Plant Cytology PDF

# Plant Cytology and Physiology The minimal cell should have three things: 1. The oily film separating the cell from its environment (membrane). 2. Protein-synthesizing apparatus (from DNA to RNA and proteins). 3. Space designated for all other chemical reactions (jellylike cytoplasm). ## Prokaryot...

# Plant Cytology and Physiology The minimal cell should have three things: 1. The oily film separating the cell from its environment (membrane). 2. Protein-synthesizing apparatus (from DNA to RNA and proteins). 3. Space designated for all other chemical reactions (jellylike cytoplasm). ## Prokaryotic Cell - DNA surrounded by the cytoplasm - Flagella (rotating protein structure) - Cell wall - Vesicles - Membrane folds / pockets ## Eukaryotic Cells - Nucleus: DNA in a membrane-bound - Vacuoles - Chloroplasts - Mitochondria: break down organic molecules into carbon dioxide and water in a process known as oxidative respiration. - Ribosomes, found in the cytoplasm, help to synthesize proteins. - The endoplasmic reticulum (ER), where proteins are synthesized, packaged, and transported - Golgi apparatus directs proteins and other substances to the part of the cell where they need to go. - Cell Wall: surrounds the cell and limits how far the cell can expand due to osmosis ## Cell Membrane The cell membrane consists of 2 layers: 1. One end of each layer is polar and hydrophilic, while the other end is hydrophobic. These layers are made with phospholipid. (Phospholipids are typical lipids but have a polar head with phosphoric acid and two hydrophobic, non-polar tails). 2. Other components (lipids like cholesterol in animal cells only and chlorophyll in plant cells) and proteins and carbohydrates. ## Figure 1: Prokaryotic Cell This diagram depicts a prokaryotic cell with the following labeled components: - Cell wall - Membrane - Vesicle (vacuole) - Membrane pocket - Circular DNA - Prokaryotic flagella ## Figure 2: Membrane and Phospholipids This diagram illustrates the structure of a cell membrane, composed of two phospholipid layers, with the following details: - The hydrophilic heads of the phospholipids face outward, while the hydrophobic tails are oriented inwards. - The hydrophilic head is depicted with a blue circle, and the hydrophobic tail is represented with a red and black line. ## Vacuole(s) - **Osmosis** is the movement of solvent molecules through a permeable membrane into a region of higher solute concentration from a low concentration region. - **Osmosis** may result in uncontrollable expansion of a cell. Cells without cell walls must find a way to pump out excess water. - **Vacuole(s)** is/are the large vesicle(s) which can do a variety of things for the cell, for instance store nutrients, accumulate ions, or become a place to store wastes. It plays an important role in **turgor** (cell rigidity). - **Turgor pressure** is the combined pressure of the cell and vacuoles wall that supports the shape of the cell. ## Figure 3: Plant Cell Structure This diagram depicts a plant cell with the following labeled components: - Golgi Vesicles - Ribosome - Smooth ER (no ribosomes) - Nucleolus - Nucleus - Rough ER (endoplasmic reticulum) - Large central vacuole - Amyloplast (starch grain) - Cell wall - Cell membrane - Golgi apparatus - Chloroplast - Vacuole membrane - Raphide crystal - Druse crystal - Mitochondrion - Cytoplasm ## Mitochondria and Chloroplasts - To escape from competition, cells which were prokaryotic became larger. - To facilitate communication between all parts of this larger cell, they developed cytoplasm mobility using actin protein. - In turn, this mobility resulted in acquiring phagocytosis. - **Phagocytosis** is when a large cell changes shape and can engulf other cells like bacteria and digested bacteria in lysosomes. ## Phagocytosis - **Phagocytosis** of smaller cells mainly provides food and ATP as a source of energy. - **Mitochondria** is some engulfed cells which were not digested, and turned out to be useful in providing ATP. Due to natural selection, this is called **symbiogenesis**, or the formation of two separate organisms into a single organism. ## Figure 4: Symbiogenetic Origin of Eukaryotic Cell This diagram depicts the symbiogenetic origin of a eukaryotic cell and an algal cell. - The top row illustrates the evolution of a eukaryotic cell with the following steps: 1. A prokaryotic cell engulfs another prokaryotic cell. 2. The engulfed cell becomes a mitochondrion. 3. The cell continues to grow and incorporates more prokaryotic cells. 4. The engulfed cells become chloroplasts. - The bottom row illustrates the evolution of an algal cell with the following steps: 1. Two prokaryotic cells come together. 