Biology Exam 1 PDF

Science Science is a way of investigating phenomena – The aims or goals of science: To ask questions To answer questions using rational logical thinking – The limitations of science: technological ethical issues no consideration of supernatural or religious e...

Science Science is a way of investigating phenomena – The aims or goals of science: To ask questions To answer questions using rational logical thinking – The limitations of science: technological ethical issues no consideration of supernatural or religious entities  The Scientific Method (Process) The Scientific Method is used to – answer questions – test hypotheses Used in all areas of science and within other disciplines Consists of six steps  Step #1: Observation Observe some aspect of nature Goal: to gain valuable background information and to see what is already known with regards to some area of science May be replaced with research  Step #2: Question Develop a question that – Determines the focus of study – Intent is to ultimately develop a way to answer the question – Example: What would happen if a plant does not receive enough light?  Step #3: Hypothesis Making an educated guess about the question posed – Educated because of the earlier observations/research performed – Example: When a plant does not receive enough light, its growth is stunted.  Step #4: Prediction Formulating an If-Then statement from previously made hypothesis – Gives a testable conditional statement – Example: If a plant does not receive enough light, then its growth will be stunted.  Step #5 - Experimentation Developing a method by which the prediction can be tested – Every experiment must have at least two groups: Control group: situation in which normal or typical conditions exist – Used for the sake of comparison. – Example: a plant grown in light Experimental group: situation in which conditions are altered – Example: a plant grown in darkness or with reduced light exposure  Experimental Variables Independent variables: under direct control by the researcher. Indicated in the If portion of the prediction. Example: the amount of light a plant is exposed to.  Experimental Variables Dependent variables: may or may not be influenced by an independent variable Indicated in the Then portion of the prediction. Example: the amount a plant grows  Controlled Variables Variables that are not being studied Must be consistent between control and experimental groups Data Collection: all variables must be measurable. Measurements of independent and dependent variables must be taken and then statistically analyzed.  Step #6: Conclusion Based on statistical analysis of data Either accept or reject hypothesis If hypothesis is accepted, write report to share findings  Biology The study of life To qualify as living, eight characteristics must exist  Characteristics of Life #1. Cellularity – All organisms are comprised of cells. Unicellular Multicellular – Cell type can vary Prokaryotic – cells with unbound DNA. No nucleus exists. DNA is found within the fluid of the cell. Eukaryotic – cells with DNA contained within a nucleus. Characteristics of Life #2. Reproduction - Ability to produce viable offspring Asexual reproduction – a single parent produces genetically identical offspring Sexual reproduction – typically two parents contributing genetics to produce genetically varied offspring Characteristics of Life #3. Nutritional Requirements – all organisms require nutrients -Glucose is needed by all organisms to produce energy. -Autotrophs (Self-feeders) – produce their own glucose possibly through photosynthesis -Heterotrophs – obtain glucose from an outside source by absorbing or ingesting it Characteristics of Life #4 – Growth and Development All organisms experience an increase in size. All organisms experience the differentiation of cells or parts to give rise to the complete body Characteristics of Life #5 Irritability -An organism’s ability to respond to stimuli. A stimulus can be environmental or organismal Characteristics of Life #6 Homeostasis -an organism’s ability to change in order to remain the same. *balance/internal consistency *maintaining body temperature is a classic example Characteristics of Life #7 Mutation -any change in the DNA or genetic material of a cell or organism *most are neutral and have no impact *some are harmful *others are beneficial Characteristics of Life #8 Adaptation -the evolution of a new feature or structure that better equips an individual for survival -only will appear following a beneficial mutation Viruses Are they living? Based on traditional characteristics of life…....... NO!!! -not comprised of cells -do not reproduce on their own -do not need nutrients to survive -do not grow or develop  Hierarchy (Levels) of Organization in Nature Ecosystem A distinct geographical region in which similar biota exist and in which similar abiotic conditions persist. Biota are the living organisms. Abiotic conditions are the environmental aspects of the ecosystem. Examples: *tropical rainforest *desert *tundra *coral