Combined Lectures 16-24 PDF

Photosynthesis Overview What is Photosynthesis? Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water. Chemical Equation: The overall equation for photosynthesis is: 6CO2+6...

Photosynthesis Overview What is Photosynthesis? Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water. Chemical Equation: The overall equation for photosynthesis is: 6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_26CO2+6H2O→C6 H12O6+6O2 Stages of Photosynthesis 1. Light-Dependent Reactions: o Location: Thylakoid membranes in chloroplasts. o Process: ▪ Capture sunlight using chlorophyll. ▪ Convert light energy into ATP and NADPH. ▪ Water molecules are split, releasing oxygen as a byproduct. 2. Light-Independent Reactions (Calvin Cycle): o Location: Stroma of chloroplasts. o Process: ▪ Utilize ATP and NADPH to convert CO2 into glucose through a series of reactions known as carbon fixation. Key Components Chloroplasts: Organelles where photosynthesis occurs; contain thylakoids and stroma. Thylakoids: Membrane-bound structures within chloroplasts where light-dependent reactions take place. Stroma: Fluid surrounding thylakoids; site of light-independent reactions. Chlorophyll: Pigment that captures light energy; primarily absorbs blue-violet and red light. Autotrophs vs. Heterotrophs Autotrophs (e.g., Plants): Organisms that produce their own food through photosynthesis. Heterotrophs (e.g., Humans): Organisms that consume other organisms for food. Opposites in Respiration The products of photosynthesis (glucose and oxygen) are the reactants of cellular respiration, and vice versa. Electromagnetic Spectrum Visible Light Spectrum: Wavelengths between 400-700 nm are visible to humans; chlorophyll reflects green light while absorbing other wavelengths. Importance of Pigments Pigments: Molecules that absorb specific wavelengths of light. Different pigments allow plants to capture more of the sun’s energy. Chlorophyll a and b: The primary pigments involved in photosynthesis, with chlorophyll a being crucial for the light-dependent reactions. Concept Check Questions 1. Autotroph vs. Heterotroph: o Autotrophs produce their own food through photosynthesis, while heterotrophs obtain energy by consuming other organisms. Their connection lies in the energy flow within ecosystems. 2. Chloroplast Diagram: o A chloroplast consists of an outer membrane, inner membrane, thylakoids (stacked in grana), and stroma. Light-dependent reactions occur in the thylakoids, while light-independent reactions occur in the stroma. 3. Importance of Chloroplasts: o Chloroplasts are vital for converting solar energy into chemical energy stored in glucose, supporting life on Earth. 4. Thylakoid Function: o Thylakoids are where the light-dependent reactions occur; they contain chlorophyll and are integral in capturing light energy. 5. Function of Chlorophyll: o Chlorophyll absorbs light energy, exciting electrons that initiate the electron transport chain, ultimately leading to ATP and NADPH production. 6. Steps in Photosynthesis: o Capture light energy → Water splitting (light-dependent reactions) → Produce ATP and NADPH → Convert CO2 into glucose (Calvin cycle). Final Thought The process of photosynthesis is essential not only for the plants but for all life on Earth, as it forms the basis of food chains and oxygen production. Light and Photosynthesis Light and Pigments Light: Electromagnetic radiation visible to plants, primarily in the wavelengths of 400-700 nm. Pigments: Molecules that absorb light. Key pigments in plants include: o Chlorophyll a: Main photosynthetic pigment; absorbs blue-violet light and reflects blue-green. o Chlorophyll b: Accessory pigment; absorbs red-blue light and reflects yellow- green. o Carotenoids: Accessory pigments; absorb blue-purple light and reflect orange. o Xanthophyll: Accessory pigments; absorb blue-purple light and reflect yellow. Chlorophyll and Photosystems Chlorophyll Structure: The shape of chlorophyll determines the wavelengths it absorbs and reflects. Chlorophyll a reflects bluish-green light, while chlorophyll b, with a slight structural change, reflects more yellow light. Photosystems: Complexes of pigments (including chlorophyll) and proteins located in the thylakoid membranes. They capture light energy and excite electrons. Two types: o Photosystem II (PSII): Absorbs light at 680 nm (P680); splits water to replace electrons. o Photosystem I (PSI): Absorbs light at 700 nm (P700); accepts electrons from the