Honors Biology Final
Mitochondria
Definition & Structure:
- Mitochondria are known as the powerhouses of the cell, providing energy through cellular respiration.
- Structure includes:
- Outer Membrane: Smooth membrane that encloses the organelle.
- Inner Membrane: Contains folds known as cristae, which increase surface area for biochemical reactions.
- Mitochondrial Matrix: Fluid-filled space inside the inner membrane.
- Intermembrane Space: The space between the inner and outer membranes.Endosymbiont Theory:
- Proposes that mitochondria and chloroplasts originated as independent prokaryotic cells that were engulfed by ancestral eukaryotic cells. This engulfment allowed the ancestral cells to benefit from the aerobic respiration and photosynthesis that these prokaryotes provided.
- Key points:
- Chloroplasts function similarly as they are involved in photosynthesis.
- Reasoning behind theory includes similarities in DNA structure and replication between mitochondria and prokaryotes.
Endomembrane System
Definition & Function:
- The endomembrane system comprises a network of membranes within the cell that organize various cellular functions and transport materials.Main Components:
- Smooth Endoplasmic Reticulum (SER):
- Lack ribosomes, involved in synthesizing lipids, storing calcium ions, detoxifying substances in the liver, and metabolizing carbohydrates.
- Rough Endoplasmic Reticulum (RER):
- Studded with ribosomes, its main role is to secrete glycoproteins (proteins with carbohydrates) and produce membranes.
- Golgi Apparatus:
- Known as the shipping and receiving center for the cell. It consists of flat membranous sacs called cisternae.
- It modifies, sorts, and packages materials into transport vesicles, also manufactures lysosomes and peroxisomes.
- Lysosomes:
- Membrane sacs filled with hydrolytic enzymes useful in digestion and recycling cellular components.
- Functions include:
- Phagocytosis: The process of engulfing food through vesicles.
- Autophagy: The recycling of the cell's own organelles and macromolecules.
- Apoptosis: Programmed cell death, facilitated by lysosomal enzymes.
- Vacuoles:
- Larger vesicles that may form from the ER or Golgi apparatus, important for storing substances.
- Examples include contractile vacuoles in protists and central vacuoles in plant cells.
Eukaryotic vs. Prokaryotic Cells
Key Differences:
- Prokaryotic Cells:
- Lack a nucleus and membrane-bound organelles.
- Circular DNA structure, generally smaller in size.
- Eukaryotic Cells:
- Contain a nucleus and various membrane-bound organelles.
- Linear DNA and generally larger size.Surface Area to Volume Ratio:
- High surface area to volume ratio enhances efficiency in processes such as nutrient uptake and waste elimination.
Protein Folding
Levels of Structure:
- Primary Structure: Sequence of amino acids in a polypeptide chain.
- Secondary Structure: The local folding of the polypeptide into structures such as alpha helices and beta-pleated sheets.
- Tertiary Structure: The overall three-dimensional structure formed by the interactions of R groups in the polypeptide chain, usually where proteins begin to function.
- Quaternary Structure: The assembly of multiple polypeptides in a multi-subunit complex (e.g., hemoglobin).Enzymes:
- Definition: Biological catalysts that lower the activation energy of chemical reactions, thereby speeding up metabolic processes.
- Enzyme-Substrate Interaction:
- Each enzyme has specificity for its substrate due to the shape of the active site.
- Induced Fit Model: The enzyme changes shape when the substrate binds, enhancing the enzyme's ability to catalyze reactions.Factors Affecting Enzyme Activity:
- Temperature, pH, and substrate concentration influence enzyme functionality.
Specific Metabolic Processes
Photosynthesis
General Purpose: Conversion of light energy into chemical energy (glucose).
- Chemical Equation:
Two Stages:
1. Light-Dependent Reactions:
- Location: Thylakoid Membranes.
- Reactants: Light and water ( ext{H}_2O) producing ATP and NADPH.
- Involves the processes of Photosystem II (PSII) and Photosystem I (PSI).
2. Light-Independent Reactions (Calvin Cycle):
- Location: Stroma.
- Uses ATP and NADPH from light-dependent reactions to convert carbon dioxide into glucose.
- Main enzyme: Rubisco (ruBP carboxylase).
- For every 3 cycles, one G3P (glyceraldehyde-3-phosphate) is produced;
- Requires 6 cycles to produce one glucose molecule.Photorespiration: A process where Rubisco fixes O2 instead of CO2, leading to decreased efficiency in photosynthesis.
- CAM Plants: Adapted to conserve water; absorb CO2 at night by converting it to an organic acid for use during the day.
