Download Name: Cell Biology Test #1: 50 points

Unit Written Questions: 10 points
Please write your answers on the paper provided:
Abbreviations for the 20 different amino acids: Phenylalanine-Phe, Leucine-Leu, Isoleucine-Ile, MethionineMet, Valine-Val, Serine-Ser, Proline-Pro, Threonine-Thr, Alanine-Ala, Tyrosine-Tyr, Histidine-His, GlutamineGin, Asparagine-Asn, Lysine-Lys, Aspartate-Asp, Glutamate-Glu, Cysteine-Cys, Tryptophan-Tyr, ArginineArg, and Glycine-Gly.
--------------------------------------------------------------------------------------------------------------------59) 5 pt: Examine the mRNA below and determine the protein (aa sequence) that would result from successful
translation by a ribosome.
a) # of amino acids ______
b) # of codons?_____ c) # of peptide bonds in protein?_____
d) Find the start codon and show the specific amino acids (names) in the specific sequence of the peptide
resulting from translation of this mRNA.
5’-AGCCUUAUGAGGCAGGGGAUGACCGAGCGCUAAGGCCGG-3’
Methionine-Typtophan-Glutamine-Glycine-Methionine-Threonine-Stop codon
Seven codons (last is stop codon-not an amino acid) Six amino acids Five peptide bonds
60) 2pt: The mRNA above was transcribed from a single template strand of DNA that was unwound from a
double helix. What was the base sequence of this template ssDNA?
5’-AGCCUUAUGAGGCAGGGGAUGACCGAGCGCUAAGGCCGG-3’
3’-TCGGAATACTCCGTCCCCTACTGGCTCGCGATTCCGGCC-5’ ssDNA
61) 3 pt: Compare and contrast the function of the smooth endoplasmic reticulum, the rough endoplasmic
reticulum and free ribosomes that are not bound to the ER? 20-40 words
rRNA: smaller segments of RNA that make up the large and small subunit of a ribosome. These two subunits
permit translation of mRNA to a peptide sequence and create docking sites for tRNA.
tRNA: 64=61 different types of tRNA can deliver amino acids to the A-site of a ribosome, the anticodon of the
tRNA must match (antiparallel) the codon of the mRNA
mRNA: this caries the codons (including start-methionine and stop-no tRNA) that are translated (3 amino acids
at a time) into an amino acid sequence
micoRNA: These are the RNA fragments that help fine tune transcription and probably even translation of our
genetic information into a peptide library. They let us as eukaryotic cells fine tune protein production and effect
to meet the ever changing demands of the cellular environment. We are finding that microRNA probably
represents the single largest quantity of RNA found in most cells.
Comprehensive Written Questions (12 points)
Choose 4 of the following 6 questions (3 pts each)
Please write answers on the paper provided
Useful Formulas:
Keq= [products]/[reactants] R=1.987 cal/mol K T=298 K
MM kinetics: v= Vmax [S]/(Km+[S]) LB Kinetics: 1/v= (Km/Vm)(1/[S]) + 1/Vmax
∆G= ∆G’o + 2.303 RT log [products]/[reactants]
Remember!!!!! 2.302(log X) = ln X
59) Consider this reaction in a skeletal muscle cell:
Phosphocreatine + ADP  Creatine + ATP
Phosphocreatine= 28 mM, Creatine = 8 mM, ADP=1 mM, ATP=8 mM, PO4=8mM
A) What is the standard ∆G’o for this reaction?
Show math, and final mathematical answer in CORRECT UNITS in correct formula.
B) Show the formula with numbers set in proper units that would permit you to properly calculate the
physiological delta G for the reaction under the conditions described above if you have access to a good
calculator
See Notes and Prior Delta G assignments
62) Draw and label the Michealis-Menton Plot for an enzyme-linked reaction and show the relationship
of Vmax and Km.
