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

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 (removal of waste)
• Surrounds and holds other organelles in cell
• Interact with outside chemicals (e.g., hormones)
• 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: 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
• Substances enter and exit the nucleus via nuclear pores. Nuclear pores are holes in the membrane that allow proteins and nucleic acids into the cytoplasm
• Messenger RNA (mRNA) is encoded from DNA and sent to ribosomes to produce proteins
• Humans have ~2 meters of genes per cell per nucleus tightly wrapped

Nucleolus

• 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

• 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
• Transports proteins via cytoskeleton in vesicles

Specific to Rough ER

• 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
  • Transports synthesized proteins to Golgi apparatus for packaging and distribution
  • About half the cell’s proteins are produced here
• Folds, fixes and modifies both newly-created and pre-existing proteins somewhat like proof-reading

Specific to 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

• Also known as Golgi body, Golgi complex, etc.
• Receives, modifies and transports proteins that were produced by the rough ER
• Packages proteins into vesicles and sends them cell membrane for export

Lysosome

• Spherical vesicle that containing enzymes
• Digests and kills foreign matter which is then excreted
  • E.g., white blood cells use lysosomes to kill bacteria then spit it out
• Digests and breaks down old and unused material/non-functional organelles as needed
• If lysosome ruptures everything dies, hence they are known as “suicude sacs”

Mitochondria

• Singular form is “mitochondrion”
• 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
  • ATP is needed for daily function of the cell

Cytoskeleton

• Made of protein filaments
• Maintains and changes cell structure, much like a human skeleton + muscular system
  • Moves cells
  • Modifies and adjusts cell structure as needed
• Chemicals can travel along cytoskeleton, e.g., organelles, vesicles, etc.

Organelles specific to animal cells

1. Centrioles and centrosomes
2. Lysosomes

Centrosomes

• Made of same protein as cytoskeleton
• Crucial to mitosis in animal cells
• Create and manipulate spindle fibres during mitosis in animal cells

Lysosomes

• Explained before.

Organelles specific to plant cells

1. Cell wall
2. Chloroplast
3. Central Vacuole

Cell wall

• Provides structure and prevents cell rupture
• 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, killing it

Chloroplast

• The solar panel of the plant cell
• Conducts photosynthesis
• All chlorophyll is located in chloroplasts
• Looks green
• Parts of the plant that do not photosynthesize do not have chloroplasts

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)
• Maintains cell shape and resistance
  • Plant cells that lack turgor pressure (e.g., celery left in fridge) become flaccid

Cell Division

Purpose

1. Reproduction

• Single-cellular organisms reproduce via division asexually
• Multicellular organisms reproduce via combining two germ cells (“sex cells”) that contain half the DNA each of two organisms
  • This is sexual

2. Growth

• Cells have maximum size before transportation of substances within cell becomes inefficient, due to larger cells decreasing efficiency of diffusion
• Cells transport chemicals (e.g., nutrients) via diffusion, this limits cell size
• The only way to maintain proper function and get bigger is to add more cells

3. Repair

• Organisms need to repair cells to stay alive and maintain proper health
• Millions of cells are replaced everyday
• Cells naturally die and need to be replaced
  • e.g., red blood cells, hair cells, skin, injuries, broken bones

Cell cycle

• Interphase
  • Large majority of a cell’s time is spent in interphase
  • G1: (normal growth and function),
  • Prepare for cell divison
  • 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, Metaphase, Anaphase, Telophase
  • Division of the nucleus
• Cytokinesis
  • cell division
  • The parent cell splits into two daughter cells
• G0
  • 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		- Chromatin condenses into two identical sister chromatids which condense into chromosomes - Happens to 23 pairs of chromosomes - Nuclear membrane dissolves - Centrosomes move to opposite ends (poles) of cell, creating spindle fibres that begin to attach to centromeres in animal cells
Metaphase		- Chromosomes line up in centre of cell to ensure they divide evenly - Everything in prophase has completed (e.g., nuclear membrane has dissolved completely)
Anaphase		- Centromeres split, separating sister chromatids - Sister chromatids are pulled towards opposite sides of cell via shortening spindle fibres - Sister chromatids are now called daughter chromomsomes
Telophase		- Effectively opposite of prophase - Nuclear membranes form across each of the two new nuclei - Daughter chromosomes unwind into chromatin and are no longer visible - Nucleolus forms in each nucleus - Spindle fibres break apart - Cytokinesis usually begins in telophase - 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 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.
• Can either divide to two stem cells or one stem cell and one specialised cell
• Specialised cells generally do not divide

Type of Stem Cell	Obtaining	Potential	Pros	Cons
Totipotent	Morula (16-cell ball) 3-4 days after lab-fertilised zygote	Unlimited	Unlimited potential, does not initiate immune response	Ethical concerns of destroying fertilized embryos
Pluripotent	Blastocyst (200-300 cell ball) 4-7 days after fertilisation	Nearly unlimited	Nearly unlimited potential, no need to create new embryo as most are taken from discarded in vitro fertilisation	Ethical concerns of destroying embryos, greater chance of initiating immune response
Multipotent	Adult stem cells	Limited to cells of their group/organ/location (e.g., blood stem cells to red blood cells, white blood cells, etc.)	Easy to harvest, easy to find	Immune response, limited potential
Induced pluripotent	Multipotent stem cells	Reprogramming multipotent stem cells using embryonic genes using a virus	Same as pluripotent	Does not require new embryos, immune response not expected, high potential

Potential uses of stem cells

• Studying cell growth and function
• Testing drugs on specific target cells
• Lab-grown meat for vegetarian purposes
• Regenerative medicine to replace tissues (e.g., blindness, bone marrow transplant, cancers, limb regrowth)