AP Bio Final
Polarity of Water and Hydrogen Bonds: Water is a polar molecule, meaning it has a slight positive charge on the hydrogen atoms and a slight negative charge on the oxygen atom. This occurs because oxygen is more electronegative than hydrogen, causing electrons to be pulled closer to oxygen. The ability of water molecules to form hydrogen bonds explains its cohesive and adhesive properties. Cohesion refers to water molecules sticking to each other due to hydrogen bonding, which leads to high surface tension. Adhesion occurs when water molecules interact with other surfaces, such as plant cell walls, which is critical in processes like capillary action in plants.
Four Classes of Organic Compounds:
Carbohydrates: Examples: glucose (energy source) and starch (energy storage in plants).
Proteins: Examples: enzymes (catalyze biochemical reactions) and hemoglobin (transport oxygen in blood).
Lipids: Examples: triglycerides (fat storage) and phospholipids (major component of cell membranes).
Nucleic Acids: Examples: DNA (stores genetic information) and RNA (translates genetic information for protein synthesis).
Monomers, Polymers, Dehydration Synthesis, and Hydrolysis:
Monomers are the building blocks of polymers. Examples include amino acids (for proteins), nucleotides (for nucleic acids), monosaccharides (for carbohydrates), and fatty acids/glycerol (for lipids).
Polymers are long chains of repeating monomers. Examples include proteins (chains of amino acids) and polysaccharides (chains of sugar molecules).
Dehydration Synthesis is the process where monomers join together, releasing a water molecule. This builds polymers.
Hydrolysis is the opposite, where water is added to break a polymer into its monomers.
Four Levels of Protein Structure:
Primary Structure: The linear sequence of amino acids. The specific sequence determines the protein’s properties. Amino acids differ in their side chains (R groups), influencing the protein’s folding.
Secondary Structure: The folding of the polypeptide into α-helices or β-pleated sheets due to hydrogen bonds between backbone atoms.
Tertiary Structure: The 3D shape formed by interactions between side chains (hydrophobic interactions, hydrogen bonds, disulfide bridges).
Quaternary Structure: The interaction of multiple polypeptide chains in a multi-subunit protein, such as hemoglobin.
The specific properties of amino acids (size, charge, polarity) influence the protein's folding and function.
Structure Determines Function in Proteins: A protein’s function is closely linked to its shape. If a protein’s structure is altered (denaturation), such as by heat or extreme pH, it may lose its functionality. For example, heat or incorrect pH can break hydrogen bonds and other forces maintaining the protein’s shape, leading to an inactive protein.
Prokaryotes vs. Eukaryotes:
Prokaryotes: Single-celled organisms without a nucleus (e.g., bacteria). They lack membrane-bound organelles.
Eukaryotes: Organisms with cells that have a nucleus and membrane-bound organelles (e.g., plants, animals). Eukaryotic cells are typically more complex and larger.
Endomembrane System and Protein Production: The endomembrane system includes the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vesicles. Protein synthesis begins in the rough ER (which is studded with ribosomes) where polypeptides are synthesized. The proteins are then transported to the Golgi apparatus for modification and packaging. Finally, the proteins are shipped out in vesicles, either to the cell surface or to be secreted outside the cell.
Functions of Major Cell Parts:
Nucleus: Stores genetic information and controls cell activities.
Mitochondria: Produce energy (ATP) through cellular respiration.
Ribosomes: Synthesize proteins.
Endoplasmic Reticulum (ER): Rough ER synthesizes proteins, while smooth ER is involved in lipid synthesis and detoxification.
Golgi Apparatus: Modifies, sorts, and packages proteins.
Lysosomes: Break down waste materials and cellular debris.
Plasma Membrane: Controls what enters and exits the cell.
Enzyme Terms:
Activation Energy: The energy required to start a chemical reaction.
Active Site: The region of an enzyme where the substrate binds and the reaction takes place.
Substrate Specificity: The ability of an enzyme to recognize and bind to a specific substrate.
