Cell Biology Lecture Notes PDF

Cell Biology (4 Lectures) Prof. A.A. Mahdi Department of Biochemistry King George’s Medical University Lucknow  Water Atomic view Prof. A.A. Mahdi Department of Biochemistry I...

Cell Biology (4 Lectures) Prof. A.A. Mahdi Department of Biochemistry King George’s Medical University Lucknow  Water Atomic view Prof. A.A. Mahdi Department of Biochemistry Ice  Water Vessels : Intercellular (ECF) : Intracellular (ICF) Liters : 3; 13; 30 % : 5; 15; 50 75% to 50%. 90% in brain tissue; 10% adipose tissue. Ions/neutral molecules – Soluble, Proteins – Colloids. Lipoproteins – Pseudomicelles. Substrate as well as a product. Both deficiency as well as excess impairs functioning. Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  CYTOSOL Fluid compartment, permeates whole internal environment, represent 50-60% of total cell volume. Contains cytoskeleton having microtubules and microfilaments. Composition: Viscous gel having proteins 20 gm/100 ml. Have storage molecules like glycogen granules in liver or fat droplets in adipocytes. Enzymes of glycoloysis, HMP shunt, glycogen metabolism, AA metabolism, Fatty acid synthesis, heme biosynthesis, urea cyle. Transport proteins and carrier of metals/steroid hormones. Inorganic ions such as Sodium, potassium, calcium, magnesium, Chloride, phosphate, etc. Prof. A.A. Mahdi Department of Biochemistry  Biological Membranes
Composed of mainly lipids and proteins
Give cell its individuality and also compartmentalize intracellular organelles.
Biomembranes are thin films which are not rigid or impermeable, rather highly mobile and dynamic structures.
They are gatekeepers of the cells.
Control access to cell by inorganic ions, nutrients and biological compounds. Prof. A.A. Mahdi Department of Biochemistry  IMPORTANCE Highly selective permeability barriers. Have specific receptors for external stimuli. Generate signals: chemical or electrical. Energy conservation processes occur in membranes. COMMON FEATURES  Sheet like structures, form closed boundaries, thickness between 60-100 Ao.  Composed of lipids and proteins, ratio between 4:1 to 1:4.  Non-covalent assemblies.  Asymmetric.  Fluid structure. Prof. A.A. Mahdi Department of Biochemistry  LIPIDS  Phospholipids : amphipathic molecules. Phosphatidyl choline and Phosphatidyl ethanolamine.  Neutral lipids : Cholesterol. Cholesterol esters, triglycerides, free fatty acids. ROLE OF LIPIDS  Fluidity and flexibility of membrane dependent on degree of unsaturation of fatty acids. More unsaturation, more flexible and fluid.  Conditions of nutritional deficiency of essential fatty acids are displayed.  Damage to PUFA leads to loss of membrane structure and functioning. Prof. A.A. Mahdi Department of Biochemistry Molecular structure Name Stearic acid: saturated C18 Oleic acid: monounsaturated C18 Linoleic acid: diunsaturated C18 γ-Linolenic acid: triunsaturated C18 Arachidonic acid: tetraunsaturated C20 Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry Phosphatidyl ethanolamine Prof. A.A. Mahdi Department of Biochemistry  Respiratory Chain IMS + H FeS C1 cyt c CoQ a Q0 a3 FeS cyt c N-2 b b CuB SDH Qi III FeS N-1, N-3, N-4 FMN Succinate MATRIX NADH Complex I Complex II Complex III Complex IV  Prof. A.A. Mahdi Department of Biochemistry  Lipid Composition of Membranes ER(%) PM(%) Total Phospholipids 84.9 61.9 Phosphatidyl choline 60.9 39.9 Phosphatidyl ethanolamine 18.6 17.8 Phosphatidyl inositol 8.9 7.5 Sphingomyelin 3.7 18.9 Total Neutral lipids 15.1 38.1 Cholesterol 24.6 34.5 Free fatty acids 40.6 35.5 Triacylglycerols 24.7 22.4 Cholesterol esters 10.1 8.0 Prof. A.A. Mahdi Department of Biochemistry Animal PC Rat Liver 60% Sheep liver 58% Sheep kidneys 40% Sheep heart 20% Sheep brain 30% RBCs C PL Rat 28% 60% Human 25% 58% Sheep 28% 60% Ox 32% 55% Prof. A.A. Mahdi Department of Biochemistry  Phospholipid composition of subcellular organelles prepared from rat: PC PE C CE Whole mitochondria 45% 40% - - RER 62% 20% 5% 1% Golgi 42% 15% 10% 2% Plasma membrane 35% 20% 20% 1% Inner Mito. Memb. 50% 38% - - Outer Mito. Memb. 55% 32% - - Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  Proteins
Specific proteins mediate distinctive functions.
