Biological Sciences Modules - Essay Example

Assignment Biological Module Bhuvana Jaiganesh Biological sciences module a) i) The key features that indicate that this is a plant cell: (a) Cell wall: The rigid wall made of polysachharides is the most distinct feature of a plant cell. It is rigid and serves a protective function. (b) The large vacuole: These membrane bound sacs are important for intracellular digestion and for releasing waste products. The vacuoles in plant cells are very large and occupy almost the whole of the cell. This is vital for maintaining turgor pressure in the cells. (c) Chloroplasts: The chloroplasts are special pigments that are designed for trapping the sun's energy and converting substrates absorbed from the soil into food for the plant. This feature is absent in the animal cell. ii) (a)Nucleus (b)Mitochondra (c) Golgibodies. b) Endosymbiosis refers to an association between two or more species of where one lived inside another. Current theories indicate that prokaryotes gave rise to eukaryotes through Endosymbiosis. The mitochondria and chloroplasts show endosymbiotic evolution where heterotropic prokaryotes were engulfed by large eukaryotes. In the mitochondria , the prokaryotic cells received organic and inorganic substances from the host and the host increased ATP output increased cellular efficiency. The relationship lead to the permanent association and integration leading to eventual evolution of eukaryotes. In the case of chloroplasts, fewer cells than ingested them. The prokaryote fixed carbon to supplied food, the host supplied inorganic substances like Carbon-dio-xide. The independent DNA & RNA strands, ribosomes and inner membrane, suggests their prokaryotic evolution. c) Membranes Membranes that may be double or single layered line cell organelles. The Mitochondria, chloroplast and the nucleus (not strictly an organelle) have double layered membranes, while the Lysosomes, Golgi apparati, vacuoles and so on have a single membrane. The Ribosomes are non-membranous structures. Structure-Fluid Mosaic model The structural representation in the fluid mosaic model of the plasma membrane is universal in all living cells (plants & animals) and consists of two layers of phospholipids (lipids attached to a phosphate unit, proteins that dynamically move about the membrane and a small amount of glycoproteins (glucose bonded to proteins). The lipid molecules are "amphiphilic," having a hydrophilic (water loving) portion facing outside and a hydrophobic (water shunning) lipid portion turned inside. (Campbells' Biology Chapter 8; Dalton.M Chapter2/membrane/html.) Primarily, there are10 different types of lipids reported in cell membranes with different types of cells/organelles having differing percentage of each lipid, protein, and carbohydrate. They are: (1)Cholesterol, (2)Glycolipids, (3) Phosphatidylcholine, (4)Sphingomyelin, (5)Phosphatidylethnolamine, (6)Phosphatydilinositol, (7)Phosphatidylserine, (8) Phosphatidylglycerol, (9)Diphosphatidylglycerol (Cardiolipin), (10)Phosphatidic acid (Dalton.M Chapter2/membrane/html). Proteins in the cell membrane may have limited movement (being bound to the cell's exoskeleton or other membrane structures) or move freely if unbound (Campbells' Biology Chapter 8; Cellmembranes.html 10 Aug. 2003) . These proteins could be in the hydrophobic (integral proteins) or in the hydrophilic (peripheral proteins) regions. The proteins vary in structure and function but have distinct directional orientation (Campbells' Biology Chapter 8). Differential permeability The membranes are responsible for maintaining an almost constant cell or organelle environment. For instance the pH with the Lysosome is maintained at 5. This has been made possible by the selective permeability of the membrane that allows ready entry of glucose, amino acids and lipids and prevents the exit of metabolic intermediates while allowing external passage of wastes. The membranes' hydrophobic portions are typically impermeable to water-soluble materials like glucose, amino acids and ions. The movement of these substances is effected through transport proteins. In order to address the unique needs of varying cell types/organelles, Transport proteins are present in varied compositions in different cell types and organelles. Transport across membranes may be : Passive diffusion along the concentration gradient makinguse of the kinetic energy in the molecule. Active- A movement against the concentration chemical or electrostatic gradient using specific bio-pumps/transport proteins. The ATP system supplies energy for the process. The process is usually rapid and unidirectional as the Transport proteins change conformation and allow pumping in only one direction. Source- Transport across cell membranes- Palgrave.com Vesicular transport Exocytosis- Substances to be released into extra cellular space are enclosed in a membranous sac and moved towards the cell membrane, fuses with it and ruptures the contents. Endocytosis- Subtances and enfolded into the cell by folding of the membrane around it. 2 Aerobic respiration is a three step process that converts Glucose into Carbon-di-oxide and water and in the process synthesising 2 ATP molecules. It has three steps, Glycolysis, Krebs cycle and the electron transport system. Step 1- Glycolysis Glycolysis takes place in the cytoplasm during which Glucose molecule with 6 carbon atoms is split into two Pyruvate molecules have three carbon atoms each. The splitting produces by energy from 2 molecules of ATP and 2 molecules of NADH. This stage does not require oxygen. Chemical reaction: C6H12O6 + 2ATP + 2NAD+2pyruvate + 4ATP + 2NADH Step 2 - Krebs cycle The two NADH molecules produced in Glycolysis travel to the Mitochondria where the Krebs cycle takes place. The cycle needs by products from the Electron Transport Chain (ETC) and therefore needs oxygen. The cycle begins with the formation of the 4 carbon Oxaloacetate and ends with it. The three carbon pyruvate is broken down to two carbon acetate which combines with Coenzyme A to form Acetyle coA. The energy produced is used to form NADH, which gets into the electron transport chain. Acetyle coA + Oxaloacetate form 6 carbon Citric acid. The citric acid undergoes a series of 8 chemical reactions to break down the molecule to produce oxaloacetate and carbon-di-oxide. The breakdown process produces energy that is stored in ATP, NADH and FADH 2. The NADH and FADH enter the ETC. Step 3- Electron Transport Chain It is a process requiring oxygen-taking place inside the mitochondria. The