Denaturation: The process by which an enzyme loses its shape and function due to factors like heat or extreme pH.
Optimum Temperature & pH: The temperature and pH at which an enzyme's activity is highest.
Fluid Mosaic Model of Membrane Structure: The fluid mosaic model describes the cell membrane as a flexible structure composed of a phospholipid bilayer with embedded proteins. The membrane is fluid, allowing movement of components like lipids and proteins. The proteins in the membrane serve various functions like transport, signaling, and structural support.
Types of Membrane Transport:
Passive Transport: Moves substances across the membrane without energy (e.g., diffusion, osmosis, facilitated diffusion).
Active Transport: Requires energy (usually ATP) to move substances against their concentration gradient (e.g., sodium-potassium pump).
Endocytosis/Exocytosis: Active transport mechanisms for bulk movement of substances into or out of the cell in vesicles.
Major Steps in Cellular Respiration: Cellular respiration is a process that converts glucose into ATP, the cell’s energy currency. It consists of three main stages:
Glycolysis:
Input: 1 glucose molecule (C₆H₁₂O₆), 2 ATP, 2 NAD⁺, 4 ADP, 4 inorganic phosphate.
Output: 2 pyruvate molecules, 2 ATP (net), 2 NADH.
Location: Cytoplasm.
Summary: Glycolysis splits one molecule of glucose into two molecules of pyruvate, producing a small amount of energy (ATP) and high-energy electron carriers (NADH).
Citric Acid Cycle (Krebs Cycle):
Input: 2 acetyl-CoA (derived from pyruvate), 6 NAD⁺, 2 FAD, 2 ADP, 2 inorganic phosphate.
Output: 4 CO₂, 6 NADH, 2 FADH₂, 2 ATP.
Location: Mitochondrial matrix.
Summary: Acetyl-CoA is oxidized, producing NADH and FADH₂ (electron carriers) and releasing CO₂ as a waste product. A small amount of ATP is also produced.
Electron Transport Chain (ETC) and Oxidative Phosphorylation:
Input: NADH, FADH₂, O₂, ADP, inorganic phosphate.
Output: 34 ATP, H₂O (water), NAD⁺, FAD.
Location: Inner mitochondrial membrane.
Summary: Electrons from NADH and FADH₂ are transferred through a series of protein complexes, generating a proton gradient that powers ATP synthase to produce ATP. Oxygen acts as the final electron acceptor, forming water.
Total Inputs and Outputs of Cellular Respiration:
Input: Glucose (C₆H₁₂O₆), O₂
Output: CO₂, H₂O, and approximately 38 ATP molecules (in eukaryotes).
ATP Structure, Energy Release, and ATP/ADP Conversion Cycle:
Structure: ATP (adenosine triphosphate) consists of an adenine base, a ribose sugar, and three phosphate groups.
Energy Release: The energy stored in ATP is released when the bond between the second and third phosphate groups is broken, converting ATP into ADP (adenosine diphosphate) and inorganic phosphate (Pi). This reaction releases energy that is used in cellular processes.
ATP/ADP Conversion Cycle:
ATP to ADP: When cells need energy, ATP is hydrolyzed to ADP and Pi, releasing energy.
ADP to ATP: During cellular respiration (or photosynthesis), ADP and Pi are rejoined through the process of phosphorylation, which stores energy in ATP for future use.
Fermentation Process for Energy Production:
Fermentation occurs when oxygen is scarce (anaerobic conditions), and cells use alternative pathways to regenerate NAD⁺ and continue glycolysis.
Types of Fermentation:
Lactic Acid Fermentation:
Input: Glucose (or other sugars).
Output: 2 lactic acid molecules and 2 ATP (per glucose molecule).
Location: Cytoplasm (muscle cells in animals).
Summary: In muscle cells, during strenuous exercise, glucose is broken down into pyruvate, which is then converted into lactic acid to regenerate NAD⁺, allowing glycolysis to continue.