Serve as pumps, gates, receptors, energy transducers and enzymes.
Play most of the functions of the biological membranes.
Not only structural components but also carry out membrane transport.
Also act as recognizing sites for hormones.
Distinguish between like and unlike cells. Carbohydrates
Some oligosaccharidic units present in the membrane play role in cell-cell recognition Prof. A.A. Mahdi Department of Biochemistry  Fluid Mosaic Model Proposed by S. J. Singer and G. Nicholson in 1972 for biological membranes Membranes are two dimensional solutions of oreintal globular proteins and lipids. Salient features are: 1. Most of the membrane phospholipids and glycolipid molecules are arranged in a bilayer. This bilayer has dual role; it is both a solvent and permeability barrier. 2. Small proportion of membrane lipids interacts specifically with particular membrane proteins and this may be essential for their functioning. 3. Membrane proteins are free to diffuse laterally in the lipid matrix, unless restricted by specific interactions, whereas they are not free to rotate from one side of the membrane to the other. Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  Peroxisome Diagrammatic view Prof. A.A. Mahdi Department of Biochemistry Electron microscopic view  PEROXISOMES Enzymes: Catalase, urate oxidase, D-AA/L-AA oxidase, glycolate oxidase, glyco-oxylate oxidase, isocitrate oxidase. Oxidation of fatty acids: FA transport independent of carnitine; instead of FAD-linked acyl-S-CoA dehydrogenase it has FAD- linked acyl-S-CoA oxidase which transfer electrons from oxygen to form hydrogen peroxide. Catalase H2O2 H2O Peroxisomes also play an important role in detoxification. Almost half of alcohol consumed is oxidized to acetaldehyde in them. Prof. A.A. Mahdi Department of Biochemistry  Golgi complex Electron microscopic view Prof. A.A. Mahdi Department of Biochemistry  Golgi Body (Dictyosome) Director or editor of macromolecular traffic. Accurate sorting of proteins for selective export. Prof. A.A. Mahdi Department of Biochemistry Lysosome Prof. A.A. Mahdi Department of Biochemistry  LYSOSOMES Number varies, numerous in Macrophages, less in lymphocytes. Contains hydrolytic enzymes, hydrolyses C-C, C-N, C-O bonds and general rxn. is : A – B + H2 O AH + BOH Esterases, lipases, phospholipases, acid phosphatase, nucleotidase, DNAses, RNAses, collegenases, cathepsin, peptidases, hyaluronidase, α-glucosidase, β-glucosidase, sulphatase, phosphotases, etc. pH : 4-5 (acidic) Cathepsins are sulphahydryl enzymes having –SH gps which are generally free. Enzymatic activity lost in presence of iodoacetamide, metal ions like copper and mercury. Prof. A.A. Mahdi Department of Biochemistry Proteins, NA, polysaccharides cannot pass lysosomal membrane. They gain entry either through autophagy or by heterophagy. Products like AAs, monosccahrides, nucleosides can pass through the membrane. Kidneys: Autophagy in all parts, but in poximal tubules heterophgy, Albumin and hemoglobin removed. 10-15% of total serum albumin degraded in kidneys. Nervous system: Present in neurons and Schwann cells, have autophagic role. In diseased states lysosomes accumulate lipids and polysaccharides. Bone: Hyaluronidase, peptidase, collagenase present play a role in reabsorbing and remodeling of osteocytes. Spermatozoa: lysosomal hyaluronidase participate in fertilization process. Prof. A.A. Mahdi Department of Biochemistry Vitamin A toxicosis: release of lysosomal enzymes. Hurler’s syndrome (mental retardation, dwarfism): increased dermatan sulphate and heparan sulphate. Arthritis: Cathepsins, hyaluronidase. Immunity: Mammary glands, Uterus Prof. A.A. Mahdi