# Unit 2: Biology ## Cellular Biology A person contains roughly 100 trillion cells - Cells are roughly 20 `μm` (micrometre, 10-6 m), around 250 cells / cm ## Cell Theory 1. All living things are composed of cells 2. Cells are the basic units of living organisms 3. All cells came from pre-existing cells ## Eukaryotic versus Prokaryotic Cells `Prokaryotic cell`: Meaning before/lacking nucleus `Eukaryotic cell`: Means complete nucleus |Factors|Prokaryotic|Eukaryotic| |:-----------|:----------|:---------| |DNA|In nucleoid region|Usually in membrane-bound nucleus| |Size|Usually smaller|Usually larger| |Organelles|Not membrane-bound, smaller|Membrane-bound, more complex| |Organization|Usually singlecelled|Often form multicellular organisms| |Metabolism|May not need oxygen|Usually need oxygen| ## Cellular Organelles ### Business Analogy | In a business | In a cell | | ------------- | --------- | | Building | Cytoplasm & Cytoskeleton | | Department Head | Organelles | | Boss | DNA | | Workers | Ribosomes & Enzymes | | Waste management | Lysosomes | | Storage | Vacuoles | | Powerhouse | Chloroplasts & Mitochondria | | Security gate | Cell membrane controls entrance and exit from the cell | | Transportation Department | IMPORT: Cell membranes and vesicles, INTERNAL: Endoplasmic reticulum & vesicles, EXPORT: Golgi apparatus, vesicles, and cell membrane | ### Cell Membrane - Controls what substances enter/leave the cell selectively via various receptors/osmosis - Allows nutrients to enter - Allows waste products to leave - Surrounds and holds other organelles in cell - Interact with outside chemicals (e.g., hormones) ### Nucleus - Holds deoxyribonucleic acid (DNA) in form of `chromatin` - DNA is a double helix that make genes - `Genes` are a complete set of instructions to make a complete product (typically proteins) - `Genes`: one of the many sets of instructions, in your DNA, found on a **chromosome**, for making a functional product (mostly proteins) - `Chromatin` is DNA wrapped tightly in protein - `Chromosomes` are even more tightly wrapped chromatin used in cell division only - Surrounded by a double membrane - Substances enter and exit the nucleus via nuclear pores - Messenger RNA (mRNA) is encoded from DNA and sent to `ribosomes` to produce proteins ### Nucleolus - Dense region of DNA located in the nucleus - This area of DNA is specially for ribosomal DNA (rDNA), or DNA used to make ribosomes - Produce "large" and "small" subunits of ribosomes, which either form complete ribosomes in cytosol or mix with endoplasmic reticulum, forming rough endoplasmic reticulum (RER) - Is *not* surrounded by a membrane, literally is just same as rest of nucleus but denser ### Cytoplasm & Cytosol - `Cytosol` is the fluid cells contain - **All organelles** are suspended in `cytosol` - `Cytoplasm` is the `cytosol` along with everything in a cell, excluding the nucleus ## Endoplasmic Reticulum - The endoplasmic reticulum is a network of tubules and flattened sacs with a "rough" appearance because of the presence of `ribosomes` on the surface - Network of tubules and flattened sacs - **Transport** proteins via cytoskeleton in vesicles ## Rouch Endoplasmic Reticulum - Appears "rough" due to the `ribosomes` attached to its outer surface - Located directly adjacent and attached to nucleus - Located next to `Golgi apparatus` - `Ribosomes` in rough ER synthesize proteins - Only specific proteins are synthesized by ribosomes of rough ER - Proteins synthesized in `ribosomes` of rough ER are always sent to either `Golgi apparatus` via `vesicles` or stay in `rough ER` - `Ribosomes` attach to and leave the `rough ER` regularly - About half the cell's proteins are produced here - **Modify, fold, and fix proteins** ### Functions - **Protein synthesis** - About half of the cell's proteins are made here, by the `ribosomes` - **Protein movement** - Proteins are transported by vesicles throught the cell to other organelles, like the `golgi apparatus` - **Protein "Proof-Reading"** - pre-existing proteins can enter the `rough-ER` for **modification** ## Smooth ER - Does not synthesize proteins - Appears "smooth" due to lack of `ribosomes` - Located directly adjacent and attached to nucleus - Synthesizes lipids (fats, e.g., cholesterol) - Metabolises carbohydrates ## Golgi Apparatus (Golgi Complex) - **Receives, modifies and transports** proteins that were produced by the `rough-E.R` - **Packages** proteins into `vesicles` and sends them `cell membrane` for export ## Lysosome - `White blood` cell uses the cytoskeleton to reach out and swallow up a bacterium, then uses `lysosomes` to break it down - Spherical vesicle that contains `enzymes` - Digests and kills foreign matter which is then excreted - Digests and breaks down old and unused material to be recycled - Digests and breaks down old or non-functional organelles as needed - Only plays a very minor role in cell suicide (`apoptosis`) - If lysosome does rupture (accidentally) everything dies ### Functions - **Digestion** - Food or foriegn matter (invaders) are swallowed up and executed - **Recycling** - When an organelle "dies" `lysosomes` will recycle the dea material back into raw materials cellular suicide - **Cellular suicicde** - This is not good for the cell (obviously, but it is good for us. (E.g reasons why most of us don't have web feet/hands) ## Midtochondria - **Plural is "mitochondria"** - Contains an inner and outer membrane - Processes glucose + oxygen gas to form carbon dioxide + adenosine triphosphate (ATP) - ATP allows proteins to do things (e.g., spend 1 ATP break 1 molecule) - ATP cannot be stored - Mitochondria have their own DNA ## Cytoskeleton - The cytosekleton **is** the skeleton of the cell, found in the `cytosol`, made up of protein. - The cytoskeleton is also like the muscular system, able to change teh sahpe of cells in a flash - Made of protein filaments - Maintains and changes cell structure, much like a human skeleton + muscular system - Moves cells - Chemicals can travel along cytoskeleton, e.g., organelles, vesicles, etc. ## Organelles Specific To Animal Cells 1. centrioles and centrosomes 2. lysosomes ### Centrioles and Centrosomes - Involved in the process of cell division for animal cells, plant cells **DO NOT** use centrioles - Made of same protein as cytoskeleton - A centrosome is a pair of centrioles - Very important to cell division - Split chromosomes apart after DNA has been replicated into daughter cells - Helps regulate cell division - Create cilia and flagella (e.g., small hair-like things that swipe dirt out of lungs and tails of sperm, respectively) ### Lysosomes - Present in all animal cells but not present in the cells of most plants ## Organelles Specific To Plant Cells 1. Cell wall 2. Chloroplast 3. Central Vacuole ### Cell wall - Provides structure and prevents cell rupture - Can be tough, flexible, and/or rigid - Permeable to small molecules - Made of cellulose (type of sugar) - Also present in most bacteria, fungi, and protists ### Chloroplast - The `solar panel` of the plant cell. - Conducts photosynthesis - All chlorophyll is located in chloroplasts - Looks green ### Central Vacuole - Extremely large, may take up to 90% of volume in cell - Contains water - Maintains `turgor` pressure against cell wall (pushes against cell wall in all directions) - **Provides the cell with shape**