Exam 2 Cell Bio

• cell type that is always turning over, and you are required to replenish them to maintain the epidermal barrier • they have very infrequent cell cycles. Some of those stem cells begin the differentiation cascade. So they become skin progenitor cells. • as these commit to these progenitor states, you see this very rapid cell division and then eventually these cells terminally differentiate. In which case, they stop dividing and become the differentiated cells of your skin and then eventually will be shed

gives rise to a progenitor cell that’s now committed, you often see this transit amplifying stage where those progenitor cells are the ones that then start dividing very rapidly.

Embryonic development and Adult tissue homeostasis

• These unicellular organisms where just trying to divide and divide • That is how they propagate themselves and they are successful relative to other organisms • As they divide they pass down their genetic material

• types of organisms that spend part of their lifetime as single cells in part as these colonies where the cells stick together • these are thought to be sort of the origins of multicellularity

• If a cell keeps dividing really fast you won’t get the precise coordination that you need to form a well-formed organism • If the cell is selfish and decides it wants to divide and divide and divide, that also creates disease states, things like cancer.

• Experiment: pulse label newly synthesized DNA with radioactive phosphate and then view the cells at intervals to learn when they divide • Reveals that there is a distinct phase when DNA is synthesized • Synthesis of RNA and proteins occurs continuously during the cell cycle, DNA synthesis only occurs during S-phase • only a subset of cells are labeled, indicating that there’s a discrete phase during the cell cycle when DNA is being synthesized

• S + G1 = S phase cell contains factors that promote G1 to S phase progression • S + G2 = G2 cel is resistant to S phase promoting factor • G1 + G2 = G1 and G2 do not influence each other • interphase + M = mitotic cells cause all interphase cells to enter mitosis

the period between the mitotic events

• Also known as fission yeast • isolated from millet beer Pombe is the Swahili word for beer

• Commonly used in cooking etc. • Cerevisiae is Latin for “of beer” • Also known as budding yeast

the early cell divisions of the embryo are synchronized. So they’re happening all at the same time

like randomly mutating the genome and then looking for defects in cell cycle progression and then going back and trying to figure out what those genes are

Identify important proteins in this process

• they form this bud which will become the daughter cell • G1: you see a round cell • S: you see this little bud forming which progressively gets bigger as it goes through the cell cycle until eventually, this cell will divide

they continuously elongate. So they have this kind of cylindrical shape and during the cell cycle they elongate and then eventually they will undergo this fission process, which will divide the two daughter cells and then the two daughter cells will then start to elongate again

• involved in inhibiting the progression from G2 to M phase. So it keeps the cell in G2 allowing it to grow during the second gap phase. • If you get rid of the Wee1 it goes through that process too fast. So it hasn’t grown very much and then it divides. So the result is that you get these abnormally small cells in culture

• helps progress the cell from G2 to M. • If you get rid of CDC25 the cell gets stuck in G two, which again is a growth phase and you get these abnormally long cells because they’re hanging out in G2 and continuing and continuing to grow.

• allow you to study factors involved in essential processes • the protein to function properly in one condition but not in another (temperature is the condition for these experiments) • often missense mutations that destabilize or disrupt protein interactions at the restrictive temperature (high temperature) • you can grow the yeast at what you call the permissive temperature, which is a lower temperature, the proteins will function normally • As you increase the temperature those mutations destabilize the protein at these higher temperatures • So there’s more energy coming in and they can’t hold their natural shape and that causes them to become nonfunctional. • you can grow these mutants just fine at the permissive temperature and then shift them to the restrictive temperature and then look to see what happens.

• the density is low enough that when they grow individual colonies that appear on the plate are assumed to have arisen from a single cell that was originally plated • within these colonies, it’s assumed that there’s sort of clonality that they’re all related to each other. • you can go back and isolate that colony and then grow it up and then do experiments with it by having sort of this culture of cells and then changing its temperature to see what happens.

So you kind of take a stamp and you stamp these colonies onto two new plates and they’re basically in exactly the same orientation as they were from this original plate

If that mutation is in a gene that’s essential for cell cycle progression, after you shift it to the restrictive temperature, and then look at the cells, you might see that they’ve all arrested in one particular phase of the cell cycle.

• nomenclature • These genes are present in all eukaryotes including humans (sometimes the name CDC is used and sometimes it has been changed)

• determine the order in which these genes function during the cell cycle • with double mutants make it possible to order the activities of cell cycle genes • try to order proteins in a linear pathway to determine the order in which they function • CDC 28 functions before CDC7