Cell Biology PDF

Cell Biology The cell: cell membrane, cell organelles, nucleus and cytoskeleton  Cell: functional and morphological unit of living organisms Unicellular organisms - single cell Multicellular organisms - several cells grouped together and specialized in certain functions ...

Cell Biology The cell: cell membrane, cell organelles, nucleus and cytoskeleton  Cell: functional and morphological unit of living organisms Unicellular organisms - single cell Multicellular organisms - several cells grouped together and specialized in certain functions  Levels of organization Muscle cell Bone cell Cells Muscle tissue Bone tissue Tissues Muscle Bone Locomotor Apparatus Organs Organ Muscular system Skeletal system systems (skeletal muscles) (skeleton)  Prokaryotes (bacteria) - absence of nucleus, no cellular organelles other than ribosomes. Eukaryotic cells - differentiated nucleus with more complex DNA, numerous organelles, larger size.  Animal eukaryotic cell 1. Nucleolus 2. Nucleus 3. Ribosome 4. Granules 5. Rough endoplasmic reticulum (RER) 6. Golgi apparatus 7. Cytoskeleton 8. Smooth endoplasmic reticulum (SER) 9. Mitochondria 10. Vesicles 11. Cytosol 12. Granules 13. Centriole Common characteristics of all animal cells: surrounded by plasma membrane inside of the cell: cytoplasm, cell organelles (to carry out its functions) and the nucleus (genetic material). The number and arrangement of the organelles will vary depending on the type of cell. Cell Membrane Plasma Membrane CELL MEMBRANE Extracellular space Carbohydrate Glycoprotein Cholesterol Protein Cytoskeleton Cytoplasm Permeable and selective barrier that separates the external environment from the inside of the cell Functions of the cell membrane: Permeable and selective barrier that separates the external environment from the interior of the cell Delimits the cell and maintains its integrity Regulates interactions with other cells Controls the movement of substances from inside to outside or vice versa Recognizes molecules and other cells Maintains a potential difference between the inside and outside of the cell Transduces physical or chemical signals from the external environment into intracellular events Components: The cell membrane consists mainly of lipids and proteins of different types: Phospholipids Lipids (40-50%): Glycolipids Cholesterol (sterol) Intrinsic proteins (~70%): Proteins (60-50%): Integral or transmembrane Extrinsic proteins (~30%): Peripheral Phospholipids Phosphoglycerides Serine → phosphatidylserine Choline → phosphatidylcholine Nitrogenous compound Ethanolamine → phosphatidylethanolamine Inositol → phosphatidylinositol Hydrophilic head Phosphate bridge (polar) Glycerol Sphingomyelin Choline Hydrophobic tail Hydrophilic head (non polar) Phosphate bridge Saturated Fatty (polar) Acid Sphingosine Hydrophobic tail Unsaturated Fatty Acid (non polar) Phospholipids - most abundant lipids in the membrane. Form a double layer with the nonpolar tails on the inside of the membrane and the polar heads on the surface of the membrane, providing flexibility and maintaining the integrity of the membrane.  Glycolipids Cholesterol 26 CH3 25 27 CH CH3 Glucids Hydrophilic head Lateral 24 23 CH2 CH2 (sugars) (polar) chain 22 CH2 20 21 CH CH3 18 CH3 12 17 11 13 16 Hydrophobic tail 19 C D CH3 9 14 15 (non polar) 1 2 A 10 B 8 Steroid Nucleus 3 5 7 OH 4 6 Polar Group In the plasma membrane there are also other lipid molecules with a polar part and a non- polar part in a lower proportion than the phospholipids - glycolipids and cholesterol. Glycolipids - have two tails of fatty acids linked to a carbohydrate, located in the membrane between the phospholipids in the same arrangement as these. Cholesterol - located in the spaces between unsaturated tails, limiting the ability of movement, but at the same time prevents strong bonds between fatty acids being established, providing fluidity to the bilayer. Membrane proteins Extrinsic or peripheral proteins - associated with the membrane, generally by its cytosolic side Intrinsic or integral proteins - integrated into the membrane. Most intrinsic proteins completely cross the membrane (transmembrane proteins). Integral (~70%): ▪ Peripheral (~30%): – Transmembrane Attached to lipids Attached to proteins – Partially integrated FUNCTIONS of membrane proteins: Transport: join molecules to take them from one side of the membrane to the other, or form channels that open up to certain stimuli. Adhesión: establish cell junctions with other cells or with the medium, and can fix internal structures of the cell itself. Signal reception: the cells need to receive information from the medium and from other cells in order to coordinate within the multicellular organism. Enzymes: catalyze reactions in the vicinity of the membrane. TRANSPORT ADHESION RECEPTORS ENZYMES  T T T TT TT T Protoplasm T T TT T The protoplasm is the living substance of the cell and is divided into two compartments: - Cytoplasm: extends from the plasma T TT membrane to the nuclear envelope. The T T T TT liquid part of the cytoplasm is the cytosol. It is composed mainly of water, and numerous organic and inorganic chemical substances. In addition to the cytosol, there are organelles and the cytoskeleton. - Carioplasm: material that forms the content of the nucleus.  