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
• 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 containing genes
    • Genes are a full set of instructions in DNA to make either RNA or a protein
  • 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
• Humans have ~2 m 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 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)

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

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

Centrioles and centrosomes

• Made of same protein as cytoskeleton
• A centrosome is a pair of centrioles
• 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)

Lysosomes

Organelles specific to plant cells

Cell wall

• Provides structure and prevents cell rupture
• Can be tough, flexible, and/or rigid
• 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)
• Maintains cell shape and resistance
  • Plant cells that lack turgor pressure (e.g., celery left in fridge) become flaccid

Cell division

Purpose

Growth

• Cells have maximum size before transportation of substances within cell becomes inefficient
• Cells transport chemicals (e.g., nutrients) via diffusion

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

Repair

• Cells naturally die and need to be replaced
  • e.g., red blood cells, hair cells, skin, injuries

Cell cycle

• Interphase
  • G1
  • S
  • G2
• Mitosis
  • Occurs only in eukaryotic cells
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
• Cytokinesis
• G0
  • Cell no longer divides
  • Outisde of cell cycle