Cell division expansion

Grade 10/Science/SNC2DZ/Unit 2: Biology.md

@@ -45,13 +45,13 @@ A person contains roughly 100 trillion cells
     - Allows **waste products** to leave (removal of waste)
 - Surrounds and holds other organelles in cell
 - Interact with outside chemicals (e.g., hormones)
-- Must transport food (ATP), nutrients into the cell
+- Transports food and nutrients into the cell
 
 ### Nucleus
 - Is the control center of the cell
 - Holds deoxyribonucleic acid (DNA) in form of `chromatin`
     - DNA is a double helix containing genes
-        - `Genes` are a full set of instructions in DNA to make either RNA or a protein, they are **found** in the DNA
+        - `Genes`: any section of DNA that contains a full set of instructions to make either RNA or a protein, **found** in nucleus
     - `Chromatin`: is DNA **wrapped tightly** in protein
 - `Chromosomes`: are even more tightly wrapped `chromatin` used in cell division only, formed when `DNA` **condenses** in `mitosis`
 - Surrounded by a double membrane
@@ -61,8 +61,8 @@ A person contains roughly 100 trillion cells
 
 
 ### Nucleolus
- - Dense region of DNA located in the nucleus (codes `ribosomes`; enzyemes that make protein)
- - This area of DNA is specially for ribosomal DNA (rDNA), or DNA used to make ribosomes
+ - Dense region of DNA located in the nucleus
+ - This area of DNA is specially for ribosomal DNA (rDNA), or DNA used to code `ribosomes`, enzymes that assemble proteins
  - Produce "large" and "small" subunits of `ribosomes`, which either form complete `ribosomes` in `cytosol` or mix with `endoplasmic reticulum`, forming `rough endoplasmic reticulum` (RER)
 
 ### Cytoplasm & Cytosol
@@ -122,10 +122,10 @@ A person contains roughly 100 trillion cells
 1. Centrioles and centrosomes
 2. Lysosomes
 
-### Centrioles and centrosomes
+### Centrosomes
  - Made of same protein as `cytoskeleton`
- - Important to cell division in animal cells
- - Create cilia and flagella (e.g., small hair-like things that swipe dirt out of lungs and tails of sperm, respectively)
+ - Crucial to mitosis in animal cells
+ - **Create and manipulate spindle fibres** during mitosis in animal cells
 
 ### Lysosomes
 - Explained before.
@@ -140,7 +140,7 @@ A person contains roughly 100 trillion cells
 - A more stronger, thicker, rigit version of the `cell membrane`
 - Made of **cellulose** (type of sugar)
 - Also present in most bacteria, fungi, and protists
-- The antibotic **Penicillin** works by destroying the cell walls of bacteria, thereby killing the bateria
+- The antibotic **penicillin** works by destroying the cell walls of bacteria, killing it
 
 ### Chloroplast
 - The **solar panel** of the plant cell
@@ -158,7 +158,7 @@ A person contains roughly 100 trillion cells
 
 ## Cell Division
 
-## Purpose 
+### Purpose 
 
 ### 1. Reproduction
  - Single-cellular organisms reproduce via division **asexually**
@@ -177,32 +177,59 @@ A person contains roughly 100 trillion cells
 - Cells naturally die and need to be replaced
     - e.g., red blood cells, hair cells, skin, injuries, broken bones
 
