Topic 3: Chemistry of Life: Assessment Statements and Terms

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State that the most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen, and nitrogen

All living things are composed of elements in the form of atoms, ions and molecules. The 4 most common elements found in all living things are carbon, hydrogen, oxygen and nitrogen. These elements are used in the molecular structures of all carbohydrates, proteins, lipids, and nucleic acids.


State that a variety of other elements are needed by living organisms, including sulfur, calcium, phosphorous, iron, and sodium

There are many other elements found in living organisms, they are just less common including sulfur, calcium, phosphorous, iron, and sodium. These elements are found in amino acids, enzymes, bones, ATP, cytochromes, hemoglobin, in the cell membrane and many other components of life.


State one role for each of the elements: sulfur, calcium, phosphorous, iron, and sodium

Sulfur- found in some amino acids
calcium- is a co-factor in some enzymes and a component of bones
phosphorous- phosphate groups in ATP
iron- is found in cytochromes and in haemoglobin
sodium- in membrane function and sending nerve impulses


Draw and label water molecules to show their polarity and hydrogen bond formation

There is a slight negative charge at the oxygen end and a slight positive charge at the hydrogen end


Outline the thermal, cohesive and solvent properties of water

Thermal properties: water can absorb or give off a great deal of heat. Water is relatively stable in temperature. Temperature stabilizer. Absorbs a great deal of heat when it evaporates
Cohesive properties: water molecules are highly cohesive, meaning they are attracted to each other. Attraction is do to polar bonding. This allows molecules to move together and form crystals.
Solvent properties: water can be a solvent for many polar molecules such as carbohydrates, proteins, and nucleic acids. Water is also used as a medium in which chemical reactions take place. Aqueous solutions


Explain the relationships between the properties of water and its uses in living organisms as a coolant, medium for metabolic reactions and transport medium

Water's thermal properties make it a good coolant for animals. When animals sweat the process of the water evaporates make the animal cooler because it requires a great deal of energy to evaporate water. Water is used as a solvent for many polar molecules and these polar molecules can than perform metabolic reactions. These metabolic reactions take place in aqueous solutions.


Distinguish between organic and inorganic compounds

All organic molecules contain the element carbon, but not all molecules that contain carbon are organic, some are inorganic.


Identify amino acids, glucose, ribose, and fatty acids from diagrams showing their structures



List three examples of each, monosaccharides, disaccharides and polysaccharides

Monosaccharides: glucose, galactose, fructose
Disaccharides: maltose, lactose, sucrose
Polysaccharides: starch, glycogen, cellulose


State one function of glucose, lactose and glycogen in animals, and of fructose, sucrose and cellulose in plants

Glucose- chemical fuel for cell respiration
lactose- makes up some of the solutes in milk
glycogen- stores glucose in liver and muscles
Fructose- makes many fruits sweet
sucrose- often transported from leaves of plants to other locations in the plants by vascular tissue
cellulose- one of the primary components of plant cell walls


Outline the role of condensation and hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides; between fatty acids, glycerol and tryglycerides; and between amino acids and polypeptides

during hydrolysis one disaccharide molecule and one water molecule react to form two monosaccharides, one polysaccharide and many water molecules react to form many monosaccharides, one triglyceride and 3 water molecules react to form glycerol and 3 fatty acids, and one polypeptide (protein) reacts with many water molecules to form many amino acids. In condensation the reverse of these processes take place.


State three functions of lipids

Lipids store energy, are used for thermal insulation, and are an important part of the phospholipid bilayer of all cell membranes.


Compare the use of carbohydrates and lipids in energy storage

Carbohydrates and lipids are both used to store energy in living things. Lipids, however, store approximately twice as much chemical energy as carbohydrates when comparing an equal mass of both.


Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate

DNA is composed of subcomponents called nucleotides which contain a phosphate group, a sugar (deoxyribose) and and a nitrogenous base (either A, T, C or G)



Deoxyribonucleic acid



subcomponents of DNA. Composed of a phosphate group, a deoxyribose, and a nitrogenous base


State the Names of the four bases in DNA

Four nitrogenous bases:
Adenine, A
Thymine, T
Cytosine, C
Guanine, G


Outline how DNA nucleotides are linked together by covalent bonds into a single strand

DNA is shaped like a double helix and is composed of two strands shaped like staircases. Each strand is composed of nucleotides attached by covalent bonds.