A) Normal Reaction (Km and Vm)
B) Plot of reaction in the presence of a competitive inhibitor (Km ci and Vm ci)
C) Plot of reaction in presence of a non-competitive inhibitor (Km nci and VM nci)
D) Can an enzymes Vm ever in practice be reached? Yes or No
Draw a plot like this on your answer sheet
Rxn
See Notes for three different curves
Velo
city
[S]
63) What is the Fluid Mosaic Model of a cell membrane? What are the characteristics of membrane
lipids and proteins that make this model work? (20-40 words with diagrams if this helps)
This model states that the plasma membrane consists of a phopholipid bilayer with polar heads facing
water (out) and the fatty acid tails facing each other in the hydrophobic center. Membrane proteins
either span the bilayer (transmembrane) or associate with just the cytosolic or extracellular sides
(integral or lipid-associated). Within each monolayer, phospholipids and proteins can float about or
diffuse laterally across their respective phospholipid monolayers, however they are unable to change
sides (flip-flop) because their polar ends or polar amino acids are unable to pass through the
hydrophobic center of the bilayer.
One limitation is that some proteins are securely anchored to intracellular structures. Ankyrin,
spectrin and actin can all participate in this regard. This way some proteins are expressed on only one
part of a cell’s plasma membrane.
64) With respect to glycolysis, many of the chemical reactions have a positive ∆G’o value. Describe
three things that a cell could use to improve product formation? (20-40 words)
Best: Remove product to pull substrates forward
Another good one: Increase Substrate concentrations
One fine trick: Link an unfavored reaction (+ΔG) with a favorable reaction (-ΔG) I nthe same
compartment/close proximity (no membranes between reactions)
Another fine trick: Use allosteric regulation where the product of a reaction or reaction pathway is used
to change enzyme function when you need more or less product by binding non-covalently at an allosteric
site
Other options: Change temperature, Km values, make/destroy enzymes, change [P] or [S] concentrations,
pH where reaction occurs, etc.
65) With respect to second messenger systems, why is intracellular amplification needed so that a
hormone such as insulin can change cellular function? Name and describe a hormone that does not require
amplification and how it functions in this regard. (20-40 words with diagrams if this helps)
Some hormones are unable to enter the cytosol and otherwise unable to modify the intracellular functions
of a cell. Other hormones are produced in such small amounts that they would be unable to create
changes in cellular function. Fro these hormones amplification of the extracellular message is made
possible by causing intracellular enzymes to change their function. For example insulin stimulates a
tyrosine kinase on the intracellular side which then potentially phosphorylates thousands of proteins
inside the cell, each target enzyme if a kinase or phosphatase can in turn modify the activity of thousands
of other proteins.
Testosterone and thyroxine are examples of hormones that do nto always cause or require amplification
inside the cell. These hormones tend to be lipid soluble and can, though do not always, directly bind to
DNA and alter the transcription of DNA into mRNA (enhancing or suppressing transcription and
translation). Sometimes after entering the cytosol a nuclear binding protein will carry the hormoneprotein complex to the nucleus where it will exert its effects.
66) Consider microtubules and microfilaments: compare and contrast their structure (subunits) and
function (describe two cellular functions that each is responsible for).
(20-40 words with diagrams if this helps)
Microtubules are the largest of the cytoskeletal systems and straight hollow cylinders
Have an outer diameter of 25 nm Inner diameter of 15 nm
Two general groups of microtubules in eukaryotic cells: Axonemal or Cytoplasmic microtubules
Microtubules structurally are straight hollow cylinders composed of protofilaments
Form a protofilament using simple monomers with Multiple (13 in total) protofilaments must interact to
form cylindrical structure. The basic unit (monomer) of a protofilament is tubulin (α-tubulin or Βtubulin )
Unit Extra Credit (2 pts 4 X ½ pt): Draw/Name and amino acid that would do the following:
a) Associate with the hydrophobic core of the lipid bilayer
b) Could be phosphorylated by a kinase
c) Would have a charged R-group that could attract calcium
d) Would permit collagen to form tight bundles due to its small size
See Notes
Comprehensive Extra Credit (up to 4 pts): Create a diagram/flow chart that names the substrates, products,
organelles and enzyme complexes that permit a single glucose molecule in the cytosol of a well oxygenated
eukaryotic cell (cardiac cell) to be completely oxidized in a mitochondria to carbon dioxide, generate a proton
gradient for ATP synthesis, as well as consume oxygen and ultimately produce of water. (chemical structures
optional)
See Notes