reef *temperate deciduous forest Community All of the species of organisms living together within an ecosystem. -does not include environmental attributes Species within a community interact through predation and competition. Population A group of successfully interacting individuals of the same species. -interacting = successful reproduction Common population terms: herd, pack, school, flock, pride, den, pod, colony, stand, etc. Organism Individual organisms: -one bacterium -one alga -one fungus -one plant -one animal  Hierarchy (Levels) of Organization in Nature System A group of interacting organs that together perform a common function. Examples: *digestive *cardiovascular *respiratory *nervous *urinary/excretory *reproductive Organ A structure comprised of numerous tissues. -all of the tissues work together to complete a common function. Examples: *heart *brain *stomach *liver *kidney Tissue A sheet or sheets of interacting and communicating cells that work together. Examples: *muscle *nervous tissue *epidermis *cartilage *adipose tissue Cellular Individual cells of an organism Examples: *one neuron *one skin cell *one blood cell *one bacterium  Chemical/ Molecular The molecules and chemicals of cells -a complete non-living level Examples: *water *oxygen *organic compounds protein carbohydrates lipids nucleic acids  Areas of Biology Anatomy Physiology The study of an organism’s The study of chemical structure concentrating on interactions that occur the systems, organs, tissues within an organism’s body and cells of an organism. and focuses on function.  Areas of Biology Cytology Histology The study of cells The study of tissues  Areas of Biology Ecology Genetics The study of the The study of DNA, heredity environment and the and hereditary variation organisms that inhabit ecosystems  Areas of Biology Pathology Biochemistry The study of disease The study of organic molecules and their role and function in organisms  Areas of Biology Bacteriology Virology The study of bacteria The study of viruses  Areas of Biology Phycology Mycology The study of algae The study of fungi  Areas of Biology Botany Zoology The study of plants The study of animals  Taxonomy A science dealing with the naming and classification of organisms. First introduced by Carolus Linnaeus There are 2 major classification schemes – 3 domain system of classification – 5 kingdom system of classification  Domain system of classification Domain Archaea Domain Bacteria “ancient bacteria” Traditional “contemporary” Bacteria that today thrive in bacteria extreme environmental Bacteria found in all typical conditions. environments and includes All are unicellular prokaryotes pathogenic bacteria. All are unicellular prokaryotes  Domain Eukarya All eukaryotic organisms – Each possesses nuclei in their cells  Kingdom system of classification Developed by Robert Whittaker in 1969 – Kingdom Monera – Kingdom Protista – Kingdom Plantae – Kingdom Fungi – Kingdom Animalia Kingdom Monera Includes bacteria and cyanobacteria All are unicellular prokaryotes. Bacteria are heterotrophic and cyanobacteria are autotrophic. All have cell walls of peptidoglycan. Kingdom Protista Protists include algae, slime molds and protozoans. Most are unicellular. All are eukaryotic. Algae are autotrophic, slime molds and protozoans are heterotrophic Only protozoans are motile. Protozoans lack cell walls, while algae and slime molds have them. Kingdom Plantae Includes all plants All are multicellular. All are eukaryotic. All are autotrophic. Plants are non-motile. Plants have cell walls of cellulose around their cells. Kingdom Fungi Fungi include mushrooms, molds, mildews and yeast Most are multicellular. (except yeast) All are eukaryotic. All are heterotrophic. Fungi are non-motile. Fungi have cell walls of chitin around their cells. Kingdom Animalia Includes all animals All are multicellular. All are eukaryotic. All are heterotrophic. Animals are motile at some point during their lives. Animal cells lack cell walls.  Evolution and The Theory of Natural Selection Proposed by Charles Darwin Natural selection involves nature selecting who survives. “Survival of the fittest” Some individuals are better genetically suited for survival. 1. Organisms in a population are genetically diverse. 2. Certain individuals, based on their traits, are better suited for survival. 3. Survivors are capable of reproduction and produce offspring. 4. Offspring will inherit traits from their parents that better suit them for survival. Chemistry Chapter 2  Matter Matter is any substance that possesses weight and takes up space. Matter can exist in different states, but there are only 3 primary states of matter.  