Name two of the three types of cytoskeletal fibers and briefly define their func

Question

Name two of the three types of cytoskeletal fibers and briefly define their function in the cell.

Most mRNAs coding for protein have long stretches of adenine ribonucleotides [poly(A)] on the 3' end of the message. Does that mean that each gene from which these mRNAs are derived has a corresponding stretch of poly(dT) at the 5' end of the template from which the mRNA was formed.

Describe two mechanisms used by the cell to convert a protein from an active to an inactive state.

Consider the DNA sequence shown below. If RNA polymerase transcribes the sequence from left to right, using the top strand as its template, what will the sequence of the RNA molecule produced be?

5’-ATGACGAAAAGA-3’ |||||||||||| 3’-TACTGCTTTTCT-5’

The structure of biological membranes is determined primarily by the lipid bilayer but the specific functions of these membranes are carried out by proteins associated with the membrane. State whether you believe this statement is True or False and explain your answer.

Would you agree or disagree with the statement that differences in gene expression patterns can always be attributed to a difference in DNA sequence?

cAMP (cyclic AMP) is a secondary messenger (diffusible in the cytoplasm of the cell) involved in cell signaling processes. Describe in as much detail as possible how this secondary messenger is generated in response to cell signals and how it functions to modulate downstream events in cell signaling pathways-including changes in gene expression. Start your discussion by describing the class of cell surface receptor associated with increases in this second messenger and note in your response at least one step in signal transduction process where the signal initiated at the cell surface is amplified.

You have learned that the chemical nature of the side chains of amino acids (polar, nonpolar, charged) are important in determining overall protein structure. Given this, why do you think that addition of phosphate groups to proteins (as occurs during signal transduction) might affect protein structure/activity?

When cells are grown in the presence of radioactive thymidine it is incorporated into DNA during S phase. The results shown in the graph below come from an experiment in which cells are grown for 30 minutes in the presence of radioactive thymidine then the medium is replaced with medium containing non-radioactive thymidine (in other words, a pulse-chase procedure (for a brief description of pulse-chase experiments, see page 747 of your text)). The pulse chase approach allows investigators to track biomolecules labeled at the time of the pulse. At different times after replacement of the medium, the cells are examined by microscope to determine the number of cells undergoing mitosis (mitotic cells are easy to recognize as their chromosomes are obviously condensed). The fraction of mitotic cells that have incorporated the radioactive thymidine can also be determined and plotted as a function of time after thymidine labeling (see below).

a. At 10 hours –essentially 100% of the mitotic cells contain radioactive DNA-what phase of the cell cycle were these cells in when the radioactive thymidine was present? (4 points)

b. Why are there no mitotic cells that contain radioactive DNA at the initial time points? ( 4 points)

Althoughincorporationofthewrongnucleotideisnotdesirableineitherthesynthesisof DNA corresponding to a particular gene or in the mRNA transcribed off that DNA-explain why such a mistake is more deleterious at the DNA than RNA level.

A single mutation in the beta-globin chain of hemoglobin results in sickle cell anemia, a serious disease in which misshapen red blood cells can clog small blood vessels. The mutation results in the use of a valine rather than a glutamic acid as the seventh amino acid in the beta-globin protein. Do you think the results would be as devastating if the mutation resulted in aspartic acid being substituted for the glutamic acid? Why or why not?

11.

Explanation / Answer

Ques-1: Name two of the three types of cytoskeletal fibers and briefly define their function in the cell.

Answer:

Microtubules are the main cytoskeletal filaments, which are going to promote the growth of spindle fiber during formation of metaplate of cell division. Therefore, kinetochore is going to microtubules through plus ends & minus ends. Minus ends are going to shrink due to a dyenin whereas microtubules toward plus ends with growing due to kinesin protein. However, if at plus end catastrophin binding proteins are going to bind to initiate dynamic instability of the microtubules result in GTP hydrolysis at the plus ends

Extensive cytoskeletal filaments such as actin and microtubules resist pulling force, compression and shearing forces within the cells to support cell organelles to slides in the cytosol of eukaryotes. This prokaryotic feature is having microtubules also existing in human respiratory ciliated epithelium that support mucous movement in respiratory tract.

Ques-2: The structure of biological membranes is determined primarily by the lipid bilayer but proteins associated with the membrane carry out the specific functions of these membranes. State whether you believe this statement is True or False and explain your answer.

Answer: True

Reason:

Specific protein channels such as "Na+-K+ ATPase" and voltage gated ion channels & other ion channels of the cell memebrane are specifically involved in various functions apart from lipid bilayers mainly in mediating cell homeostatis between ECF & ICF. Integral membrane proteins are the proteins those that are embedded within the lipid bilayer of membrane. They are not rigid structures; they often change their structure to ensure good hydrophobic matching to the lipid layer surrounding them. The structure of the lipid head group region is defines the structure of a membrane protein located in that lipid head group region.

Carrier protein is an integral membrane spanning protein and enables the movement of solutes such as sodium, potassium, glucose etc into the cells. Example of a carrier protein is in transporting glucose solute into the cell through GLUT1 carrier protein. This protein has the following typical structural modifications with 12 membranes spanning alpha helices. Flip-flop conformational change of the membrane spanning carrier protein (GLUT1) occurs when the solute molecule is bound to the carrier protein. Symproters, antiporters, ABC transporters, channels proteins, Na+-K+- ATPases uses active transport & passive transport of ions, solute molecules against & down the concentration gradients respectively to maintain intracellular stable PH 7.

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