Explain how DNA double helix is formed using complementary base pairing and hydrogen bonds

The double helix looks like a ladder that has been twisted. The sides of the ladder are formed by phosphate groups and deoxyribose sugars and the rungs are made up of two complementary base pairs. The pairs are Adenine and thymine which are connected by 2 hydrogen bonds and Cytosine and Guanine which are connected by 3 hydrogen bonds.


Draw and Label a simple diagram of the molecular structure of DNA



Double Helix

Sides: phosphates and deoxyribose
Rungs: nitrogenous bases


Complementary base pairs

Adenine and thymine: 2 hydroden bonds
Cytosine and Guanine: 3 hydrogen bonds


The most frequently occurring elements

hydrogen, oxygen, carbon, nitrogen


Elements important to living things

sulphur, calcium, phosphorus, sodium, iron


Sulphur, S

Needed to make two of the twenty amino acids that proteins contain


Sodium, Na

Pumped into the cytoplasm to raise the solute concentration and cause water to enter by osmosis


Iron, Fe

Needed to make cytochromes- proteins used for electron transport during aerobic cell respiration, and is needed to make hemoglobin


Phosphorus, P

Part of the phosphate groups in ATP and DNA molecules


Calcium, Ca

Acts as a messender, binding to calmodulin and other proteins that regulate processes inside cells, including transcription, and is needed to make minerals that strengthen bones and teeth


Bond in a water molecule

Polar covalent


Bonds between water molecules

Hydrogen bonds


Organic compounds

Compounds containing carbon that are found in living organisms. Three types of organic compounds: carbohydrates, lipids, and proteins.


Inorganic compounds

All compounds that contain no carbon compounds, some exceptions: Carbon dioxide, carbonates and hydrocarbons



Glucose, Fructose, Galactose



Sucrose, Lactose, Maltose



Starch, Glycogen, Cellulose



Broken down to release energy during respiration. Monosaccharides



Sugar in mammal's milk. Disaccharides



used to store energy in liver and muscles. Polysaccharides



Sugar in fruit. Monosaccharides



transported energy within plant. Disaccharides



Main component of cell wall. Polysaccharides



Two molecules are joined together to form a larger molecule and water molecule(s).
2 amino acids = a dipeptide + water
amino acid + dipeptide = polypeptide + (water)
2 monosaccharides = disaccharide + water
many monosaccharides + disaccharide = polysaccharide + water
3 fatty acids + glycerol = triglyceride + 3 water



Large molecules are broken down with the use of water to form smaller molecules. Reverse of condensation reactions


Three functions of lipids

Buoyancy: lipids are less dense than water so help animals float
Energy Storage: as fat in humans and oil in plants
Heat Insulation: a layer of fat under the skin prevents loss of heat
Phospholipid bilayer



Large organic compounds built up using small and relatively simple subunits.


Advantages of storing energy as lipids

1. Contain more energy per gram than carbs
2. lipids are insoluble in water and do not cause problems with osmosis


Advantages of storing energy in Carbohydrates

1. More easily digested than lipids, easy release of energy
2. Soluble in water, easier to transport



Biological catalysts, speed up the rate of a chemical reaction by decreasing the amount of energy needed during the reaction


Types of bonds

Peptide: between two or more amino acids
Glycosidic: Between two or more Carbohydrates
Ester: Between two or more lipids



reactions that build molecules: Condensation



reactions that break down molecules: Hydrolysis


Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands by DNA polymerase

DNA replication takes place during the synthesis phase of interphase. Inorder for the DNA to be replicated the chromatin, or free DNA, must be separated into two single strands. This means that the double helix needs to be unwound. The enzyme helicase initiates the separation starting at one end of the DNA molecule. It then moves along the DNA molecule breaking every hydrogen bond between complementary base paired nitrogenous bases. The enzyme polymerase then catalysis the formation of new hydrogen bonds between the strands and new free nucleotides which leads to the creation of 2 identical strands of DNA each containing part of the parent strand.


