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