electron transport chain. Light-Dependent Reactions Location: Thylakoid membranes in chloroplasts. Process: o Photon Absorption: Light energy is absorbed by chlorophyll, exciting electrons. o Electron Transport Chain (ETC): Excited electrons are transferred through a series of proteins, generating a proton gradient (H+). o ATP and NADPH Production: H+ ions flow back through ATP synthase, creating ATP. Electrons reduce NADP+ to form NADPH. Inputs and Outputs: o Inputs: Light, water (H2O). o Outputs: Oxygen (O2), ATP, NADPH. Calvin Cycle (Light-Independent Reactions)  Location: Stroma of chloroplasts. Process: o Carbon Fixation: CO2 is incorporated into ribulose bisphosphate (RuBP) using the enzyme RuBisCO. o Reduction Phase: ATP and NADPH from light-dependent reactions are used to convert 3-phosphoglycerate (3-PGA) into glyceraldehyde-3-phosphate (G3P), a precursor to glucose. o Regeneration Phase: Some G3P molecules are used to regenerate RuBP, allowing the cycle to continue. Inputs and Outputs: o Inputs: CO2, ATP, NADPH. o Outputs: G3P (sugar precursors). Role of Chemiosmosis Chemiosmosis: The process by which H+ ions flow down their concentration gradient through ATP synthase, driving the conversion of ADP and inorganic phosphate (Pi) into ATP. This process is crucial in both light-dependent reactions and cellular respiration. Concept Check Questions 1. Describe light, pigments, chlorophyll (properties, function): o Light is electromagnetic radiation that plants utilize. Pigments absorb specific wavelengths; chlorophyll a is the main pigment, while chlorophyll b and carotenoids assist in capturing a wider range of light energy. 2. Compare components of light-dependent and light-independent reactions: o Light-Dependent: Occurs in thylakoids, requires sunlight, produces ATP and NADPH, and releases O2. o Light-Independent (Calvin Cycle): Occurs in the stroma, does not require sunlight directly, uses ATP and NADPH to synthesize sugars. 3. Describe a photosystem and its role: o A photosystem is a complex of pigments and proteins that captures light energy and excites electrons for the electron transport chain, facilitating ATP and NADPH production. 4. Explain the role of chemiosmosis in photosynthesis: o Chemiosmosis generates ATP by utilizing the proton gradient created during electron transport, allowing H+ ions to flow through ATP synthase.  5. Describe inputs and outputs of light-dependent vs light-independent reactions: o Light-Dependent: Inputs: Light, H2O; Outputs: ATP, NADPH, O2. o Light-Independent: Inputs: CO2, ATP, NADPH; Outputs: G3P (sugar precursors). Overview of Cellular Energy Processes ATP (Adenosine Triphosphate) Usage: A human at rest uses about 45 kg (99 lbs) of ATP daily but typically has a surplus of less than 1 gram at any given moment. Production: Each cell generates and consumes approximately 10 million molecules of ATP per second. Structure: ATP is an RNA nucleotide consisting of: o Adenine o Ribose (sugar) o Three phosphate groups Function: ATP acts as the energy currency of the cell, allowing for the transport and storage of energy to support endergonic (energy-consuming) reactions. When ATP is used, it can lose one or two phosphates, forming ADP (adenosine diphosphate) or AMP (adenosine monophosphate). Fermentation Process: Fermentation begins with glycolysis, generating 2 ATP and reducing NAD+ to NADH. In the absence of oxygen, NADH is oxidized back to NAD+ to continue glycolysis. Types: o Lactic Acid Fermentation: Pyruvic acid from glycolysis is converted to lactic acid and NAD+. This occurs in muscle cells and some bacteria (e.g., yogurt production). o Alcoholic Fermentation: Pyruvic acid is converted to ethanol and carbon dioxide, primarily performed by yeasts and some bacteria. Redox Reactions Definition: Oxidation-reduction (redox) reactions involve the transfer of electrons between compounds. o Oxidation: Loss of electrons. o Reduction: Gain of electrons. Importance: These reactions are crucial for energy production in cellular respiration and photosynthesis. Electron Transport Chain (ETC) Location: In cellular respiration, it occurs in the inner mitochondrial membrane; in photosynthesis, in the thylakoid membrane. Function: The ETC consists of a series of proteins and organic molecules that pass electrons in energy-releasing steps, creating an electrochemical gradient (proton gradient) that is used to produce ATP through chemiosmosis. Comparison of Cellular Processes Aerobic vs. Anaerobic Respiration Aerobic