3 primary states of matter Solids – Have 3 obvious dimensions – Have a definite shape and volume – Solids are the most compact state of matter Liquids – Matter that flows freely – Less compact than solids – Liquids fill containers Gases/Vapors – Least compact state – Have no definite shape or volume – Gases expand indefinitely  Mass vs. Weight Mass Weight – The amount of matter – The “heaviness” of an contained within an object. object – Weight = mass x – Always constant gravitational pull – Measured in grams, – Changes based on what milligrams or kilograms gravity exists – Measured using a balance  Matter All matter can be broken down into simple elements An element is the simplest form of matter that can not be broken down my normal chemical or mechanical means. All known elements are displayed in the Periodic Table of Elements Periodic Table of Elements Elements There are 92 naturally occurring elements comprising an organism’s body or found in the environment. All others are man-made O, C, H and N – comprise over 96% of a human’s body weight Trace elements are elements that comprise less than 0.01% of body weight  Elements are comprised of atoms An atom is the structural unit of an element – Atoms contain dozens of subatomic particles – 3 most important subatomic particles Proton – positively charged – located in nucleus of atom Neutron – no charge – located in nucleus of atom Electron – negatively charged – located in shells (orbitals) outside nucleus  Subatomic particles Protons and neutrons are stationary within the nucleus Electrons move at the speed of light around nucleus. Electrons furthest from the nucleus possess more energy.  Determining subatomic particle number for an atom Atomic number – located above elemental symbol in Periodic Table – Equal to the number of protons for an atom of that element – the number of protons will equal the number of electrons Atomic mass (Atomic weight) – located below the elemental symbol in Periodic Table – Equal to the sum of protons plus neutrons – number of neutrons = Atomic Mass – Atomic number  Isotopes Atoms of the same element with differing neutron number – This changes the atom’s atomic mass – Some isotopes will have radioactivity.  Atomic Structure and Electron Configuration 1st shell/orbital holds up to 2 electrons 2nd shell/orbital holds up to 8 electrons 3rd shell/orbital holds up to 8 electrons 4th shell/orbital holds up to 8 electrons *How many shells/orbitals an atom has depends on the total number of electrons  Electron configuration The outermost shell/orbital is the valence shell. – It holds valence electrons. – Valence electron number determines an atom’s stability. – If valence shell is filled to capacity with electrons, the atom is stable. – If valence shell is not filled to capacity with electrons, the atom is unstable.  Ions An atom may become stable by forming an ion. – An ion is an atom with a charge Cation is a positively charged atom – Forms by an atom losing electrons – Occurs with atoms whose valence electron number is 1, 2 or 3 Anion is a negatively charged atom – Forms by an atom gaining electrons – Occurs with atoms whose valence electron number is 5, 6 or 7  Molecules & Compounds An atom may become stable by forming bonds with other atoms to create molecules Molecules are groups of atoms bonded together – Compounds are molecules with groups of different atoms bonded together Organic compounds contain carbon, oxygen and hydrogen Inorganic compounds lack carbon or are compounds possessing carbon without hydrogen or oxygen  Chemical vs. Structural Formula H2O – chemical formula for water – Indicates number of each atom type present – Short hand notation of molecules Structural Formula – Indicates the arrangement of atoms  Isomers Molecules with the same chemical formula, but different structural formulas – Vary by arrangement of atoms – These are examples Types of Chemical Bonds that hold molecules together Ionic bonds – Bonds that involve a transfer of electrons between 2 atoms 2 atoms involved are usually ions (one cation, one anion) – Forms a weak bond – Example: NaCl (sodium choride) A salt crystal is composed of numerous sodium chloride molecules attracted together. Positive Na+ is attracted to negative Cl-.  Types of Chemical Bonds Covalent bonds – Bonds that involve a sharing of electrons between 2 atoms – Forms a strong bond – Covalent bonds hold together all organic compounds – Single covalent bond – one pair of electrons shared – Double covalent bond – two pairs of electrons shared In these examples, unstable atoms have overlapping valence shells which allows for each atom to feel “stable” by equally sharing some of its own valence electrons with those of another atom.  Types of Chemical Bonds Polar covalent bonds – A type of covalent bond where atoms unequally share electrons – some atoms have a greater affinity to electrons Example: water This produces a polar molecule with a + end and a – end due to oxygen pulling more strongly on the electrons  Types of Chemical Bonds Hydrogen bonds – Must involve a hydrogen atom – The hydrogen atom must already be bonded (through a polar covalent bond) to an oxygen, nitrogen or fluorine which makes it positively charged. – The positively charged hydrogen is then weakly attracted to another negatively charged oxygen, nitrogen or fluorine on a second molecule. Hydrogen bonds hold together different water molecules.  