DNA Structure and Cell Membrane - Assignment Example

Journal entry: Chapter 2 Six naturally occurring elements account for 98.5% of the body weight: oxygen, carbon, nitrogen, hydrogen, calcium and phosphorus. Trace elements, including minerals constitute important components. According to the elementary atomic model proposed by Neils Bohr, the nucleus is at the centre of the atom and is surrounded by negatively charged particles with insignificant mass, known as electrons, which are arranged around the nuclear core in energy shells. The electrons in the outermost shell are known as valence electrons and each atom tries to complete a complement of 8 electrons to attain electrical stability. The different forms of an element are known as isotopes, and the unstable isotopes capable of decay, are called radioisotopes. This phenomenon is known as radioactivity. Radiations are of three main types: alpha, beta and gamma rays. They are measured in Sieverts(> 5 Sv are fatal). Ions are atoms with unequal numbers of protons and electrons. Electrolytes are salts that from ions in solution and thus transmit electricity. Free radicals are particles with an odd number of electrons. Their damaging effects in the body are prevented by antioxidants like SOD, selenium and vitamin E. Two or more atoms unite by means of chemical bonds to from molecules. The bonds can be ionic(formed by gaining or losing an electron), covalent(formed by sharing electrons) and hydrogen bonds(formed by weak attraction between polarized molecules.) Water constitutes 50 to 75% of our body weight. The molecule is polar with a slightly negative charge on oxygen and a slightly positive charge on hydrogen. Other substances, when added to water, can form solutions(solute +solvent), colloids(cloudy) or suspensions(particles too heavy to remain permanently suspended.) Molecules that are proton donors in solution are acids, those that are proton acceptors are basic. Normal body Ph is between 7.35 and 7.45. it is maintained in this range by means of buffers. Chemical reactions are either synthetic(A+B= AB), exchange(AB+CD=AC+BD) or reversible reactions which can go in either direction. Carbon atoms have the ability to form long chains called polymers. Carbohydrates are organic molecules with the empirical formula (CH2O)n. The simplest sugars are monosaccharides(glucose, fructose). Two monosaccharides combine to form disaccharides(sucrose, lactose). Carbohydrates containing long chains of monosaccharides are known as polysaccharides(cellulose, starch). Lipids are hydrophobic molecules containing relatively large amounts of hydrogen. They are of 5 main types; fatty acids(saturated and unsaturated), eicosanoids, steroids, triglycerides, and phospholipids. Proteins are polymers of amino acids, attached by means of peptide bonds, that have important structural and functional roles in the cell. The sequence of amino acids on the polypeptide chain is known as the primary structure. The interactions of the different peptide groups and different polypeptide chains give rise to secondary and tertiary structure of the protein. Nucleotides are organic compounds with 3 main components; Nitrogenous base One or more phosphate groups Monosaccharide One of the most important nucleotides in the body is ATP which is the bodies main energy resource without which life cannot be supported. Journal entry: Chapter 3 According to the cell theory put forward by Hooke and Schwann, all living things are made up of cells. Cells are of different types: Squamous-flat Cuboidal- squarish Columnar-taller than broad Spheroid-e.g. fat calls and ova Polygonal-with 4-5 sides Cells have 3 main components: cell membrane, cytoplasm, organelles. CELL MEMBRANE: A. lipids: constitute 98% of cell membrane. 75% are phospholipids. 20 % are cholesterol. 5 % glycolipids. They are arranged in the form of a bilayer B. proteins:are either transmembrane or peripheral. They function as: 1. receptors for hormones e.g. epinephrine 2. second messenger systems 3. channels for ions, etc. which may be ligand gated, voltage gated or mechanically regulated 4. enzymes 5. in active transport. EXTENSIONS FROM CELL SURFACE INCLUDE: 1. microvilli-serve to increase surface area of the cell for purpose of absorption as in the intestine 2. cilia-may be motile(respiratory tract) or immotile(sensory function in inner ear) 3. flagella(whip-like. Role in motility of sperms) TRANSPORT ACROSS CELL MEMBRANE: A. simple diffusion: occurs down a concentration gradient. The rate is increased by higher temperature, steeper concentration gradient, lighter molecules and availability of a large surface area for the transport to take place B. carrier mediated transport: can be 1. uniport: transports only one molecule at a time 2. symport: transports 2 molecules…in same direction (contransport) or opposite directions(counter transport) 2 transport processes are employed 1. facilitated transport- passive process 2. active transport-against a concentration gradient C. vesicular transport: is used for large molecules. It can take the form of 2 types of processes: 1. phagocytosis-‘cell-eating’ 2. pinocytosis-‘cell drinking’ ORGANELLES: nucleus: is the largest cell organelle. Cells may be uninucleate, anucleate(RBCs) or multinucleate(liver cells). Nucleus is composed of nuclear envelop and nucleoplasm. endoplasmic reticulum: is of rough and smooth types. It is involved in synthesis of cell membranes, detoxification and synthetic functions golgi complex: synthesizes carbohydrates and puts finishing touches on synthesis of proteins peroxisomes: produce H2O2, neutralize free radicals and detoxify alcohol mitochondria:produce ATP. Structurally they have a double membrane and contain cristae and a matrix. They have their own DNA. Because of the ATP producing function, the mitochondria are known as the “power house” of the cell Centrioles: consist of a