-## Cell cycle
+### Cell cycle
+
+<img src="https://www2.le.ac.uk/projects/vgec/diagrams/22-Cell-cycle.gif" width="600">
+
 - **Interphase**
-    - **G1** (normal groth and function), 
+    - Large majority of a cell's time is spent in interphase
+    - **G1**: (normal growth and function), 
     - Prepare for cell divison
-    -   Duplication of DNA **S**,
-    -   Duplication of organelles **G2**
+    - **S**: Replication of DNA
+    - **G2**: Replication of organelles
+    - Checkpoints
+        - Cells check various things before progressing through various stages in interphase
+        - Causes of stopping via checkpoints include damaged DNA, not replicated DNA, lack of nutrients for cell growth, and/or signals from other cells
 - **Mitosis**
     - Occurs only in eukaryotic cells
-    - P-MAT: Prophase Prometaphase, Metaphase, Anaphase, Telophase Cytokinesis
-    - nuclear divison
+    - P-MAT: Prophase, Metaphase, Anaphase, Telophase
+    - Division of the nucleus
 - **Cytokinesis**
     - **cell division**
+    - The parent cell splits into two daughter cells
 - **G0**
-    - Cell no longer divides
-    - Outisde of cell cycle 
+    - Cell no longer divides ("cell cycle arrest")
+    - Outside of cell cycle 
 
 ### Mitosis
+- `Chromatid`: Supercoiled DNA, only visible during mitosis, cannot be read without unwinding, similar to compressed zip file
+- `Chromosome`: Two identical "sister chromatids" held together in centre by `centromere`, or one sister chromatid after anaphase
+- `Centromere`: Proteins sticking sister chromatids
 - PMAT (prophase, metaphase, anaphase, telophase)
+- Division of the nucleus
 
+| Phase | Diagram | Description |
+| :--- | :--- | :--- |
+| Prophase | <img src="http://www.edupic.net/Images/Mitosis/prophase_3D.png" width="250"> | - Chromatin condenses into two identical `sister chromatids` which condense into `chromosomes` <br>      - Happens to 23 pairs of chromosomes <br> - Nuclear membrane dissolves <br> - Centrosomes move to opposite ends (`poles`) of cell, creating `spindle fibres` that begin to attach to `centromeres` in animal cells |
+| Metaphase | <img src="http://www.edupic.net/Images/Mitosis/metaphase_3D.png" width="250"> | - Chromosomes line up in centre of cell to ensure they divide evenly <br> - Everything in prophase has completed (e.g., nuclear membrane has dissolved completely) |
+| Anaphase | <img src="http://www.edupic.net/Images/Mitosis/anaphase_3D.png" width="250"> | - Centromeres split, separating sister chromatids <br> - Sister chromatids are pulled towards opposite sides of cell via shortening spindle fibres <br>     - Sister chromatids are now called `daughter chromomsomes` |
+| Telophase | <img src="http://www.edupic.net/Images/Mitosis/telophase_3D.png" width="250"> | - Effectively opposite of prophase <br> - Nuclear membranes form across each of the two new nuclei <br> - Daughter chromosomes unwind into chromatin and are no longer visible <br> - Nucleolus forms in each nucleus <br> - Spindle fibres break apart <br> - **Cytokinesis** usually begins in telophase <br>     - Cells starts to **cleave** (cell centre starts to pinch itself) |
+
+### Cytokinesis
+ - Cell division
+ - Cell splits completely to two daughter cells
+ - In **animal cells**: Cell membrane pulled inward by cytoskeleton
+ - **"Pinches in"** along equator of cell, forming **"cleavage furrow"**
+ - In **plant cells**: Golgi apparatus produces and sends vesicles to centre of plant cell **"cell plate"** to make new cell wall and membrane between daughter cells
 
 ## Cell Specialization
-- `Zygote`: A one-celled organism formed from the fertilization of an egg by a sperm cell
+- `Zygote`: A single-celled organism formed from the fertilization of an egg by a sperm cell, is a totipotent stem cell
 - A cell's position in the `gastrula` (outer, middle, inner layer) will determine the fate of the cell, or its potiental. 
+- Chemical signals from other cells will also determine activated genes that lead to specialisation
 - (LOCATION LOCATION LOCAION!)
+- Specialisation is determined by reading only certain genes
 
 ### Stem Cells
 - They are an **unspecialized** cell that has the potential to become one of several types of cells. 
-- After cell division, either both can become stem cells or one stays as a stem cell and the other becomes a specialized cell
-- 
+- Can either divide to two stem cells or one stem cell and one specialised cell
+- Specialised cells generally do not divide