Alcoholic Fermentation:
Input: Glucose (or other sugars).
Output: 2 ethanol molecules, 2 CO₂, and 2 ATP.
Location: Cytoplasm (yeast and some bacteria).
Summary: In yeast, glucose is converted into pyruvate, which is then fermented into ethanol and CO₂, regenerating NAD⁺.
Major Steps in Photosynthesis: Photosynthesis occurs in two stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).
Light-Dependent Reactions (Photosynthesis I & II):
Input: Light energy, H₂O, NADP⁺, ADP, inorganic phosphate.
Output: O₂, NADPH, ATP.
Location: Thylakoid membranes of chloroplasts.
Summary: Light energy excites electrons in chlorophyll, driving water splitting (photolysis) to release O₂. The energy is used to generate ATP and NADPH, which are used in the next stage.
Calvin Cycle (Light-Independent Reactions):
Input: CO₂, NADPH, ATP.
Output: G3P (glyceraldehyde-3-phosphate), which can be used to form glucose and other carbohydrates.
Location: Stroma of chloroplasts.
Summary: In the Calvin cycle, CO₂ is fixed into an organic molecule and converted into G3P using the ATP and NADPH produced in the light-dependent reactions.
Total Inputs and Outputs of Photosynthesis:
Input: CO₂, H₂O, light energy.
Output: Glucose (C₆H₁₂O₆) and O₂.
Importance of Light Pigments and Photosystems in Plants:
Light Pigments: Chlorophyll a and chlorophyll b are the main pigments involved in photosynthesis. Chlorophyll a absorbs light primarily in the red and blue wavelengths and is essential for the light-dependent reactions. Chlorophyll b assists in light absorption by capturing light in different wavelengths and passing the energy to chlorophyll a.
Photosystems: Photosystem I and Photosystem II are complexes of proteins and pigments in the thylakoid membrane. Photosystem II captures light energy and uses it to split water molecules, releasing oxygen and electrons. Photosystem I receives electrons from Photosystem II and uses them to reduce NADP⁺ to NADPH. These two photosystems work together to convert light energy into chemical energy stored in ATP and NADPH, which are then used in the Calvin cycle to produce glucose.
Two Major Types of Vascular Tissue in Plants:
Xylem: Xylem is responsible for transporting water and minerals from the roots to the rest of the plant. It contains specialized cells called tracheids and vessel elements that form tubes to allow for efficient water movement. Xylem also provides structural support due to the presence of lignin in its cell walls.
Phloem: Phloem is responsible for transporting the products of photosynthesis (mainly sugars, like sucrose) from the leaves (where they are produced) to other parts of the plant, including roots and stems. Phloem is made up of sieve tube elements, which are specialized cells that form long tubes through which food is transported, and companion cells that support the sieve tubes.
Water Potential and Its Relationship with Transpiration:
Water Potential: Water potential is a measure of the potential energy of water in a system, indicating the direction water will flow. It combines both the solute potential (due to dissolved substances) and pressure potential (due to physical pressure). Water moves from regions of higher water potential (less negative) to regions of lower water potential (more negative).
Transpiration: Transpiration is the process where water is absorbed by the roots from the soil, travels through the plant, and evaporates through small pores in the leaves called stomata. The water potential gradient created by transpiration helps draw more water from the soil into the roots. As water evaporates from the leaf, it decreases the pressure potential inside the plant, and the cohesion of water molecules allows for continuous flow from the roots to the leaves.
Seed and Germination:
Seed: A seed is a mature fertilized ovule that contains an embryo, stored nutrients, and a protective seed coat. The embryo consists of the developing plant's roots, stem, and leaves.
Germination: Germination is the process by which a seed begins to grow into a new plant. It starts when the seed absorbs water, which activates enzymes that begin breaking down stored nutrients. The embryo begins to grow, with the radicle (embryonic root) emerging first to anchor the plant, followed by the shoot (stem and leaves) growing toward the light. Germination requires optimal conditions such as water, oxygen, and the right temperature.
