Science Mastery Assessments Flashcards
(104 cards)
In a neutral solution, most amino acids exist as:
Zwitterions
The carboxylic acid is deprotonated and the amine will remain protonated. This dipolar ion is a zwitterion
At pH 7, the charge on a glutamic acid molecule is…
-1
Both carboxyl groups are negatively charged and the amino group is positively charged = overall -1 charge
Nonpolar R groups in aqueous solution are…
Hydrophobic and found buried with proteins
Scientists discover a cDNA sequence for an uncharacterized protein. In their initial studies, they use a computer program designed to predict protein structure. Which of the following levels of protein structure can be most accurately predicted? A. Primary B. Secondary C. Tertiary D. Quaternary
A. Primary
cDNA is a DNA copy of the mRNA used to generate a protein
A computer program can identify the amino acid that corresponds to each codon and generate a list of these amino acids. This amino acid sequence is the primary structure
How many distinct tripeptides can be formed from one valine molecule, one alanine molecule, and one leucine molecule?
6
3 for valine, 2 for alanine, and 1 for leucine: 3x2x1=6
VAL, VLA, ALV, AVL, LVA, and LAV
What happens to the entropy of water and protein during protein folding?
Entropy of the water increases and entropy of the protein decreases.
As protein foods, it takes on an organized structure = decrease entropy
An a-helix is most likely to be held together by…
Hydrogen bonds between the carboxyl and amino groups
Side chains are too far apart to participate in string interactions
Which of the following is least likely to cause denaturation of proteins?
A. Heating the protein to 100C
B. Adding 8M urea
C. Moving it to a more hypotonic environment
Adding a detergent such as sodium dodecyl sulfate
C. Moving it to a more hypotonic environment
High salt concentrations, detergents, and high temps. denature a protein, but a lower solute concentration does not
A particular a-helix is known to cross the cell membrane. Which of these amino acids is most likely to be found in the transmembrane portion of the helix? A. Glutamate B. Lysine C. Phenylalanine D. Aspartate
C. Phenylalanine
Transmembrane of a-helix will be exposed to a hydrophobic environment, so we need an amino acid with a hydrophobic side chain
Which of these amino acids has a chiral carbon in its side chain?
A. Serine
B. Threonine
C. Isoleucine
Threonine and Isoleucine
Every amino acid, except glycine, has a chiral a-carbon, but threonine and isoleucine are the only two that also have a chiral carbon in their side chains
Following translation and folding, many receptor tyrosine kinases exist as monomers in their inactive state on the cell membrane. Upon the binding of a ligand, these proteins dimerize and initiate a signaling cascade. During this process, their highest element of protein structure changes from ___ to ___.
Tertiary to quaternary
In their inactive state, tyrosine kinases are fully folded single polypeptide chains and have a tertiary structure. When they dimerize, they become a protein complex and have a quaternary structure.
Which of these amino acids has a side chain that can become ionized in cells? A. Histidine B. Leucine C. Proline D. Threonine
A. Histidine
The imidazole ring has a nitrogen atom that can be protonated
In lysine, the pKa of the side chain is about 10.5. Assuming that the pKa of the carboxyl and amino groups are 2 and 9, respectively, the pI of lysine is ___.
9.75
Lysine has a basic side chain so we ignore the pKa of the carboxyl group. We average the pKa of the amino and side chain groups: (9 + 10.5)/2 = 9.75
Which of the following is a reason for conjugating proteins?
A. To direct their delivery to a particular organelle
B. To direct their delivery to the cell membrane
C. To add a cofactor needed for their activity
All of the above
Conjugated proteins can have lipid or carbohydrate “tags” added to them. These tags indicate that the protein should be directed to the cell membrane or to a specific organelle. They can also provided the activity of the protein.
Collagen consists of 3 helices with carbon backbones that are tightly wrapped around one another in a “triple helix.” Which of these amino acids is most likely to be found in the highest concentration? A. Proline B. Glycine C. Threonine D. Cysteine
B. Glycine
Triple helix means the carbon backbones are close together and steric hindrance is an issue. Glycine has a small side chain that reduces this issue
Hyperbaric oxygen may be used as a treatment for certain types of bacterial infections. In this therapy, the patient is placed in a chamber in which the partial pressure of oxygen is significantly increased, increasing the partial pressure of oxygen in the patient’s tissues. This treatment is most likely used for infections with…
Obligate anaerobic bacteria
These can’t survive with oxygen and would be killed by kuscheln therapy
Which of the following does NOT describe connective tissue cells?
A. They account for most cells in muscles, bones, and tendons
B. They secrete substances to form the extracellular matrix
C. In organs, they tend to form the stroma
D. In organs, they provide support for epithelial cells
A. They account for most cells in muscles, bones, and tendons
Bones and tendons are predominantly composed of connective tissue, but muscle tissue is different
Which type of nucleic acid could form the genome of a virus?
Single-stranded RNA, double-stranded DNA, and single-stranded DNA
The theory of spontaneous generation states that living organisms can arise from nonliving material. In 1859, Pasteur demonstrated that no organisms emerged from sterilized growth media, weakening the theory of spontaneous generation and supporting which tenet of cell theory?
Cells arise only from preexisting cells
Sterilization kills all living cells so no growth in this environment supports this tenet
Mitochondrial DNA is ___ and ___.
Circular and self-replicating
Mitochondrial DNA evolved from an anaerobic prokaryote engulfing an aerobic prokaryote and establishing a symbiotic relationship, so mDNA is similar to bacterial DNA. Both are organized into a single circular chromosome of double-stranded DNA that can replicate during binary fission
Which I of the following is NOT a function of the smooth ER? A. Lipid synthesis B. Poison detoxification C. Protein synthesis D. Transcription of proteins
C. Protein synthesis
Protein synthesis is a function of the ribosomes associated with the rough ER
What is the main function of the nucleolus?
Ribosomal RNA synthesis
Which of the following organelles is surrounded by a single membrane? A. Mitochondria B. Lysosomes C. Nuclei D. Ribosomes
B. Lysosomes
Mitochondria and nuclei are surrounded by double membranes. Ribosomes are surrounded by no membranes since they are present in eukaryotes and prokaryotes.
Which of the following is NOT a difference that would allow one to distinguish a prokaryotic and a eukaryotic cell?
A. Ribosomal subunit weight
B. Presence of a nucleus
C. Presence of a membrane on the outside surface of a cell
D. Presence of membrane-bound organelles
C. Presence of a membrane on the outside surface of the cell
Both gram- negative bacteria and animal cells share this feature