Respiration: Uses oxygen, producing approximately 38 ATP per glucose molecule. Anaerobic Respiration (Fermentation): Produces only 2 ATP per glucose molecule, utilizing processes like lactic acid or alcoholic fermentation. Chemiosmosis Definition: The movement of protons across a membrane, generating ATP. In Cellular Respiration: Protons are pumped from the mitochondrial matrix to the intermembrane space, creating a gradient that drives ATP synthase. In Photosynthesis: Protons accumulate in the thylakoid lumen, and ATP is generated as they flow back into the stroma through ATP synthase. Photophosphorylation vs. Oxidative Phosphorylation Similarities: o Both involve an electron transport chain and the creation of a proton gradient that drives ATP synthesis through ATP synthase. Differences: o Source of Electrons: Water in photosynthesis vs. NADH/FADH2 in oxidative phosphorylation. o Direction of Proton Pumping: Into the thylakoid space for photosynthesis vs. out of the mitochondrial matrix for oxidative phosphorylation. o Terminal Electron Acceptor: NADP+ in photosynthesis vs. O2 in oxidative phosphorylation. Key Questions 1. Describe oxidation-reduction reactions and their importance: o Redox reactions are essential for transferring energy through electron transfers in cellular respiration and photosynthesis, enabling ATP production. 2. Explain why photosynthesis is endergonic and cellular respiration is exergonic:  o Photosynthesis requires energy input (endergonic) to convert CO2 and water into glucose, while cellular respiration releases energy (exergonic) by breaking down glucose. 3. Compare the electron transport chain and chemiosmosis in cellular respiration and photosynthesis: o Both processes involve a chain of proteins transferring electrons, generating a proton gradient to drive ATP synthesis. The main difference lies in the source of electrons and the location of the processes. 4. Describe the generation of oxygen in photosynthesis and water in cellular respiration: o In photosynthesis, oxygen is produced from the splitting of water molecules during the light-dependent reactions. In cellular respiration, water is formed when electrons combine with oxygen and protons at the end of the ETC. 5. Compare NAD+ and NADH; NADP+ and NADPH: o NAD+ is the oxidized form; NADH is the reduced form (carries electrons). Similarly, NADP+ is the oxidized form for photosynthesis, while NADPH is the reduced form used in the Calvin cycle. Here’s a summary of the key points about cell division and the cell cycle: Cell Growth Limits Diffusion: Effective over short distances but inefficient for larger organisms, preventing them from being one giant cell. Cell Division Purpose: Essential for growth, development, and injury repair. Types of Division: o Mitosis: Asexual division resulting in two identical daughter cells, important for growth and repair. o Meiosis: Produces haploid gametes for sexual reproduction, contributing to genetic variation. Cell Division Rate Cells divide at different rates. For example, gut lining cells divide constantly, while skin cells are replaced approximately every 28-40 days. Chromatin vs. Chromosomes Chromatin: Unwound DNA present during normal cell function. Chromosomes: Condensed DNA present during cell division. Prokaryotic vs. Eukaryotic Cell Division Prokaryotes: Divide via binary fission (asexual, identical cells). Eukaryotes: Use mitosis (asexual, identical cells) and meiosis (sexual, genetically diverse cells). Advantages/Disadvantages of Reproduction Asexual: o Pros: Many offspring, low energy. o Cons: Little genetic variation. Sexual: o Pros: Unique offspring, higher adaptability. o Cons: Fewer offspring, higher energy requirement. Eukaryotic Cell Cycle 1. Interphase: o G1 (Gap 1): Cell growth and organelle synthesis. o S (Synthesis): DNA replication. o G2 (Gap 2): Final preparations for mitosis. 2. M-phase (Mitotic): o Involves mitosis (nuclear division) and cytokinesis (cytoplasm division). o Phases of Mitosis: ▪ Prophase: Chromosomes condense, nuclear envelope breaks down. ▪ Metaphase: Chromosomes align at the metaphase plate. ▪ Anaphase: Sister chromatids separate. ▪ Telophase: Nuclear envelopes reform around chromosomes. G0 Phase Cells can exit the cycle into a quiescent state (G0), remaining inactive until signaled to re- enter the cycle. Checkpoints in the Cell Cycle G1 Checkpoint: Checks for DNA damage and conditions for division. G2 Checkpoint: Ensures DNA is replicated and undamaged.  