Ch 2: Cells Flashcards
What is life?
- Response to the environment
- Exchange of materials with the environment
- Metabolism
- Growth
- Reproduction
Cell is first fundamental sign of life.
Virus is not alive
Prokaryotic cells
- No true nucleus
- 1 to 10 µm
- ex: bacteria
Eukaryotic cells
- Have a true nucleus
- 10 to 100 µm (1/100 to 1/10 mm)
- almost all other cells that are not bacteria
Unicellular
- Each cell carries out all life processes
- Usually found in clusters
- Bacteria are unicellular
Multicellular
Made up of many cells, with different cells specialized to perform different functions
Why are cells so small?
Cells are small because they require a high surface to volume ratio to exchange materials with their environment.
Bacterial cells
- Prokaryotic
- no true nucleus
- no endoplasmic reticulum
- no Golgi apparatus
- no mitochondria
- no chloroplasts
- no vesicles or vacuoles
- no centrosome
Bacterial cell anatomy: Cytosol
- Mixture of enzymes and many other molecules in water.
- Many chemical reactions take place in the cytosol.
Bacterial cell anatomy: Flagellum
- Hair-like
- Attaches at plasma
- Rotates to provide mobility
- Not all bacteria have it
Bacterial cell anatomy: Thylakoid
Provides a membrane for photosynthesis
Not all bacteria have this
Bacterial cell anatomy: Capsule
- Not all bacteria have this
- Thick, sticky, gooey layer
- Protects the cell from attack or dehydration
- Allows some cells to stick together
- When bacteria with a capsule infect you, your immune system doesn’t recognize them/kill them.
Bacterial cell anatomy: Plasmid
- Not all bacterial cells have this
- Accessory genetic information
- Bacteria can trade these
- Scientists can use it to add extra genes for our purposes
Bacterial cell anatomy: Cell wall
- NOT a fluid like the plasma membrane
- Relatively rigid (gives the cell its shape)
- Prevents it from bursting
- Porous
- Most bacteria (not all) have this
Bacterial cell anatomy: Plasma Membrane
- AKA cell membrane
- Boundary between cell and environment.
- Controls movement of material in and out (exchange)
- Made of a phospholipid bilayer
Plasma membrane: Phospholipid bilayer
- Made of lipid molecules that have a polar head and non-polar tails.
- In water, the tails go in towards the center and the heads form two layers surrounding the tails because the heads like water but not the tails (semi-permeable)
- This bilayer is actually a fluid (not solid)
- The non-polar layer makes it relatively non-permeable to polar molecules.
- The non-polar molecules pass through easily (CO2 , O2 , lipids, …). They diffuse through freely.
- Some small polar molecules can actually sneak in, but very slowly.
- Larger polar molecules (ex: glucose) and ions diffuse through hardly at all, but there are some proteins embedded in the bilayer that will let some of the important stuff in.
Facilitated Diffusion (plasma membrane)
- Channel protein: Very specific about what it lets in. No control over in-out direction. Aquaporins (water channels)
- Gated channel proteins: Gates open or close depending on what the cell needs (or other various events)
- Carrier protein: only allows in a specific, but larger molecule.
- All 3 of these help with facilitated diffusion or passive transport (diffusion to areas of smaller concentration)