Dawn - BIO - Flashcards
How are Vmax and Km affected with a competitive inhibitor?
For Competitive inhibition the Vmax does not change, and the Km increases
What is secondary active transport and how does it differ from primary active transport?
Secondary active transport requires the input of energy to transport molecules across a membrane, BUT it does not have direct coupling of ATP (seen in primary active transport).
How does an uncompetitive inhibitor work? and what are the ideal conditions?
Uncompetitive inhibitors cannot act until the Enzyme and substrate bind together, thus, it works best when substrate concentration is high. (note: this causes Km and Vmax to decrease, meaning that the enzymes apparent affinity for the substrate increases and the maximum enzyme activity decreases)
What does a hill coefficient of 2.8 mean?
A hill coefficient greater than 1 = positive cooperativity (binding at one position or active site = occurs more easily). This creates a sigmoidal graph not a linear graph. Meaning that the second substrate molecule binds significantly more readily than its first
What is difference between cofactor, coenzyme, prosthetic group and apoenzyme
- Metal ions = cofactors (inorganic)
- Coezyme = organic cofactors
- Prosthetic group = cofactors that are tightly bonded to their enzymes
- Apoenzyme = Enzyme without its required cofactors
What is the difference between phosphatases and kinases?
- Phosphotases remove phosphate groups
- Kinases add phosphate groups (phosphorylation)
What pathways uses allosteric enzymes the most?
Feedback loops
Which amino acids are most likely to become phosphorlyated?
- Kinases phosphorylate the substrate!
- Most likely to be phosphorylated if they have -OH group attached (STY)
If the oxidation of NAD is blocked what happens to the NADH/NAD+ ratio?
The ratio will increase because the NADH cannot be oxidized to NAD+
How many carbons do oxaloacetate, acetyl-CoA, Ribose, and g-3-p have?
- Oxaloacetate = 4C
- Acetyl CoA = 2
- Ribose = 4
- g-3-p = 6
What is the greatest contributor to the change in free energy associated with protein folding?
- Change in DeltaS (entropy) because you want a large negative number to get a large negative deltaG
- Primary driving force behind protein folding is increased entropy made possible by the sequestration of hydrophobic residues in the protein core (make a tight, ordered cage = entropically unfavorable)
What would most likely increase glycolytic enzyme activity via allosteric regulation?
- Upregulation of glycolytic activity
- Increase [AMP] and low [ATP]
What does it mean for an amino acid to be ketogenic?
- Ketogenic amino acids that yield acetyl-
CoA or acetoacetyl-CoA - Meaning they do NOT produce intermediates that can be converted to glucose
- Lysine
(K) and Leucine (L) are the only amino acids that are exclusively ketogenic.
What is the best explanation for the finding that the substitution of pro residues on a protein can cause up to a
75% decrease in alpha helix formation compared with the native protein?
The ring on proline causes too much strain to be bent sufficiently in the helix.
- Proline is the only amino
acid whose amine group forms a ring. This means that it is unable to twist and turn with the same fluidity as
other amino acids.
What does it mean for an amino acid to be glucogenic?
- Glucogenic amino acids are amino acids which, when metabolized, yield pyruvate or Krebs cycle
intermediates, or that can be converted to glucose through gluconeogenesis. - They are alanine (A), arginine (R),
asparagine (N), aspartate (D), cysteine (C), glutamic acid (E), glycine (G), histidine (H), valine (V), methionine
(M), proline (P), and serine (S).
How many turns per residue are there for an alpha and a pi helix?
- Alpha - every 4th AA (3.6) with 5.4 angstroms between
2. Pi - every 5th (4.1)
A dipeptide is formed through the reaction of one
amino acid with another to form a peptide bond.
During this reaction, the nucleophile is:
- The amino terminal nitrogen of one of the
amino acids. - Peptide
bonds form between the amino terminal of one
amino acid and the carboxylic acid terminal of
another - They do not directly involve side chains
and the amino terminal nitrogen of one amino acid attacks the carbonyl carbon
of another.
