Chapter 1- Eukaryotic cell structure

Question 1

Cell

Answer 1

A unit of space enclosed by a membrane, which is the basis of all living organisms

Question 2

Plasma membrane

Answer 2

The external cellular membrane, which is composed of amphipathic phospholipids and protein. It separates the relatively constant internal cellular environment from the potentially hostile external environment. The protein composition of the membrane varies between cell types, but the lipid composition is common to all cells. The two sides of the plasma membrane have a different lipid composition. Proteins and lipids are not randomly distributed throughout the membrane

Question 3

Characteristics of a cell (8)

Answer 3

1. Many cells contain the same inorganic ions and organic molecules- carbohydrates, lipids, proteins, and nucleic acids
2. A plasma membrane
3. Systems that link the internal and external environment
4. The ability to transform external energy sources into utilizable energy that powers cellular reactions
5. The ability to convert ingested nutrients into necessary components of the cell, and to eliminate waste products
6. The ability to synthesize macromolecules
7. A DNA genome
8. The ability to replicate, transferring the cell’s genetic information to offspring

Question 4

Prokaryotes

Answer 4

Cells with single stranded DNA lacking a defined nucleus and internal membrane structures. Includes common bacteria and archaea. Prokaryotes are usually unicellular but can form colonies or filaments

Question 5

3 major domains

Answer 5

Archaea, eubacteria (common bacteria), and eukaryotes
All organisms are grouped into one of these 3 domains

Question 6

Nucleoid region

Answer 6

Prokaryotes contain a single circular strand of DNA, which is confined to a separate mass in the cell called the nucleoid. The nucleoid is not surrounded by a membrane or envelope

Question 7

Eukaryotes

Answer 7

Includes single celled organisms like yeasts and fungi, as well as multicellular plants and animals. Eukaryotes have a defined nucleus with a well defined membrane that contains most of the cell’s DNA. They also have extensive membrane systems and intracellular organelles surrounded by membranes

Question 8

Compartmentalization in eukaryotic cells

Answer 8

The intracellular membrane systems in eukaryotes establishes cellular compartments, which allows for subcellular organization. Due to these compartments, different chemical reactions that require different environments can occur simultaneously

Question 9

Chemical structure of water

Answer 9

In water, two hydrogen atoms share their electrons with an unshared pair of electrons of an oxygen atom. Water is polar because oxygen is more electronegative than hydrogen, and therefore electrons are unevenly distributed in the molecule. The hydrogens have a partial positive charge while oxygen has a partial negative charge

Question 10

Hydrogen bond

Answer 10

A relatively weak bond where a hydrogen that is bonded to an electronegative atom forms a bond with another electronegative atom (like O or N). Partially positive atoms (like hydrogen) are attracted to partial negative atoms (like oxygen). Water molecules interact with each other to form hydrogen bonds.

Question 11

How does hydrogen bonding contribute to the properties of water?

Answer 11

The large number of hydrogen bonds contributes to the stability of water. The atoms of water can also hydrogen bond to other ions and other chemical structures. When water interacts with other molecules, its orientation changes. For example, water molecules near membranes are more ordered due to the amphipathic nature of cell membranes. Liquid water has a high amount of hydrogen bonds, which accounts for its high heat of vaporization. Hydrogen bonds are disrupted as water transitions from liquid to the vapor state

Question 12

How does water interact with other biological molecules?

Answer 12

Water can be present on/within nucleic acid and protein molecules, and it stabilizes these molecules. Substances that are required for cellular functions are dissolved in an aqueous medium, and their activities are influenced by the orientation of water molecules. Microenvironments with different structures of water form on the surface of macromolecules and lipid membranes because water interacts with groups on these molecules. Microenvironments can change the activity of ions and molecules in different areas of the cell

Question 13

Tetrahedral structure

Answer 13

5 molecules of water form a tetrahedral structure due to hydrogen bonding. This is because each oxygen shares its electrons with 4 hydrogen atoms, and each hydrogen shares electrons with another oxygen. This tetrahedral structure is responsible for the crystal structure of ice. As ice transitions to liquid water, only a few hydrogen bonds are broken

Question 14

Why does water act as a solvent?

