Cell Structure PDF

# CELL STRUCTURE ## **Definition** > The basic structural and functional unit of life. * **Cellular organization:** New cells arise from existing ones via passing genetic material from one cell to another. * **Importance of organization:** If a cell dies, the organism dies because of the organi...

# CELL STRUCTURE ## **Definition** > The basic structural and functional unit of life. * **Cellular organization:** New cells arise from existing ones via passing genetic material from one cell to another. * **Importance of organization:** If a cell dies, the organism dies because of the organization of the cells within the organism. ## **Hierarchy of Organization:** * **Cells** → **Tissues** → **Organs**→ **Systems** → **Organisms** ## **Types of Cells:** 1. **Prokaryotes** 2. **Eukaryotes** ## **Living Organisms** * Living organisms are either made up of prokaryotic or eukaryotic cells. * **Prokaryotes:** Have a primitive karyon-nucleus. * **Eukaryotes:** Have a true karyon-nucleus (the "proper nucleus"). ## **True Nucleus** * **Size:** 10 - 100 μm (size of a eukaryotic cell) * **Structure:** Enveloped in a double membrane. * **DNA:** * Linear * Wrapped around a protein called **Histone**. * Histone is contained in the **chromosome**. * DNA neither lies freely nor naked in the cytoplasm. ### **DNA Packaging** * **Problem:** DNA (10 m) is too large to fit into the 10 μm nucleus. * **Solution:** * DNA is wrapped around a protein called **histone**. * Multiple histones wrap around the DNA to form a **nucleosome**. * Nucleosomes are further compacted into **chromatin threads**, which are collectively called **chromosomes**. ## **Prokaryotic Cells** * **Nucleus:** No true nucleus. * **DNA:** Circular, does not wrap around any protein. * **DNA Location:** Lies freely or naked in the cytoplasm, * **Organelles:** Few organelles are found, and none are membrane-bound. ## **Living Organisms** * **Prokaryotes:** * Prokaryotae: All bacteria * **Eukaryotes:** * Protoctista: Amoeba, plasmodium, etc. * Fungi: Yeast * Plantae: Plants * Animalia: Animals ## **Comparing Prokaryotes and Eukaryotes** | Feature | Prokaryotes | Eukaryotes | |:----------------------|:------------------|:----------------------| | **Size** | 1 - 10 μm | 10 - 100 μm | | **Nucleus** | No true nucleus | True nucleus & nucleolus present| | **DNA** | Circular DNA | Linear DNA | | **DNA wrapping** | Not wrapped | Wrapped around histones | | **Metabolic Activity** | Low | Increased | ## **Features of Prokaryotes** * **Ribosomes:** * Present and freely distributed * Not enveloped * Produce proteins * **Size:** The ribosome size for prokaryotes is 18nm, therefore they are called **70s ribosomes**. * **Organelles:** * Few organelles * Non-membrane bounded * **DNA:** Located in chromosomes. * **Cell Wall:** Present in all prokaryotes * Composed of **murein** or **peptidoglycan**. * **ER:** Absent * **Mitochondria:** Absent * **Respiration:** Specialized organelles for respiration are absent. * **Division:** Divide through a process called **binary fission** (they do not have a nucleus). ## **Features of Eukaryotes** * **Ribosomes:** * Present in cytoplasm * Membrane bounded (most, not all) * **Size:** The ribosome size for eukaryotes is 22nm, therefore they are called **80s ribosomes** * **Cell Wall:** Present only in fungi and plant cells. * **Fungi:** Cell walls made of **chitin**. * **Plants:** Cell walls made of **cellulose**. * **ER:** Present * **Mitochondria:** Present ## **Division** * **Prokaryotes:** Binary fission. * **Eukaryotes:** Mitosis or meiosis (both through nuclear division). ## **Bacterial Cell** ### **Structure** * **Flagella:** For movement. * **Plasma membrane:** * Enfolded * Used to transport nutrients. * **Ribosomes:** 70s ribosomes. * **DNA:** * Carries genetic information for proteins and other cell functions. * **Cell membrane:** * Encloses cell * Controls what enters and leaves. * **Slimy capsule:** Provides additional protection * **Pilli:** * Aid in adhesion to other cells. * Help with binding. * **Plasmid:** * Carries additional genetic information. * Can be passed to other bacteria. * **Cytoplasm:** * Contains all the organelles and other chemicals within the cell. * Glycogen granules and lipid droplets are present and used for storage. ### **Photosynthesis in Bacteria** * If bacteria perform photosynthesis, the cell membrane is enfolding to contain **bacterial chlorophyll.