2020 AP Biology Exam Review

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Unit 1: The Chemistry of Life

Jamie Castle

PA Leadership Charter School, West Chester, PA

@jamiencastle

Housekeeping Items

Linked below this video:

• The slide deck from this presentation
• The schedule of remaining review sessions
• The question submission form for the remaining review sessions
• Submit a week ahead of time to maximize the possibility your question is answered in the session

How to Use This Video

• To refresh your memory of content from early in the course
• To consider how the material from Unit 1 might be incorporated into this year’s AP exam
• To support (not replace!) your own in-depth review of Unit 1 material

Things to Keep in Mind

• I will make mistakes. It’s unavoidable.
• Ask lots of questions in the chat.
• AP questions are always about content plus skills.
• Review the AP Biology Science Practices (linked below)
• Mental health is more important than exam prep!

Your Moderators

Hannah Hathaway

DSST: Montview HS, Denver, CO

Sedate Kohler

Reedsburg Area HS, Reedsburg, WI

Clifford Nafrada

Arcadia HS, Phoenix, AZ

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Please thank them for volunteering their time!

1.1 Structure of Water and Hydrogen Bonding

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Explain how the properties of water that result from its polarity and hydrogen bonding affect its biological function.

Structure of Water: Covalent Bonding

• A polar covalent molecule composed of two H and one O
• Polarity = uneven distribution of charge throughout a molecule

Image: Khan Academy

Structure of Water: Hydrogen Bonding

• H-bonding is the strongest type of intermolecular attractive force (IMAF) between molecules
• Attraction is between N, O, or F of one molecule and H bonded to N, O, or F on another molecule
• Each individual water molecule can form hydrogen bonds with four other water molecules

Image: Wikipedia

Image: Wikimedia Commons

These Hs will not form H bonds.

Properties of Water

• Cohesion = water molecules attracted to one another via H-bonding
• Reason for high surface tension (penny lab!)
• Adhesion = water molecules attracted to other polar molecules via H-bonding

Image: Wikipedia

Properties of Water

• High specific heat = Takes more energy to ↑ water temp
• Evaporative cooling = Highest energy molecules evaporate first, cooling surface of remaining liquid
• Floating ice = Solid ice is less dense than liquid water
• Versatile solvent = Dissolves ionic and polar covalent solutes

Image: Encyclopedia Britannica

1.2 Elements of Life

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Describe the composition of macromolecules required by living organisms.

Biological Macromolecules

• Most organic molecules are composed of rings or chains of C bonded to H, O, and/or N. All are covalent.
• Biomolecules are a subset of organic molecules synthesized by living organisms.

1.3 Introduction to Biological Molecules

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Describe the properties of the monomers and the type of bonds that connect the monomers in biological macromolecules.

Monomers and Polymers

Polymers = large molecules made up of many similar molecular building blocks

Monomers = the building blocks

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Image: General Chemistry: Principles, Patterns, and Applications v 1.0

Joining Monomers

Dehydration synthesis (aka condensation) reactions join two monomers together into a polymer. A water molecule is removed in the process.

Hydrolysis reactions add a water molecule to cleave the covalent bond between two monomers in a polymer.

Image: Western Oregon University

1.4 Properties of Biological Molecules

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Describe the properties of the monomers and the type of bonds that connect the monomers in biological macromolecules.

Carbohydrates

• Main fxns = energy (glucose, glycogen, starch), structure (cellulose, chitin)
• Monosaccharides = carbohydrate monomers
• Chains or rings, most often 5-6 C
• End in -ose
• Polysaccharides = complex carbs (polymers)
• Bonds between monosaccharides are called glycosidic bonds
• Presence of O makes some carbs polar enough to dissolve in water

Image: cnx.org

Image: dlc.dcccd.edu

Image: Wikipedia

Lipids

• Fxns = energy storage, structure, ligands
• All lipids are nonpolar and thus do not dissolve in water
• Triglycerides (fats) = three fatty acids + glycerol
• Phospholipids = two fatty acids + glycerol + phosphate group
• Steroids = four fused carbon rings

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Image: BC Open Textbooks

Image: CK-12 Foundation

Image: Wikipedia

Triglycerides

• Glycerol = 3 Cs, each with -OH group
• Fatty acid (FA) - Long hydrocarbon chains with -COOH on the end
• Bond btwn glycerol and an FA is a covalent ester bond (R-C=O)
• Saturated FAs = all single C-C bonds; solid at room temp
• Unsaturated FAs = one or more double or triple C-C bonds; liquid at room temp

