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

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

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)

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)
- 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

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