All Biochemistry Resources
Example Questions
Example Question #1 : Anabolic Pathways And Synthesis
Which of the following statements is false about the human genome?
None of the other answers are false
The sequences which code for proteins make up about 2% of the genome
Repeated sequences make up about 5% of the genome
There are about 20,000 proteins that are coded for by the genome
Paralogs are homologous gene sequences caused by duplication events within the genome
Repeated sequences make up about 5% of the genome
Scientists have indeed counted about 20,000 proteins coded for by the genome. Coding sequences are only about 2% or less of the genome. The definition of paralogs is genes related by duplication within a genome. Within the genome, not about 5%, but rather about 50%, of DNA sequences are repeated.
Example Question #1 : Anabolic Pathways And Synthesis
Where does the pentose phosphate pathway primarily take place?
The brush border of the small intestine
The mitochondria of the kidney
The mitochondria of the liver
The cytosol of the liver
The cytosol of the liver
The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), which mainly serves to produce for anabolic reduction reactions and ribose-5-phosphate for nucleic acid production, takes place in the cytosol of hepatic cells.
Example Question #1 : Protein Synthesis
Which of the following amino acids can be created from the carbon skeleton of oxaloacetate?
Glutamine
Leucine
Valine
Histidine
Methionine
Methionine
From the carbon skeleton of oxaloacetate, methionine can be created. However, glutamine comes from alpha ketoglutarate, valine and leucine come from pyruvate, and histidine comes from ribose-5-phosphate.
Example Question #1 : Regulating Protein Synthesis
Which of the following molecules is not necessary to create glutamate from alpha-ketoglutarate?
Alpha-ketoglutarate
ATP
NADPH
Carbon dioxide
Carbon dioxide
The reaction for the conversion of glutamine into glutamate is:
As seen in the reaction above, carbon dioxide is uninvolved.
Example Question #1 : Regulating Protein Synthesis
Which of the following correctly lists the severity of damage done by mutations in DNA from most severe to least?
Missense, nonsense, silent
Nonsense, silent, missense
Silent, missense, nonsense
Nonsense, missense, silent
Nonsense, missense, silent
When a change results in an early stop codon, nonsense mutation occurs and the protein is done being read early, often resulting in a nonfunctional protein. When a base change results into a different amino acid, this is a missense mutation. When a base change occurs but results in the same amino acid being read, this is considered a silent mutation.
Example Question #6 : Regulating Protein Synthesis
Which of the following correctly describes the function of a signal sequence with respect to proteins?
Marks the protein to be destined inside the nucleus
Allows the protein to be recognized by the ubiquitination pathway for degradation
Serves as a signal for chaperone proteins to help fold the protein into the correct conformation
Allows the protein or peptide to act as a signaling molecule by recognizing its associated receptor
Transports proteins that are destined for the secretory pathway within cells
Transports proteins that are destined for the secretory pathway within cells
To answer this question, it's essential to have an understanding of what a signal sequence is.
A signal sequence (also sometimes called a signal peptide) is a specific sequence of amino acids on a polypeptide that appears near the beginning of translation. When this signal sequence is present, it causes a temporary halt in the translation process. Meanwhile, another protein called a signal recognition particle (SRP) comes along and binds to the ribosome that is translating the polypeptide. Together, this polypeptide-ribosome-SRP complex is transferred from the cytosol to the surface of the endoplasmic reticulum (ER). Once there, the complex allows the polypeptide to resume synthesis, but in doing so, causes it to be synthesized into the inner lumen of the endoplasmic reticulum. Consequently, this polypeptide will go on to be modified within the ER and also the Golgi apparatus. Afterwards, it will be sent off within a vesicle, where is will either be A) secreted outside of the cell or B) incorporated into the endomembrane system of the cell (in other words, the peptide will be inserted into a membrane such as the plasma membrane, ER membrane, Golgi membrane, etc.). Lastly, it is the nuclear localization sequence (NLS) that, when added to a protein, allows it to enter the nucleus through the nuclear membrane.
Example Question #2 : Regulating Protein Synthesis
Which of of the following are the termination signals for translation?
GUA, UAA, UAG
UAG, UAA, UTA
GUA, GAU, UAA
TUA, UAG, GAU
UAA, UGA, UAG
UAA, UGA, UAG
Just as there is an initiation codon regulating translation, there are termination codons that code for the end of translation. The three termination codons are UAA, UAG, and UGA.