Answer 14

Water has a polar nature and it is able to form hydrogen bonds, which allows it to dissolve inorganic (salts) and organic molecules

Question 15

How does water dissolve salts?

Answer 15

Salts are held together by attraction of positively and negatively charged atoms or groups. In water, the electrostatic forces in the salt are overcome, as the ions in the salt are attracted to the dipoles of water. Na+ is attracted to oxygen, Cl- is attracted to hydrogen. In solution, the ions are surrounded by a shell of water

Question 16

Which organic molecules are soluble in water?

Answer 16

Organic molecules that contain weakly polar groups are soluble in water, as the polar groups are attracted to molecules of water. This is why sugars and alcohols are soluble in water

Question 17

Amphipathic molecules

Answer 17

Molecules that contain both polar and nonpolar groups

Question 18

Does water dissolve amphipathic molecules?

Answer 18

Amphipathic molecules dissolve in water if attraction of the polar group to water overcomes the hydrophobic interactions from nonpolar parts of the molecule

Question 19

Cations

Answer 19

Positively charged ions

Question 20

Anions

Answer 20

Negatively charged ions

Question 21

Electrolytes

Answer 21

Molecules that dissociate in water to form ions (cations or anions). The ions facilitate the conductance of an electrical current

Question 22

Nonelectrolytes

Answer 22

Molecules that dissolve in water but do not carry a charge or dissolve into charged molecules. This includes sugars and alcohols

Question 23

Strong electrolytes

Answer 23

Salts that dissociate completely in water

Question 24

Salts in biological systems

Answer 24

Salts of alkali metals (Li, Na, K) and acids like hydrochloric and sulfuric acid dissolve completely in water at low concentrations. Since these compounds are at low concentrations in biological systems, they always dissociate completely. Salts only exist as ions in solution, not as complete molecules like NaCl. In water, the dissociated anions of organic salts react with free protons (H+) from the dissociation of water to form the undissociated acid

Question 25

Acid equilibrium

Answer 25

Some acids, like lactic acid, do not dissociate completely in water. They form an equilibrium between the dissociated components and the components that have not dissociated. The products of the reaction reform the undissociated reactant while other molecules dissociate

Question 26

What determines whether an electrolyte completely dissociates in water?

Answer 26

It is depends on the electrolyte anion’s affinity for a proton. There is more dissociation if the dipole forces of water that interact with the anion are stronger than the electrostatic forces between the anion and a proton

Question 27

Weak electrolytes

Answer 27

Molecules that do not dissociate completely in water. They have a lower capacity to carry an electrical charge than strong electrolytes

Question 28

Hydronium ion

Answer 28

H3O+. The hydronium ion forms when protons interact with the oxygen of another water molecule. Water dissociates into OH and H, producing free protons that will interact with other molecules

Question 29

pH

Answer 29

The inverse logarithm of the number of protons in a solution, or pH= log (1/H+). Blood plasma and interstitial fluid have a neutral pH of 7.4. Gastric juice has a normal pH of 1.5-3.

Question 30

Proton donor

Answer 30

A Bronsted-Lowry acid is described as a proton donor. For example, HCl is considered a strong acid because it totally dissociates in water, releasing a proton.

Question 31

Proton acceptor

Answer 31

A Bronsted-Lowry base is described as a proton acceptor. For example, OH- is considered a strong base because it readily associates with protons to form water.

Question 32

Weak acids

Answer 32

Most organic acids in biological systems partially dissociate and are classified as weak acids. They establish equilibrium between the proton donor, an anion of the dissociated acid, and a proton. The anion formed in this dissociation is a base because it can accept a proton to reform the acid

Question 33

Conjugate pair

Answer 33

A weak acid and its base (anion) that was formed during dissociation

Question 34

Small Keq

Answer 34

The smaller the Keq value, the less the tendency of a conjugate acid to release a proton and the weaker the acid. Water has a low Keq and is considered a very weak acid

Question 35

Blood pH

Answer 35

In mammals, there are different intra- and extracellular aqueous environments. However, the pH of these different environments is in a dynamic steady state. The blood pH reflects changes in pH in tissues. The normal blood pH range is 7.35-7.45. Any pH value outside of this range indicates potential disease. Measuring blood pH is normal practice since irregular increase or decrease may lead to life threatening conditions.