** ### **Transfer of Plasmids** * Plasmids can be transferred through pilli. Pilli from two bacteria link, and the plasmid passes through the pilli. ## **Eukaryotes** ### **Animal cells** * **Light Microscopy:** * **Cell membrane:** Encloses cytoplasm * **Cytoplasm:** Contains all the organelles. * **Glycogen granules:** Store carbohydrates. * **Centriole:** Aid in chromosome movement. * **Chromatin:** DNA associated with proteins. * **Nucleoplasm:** The fluid inside the nucleus. * **Nuclear membrane:** Encloses the nucleus. * **Nucleolus:** The site of ribosome synthesis. * **Mitochondria:** Carry out cellular respiration. * **Golgi Apparatus:** Modifies and packages proteins. * **Electron Microscopy:** An electron microscope provides higher resolution than a light microscope, allowing us to see more details within a cell. * **Microvilli:** Increase the surface area for absorption. * **RER:** Rough endoplasmic reticulum. Rough because it is studded with ribosomes. * **SER:** Smooth endoplasmic reticulum. Smooth because it has no ribosomes. * **Nucleoplasm:** Contains the nucleus and nucleolus. * **Nuclear pores:** Allow transport in and out of the nucleus. * **Lysosomes:** Digestive organelles. * **Cell membrane:** Encloses the cytoplasm. * **Microtubules:** Aid in cell structure. * **Centrioles:** Aid in chromosome movement. * **Free 80s Ribosomes:** Synthesize proteins. * **Mitochondria:** Carry out cellular respiration. * **Golgi Apparatus:** Modifies and packages proteins. * **Golgi Vesicles:** Transport proteins throughout the cell. ### **Plant Cells** * **Light microscopy:** * **Cell membrane:** Encloses cytoplasm. * **Cell wall:** Surrounds cell membrane and provides structure. * **Cytoplasm:** Contains all the organelles. * **Middle Lamella:** The layer between the cell wall and plasma membrane. * **Plasmodesmata:** Channels between plant cells for communication and transport. * **Chloroplast:** Contains chlorophyll for photosynthesis. * **Mitochondria:** Carries out the process of cellular respiration. * **Nucleus:** Contains DNA and the nucleolus. * **Large Central Vacuole:** A large fluid filled vessel that helps support the plant. * **Starch granules:** Store carbohydrates (used for energy). * **Golgi Apparatus:** Modifies and packages proteins. * **Electron microscopy:** * **Cell membrane:** Encloses cytoplasm. * **Cell wall:** Surrounds cell membrane and provides structure. * **Mitochondria:** Carries out the process of cellular respiration. * **Nucleus:** Contains DNA and the nucleolus. * **Large Central Vacuole:** A large fluid filled vessel that helps support the plant. * **Starch granules:** Store carbohydrates (used for energy). * **Chloroplast:** Contains chlorophyll for photosynthesis. * **Golgi Apparatus:** Modifies and packages proteins. * **Free 80s Ribosomes:** Synthesize proteins. * **SER:** Smooth endoplasmic reticulum. * **RER:** Rough endoplasmic reticulum. * **Golgi Vesicles:** Transport proteins throughout the cell. ## **Nucleus** * **Function:** Serves as the control center of the cell. * **Structure:** * Spherical * Size = 10-20 μm * Contains DNA. * **Importance:** Very important because it houses the DNA (chromatin). * **Nucleoplasm:** The ground substance of the nucleus, which is there to protect the DNA. * **DNA:** Does not mix with cytoplasm, even though nuclear pores are present because nucleoplasm is more viscous. * **Nuclear pores:** DNA cannot pass through the nuclear pores because the DNA is in the form of chromatin, which is a large, compacted piece of DNA. * **Function:** * **Entry/Exit:** Entry: proteins, partially assembled ribosomes. Exit: mRNAs * **Ribosome synthesis:** Provides the site for ribosome synthesis. * **Protection of DNA** * **RNA synthesis** ## **Chloroplast** * **Function:** Perform the process of photosynthesis. * **Structure:** * 3-10 μm in size * 1 μm thick * Biconvex disk. * Enveloped * **Granna:** Stacks of thylakoids. * **Lamella:** Connects granna. * **Stroma:** The fluid filling the space within chloroplast. * Inner membranes: Have 70s ribosomes and circular DNA. * **Origin:** Endosymbiosis. * **Theory:** Chloroplasts were once prokaryotic bacteria that lived as symbiotic organisms (mutualism) in the eukaryotic cell. Then they became their own organism and became organelles of