The pKa of the side chain of histidine is
approximately 6. In a solution with a pH of 8, the
side chain of histidine is most likely to be:
Since the
side chain of histidine contains an N-H (which
is specifically part of an imidazole ring), it will
be positively charged when it is protonated and
uncharged when it is deprotonated.
How do you calculate the PI of histidine?
calculate isoelectric point, you
must consider the pKa values of the amino acid in
question. Histidine has a carboxylic acid group
(pKa ~ 2), an amino group (pKa ~ 9), and its side
chain (pKa ~ 6). Note that we should not average all
three of these values; instead, since histidine is a
basic amino acid, we should average the two most
basic pKas. (6 + 9) / 2 = 7.5.
What are the steps to Gabriel malonic ester synthesis?
- malonic ester
with a good leaving group (usually a halide, such as Br) attached to the alpha carbon - An SN2 reaction then takes
place with a nitrogen that is very carefully protected in the form of a bicyclic compound known as phthalimide. - The –H at the alpha-carbon is slightly acidic, so treatment with a strong base will deprotonate and allow R–X (where R is the side group of the
amino acid we’re interested in synthesizing and X is usually a halide) to attach to the alpha carbon. - Remove substituents
- Hydrolysis under basic
or acidic conditions will remove the phthalamide ring and convert the ester (COOR) groups to carboxylic acids
(COOH) - one round of decarboxylation through heat will remove the surplus COOH group, leaving us
with our amino acid.
What values of Kcat and Km do you need to have to display high specificity?
High Kcat, and low Km bc = Kcat/Km
What is the primary difference between microtubules and actin filaments?
Only actin filaments are capable of branched assembly, microtubule assembly can only produce single, straight microtubules, without branch points
If researchers wished to determine if myosin were necessary for proper cell function, which motility function
should be monitored in the experiment?
- Cleavage furrow formation in hepatocytes
- which aids the process of cytokinesis (daughter cell separation at the end of cell division), is based on the contraction of an array of actin filaments that are anchored to the plasma membrane
- The sliding of actin filaments is induced by the action of the motor protein myosin, which splits the parent cell into 2 daughter cells.
What is composed of actin?
- Microfilaments, not microtubules
In a G protein-coupled receptor system, the G protein:
A. is activated by the phosphorylation of GDP into GTP, and is inactivated by the hydrolysis of GTP.
B. is activated by the phosphorylation of GDP into GTP, and is inactivated when GTP dissociates and is replaced by GDP.
C. is activated when a GDP molecule is exchanged for a GTP molecule, and is inactivated by the hydrolysis of GTP.
D. is activated when a GDP molecule is exchanged for a GTP molecule, and is inactivated when GTP dissociates and is replaced by GDP.
- Answer C
- G proteins are activated when bound to GTP
- this binding occurs when a GDP molecule is exchanged for GTP
- Note that GDP is not simply phosphorylated; it is actually replaced by an entirely new GTP
- G proteins are rendered inactive by the hydrolysis of GTP
What bond type is on the 3’ end of a strand of viral DNA?
P-O bond
What is the average molecular weight of an AA?
110 Da
What is the difference between a denaturing, reducing and native gel electrophoresis?
- Denaturing - Disrupt the interactions between the monomers
- Reducing - only disrupts disulfide bonds
- Native - allows you to see the protein in its native state (can tell if something is integrated into a dimer)
What is an amide group and what amino acid has it?
-C=O-NH2
Tumors only occur if there is a mutation in here
Tumors only occur if there is a mutation in here
How does glucose act as antifreeze for the body?
the protection of glucose in this harsh environment is due to its effects on the diffusion of water (i.e., its osmotic effects). Glucogen stores raises the osmotic pressure of the body fluids and dehydrates cells protecting themm from freezing
Hyperglycemia normally elicits the secretion of what and suppresses what?
Elicits insulin secretion, suppresses glucagon
What does the extracellular fluid consist of?
- Blood plasma and lymph
Where is hemoglobin typically found? and what does it mean if its found someplace else?
- Typically found in RBC
- If found in plasma = cause the RBC to rupture or lyse
A prolonged increase in heart and breathing rates during the snow skiing trip was probably a result of:
hypoxia caused by insufficient blood hemoglobin concentration to supply oxygen for exercise at the low oxygen pressure found at high altitudes.