Explain the significance of complementary base pairing in the conservation of the base sequence of DNA

Each DNA molecule is comprised of complementary base pairs. When the DNA molecule is separated, the separate strands of nucleotides act as templates which insures the creation of 2 identical DNA molecules.


State that DNA replication is semiconservative

DNA replication is semiconservative because have of every new strand is composed of half new nucleotides and half nucleotides that were saved or conserved from the original strand of DNA


DNA Replication

to double the quantity of DNA and ensure the creation of an exact copy



Free form DNA that is not coiled to form a chromosome



enzyme that initiates the separation of the two anti-parallel parent strands of a DNA molecule



Catalyzes the formation of a covalent bond between two adjoining nucleotides


Nucleoside Triphosphates

free nucleotides that have not yet bonded and are floating freely in the nucleoplasm


Direction of Replication

The two new strands form in opposite directions. One replicates in the same direction as helicase and the other strand replicates in the opposite direction


Compare the structures of RNA and DNA

Both DNA and RNA contain a 5-carbon (pentose) sugar, but DNA contains deoxyribose where as RNA contains ribose. Each nucleotide contained in either molecules has one of 4 nitrogenous bases that complementary base pair. The only difference is that RNA contains Uracil instead of thymine. DNA: A,T,C,G. RNA: A,U,C,G. DNA is a double stranded molecule where as RNA is a single stranded molecule.


Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase

When transcription takes place the certain section of DNA containing the gene is unzipped. Only one of the two strands is used as a template for the RNA because RNA is single stranded. RNA polymerase moves slowly along the section of DNA containing the gene and puts the proper RNA nucleotides in place. Uracil is used instead of Thymine in the RNA strand and the RNA nucleotides contain ribose instead of deoxyribose.


Describe the genetic code in terms of codons composed of triplets of bases

Genes that are transcribed to form mRNA are used to synthesis polypeptides. Within a mRNA molecule are codon triplets which are three bases that determine the identity of a single amino acid. using this information the mRNA can be used to determine the order of the amino acids in a polypeptide and which amino acids are contained in the polypeptide.


Explain the process of translation, leading to polypeptide formation

During translation a mRNA molecule will align with a ribosome so the first 2 codon triplets are within the boundary of the ribosome. 2 tRNA molecules that are complementary to the first 2 triplets enter the ribosome and their anticodons attach to the codons on the mRNA molecule. Each tRNA bonds to a specific amino acids. An enzyme then comes and performs a condensation reaction between the two amino acids. the first tRNA molecule then detaches and leaves the ribosome. The 2nd tRNA molecule then moves to make room for a 3rd tRNA molecule which bonds to a specific amino acid and so on. the process repeats until the ribosome reaches the final codon which signals the end of translation. when this happens the entire polypeptide breaks away and moves out into the cytoplasm


Discuss the relationship between one gene and one polypeptide

A single gene codes for a single mRNA molecule. After being coded mRNA can be modified which can lead to the production of a different polypeptide than the mRNA molecule was originally coded for.


Nitrogenous bases in RNA

Adenine, Uracil, Guanine, and Cytosine



sections of DNA that code for polypeptides and are specific sequences of nitrogenous bases found in a specific location



messenger RNA which is a molecule that carries the message of the DNA from the nucleus to the cytoplasm where enzymes, ribosomes, and amino acids are found. Complementary copy of one gene of DNA, the transcribed version of the original DNA sequence. Determines the order of the amino acids in a polypeptide



fluid in the nucleus


RNA Polymerase

Catalyzes the formation RNA by taking RNA nucleotides from the nucleoplasm and bonding them together



composed of amino acids covalently bonded together



three bases that determine the identity of one amino acid


Codon triplet

A triplet found in a mRNA molecule



ribosomal RNA, each ribosome is composed of rRNA and a ribosomal protein



transfer RNA, transfers 1 of 20 amino acids to the ribosome for polypeptide formation


Define enzyme and active site

An enzyme is a protein that takes a specific three-dimensional shape that is very specific designed to match a specific molecule known as that enzyme's substrate. Enzymes speed up the rate of reactions by lowering the energy level needed. The active site is the site that matches the substrate. The active site fits to the substrate like a glove fits to a hand.