Stomata and Guard Cells:
Stomata: Stomata are small openings on the surface of plant leaves and stems that allow for gas exchange. Through these pores, plants exchange gases like carbon dioxide (for photosynthesis) and oxygen (as a byproduct of photosynthesis), as well as release water vapor in a process called transpiration.
Guard Cells: Guard cells are specialized cells that surround each stoma. They control the opening and closing of the stomatal pores. When guard cells are turgid (filled with water), they swell and open the stomata; when they lose water and become flaccid, the stomata close. This regulation helps the plant conserve water while still allowing for gas exchange, particularly important in preventing excessive water loss during hot or dry conditions.
Types of Cell Division and Stages of the Cell Cycle:
Types of Cell Division:
Mitosis: A type of cell division that results in two genetically identical daughter cells. It is used for growth, repair, and asexual reproduction in multicellular organisms.
Meiosis: A type of cell division that reduces the chromosome number by half and produces four non-identical daughter cells (gametes—sperm and eggs in animals). It is essential for sexual reproduction.
Stages of the Cell Cycle: The cell cycle is a series of phases that a cell goes through to divide and produce two daughter cells.
Interphase: The phase where the cell prepares for division. It is divided into three stages:
G1 phase (Gap 1): The cell grows and performs its normal functions.
S phase (Synthesis): DNA is replicated, ensuring that the two daughter cells will have identical genetic material.
G2 phase (Gap 2): The cell continues to grow and prepares for mitosis.
M phase (Mitosis): The actual division of the cell, which consists of mitosis and cytokinesis (division of the cytoplasm).
Cytokinesis: The process where the cytoplasm and cell membrane divide, resulting in two daughter cells.
Stages of Mitosis and Meiosis, and Comparison:
Mitosis Stages:
Prophase: Chromosomes condense and become visible, the nuclear envelope dissolves, and the mitotic spindle begins to form.
Metaphase: Chromosomes align at the cell's equator.
Anaphase: Sister chromatids are pulled apart by the spindle fibers toward opposite poles of the cell.
Telophase: Chromatids reach the poles, and the nuclear envelope re-forms around each set of chromosomes.
Cytokinesis: The cytoplasm divides, resulting in two genetically identical daughter cells.
Meiosis Stages:
Meiosis I:
Prophase I: Chromosomes condense, homologous chromosomes pair up (synapsis), and crossing-over occurs.
Metaphase I: Homologous chromosomes align at the cell's equator.
Anaphase I: Homologous chromosomes are separated and pulled to opposite poles (note: sister chromatids remain together).
Telophase I and Cytokinesis: Two daughter cells are formed, each with half the number of chromosomes (haploid).
Meiosis II:
Similar to mitosis, but with no DNA replication before the division.
Prophase II: Chromosomes condense in both daughter cells.
Metaphase II: Chromosomes align at the equator in both cells.
Anaphase II: Sister chromatids are pulled apart.
Telophase II and Cytokinesis: Four non-identical haploid cells are formed.
Comparison:
Mitosis results in two identical diploid cells, while meiosis results in four genetically diverse haploid cells.
Crossing-over only occurs during meiosis in prophase I, not in mitosis.
Crossing-over and Genetic Diversity:
Crossing-over occurs during prophase I of meiosis, when homologous chromosomes pair up and exchange portions of their chromatids. This process shuffles genetic material between chromosomes, creating new combinations of alleles in the resulting gametes.
Genetic Diversity: By mixing alleles, crossing-over increases genetic variation, which is important for evolution and adaptation in populations.
Genetic Diseases - Down Syndrome, Sex Chromosome Abnormalities, and Nondisjunction:
Down Syndrome: Caused by an extra copy of chromosome 21 (trisomy 21). Symptoms include intellectual disabilities, characteristic facial features, and increased risk for certain health problems.