Cylindrical arrangement of 9 groups, each containing three microtubules. they play an important role in cell division Ribosomes: are Involved in assembly of proteins. Journal entry: chapter 4 DNA STRUCTURE: The genetic material of the cell is in the form of DNA. There are 46 molecules of DNA in each human cell. The DNA is present in the form of a string known as a nucleosome bound around octamers of protein known as histones. The nucleosome is a polymer of nucleotides. Each nucleotide has 3 components: Deoxyribose sugar Phosphate group Nitrogenous base: these are of 2 types; 1. purines-bases with double rings-adenine(A) and guanine(G) 2. pyrimidines-bases with single ring-thymine(T), cytosine(C) and uracil(U). The molecule is arranged in the form of a double helix with the nitrogenous bases in the centre and the phosphate and sugar groups forming the backbone. A binds with T and G with C having double and triple hydrogen bonds respectively. RNA structure: RNA is a single stranded molecule. It is of 3 types: transfer RNA(tRNA) messenger RNA(mRNA) ribosomal RNA(Rrna) PROTEIN SYNTHESIS: In DNA a gene is activated- a mirror image of the gene known as m-RNA is produced(transcription) m-RNA is transferred to cytoplasm translated by ribosomes using amino acids brought by t-RNA. The sequence of nucleotides on the m-RNA strand determines the sequence on amino acids in a polypeptide- 3 nucleotides code for one amino acid(forming a codon). TRANSLATION This is the process of formation of a polypeptide chain from m-RNA. The leader sequence on m-RNA serves as binding site for small ribosomal subunit ribosome begins moving along m-RNA strand when it reaches start codon(AUG) it begins to synthesize protein using amino acids brought by one of the 61 types of t-RNA, as specified by the codons on the m-RNAeach m-RNA strand has 10- 20 ribosomes attached to it forming a polyribosome and facilitating translation. POST-TRANSLATIONAL MODIFICATION Polypeptide chain reaches rough ER bound to chaperone protein post translational modification occurs protein is budded off in clathrin coated vesicles taken up by golgi apparatus further modification plus carbohydrate added to structure released in vesicles that migrate to plasma membrane exocytosis. DNA REPLICATION: According to the Watson and crick model of DNA, the DNA helix unwinds DNA helicase separates the two strands DNA polymerase finds complementary nucleotides for the exposed bases new histones are synthesized in the cytoplasm two identical strands are formed. CELL CYCLE: has 4 main phases. It starts with G1, first gap phase during which the cell replicates its centrioles. Next is the synthetic phase(S) during which the cell replicates its DNA. G2 which is the second gap phase is chacterized by a brief interval between DNA replication and cell replication the last phase is the M phase or the phase of active mitotic cell division MITOSIS: In PROPHASE there is condensation of nuclear material to form chromatin and disappearance of nuclear envelop. In Metaphase the chromosomes arrange themselves along the midline of the cell. In ANAPHASE division of centromeres and migration of chromatids takes place. In Telophase, completion of migration and reformation of nuclear envelop occurs. HEREDITY Heredity is dependent on chromosomal material. The Full complement of chromosomes present in an individual is known as the karyotype. The 2 copies of each type of chromosome are known as homologous chromosomes.Humans have 22 pairs of autosomes and one pair of sex chromosomes. Chromosomes carry genes…each gene has two forms known as alleles…a gene may be dominant(manifests in a heterozygote) or recessive(manifests only in homozygotes).Traits controlled by genes present on the sex chromosomes(X or Y) are called sex linked. Journal entry: chapter 5 TISSUE TYPES: 1. epithelial 2. connective 3. nervous 4. muscular EPITHELIAL TISSUE: It is composed of flat square cells resting on a basement membrane. It covers body surface and lines body cavities. It is of 2 types: simple, which is composed of one layer of cells(squamous, cuboidal, columnar, pseudostratified); and stratified: (squamous, cuboidal, columnar, transitional). Stratified epithelium is further subdivided into two types: keratinized (e.g. skin), non keratinized( e.g. GIT and reproductive tract) CONNECTIVE TISSUE: It is Composed of: fibers, ground substance and widely separated cells Its functions include: support protection immune protection storage binding of organs types are: fibrous connective tissue: composed of: 1. cells( fibroblasts, leukocytes, plasma cells, mast cells, adipocytes) 2. fibers( collagenous, reticular, elastic) 3. ground substance( glycoseaminoglycans, proteoglycans and adhesive molecules) Subtypes LOOSE DENSE 1. areolar 1. dense regular e.g. vocal cords. 2. reticular 2. dense irregular e.g. around kidneys, testes 3. adipose cartilage: supportive connective tissue. Composed of chondrocytes. Lacks blood supply. 1. hyaline 2. elastic 3. fibrocartilage bone 1. spongy 2. compact blood. MUSCULAR TISSUE: It is of three 3 types: 1. skeletal- which is composed of long striated cells, is attached to bones 2. cardiac- its limited to the heart. Also striated. 3. smooth- involuntary, lacks striations. INTERCELLULAR JUNCTIONS: 1. tight junctions-e.g. stomach and intestine. 2. desmosomes- e.g. epidermis, cardiac muscle. 3. gap junctions-e.g. some types of smooth muscles GLANDS 1. exocrine-serous(thin watery fluids produced), mucous glands(sticky fluids), mixed glands( both types of cells) 2. endocrine 3. apocrine- axillary sweat glands and mammary glands TISSUE REPAIR: 2 types, fibrosis and regeneration 1. bleeding into wound and immune reaction along wound margins 2. formation of scab 3. infiltration by blood vessels and fibroblasts and formation of granulation tissue 4. migration of surface epithelial cells into wound and remodeling. Read More