BSC2010 Final Exam Study Guide
BSC2010 Final Exam Study Guide BSC 2010
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This 17 page Study Guide was uploaded by Stefanie Villiotis on Wednesday December 9, 2015. The Study Guide belongs to BSC 2010 at Florida State University taught by Dennis in Fall 2015. Since its upload, it has received 116 views. For similar materials see General biology in Biological Sciences at Florida State University.
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Date Created: 12/09/15
BSC2010L Final Exam Study Guide Water - Draw water - Structure - Bond angle is 105, oxygen is electronegative, H has a + charge - Emergent properties - Cohesion = transport water against gravity in plants (holds molecules together) - Adhesion = attraction between different substances, water/plant cells - Surface Tension= how hard it is to break the surface of a liquid— related to cohesion. - Acid base chemistry - Water reaches its greatest density at 4C - Water is a versatile solvent, allows it to form H bonds easily - Hydrophilic = affinity for water - Hydrophobic = does not like water - Oil molecules = hydrophobic because of nonpolar bonds - Water is in state of dynamic equilibrium in which molecules dissociate at the same rate at which they are reformed. - A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other - The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+) - In any aqueous solution at 25°C the product of H+ and OH– is constant and can be written –14 [H+][OH–] = 10 - The pH of a solution is defined by the negative logarithm of H+ concentration, written as pH = –log [H+] - For a neutral aqueous solution [H+] is 10 = –(–7) = 7 - Acidic solutions have pH values less than 7 - Basic solutions have pH values greater than 7 - What causes an imbalance in H+ and OH- concentrations? Acids and Bases - Acids increases the hydrogen ion concentration - Hydrochloric Acid = HCl + - - HCl -> H + Cl (single arrow = complete dissociation = STRONG) - Bases reduce the hydrogen ion concentration two ways - Accepting a H+ - Ammonia: NH + H 3-> NH+ 4 - Providing and OH- (which ultimately makes another molecule of water) + - - Sodium Hydroxide: NaOH -> Na + OH - Internal pH of all living cells is close to 7 - Buffers = substances that minimize changes in concentrations of H+ and OH- - Most buffers consist of an acid-base pair that reversibly combines with H+ - The weak acid, carbonic acid, is formed when CO reacts w2th H2O in blood plasma - + H 2O 3 HCO 3 H 2 H donor H acceptor + H ion (acid) (base) Carbon - Forms bonds with H, N, O, P, and S to make biological macromolecules (DNA, RNA, proteins) - Bonds to 4 other atoms - Ranges from small molecules CH4 to huge molecules: chromosomes - HAS 6 ELECTRONS, 2 in 1 shell, 4 in 2 ndshell (4 VALENCE ELECTRONS) - Completes outer shell by sharing 4 valence electrons with other atoms - Hybrid orbitals and tetravalence give methane a tetrahedral geometry —BOND ANGLES 109.5 - Hybrid orbitals of double bonds create a trigonal planar molecule— Bond angles of 120 - Backbone variation: - Length, Branching, Double Bonds, Circularization - Bonding (TETRAVALENCE) - The valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the “building code” that governs the architecture of living molecules - Hybridization of orbitals (TETRAHEDRAL GEOMETRY) - Hydrocarbons are organic molecules consisting of only carbon and hydrogen - Many organic molecules, such as fats, have hydrocarbon components - Hydrocarbons can undergo reactions that release a large amount of energy >>>>2 backbones with exact same formula but different structure<<<< - Structural isomers have different covalent arrangements of their atoms - Geometric isomers have the same covalent arrangements but differ in spatial arrangements - Enantiomers are isomers that are mirror images of each other 3 Biological Macromolecules Monomers or Polymer or Components larger molecule Type of Linkage Sugars Glycosidic Linkage Monosaccharide Polysaccharides s Lipids Fatty Acids Ester Linkages Triacylglycerols Proteins Amino Acids Polypeptides Peptide Bonds Nucleic Acids Nucleotides Phosphodiester Linkages Polynucleotides 1.Sugars= Monosaccharides, Polysaccharides, Glycosidic Linkages (MPG= mono-poly- glyco) 2.Lipids= Fatty Acids, Triacylglycerols, Ester Linkages (FTE= fat-tri-ester) 3.Proteins= Amino Acids, Polypeptides, Peptide Bonds (APP= Am-Po-Pep) 4.Nucleic Acids= Nucleotides, Polynucleotides, Phosphodiester Linkages (NPP= Nu-Po- Pho) - Small organic molecules join together to form