amankg4251

One billiard ball is shot east at 2.2m/s. A second, identicalbilliard ball is shot west at 1.2m/s. The balls have a glancingcollision. not a head on collision, deflecting the second ball by90 degrees and sending it north at 1.6m/s. What are the speed anddirection of the first ball after the collision?
_____________m/s

________degrees south of east

Two billiard balls of equal mass undergo a perfectly elastic head-on collision. If one ball's initial speed was 2.00m/s, and the other's was 3.00m/s in the opposite direction, what will be their speeds after the collision?

Two  blocks  of  masses      and     Fig. 11 approach  each  other  on  a  horizontal  table  with  the  same  constant speed,     ,  as  measured  by  a  laboratory  observer.  The  blocks  undergo  a  perfectly  elastic  collision,  and  it is  observed  that     stops  but     moves  opposite  its  original  motion  with  some  constant  speed,    .  (a) Determine  the  ratio  of  the  two  masses,        .  (b)  What  is  the  ratio  of  their  speeds,       ,? 

QUESTION 1:

(a)Examine the Figure below relating to the S.pombe cellcycle:

1) Describe the function of Cdc25 and Wee1and why deficit of Cdc25 or excess of Wee1 can cause G2arrest

2) b) Describe how deficit of Wee1 or excess ofCdc25 may result in abnormally small cells

(b) Theactivities of Wee1 tyrosine kinase and Cdc25 tyrosine phospatasedetermine the state of phosphorylation of tyrosine 15 in the Cdk1component of mitotic cyclin-Cdk complexes (MPF). When tyrosine 15is phosphorylated, M-Cdk is inactive; when tyrosine 15 is notphosphorylated, M-Cdk is active. Just as the activity of M-Cdkitself is controlled by phosphorylation, so too are the activitiesof Wee1 kinase and Cdc25 phosphatase. The regulation of thesevarious activities can be studied in extracts of frog oocytes. Insuch extracts Wee1 tyrosine kinase is active and Cdc25 tyrosinephosphatase is inactive. As a result M-Cdk is inactive because itsCdk1 component is phosphorylated on tyrosine 15. M-Cdk in theseextracts can be rapidly activated by addition of okadaic acid,which is a potent inhibitor of serine/threonine phosphatases. Usingantibodies specific for each component it is possible to examinetheir phosphorylation states by changes in mobility upon gelelectrophoresis.

(Phosphorylated proteins generally run slower than theirnon phosphorylated counterparts).

1) Based on theresults with okadaic acid, decide whether the active forms of Wee1and Cdc25 are phosphorylated or unphosphorylated. In the figureindicate the phosphorylated forms of Wee 1 and Cdc25 and label thearrows connecting their active and inactive forms to show whichtransitions are controlled by protein kinases and which by proteinphosphatases.

2) Are the proteinkinases and phosphatases that control Wee1 and Cdc25 specific forserine/threonine side chains or for tyrosine side chains? How doyou know?

3) How doesaddition of okadaic acid cause an increase in phosphorylation ofWee1 and Cdc25, but a decrease in phosphorylation ofCdk1?

4) If you assumethat Cdc25 and Wee1 are targets for phosphorylation by activeM-Cdk, can you explain how the appearance of a small amount ofactive M-Cdk would lead to its rapid and completeactivation?

Proteins have different parts, or domains, that have differentfunctions. What is the function of an SH2 domain?

A. Binds to a phosphorylated tyrosine on a differentprotein
B. binds to a proline rich sequence in another protei
C.Binds to a kinase

D. Binds to a phosphorylated tyrosine on itself

5. The SH3 domain is about 60 amino acids long. It recognizes and binds to structural motifs in other proteins. The motif recognized by SH3 domains was found by constructing a fusion protein between an SH3 domain and glutathione-S-transferase (GST). GST fusions allow for easy purification fusing a glutathione affinity column that binds GST specifically. After tagging the purified GST-SH3 protein with biotin to make it easy to detect it was used to screen filters containing E. coli colonies expressing a cDNA library. Two different clones were found to bind to the SH3 domain: in both cases binding was shown to occur at short proline-rich sequences.

a. Could you use biotin tagged GST-SHE proteins in the same way to find cDNA domains? Why? Explain.

b. Many proteins bind to short strings of amino acids in other proteins. How do you think these kinds of interactions differ from the binds of interactions found between protein subunits of multi-subunit enzymes?