2. One prokaryotic cell is engulfed by the other, becoming a mitochondrion. ## Mitochondria - **Mitochondria** produce most of the cytoplasmic ATP. - They are covered with two membranes and contain circular DNA and ribosomes similar to bacterial. - **Mitochondria** could be branched and interconnecting. ## Chloroplasts - **Chloroplasts** synthesize organic compounds. - They store carbohydrates as starch grains. - **Chloroplasts** are covered with two membranes and contain circular DNA and ribosomes similar to bacterial. - **Chloroplasts** have thylakoids, or inner membrane pockets and vesicles and outer stroma. - **Chloroplasts** are normally green because of **chlorophyll**, which converts light energy into chemical energy. - Some **chloroplasts** lose chlorophyll and become transparent, "white", they are called **leucoplasts**. - Other **chloroplasts** could be red and/or orange **(chromoplasts)**, because they are rich in carotenes and xanthophyls. - These pigments facilitate photosynthesis and are directly responsible for the fall colors of leaves. ## Figure 5: Chloroplast This diagram depicts a chloroplast with the following labeled components: - Stroma lamellae - Inner membrane - Outer membrane - Lumen - Thylakoid - Intermembrane space - Granum - Stroma ## Figure 6: Mitochondria Structural Features This diagram depicts a mitochondrion with the following labeled components: - Cristae - Matrix - Inner membrane - Outer membrane ## Eukaryotic Cells - Eukaryotic cells are typically 10-100 fold larger than prokaryotic so that the size of DNA will increase, and to hold it, the cell will form a nucleus. - Some eukaryotes also captured cyanobacteria (or another photosynthetic eukaryote), which became chloroplasts. These photosynthetic protists are called algae. ## Advantages of Nucleus: - Nucleus protects the DNA by enclosing it. - Prevents alien organisms from transferring their genes. - Improves isolation from these harmful chemicals. - **N.B.** Nucleus formation and symbiogenesis leaded cells to become eukaryotic. ## Cell Wall and Plasmodesmata - Among eukaryotic cells, plant cells are largest. - Plant cells **do not have** well-developed internal cytoskeleton, but the cell wall provides an external one. - There are two stages of development of cell walls: **Primary** and **secondary cell wall**. - The **primary cell wall** is typically flexible, frequently thin and is made of cellulose, different carbohydrates, and proteins. - The **secondary cell wall** contains also lignin and highly hydrophobic suberin. - These chemicals completely block the exchange between the cell and the environment. - Cell with a secondary wall will soon die. - Dead cells can still be useful to plants in many ways, for example as a defense against herbivores, support and water transport. In fact, more than 90% of wood is dead. ## Plasmodesmata: - **Plasmodesmata** are thin cytoplasmic bridges between neighboring cells. (Role for communication). - **Symplast** is the name of the continuous cytoplasm inside of cells. - **Apoplast** are cell walls and space outside the cell where communication and considerable metabolic activity take place. - Both the symplast and apoplast are important to the transportation of nutrients needed by the cell. ## Comparing with Animal Cells: - Comparing with animal cells, plant cells have chloroplasts, vacuoles, cell walls, and plasmodesmata, but they hardly have any phagocytosis and true cytoskeleton. - Animal cells do not photosynthesize (no chloroplasts). - Animals will support the shape of the cell from the cytoskeleton (no need for vacuole turgor system). ## Figure 7: Cytoskeleton Elements This diagram depicts the cytoskeleton elements with the following labeled components: - Cell membrane - Rough endoplasmic reticulum - Ribosome - Mitochondrion - Actin filament - Intermediate filament - Microtubule ## Protein Synthesis from the Nucleus to the Ribosomes - DNA will be converted into RNA by a process called transcription and RNA will be converted to protein by a process called translation. - Translation in non-reversible whereas transcription could be reverted: there are viruses, such as HIV, that can make DNA from RNA with the enzyme called reverse transcriptase. - Ribosomes, which are particles that contain RNA and, synthesize proteins. - The rough endoplasmic reticulum (RER) has ribosomes along its surface, and the proteins they create are either secreted or incorporated into membranes in the cell. ## Photosynthesis - Photosynthesis is produced by CO2 + H2O + Minerals from soil, and light and photosynthesis produce starch. ## Photosynthesis has two Stages - **The First Stage** is a light stage. This stage relates to the intensity of the light. Light reactions depend on the amount of light and water. They produce oxygen and energy in the form of ATP. - **The Second Stage** is the enzymatic (light-independent) stage which relates more with the temperature. Enzymatic reactions depend on carbon dioxide and water. They take energy from the light reactions and produce carbohydrates. ## Light Stage - The light stage participants include photosystems I and II ("chlorophyll"), light, water, ATPase, protons, and a hydrogen carrier (NADP+). - The basic idea of the light stage is that the cell needs ATP to assemble carbon dioxide into sugar which is produced in the enzymatic stage. ## Requirements for Light Stage: 1. To make ATP, the cell needs electrical current. 