Water Along with molecular oxygen, water is the most important inorganic compound to life. Comprises between 50-90% of all organism’s bodies. In humans, water is the most abundant compound (60%).  Properties of Water Temperature stability – An enormous amount of energy is required to change the temperature of water – This attribute provides a stable environment for aquatic organisms The temperature stability of water allows coastal communities to benefit from the cooler ocean temperatures of the Pacific Ocean during spring and summer months. The same is true for Jersey shore communities. I winter, Jersey shore communities remain slightly warmer due to warmer Atlantic Ocean temperatures.  Properties of Water Water exhibits polarity. – Due to polar covalent bonds, water has a positive charge on one end (where the hydrogens are positioned) and a negative charge on the other end (where the oxygen is positioned).  Properties of Water Cohesion – Cohesion is the ability of one water molecule to be attracted to other water molecules This is due to hydrogen bond formation  Cohesion allows for surface tension. Water molecules are more tightly bonded through hydrogen bond formation at the surface than in the deeper water.  Properties of Water Adhesion – Adhesion is the ability of one water molecule to be attracted to molecules other than water. – This allows for condensation build up on a surface and for the meniscus within a graduated cylinder.  Properties of Water Water exhibits solvent properties. – A solvent is a fluid or gas in which particles are dissolved. – Solute are the particles dissolved within a solvent. – Water is considered a universal solvent. Water can dissolve most substances. Since water is polar, only polar solutes dissolve in it. “Like dissolves like” Nonpolar substances (oil, fat, etc.) will not dissolve in water. This is why water dissolves salt easily. Water is polar. Salt is polar. The positively charged hydrogens on water bind with the negatively charge chlorines of salt. The negatively charged oxygens on water bind with the positively charged sodiums of salt.  Properties of Water Water has a unique density when in a liquid state. – Density = mass/volume – Liquid water has a density of 1 g/mL – Solid water (ice) has a density less than 1 g/mL This allows ice to float (Ice is less dense than liquid water). An ice layer provides insulation to the environment below. Water molecules comprising ice are further spaced out, but the hydrogen bonds are more stable allowing ice to be a solid. Water molecules comprising liquid water are closer together, but the hydrogen bonds between them continually break and reform.  pH pH is most commonly thought of as a measure of acidity pH is a measure of the hydrogen ion (H+) concentration in a substance or solution H2O --------------> H+ + OH- (hydroxyl ion) Water molecules continually split into hydrogen ions and hydroxyl ions. These two ions are in perfect balance with each other when comprising pure water.  pH scale pH 7.0 = neutral [H+] = [OH-] pH values less than 7.0 = acids (acidic) [H+] > [OH-] pH values greater than 7.0 = bases (basic) [H+] < [OH-]  Buffers Buffers are special molecules that prevent extensive changes in pH – If a solution has a pH of 7 and acid is added, the pH will decrease – If a solution has pH of 7 and contains a buffer specific to pH 7, when an acid is added, it will have no effect on the pH *buffers in organisms are an example of homeostasis  Organic Compounds Organic Chemistry – the study of the structure and function of organic compounds Biochemistry – the study of organic compounds and their role in living organisms These two areas of science are related since they both deal with organic compounds.  Organic Compounds Carbon is a tetravalent atom and is the basis of all organic compounds. Tetravalent refers to the presence of four valence electrons and therefore allows for carbon to form four separate covalent bonds. Hydrogen and oxygen must also be present. Additional atoms such as nitrogen, sulfur and phosphorus may also be present. Organic compounds are held together by covalent bonds. All organic compounds are composed of a carbon backbone (skeleton) which is a chain of carbons with additionally attached atoms. Organic compounds can vary by length (how many carbons are in the chain). Some organic compounds are completely linear while others may have branches. Some organic compounds may have double bonds in the chain. Some organic compounds may form ring-like structures where two atoms at opposite ends of the chain are attracted to each other.  