M Checkpoint: Confirms all chromosomes are properly attached to the spindle. Cytokinesis Animal Cells: Cleavage furrow pinches the cell. Plant Cells: A cell plate forms, leading to a new cell wall. Ploidy Somatic Cells: Diploid (2n), containing two sets of chromosomes. Gametes: Haploid (1n), containing one set of chromosomes. Concept Check Differentiate between binary fission, mitosis, and meiosis. Compare asexual and sexual reproduction. Explain the stages of the cell cycle and mitosis. Discuss haploid vs. diploid cells and their relation to cell division. Describe cytokinesis in plant and animal cells. Understand the role of checkpoints in the cell cycle. Here’s a comprehensive overview of the key concepts related to DNA in eukaryotes, meiosis, and sexual reproduction: DNA in Eukaryotes Location: Found in the nucleus. Structure: DNA is wound around histone proteins, forming chromatin (loose, active form) and chromosomes (tight, condensed form during cell division). Chromatid: A single strand of DNA; two chromatids form a chromosome, connected at the centromere. Chromosomes and Homologous Chromosomes Homologous Chromosomes: A pair of chromosomes (one from each parent) with the same gene sequence, chromosomal length, and centromere position. Human Chromosomes: 46 total chromosomes (22 pairs of autosomes + 1 pair of sex chromosomes, X or Y). Mitosis vs. Meiosis Mitosis: o Type: Asexual reproduction.  o Process: DNA replication leads to the formation of two identical diploid cells (2n). o Outcome: Sister chromatids separate. Meiosis: o Type: Sexual reproduction. o Process: Two rounds of division produce four genetically diverse haploid cells (1n). o Stages: ▪ Meiosis I: Separates homologous chromosomes, leading to genetic reduction. ▪ Meiosis II: Separates sister chromatids, similar to mitosis. Genetic Variation in Meiosis Crossing Over: Occurs during prophase I when non-sister chromatids exchange genetic material, creating new allelic combinations. Independent Assortment: During metaphase I, homologous pairs orient randomly, resulting in diverse gametes. Gametogenesis Spermatogenesis: Meiosis produces four equal sperm cells. Oogenesis: Meiosis produces one egg and three polar bodies (unequal distribution of cytoplasm). Zygotes and Chromosomes Zygote Formation: Fusion of haploid sperm (1n) and egg (1n) during fertilization forms a diploid zygote (2n). Karyotype: A visual representation of an individual's complete set of chromosomes, arranged in numerical order. Sexual Reproduction Diagram Terms to Complete the Diagram: o Meiosis o Fertilization o Haploid o Diploid o Egg (n) o Sperm (n)  o Ovary (produces egg) o Testis (produces sperm) o Zygote (2n) o Multicellular diploid adults (2n = 46) Learning Objectives Meiosis Steps: Understand the process and purpose, including crossing over. Chromatid vs. Homologous Chromosomes: Identify where they are in meiosis. Zygote vs. Gamete: Understand formation processes. Mitosis vs. Meiosis: Compare DNA replication and ploidy. Crossing Over: Explain its significance for genetic diversity. Germ-Line Cells: Understand their role in gametogenesis. Chromosome Duplication and Separation: Describe the processes in both mitosis and meiosis. DNA Structure and Function Euchromatin vs. Heterochromatin: o Euchromatin: Loosely wound DNA, transcriptionally active. o Heterochromatin: Tightly wound DNA, not transcriptionally active. DNA Replication and Mutations Mutations: o Somatic cell mutations are not passed to offspring. o Gamete mutations can be inherited. Genetic Disorders Trisomy 21: Three copies of chromosome 21, leading to developmental issues; an autosomal disorder. Twins Identical (Monozygotic): One fertilized egg splits into two. Fraternal (Dizygotic): Two separate eggs fertilized by different sperm. Genetic Variation Crossing Over: Occurs during prophase I of meiosis, leading to genetic variation.  