2. To make this current, the cell needs the difference of electric charge (between thylakoid (vesicle or membrane pocket) and matrix (stroma) compartments of the chloroplast). 4. Positive charges go from outside and stay inside, Negatively charges go from inside to outside. 5. To segregate, the cell needs the energy of sun rays caught by the chlorophyll molecules embedded in the thylakoid membrane. 6. The chlorophyll molecule is non-polar and contains magnesium (Mg). It is easy to excite the chlorophyll molecule with light; excited chlorophyll may release the electron if the energy of light is high enough. ## Figure 8: Light Stage: Chlorophyll + Light; Electron + Proton and NADP+; NADPH This diagram depicts the light stage of photosynthesis with the following details: - Chlorophyll + light are input components. - The result of chlorophyll + light are: - Oxygenated, positively charged chlorophyll (highly reactive) - Electron. - The oxygenated, positively charged chlorophyll (highly reactive) reacts with H2O and creates: - Protons - Oxygen (O2) - Electron. - The protons and the electron react with NADP+ to create NADPH. ## Figure 9: Light Stage: Proton Pump; The Electron Returns to Chlorophyll; Uncharged Chlorophyll; ATP Synthesis; On the Other Side of Membrane This diagram depicts the light stage of photosynthesis with the following details: - The proton pump starts to work as protons (H+) pass along the gradient. - The energy of the passing protons drives ATP synthesis from ADP and Pi (inorganic phosphate). - The electron returns to chlorophyll which creates uncharged chlorophyll. - On the other side of the membrane, these protons make water with hydroxide ions. ## Figure 10: Light Stage: Scheme of the Light Stage of Photosynthesis This diagram depicts the scheme of the light stage of photosynthesis with the following components- - The light stage starts with light, water, NADP+, ADP and results in the accumulation of energy (ATP) and hydrogen (NADPH) with a release of oxygen which is a kind of exhaust gas. - ATP synthase membrane - ADP + Pi - ATP - OH- - H+ + OH- = H2O - H2O - Light energy is produced to drive the process. - P700 & P680 - H+ - Thylakoid - H+ + O2 - e- - NADP+ - NADPH - OH- - H2O = H+ + OH- - Matrix (stroma) ## "Chlorophyll" is Actually Two Photosystems - "Chlorophyll" is actually two photosystems: photosystem II (P680) and photosystem I (P700). - Photosystem II (contains chlorophyll and carotenes) is more important. It splits water, makes a proton gradient and then ATP, and forwards electrons to photosystem I. - Photosystem I contains only chlorophylls and makes NADPH. ## Figure 11: Photosystem I: NADP+ - NADPH; H2O = H+ + OH- - This diagram depicts photosystem I with the following components: - Water is being split, which creates H2O. - P700 & P680 are present - The electron is being moved from the photosystem I to drive the production of NADPH. - H+ is located inside the thylakoid membrane with OH- located outside the membrane. ## Enzymatic Stage - The enzymatic stage has many participants. These include carbon dioxide, hydrogen carrier with hydrogen (NADPH), ATP, ribulose biphosphate (RuBP, or C5), and Rubisco along with some other enzymes.. - The enzymatic stage occurs in the matrix (stroma) of the chloroplast. ## The Enzymatic Stage Steps: 1. CO2 assimilation assimilation with C5 into short-living C6 molecules which require Rubisco as an enzyme. 2. C6 molecule breaks into two C3 molecules phosphoglyceric acid (PGA). 3. PGA will participate in the complex set of reactions which spend NADPH and ATP as sources of hydrogen and energy, respectively, and yields one molecule of glucose (C6H12O6) for every six assimilated molecules of CO2. 4. NADP+, ADP, and Pi will go back to the light stage. 5. RuBP (C5) which will start the new cycle of assimilation. ## Figure 12: Scheme of the Enzymatic Stage of Photosynthesis: - **The diagram depicts the enzymatic stage of photosynthesis with the following components:** - 6CO2 - 6C5 (RuBP) - Rubisco - ATP and NADPH - 6[C6] - 10C3 regroups into 6Cs - 12C3 (PGA) - ADP, Pi, and NADP+ - 2C3 (PGAL) - Glucose (1C6) - The green numbers indicate how carbon is assimilated without changing the amount of RuBP. ## Figure 13: Rubisco is Two-Faced Enzyme - The diagram depicts the different reactions associated with the enzyme rubisco with the following details: - It catalyzes both the normal C3 cycle and photorespiration. - Sugars and ATP are produced during the normal C3 cycle. - Photorespiration produces CO2 and ATP from sugars and RuBP. ## C4 Pathway, - Rubisco is "two-faced" since it also catalyzes photorespiration. - Photorespiration means that plants take oxygen instead of carbon dioxide. - Rubisco catalyzes photorespiration if there is a high concentration of oxygen. - Photorespiration wastes C5 and ATP.