A helpful mnemonic for these are the phrases:
You are annoying (UAA)
You are gross (UAG)
You go away (UGA)
Example Question #2 : Anabolic Pathways And Synthesis
What are some post-translational modifications collagen goes thru before attaining its final structure?
I. The precursor collagen molecule undergoes hydroxylation of selected proline and lysine amino acids.
II. The procollagen precursor is glycosylated by the addition of galactose and glucose.
III. Procollagen has amino and carboxy procollagen extension propeptides that make it soluble.
IV. Procollagen proteinases remove extension peptides from the ends of the molecule to form collagen.
I and IV
I, II, III, and IV
I, II, and III
I, III, and IV
I and II
I, II, III, and IV
Procollagen has amino and carboxy procollagen extension propeptides that make it soluble. The preprocollagen undergoes both hydroxylation and glycosylation at specific aminoacid residues to form procollagen. Once secreted extracellularly, proteinases remove the extension peptides from procollagen to form the final collagen molecule.
Example Question #1 : Anabolic Pathways And Synthesis
Which of the following enzyme cofactors transfer methyl groups?
B12 cobalamin, S-adenylosyl methionine, tetrahydrofolate
S-adenylosyl methionine, tetrahydrofolate
Tetrahydrofolate, biotin
B12 cobalamin, S-adenylosyl methionine, tetrahydrofolate, biotin
B12 cobalamin, S-adenylosyl methionine, tetrahydrofolate
Biotin moves carboxyl groups in the enzyme acetyl-CoA carboxylase. Tetrahydrofolate and S-adenylosyl methionine move methyl groups in amino acid synthesis and post-translational modifications such as DNA methylation. B12 cobalamin is a cofactor in the reactions producing succinyl-CoA and methionine, where it transfers methyl groups to complete the products.
Example Question #1144 : Biochemistry
Which of the following is a true statement regarding translation in eukaryotes?
During translation, the polypeptide is synthesized beginning from its carboxy terminus and ending with its amino terminus
All translation begins on bound ribosomes attaches to the rough endoplasmic reticulum
tRNA acts as the template for polypeptide synthesis during translation
The Shine-Delgarno sequence is a stretch of nucleotides on the RNA to be translated, which helps to initiate polypeptide synthesis by allowing the ribosomes to bind to the RNA
All translation begins in the cytoplasm on free ribosomes
All translation begins in the cytoplasm on free ribosomes
Translation is a process by which polypeptides are synthesized from a mRNA transcript, which was previously synthesized from the process of transcription. During this process, tRNA acts as a carrier by bringing with it specific amino acids to the ribosome, which are then incorporated into a growing polypeptide chain.
Eukaryotic translation differs in quite a few ways from prokaryotic translation. For one thing, prokaryotic mRNA contains a Shine-Delgarno sequence, which serves as a binding site for prokaryotic ribosomes to assemble on the mRNA. This binding, in turn, helps to initiate translation in prokaryotic cells. Eukaryotic cells do not contain a Shine-Delgarno sequence.
Furthermore, in eukaryotes, translation always begins with the assembly of ribosomal subunits on mRNA in the cytosol. Therefore, translation always begins on free ribosomes in the cytosol! Sometimes, translation will also finish on free ribosomes if the resulting protein is destined to stay within the cytosol where it will serve its function. Alternatively, if the first few amino acids of the polypeptide consists of a specific "signal sequence," translation will be temporarily paused. During this time, the entire ribosome-mRNA-polypeptide complex will be translocated to the rough endoplasmic reticulum. Once attached, polypeptide synthesis will resume and the polypeptide will thread its way into the endoplasmic reticulum. As it does so, additional folding and post-translational modifications are usually done to the polypeptide for it to carry out its proper function. Generally, polypeptides that make their way through the endoplasmic reticulum are destined either to be secreted out of the cell, or to become incorporated into the endomembrane system of the cell. And finally, as polypeptides are synthesized on a ribosome, whether it is free or bound, the amino terminus (aka N-terminus) side of the polypeptide is synthesized first and the carboxy terminus (aka C-terminus) is synthesized last.
All Biochemistry Resources
![Learning Tools by Varsity Tutors](https://vt-vtwa-app-assets.varsitytutors.com/assets/problems/og_image_practice_problems-9cd7cd1b01009043c4576617bc620d0d5f9d58294f59b6d6556fd8365f7440cf.jpg)