Why would myoglobin be detected in the urine?
- Myoglobin holds oxygen in muscles and organs, thus, if it is in urine then there is muscle or organ damage
Control of heart rate, muscle coordination, and appetite is maintained by what?
brain stem, cerebellum, and hypothalamus, respectively.
Why do blood vessels periodically dilate in cold environments?
Dilate for short periods of time to enable a sufficient supply of blood (and oxygen) to her cells. Due to the physical exertion of skiing, her cells had an increased need for oxygen.
How does BP affect glomerular filtration rate?
- Low BP = decrease filtration rate = more time for reabsorption = decreasing amount of substance in urine
- High BP = increase filtration ate = less time for reabsorption = increase in urine
Most bacterial cells and human cells are alike in:
A. the ability to produce ATP via ATP synthase.
B the chemical composition of their ribosomes.
C their enclosure within cell walls.
D the shape of the self-replicating structures that carry their DNA.
A
- Both types of cells possess a membrane-embedded electron transport chain capable of generating a H+ gradient, which drives synthesis of ATP via ATP synthase.
- This ATP synthesis takes place on the plasma membrane of bacteria and on the inner mitochondrial membrane in human cells.
Under what condition would the level of calcitonin tend to increase?
- When calcium in plasma is high
- Calcitonin reduces bone resorption. Bone resorption occurs when the level of calcium in the blood plasma is low
What happens if you remove the parathyroid gland?
- Removal of the parathyroid gland would lead to hypocalcemia, a condition of low blood calcium
- This would cause increased neuromuscular excitability because of the change in membrane potential, which under normal physiological conditions, is partially kept in balance with extracellular calcium
How does vasdilation of cutaneous blood vessels help to regulate the body temp of a human?
- Radiating excess body heat into the environment
Kidney failure during severe dehydration is most likely due to what?
severe dehydration greatly reduces the volume of filtrate moving through the nephrons of the kidney. If fluid volume is too drastically reduced, the kidney will be unable to effectively do its job of filtering and maintaining homeostasis within bodily fluid
Where do T cells mature?
Thymus
What cells are part of the innate immune system?
Neutrophils, macrophages, mast cells
In a viral infection what cell fights off this infection?
T cells –> grow up in thymus
Which innume cells act most immediately against bacterial pathogens following infection of a native host?
Neutrophils are a component of the
innate immune system. They recognize nonspecific
molecular motifs common to a wide range of
pathogens. This allows them to respond more
rapidly than B cells or T cells, which must be
generated via clonal expansion from their activated
precursors.
Where does an antigen bind to an immunoglobulin molecule?
In variable region, located on both light and heavy chains
Immune cells are capable of generating antibodies
with variable regions that are highly specific
for an immense number of antigenic epitopes.
The number of potential epitopes that can be
recognized far exceeds the number of genes coding
for immunoglobulin molecules. This variation is
made possible by:
A. alternative RNA splicing.
B. recombination of DNA sequences.
C. post-translational modifications.
D. histone modifications.
B
- The DNA sequence coding for the
antibody variable region is developed randomly
via recombination of a relatively small number
of genes
- This process results in a cell with a
genome that differs from that of all other somatic
cells
- Cells that happen to express genes coding
for variable regions specific for self antigens are
selected against, while those not specific for self
antigens are allowed to develop.
What is adaptive immunity and what does it consist of?
- Adaptive immunity is the branch of the immune response that recognizes and responds to specific pathogens. (In contrast, innate immunity provides general, non-pathogen- specific protection.)
- Adaptive immunity includes B lymphocytes, which produce antibodies (alternatively termed immunoglobulins). T lymphocytes are also a component of the adaptive immune response, but macrophages are part of innate immunity.
What structure do prokaryotes establish a proton gradient against?
Plasma membrane bc they lack membrane bound organelles (cant use mitochondrial membrane) and not all of them have cell walls
What is the difference between transformation and transduction?
