Cells & the Evolution of Life
Cells & the Evolution of Life BIOL 115
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This 4 page Class Notes was uploaded by Oma Larkin on Friday October 23, 2015. The Class Notes belongs to BIOL 115 at University of Idaho taught by Staff in Fall. Since its upload, it has received 13 views. For similar materials see /class/227883/biol-115-university-of-idaho in Biology at University of Idaho.
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Date Created: 10/23/15
Carbohydrates Slide 2 When you hear the word carbohydrate you may initially think of breads pastas or the PowerBar you had before your last workout While it is true that these foods contain carbohydrates they contain only a fraction of the types of molecules that are classi ed as carbohydrates Carbohydrates in fact are a diverse group of organic molecules found in all living organisms Carbohydrates can play a number of important roles for organisms including 1 providing an energy source or store 2 providing a source of carbon skeletons useful for making other types of molecules receiving chemical signals giving structural support to cells and organisms bu VV Slide 3 Carbohydrates are composed primarily of carbon hydrogen and oxygen as one would expect from their name and can range in size from molecular weights of 100 Daltons or less to hundreds of thousands of Daltons Carbohydrates are considered to be macromolecules because they often form polymers of repeating subunits or monomers The simplest form of a carbohydrate is called a monosaccharide meaning single sugar Many biologically important monosaccharides have either ve or six carbon atoms Glucose and fructose for example contain six carbon atoms Ribose and deoxyribose found in RNA and DNA respectively have ve carbons You might note that monosaccharides often follow the general formula of CnHZHOn and so have their carbon hydrogen and oxygen atoms in the ratio of 121 For example glucose has the molecular formula C5H1205 Slide 4 39 ides while car39 39 J 39 quot 39 are also the repeating subunits or monomers for larger carbohydrates Monosaccharides may be linked together covalently during a condensation reaction just like amino acids are linked together by condensation reactions to form polypeptides and just as nucleotides are linked to form nucleic acids The bond that forms between monosaccharides is called a glycosidic linkage When two monosaccharides are covalently linked together through a condensation reaction they form a disaccharide Sucrose the carbohydrate that is transported through plant vascular tissue is a disaccharide composed of fructose and glucose Slide 5 When several monosaccharides 320 or so are covalently linked together through condensation reactions they form an oligosaccharide Oligosaccharides are often found associated with membranes where they may bind chemical signals from the cell s environment or from other cells Your blood type for instance is determined by oligosaccharides bound to the cell membranes of your red blood cells Slide 6 When many monosaccharides are linked together by glycosidic linkages they form what is called a polysaccharide Polysaccharides of course are the largest carbohydrates and play diverse and important roles for organisms In some cases polysaccharides consist of linearly connected unbranched chains of monosaccharides Cellulose which is found in the cell walls of plants and protists consists of linear chains of covalently linked glucose molecules Cellulose is the most abundant organic compound on earth Starch and glycogen the storage compounds found in plants and animals respectively are also made up of many covalently linked glucose molecules However the glucose molecules of starch and glycogen may be linked covalently in two ways technically these linkages involve the first and fourth carbon or the first and sixth carbon of the glucose molecules As a result these polysaccharides are branched Slide 7 It is worthwhile here to consider the monosaccharide glucose specifically as glucose is utilized in the metabolic pathways of the vast majority of organisms and is an integral component of many other types of molecules as we will see shortly Glucose most often is found in a ring form although a small portion of the time it converts to a linear molecule When it is in the ring form glucose interconverts between two forms or isomers 7 xglucose and Bglucose The difference between these two molecules concerns the orientation of the hydrogen and hydroxyl groups on the number one carbon Because of this difference in orientation slightly different glycosidic linkages result when molecules of glucose are covalently bound together depending on whether the glucose molecules are or or Bglucose Further different molecules will also result from this bonding For example when an orglucose is covalently linked to a Bglucose an 0Ll4 glycosidic linkage results forming the disaccharide maltose Alternatively if two B glucose molecules are linked together a Bl4 glycosidic linkage results forming the disaccharide cellobiose On a similar note the polysaccharides cellulose starch and glycogen are all composed of glucose monomers Each of these molecules however has a different shape In part this shape is determined by whether each molecule consists of or or 5 glucose monomers and so or or Bglycosidic linkages It is not important here to memorize the names or structures of maltose and cellobiose Rather be aware that the alpha and beta forms of glucose can affect the higher structure of di oligo and polysaccharides Slide 8 Lastly in many cases sugars are chemically modified by adding other molecular entities Perhaps most simply oxygen may be added to the number six carbon of a monosaccharide to form a carboxyl group The result What was previously a carbohydrate is now an acid Other groups may be added to carbohydrates as well most notably phosphates amino groups and N acetyl groups Take for example chitin which makes up insect and crustacean exoskeletons and is also found in the cell walls of fungi Chitin consists of covalently linked molecules of glucosamine which are glucose molecules that carry an amino group on their number two carbons In the case of chitin glucosamine is further modified by adding an acetyl group to the amino group resulting in each monosaccharide carrying an Nacetyl group Photos thesis Properties of Light Slide 2 Visible light is a small part of the electromagnetic spectrum that includes Xrays microwaves and radio waves It appears white to us but is actually a combination of light at different wavelengths This is evident when we see a rainbow or pass light through a prism The white light is refracted separating out the different wavelengths of light which are visible as different colors Slide 3 Light travels in waves with different levels of energy longer wavelengths found towards the red region of the visible spectrum have lower energy compared to the high energy wavelengths toward the blue region of the spectrum Although light travels in waves light behaves as though it contains discrete particles or photons The energy in each photon is relative to the wavelength of light 7 ie the highest energy photons are associated with blue light Note that the visible spectrum ranges from 400 nanometers violet light high energy photons to 700 nanometers farred light low energy photons Slide 4 When light strikes a colored object it may be absorbed or re ected by the object or it may be transmitted through it Pigments are molecules that are involved with the absorption or re ection of light energy different pigments absorb light of different wavelengths For example in the figure the leaves on the tomato plant appear green because certain pigments chlorophylls absorb the red and blue wavelengths of light and re ect the green wavelength of light The red tomato contains a different group of pigments carotenoids that are absorbing the green and blue wavelengths of light and re ecting red light Some pigments absorb most of the wavelengths of light making the object appear dark in color Melanin pigments in animals and some of the phycobilins in algae behave this way producing dark coloration So every organism or object that we see around us is absorbing and re ecting light of different wavelengths giving it a particular color Slide 5 This figure shows the absorption spectra for the pigments chlorophyll a chlorophyll b and the carotenoids found in eukaryotic plant cells Absorption spectra are diagrams that show how effectively pigment molecules absorb different wavelengths of light Note the wavelengths of light which are associated with each pigment Also shown on the figure is the action spectrum for photosynthesis An action spectrum shows the effectiveness of different wavelengths of light for a particular light requiring process Note that the action spectrum for photosynthesis peaks in the red and blue regions of the spectrum coinciding with the absorption spectra for the carotenoid and chlorophyll pigments This indicates that these pigments are involved in the process of photosynthesis and red and blue light are the most effective for this process
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