Question 36

Acidosis

Answer 36

A blood pH below 7.35, due to increase in acid (excess lactic acid or ketones) or the loss of the bicarbonate base. This can be caused by a metabolic or respiratory change.

Question 37

Alkalosis

Answer 37

Blood pH above 7.45. This is also due to a metabolic or respiratory change. Metabolic alkalosis is caused by retention of bicarbonate and ingestion of bases. Respiratory alkalosis is caused by hyperventilation, overdose of some drugs, or fever

Question 38

Metabolic acidosis

Answer 38

It can indicate conditions like diabetes, hypoxemia, and metabolism of xenobiotics that form acids. Loss of bicarbonate changes the acid-base balance and occurs in severe diarrhea, uremia, and chronic renal diseases.

Question 39

Respiratory acidosis

Answer 39

Respiratory acidosis occurs when carbon dioxide is retained, caused by conditions that restrict exhalation of carbon dioxide. These conditions include emphysema, trauma, asthma, polio, and severe obesity

Question 40

Hypoxemia

Answer 40

Excess lactic acid production, which can occur in long distance runners

Question 41

Carbonic acid

Answer 41

H2CO3, which is a weak acid that is important in controlling pH in mammals. Carbon dioxide is constantly produced in catabolic reactions and is removed by the lungs. Medical conditions that restrict exhalation of carbon dioxide from the lungs lead to accumulation of carbonic acid and respiratory acidosis

Question 42

CO2/HCO3 system

Answer 42

Carbon dioxide, when dissolved in aqueous systems, is involved in equilibrium reactions. Carbonic acid (H2CO3) is in equilibrium with dissolved carbon dioxide, or CO2 and water. Dissociated carbonic acid can also form a proton and bicarbonate (HCO3). Therefore, the increase or decrease of one component – CO2, H2CO3, H+, or HCO3- causes a change in pH. The CO2/ HCO3- system is extremely important for maintaining pH homeostasis

Question 43

Henderson-Hasselbach equation

Answer 43

Defines the relationship between pH and concentrations of conjugate acid and base. A change in any component of an equilibrium reaction requires a corresponding change in the other components. For example. an increase in acid/protons decreases the concentration of conjugate bases and increases the concentration of the conjugate acid. pH = pK’ + log [conj. base] / [conj. acid]

Question 44

Buffering

Answer 44

The ability of a solution to resist a change in pH when an acid or base is added. This is important for regulating pH in the body. For example, cellular production of acids leads to the acidification of blood, where the H+ is buffered by several different bases. These bases include HCO3-, hemoglobin and HPO42-. As a result, the pH of the blood will decrease due to the using of all the bases to buffer resulting in loss of buffering capacity

Question 45

Buffering capacity

Answer 45

Depends on the concentrations of the conjugate acid and base. The higher the concentration of conjugate base, the more it can react with a high H+ concentration. However, if all bases are consumed, buffering capacity decreases and pH will also decrease drastically. For this reason, bicarbonate is very important to pH. Bicarbonate buffers against acid, and if too much is lost, the pH would decrease and the patient would likely die

Question 46

Embryonic stem cells

Answer 46

In the postfertilization period of an egg, these cells have the potential to develop into every cell of every organ in the adult organism. They are referred to as pluripotent cells

Question 47

Multipotent cells

Answer 47

Cells that can differentiate into a limited number of different cell types. They are found in differentiated tissues. The genome of differentiated cells can be reprogrammed to form multipotent or pluripotent cells, suggesting that parts of its genome are suppressed rather than lost entirely

Question 48

Catabolic reactions

Answer 48

Degradative reactions

Question 49

Anabolic reactions

Answer 49

Synthesis reactions

Question 50

Cytosol

Answer 50

Intracellular fluid

Question 51

Chemical composition of mammalian cells

Answer 51

In different types of cells, the concentrations of intracellular inorganic ions are mostly the same, however, the ion concentration intracellularly is much different from that in the extracellular environment. Certain ions are more prevalent inside the cell, while others are more prevalent outside the cell. With some exceptions, total cation equals total anion concentration in different fluids

Question 52

All cells contain the same genome, except for which cells?

