § The vital function of central vacuole apart from storage is to sustain turgid pressure against the cell wall. § The central vacuole consists of cell sap. It is a mixture of salts, enzymes and other substances. u They are found in all eukaryotic cells which are involved in distributing synthesized macromolecules to various parts of the cell. Ass.Prof. Hanaa Elbadawy