- transformation - occurs when bacteria pick up genetic material from their surroundings
- Conjunction = bacterium exchanges genetic material with another cell via specialized sex pilus - Transduction - Bacteriophage transfers genetic material from one bacterial cell to another during infection
In conjugation what happens to the population and genetic diversity and how can genetic material be transfered?
- NO change in population size, but INCREASE in genetic diversity
- Hfr strain can only mate with other females (F-) because they lack factor
What is the difference between class I and Class II transposons?
BOTH - first undergo transcription into RNA using RNA polymerase; as their name implies, they are then reverse transcribed back into DNA and placed in a distinct location elsewhere in the genome.
- Class I - COPY and paste (so it makes an additional copy of the transposon)
- Class II - CUT and paste - so no additional copy
Which of the following is true of a typical viral capsid?
A. It is typically amorphous and lacks discernible symmetry.
B. Lipids comprise a substantial amount of the capsid material.
C. Most viruses have only one or two genes coding for capsid proteins.
D. The capsid monomers are assembled into a complete structure by host ribosomes.
C - bc Most viral capsids are composed of repeated identical monomers, reducing the need for a large genome containing multiple different genes for structurally distinct capsid proteins.
What is the hallmark of prion disease pathology?
- Protein aggregation problems
- ie: if missing heat shock activity (whcih helps fix misfolded proteins) then likely not a prion issue
“Which sequence properly indicates the transmission path of impulses as a direct result of transcranial magnetic stimulation?
A. Sensory neurons, cerebral cortex, afferent neurons, skeletal muscle cells
B. Skeletal muscle cells, afferent neurons, spinal cord, cerebral cortex
C. Cerebral cortex, spinal cord, efferent neurons, skeletal muscle cells
D. Efferent neurons, afferent neurons, interneurons, cerebral cortex
“
C bc its efferent not afferent and the others dont end in skeletal muscle
"TMS pulse causes depolarization of the motor cortex and an electrical and motor response in the muscle tissue, Which of the following processes is involved in the motor-evoked potential elicited by transcranial magnetic stimulation? I. Na+ influx II. Ca2+ release III. Cl- efflux A. I only B. II only C. II and III only D. I and II only "
D bc depolarization means influx of Na+ and muscle activation means release of Ca2+ from sarcoplasmic reticulum
“The peptide bond that forms the backbone of proteins is especially stable because it:
A. consists of a triple bond, which is significantly stronger and more stable.
B. is a carboxylic acid derivative.
C. would result in proteins that denatured easily if it were unstable.
D. exhibits resonance stabilization.
“
D - A peptide is an amide linkage between the amine group of one amino acid and the carboxylic acid group of another. Amides are stable because they exhibit resonance stabilization between the lone pair on the nitrogen and the double-bond in the carbonyl group, as shown below.
“In prokaryotes, genes can exist as operons that are transcribed into a polycistronic mRNA, containing multiple genes in a single transcript. In eukaryotes, transcripts exist only as monocistronic mRNA containing a single gene. What fundamental genetic difference is responsible for this distinction?
A. mRNA is transported outside of the nucleus in eukaryotes.
B. Prokaryotic mRNA has a 5’ GTP cap.
C. Prokaryotic ribosomes differ from eukaryotic ribosomes.
D. In eukaryotes, each gene has its own transcription initiation site.
“
D - note A is true but doesnt answer the question because it talks about transport not number of genes per mRNA transcript
“In miRNA-directed gene silencing, a small RNA binds to an mRNA and directs degradation of the mRNA or prevents translation of the mRNA. Which of the following terms describes the process through which binding occurs?
A. RNA polymerization
B. Hybridization
C. Elongation
D. Transcription”
“B is correct. This is a question of definition; only hybridization describes a process of binding through complementary nucleotides.
A: Polymerization is the process by which nucleotides are strung together to form a single-stranded RNA strand, not the joining of two complementary strands.”
” Which of the following enzymes should the researchers add to the cell samples if they want to reverse the general catalytic effects of protein kinase A?
