Chapter 5: Organelles

Exocytosis

process by which cell release proteins and other molecules into extracellular environment through fusion of transport vesicles with plasma membrane

List some of the lysosomal storage diseases.

-Tay-Sachs Disease -Hunter syndrome -Hurler syndrome -Gaucher syndrome

An organelle with DNA, distinct from genomic, chromosomal DNA and ribosomes is believed to have originally been a single-celled independent organism engulfed by ancestral eukaryotic cells. This organelle is A. A mitochondrion. B. The cis Golgi complex. C. Rough endoplasmic reticulum. D. A nucleus. E. A peroxisome.

A. A mitochondrion. A mitochondrion is an organelle with its own DNA that is separate from the genomic DNA of the nucleus. Mitochondria are believed to have been engulfed by ancestral eukaryotic cells. The cis Golgi is a portion of flattened sacs between the rough ER and medial Golgi and contains no DNA. Rough ER have attached ribosomes and function in translation of protein from mRNA. Nuclei contain genomic DNA within chromosomes. Peroxisomes are bounded by single membranes and breakdown fatty acids and purines and detoxify hydrogen peroxide.

A single membrane-enclosed organelle is observed to be in close proximity to the plasma membrane. It appears to surround newly modified proteins in membrane-enclosed structures. The most likely identity of this organelle is A. Golgi complex. B. Lysosome. C. Mitochondria. D. Nucleus. E. Peroxisome.

A. Golgi complex. The Golgi complex is a series of membrane-enclosed tubules involved in protein processing. It is localized near the plasma membrane and places newly modified proteins within the vesicles that bud off from the Golgi. Mitochondria and nuclei have double membranes. Lysosomes and peroxisomes do have single membranes but are not involved in protein processing. Lysosomes are produced from the Golgi and peroxisomes from the endoplasmic reticulum.

An organelle is bounded by a single membrane and contains hydrolytic enzymes that were synthesized on free ribosomes. From which structure was this organelle derived? A. Mitochondria B. Nucleus C. Endoplasmic reticulum D. Golgi E. Lysosome

C. Endoplasmic reticulum The organelle described is a peroxisome, which is derived from regions of the endoplasmic reticulum, and not from regions of the Golgi complex, which form lysosomes. Mitochondria and nuclei do not directly give rise to the structures of other organelles.

Two-cell types are compared for their ability to produce ATP from glucose, and while one produces only 2 ATP per glucose, the other has an ATP yield of 32 ATP from the glucose. The most likely difference between these cells that contributes to this finding is A. Mutation in acid hydrolase within lysosomes of one cell type only. B. Presence of mitochondria in one cell type but not in the other. C. Absence of a particular peroxisomal hydrolase in one cell type only. D. One cell types' inability to breakdown fatty acids and purines to extract energy. E. Accumulation of glycosaminoglycans in one cell type, inhibiting ATP production.

B. Presence of mitochondria in one cell type but not in the other. The presence of mitochondria within a cell enhances the amount of ATP produced per glucose. One cell type was likely to be red blood cells, which lack mitochondria and produce only 2 ATP per glucose compared with 32 ATP per glucose in cells with mitochondria. This mitochondrial-dependent process of ATP production in mitochondria is oxidative phosphorylation. It is not dependent on peroxisomes or lysosomes (or their acid hydrolases) or breakdown of fatty acids and purines, a process that normally occurs in peroxisomes. Glycosaminoglycans accumulate in particular lysosomal storage diseases, unrelated to ATP production from mitochondria.

A 7-month-old girl who previously had a normal development now exhibits signs and symptoms of Tay-Sachs disease. Which of the following organelles is affected in this disorder? A. Endoplasmic reticulum B. Golgi C. Lysosomes D. Mitochondria E. Peroxisomes

C. Lysosomes Tay-Sachs disease in an infant is acquired via autosomal recessive inheritance, with one mutant HEXA gene from each parent. The HEXA gene is on chromosome 15, not on the X chromosome or encoded by mitochondrial DNA. Inheritance is autosomal recessive, not autosomal dominant. The disorder is lysosomal, not peroxisomal; peroxisomes are not engulfed by cells but are intracellular organelles.