Sex Chromosome Abnormalities:
Turner Syndrome (45,X): A condition in females where one X chromosome is missing or incomplete, leading to short stature, infertility, and possible developmental issues.
Klinefelter Syndrome (47,XXY): A condition in males with an extra X chromosome, causing reduced testosterone levels, infertility, and developmental delays.
Triple X Syndrome (47,XXX): A condition in females with an extra X chromosome, often with mild symptoms, including learning difficulties.
Jacobs Syndrome (47,XYY): A condition in males with an extra Y chromosome, which may cause taller stature, learning difficulties, and behavioral issues.
Nondisjunction: Nondisjunction is the failure of chromosomes to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes. This can result in disorders like Down syndrome or sex chromosome abnormalities.
Types of Direct Communication Between Cells:
Plant Cells:
Plasmodesmata: Channels that connect plant cells, allowing for direct exchange of materials and communication between adjacent cells.
Animal Cells:
Gap Junctions: Protein channels that allow the direct passage of ions and small molecules between adjacent animal cells, enabling synchronized activity.
Bacteria:
Quorum Sensing: Bacteria communicate through the release of signaling molecules that allow them to sense population density and coordinate gene expression for processes like biofilm formation or virulence.
Signal Transduction Pathways:
Signal Reception: The process begins when a signaling molecule (ligand) binds to a receptor on the surface of the target cell (such as a G-protein-coupled receptor or receptor tyrosine kinase).
Second Messengers: The binding of the ligand activates intracellular signaling molecules called second messengers (such as cyclic AMP, calcium ions, or inositol trisphosphate). These messengers amplify the signal and propagate the response within the cell.
Responses: The final response can include changes in gene expression, enzyme activity, or cell behavior (e.g., cell division, differentiation, or apoptosis). The cascade of signaling events ensures that the signal is appropriately processed and results in a specific cellular outcome.
Cell Communication in the Endocrine and Nervous Systems:
Endocrine System:
The endocrine system uses hormones, which are signaling molecules secreted by glands (e.g., thyroid, adrenal glands). These hormones travel through the bloodstream to target organs or tissues, regulating processes like growth, metabolism, and reproduction. Hormonal signaling is typically slower but longer-lasting.
Nervous System:
The nervous system uses electrical impulses and neurotransmitters to transmit signals quickly across neurons. Neurotransmitters are released from synaptic vesicles into synapses, where they bind to receptors on target cells (like muscle cells or other neurons). Nervous system communication is fast and typically results in rapid, short-term responses (e.g., muscle contraction, reflexes).
Pedigrees and Their Use in the Study of Human Genetic Disease:
Pedigrees are diagrams that show the inheritance patterns of specific traits or genetic disorders within a family over several generations. Each individual in the pedigree is represented by a symbol (a square for males, a circle for females), and relationships are shown with lines connecting individuals.
Pedigrees are used to trace the inheritance of genetic diseases, determine whether a disease is inherited in a dominant or recessive pattern, and identify potential carriers of genetic conditions. For example, autosomal dominant diseases show up in every generation, while autosomal recessive diseases may skip generations and have carriers who do not show symptoms.
Difference Between Incomplete Dominance and Codominance:
Incomplete Dominance: In this pattern of inheritance, neither allele is completely dominant over the other, leading to a phenotype that is a blend of both traits. For example, in the case of flower color in certain plants, a cross between a red-flowered plant (RR) and a white-flowered plant (WW) may produce pink flowers (RW) in the offspring.
Codominance: In codominance, both alleles are fully expressed in the heterozygote. Instead of blending, both traits appear separately and equally in the phenotype. An example is the ABO blood group system in humans, where individuals with both A and B alleles (AB) have both A and B antigens on their red blood cells.
Using a Punnett Square for X-linked Genetics Problems: A Punnett Square is a tool used to predict the possible genetic outcomes of a cross between two individuals, based on their genotypes.
For X-linked traits, the X chromosome carries the gene, and males (XY) have only one X chromosome, while females (XX) have two.
