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179 lines
6.6 KiB
Markdown
179 lines
6.6 KiB
Markdown
# Unit 2: Biology
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## Cellular Biology
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A person contains roughly 100 trillion cells
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- Cells are roughly 20 `μm` (micrometre, 10<sup>-6</sup> m), around 250 cells / cm
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## Cell Theory
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1. All living things are composed of cells
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2. Cells are the basic units of living organisms
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3. All cells came from pre-existing cells
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## Eukaryotic versus Prokaryotic Cells
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`Prokaryotic cell`: Meaning before/lacking nucleus
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`Eukaryotic cell`: Means complete nucleus
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|Factors|Prokaryotic|Eukaryotic|
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|:-----------|:----------|:---------|
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|DNA|In nucleoid region|Usually in membrane-bound nucleus|
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|Size|Usually smaller|Usually larger|
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|Organelles|Not membrane-bound, smaller|Membrane-bound, more complex|
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|Organization|Usually singlecelled|Often form multicellular organisms|
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|Metabolism|May not need oxygen|Usually need oxygen|
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## Cellular Organelles
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### Business Analogy
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| In a business | In a cell |
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| ------------- | --------- |
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| Building | Cytoplasm & Cytoskeleton |
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| Department Head | Organelles |
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| Boss | DNA |
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| Workers | Ribosomes & Enzymes |
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| Waste management | Lysosomes |
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| Storage | Vacuoles |
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| Powerhouse | Chloroplasts & Mitochondria |
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| Security gate | Cell membrane controls entrance and exit from the cell |
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| Transportation Department | IMPORT: Cell membranes and vesicles, INTERNAL: Endoplasmic reticulum & vesicles, EXPORT: Golgi apparatus, vesicles, and cell membrane |
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### Cell Membrane
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- Controls what substances enter/leave the cell selectively via various receptors/osmosis
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- Allows nutrients to enter
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- Allows waste products to leave
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- Surrounds and holds other organelles in cell
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- Interact with outside chemicals (e.g., hormones)
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### Nucleus
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- Holds deoxyribonucleic acid (DNA) in form of `chromatin`
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- DNA is a double helix containing genes
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- `Genes` are a full set of instructions in DNA to make either RNA or a protein
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- `Chromatin` is DNA wrapped tightly in protein
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- `Chromosomes` are even more tightly wrapped chromatin used in cell division only
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- Surrounded by a double membrane
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- Substances enter and exit the nucleus via nuclear pores
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- Messenger RNA (mRNA) is encoded from DNA and sent to `ribosomes` to produce proteins
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- Humans have ~2 m of genes per cell per nucleus tightly wrapped
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### Nucleolus
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- Dense region of DNA located in the nucleus
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- This area of DNA is specially for ribosomal DNA (rDNA), or DNA used to make ribosomes
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- Produce "large" and "small" subunits of ribosomes, which either form complete ribosomes in cytosol or mix with endoplasmic reticulum, forming rough endoplasmic reticulum (RER)
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### Cytoplasm & Cytosol
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- `Cytosol` is the fluid cells contain
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- **All organelles** are suspended in `cytosol`
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- `Cytoplasm` is the `cytosol` along with everything in a cell, excluding the nucleus
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## Endoplasmic Reticulum
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- The endoplasmic reticulum is a network of tubules and flattened sacs with a "rough" appearance because of the presence of `ribosomes` on the surface
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- Network of tubules and flattened sacs
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- **Transports** proteins via cytoskeleton in vesicles
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## Specific to Rough ER
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- Appears "rough" due to the `ribosomes` attached to its outer surface
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- Located directly adjacent and attached to nucleus
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- Located next to `Golgi apparatus`
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- `Ribosomes` in rough ER **synthesize proteins**
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- Transports synthesized proteins to `Golgi apparatus` for packaging and distribution
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- About half the cell's proteins are produced here
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- Folds, fixes and **modifies both newly-created and pre-existing proteins** somewhat like **proof-reading**
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## Specific to Smooth ER
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- Does not synthesize proteins
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- Appears "smooth" due to lack of `ribosomes`
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- Located directly adjacent and attached to nucleus
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- Synthesizes lipids (fats, e.g., cholesterol)
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- Metabolises carbohydrates
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## Golgi Apparatus
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- Also known as Golgi body, Golgi complex, etc.
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- **Receives, modifies and transports** proteins that were produced by the rough ER
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- **Packages** proteins into `vesicles` and sends them `cell membrane` for export
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## Lysosome
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- Spherical vesicle that containing `enzymes`
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- **Digests and kills** foreign matter which is then excreted
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- E.g., white blood cells use lysosomes to kill bacteria then spit it out
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- **Digests and breaks down** old and unused material/non-functional organelles as needed
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- If lysosome ruptures everything dies, hence they are known as "suicude sacs"
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## Mitochondria
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- **Singular form is "mitochondrion"**
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- Contains an inner and outer membrane
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- Processes glucose + oxygen gas to form carbon dioxide + adenosine triphosphate (ATP)
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- ATP allows proteins to do things (e.g., spend 1 ATP break 1 molecule)
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- ATP cannot be stored
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## Cytoskeleton
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- Made of protein filaments
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- Maintains and changes cell structure, much like a human skeleton + muscular system
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- Moves cells
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- Modifies and adjusts cell structure as needed
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- Chemicals can travel along cytoskeleton, e.g., organelles, vesicles, etc.
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## Organelles specific to animal cells
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### Centrioles and centrosomes
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- Made of same protein as cytoskeleton
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- A centrosome is a pair of centrioles
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- Important to cell division in animal cells
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- Create cilia and flagella (e.g., small hair-like things that swipe dirt out of lungs and tails of sperm, respectively)
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### Lysosomes
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## Organelles specific to plant cells
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### Cell wall
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- Provides structure and prevents cell rupture
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- Can be tough, flexible, and/or rigid
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- Made of cellulose (type of sugar)
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- Also present in most bacteria, fungi, and protists
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### Chloroplast
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- The `solar panel` of the plant cell
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- Conducts photosynthesis
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- All chlorophyll is located in chloroplasts
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- Looks green
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### Central Vacuole
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- Extremely large, may take up to 90% of volume in cell
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- Contains water
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- Maintains `turgor` pressure against cell wall (pushes against cell wall in all directions)
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- Maintains cell shape and resistance
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- Plant cells that lack turgor pressure (e.g., celery left in fridge) become flaccid
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## Cell division
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### Purpose
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#### Growth
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- Cells have maximum size before transportation of substances within cell becomes inefficient
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- Cells transport chemicals (e.g., nutrients) via `diffusion`
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#### Reproduction
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- Single-cellular organisms reproduce via division asexually
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- Multicellular organisms reproduce via combining two germ cells ("sex cells") that contain half the DNA each of two organisms
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- This is sexual
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#### Repair
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- Cells naturally die and need to be replaced
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- e.g., red blood cells, hair cells, skin, injuries
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### Cell cycle
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- Interphase
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- G1
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- S
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- G2
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- Mitosis
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- Occurs only in eukaryotic cells
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- Prophase
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- Prometaphase
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- Metaphase
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- Anaphase
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- Telophase
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- Cytokinesis
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- G0
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- Cell no longer divides
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- Outisde of cell cycle |