Cell organelles Cell organelles RIBOSOMES 25-30nm Ribosomes - small organelles made of ribosomal RNA (rRNA) that are responsible for protein synthesis. The messenger RNA (mRNA, transcribed from DNA) will bind to the ribosome, which will read the information contained in that mRNA chain. The transfer RNA (tRNA) will add the corresponding amino acid that indicates the mRNA, and as the ribosome reads the mRNA chain, amino acids will be added to form a protein. Ribosomes associated with membranes The proteins synthesized here may be part of the membranes or may be released outside the cell. POLYRIBOSOMES or POLYSOMES In the cytosol ribosomes usually ARN mRNA mm associate in groups through a chain of mRNA to synthesize proteins that will be destined to the cell itself. Endomembrane System ORIGIN: Invagination of the membrane: similar structure and composition ENDOPLASMIC RETICULUM GOLGI APPARATUS NUCLEAR ENVELOPE ENDOPLASMIC RETICULUM Largest membranous system in the cell formed by a system of tubules and vesicles (lumen of ER = cistern). Smooth Endoplasmic Reticulum (SER) Rough Endoplasmic Reticulum (RER) – with ribosomes ROUGH ENDOPLASMIC RETICULUM System of elongated cisternae that arise near the nuclear membrane. The RER membrane is continuous with the nuclear envelope and contains ribosomes (rough appearance). 30% lipids 70% proteins  RER Function of the RER: participates in protein synthesis. ribosomes Distribution of the proteins synthesized in the ribosomes of the RER: can remain in the RER membrane become part of the plasma membrane other proteins will be stored inside the RER cisternae and then will undergo processing. They will come out through vesicles and go to other organelles or outside the cell. SMOOTH ENDOPLASMIC RETICULUM Network of anastomosed tubes located after the RER. The SER does not have ribosomes associated with the membrane. Main functions: lipids synthesis (steroids, cholesterol, triglycerides) and calcium storage. GOLGI APPARATUS 1898 - Camilo Golgi Consists of one or several series of stacked cisternae, surrounded by vesicles in the process of fusing or detaching from this organelle. 4 – 40 Cisternae = Dictyosome Morphological polarity: cis face: closest to the RER and the nucleus. Vesicles from the RER will enter the dictyosome through the cis face. trans face: concave shape, oriented towards the plasmatic membrane. This is the exit face of the vesicles. Golgi ap. composition: 65% proteins 35% lipids Transport of proteins from RER Most of he proteins synthesized and modified in the RER will be transported in vesicles to the Golgi apparatus. They enter through the cis face and they will suffer processing and packaging inside of it. Then they will go out through the trans face of the Golgi to go to their final destination.  LYSOSOMES Organelles surrounded by membrane, spherical in shape Contain acid hydrolases (enzymes responsible for the degradation of macromolecules, phagocytosed microorganisms, cell debris or aged organelles). The lysosome membrane has proton pumps that maintain an acid pH (pH 5) in the interior suitable for the function of these enzymes. The lysosome membrane also prevents the acid pH from damaging other structures of the cell. Degraded material can be reused by the cell, or is expelled to the outside.  Lysosomal vesicles: lysosomes 1º Lysosome formation Golgi Lysosomes are released from the (trans face) trans face of the Golgi apparatus clathrin with the enzymes inside and are covered with clathrin. Subsequently, these vesicles fuse Fusion with existing with other lysosomes or with lysosomes endocytosis vesicles and thus pour 1 or 2 their enzymes into these vesicles to begin the digestion of their contents. PRIMARY LYSOSOME: vesicle formed in the Golgi that has never intervened in catabolic processes. SECONDARY LYSOSOME: vesicle that has already participated in catabolic processes. TERTIARY LYSOSOME (or residual body): lysosome that storages compounds resistant to complete digestion.  PEROXISOMES Organelles surrounded by membrane, spherical or oval in shape Contain oxidative enzymes (degradation of fatty acids, giving rise to hydrogen peroxide, H2O2). H2O2 is a very reactive substance that degrades some toxic agents and microorganisms, but it can also damage structures of the cell itself. MITOCHONDRIA Organelles responsible for using oxygen from the air (cellular respiration) and glucose to obtain energy for the cells to carry out their functions. Oxidative phosphorylation is performed to obtain ATP (stable molecule that stores energy).  Smooth mitochondrial outer membrane - permeable to small molecules Inner mitochondrial membrane - with cristae that greatly increase the surface of this membrane, and protein complexes that form the ATP synthase and the electron transport chain (both responsible for the generation of ATP) Mitochondrial matrix - contains the enzymes of the Krebs cycle (previous step to the electron transport chain), ribosomes (synthesis of mitochondrial proteins) and mitochondrial DNA (circular and unpacked DNA, more similar to prokaryotic organisms) NUCLEUS Largest organelle in the cell, responsible for storing the genetic material. Contains most of the cell's DNA, the mechanisms for the synthesis of RNA and the assembly of ribosomes. Usually located in the center of the cell, spherical shape. The nucleus can vary its position, shape and size depending on the function of the cell, its cytoplasmic content or its shape. Most cells have a single nucleus, but in humans, some cells have several nuclei (osteoclasts, muscle fibers), and others have lost it (erythrocytes).  