Department of Biochemistry Fingers affected with rheumatoid nodules Prof. A.A. Mahdi Department of Biochemistry  Prof. A.A. Mahdi Department of Biochemistry  ENDOPLASMIC RETICULUM Detoxification of drugs and xenobiotics. Steroid hormones are synthesized. Glucose – 6 – phosphatase, plasma lipoprotein synthesis, synthesis of TGs, PL, cholesterol, bile acid, inactivation of steroid hormones, conjugation rxn., (phosphatidyl glycerol and cardiolipin not synthesized). Muscle cells has sarcoplasmic reticulum. Ribophorins. Cisternae Prof. A.A. Mahdi Department of Biochemistry  MITOCHONDRIA Diagrammatic view Prof. A.A. Mahdi Department of Biochemistry Electron microscopic view  MITOCHONDRIA
Operation of citric acid cycle and production of reducing equivalents – NADH.
β-oxidation of fatty acids producing acetyl-SCoA, FADH and NADH.
Oxidation of NADH/FADH by ETC and production of ATP.
Accumulation of divalent ions such as calcium. Prof. A.A. Mahdi Department of Biochemistry Mitochondrion (mitos thread + khondrion granule) or "cellular power plants". Convert organic materials into energy in the form of ATP. There can be hundreds or thousands of mitochondria, which can occupy up to 25% of the cell's cytoplasn. Mitochondria have their own DNA and may, according to the endosymbiotic theory, be descended from free-living prokaryotes. Mitochondrion has outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes, however, have different properties. There are 5 distinct compartments within mitochondria: (1) outer membrane (2) intermembrane space (3) inner membrane (4) cristae space and (5) matrix. Prof. A.A. Mahdi Department of Biochemistry  MITOCHONDRIA Outer Membrane: Fatty acid elongating enzymes, transferases, phosphatases, phospholipases. Inter-membrane space: Enzymes of nucleotide synthesis, adenylate kinase, creatinine kinase etc. Inner membrane: Transport systems (phosphate carrier, pyruvate carrier, glutamate carrier, ornithine carrier, tricarboxylate carrier), ETC and oxidative phosphorylation components and enzymes. Matrix: Enzymes of TCA cycle, β-oxidation of FAs, replication of DNA and protein synthesis including RNA polymerase, tRNA, ribosomes, AA activating enzymes. Prof. A.A. Mahdi Department of Biochemistry Outer membrane: Encloses the entire organelle, has a protein-to-phospholipid ratio similar to the eukaryotic plasma membrane (about 1:1 by weight). Has integral protein called porins, which contain a relatively large internal channel (about 2-3 nm) that is permeable to all molecules of 5000 daltons or less. Larger molecules can only traverse the outer membrane by active transport. It also contains enzymes involved in such diverse activities as the elongation of fatty acids, oxidation of epinephrine (adrenaline), and the degradation of tryptophan. Prof. A.A. Mahdi Department of Biochemistry Inner membrane: The inner membrane contain proteins with four types of functions: Oxidation reactions of the respiratory chain. ATP synthase, which makes ATP in the matrix. Specific transport proteins that regulate the passage of metabolites into and out of the matrix. Protein import machinery. Contains more than 100 different polypeptides, with high protein-to- phospholipid ratio (more than 3:1 by weight, which is about 1 protein for 15 phospholipids). Has an unusual phospholipid, cardiolipin, a characteristic of bacterial plasma membranes. Does not contain porins, and impermeable; Cristae, expand the surface area, enhancing ability to generate ATP. In typical liver mitochondria, for example, the surface area, including cristae, is about five times that of the outer membrane. Mitochondria of cells which have greater demand