the eukaryotic cell. * **Internal Membrane network:** * **Thylakoids:** Flattened fluid filled sacs. * **Granna:** stacks of thylakoids. * **Lamella:** Connect granna. * **Products of light-dependent reactions:** ATP and reduced NADP. ## **Mitochondria** * **Structure:** * Rod-like structure * Double membrane * 1- 3 μm in length, 0.5-1 μm in diameter * Inner membrane creates folds called **cristae** (increases surface area) * Contains circular DNA and 70s ribosomes * **Origin:** Endosymbiosis * **Function:** Carry out aerobic respiration to produce ATP (ADP + Pi) * **Location**: Found in both plant and animal cells. * **Stages of Respiration:** 1. **Glycolysis:** Occurs in the cytoplasm. 2. **Link reactions:** Occurs in the matrix of the mitochondria. 3. **Kreb's Cycle:** Occurs in the matrix of the mitochondria. 4. **Oxidative phosphorylation:** Occurs in the cristae of the mitochondria. ## **Endoplasmic Reticulum (ER)** * **Structure:** * A network of tubules and flattened sacs (cisternae). * Enclosed in a membrane. * Extends throughout the cytoplasm. * **Types:** * **Rough ER (RER):** Studded with ribosomes. * **Smooth ER (SER):** Does not contain ribosomes. * **Function:** * **RER:** * Protein synthesis * Transport proteins * **SER:** * Lipids and steroid synthesis. * Transport lipids and steroids. ## **Ribosomes** * **Structure:** Small in mass, but are present in large quantities in all cells. * **Function:** Synthesize proteins. * **Types:** * **70S:** Found in prokaryotes, 18 nm in size. * **80S:** Found in eukaryotes, 22 nm in size. * **Sedimentation:** The *sedimentation rate* is the rate at which an organelle will sediment out of a solution during a centrifugation process. The higher the sedimentation rate, the heavier the cell. * **Polysome:** A group of ribosomes bound together to synthesize multiple proteins. ## **Golgi Apparatus** * **Structure:** Stacks of flattened, membrane bound sacs (cisternae) and associated vesicles. * **Function:** * Modify and package proteins. * Store and transport proteins. * Store and transport lipids and steroids. * Remove methionine, the first amino acid of a protein chain. * Attach carbohydrate antennae to some proteins. * Synthesize glycoproteins, which aid in making cell membranes. * Synthesize enzymes for making cell walls in plants. * Synthesize lysosomes in animal cells. * Produce secretory enzymes in animal cells. ### **Methionine** The first amino acid in each protein chain is methionine. The ribosomes will not start making proteins until they encounter a methionine molecule. The Golgi apparatus removes methionine from a protein to make the protein functional. ## **Lysosomes** * **Function:** * Cellular digestion. * Secretion (exocytosis) * **Structure:** * Single-membrane bound sac. * 0.1 - 0.5 μm in size, 1.0 μm in diameter. * Acidic environment (because the enzymes in lysosomes are only active in an acidic environment). * **Location:** Animal cells. * **Origin:** Vesicles bud off from the Golgi apparatus * **Enzymes:** Contain enzymes that break down lipids, proteins, carbohydrates, and nucleic acids. ## **Functions of Lysosomes** 1. **Digestion of food:** For example, white blood cells (WBCs) will digest bacteria. 2. **Autophagy:** Destroy worn out or damaged organelles. 3. **Autolysis:** The lysosomes release their contents and cause the cell to self-destruct. For example, extrauterine cells are destroyed after a baby is born. ## **Cell Wall** * **Location:** Found in prokaryotes (murein or peptidoglycan), fungi (chitin), and plants (cellulose). * **Structure:** * Matrix: made up of pectin and hemicellulose. * Cellulose fibers. * **Function:** * Provides structural support and shape. * Helps the cells retain their definite shape. * Helps the cells maintain osmotic potential (lets water enter the cell, but not exceed the cell's structural integrity). ## **Cell Membrane** * **Function:** * Controls the movement of substances in and out of the cell. * Partially permeable. * **Structure:** A thin, selectively permeable membrane. * **Middle Lamella:** * The layer between the cell walls of two cells. * Made of calcium and magnesium pectin/pectin salts. ## **Plasmodesmata** * **Structure:** * Pores that run through the cell wall. * Allow communication between cells. * **Symplast:** The system of interconnected cell cytoplasms. ## **Microtubules** * **Structure:** * Hollow, tube-like