Answer 52

Erythrocytes- mature erythrocytes don’t contain DNA

Question 53

Major intracellular ions

Answer 53

Cations- potassium, magnesium (present in both environments)
Anions- inorganic phosphate, organic phosphate, and proteins

Question 54

Major extracellular ions

Answer 54

Cations- sodium, magnesium (present in both environments)
Anions- chlorine, bicarbonate, smaller amounts of phosphate and sulfate

Question 55

Integrins

Answer 55

Transmembrane proteins that bind to the cytoskeleton inside the cell and participate in bidirectional signaling across the membrane. Integrins are how the outer surface of the plasma membrane interacts with other cells

Question 56

Cytoskeletal elements

Answer 56

Allow the plasma membrane to be involved in determining cell shape and movement

Question 57

Transport of substances through the plasma membrane

Answer 57

The membrane contains lipids, which excludes many substances. However, transport mechanisms allow ions, organic molecules, and water to move across the membrane

Question 58

Protein receptors

Answer 58

Proteins on the outer surface of the plasma membrane which bind to extracellular signals like hormones or neurotransmitters. Therefore, protein receptors allow for intracellular communication

Question 59

Nuclear envelope

Answer 59

The two membranes that surround the nucleus. The outer membrane is continuous with membranes of the endoplasmic reticulum. The envelope contains nuclear pore complexes. The nuclear envelope may play a role beyond just being a barrier between the nuclear matrix and the cytoplasm- the nuclear envelope of progeria patients appears distorted

Question 60

Perinuclear space

Answer 60

The space between the two membranes of the nuclear envelope, which is continuous with the lumen of the rough endoplasmic reticulum

Question 61

Nuclear pore complexes

Answer 61

Multi protein complexes that cross the nuclear envelope. They allow for controlled movement of particles and large molecules between the nuclear matrix and the cytoplasm. Transport of macromolecules requires energy. It is facilitated by cargo proteins and soluble transport factors which cycle between the 2 compartments

Question 62

Nuclear matrix

Answer 62

An intricate meshwork of proteins spread throughout the nucleus

Question 63

Hutchinson-Gilford progeria syndrome (HGPS)

Answer 63

This syndrome is observed in 1 in 4 million births. These patients experience accelerated aging, 6-8 times the normal rate. Symptoms include limited growth, loss of hair, small fragile bodies, wrinkled skin, atherosclerosis, distinct facial features, and cardiovascular problems common to the elderly. They do not exhibit any neurodegeneration. Patients rarely live past their early teens

Question 64

Biochemical basis of HGPS

Answer 64

The nuclear envelope of these patients appears to be distorted. Lamina A is a structural protein in the nucleus that is involved in nuclear synthesis of DNA and RNA. It is formed from a precursor and attached to the nuclear membrane by an enzyme catalyzed reaction. HGPS patients have a deficit in this reaction, which leads to accumulation of abnormal lamina A in normal cells with aging. The presence of the abnormal protein causes blebbing of the nucleus, changes gene expression, and interferes with mitosis

Question 65

Nucleolus

Answer 65

An intranuclear sub compartment. It is involved in RNA processing and ribosome synthesis, which is required for protein synthesis in the cytosol

Question 66

Nuclear lamina

Answer 66

A meshwork structure that underlies the inner nuclear membrane and supports the structure of the nucleus

Question 67

Functions of the plasma membrane (5)

Answer 67

1. Transport of ions and small molecules
2. Exo- and endocytosis
3. Cell-cell recognition
4. Receives small and large molecules using receptors
5. Cell morphology and movement

Question 68

Nucleus

Answer 68

Contains most of the genome of the cell, involved in DNA synthesis and repair, and in RNA synthesis. The nucleus contains the proteins and enzymes that help with replicating DNA and repairing DNA.