larger molecules - Molecular structure and function are inseparable - Polymer = long molecule consisting of many similar small building blocks called monomers - 3 of the 4 classes of life’s organic molecules are POLYMERS - Polysaccharides are built from Monosaccharides - Nucleic Acids are built from Nucleotides (A, T, U, C, G) - Proteins are built from Amino Acids - Polymers are formed by Dehydration Synthesis 4 - A dehydration synthesis occurs when two monomers bond together through the loss of a water molecule - Enzymes are macromolecules that speed up dehydration - Disassembled by hydrolysis (addition of water to break a bond) - Polymers are disassembled to monomers by hydrolysis - Carbohydrates include sugars and the polymers of sugars - The simplest carbohydrates are monosaccharides, or single sugars - Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks called monosaccharides - Numbering of monosaccharide carbons form functional group - Glucose C H 6 i12th6 most common monosaccharide - Monosaccharides are classified by: - Location of carbonyl group (aldose or ketose) - Number of carbons in the carbon skeleton - Monosaccharides serve as major fuel for cells and raw material for building molecules - Can be linear chains or ring structures - Disaccharides form when a dehydration reaction joins two monosaccharides (this covalent bond is called a glycosidic linkage) - The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages - Glycogen is a storage polysaccharide in animals, and Starch is a storage polysaccharide in plants - The difference is based on two ring forms for glucose: alpha () and beta () A. Structure function relationships 1. Polymers with -glucose are helical 2. Polymers with -glucose are straight LIPIDS - Lipids mix poorly with water and are not true polymeric macromolecules - Generally non-polar hydrocarbons - Fats are constructed from two smaller molecules: glycerol and fatty acids - Fatty acid consists of a carboxyl group attached to a long carbon skeleton - Glycerol= 3-carbon alcohol with a hydroxyl group attached to each carbon - 3 fatty acids are joined to glycerol by an ester linkage, creating triglyceride - Saturated Fatty Acids: - Max # of hydrogen atoms and no double bonds - Solid at room temperature - Animal fats - Unsaturated Fatty Acids - 1 or more double bonds - liquid at room temperature - Hydrogenation 5 - Converting unsaturated fats to saturated fats by adding hydrogen - Hydrogenating vegetable oil creates unsaturated fats with trans double bonds - Store fat in Adipose cells which cushions vital organs and insulates body - Phospholipids - 2 fatty acids and a phosphate group attached to glycerol - Hydrophobic Tail: two fatty acids - Hydrophilic Head: phosphate group and its attachments - When added to water, self-assemble into bilayer with hydrophobic tails - Steroids - Lipids characterized by a carbon skeleton consisting of 4 fused rings - Cholesterol= essential in animals, high levels contribute to cardiovascular disease - Signal gene expression PROTEINS - More than 50% of fry mass of most cells - Structural support, storage, transport, cellular communications, movement, defense against foreign substances - Polypeptides are polymers built from the same set of 20 amino acids - Consists of 1 or more polypeptides - Amino Acids 1. Organic molecules with carboxyl and amino groups 2. Differ in properties due to differing side chains, called R GROUPS 3. R- groups give specific chemical properties: - NON-POLAR—equal distribution of electrons - POLAR—unequal distribution of electrons - CHARGED—acidic or basic - Amino acids are linked by PEPTIDE BONDS - A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape - 4 Levels of Structure: 1. Primary Structure of a protein is its unique sequence of amino acids - Determined by inherited genetic information 2. Secondary Structure, found in most proteins, consists of coils and folds in the peptide chain - Structures = alpha helix or folded structure/pleated sheet 3. Tertiary Structure is determined by interactions among various side chains (R-GROUPS) - Hydrogen bonds, ionic bonds, hydrophobic interactions, van der Waals interactions 6 4. Quaternary Structure results when a protein consists of multiple polypeptide chains - Collagen is a fibrous protein consisting of three polypeptides coiled like a rope - Hemoglobin is a globular protein consisting of 4 polypeptides: 2 alpha and 2 beta chains - Alterations in pH, salt concentration, temperature, etc. can cause a protein to denature (loss of protein’s