Cell Biology Exam #2

The sequence for three different tripeptides are written out below. Indicate which sequence you would expect to find in the inner core of a cytosolic protein.

Alanine-Glycine-Leucine

The sequence for three different tripeptides are written out below. Indicate which sequence you would expect to find on the outer surface of the protein.

Serine-threonine-Thyrosine

Which of the following statements is untrue about protein secondary structure?

The hydrophilic/hydrophobic character of amino acid residues is important to secondary structure

Which of the following statements about allostery is true?

Allosteric regulators are often products of other chemical reactions in the same biochemical pathway.

The information stored in DNA sequences is used directly as a template to make...

RNA

Which of the following statements is true?

Disulfide bonds stabilize but do not change a proteins final confirmation

Consider the process that a cell uses to replicate it's double stranded DNA to make copies for daughter cells. Which statement describes the DNA in daughter cells?

The double he lives in each daughter cell consist of one parental strand and one newly made strand

Continuous synthesis occurs on the ___ orientated parent strand and is further referred to as the ___ strand

3'-5', leading

The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation?

Gene silencing

Which of the following statements about the newly synthesized strand of human chromosome is true?

It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis

The biosynthetic pathway for the two amino acids E and H is shown schematically in the figure below. You are able to show that E inhibits enzyme V, and H inhibits enzyme X. Enzyme T is most likely subject to feedback inhibition by ___ alone.

C

Which of the following DNA strand can form a DNA duplex by pairing with itself at each position?

5'-AAGCGCTT-3'

Non homologous end joining can result in all but which of the following?

The recovery of lost nucleotides on a damaged DNA strand

Which of the following statements is true?

Non polar amino acids tend to be found in the interior of proteins

The octameric histone core is composed of four different histone proteins, assembled in a step wise manner. Once the core octamer has been formed, DNA wraps around it to form nucleosome core particle. Which of the following histone proteins does not form

H1

The core histones are small, basic proteins that have a globular domain at the C-terminus and a long, extended confirmations at the N-terminus. Which of the following is not true of the N-terminus "tail" of these histones?

It binds to DNA in a sequence specific manner

Homologous recombination is an important mechanism in which organisms use a back up copy of DNA as a template to fix double strand breaks without loss of genetic information. Which of the following is not necessary for homologous recombination to occur?

5' DNA strand over hangs

Which of the following is not a chemical modification commonly found in core histone N-terminus tails?

Hydroxylation

Specific regions of eukaryotic chromosomes contain sequence elements that are absolutely required for the proper transmission of genetic info from a mother cell to each daughter cell. Which of the following is not known to be one of these required element

Terminators of replication

Assuming that all of the sequences below begin as stable double stranded DNA molecules, which has the lowest melting temperature?

TATTGTCT

Referring to question #20, which of the stable double stranded DNA molecules has the highest melting point?

GGCGCACC

Which of the following chemical groups is not used to construct a DNA molecule?

Six carbon sugar

DNA replication is considered semiconservative because:

Each daughter DNA molecule consist of one strand from parent DNA molecule and one new strand

DNA polymerase catalyzed the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction?

Hydrolysis of pyrophosphate (PPi) to inorganic phosphate (Pi) + Pi

Assuming the sequence below are a part of a stable double strand DNA molecule in which sequence would you most likely expect to locate the replication of origin?

AAATTTGTTC

Running size exclusion chromatography you have a protein elute at 25 min, with approximate mass of 55kDa. It also contains 7 leucine amino acids which you decide to replace with 7 isoleucine. What would be the time the new protein would elute?

25 min

Which of the choices below represents the correct way to repair the mismatch shown in the figure below?

New strand- A
Template strand- T

The repair of mismatch base pairs or damaged nucleotides in a DNA strand require a multistep process. Which of the following choices describes the known sequence of events in this process?

DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap if filled by DNA polymerase and the strand is sealed by ligase

If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?

TUAT

Mutations in the gene for RAS are found in many cancers. Of the choices below, which alteration of ras activity is most likely to contribute to the uncontrollable growth of cancer cells?

A change that decreases the rate of hydrolysis of GTP by Ras

Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin remodeling complexes provide this access by ___

Using the energy of ATP hydrolysis to move nucleosomes

Examine the reverse phased chromatography below. Each peak, A-G represents different protein. Rank the proteins from decreased to increased hydrophobicity of the protein.

A,B,C,D, E, F, G

Protein B, in the figure above has an absorbance reading of approximately .5 AU at 215 mm. Analysis yields 3 threonine amino acids which you replace with 3 tyrosines. Re analysis will show an absorbance reading also at 215nm will be___

The same as the protein with 3 threonines

Analysis of protein D in the figure indicate the protein contains 74 amino acids with polypeptide sequencing containing 2 alanines peptide bonded to 2 prolines which are all replaced with 2 asparagines bonded to 2 glutamines. The new protein will elute:

Closer to protein C

DNA molecules like proteins consist of a single long polymeric chain that is assembled from small monomer if subunits

False

The telomere is a specialized DNA sequence where micro tubules from te mitotic spindle attach to the chromosome so that duplicate copies move to opposite ends of dividing cells.

False

Generally the total number of non polar Amino acids has a greater effect on protein structure than the exact order of amino acids in a polypeptide chain

False

Studies conducted with lysozyme mutant contains an asp-->asn at position 52 and glu-->gln at 35 resulting in loss of enzymatic activity. What is the most likely explanation for this?

Absence of negative charges in the active site

Primase is needed to initiate DNA replication on both leading and lagging strand.

True

Phosphorylation of the amino acid threonine may alter the conformation of a protein by attracting which of the following amino acids?

Lysine