Cellular Respiration
General Purpose: Break down glucose to produce ATP through multiple stages:
1. Glycolysis:
- Location: Cytoplasm. Reactants: Glucose, 2 ATP; Products: 4 ATP (net gain of 2 ATP), 2 pyruvate, and 2 NADH.
2. Pyruvate Oxidation:
- Converts pyruvate into Acetyl-CoA, producing CO2 and NADH.
3. Krebs Cycle (Citric Acid Cycle):
- Acetyl-CoA enters the cycle, producing NADH, FADH2, ATP, and releasing CO2.
4. Electron Transport Chain (ETC) and Chemiosmosis:
- Produces the majority of ATP in mitochondria through oxidative phosphorylation by using high-energy carriers NADH and FADH2.Anaerobic Respiration:
- Includes fermentation processes such as alcoholic fermentation (yeast) and lactic acid fermentation (in muscles and some bacteria).
Cell Cycle and Meiosis
Stages of the Cell Cycle:
- Interphase (90% of the cycle): Cell growth and preparation for division, includes:
- G1 Phase: Growth phase.
- S Phase: Synthesis phase (DNA replication).
- G2 Phase: Preparation for mitosis.
- Mitotic Phase (M-phase): Division of the cell via mitosis (PPMAT) which includes:
1. Prophase: Chromatin condenses to form chromosomes, nuclear envelope breaks down and spindle apparatus forms.
2. Metaphase: Chromosomes align at the metaphase plate.
3. Anaphase: Sister chromatids separate and move to opposite poles.
4. Telophase: Nuclear envelope reforms, chromosomes decondense, and the mitotic spindle breaks down.
5. Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.Meiosis:
- Similar to mitosis, but involves two rounds of division and results in four haploid gametes.
- Meiosis I features crossing over and independent assortment for genetic variation in offspring.
- Key Terminologies:
- Sister Chromatids: Identical copies formed by the replication of a chromosome.
- Homologous Chromosomes: Chromosomes that are similar in shape, size, and genetic content.
- Tetrad: A structure containing four chromatids that forms during prophase I of meiosis.
Genetics
- Non-Mendelian Ratios: Examples of inheritance patterns not following Mendel's laws:
- Incomplete Dominance: Traits blend in heterozygotes.
- Codominance: Both alleles expressed distinctly (e.g., roan cattle).
- Epistasis: One gene masks the expression of another gene (e.g., Labrador coat color).
- Pleiotropy: One gene influences multiple phenotypic traits.
DNA Replication
General Characteristics:
- DNA replication is semi-conservative, meaning each new DNA molecule consists of one original strand and one new strand.
- The process involves several key enzymes:
- Helicase: Unwinds the DNA double helix.
- Primase: Synthesizes RNA primers.
- DNA Polymerase: Synthesizes new DNA by adding nucleotides.
- Topoisomerase: Relieves supercoiling ahead of the replication fork.
- Ligase: Joins Okazaki fragments on the lagging strand.Leading vs. Lagging Strand:
- Leading Strand: Synthesized continuously towards the replication fork.
- Lagging Strand: Synthesized in Okazaki fragments away from the replication fork.
Transcription and Translation
Eukaryotic Transcription:
- Initiation involves RNA polymerase binding to the promoter, which contains a TATA box important for forming the transcription initiation complex.
- During elongation, RNA polymerase moves along the DNA and unwinds the helix, transcribing the DNA into mRNA.
- Termination involves RNA polymerase stopping at the terminator sequence.Modifications of pre-mRNA:
- Capping and polyadenylation for mRNA stability and export from the nucleus to the cytoplasm.Translation Process:
- Involves ribosomes reading mRNA and synthesizing polypeptides by adding amino acids based on the codon sequence, using tRNA as the adapter.
- Direction of synthesis: DNA is read 3' to 5', RNA built 5' to 3'.
Cellular Transport
Active Transport vs. Passive Transport:
- Active Transport: Requires energy to move substances against their concentration gradient; a key example is the sodium-potassium pump (3 Na⁺ out, 2 K⁺ in).
- Passive Transport: Does not require energy and includes processes such as diffusion and osmosis.Types of Cellular Import:
- Endocytosis: Involves engulfing materials into the cell (e.g., phagocytosis, pinocytosis).
- Exocytosis: Release of materials from the cell.Diffusion Principles:
- Simple Diffusion: Occurs directly through the membrane for small or nonpolar molecules.
- Facilitated Diffusion: Involves membrane proteins to assist larger molecules.
- Osmosis: Movement of water across a selectively permeable membrane, typically through aquaporins.
- Tonicity Effects on Cells:
- Isotonic: No net movement of water.
- Hypertonic: Water moves out, causing cells to shrivel.
- Hypotonic: Water moves in, causing cells to swell or burst in animal cells, while in plant cells it causes turgidity.