Independent Assortment: Homologous chromosomes orient randomly during metaphase I, increasing diversity. Mendelian Genetics Mendel's Experiments: Demonstrated dominant and recessive traits using pea plants. Genotype vs. Phenotype: o Genotype: Genetic makeup (e.g., Aa, AA, aa). o Phenotype: Observable traits (e.g., tall, short). Types of Dominance Complete Dominance: One trait masks another (e.g., violet over white flowers). Incomplete Dominance: Blending of traits (e.g., red and white flowers producing pink). Codominance: Both traits are fully expressed (e.g., AB blood type). Inheritance Patterns Multiple Alleles: More than two allele options for a gene (e.g., ABO blood types). Polygenic Traits: Traits controlled by multiple genes (e.g., height, skin color). Sex-Linked Traits: Traits associated with genes on sex chromosomes (e.g., color blindness). Test Cross Used to determine if an organism with a dominant phenotype is homozygous or heterozygous by crossing it with a homozygous recessive organism. Probability in Genetics Product Rule: Probability of multiple independent events occurring together. Sum Rule: Probability of either of multiple mutually exclusive events occurring. Advanced Concepts Pleiotropy: One gene influences multiple traits (e.g., cystic fibrosis). Epistasis: One gene masks the expression of another. Blood Types Universal Donor: O type (no antigens). Universal Recipient: AB type (no antibodies against A or B antigens). Heterozygote Advantage  The condition where heterozygous individuals have a survival advantage (e.g., sickle-cell trait provides malaria resistance). Healthy Carriers Definition: Healthy carriers are individuals who possess one copy of a recessive allele for a genetic disorder but do not exhibit symptoms of the disorder themselves. They are often heterozygous (Aa), where "A" is the dominant allele and "a" is the recessive allele. Recessive Disorders Example: Cystic Fibrosis Genotypes: o Carriers: Aa (healthy) o Affected: aa (has the disorder) Inheritance Odds for Carrier Parents (Aa x Aa): o 25% chance of having an affected child (aa) o 50% chance of having a healthy carrier child (Aa) o 25% chance of having a healthy child without the allele (AA) Carrier with Affected Individual (Aa x aa): 50% chance of being a healthy carrier (Aa) 50% chance of having the disorder (aa) Dominant Disorders Examples: Huntington's disease, achondroplastic dwarfism, polydactyly. Individuals with one dominant allele (Aa or AA) express the disorder. If one parent has a dominant disorder (Aa) and the other is unaffected (aa): o 50% chance of inheriting the disorder (Aa) o 50% chance of being normal (aa) Mendel’s Laws 1. Law of Independent Assortment: Chromosomes align randomly during meiosis, leading to different combinations of alleles. 2. Law of Segregation: During gamete formation, alleles for each gene segregate from each other. Test Cross  Purpose: To determine the genotype of an individual showing a dominant trait. Involves breeding the individual with a homozygous recessive individual to observe offspring. Monohybrid and Dihybrid Crosses Monohybrid Cross: Involves one trait (e.g., YY x yy). o F1 Generation: All heterozygous (Yy). o F2 Generation: 3:1 ratio (3 yellow: 1 green). Dihybrid Cross: Involves two traits (e.g., AaBb x AaBb). o Use FOIL method to determine possible gametes. Genetic Interactions Pleiotropy: One gene affects multiple traits. Epistasis: One gene masks or modifies the expression of another. Pedigree Analysis A diagram showing the inheritance of traits in a family across generations. It helps identify carriers and affected individuals. X-Inactivation Occurs in female mammals to balance gene dosage between XX females and XY males. One X chromosome is randomly inactivated, forming a Barr Body. In tortoiseshell cats, this results in a mix of orange and black fur due to X-linked fur color genes. Genetic Variation Causes: Mutations, random mating, fertilization, crossing over, independent assortment. Important for adaptation and survival of populations. Nondisjunction The failure of chromosomes to separate properly during cell division, leading to an abnormal number of chromosomes (e.g., trisomy). Sex-Linked Inheritance X-linked disorders are more common in males since they have only one X chromosome. Males inherit X-linked traits from their mothers. Concept Check 1. Test Cross vs. Dihybrid Cross: A test cross reveals an individual's genotype by crossing with a homozygous recessive. A dihybrid cross examines two traits simultaneously. 2. X Inactivation Importance: It equalizes gene expression between sexes and prevents overexpression of X-linked genes in females. 3. Calico Cats: Almost always female due to X-linked color genes and random X inactivation. 4. Somatic vs. Sex-Linked Mutations: Somatic mutations occur in non-germline cells; sex- linked mutations affect genes on sex chromosomes. 5. X-Inactivation Explanation: It occurs to balance gene dosage between sexes and is stable in subsequent cell generations. 6. Mendel’s Laws Connection to Meiosis: They explain how genes segregate and assort independently during gamete formation.