native structure) - Chaperonins are protein molecules that assist proper folding of other proteins Nucleic Acids – Store and transmit hereditary information - The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene - DNA provides directions for its own replication - DNA directs synthesis of messenger RNA (mRNA) and through mRNA, controls protein synthesis - PROTEIN SYNTHESIS OCCURS IN RIBOSOMES - Nucleic acids are polymers called polynucleotides - Each polynucleotide is made of monomers called nucleotides - Each nucleotide consists of a nitrogenous base, pentose sugar, phosphate group - Portion of a nucleotide without the phosphate group is called a nucleoside - Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring - Purines (adenine and guanine) have a six-membered ring fused to a five- membered ring - The sugars between DNA and RNA differ: - DNA, the sugar is deoxyribose - RNA, the sugar is ribose - Nucleotide polymers are linked together to build a polynucleotide 7 - Adjacent nucleotides are joined by covalent bonds that form between the –OH group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon on the next - A DNA molecule has 2 polynucleotides spiraling around an imaginary axis, forming a double helix - Two backbones run in opposite 5’ 3’ directions from each other = ANTIPARALLEL DRAW Amino Acid Steroid Fatty Acid Purine Pyrimidine Phospholipid Bilayer Nonpolar Tails Polar Heads Water Cells - Visualization - Prokaryotic/ Eukaryotic - Endomembrane system - Nucleus- Information central - Nucleus contains the most of the cell’s genes and is usually the most conspicuous - Nuclear envelope encloses nucleus, separating it from cytoplasm - Nuclear membrane is a double membrane, each membrane consists of a lipid bilayer - Genetic material is called chromatin - Endoplasmic reticulum- factory - Endoplasmic Reticulum accounts for more than half of the total membrane in many eukaryotic cells 8 - Golgi Apparatus- shipping and receiving - Golgi Apparatus consists of flattened membranous sacs called cisternae - Lysosomes- digestive compartments, disassembly - Lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules - Vacuoles- maintenance compartments - Energy Conversion (mitochondria, chloroplasts, peroxisomes) - The Citric Acid Cycle occurs in the mitochondria of eukaryotic cells or in the cytoplasm of prokaryotes. It completes the breakdown of glucose by oxidizing a derivative of pyruvate to carbon dioxide. - Peroxisome uses oxygen to break down different types of molecules - Chloroplasts make sugars small carbohydrates (has own DNA, double phospholipid bilayer) Cytoskeleton (microtubules, microfilaments, intermediate filaments) - Extracellular components (cell walls of plants, ECM of animal cells, intercellular junctions) - ECM protein binds to receptor proteins in plasma membrane called integrins - Animal cells lack cell walls but are covered by ECM - ECM = support, adhesion, movement, regulation Intercellular Junctions: - Plasmodesmata - channels that perforate plant cell walls. Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell - Tight junctions - membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid - Desmosomes - (anchoring junctions) fasten cells together into strong sheets - Gap junctions - (communicating junctions) provide cytoplasmic channels between adjacent cells Plasma membrane (phospholipids, fluidity, functions, water balance, transport) - The plasma membrane exhibits selective permeability allowing substances to cross it more easily than others - Phospholipids- most abundant lipid in the plasma membrane, hydrophobic and hydrophilic regions. - Temperature decreases—membrane can solidify - Membranes rich in unsaturated fatty acids are more fluid than those in saturated fatty acids - Integral proteins that span membrane are called transmembrane proteins 9 - The hydrophobic regions of integral protein consist of one or more stretches of nonpolar amino acids coiled into alpha helices - Hydrophobic (non-polar) molecules, such as hydrocarbons, dissolve in the lipid bilayer and pass through membrane rapidly - Transport Proteins-- Aquaporin’s provide hydrophilic channels through which polar molecules can pass. 6 Functions of membrane proteins 1. Transport 2. Enzymatic Activity 3. Signal Transduction 4. Cell-Cell recognition 5. Intercellular joining 6. Attachment to the cytoskeleton and ECM - The diffusion of a substance across a biological membrane is passive transport because it requires no energy - Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another **(move from high concentration to low concentration) - A Hypertonic Solution Is one in which the solute concentration is greater than inside the cell. - An Isotonic solution is one in which the concentration is the same as that inside the cell - A Hypotonic Solution is less than that inside the cell, cell gains water - Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments - Channel proteins allow specific molecules to cross the cell membrane - Active Transport = requires energy, usually ATP - Active transport moves substances against their concentration gradient. - Facilitated diffusion is still passive because the solute moves down its concentration gradient Metabolism and Thermodynamics - Anabolic pathways consume energy to build complex molecules from simpler ones - Catabolic pathways release energy by breaking down complex molecules into simpler compounds - In Feedback Inhibition the end product of a metabolic pathway shuts down the pathway. This process prevents a cell from wasting chemical resources by synthesizing more product than is needed. Laws of energy transformation - Energy can be transferred and transformed, but it cannot be created or destroyed - Energy exists in the form of heat and flows into an ecosystem in the form of light 10 - Thermodynamics is the study of energy transformations Free energy ( ∆ G) - Heat is kinetic energy associated with random movement of atoms or molecules - Potential Energy is energy that matter possesses because of location or structure - Chemical Energy is potential energy available for release in a chemical reaction - Free Energy is a measure of a system’s instability, its tendency to change to a more stable state - Only processes with a positive ∆G are non spontaneous, occur with addition of energy, and decrease the stability of a system - Closed = Isolated/ Open = energy can be transferred - The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T) - Energy transfer of transformation increases the entropy or disorder of the universe - MORE FREE ENERGY (HIGHER G), LESS STABLE, GREATER WORK CAPACITY - LESS FREE ENERGY (LOWER G), MORE STABLE, LESS WORK CAPACITY - During a spontaneous change, free energy decreases and the stability of a system increases - Exergonic reaction proceeds with a net release of free energy and is spontaneous - Endergonic reaction absorbs free energy and is nonspontaneous ATP - ATP powers cellular work by coupling exergonic reactions to endergonic reactions - ATP is composed of: 1. Ribose (a sugar) 2. Adenine (a nitrogenous base) 3. 3 phosphate groups - The bonds between the phosphate group of ATP’s tail can be broken by hydrolysis - Energy is released from ATP when the terminal phosphate bond is broken - ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to another molecule - To do work, cells manage energy resources by energy coupling, the use of exergonic processes to drive an endergonic one. 11 - Regenerated by addition of a phosphate group to adenosine diphosphate (ADP) - Regeneration comes from catabolic reactions in the cell - Know how to draw ATP Enzymes - Enzymes speed up metabolic reactions by lowering energy barriers - Catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction - In enzymatic reactions, the substrate binds to the active site of the enzyme called the CATALYTIC SITE - The reactant that an enzyme acts on is the enzyme’s substrate - Cofactors are non-protein enzyme helpers - Fermentation leads to partial degradation of sugars without the use of oxygen - The initial energy needed to start a chemical reaction is activation energy - Enzymes catalyze reactions by lowering the EA barrier - The active site is the region on the enzyme where the substrate binds - Regulation of enzyme activity helps control metabolism - Regulation occurs by switching on or off the genes that encode specific enzymes or by regulating activity of enzymes Redox Reactions - Release energy when electrons move close to electronegative atoms - - Reactions that result in the transfer of one or more electrons (e ) from one reactant to another are redox reactions - The loss of electrons from a substance is called oxidation - The addition of electrons to another substance is called reduction - Organic fuel molecules are oxidized during cellular respiration - In a series of reactions, glucose is oxidized and oxygen is reduced. + - Fall of electrons during respiration is stepwise via NAD and an electron transport chain - Organic cofactor is called a coenzyme Cellular respiration - Glycolysis (investment and payoff phase) - During glycolysis, a six-carbon sugar is split into 2 three-carbon sugars 1. In the energy INVESTMENT phase, the cell spends ATP 2. In the energy PAYOFF phase, the investment is repaid, ATP is produced by substrate-level phosphorylation, and NAD+ is reduced to NADH by electrons released by the oxidation of glucose. - NET YIELD from glucose is 2 ATP and 2 NADH per glucose - As an electron acceptor, NAD+ functions as an oxidizing agent during respiration 12 - Pyruvate entering mitochondrion via active transport is converted to a compound called acetyl coenzyme A or acetyl CoA - Citric acid cycle - For each Acetyl group that enters the cycle, 3 NAD+ are reduced to NADH - FAD accepts 2 electrons and 2 protons to become FADH2 - 2 turns of the CAC will produce 2 molecules of ATP by substrate level phosphorylation - 3 molecules of glucose will produce enough dinucleotides in the CAC to make 66 molecules of ATP by oxidative phosphorylation - As 7 molecules of pyruvate are converted to Acetyl CoA, 7 molecules of NADH are made - Dehydrogenase enzyme catalyzes the oxidation of Isocitrate to α -ketoglutarate - In the reaction between Malate and Oxaloacetate, Malate is oxidized and NAD+ is reduced, thus producing the reduced dinucleotide NADH - Oxidative phosphorylation - Protein phosphatase removes the phosphates from proteins, a process called dephosphorylation, while protein kinase transfers phosphates from ATP to protein, a process called phosphorylation. - During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis - 2 ATP during glucose and 2 ATP during CAC - Inner mitochondrial membrane couples electron transport to ATP synthesis - In prokaryotes, the ETC is located in plasma membrane - A protein complex in the cristae of mitochondria, ATP synthase, actually makes ATP from ADP and Pi Photosynthesis Respiration Reactants Sunlight, H O, 2O 2 Glucose, O 2 Products Sugar, O 2 ATP, H O2 CO 2 Electron H 2 Glucose Source Major Organelle Chloroplast Mitochondria NADP NAD+ FAD Electron Carrier(s) 13 - Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the chloroplast - Chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast) - Photosynthesis is a redox process, H O is oxidi2ed and CO is 2 reduced - Chloroplasts are found mainly in the cells of the mesophyll Light reactions (in the thylakoids) 1. Split H 2 2. Reduce NADP+ to NADPH 3. Generate ATP from ADP by photophosphorylation The Calvin Cycle (in the stroma) 1. Form sugar from CO usin2 ATP and NADPH 2. Begin with carbon fixation, incorporating CO into 2rganic molecules Splitting of Water 1. Chloroplasts split H O2into hydrogen and oxygen, incorporating electrons of hydrogen into sugar molecules - Calvin Cycle 1. Carbon fixation (catalyzed by Rubisco) 2. Reduction 3. Regeneration of the CO acce2tor (RuBP) - Carbon enters the cycle as CO and 2eaves as a sugar named glyceraldehyde-3-phosphate (G3P) - Rubisco can bind O wi2h catalytic efficiency - CAM plants open their stomata at night to incorporate CO into organic 2 acids and close the stomata during the day, thus releasing CO to be 2 used in the Calvin Cycle. - C4 plants minimize the cost of photorespiration by incorporating CO 2 into four-carbon compounds in mesophyll cells. Landmarks in gene regulation - Griffith- demonstrations of bacterial transformation - Avery McCarty and MacLeod- transforming factor is separable - Hershey and Chase- transforming factor is DNA - Chargaff- ratios of DNA within and between species - Watson and Crick- description of 3D structure of DNA - Franklin- X-ray crystallography of DNA structure - Meselson and Stahl- Semi-conservative replication Replication 14 - Initiation –at special sites called origins of replication where two DNA strands are separated - Elongation—catalyzed by DNA polymerases at a replication fork; rate of elongation is 500 nucleotides per second in bacteria and 50 per second in humans - Replicating ends of DNA (telomeres)—eukaryotic chromosomal DNA molecules have their ends nucleotide sequences called telomeres -DNA polymerases proofread newly made DNA, replacing incorrect nucleotides Flow of Genetic information - Proteins are the links between genotype and phenotype - Gene expression, the process by which DNA directs protein synthesis, includes two stages: Transcription and Translation - In prokaryotes, mRNA produced by transcription is immediately translated without more processing - RNA is the intermediate between genes and the proteins for which they code - Transcription is the synthesis