GRE Subject Test: Biology : Other Organelles

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

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Example Question #1 : Other Organelles

How are proteins imported into the nucleus?

Possible Answers:

Proteins are only exported from the nucleus

Translocation through nuclear pore complexes while they are being translated by membrane-bound ribosomes

Passive diffusion through nuclear pore complexes

With the assistance of special proteins known as importins 

Correct answer:

With the assistance of special proteins known as importins 

Explanation:

Nuclear import and export is tightly regulated by importin and exportin proteins. These proteins interact with target proteins to carry them into or out of the nucleus, respectively. Proteins cannot passively diffuse into the nucleus and they are not translocated into the nucleus during translation.

Example Question #2 : Other Organelles

Which of the following is true regarding the nucleus?

Possible Answers:

The nucleus is surrounded by multiple membranes

All of these answers

The nucleus is the site of assembly for ribosomal subunits

The nucleus is studded with many openings called nuclear pore complexes

Correct answer:

All of these answers

Explanation:

All of these choices are correct regarding the nucleus. Nuclear pore complexes are incredibly important for regulating nuclear import and export. Ribosomal subunits are assembled in the nucleolus, which is a portion of the nucleus. The nucleus is covered by two lipid bilayers, which constitute the nuclear envelope.

Example Question #3 : Other Organelles

What provides structural support for the nucleus and binds chromatin?

Possible Answers:

Lamina 

Nuclear envelope

Cytoskeleton

Nuclear pores

Nucleolus

Correct answer:

Lamina 

Explanation:

The correct answer is lamina. This is a fibrous network of filaments within the nucleus that provides architectual support similar to the cytoskeleton. Chromatin also is held in place by association with the lamina. 

Example Question #1 : Understanding Mitochondria And Chloroplasts

The inner mitochondrial membrane is organized into cristae, which essentially results in a series of folds within the mitochondria. Which of the following best describes the primary advantage to having cristae in inner compartments of mitochondria?

Possible Answers:

ATP synthase is sequestered from the outer membrane, thus increasing its potential energy. 

Increased surface area for the biochemical reactions to produce ATP, thus increasing metabolic output of each mitochondrion. 

Decreased requirement for input to the mitochondrion due to increased presence of glucose on the cristae membrane. 

Increased spacing of cytochromes to increase metabolic output.

Protection of integral membrane proteins from the extremely basic intracristal space of the mitochondria. 

Correct answer:

Increased surface area for the biochemical reactions to produce ATP, thus increasing metabolic output of each mitochondrion. 

Explanation:

ATP synthase and cytochromes stud the inner membrane, and more surface area means that more of them can be present in each mitochondrion. This increases the capacity to generate ATP. 

Example Question #1 : Understanding Mitochondria And Chloroplasts

Chloroplasts are found primarily in which cell type?

Possible Answers:

None of these

Mesophyll

Sclerenchyma

Collenchyma

Parenchyma

Correct answer:

Mesophyll

Explanation:

Chloroplasts are found primarily in the mesophyll cells. Mesophyll cells are the green colored tissue that is found within the leaf. It is the abundance of chloroplasts containing chlorophyll that give the mesophyll cells their green coloring. Parenchyma, sclerenchyma, and collenchyma cells are all found within the shoot and root of the plant, not in the leaves. These cell types have little to no chloroplasts within their membranes.

Example Question #1 : Understanding The Golgi Body And Endoplasmic Reticulum

Which of the following is not a common destination for proteins translated by membrane-bound ribosomes?

Possible Answers:

Plasma membrane

Cytosol

Secretory vesicles

Lysosomes

Correct answer:

Cytosol

Explanation:

Membrane-bound ribosomes are found on the surface of the rough endoplasmic reticulum. Proteins synthesized by membrane-bound ribosomes are translocated into the endoplasmic reticulum while they are being translated.

These proteins generally undergo modification in the rough endoplasmic reticulum and are packaged into vesicles by the Golgi apparatus. Vesicles from the Golgi apparatus then interface with the plasma membrane of the cell or the membranes of other organelles. Proteins from the interior of the vesicle can be released into the extracellular space or interior of other organelles. Proteins in the membranes of the vesicle become embedded in the plasma membrane of the cell or the organelle.

Proteins synthesized on free ribosomes commonly remain in the cytosol and are modified by different processes than protein synthesized on the rough endoplasmic reticulum.

Example Question #91 : Cell Biology

Which organelle is used to create triglycerides and other lipids?

Possible Answers:

Ribosome

Smooth endoplasmic reticulum

Golgi apparatus

Rough endoplasmic reticulum

Correct answer:

Smooth endoplasmic reticulum

Explanation:

The smooth endoplasmic reticulum serves several different purposes in the cell, one of which is lipid synthesis. This structure is responsible for producing phospholipids and cholesterol, as well as some steroid hormones and other lipid molecules. It also helps to eliminate foreign toxins from the cell.

The rough endoplasmic reticulum houses ribosomes that synthesize proteins that are destined for the membrane or extracellular environment. The Golgi apparatus is responsible for packaging proteins in vesicles, allowing for transport out of the cell. Ribosomes are involved in protein synthesis (translation).

Example Question #1 : Other Organelles

Which of the following is true about eukaryote ribosomes?

Possible Answers:

Eukaryote ribosomes are 80S, with one large 50S subunit and one small 40S subunit

Eukaryote ribosomes are 70S, with one large 60S subunit and one small 40S subunit

Eukaryote ribosomes are 80S, with two large 60S subunits and one small 40S subunit

Eukaryote ribosomes are 80S, with one large 50S subunit and one small 30S subunit

Eukaryote ribosomes are 80S, with one large 60S subunit and one small 40S subunit

Correct answer:

Eukaryote ribosomes are 80S, with one large 60S subunit and one small 40S subunit

Explanation:

Eukaryotic ribosomes are 80S with one large 60S subunit and one small 40S subunit. Prokaryotic ribosomes are 70S, with one large 50S subunit and one small 30S subunit. "S" refers to the sedimentation coefficient (Svedberg), which is a particles sedimentation velocity for a given applied acceleration.

Example Question #1 : Other Organelles

Which of the following best describes the ribosome in terms of its structural components?

Possible Answers:

DNA-protein complex

Protein subunit

RNA-protein complex

Multimeric protein complex

RNA monomer

Correct answer:

RNA-protein complex

Explanation:

Ribosomes can be classified as ribonucleoproteins because the proteins are associated with ribonucleic acids (RNA). Thus, RNA-protein complex is the best descriptor. 

Example Question #1 : Other Organelles

Ribosomes are the organelle responsible for the translation of mRNAs into proteins. To do this, ribosomes translate the mRNA codons into amino acids which are joined to form a long polypeptide. The ribosome has a catalytic domain that is responsible for the formation of the peptide bonds between these amino acids. What is the name, i.e. the enzymatic classification, of this domain in the ribosome?

Possible Answers:

AminoATPase

Polymerase

Peptidyl acylase

Ester transferase

Peptidyl transferase 

Correct answer:

Peptidyl transferase 

Explanation:

Interestingly, ribosomes are one of the only examples of an RNA structure that has enzymatic activity. The primary enzymatic function of the ribosome is one of a peptidyl transferase; that is, the catalysis of peptide bond formation between amino acids as those acids are brought to the nascent strand. 

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