2. Protein-DNA binding

a) List the types of interactions that are involved between a protein that binds DNA non-specifically and DNA.

b) List two proteins that bind to DNA non-specifically.

c) List the types of interactions usually involved between a sequence-specific DNA binding protein and DNA.

d) List two proteins that bind DNA specifically.

e) What is the difference between non-specific and specific protein binding to DNA?

1.The yeast two-hybrid system is apowerful molecular genetic method to identify a protein(s) thatinteracts with a known protein or protein domain. You have isolatedthe glucocorticoid receptor (GR) and have evidence that is amodular protein containing an activation domain, a DNA bindingdomain and a second ligand binding-activation domain. Furtheranalysis reveals that in the pituitary cells the GR is anchored inthe cytoplasm in the absence of its hormone ligand. This resultlead you to speculate that GR binds to an inhibitory protein in thecytoplasm of the pituitary cells. (i) Describe how a yeast-twohybrid analysis system could help you to identify the protein withwhich GR interacts. ii) How would you specifically identify thedomain in the GR that binds the inhibitor? (20%)

1.Steroid hormones are known to increase theexpression of specific genes in selected target cell types.Testosterone increases the production of a protein calledalpha-2-microglobulin (?2m) in the liver and hydrocortisone (aglucocorticoid) increases the production of tyrosineaminotransferase (TAT) in the liver. (Each hormone does many otherthings). All steroid hormone receptors consists of 3 related, butdistinct, protein domains: a hormone binding domain, a DNA bindingdomain, and a regulatory domain.

A.How is it that testosterone and hydrocortisone can selectivelyinfluence the expression of two different genes in the sametissue?

B.By what you know of domains, suppose you carry out a domainswap experiment to exchange the DNA binding domains of testosteronereceptor and glucocorticoid receptor with each other. What effectswould you now expect the two hormones to have in cells containingthe altered receptors?

The differentiation of muscle cells from the somites (segments of mesoderm) of a developing embryo is controlled by myogenin, an helix-loop-helix gene regulatory protein that functions as a heterodimer with another member of the MyoD family of HLH proteins (see Figure A below). The activity of myogenin must be carefully controlled to prevent it from triggering premature expression of the muscle program of cell differentiation. The myogenin gene is turned on in advance of the time when it is needed, but myogenin is prevented from functioning by phosphorylation of its DNA-binding domain and by tight binding to

Id, an HLH protein that lacks a DNA-binding domain (see Figure B below). Explain how dimerization with Id and phosphorylation of the DNA-binding domain might act to keep myogenin nonfunctional. (2 pts)

One person sending a message and another person understanding it is called _____ ?

3. The activity of myogenin must be carefully controlled lest it trigger premature expression of the gene essential for cell differentiation. The myogenin gene is turned ON in before it is actually needed (and myogenin is expressed), but myogenin is prevented from functioning by phosphorylation of its DNA-binding domain AND by its tight binding to Id, a helix-loop-helix protein that lacks the DNA binding domain.

A. What types of interactions would hold the heterodimer together and you expect them to be the same as those that are necessary for Id binding? Where would you find these bonds/interactions (use the figure).

B. Explain how phosphorylation of the DNA binding domain and dimerization with Id might act to keep myogenin nonfunctional.

Extra credit. Why might this method of protein regulation be preferred over transcriptional control in this case?