structures. * Rigid. * 25 nm in diameter, but very long. * Made of tubulin. * **Location:** Found throughout the cytoplasm. * **Function:** * Part of the **cytoskeleton** (provides shape, support, and strength). * Aid in the **intracellular movement** of organelles. * Aid in **cell locomotion** * Form **spindle fibers** to pull chromatids apart during cell division. ## **Centrioles** * **Location:** Found in animal cells and some algae and fungi. * **Structure:** * Found in pairs at right angles to one another * Made up of nine microtubule triplets. * 500 nm in length. * 200 nm in diameter. * **Function:** * Act as **microtubule organizing centers (MTOCs)** * Aid in the formation of the **spindle fibers** during cell division. * Aid in the formation of **basal bodies**. * **Basal bodies:** * Special types of centrioles located at the base of cilia and flagella. * Aid in assembling cilia and flagella. ## **Microscopy** ### **Light Microscopy** * **Magnification:** The number of times an object is magnified (the image size is greater than the actual size of the object). * **Procedure:** 1. Calculate the image size (drawing). 2. Calculate the actual size. 3. Determine the magnification (image size / actual size). * **Resolution:** The ability to distinguish between two points. The higher the resolution, the closer two points can be and still be viewed as separate entities. * **Resolution of Light Microscopy:** 200 nm (or 0.2 µm) * Therefore, objects smaller than 200 nm cannot be seen with light microscopy. * Ribosomes (~22nm) * Lysosomes (~100nm) * **Advantages:** * Inexpensive * Simple operation * No special preparation needed. * **Disadvantages:** * Limited resolution * Limited depth of field. ### **Electron Microscopy** * **Types:** * **Transmission Electron Microscopy (TEM)** * **Scanning Electron Microscopy (SEM)** * **Source of energy:** Electrons. * **Resolution:** Much higher resolution. * TEM: 8 nm * SEM: 10 nm * **Advantages:** * Very high resolution. * **Disadvantages:** * Requires specialized equipment * Can only view dead specimens. * Very thin specimens are needed (requires special equipment to slice specimens). * **Procedure:** 1. Specimen is dehydrated and coated with a thin layer of metal atoms. 2. Electrons are emitted from a tungsten filament. 3. Electron beams are focused with electromagnetic lenses. 4. When the electron beam hits the specimen, some electrons are scattered, and others pass through. 5. The scattered electrons are detected by a fluorescent screen. 6. The image is produced based on the pattern of the scattered electrons. * **Types:** * **Transmission Electron Microscopy (TEM):** Used for viewing thin sections of specimens. * **Scanning Electron Microscopy (SEM):** Used for viewing the surface of specimens. ## **Virus** * **General structure:** * No cell membrane * No cytoplasm * No organelles * **Structure:** * **Capsid:** A protein coat. * **Capsomere:** Each individual protein unit that makes up the capsid. * **Genetic material:** DNA or RNA * **Reproduction:** * **Replication** * Uses a host cell's machinery to reproduce, as viruses cannot replicate independently. * Invade host cells and take over the host's mechanisms to reproduce. ## **Vacuoles** * **Location:** Plant Cells * **Structure:** * Large, fluid-filled sacs. * Surrounded by a membrane called the **tonoplast.** * **Function:** * Provide storage for: water, ions, sugars, pigments. * Helps maintain turgor pressure (structural support in plants). * Push chloroplasts to the cell's edge. * ## **Organelles involved in Making ATP** * **Chloroplasts:** Found in plants * **Mitochondria:** Found in both plants and animals. ## **Intracellular Transport** * The movement of vesicles (or other organelles) throughout an animal cell requires the **RER** and the **cytoskeleton.** * The **RER** aids in the production and transport of proteins. * **The cytoskeleton** acts as a framework and provides pathways for the movement of organelles. ## **Other Interesting Facts** * **Svedberg Unit:** A unit for measuring the sedimentation rate. * **Cytoskeleton:** The framework of a cell that provides shape, support, and strength. * **Centrosome:** The region in a cell where the centrioles are located. * **Symplast:** The system of interconnected cell cytoplasms. * **Tonoplast:** The membrane surrounding a vacuole.