for ATP. Prof. A.A. Mahdi Department of Biochemistry Mitochondrial matrix: Contains concentrated mixture of hundreds of enzymes, in addition to the special mitochondrial ribosomes, tRNA, and several copies of the mitochondrial DNA genome. Of the enzymes, the major functions include oxidation of pyruvate and fatty acids, and the citric acid cycle. Mitochondria has its own genetic material, and the machinery to manufacture their own RNAs and proteins. This DNA encodes a small number of mitochondrial peptides (13 in humans) that are integrated into the inner mitochondrial membrane, along with polypeptides encoded by genes that reside in the host cell's nucleus. Mitochondrial functions: Although it is well known that the mitochondria convert organic materials into cellular energy in the form of ATP. mitochondria play an important role in many metabolic tasks, Prof. A.A. Mahdi Department of Biochemistry  Apoptosis-programmed cell death Glutamate-mediated excitotoxic neuronal injury Cellular proliferation Regulation of the cellular redox state Heme synthesis Steroid synthesis Mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste product of protein metabolism. A mutation in the genes regulating any of these functions can result in mitochondrial diseases. Energy conversion A dominant role for the mitochondria is the production of ATP carried out by oxidising products of glycolysis: pyruvate and NADH, produced in cytosol. This process of cellular respiration, also known as aerobic respiration, is dependant on the presence of oxygen. Prof. A.A. Mahdi Department of Biochemistry Origin Mitochondria contain ribosomes and DNA. Formed by the division of other mitochondria, it is generally accepted that they were originally derived from endosymbiotic prokaryotes. Mitochondrial DNA, is circular and employs a variant genetic code, show their ancestor, the so-called proto-mitochondrion, was a member of the Proteobacteria. This relationship developed at least 2 billion years ago and mitochondria still show some signs of their ancient origin. Mitochondrial ribosomes are the 70S (bacterial) type, in contrast to the 80S ribosomes found elsewhere in the cell. As in prokaryotes, there is a very high proportion of coding DNA, and an absence of repeats. Unlike their nuclear cousins, mitochondrial genes are small, generally lacking introns, and many chromosomes are circular, conforming to the bacterial pattern. Prof. A.A. Mahdi Department of Biochemistry  Mitochondrial Genes: Mitochondrial genome is circular double-stranded. Each mitochondria has five copies of this genome. Human Mt chromosome contains 37 genes (16568 bp), including 13 that encode subunits of proteins of the respiratory chain, the remaining genes code for rRNA and tRNA molecules essential to the protein synthesizing machinery of Mt. About 900 different Mt. proteins are encoded by nuclear genes, synthesized on cytoplasmic ribosomes, then imported and assembled within the mt. Mutations in Mt genes cause a number of diseases: Mitochondrial encephalopathies, affect brain and skeletal muscles Lever’s hereditary optic neuropathy (LHON) : affects CNS including optic nerves, causing bilateral loss of vision Prof. A.A. Mahdi Department of Biochemistry Respiratory proteins encoded by Mt genes in Humans: I NADH dehydrogenase 43 7 II Succinate dehydrogenase 4 0 III Ubiquinone cyt C oxidoreductase 11 1 IV Cytochrome oxidase 13 3 V ATP synthase 8 2 Prof. A.A. Mahdi Department of Biochemistry Protein:Lipid Ratio in Membrane of Myelin 0.23 Mouse liver 0.85 Human RBCs 1.1 Amoeba 1.3 Retinal rods 1.0 Mitochon. OM 1.1 SER 2.0 Mitochon. IM 3.2 Prof. A.A. Mahdi Department of Biochemistry