Image: Lumen Learning

Image: Vision Learning

Image: dlc.dcccd.edu

Saturated fatty acid

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Unsaturated fatty acid

Image: Wikipedia

Phospholipids

• Phospholipids are amphipathic
• Phosphate group = polar region that interacts with other polar molecules, such as water
• Fatty acids = nonpolar regions that are often hydrophobic
• Major component of plasma membranes

Image: CK-12 Foundation

Image: Khan Academy

Proteins

• Fxns = structure, signaling, catalysis, and more
• Monomers are amino acids
• Directionality: amino (-NH₂) terminus and carboxyl (-COOH) terminus
• R groups are categorized by chemical properties (hydrophobic, hydrophilic, or ionic)
• Interactions of R groups determine structure and function of regions of proteins

Both images: Wikipedia

Nucleic Acids

• In nucleic acids, biological information is encoded in sequences of nucleotide monomers
• Each nucleotide has structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate, and a nitrogen base (adenine, thymine, guanine, cytosine, or uracil).
• DNA and RNA differ in structure and function

Image: Wikipedia

Image: Wikipedia

1.5 Structure and Function of Biological Molecules

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Explain how a change in the subunits of a polymer may lead to changes in structure or function of the macromolecule.

Complex Carbohydrate Structure

• Polysaccharides comprise linear chains of sugar monomers connected by covalent glycosidic bonds
• Carbohydrate polymers may be linear or branched

Both images: Khan Academy

Protein Structure

Proteins comprise linear chains of amino acids connected by the formation of covalent peptide bonds at the carboxyl terminus of the growing polypeptide chain.

Image: Khan Academy

Image: College of Saint Benedict

Levels of Protein Structure

• 1^o structure = sequence order of amino acids
• 2^o structure = folding of the amino acid chain into alpha-helices and beta-sheets due to H-bonds between polypeptide backbone atoms
• 3^o structure = overall 3D shape of the protein formed by non-covalent interactions between R group atoms; often minimizes free energy
• 4^o structure = non-covalent interactions between multiple polypeptide units

Image: Wikipedia

Levels of Protein Structure

• 2^o structure = folding of the amino acid chain into alpha-helices and beta-sheets due to H-bonds between polypeptide backbone atoms

Image: Khan Academy

Levels of Protein Structure

• 3^o structure = overall 3D shape of the protein formed by non-covalent interactions between R group atoms; often minimizes free energy
• 4^o structure = non-covalent interactions between multiple polypeptide units

Images: Khan Academy

Protein Structure

• 2^o, 3^o, 4^o structure can be denatured (broken down) by changes in temperature and pH because of the weaker nature of the non-covalent interactions they are built upon
• Denaturing → structural change → functional change

Image: Wikipedia

Nucleic Acid Structure

• Linear sequences of nucleotides
• Ends are defined by the 3’ hydroxyl and 5’ phosphates of the sugar in the nucleotide
• During DNA and RNA synthesis, nucleotides are added to the 3’ end of the growing strand, forming covalent bonds between nucleotides

Image: Khan Academy

Image: Wikipedia

Nucleic Acid Structure

• DNA is structured as an antiparallel double helix
• Each strand runs in opposite 5’ to 3’ orientation
• Adenine nucleotides pair with thymine nucleotides via two hydrogen bonds
• Cytosine nucleotides pair with guanine nucleotides by three hydrogen bonds

Image: Wikipedia

1.6 Nucleic Acids

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Describe the structural similarities and differences between DNA and RNA.

Nucleotide Structure

• Three components: sugar, phosphate group (-), and nitrogenous base
• Connected by covalent bonds to form a linear molecule with 5’ and 3’ ends
• Nitrogenous bases are perpendicular to the sugar-phosphate backbone

Image: ThoughtCo.

Image: Wikipedia

DNA vs. RNA

• Basic structural differences:
• DNA contains deoxyribose and RNA contains ribose
• RNA contains uracil and DNA contains thymine
• DNA is usually double stranded; RNA is usually single stranded

Image: ThoughtCo.

Sample Released FRQs

• Many biological structures are composed of smaller units assembled into more complex structures having functions based on their structural organization. For the following complex structures, describe the smaller units, their assembly into the larger structures, and one major function of these larger, organized structures.
• Ex. - An enzyme, a phospholipid, a carbohydrate, DNA, RNA
• Describe how the properties of water contribute to plasma membrane structure.
• The physical structure of a protein often reflects and affects its function. Describe THREE types of chemical bonds/interactions found in proteins. For each type, describe its role in determining protein structure.

Thank you!

Stay safe and healthy!

Good luck on the AP exam!

Questions? @jamiencastle

Next session: 1 PM EST tomorrow, Unit 2 - Cell Structure and Function

(info linked below)