electrons in the hydrogen of NADH and FADH2 have high energy and react with many other molecules to donate energy to them. This energy is utilized by the mitochondria to operate the proton pumps that maintain high proton concentrations inside the organelle. This electrochemical environment drives the increased Chemosmotic production of ATP. Here energy from NADH and FADH along with the protein ATP synthase is used to synthesise ATP. NADH is a molecule that can be easily oxidised or hydrolysed (reduced) . When reduced , it releases the hydrogen and becomes a free ion (highly reactive) NAD+ which is free to receive more hydrogen. This is the key driver for ATP production which cannot be carried out without continual electron transport. The residual electrons are absorbed by oxygen whose charge is neutralised by protons formed by oxidation of NADH to NAD+ to form water. Aerobic respiration: C6H12O6 + 6 O2 + 6 H2O + 38 ADP +38 P 6 CO2 + 12 H2O + 38 ATP + 420 Kcal Oxidative component: C6H12O6 6 CO2 Reducing Component 6 O2 6 H2O 3 i) Autosomal: Autosomal refers to those traits that are contained in chromosomes that are not sex chromosomes. Recessive gene: A gene that can be expressed only if two copies of the same code are present in the individual. This automatically means that the individual has received on copy from each of his/her parents. Heterozygote: A Heterozygote is a person who carries one copy of the dominant gene and one copy of the recessive gene and they usually do not exhibit symptoms of the disease phenotypically. ii) Cystic Fibrosis occurs when both parents of the individual carry one copy for the mutant gene. Such people are called carriers. The following is the schematic representation of how CF s inherited. The dark portions indicate presence of the CF gene. or iii) b) 1 2 3 4 5 6 7 8 9 T A G T A G A A G C C A C A A T A G T A G A A G C C A C A A DNA A U C A U C U U C G G U G U U Ile Ile Phe Gly Val ii) CF patients with deleted 6,7,8will present with a lack of two amino acids. The following will be the sequence for CF patients. Ile- --- - ---- Gyl- Val. 5. Science Content: Proteins The word proteins come from the Greek term "proteios ,"meaning first. They form the fundamental structural and functional basis for life. They are also responsible for the phenotypic expressions of gene coding organisms. Chemically, proteins are macromolecules (large) and are made up of amino acids. A is typically made up of 200-300 amino acids. Smaller strands of amino acids are known as peptide chains. amino acids consists of a carboxylic acid group (-COOH) and an amino group (-NH2) The Amino group is the functional group. Amino acids undergo polymerisation through a condensation reaction, between the carboxyl group and amino group forms peptide chains. The peptides chains join become protein molecules. Coding and synthesis Amino acid synthesis in the body is coded by the nucleotides contained in the DNA of organisms. DNA has 2 sets of complimentary nucleotides- Adenine (A), Guanine (G), Cytosine(C) and Thiamine (T). These codes are read by RNA that have similar nucleotides that pair with the DNA codes, except that Thiamine is replaced by Uracil (U). Coding occurs through a triplet sequence of nucleotides, eg. AUG or UAA and so . Each triplet can code for a specific amino acid and therefore mathematically it makes it possible to have 20 amino acids. However, there are a multitude of combinations that are possible in the arrangement of amino acids in a protein molecule. The number of genes cannot explain the abundance of proteins in the system. It has now been found that one gene may code for more than one protein through a method called' "trans-splicing." Higher order proteins The simplest peptide chain is a dipeptide. The primary structure of proteins consists of simple polypeptide chains. These chains undergo many structural changes to give rise to higher order structures. The folded primary structures are "secondary structures,"in the form of an helix or a pleated sheet, which can get further bonded to form "super secondary structures." "Tertiary structure refers to the complete three-dimensional structure of the polypeptide units of a given protein." Here chemical attraction exists between the two secondary models. If two or three types of proteins get associated with each other through covalent bonds they are called "quaternary," structures, while complex proteins are bound with carbohydrates (Glycoproteins) or Lipids (lipoproteins). The function of the protein and its activity often depends upon the molecular organization that is found. The higher order structures lend themselves to form sheet, grooves, ridges, loop, fold, form pockets and so on. These structural differences offer sites for biochemical reactions and form the basis for pharcokinetics I the organism. The proteins primary structure determines the final configuration as this decides the type and pattern of bonding. This is a cooperative process and the formation of one region defines the next. Structure and function The structure of proteins are closely related to their functions . This is because the shape determines their interaction with molecules having a complimentary surface for interaction. This specificity forms the basis for biological regulation as in the case of enzymes, hormones etc. two examples of higher order proteins and related functions are given below. Haemoglobin: This is an example of an tetrameric allosteric protein. The structure of the molecule offers spaces for binding with oxygen and this is a quantified amount. Every molecule of haemoglobin can carry four molecules of oxygen. Insulin : This is an important hormone that has 51 amino acids. It is first produced in an inactive preproinsulin single polypeptide chain ,which is deposited outside the cell. This in the presence of certain cofactors will fold to reach the correct structure that will make it active insulin. Oxytocin and vasopresin: These are two hormones that have similar structure except for oneamino acid but have dissimilar actions. Enzymes Enzymes are proteins that serve as biocatalyts in a biological system. The binding between substrates in a reaction and the enzyme are related to the shape of the receptor site. The tertiary folds of the enzyme protein offers these venues to form bonds with the substrate to bring about the chemical reaction. A protein may have one or more site for bonding to the same or multiple types of substrates. References Stephen T Abedon. 28/03/98. http://www.mansfield.ohio-state.edu. [electronic document] Read More