A. Glycogen phosphorylase B. Phosphoglucomutase C. Protein phosphatase 1 D. Lactate dehydrogenase "
“C is correct. As a kinase, PKA functions to add a phosphate group to its substrate. The opposite of this activity is the removal of phosphate from a substrate, a function which is performed by phosphatase enzymes.
A: Phosphorylase enzymes also add phosphate groups to their substrates, so the “general effect” of a phosphorylase on its substrate is similar to that of a kinase. Specifically, kinases transfer phosphate groups from a high-energy source (usually ATP) to their substrates, while phosphorylases transfer phosphate from an inorganic phosphate source.”
“Increasing plasma concentration of aldosterone is most likely to be followed by which of the following?
A. Increased water reabsorption through increased aquaporin channels in the collecting duct
B. Increased sodium reabsorption in the distal tubule
C. Decreased water reabsorption in the collecting duct
D. Decreased plasma calcium concentration “
“B is correct. Aldosterone is released from the adrenal cortex in response to low blood pressure. Its primary function is to increase sodium reabsorption in the distal tubule and collecting duct. Aldosterone upregulates the sodium-potassium pumps along the lining of the nephron, pumping three sodium ions OUT of the nephron lining (and toward the blood) for every two potassium ions it pumps IN (toward the nephron and away from the blood). Since we have a net solute movement out of the nephron, aldosterone also increases the gradient that favors water reabsorption.
A: Although aldosterone causes an increase in passive water reabsorption, it does not do so through regulation of aquaporin channels. That’s the effect of ADH.”
“B is correct. Aldosterone is released from the adrenal cortex in response to low blood pressure. Its primary function is to increase sodium reabsorption in the distal tubule and collecting duct. Aldosterone upregulates the sodium-potassium pumps along the lining of the nephron, pumping three sodium ions OUT of the nephron lining (and toward the blood) for every two potassium ions it pumps IN (toward the nephron and away from the blood). Since we have a net solute movement out of the nephron, aldosterone also increases the gradient that favors water reabsorption.
A: Although aldosterone causes an increase in passive water reabsorption, it does not do so through regulation of aquaporin channels. That’s the effect of ADH.”
cytoplasmic components
“What aspects separate single-crossover events from double-crossover events?
A. Single-crossover events result in one-way displacement of chromosomal content from one chromosome to another, while double-crossover events always reverse this one-way displacement, resulting in chromosomes identical to the pre-crossover chromosomes.
B. Single-crossover events occur during mitosis when a cell splits into two cells, while double-crossover events can only occur during meiosis when a cell splits into four cells.
C. Single-crossover events affect only the ends of chromosome arms, while double-crossover events can affect segments in the middle of chromosome arms.
D. Single-crossover events only affect one arm of each chromosome, while double-crossover events affect two arms of each chromosome.”
C is correct. A double-crossover event is one in which chromosomal arms of homologous chromosomes cross over in two different places along the arm. This results in a section in the middle of each chromosome being exchanged
What is hyperglycemia?
High glucose levels in the blood
" In a population of Amish people, the frequency of the recessive autosomal allele for polydactyly is 1.2%. What percent of the population are heterozygotes for the polydactyly allele? A. 0.0144% B. 1.19% C. 2.37% D. 97.6% "
C
“Positron Emission Tomography (PET) scans follow the movement of a radioactively labeled compound throughout the body and are often used to detect metabolic activity in cancer cells relative to normal cells. The labeled compound is most likely:
A. pyruvate.
B. acetyl-CoA.
C. ATP.
D. glucose.”
D
What is the most significant obstacle for a cancer drug in the blood stream?
- Blood and cytosol are made of lots of water so if the drug is hydrophilic it will have a hard time moving through the blood stream
If glycolysis or fermentation are inhibited what happens to lactate levels?
Drop!
How does cholesterol affect membrane fluidity in moderate, high and low temperatures?
”- At moderate to high temperatures (including normal physiological temperature), cholesterol increases the rigidity of cell membranes by attracting adjacent phospholipid tails
- at very low temperatures; cholesterol fills in the gaps between phospholipid tails, preventing the membrane from becoming too rigid.)”
How does cholesterol affect membrane fluidity in moderate, high and low temperatures?