Organic Compounds Organic compounds vary by structure and function. There are 4 groups of organic compounds. – Carbohydrates – Lipids – Protein – Nucleic acids Functional groups are groups of atoms attached to a carbon backbone (skeleton) that typically indicate the specific type of organic compound. Functional Groups 1. Hydroxyl group -OH -can be attached in the middle or at the end of a carbon skeleton -found in all four groups of organic compounds Functional Groups 2. Methyl group -CH3 -only found at the end of a carbon skeleton -most often found in lipids Functional Groups 3. Carbonyl group -C=O -only found in carbohydrates a. Aldehyde group -COH -found at the end of a carbon skeleton b. Ketone group -C=O -found in the middle of a carbon skeleton Functional Groups 4. Carboxyl group -COOH -only found at the end of a carbon skeleton -only found in proteins Functional Groups 5. Amino group -NH2 -only found at the end of a carbon skeleton -only found in protein Functional Groups 6. Phosphate group -PO4 -mostly found in nucleic acids -typically found at the end of carbon skeletons Functional Groups 7. Sulfhydryl group -SH -can be found in the middle or at the end of a carbon skeleton -only found in certain proteins  Macromolecules Macromolecules are large organic compounds. When a large organic compound is built from smaller organic compounds, the large molecule is a polymer and the smaller “building block” molecules are monomers. There are specific monomer molecules for carbohydrates, for lipids, for proteins and for nucleic acids.  Chemical Reactions (Processes) Dehydration synthesis – Also referred to as a condensation reaction. – Allows for the building of all organic polymers from smaller organic monomers. – It requires energy. – It also produces water besides the larger compound.  Chemical Reactions (Processes) Hydrolysis – Allows for the breakdown of all large organic polymers into smaller organic monomers – It requires water – It produces energy besides the smaller monomer molecules. Organic Compounds (Macromolecules) A. Carbohydrates B. Lipids C. Protein D. Nucleic Acids  A. Carbohydrates Always contains carbon, hydrogen and oxygen Most carbs. end in –ose The monomers (building blocks) of carbohydrates are saccharides. Functional groups possible – Hydroxyl – Carbonyl ketone or aldehyde  A. Carbohydrates Carbohydrates vary by size and therefore function – Monosaccharides – single saccharide molecules Known as simple sugars Used commonly as energy source – Disaccharides – two saccharide molecules covalently bonded together Known as compound (complex) sugars – Polysaccharides – many saccharide molecules covalently bonded together Known as complex carbohydrates Can be used for energy storage or for comprising structural components of cells  Monosaccharides Contain between three and eight carbons Always have a fixed ratio of 1C:2H:1O -triose sugars C3H6O3 -pentose sugars C5H10O5 -hexose sugars C6H12O6 Contain either a ketone (ketose sugars)or an aldehyde (aldose sugars) functional group  Ketose sugars Contain ketone functional groups – Ribulose = a pentose sugar that is involved in photosynthesis – Fructose = a hexose sugar that is found in fruit  Aldose sugars Contain aldehyde functional groups – Ribose = a pentose sugar found in RNA – Glucose = a hexose sugar that is used by all organisms to produce energy Produced by autotrophs through photosynthesis – Galactose = a hexose sugar that is found in dairy products Monosaccharides tend to form ring-like structures when opposite ends get attracted to each other.  Disaccharides Consists of two monosaccharides covalently bonded together – Glycosidic linkage is the name for the specific type of covalent bond. Maltose (malt sugar) = glucose + glucose – Found in alcohol Sucrose (table sugar) = glucose + fructose Lactose (milk sugar) = glucose + galactose  Storage Polysaccharides Consists of many glucose molecules covalently bonded together by glycosidic linkages – Starch = linear chains of glucose, storage form of glucose in plants – Glycogen = branched chains of glucose, storage form of glucose in animals  Structural Polysaccharides – consists of chains of glucose molecules covalently bonded together through glycosidic linkages Cellulose – rope-like chains of Chitin – chains of glucose containing glucose, comprises the cell walls of nitrogen, comprises the cell walls of plants and algae fungi and slime molds, comprises the exoskeletons of arthropods  B. Lipids Contains C, H, and O (fewer O’s than in carbs.) The monomers (building blocks) of lipids are glycerol molecules and fatty acid chains attached by covalent bonds called ester linkages. – Glycerol is a small alcohol molecule. – Fatty acid chains are chains of 16 or 18 carbons with numerous attached hydrogens. Functional groups – hydroxyl groups and methyl groups  B. Lipids Lipids are hydrophobic which means that they are insoluble in water. – Lipids are nonpolar, while water is polar. Lipids do not have a charge difference across the molecule.  