4. Aminoacyl-tRNA synthetases attach specific amino acids to their appropriate tRNAs. The synthetase that attaches valine to tRNAval must be able to discriminate valine from threonine. Valyl-tRNA synthetase achieves this discrimination in two steps. In the first, it uses a binding pocket whose contours allow only valine and threonine to bind, but the binding of valine is preferred. This site is responsible for coupling the amino acid to the tRNA. In the second step, the enzyme checks the newly made aminoacyl-tRNA using a second binding site that is very specific for threonine and hydrolyses it from the tRNA. How do you suppose it is that the second binding site can be very specific for threonine, whereas the first binding site has only a moderate specificity for valine?

1. You are studying a steroid hormone-binding protein in mice. Youhave isolated two proteins that have similar but not identicalamino acid sequences from a mixed tissue homogenate (prepared frombrain, muscle, liver, ovary, adrenal gland and kidney of a mixedpopulation of adult mice). There are at least three differentmolecular mechanisms that can give rise to similar butnon-identical proteins. List and explain two of these.

2. The differentiation of muscle cellsin the developing embryo is controlled by myogenin, ahelix-loop-helix (HLH) gene regulatory protein that functions as aheterodimer with another HLH protein. The activity of myogenin mustbe carefully controlled so it does not trigger premature expressionof muscle cell differentiation. The myogenin gene isturned on in advance of the time when it is needed, but myogenin isprevented from functioning by its tight binding to Id, an HLHprotein that lacks a DNA-binding domain, and by phosphorylation ofits DNA-binding domain. Explain how dimerization with Id andphosphorylation of the DNA-binding domain might act to keepmyogenin non-functional.

3. Imprinting occurs only in mammals,and why it should exist at all is a mystery. One gene that isimprinted in most mammalian species is Igf2 gene, whoseproduct � insulin-like growth factor-2 � is required for prenatalgrowth. Most mammalian females can mate with multiple males,generating multiple embryos with different fathers in each litter.If one father had an Igf2 allele that caused more rapidprenatal growth, embryos carrying his genes, it would prosper atthe expense of the other embryos. While this would be good for thefather�s genes (in an evolutionary sense), it would drain theresources of the mother, potentially putting her life at risk (notgood for her genes). Thus, it is in the mother�s interest tocounter these paternal effects with maternal changes that limit thegrowth of the embryo. Based on this scenario, decide whether theIgf2 gene is more likely to be imprinted in the male or inthe female.

Steroid hormones are known to increase the expression of specific genes in selected target cell types. For example, in the liver, testosterone increases the production of a protein called alpha-2-microglobulin (α2m), while hydrocortisone (a glucocorticoid) increases the production of tyrosine aminotransferase (TAT). (Each hormone also does many other things). All steroid hormone receptors consist of 3 related, but distinct, protein domains: a hormone binding domain, a DNA binding domain, and a regulatory domain. How is it that testosterone and hydrocortisone can selectively influence the expression of two different genes in the same tissue?

Suppose you carry out a domain swap experiment to exchange the DNA binding domains of the testosterone receptor and the glucocorticoid receptor with each other. What effects would you expect the two hormones to have in liver cells containing the chimeric receptors?

What do the data show? Write a summary statement that communicates the "big idea" contained in the figure. Your summary statement should be written in such a way that if someone did not know the technical language in the figure, he/she could understand the *big idea.

Develop a series of bullet points that identifying essential details that substantiate your summary statement.

What, if any, information is missing from the figure? What more would you want to know in order to understand and evaluate the data? (Think about the issues raised by Joel Best in Damned Lies and Statistics.

What other questions do you have?

How we, as both individuals and as a society, define progress and perceive the pinnacle of human achievement determines how we face both the present and the future . For this week's journal , answer the following questions : How do you define the term "progress?" Do you think that the pinnacle of human achievement (or progress) exists in the past, the present, or the future? Why?

Explain the act utilitarianism. Give examples.

Explain rule utilitarianism. Give examples.

Is rule utilitarianism a form if hedonism why or why not?

Describe how a steroid hormone such as testosterone or estrogen, identifies and functions with its target cell:

Please help I have no clue whats going on!? Thank you!

How did the environment impact the development and lives of coastal plateau tribes?