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 that make genes
    • Genes are a complete set of instructions to make a complete product (typically proteins)
    • Genes: one of the many sets of instructions, in your DNA, found on a chromosome, for making a functional product (mostly proteins)
  • 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

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)
• Is not surrounded by a membrane, literally is just same as rest of nucleus but denser

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

• Network of tubules and flattened sacs
• Transport proteins via cytoskeleton in vesicles

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
  • Only specific proteins are synthesized by ribosomes of rough ER
  • Proteins synthesized in ribosomes of rough ER are always sent to either Golgi apparatus via vesicles or stay in rough ER
  • Ribosomes attach to and leave the rough ER regularly
  • About half the cell’s proteins are produced here
• Modify, fold, and fix proteins

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

Lysosome

• Spherical vesicle that contains enzymes
• Digests and kills foreign matter which is then excreted
• Digests and breaks down old and unused material to be recycled
• Digests and breaks down old or non-functional organelles as needed
• Only plays a very minor role in cell suicide (apoptosis)
• If lysosome does rupture (accidentally) everything dies

Mitochondrion

• Plural is “mitochondria”
• Contains an inner and outer membrane
• Processes glucose + oxygen gas to form carbon dioxide + adenosine triphosphate (ATP)