Nuclear envelope – External nuclear membrane – Inner nuclear membrane – Nuclear pores (allow the nucleus to communicate with the cytoplasm) Nucleoplasm (liquid part) – Chromatin (DNA and proteins) – Nucleolus (ribosomal RNA) Chromatin is composed of DNA and associated proteins (mainly histones). Depending on the cell’s activity, it can appear in the shape of heterochromatin (condensed), or euchromatin (more dispersed).  Chromosome structure Sister chromatids Cromátidas hermanas armto zo cor (p) largo BraShort Centrómero Centromere Kinetochore Long arm (q) Brazo Each identical copy of the DNA will form a chromatid, and two chromatids will join at the centromere to form the chromosome. In the centromere there is a structure called kinetochore, which is where the microtubules of the mitotic spindle will bind during cell division. Cytoskeleton CYTOSKELETON System of tubules and protein filaments responsible for: maintaining the shape of the cell, cell movements, the location of the organelles and their movement, stabilize cell junctions, muscle contraction and cell division. Made up of three components: Actin microfilaments (non-muscular cells) Microfilaments Myofilaments (muscular cells) Movement Intermediate filaments Structure Microtubules Shape, intracellular transport, cell division  MICROFILAMENTS (Actin) OPTICAL MICROSCOPY IMMUNOFLUORESCENCE Bundles 7 nm Networks Microfilaments - formed by actin (protein organized in two chains forming an helix). Actin filaments are grouped forming networks or bundles: Actin networks are located next to the plasma membrane and form the structural basis of the cellular cortex. Bundles of actin can be contractile or non-contractile. In muscle cells there are actin filaments that are organized in a particular way and will be responsible for muscle contraction.  Microfilaments (non-muscular cells): Contractile bundles are usually associated with another protein, myosin, which moves the actin filaments. They are responsible for the movement of organelles and vesicles, the formation of pseudopods and the formation of contractile rings for cell division. Non-contractile bundles form bundles of closely packed parallel filaments. They form structures such as microvilli. Non contractile bundles Contractile bundles Actin Myosin II Tropomyosin Actinin α Minimyosin Fimbrin Plasma mb  Microvilli Cellular membrane protrusions that have dense bundles of cross-linked actin filaments. The actin filaments form parallel and rigid bundles. These structures increase the surface area of the cell so that it has more contact with the environment. INTERMEDIATE FILAMENTS Intermediate diameter between microfilaments and microtubules. Formed by different types of proteins that share morphological and structural characteristics. Functions: support the cell, maintaining its three- dimensional structure support the nucleus anchor the cytoskeleton to the membrane. 10 nm  MICROTUBULES Centrosome Hollow cylinders nucleated from the centrosome. Each microtubule consists of 13 protofilaments, made up of α- and β- tubulin dimers. Very dynamic structures that are continuously stabilizing or depolymerizing, thus suffering changes in length depending on the needs of the cell. Provide rigidity and maintain the shape of the cell, regulate the intracellular movement of organelles and vesicles, intervene in cell division, allow the movement of cilia and flagella. 25 nm 1. Complex grouping of microtubules: CENTRIOLE The centrioles are cylindrical structures composed of 9 triplets of microtubules. In animal cells, centrioles usually reside in pairs with the cylindrical centrioles at right angles to each other. CENTRIOLES: The centrosome (or microtubule organizing center) consists of a pair of centrioles surrounded by a dense matrix (pericentriolar material, PCM). Microtubules polymerize and depolymerize from the centrosome. Centriole Pair of centrioles (Diplosome) Pericentriolar Centrosome = Pair of centrioles Material (PCM) (Diplosome) + PCM  2. Complex grouping of microtubules: CILIA They are extensions of the cell membrane with a microtubule cytoskeleton. Its main structure is formed by a central pair of microtubules surrounded by 9 doublets., The basal body is found at the base of the cilium and is formed by 9 triplets of microtubules. Cilia cover the surface of the cell and move substances from the medium. 2 92+2 MP 92+0 Basal body 93+0 3. Complex grouping of microtubules: FLAGELA Only the sperm has a flagellum. The main structure is the same as 2 that of the axonemes: 92 + 2. In the main piece of the tail of the sperm, 9 this structure is surrounded by 9 dense fibers and in the middle part, there is also a sheath of mitochondria that will provide energy for movement. Unlike cilia, each cell has a single, much larger and longer flagellum that serves to move the cell itself.