Question 69

Chromatin

Answer 69

A DNA-protein complex located in the nucleus, which is organized into chromosomes. This is how DNA is stored in the nucleus

Question 70

Endoplasmic reticulum

Answer 70

A network of interconnecting membranes that extend from the nuclear envelope to the plasma membrane, found in the cytoplasm of eukaryotic cells. Some parts of the membranes have a smooth appearance, other parts of the membranes have a rough appearance. Newly synthesized proteins are modified in the lumen of the ER (inside the membrane). Along with the Golgi apparatus, the ER is involved in formation of other cellular organelles (lysosomes, peroxisomes) and calcium signaling

Question 71

Ribosomes

Answer 71

The rough appearance of the RER is due to ribonucleoprotein particles (ribosomes) on the cytosolic side of the membrane.

Question 72

Microsomes

Answer 72

Small vesicles formed during cell fractionation. The endoplasmic reticulum network is disrupted and the membrane reseals, forming the vesicles

Question 73

Rough endoplasmic reticulum functions (2)

Answer 73

1. Biosynthesis of proteins for incorporation into membranes and cellular organelles, and for export out of the cell
2. Involved in the folding of proteins- if this system is disrupted, it can cause disease

Question 74

Smooth endoplasmic reticulum functions

Answer 74

Involved in lipid synthesis. It contains enzymes (cytochromes P450) that catalyze hydroxylation of endogenous and exogenous compounds. These enzymes play a role in the synthesis of steroid hormones, removal of toxic substances, and drug metabolism

Question 75

Endoplasmic reticulum functions (5)

Answer 75

1. Membrane synthesis
2. Synthesis of proteins and lipids for some organelles and for export
3. Lipid and steroid synthesis
4. Detoxification reactions
5. Calcium signaling

Question 76

Golgi apparatus

Answer 76

A network of cisternae and vesicles. It works with the endoplasmic reticulum, where proteins for specific destinations are synthesized. Enzymes in Golgi membranes catalyze transfer of carbohydrate units to proteins to form glycoproteins- this is important to determine the protein’s final destination. The Golgi is also a site of new membrane synthesis and helps to form lysosomes and peroxisomes

Question 77

Cisternae

Answer 77

Flattened smooth membrane stacks

Question 78

Golgi apparatus functions (3)

Answer 78

1. Modification and sorting of proteins for incorporation into membranes and organelles, and for export
2. Export of proteins
3. Moves lipids in the cell

Question 79

SNARE proteins

Answer 79

A family of proteins that help membrane vesicles to shuttle proteins between cisternae in the Golgi apparatus. The proteins pinch the vesicle off of one cisterna and help the vesicle to fuse with another cisterna

Question 80

What is the role of vesicles in the Golgi apparatus?

Answer 80

Golgi apparatus vesicles transport proteins like hormones, blood plasma proteins, and digestive enzymes to the plasma membrane for secretion

Question 81

Mitochondria functions (4)

Answer 81

1. Production of ATP
2. Cellular respiration
3. Oxidation of pyruvate, amino acids, and fatty acids
4. Urea and heme synthesis

Question 82

Mitochondria

Answer 82

Powerhouse of the cell, responsible for synthesizing 90% of cellular ATP. They play a role in cell functions like apoptosis, formation of reactive oxygen species, cell signaling, and metabolic processes. Important for protein synthesis and have a key role in aging; cytochrome c, a component of the mitochondrial electron transport system, is an initiator of apoptosis

Question 83

Mitosol

Answer 83

The internal matrix of the mitochondria

Question 84

Cristae

Answer 84

Infoldings of the inner mitochondrial membrane

Question 85

Structure of the mitochondria

Answer 85

The mitosol is surrounded by two membranes. The inner membrane forms cristae and contains small spheres that extend into the mitosol and are responsible for ATP synthesis. Components of the electron transport system and oxidative phosphorylation are part of the inner membrane. The metabolic pathways for oxidation of pyruvate and other compounds are located in the mitosol. Both the outer and inner membranes contain mechanisms for protein translocation

Question 86

Mitochondrial DNA

Answer 86

Circular DNA that contains genetic information for 13 mitochondrial proteins and some RNAs. It is inherited through maternal transmission. There are several hundred genetic diseases of mitochondrial function

Question 87

Cytochrome

Answer 87

Heme protein involved in an electron transport system in the endoplasmic reticulum or inner mitochondrial membrane

Question 88

Mitochondrial proteins

Answer 88

Mitochondria also have requisite machinery to catalyze protein synthesis. Most mitochondrial proteins are derived from genes present in nuclear DNA and synthesized in the cytosol.

