Lecture 4 Outline of Last Lecture I. Finish natural selection II. Evolution of Multicellularity a. Bacteria & Archaea b. Basic Morphology III. Advantages & Disadvantages of Multicellularity a. Characteristics b. Advantages Outline of Current Lecture c. Disadvantages i. Diffusion IV. How Genes Control Cell Fate !Current Lecture **Clicker Question** What is a difference between an e.coli cell and a human cell? •DNA is enclosed in a membranous structure in human cells Disadvantages 1. Limits of distribution and diffusion 2. Must stick together and support organism 3. Cell to cell communication 4. Regulate cell division & cell fate (development and reproduction) 5. Defense Bio 152 1!!!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !!Diffusion is a problem for multicellular organism 1. Vessels take advantage of bulk flow — movement of liquids under pressure 2. Diffusion relies solely on concentration gradients 3. Organisms without some sort of transport system are size limited Eukaryotes are larger than bacteria — surface area to volume ratio matters •as you increase the size of a sphere, the ratio gets smaller •the rate of diffusion is constant in the same medium — it will take longer to get to the center of the cell as the cell gets bigger •getting nutrients into cells will take longer —so they can’t rely on diffusion •How to eukaryotic cells deal with being too large for diffusion? •actively move —> motor proteins •some euk. cells increase their surface area with folds •they have transport vesicles •local increase of molecules —use prot. to transport them •vasculature must be developed to move past the stage where every cell is in contact with the outside environment **Clicker Question** Instead of having lungs that transfer oxygen into the bloodstream which then is moved around the organism by the heart, insects have holes in their exoskeleton (spiracles) that connect to tracheae running into the body (tubes filled with air). Stick insects can get as big as two feet long while flies remain relatively small. Why? •the volume of a stick insect is low compared to its surface area For multicullular organisms to proliferate, they must stick together, distribute nutrients, regulate cell division and defend themselves. It is most likely that: •These traits existed previously in different prokaryotes. Cadherins = proteins involved in cell to cell adhesion in animals When they don’t do their job:!1. Cells not sticking together can aid in the metastasis of neoplasms 2. Renal fibrosis 3. Several skin and hair conditions 4. Arrhythmogenic cardiomyopathy (usually in young male athletes) **Clicker Question** Holozoa are the single celled organisms most closely related to animals. Metazoa are animals. What does this graph suggest about cadherins? •That cadherins had a role in single-celled organisms—it is thought that cadherins helped them grab their prey (other cells) and eat them !!!How Genes Control Cell Fate (development & differentiation) astrocytes = type of glial cell that reinforce the connection between neurons •human astrocytes are larger and have more tendrils than mouse astrocytes **Clicker Question** Human glial progenitor cells were implanted into neonate mice. The figure below used species specific antibodies (green is human, red is mouse). What do these data suggest? !• by the end of the experiment, human cells predominated •the signal to develop into glial cells is similar in mice and humans *tells us nothing about functioning of the cells*!**Clicker Question** A separate study used a similar procedure . Either mice glial cells (allografted) or human glial cells (chimeric) were subjected to the procedure shown in A. Mice freeze as a response to threats, which they can learn to pair with a tone. This is called AFC (Auditory Fear Conditioning). What do these data suggest? •chimeric mice have progressive learning
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