Explain enzyme-substrate specificity

Each enzyme is made for a specific substrate. The substrate fits in its enzyme like a hand fits into a glove. All enzymes have specific shapes to conform t their specific substrate.


Explain the effects of temperature, pH and substrate concentration on enzyme activity

Increasing the temperature will cause the molecules to move faster which will lead to more collisions and more reactions between enzymes and substrates. This is true up to the point where the enzymes are heated to the point where they start to denature. For most reactions to take place the pH needs to be very close to neutral because the ions in acidic and basic solutions clog the negative and positive areas of the active site making it difficult or imposible for the substrate to bind. An increased concentration of substrate molecules will increase the rate of reactions up until the point where all enzymes are in use and ar working at maximum speed.


Define denaturation

Denaturation is the process by which enzymes lose their shape due to the fact that temperature has increased to the point where inter molecular bonds are stressed to the point of breaking or that the pH level is extremely acidic or basic making the enzyme less efficient or completely inactive.


Explain the use of lactase in the production of lactose-free milk

Lactase can be added to products that contain lactose, such as milk, to break down the lactose molecule into monosaccharide sugars that the body can digest.



proteins that act as biological catalysts



reactant of an enzyme-catalyzed reaction


Active site

the site on an enzyme that attaches to a substrate



substance that speeds up the rate of a chemical reaction



loss of normal shape of a protein due to heat or other factor such as pH level



a value that indicated the acidity or alkalinity of a solution on a scale of 0-14, based on the proportion of H+ ions.



a pH below 7 is acidic; contains more H+ ions than hydroxide ions (OH-)



pH above 7 is basic (alkaline); more OH- ions than H+ ions



ph of 7



enzyme that breaks down lactose



disaccharide found in milk: glucose + galactose


Define cell respiration

Cell respiration is the series of chemical reactions by which a living cell metabolizes glucose and obtains energy from them


State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP

During cell respiration a process called glycolysis is used to break down a glucose molecule into 2 pyruvate molecules which each contain 3 carbons. This process releases 2 ATP molecules.


Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no yield of ATP

Anaerobic cell respiration is the production of ATP without the use of oxygen. There are 2 types of anaerobic respiration, Alcoholic fermentation and lactic acid fermentation. During both process glycolysis is used to break down glucose to produce 2 pyruvate molecules and 2 ATP molecules. After either ethanol or lactate is formed from the 2 pyruvate molecules.


Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP

Aerobic cell respiration uses both glycolysis and a process called the krebs cycle to produce CO2, H2O and ATP from glucose and oxygen. The krebs cycle is carried out in the mitochondrion and glycolysis takes place in the cytoplasm. Aerobic cell respiration produces a much larger amount of ATP than anaerobic respiration.


Rapid Oxidation

The oxidation of a substance at a relatively high temperature. Not controlled by enzymes and results in a nearly uncontrolled energy release



to break down substances in cells to obtain energy


Breaking of bonds

releases a small amount of energy



first step in releasing the energy of glucose, in which a molecule of glucose is broken into two molecules of pyruvic acid. Takes place in the cytoplasm



Organic compound with a backbone of three carbon atoms. Two molecules form as end products of glycolysis


Cell respiration

the series of chemical reactions by which a living cell metabolizes glucose and obtains energy from them



process that does not require oxygen



process by which cells release energy in the absence of oxygen


Alcoholic Fermentation

the anaerobic process by which yeasts and other microorganisms break down sugars to form carbon dioxide and ethanol



unicellular fungi that uses alcoholic fermentation for ATP generation



a 2- carbon molecule


Lactic acid fermentation

The conversion of pyruvate to lactate with no release of carbon dioxide.



The entry compound for the Krebs cycle in cellular respiration; formed from a fragment of pyruvate attached to a coenzyme.


Krebs cycle

second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions