Please enable JavaScript.

Coggle requires JavaScript to display documents.

Cell Biology P3 (Origins of Cells (Endosymbiotic Theory: Larger cell…

Cell Biology P3

Origins of Cells

Pasteur’s Experiments:

```
Use of swan-necked flasks
```

Samples of broth in flasks with long necks then melted glass of necks and bent it into various shapes

Boiled the broth in some flasks to kill microorganisms and left others un-boiled (as controls)

Fungi + other organisms appeared in un-boiled flasks

Broth in flasks were in contact with air, apparently needed for spontaneous generation

So he snapped necks of some flasks to leave shorter neck

```
Ogranisms found in these flasks
```

Conclusion: Swan necks prevented organisms from getting air and no organisms appeared spontaneously

Endosymbiotic Theory:

Larger cell takes in smaller cell by endocytosis in a vesicle, so smaller cell performs useful function for the larger cell

Smaller cell divides as frequent as larger cell does

```
Occurred in origin of eukaryotes
```

Mitochondrion:

Cell respiring anaerobically took in bacterium respiring aerobically

Bacterium made ATP for itself and host cell, making it more efficient for host cell

Aerobic bacterium evolved into mitochondrion and large cell evolved into heterotrophic eukaryotes (animals)

Chloroplast:

Heterotrophic cell took in photosynthetic bacterium

Bacterium supplied larger cell with organic compounds, so now autotroph

Bacterium evolved into chloroplast and host cell evolved into photosynthetic eukaryotes (plants)

Thus, they both:

```
Have double membrane
```
```
Grow and divide like cells
```
```
Naked loop of DNA
```

Synthesize some of  own proteins using 70S ribosomes

Simple and Facilitated Diffusion (passive--no energy required)

Diffusion: Passive movement of particles from a region of high solute conc. to low solute conc.

occurs when there's a conc gradient in membranes too, and if membrane is permeable to it eg. O2 but not cellulose

Simple diffusion:

Movement between the phospholipid molecules in membrane as they are permeable

Facilitated diffusion:

Movement through channel proteins as not permeable through phospholipids

Channel proteins are specific—only allows 1 type of substance through (eg. Chloride channels, sodium + potassium channels in neuron membranes are voltage-gated channels)—maintains permeability of membrane

Potassium Channels In Axons:

```
Used during action potential
```

Closed when axon is polarised (as –ve inside and +ve outside)

Opens when depolarised (as +ve inside and –ve outside)

Stays open for a while before globular sub-unit blocks pore

```
Closed again
```

Active Transport

Movement of substances from region of low conc. to region of high conc. against its conc. gradient through a partially permeable membrane using energy from ATP

Eg. Protein pumps in membrane only go in one direction + control permeability of cell

Particle enters pump from side with low conc.

```
Bind to specific site
```
```
Energy from ATP changes shape of pump
```

Particle released on side with high conc.

Sodium-Potassium Pump in Axons:

Antiporter as it’s pumped in opposite directions

Inside pump there is binding site for 3Na and 2K ions as one ATP provides enough energy to pump this

ATP is converted to ADP for energy for pumping

Conc gradient generated by this helps in transmitting nerve impulses

There are 2 states for the active transport: access from outer side, and from inside

Access from outside: stronger attraction to K+ ions, so Na+ discharge and K+ bind

Transport Using Vesicles:
Exocytosis:

```
Protein made by ribosome and RER
```
```
Carried to the golgi for modification
```
```
Carried to plasma membrane then…
```
```
Vesicle fuses with membrane
```
```
Contents are expelled
```
```
Membrane flattens out
```

Endocytosis:

```
Plasma membrane pulled inwards
```
```
Droplet of fluid enclosed in a vesicle
```

Vesicle pinches off and carried to cytoplasm