Example Problem: Suppose a colorblind female (XᴄXᴄ) mates with a male with normal vision (XY). The Punnett Square would show:
Female offspring (XᴄX): 50% chance of being carriers (normal vision).
Male offspring (XᴄY): 50% chance of being colorblind.
This helps illustrate the inheritance pattern, especially in sex-linked traits, where males are more likely to express the disorder since they have only one X chromosome.
Recombination Frequencies and Chromosome Maps:
Recombination frequencies are used to determine the distance between genes on a chromosome. During meiosis, homologous chromosomes can exchange genetic material in a process called crossing-over, resulting in recombinant chromosomes. The closer two genes are on a chromosome, the less likely they are to recombine (cross over) with each other.
Constructing Chromosome Maps: The recombination frequency between two genes is used to estimate their distance on a chromosome. A recombination frequency of 1% is equivalent to 1 map unit or 1 centimorgan (cM). For example, if genes A and B show a recombination frequency of 20%, they are estimated to be 20 cM apart on the same chromosome.
Chi-Square Calculation and Its Use:
A Chi-square test is used to determine whether observed genetic data (such as Mendelian inheritance ratios) significantly differ from expected ratios.
Chi-Square Formula: χ2=∑(O−E)2E\chi^2 = \sum \frac{(O - E)^2}{E}χ2=∑E(O−E)2 Where:
O is the observed frequency (data you collected).
E is the expected frequency (what you would expect based on a hypothesis, e.g., Mendelian ratios).
The sum is taken over all categories (like different genotypes or phenotypes).
Steps:
Calculate the expected values based on genetic ratios (e.g., 3:1 ratio for a monohybrid cross).
Compare the observed values to the expected values using the Chi-square formula.
Determine the degrees of freedom (df = number of categories - 1).
Compare the Chi-square value to a critical value from the Chi-square distribution table, based on the degrees of freedom and a significance level (usually 0.05).
Interpretation: If the Chi-square value is less than the critical value, the difference between observed and expected data is not significant (null hypothesis is accepted). If the Chi-square value is greater, it suggests that other factors may be influencing the results (null hypothesis is rejected). The Chi-square test is commonly used in genetics to confirm whether inheritance patterns follow Mendelian laws or if other factors (such as linked genes or environmental effects) are at play.
Structure of DNA and Replication Process:
Structure of DNA: DNA (deoxyribonucleic acid) is composed of two long strands of nucleotides, which form a double helix. Each nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine (A), thymine (T), cytosine (C), or guanine (G)). The two strands are complementary and held together by hydrogen bonds between the bases: A pairs with T, and C pairs with G.
DNA Replication: DNA replication occurs during the S-phase of the cell cycle to ensure that each daughter cell receives an identical copy of DNA.
Leading Strand: The leading strand is synthesized continuously in the 5' to 3' direction, following the unwinding of the DNA double helix. It is synthesized by DNA polymerase, which adds nucleotides to the growing strand.
Lagging Strand: The lagging strand is synthesized discontinuously in short fragments (Okazaki fragments) because it runs in the 3' to 5' direction. DNA polymerase can only add nucleotides in the 5' to 3' direction, so it synthesizes these fragments in pieces. After the fragments are made, they are joined together by DNA ligase.
3' and 5' Ends: The DNA strands have polarity; one end has a free 5' phosphate group, and the other has a free 3' hydroxyl group. DNA polymerase works by adding nucleotides to the 3' end of the strand.
Function of DNA Polymerases, Helicase, Ligase, and Primase:
DNA Polymerase: An enzyme that synthesizes the new DNA strand by adding nucleotides complementary to the template strand. It also has proofreading activity to correct errors during replication.
Helicase: Unwinds the double-stranded DNA to create single-stranded templates for replication.
Ligase: Seals the gaps between Okazaki fragments on the lagging strand by forming phosphodiester bonds, ensuring the DNA backbone is continuous.
