A Little Blog About AP Bio

Key Concepts: DNA Structure

• DNA is made up of repeated subunits of nucleotides
• Nucleotides are made up of a sugar, phosphate, and nitrogenous base
• A—T makes 2 hydrogen bonds
• C—-G makes 3
• 5’ end has phosphate and 3’ end has hydroxyl group

Key Concepts: Cell Cycle

• The cell cycle occurs for 4 reasons:
• Growth
• Repair
• Replication
• Natural Replacement
• It consistis of G1, S, G2, and Mitosis
• The two G phases are simply for growth and the creation of proteins and enzymes
• The S phase is where the DNA/chromosomes are replicated

Key Concepts: Meiosis

In a world where the first bit of meiosis is different than mitosis, Prophase I forms tetrads instead of pairs…and then Metaphase-Telophase I proceed with these tetrads, forming two haploid cells.

but then…

• the second bit happens, and is also very much like mitosis, only the sister chromatids separate and we have a cell with only n chromosomes
• Dun
• Dun
• DUN

Key Concepts: Stages of Mitosis

PROPHASE

• Nuclear membrane disintegrates
• Strands of chromosomes condense and become visible
• Nucleolus disappears
• Centrioles begin to move to opposite sides

METAPHASE

• Chromosomes line up along the metaphase plate
• Centrioles are at opposite ends of the cell
• Spindle fibers run from centrioles to kinetochores

ANAPHASE

• Sister chromatids of each chromosome separate at the centromere
• Begins to pull apart
• Shortest phase

TELOPHASE

• Chromosomes cluster at end of cell
• Nuclear membrane reforms
• Chromosomes unravel and become invisible

Key Concepts: Beyond Mendelian Genetics

• Codominance- An equal expression of both alleles (ex. AB blood type)
• Incomplete Dominance- Traits blending (white x red= pink)
• Polygenic Inheritance-Many genes having an effect on a particular trait (ex. height, skin color, weight)
• Multiple Alleles-Many alleles are on one gene locus

Key Concepts: Mendelian Genetics

Key Concepts: Photosynthesis

• carbon dioxide+water—->glucose+hydrogen
• 6CO₂ + 6H₂O ==> C₆H₁₂O₆ + 6O₂

LIGHT REACTIONS

• There are two photosystems, PS I and PS II, each with a different pigment, P700 and P680 respectively
• There is also noncyclic and cyclic photophosphorylation
• First we’ll do noncyclic, which uses both of the photosystems
• NONCYCLIC
• The energy is first sent to PS II because it’s backwards like that
• It travels down an electron transport chain and into PS I
• During photolysis in PS II, it splits water into oxygen, H+, and electrons
• As this occurs, the gradient is established and chemiosmosis occurs
• The electrons in PS I then receive another shock and are passed down an ETC again, creating NADPH

• CYCLIC 
• Cyclic is the simpler pathway, but less efficient
• Only ATP is produced, not NADPH
• Water is not split

LIGHT-INDEPENDENT REACTIONS

• CALVIN CYCLE
• CO2 enters the cycle and attaches to RuBP (5 carbons) to make a 6 carbon compound
• This is catalyzed by rubisco
• It goes through the cycle and uses 12 ATP and NADHs total (I think) for three times around to make one molecule of G3P

PHOTORESPIRATION

• If there isn’t any CO2 and O2 gets to Rubisco, it will fix that instead and throw it into the Calvin cycle
• This destroys everything and is very bad

Key Concepts: Cellular Respiration

• Glucose+oxygen—->water+carbon dioxide+energy (ATP)
• C₆H₁₂O₆ + O₂ —-> H₂O + CO₂ + 36ATP

GLYCOLYSIS  

• Glucose is a six carbon model, and through the use of 2 ATPs and 2NADs is broken into two three carbon molecules
• Although glycolysis produces four ATPs the net gain is only two because two were used to break down glucose
• At the point of the split, two NADs are used to take a hydrogen ion from each of 3 carbon molecules, becoming NADHs.
• Summary of products: net gain 2 ATPs (total gain 4), 2 NADHs
• The cell now has two options-continue anaerobically, or switch to true aerobic respiration
• Without oxygen they will choose the former

FORMATION OF ACETYL CoA

• Pyruvic acid enters the mitochondria
• It is converted to a two carbon acetyl coenzyme A
• This means it loses a CO2 molecule
• Two NADHs are also produced

THE KREBS CYCLE

• Each of the two acetyl CoA groups enter one at a time
• Combines with four carbon oxaloacetate to form six carbon citric acid
• Loses two CO2 with the help of three NADs and one FAD. 
• Summary of products: two ATP, 6 NADHs, 2 FADH2s

ELECTRON TRANSPORT CHAIN+CHEMIOSMOSIS

• Two NADH from glycolysis, two from production of CoA, six from Krebs, and two FADHs from Krebs=12 altogether
• These molecules drop off electrons at the ETC where they travel down the mitochondrial cristae until it reaches the final electron acceptor oxygen
• Bonds with oxygen to form water
• Hydrogen ions, meanwhile, are being pumped into the intermembrane space
• These ions are only able to diffuse back across the membrane through ATP synthase, a special channel. 
• This produces ATP and is known as chemiosmosis
• Summary of product: 36 net ATP

ANAEROBIC RESPIRATION

Do you remember when I said after glycolysis the cell could continue anaerobically? Here’s that:

• Without oxygen, a cell begins a process called fermentation
• Pyruvic acid is converted into either 2 lactic acid and 2 NAD+
• or 2 ethanol and CO2 (and 2 NAD+)
• Not very efficient
• Can happen in muscle cells 

Key Concepts: Plant vs. Animal Cells

PLANT CELLS

• Cell wall made of cellulose-provides support for cell (during those rough times you know)
• Chloroplasts used in photosynthesis
• Chlorophyll-light capturing pigment that gives plants green color
• Most of cytoplasmic space is taken up by a large vacuole
• Do not contain centrioles

ANIMAL CELLS

• No cell wall, only plasma membrane
• No chloroplasts or chlorophyll (unless you do photosynthesis in which case, I don’t know what to tell you…you’re a plant)
• Contains centrioles

Key Concept: Organelles and Their Functions

• Ribosomes-Manufacture proteins. Composed of RNA and proteins. Can be free floating or attached to the endoplasmic reticulum
• Endoplasmic Reticulum (ER)-A continuous channel in the cytoplasm. Rough ER (called this because it is studded with ribosomes) makes things to be exported out of the cell. Smooth ER makes lipids, hormones, and breaks down chemicals
• Golgi Bodies-Modify, process, and sort the proteins from ribosomes. They package them in vesicles.
• Mitochondria-Convert energy from organic molecules into energy for the cell. Have their own DNA. Inner and outer membrane, inner known as cristae.
• Lysosomes-Float around in the cytoplasm breaking down old, worn-out organelles or large ingested particles using digestive enzymes.
• Centrioles-Small, paired, cylindrical structures that produce microtubules. Not found in plant cells.
• Vacuoles-Fluid-filled sacs that store water, food, wastes, salts, or pigments
• Peroxisomes-Organelles that detoxify various substances, produce hydrogen peroxide as a by product. Commonly found in liver and kidney cells.
• Cytoskeleton-holds cells together, keeps their shape. Made of Microtubules and microfilaments