of RNA under the direction of DNA, and produces mRNA - Ribosomes are the sites of translation - The DNA double helix has a uniform diameter because purines base pair with pyrimidines - The DNA sequence where RNA polymerase attaches is called the promoter, in bacteria the sequence signaling end of transcription is called the terminator - Eukaryotic Cell the nuclear membrane separates transcription from translation - Molecules of tRNA are not identical - Each carries a specific amino acid on the 3’ end - Each has an anticodon on the other end which base pairs with a complementary codon on mRNA - There are 20 amino acids, but only 4 nucleotide bases in DNA - 3 RNA bases correspond to an amino acid - Each codon specifies the amino acid to be placed at the corresponding position along a polypeptide - There are 64 codons, 61 code for amino acids, 3 triplets signal stop - Genes can be transcribed and translated after being transplanted from one species to another Transcription and Translation - Initiation—promoters signal initiation of RNA synthesis - Transcription Factors mediate the binding of RNA polymerase and the initiation of transcription 15 - Some transcription factors function as repressors inhibiting expression of a particular gene - To initiate transcription, eukaryotic RNA polymerase requires the assistance of proteins called Transcription Factors - Promoter called TATA box forms initiation complex in eukaryotes - Elongation— A number of ribosomes can translate a single mRNA simultaneously, forming a polypeptide - Termination— - The DNA sequence where RNA polymerase attaches is called the promoter; in bacteria the sequence signaling end of transcription is called the terminator - In bacteria, polymerase stops transcription at the end of the terminator RNA Modifications - The 5’ end receives a G-cap, a modified guanine nucleotide - The 3’ end gets a Poly-A Tail, 50-250 Adenine nucleotides - RNA splicing removes introns and joins exons creating a mature mRNA molecule with a continuous coding sequence - In alternative RNA splicing different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns - 3 properties RNA can function as an enzyme: - 3D structure because it can base pair with itself - contains functional groups - Hydrogen bond with other nucleic acid molecules - Binding sites for tRNA: - P site holds tRNA that carries polypeptide chain - A site holds tRNA that carries next amino acid to be added - E site is the exit site, where discharged tRNAs leave the ribosome Mutations - RNA synthesis follows the same base pairing rules as DNA, except Uracil substitutes for Thymine - Mutations are changes in the genetic material of a cell or virus - The change of a single nucleotide in DNA template strand can lead to the production of an abnormal protein - Insertions or deletions of nucleotides may alter the reading frame, producing a frameshift mutation Prokaryotic control of gene expression - Operon is the entire stretch of DNA that includes the operator, promoter, and genes that they control 16 - The regulatory switch is a segment of DNA called an operator usually positioned within the promoter - Some operons are subject to positive control through a stimulatory protein such as a catabolite activator protein (CAP), an activator of transcription. - The repressor prevents gene transcription by binding to the operator and blocking RNA polymerase - Control Elements and the proteins they bind are critical to the precise regulation of gene expression - Distal control elements called Enhancers may be far away from a gene even located in an intron Eukaryotic control of gene expression - Regulation of chromatin structure - The Histone Code Hypothesis proposes that specific combinations help determine chromatin configuration and influence transcription - In Histone Acetylation, Acetyl groups are attached to positively charges Lysines in histone tails - Chromatin-modifying enzymes provide initial control of gene expression by making a region of DNA either more or less able to bind the transcription machinery - The phenomenon of inhibition of gene expression by RNA molecules is called RNA interference (RNAi) and is caused by small inhibition RNAs (siRNAs) Arrangement of Exam - Structures to draw - Periodic chart, basic chemistry, bonds - Functional groups and aa classification - Macromolecule chemistry - Macromolecule chart - Respiration and photosynthesis - Energy and reaction energy diagrams - Regulation of gene expression 17
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