Primase: Synthesizes short RNA primers that provide a starting point for DNA polymerase to begin replication, as DNA polymerase can only add nucleotides to an existing strand.
Protein Synthesis - Transcription and Translation:
Transcription: The process by which an RNA copy (mRNA) is made from a DNA template. It occurs in the nucleus.
RNA Polymerase: RNA polymerase binds to the promoter region of the gene and unwinds the DNA. It then synthesizes a complementary mRNA strand in the 5' to 3' direction.
Translation: The process by which mRNA is decoded to synthesize a protein. It occurs in the cytoplasm at the ribosome.
Codons: mRNA is read in triplets of bases, called codons, each of which codes for a specific amino acid.
tRNA Anticodons: Transfer RNA (tRNA) molecules have anticodons that are complementary to the mRNA codons. The tRNA brings the appropriate amino acid to the ribosome to build the protein.
The ribosome reads the mRNA and assembles the protein by linking amino acids in the correct order according to the mRNA sequence.
RNA Processing:
5' Cap and 3' Poly-A Tail: After transcription, the mRNA undergoes modifications:
A 5' cap is added to the beginning of the mRNA molecule to protect it from degradation and help with ribosome binding.
A 3' poly-A tail is added to the end of the mRNA to protect it from degradation and help with the export of the mRNA from the nucleus.
Pre-mRNA (hn-mRNA): The initial transcript (called heteronuclear RNA or pre-mRNA) contains both exons (coding regions) and introns (non-coding regions).
Introns and Exons: Introns are spliced out during RNA processing, and the exons are joined together to form the final mature mRNA.
Location: RNA processing occurs in the nucleus before the mRNA is exported to the cytoplasm for translation.
Universal Genetic Code:
The universal genetic code is a set of rules that define how sequences of DNA (or RNA) are translated into amino acids during protein synthesis. Each set of three nucleotides (codon) in mRNA corresponds to one amino acid or a stop signal in the translation process. The genetic code is nearly universal across all organisms, meaning that the same codons generally code for the same amino acids in most living organisms.
Mutation and How They Affect the Reading Frame:
Mutation: A mutation is a change in the DNA sequence that can result in changes to the structure and function of the encoded protein.
Frameshift Mutation: This type of mutation occurs when nucleotides are added or deleted, causing a shift in the reading frame of the codons. This changes the grouping of the codons and often results in a completely different and nonfunctional protein. For example, if an insertion or deletion occurs, all subsequent codons will be read incorrectly, leading to a misfolded protein.
Point Mutation: A point mutation is a change in a single nucleotide pair, which may or may not affect the reading frame, depending on the type of mutation (silent, missense, or nonsense).
Basic Structure of an Operon: An operon is a cluster of genes under the control of a single promoter in prokaryotic cells, typically involved in regulating the expression of genes related to a specific function, such as metabolism.
Promoter: The region where RNA polymerase binds to initiate transcription.
Operator: A regulatory sequence where a repressor or activator protein can bind, controlling the access of RNA polymerase to the genes.
Regulator: A gene that codes for a repressor or activator protein, which can influence whether the operon is transcribed.
Structural Genes: The genes that encode the proteins involved in a specific metabolic pathway or function.
Gene Regulation in Prokaryotes and Eukaryotes:
Prokaryotes: Gene regulation in prokaryotes often involves operons, such as the lac operon, where the presence of lactose causes the repressor to detach from the operator, allowing transcription of genes that metabolize lactose. Repressors and activators help turn genes on or off depending on environmental conditions.
Eukaryotes: Gene regulation in eukaryotes is more complex. It involves the transcriptional control of genes by enhancers, silencers, and transcription factors that interact with the promoter. Eukaryotic regulation also includes post-transcriptional modifications (such as RNA splicing) and epigenetic modifications (like DNA methylation and histone modification), which can influence gene expression without altering the DNA sequence. Additionally, transcription factors, microRNAs, and long non-coding RNAs play significant roles in fine-tuning gene expression in response to various signals.