A membrane-enclosed intracellular structure is observed to release a protein through a pore into the cytosol. Following this release, biochemical reactions take place and result in the cell's death by apoptosis. The most likely identity of this intracellular structure is A. Golgi complex. B. Lysosome. C. Mitochondria. D. Nucleus. E. Peroxisome.

C. Mitochondria. Mitochondria release cytochrome c into the cytosol, initiating a cascade of biochemical events that result in apoptotic cell death. The nucleus contains the cell's DNA. The Golgi complex participates in modifying and sorting newly produced proteins. Lysosomes and peroxisomes are distinct from each other but are both involved in digestion.

The child with Tay-Sachs disease, described in question 5.8, most likely acquired this disorder via A. Inheritance of mutation on X chromosome inherited from her father. B. Autosomal dominant inheritance of mutant HEXA gene from one of her parents. C. Mitochondrial inheritance of HEXA mutation from her mother. D. Inheritance of the same or different HEXA mutations from both her parents. E. Acquisition of defective peroxisomes via engulfment.

D. Inheritance of the same or different HEXA mutations from both her parents. Tay-Sachs disease is a lysosomal storage disease. A mutant lysosomal hydrolase prevents the breakdown of certain macromolecules. In Tay-Sachs disease, gangliosides accumulate in the brain, causing the signs and symptoms. The other organelles listed are unaffected in Tay-Sachs disease.

A previously healthy 24-year-old male develops optic neuropathy and becomes blind. His mother's brother has the same condition. The patient is told that while his condition is inherited, there is no chance that he will pass his mutant gene to any of his future children. What type of disorder most likely affects this patient? A. Autosomal recessive disorder B. Disease of aging C. Lysosomal storage disease D. Mitochondrial disease E. Peroxisomal disorder

D. Mitochondrial disease This patient most likely has a mitochondrial disease. (He may have Leber hereditary optic neuropathy.) Mitochondrial diseases are inherited exclusively from the mother. Since sperms do not enter fertilized eggs, a male individual cannot pass on a defective mitochondrial gene to his children. This is the only type of condition that a male has no chance of passing on to any of his children. Autosomal recessive genes require both parents to pass on a mutant gene in order for a child to be affected. In autosomal conditions though, an affected person would have a 50% chance of passing on a mutant gene to his children. A 24-year-old man is not old enough to exhibit signs and symptoms of a disease of aging. Lysosomal storage diseases are often autosomal recessive. Peroxisomal disorders are generally present at birth and affected individuals have a very short life expectancy.

In the laboratory, you are preparing for microscope of tissue samples taken from a patient's testis where a lipid hormone was actively being made. Which of the following in the cytoplasm would you expect to be present in large amounts to aid in the synthesis of this hormone? A. major storage site for calcium ions B. multi-protein complex that digests small, misfiled proteins C. organelle that performs autophagy D. organelle where plasma membrane proteins are translated E. protein/RNA complex where translation occurs

D????

Nuclear lamina is composed mainly of A. Collagen. B. Microtubules. C. Phospholipids. D. Cholesterol. E. Intermediate filaments.

E. Intermediate filaments. Nuclear lamina is composed mainly of intermediate filaments. The interior of the nucleus containing the nucleoplasm is organized by the nuclear lamina, the protein scaffolding of the nucleoplasm that is composed mainly of intermediate filaments, which are cytoskeletal components. Microtubules are also cytoskeletal components but not the main ones found in nuclear lamina. Collagen is secreted by cells into the extracellular matrix and is not found within the nucleus. Phospholipids and cholesterol are main constituents of biological membranes.

A cytosolic cellular structure with two subunits is observed to assemble and disassemble and to bind to mRNA and to associate, at times, with endoplasmic reticulum. The most likely identity of this structure is a/an A. Golgi complex. B. Lysosome. C. Nucleus. D. Peroxisome. E. Ribosome.

