Two intracellular molecules X and Y are both normally synthesized at a constant rate of 1000 molecules per second per cell. Molecules X is broken down slowly: each molecule of X survives on average for 100 seconds, Molecule Y is broken down 10 times faster, each molecule of Y survices on average for 10 seconds.
a. calculate how many molecules X and Y the cell contains at any time
b. If the rates of synthesis of both X and Y are suddenly increased tenfold to 10,000 molecules per second per cell without any change in their degradation rates-how many molecules of X and Y will there be after one second?
c. Which molecule would be preferred for rapid signaling? Why?
d. Which molecule would be preferred for slow signaling? Why?
CELL SIGNALING MOLECULES
Two intracellular molecules X and Y are both normally synthesized at a constant rate of 1000 molecules per second per cell. Molecules X is broken down slowly: each molecule of X survives on average for 100 seconds, Molecule Y is broken down 10 times faster, each molecule of Y survives on average for 10 seconds.
(a) Calculate how many molecules X and Y the cell contains at any time
Clearly, there will be lots more A than B.
Let's just simplify the question. If we look at molecule A, 1000 are made in one second. 1000 are made in the next second. 1000 more are made in the third second. Have any of these 3000 molecules disappeared yet? No, because they stay around for ...
Proteins, Enzymes, Synthesis and Division
a) What role do microtubules play in intracellular transport?
b) Describe the structure of microfilaments and microfilament networks and explain how they are assembled and disassembled within a cell.
c) Outline two functions that microfilament networks play in cell motility.
d) What function of intermediate filaments have in eukaryotic cells?
a) What two key factors determine the specificity of Watson-Crick base pairing in B-DNA? For each of these factors, explain why this is the case.
b) What activity of E.coli DNA polymerase 1 is responsible for ensuring correct Watso-Crick pairing during DNAS synthesis?
c) Outline briefly how this activity (given in your answer to part (b)) is achieved by this enzyme.
a) What is a mitotic spindle?
b) Which to classes of motor proteins interact with spindle microtubules during mitosis?
c) What role do these motor proteins play in the process of mitosis?
d) A drug that prevents the assembly of microtubules is applied to a culture of dividing cells for four hours. How will the culture treated with the drug differ from an untreated culture of the same cells, in terms of the numbers of cells in different stages of the cell cycle? In your answer, you should explain how the difference in appearance arises.
a) Describe the cellular location and function of the following membrane-bound vesicles: (i) synaptic vesicle, (ii) phagosome.
b) Describe the roles of two of the following proteins associated with the formation of transport vesicles: Epsin, Dynamin, GGA-proteins, GTP-binding adapter proteins.
c) Give one example of a transport vesicle that moves between the ER and the Golgi apparatus, indicating its coat protein and its direction of movement.