Carbon-Based Molecules
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Transcript of Carbon-Based Molecules
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Carbon-Based Molecules
Part 3: Hydrogen Bonds and Nucleic Acids
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Objectives
• SWBAT describe and compare and contrast the functions and structures of the carbon-based molecules: carbohydrates, lipids, proteins, and nucleic acids.
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Starter
• Water has a very special property that we here in Iowa are able to appreciate on a yearly basis. With your tablemate, or if you do not have a tablemate, then the person in front or behind you, try to figure out what water’s special property is. I will give you a couple of minutes.
• Hang on to your answers – we will use them shortly.
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Hydrogen Bonds
• Life depends on hydrogen bonds (Examples: in water and between nitrogen bases in DNA. – Hydrogen bonds are weak compared to covalent bonds.
• Water is a polar molecule.– Polar molecules have slightly charged regions.
O
HH
_
++
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Hydrogen Bonds– Nonpolar molecules, like lipids (this is review) do not have
charged regions.– Hydrogen bonds form between slightly positive hydrogen
atoms and slightly negative atoms.– file:///C:/Program%20Files/McDougal%20Littell/Power%2
0Presentations-Biology/START%20Power%20Presentations.html
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Hydrogen Bonds
• Hydrogen bonds are responsible for three important properties of water.
• Cohesion – cohesion from the hydrogen bonds makes water molecules stick to each other (water forming beads and surface tension).• Cohesion is attraction among molecules of only 1 substance.
• Adhesion – attraction among molecules of different substances (water molecules stick to other things).• This is very important because it is what helps plants transport
water from their roots to their leaves.
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Hydrogen Bonds
The red liquid is water, it is curved down because of greater adhesion than cohesion.
The mercury on the left shows greater cohesion – evidenced by the upward curve of the mercury in the test tube.
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Hydrogen Bonds
• High specific heat – Hydrogen bonds give water an abnormally high specific heat.• Thus, water resists changes in temperature. • Compared to many other compounds, water must absorb
more heat energy to increase in temperature.• This property is very important in cells! • The chemical energy released by cell processes releases a
great deal of heat and water helps to absorb that heat – protecting the cell.
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Hydrogen Bonds
• Alone, oxygen and hydrogen have very low specific heats (as does methane and many other compounds we have studied) but put them together and we have chemical (and thus biological) majesty.
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Return to Starter
• Water’s special property: it expands, becomes less dense in its solid phase.– Thus it floats and does not sink as we might
suppose.
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Water in it 3 States
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Nucleic Acids
• Nucleic acids are polymers of monomers called nucleotides.
• Nucleotide – is composed of a sugar, a phosphate group, and a nitrogen containing molecule called a base (we will talk a lot more 2nd semester about these).
• DNA and RNA are the two types of nucleic acids.
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Example: Nucleotide Monomer
A phosphate group nitrogen-containing molecule,called a base
deoxyribose (sugar)
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Nucleic Acids - PolymersThis shows the two strands of DNA that connect, via hydrogen bonds, and twist to form a double helix. RNA is single stranded.
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Nucleic Acids•DNA stores genetic information.
•RNA builds proteins.
DNA
RNA
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Entrance Ticket
• What causes hydrogen bonds to form between polar molecules?
• In what kind of molecule are the instructions for building proteins stored?