”- At moderate to high temperatures (including normal physiological temperature), cholesterol increases the rigidity of cell membranes by attracting adjacent phospholipid tails
- at very low temperatures; cholesterol fills in the gaps between phospholipid tails, preventing the membrane from becoming too rigid.)”
“Which of the following correctly lists a pair of analogous structures and a pair of homologous structures, respectively?
A. The wing of a bee and the wing of a bird; the wing of a bird and the leg of a bird
B. The wing of a bee and the wing of a bird; the arm of a human and the flipper of a walrus
C. The arm of a human and the wing of a bat; the wing of a bird and the wing of a bat
D. The wing of a bird and the wing of a bat; the wing of a bee and the wing of a bat”
“B
- Analogous structures are those structures that evolved independently to carry out the same function
- Homologous structures are those that have a similar evolutionary history, arising from the same source, even if they now have different functions.”
“During sedimentation analysis, which of the following best explains why the 60S and 40S subunits together do not result in a 100S ribosome?
A. The volume of the ribosome is smaller than sum of the volumes of each subunit.
B. Buoyant force on the ribosome is smaller than the sum of the buoyant forces on each subunit
C. Drag force on the ribosome is smaller than the sum of the drag forces on each subunit
D. The gravitational force on the ribosome is greater than the sum of the gravitational forces on each subunit”
“C is correct.
- During sedimentation analysis, a tube with sucrose solution is covered with a layer which contains the sample molecules of interest.
- The tube is then centrifuged (spun at high speed) for several hours; the sucrose gradient remains stable.
- Depending on the sizes/molecular weights of the macromolecules in the sample, they migrate through the gradient at different rates: lighter molecules will move less quickly than denser molecules.
- Each molecular type will eventually form a discrete band at its isopycnic point, where its density equals that of the sucrose gradient.
- The volumes of the subunits are additive which means that the buoyant force on subunits is additive. The masses are additive so the gravitational force is additive as well.
- The drag force has the most to do with the shape of the falling particle, which will change when the subunits come together.”
"Which of the following RNA molecules forms the most stable, long-term RNA-protein structure? A. mRNA B. rRNA C. tRNA D. snRNA"
B is correct. rRNA and proteins combine to form the nucleoprotein called a ribosome. The ribosome serves as the site and carries the enzymes necessary for protein synthesis. Thus, rRNA forms most of the structure of ribosomes.
"Phosphodiester bonds connect monomers of which of the following biomolecules? A. Polypeptides B. Polysaccharides C. Nucleic acids D. Polyamines"
”- Phosphodiester bonds connect
individual nucleotide monomers to form nucleic
acid polymers, such as DNA or RNA.
- Polypeptides
are composed of amino acids joined by peptide
bonds
- Polysaccharides are composed of
monosaccharide monomers joined by glycosidic
linkages
- Polyamines are molecules with two or
more primary amino groups, but they do not
necessarily contain phosphodiester bonds like
nucleic acids.”
“Which of the following statements correctly describes a structural or functional difference between DNA and RNA?
A. The sugar found in DNA contains more -OH groups.
B. DNA is capable of a greater diversity of functions.
C. RNA is less likely to be single-stranded.
D. RNA is capable of catalyzing reactions.”
“D
- While DNA is used primarily for transmitting genetic information, RNA is capable of a greater diversity of functions (eliminate choice B).
- One of these is the ability for ribozymes, which are composed of RNA, to catalyze chemical reactions.
- DNA cannot act as a catalyst.
- Note also that ribose, the sugar found in RNA, contains one more -OH group than deoxyribose, the sugar present in DNA. DNA is typically double-stranded, meaning that RNA is more (not less) likely to be single-stranded.”
"If the percent composition of adenine in a sample of double-stranded DNA is 34%, what is the percent composition of cytosine? A. 16% B. 17% C. 32% D. 34%"
A
“All of the following are true of the sugar found in ribonucleosides EXCEPT:
A. it is a pentose.
B. it is a furanose.
C. it has a formula of C5H10O5.
D. it contains the 3’ -OH group that deoxyribonucleosides lack.”
“D
- Ribonucleosides contain ribose, while deoxyribonucleosides contain deoxyribose.
- Ribose does contain a 3’ -OH group, but so does deoxyribose; it is the 2’ -OH group that deoxyribose lacks.”
What are the units for k for the rate constant for zero, 1st, 2nd, 3rd order reactions?
“zero - Ms-1
1st - s-1
2nd M-1s-1
3rd M-2s-2”
"Which of the following PAGE conditions would allow for the accurate determination of quaternary structure of a trimeric protein? A. Native gel B. SDS-PAGE C. Reducing gel D. Non-reducing gel"
“C
– In order to determine quaternary (i.e. subunit) structure, the conditions must be able to target and then break up the links (e.g. disulfide links) holding quaternary structure together.
- Under reducing conditions interactions between polypeptides is disrupted. However, under non-reducing conditions, the interactions are preserved.
A. Native gels means the proteins runs as it exists in vivo, meaning all of its protein structure remains intact.”
“A tired research student is setting up an isoelectric focusing procedure. He accidentally adds a lysinerich protein to the pH-gradient gel instead of his desired sample, which was largely composed of hydrophobic residues. How would this mistake impact his findings?
A. The protein will be observed to move more rapidly toward the positively-charged pole.
B. The protein will become stationary at a position farther from its isoelectric point.
C. The protein will travel a greater distance toward the anode.
D. The protein will become stationary at a position closer to the cathode.”
“D is correct.
- A protein rich in lysine (a basic amino acid) will have a higher isoelectric point (pI) than a protein largely formed from hydrophobic residues.
- A higher pI means the protein will tend to be more positively charged and will thus move closer to the negative end of the gel.
- In electrophoresis, the apparatus functions like an electrolytic cell, meaning that the anode is positive and the cathode is negative.
- The lysine-rich protein, which is positively charged at physiological pH, then, will move closer to the negatively-charged cathode.
- Note that in isoelectric focusing, a protein or amino acid always becomes stationary when it has reached the portion of the gel corresponding to its isoelectric point.”
” If a protein is at a pH below its isoelectric point, which of the following is true?
A. The protein will have a net positive charge.
B. The protein will have a net negative charge.
C. The protein will have net charge of zero.
D. The protein does not contain charged side groups.”
A is correct. This question is asking us to determine the state of a protein at a pH below its isoelectric point. We can see from Figure 1 that at a pH below its pI, the protein will move toward the right, toward the cathode. Since the cathode is negative, this means that the protein must be positive.
” Which of the following is the isoelectric point of alanine?
A. 5.5
B. 6.5
C. 7
D. 9”
A is correct. We know that alanine has no acidic or basic side groups, but (like all amino acids) it does have an amino terminus and a carboxy terminus that contribute to the pI calculation. A basic understanding of pI leads us to the recognition that in an amino acid like alanine, we can simply take the average of the pKas of the amine and carboxy termini. This gives us (2 + 9) / 2 = 5.5.
What is the difference between the lysogenic and lytic phase?
“1. Lysogenic phase - the virus is dormant and its DNA is integrated with that of the host’s genome
- All of the daughter cells from the initial infected cell will carry the virus’s genetic information
- At some point, the virus will be triggered and will hijack the cellular machinery in order to produce viral progeny
- This marks the entry into the lytic phase.
2. Lytic phase - host cells are actively producing more virus progeny and are being lysed to so that the viruses can go on to infect other cells.”
“In what way does the synthesis of phage proteins in the infected cell differ from protein synthesis in a eukaryotic cell?
A. Eukaryotic protein synthesis begins prior to completion of transcription.
B. Eukaryotic protein synthesis occurs in the cytoplasm.
C. Synthesis of prokaryotic proteins occurs only from mRNA molecules coding for a single protein.
D. Eukaryotic protein synthesis takes place on 80S ribosomes.”
D is correct. Eukaryotic protein synthesis occurs on 80S ribosomes. These are distinct in their subunit composition from 70S ribosomes, which are found exclusively in prokaryotes. “Phage” is short for “bacteriophage,” meaning a virus that reproduces using the host prokaryotic machinery.