E. Ribosome. Ribosomes are composed of two subunits and exist within the cytosol, often bound to endoplasmic reticulum (ER). They participate in protein translation from mRNA and bind to mRNA during the process. Golgi, lysosomes, nuclei, and peroxisomes are not formed of subunits that assemble and disassemble. None bind to mRNA or to ER.

What major function is performed by mitochondria to keep cells alive?

Mitochondria facilitate programmed cell death called apoptosis.

Golgi complex

Performs glycosylations, phosphorylations, or proteolysis (enzyme mediated breakdown of proteins). Sorts and packages the newly synthesized and modified proteins into distinct regions within the trans Golgi.

What is the structure of ribosomes?

Ribosomes are composed of proteins and ribosomal RNA (rRNA).

What is the function of ribosomes?

Ribosomes are the cellular machinery for protein synthesis.

What is the difference between rough ER and smooth ER?

Rough ER has ribosomes bound to the outer membrane where smooth ER does not.

Endoplasmic Reticulum

surrounds the nucleus, function in the glycosylation (addition of carbohydrate) of proteins and in the synthesis of lipids

How are organelles arranged in the cytosol relative to each other and what role is played by the cytoskeleton in this arrangement?

These organelles have a characteristic arrangement within the cell and their proximity to each other allows them to carry out their function in protein processing. The cytoskeleton allows the organelles to be interconnected and joined by a framework.

Lysosomes contain potent enzymes collectively known as ____________.

acid hydrolases

Perioxisomes

break down fatty acids and purines

Mitochondria are most prominent in cells where ___________________________?

energy requirement is higher

The lysosome is responsible for performing what?

enzymatic degradation of cellular and extracellular macromolecules in response to acidification of luminal space

Mitochondria

functions in energy production, apoptosis, and they contain their own DNA (mtDNA) and ribosomes to facilitate synthesis of mitochondrial proteins

Why O-linked glycosylation?

helps maintain stability of higher order structure of proteins (resistance to proteases), important for recognition, necessary for muffins and proteoglycans to perform their function

What is the function of the nucleoplasm?

interior of the nucleus, the fluid in which the chromosomes are found

Peroxisomes are present in most cells but are most prominent in the _____________.

liver

non-secretory pathway

mRNA translated by polysomes in cytosol produces polypeptide targeted to interior of the nucleus, mitochondria, peroxisomes, or cytosol

Lysosomes

membrane enclosed organelles of various sizes that have an acidic internal pH (pH 5)

What is the function of the nuclear pores?

permit transfer of materials between the nucleus and the cytosol

Apoptosis

programmed cell death; pores are formed in the mitochondrial membrane allowing for the release of proteins that facilitate the apoptotic death process

Smooth Endoplasmic Reticulum (sER)

prominent in cells synthesizing and secreting steroid (lipid) hormones, important for synthesis and metabolism of membrane lipids, contains enzymes for drug detoxification, glycogen metabolism

proteasome

protein complex; not membrane bound; degrades proteins enzymatically

Cytochrome C

protein that can leave the inter membrane space of the mitochondria through the pores, enter the cytosol, which then stimulates a cascade of biochemical events resulting in apoptotic cell death

chaperones

proteins that assist in folding of nascent polypeptides, bind incorrectly folded polypeptides, maintain polypeptide in ER so that it can be properly folded before progressing to the Golgi apparatus

sarcoplasmic reticulum

same organelle as ER except is found in muscle cells only

Golgi apparatus

series of stacked, flattened cistern held in place by microtubules, functional relationship with ER (post translational modifications, protein sorting and packaging)

Nucleus

the organelle where the cell's genomic DNA resides

What is the function of the nuclear envelope?

the outermost structure of the nucleus; double layered phospholipid membrane (also has nuclear pores)

What is the function of the nuclear lamina?

the protein scaffolding of the nucleoplasm that is composed mainly of intermediate filaments

What is the function of the nucleolus?

the site of ribosome production

Where are lysosomes formed?

they are formed from regions of the Golgi complex that pinch off when proteins destined for the lysosome reach the trans Golgi