Types of Lipids Fats and Oils Phospholipids Waxes Sterols – Cholesterol – Sex hormones – Anabolic steroids  Fats and Oils Fats and oils are structurally similar. – Consist of triglycerides = one glycerol + three fatty acid chains Fats – Solids at room temperature – Used by animals for energy storage and insulation Oils – Liquids at room temperature – Produced by plants  Fats and Oils Saturated fats and oils – no double Unsaturated fats and oils – at least bonds exist in the fatty acid chains one double bond exists in a fatty acid chain and less than the and have the maximum number of maximum number of hydrogens hydrogens present present  Phospholipids Lipids consisting of one glycerol, a phosphate functional group and two fatty acid chains Possess a hydrophilic(water loving) end and a hydrophobic end (water fearing) Phospholipids comprise the cell membranes of all cells. Cell membranes consist of a phospholipid bilayer  Waxes Consist of numerous glycerol molecules with a single attached fatty acid chain Covers the roots, stems and leaves of plants – Prevents water loss Coats the fur and feathers of certain animals – Acts as a water proofing (water repelling) agent  Sterols Lipid-like molecules – Sterols are not composed of glycerol and fatty acid chains. There structure is different and can vary. – Sterols are hydrophobic and insoluble in water. Cholesterol is a sterol found in cell membranes. – Cholesterol is made by cells genetically and is taken in through diet. – An abundance of cholesterol leads to atherosclerosis, a hardening of the arteries than can lead to heart disease, heart attacks or strokes. The structure of cholesterol. It is not composed of glycerol and fatty acid chains as most lipids are.  Sterols Sex hormones are sterols. – Testosterone, estrogen and progesterone – Must be kept in balance Anabolic steroids are also sterols. – Man-made forms of testosterone – Does allow for the increase in muscle mass, but it stops natural testosterone and sperm production  C. Proteins Contains C, H, O, N and sometimes S The monomers (building blocks) of protein are amino acids. A protein is a chain of 100+ amino acids covalently bonded together – The type of covalent bond in protein is a peptide bond. Functional groups – amino and carboxyl groups – hydroxyl and sulfhydryl groups possible  Amino acid structure There are 20 known amino acids Each contains a central carbon, a single hydrogen, an amino group and a carboxyl group All 20 amino acids vary based on what their radical (R) group contains. Nonpolar Amino Acids Polar Amino Acids Acidic and Basic Amino Acids Proteins are built through dehydration synthesis by linking together amino acids with peptide bonds.  Functional Categories of Protein Millions of proteins exist Each is structurally unique – A certain number of amino acids in a specific sequence Each protein has a specific function  Functional Categories of Protein A. Storage proteins – used to store nourishment – Albumin – found in egg white, used to nourish embryo B. Structural proteins – comprise a body component – Keratin – found in epidermis of skin, hairs and nails – Collagen – found in dermis of skin and in bones  Functional Categories of Protein C. Contractile proteins – allows for contraction of muscle tissue – Actin and myosin – in all muscle tissue D. Protective (Defensive) proteins – part of the immune system – Antibodies – made by white blood cells to fight infection and defend against foreign agents  Functional Categories of Protein E. Transport proteins – used to transport something throughout an organism’s body – Hemoglobin – transports oxygen through the blood stream  Functional Categories of Protein F. Hormonal proteins – Insulin and glucagon – used to regulate blood sugar level G. Enzymatic (Regulatory) proteins – Enzymes – special molecules that control cellular, chemical and metabolic reactions Act as catalysts to speed up reactions while conserving energy  Levels of Protein Structure -primary level – linear chain of amino acids  Levels of Protein Structure -secondary level – alpha helix or beta pleated sheet (due to hydrogen bonding)  Levels of Protein Structure -tertiary level – multiple interactions between amino acids of the chain  Levels of Protein Structure -quaternary level – multiple chains of amino acids interacting Denaturation and Renaturation Denaturation is a change in the shape of a protein due to excessively high temperature or unfavorable pH exposure. Renaturation is the return of a protein to its normal shape.  D. Nucleic Acids Contains C, H, O, N and P Nucleic acids serve as genetic materials for a cell – DNA – Deoxyribonucleic acid – the primary genetic material – RNA – Ribonucleic acid – a secondary genetic material The monomers (building blocks) of nucleic acids are nucleotides. A nucleic acid is a chain of nucleotides covalently bonded together. Functional groups – hydroxyl and phosphate groups  Nucleotide structure Each nucleotide consists of – A phosphate group – A pentose sugar Deoxyribose (in DNA) Ribose (in RNA) – A nitrogenous base Purines – larger, double ringed bases – adenine or guanine Pyrimidines – smaller, single ringed bases – cytosine, thymine or uracil Nucleotide structure Building a Nucleic Acid occurs through dehydration synthesis by linking together nucleotides with covalent bonds.  DNA is a nucleic acid consisting of two strands of nucleotides twisted into a double helix. The two strands are connected by hydrogen bonds between complementary bases -Adenine to Thymine -Guanine to Cytosine RNA is a single strand of nucleotides Uracil replaces Thymine in RNA.