Question 89

Lufts disease

Answer 89

The first disease involving mitochondrial energy transduction, reported in 1962. Symptoms included general weakness, excessive perspiration, a high caloric intake without an increase in body weight, and an elevated basal metabolic weight. The patient had a defect in the mechanism that controls mitochondrial oxygen utilization

Question 90

Leber Hereditary Optic Neuropathy

Answer 90

The first disease identified due to a mutation of mtDNA. It causes sudden blindness in early adulthood

Question 91

Mitochondrial disease

Answer 91

Some conditions result from mutations of mitochondrial DNA, others result from mutations of nuclear DNA that code for mitochondrial proteins. Many of these diseases involve skeletal muscle and CNS. Mitochondrial DNA damage may be due to free radicals formed in the mitochondria. Mitochondrial abnormalities have been implicated in the pathophysiology of schizophrenia, bipolar disorder, Parkinson disease, Alzheimer disease, and cardiomyopathies

Question 92

Lysosomes

Answer 92

Responsible for intracellular digestion of extracellular and intracellular substances. They have one membrane and an internal acidic pH of 5. They contain enzymes called hydrolases, but the enzyme content of the lysosome varies depending on the tissue and the functions of the tissue. Lysosomes are responsible for the intracellular digestion of extracellular and intracellular substances. The material broken down by hydrolases is recycled and used for other purposes

Question 93

Hydrolases

Answer 93

A class of glycoprotein enzymes located in the lysosomes. They catalyze hydrolytic cleavage of carbon-hydrogen, carbon-oxygen, carbon-nitrogen, and carbon phosphorus bonds found in biological macromolecules. Lysosomal hydrolases are most active at an acidic pH. They split molecules into simple, low weight compounds that can be recycled.

Question 94

Phagocytosis

Answer 94

A process by which cells ingest foreign particles, like microorganisms and viruses

Question 95

Pinocytosis

Answer 95

The process by which cells ingest fluids

Question 96

Endocytosis

Answer 96

The process by which the cell ingests specific proteins

Question 97

Digestive vacuoles

Answer 97

Also called secondary lysosomes. They are vesicles that contain material to be digested and lysosomal hydrolases to carry out the digestion

Question 98

How do cells ingest foreign particles, liquids, and proteins?

Answer 98

Phagocytosis, pinocytosis, and endocytosis are receptor mediated processes. The material from the exterior of the cell is enclosed in plasma membrane bound vesicles. The vesicles containing the external material fuse with primary lysosomes to form digestive vacuoles, where they are digested

Question 99

Pathological conditions due to lysosomal enzymes

Answer 99

When the lysosomal membrane is disrupted, the lysosomal enzymes cause digestion of the cell. Pathological conditions related to the release of lysosomal enzymes include arthritis, allergic responses, several muscle diseases and drug induced tissue destruction

Question 100

Autophagy

Answer 100

A regulated process where the lysosome hydrolyzes cellular components. Cellular proteins, nucleic acids, lipids, and organelles like the mitochondria, are in a dynamic state of synthesis and degradation, with lysosomes being responsible for degrading these molecules. Substances to be degraded are either identified and taken up by lysosomes or are first encapsulated within membrane vesicles that fuse with primary lysosomes. Autophagy is important in both stressed and normal cells, and starvation and specific hormones induce autophagy

Question 101

Residual bodies

Answer 101

Vesicles containing material that couldn’t be digested by lysosomes. The contents of residual bodies are removed from the cell by exocytosis

Question 102

Lipofuscin

Answer 102

A chemically heterogenous, pigmented material found in some residual bodies. It contains polyunsaturated fatty acids and proteins. It is also called “age pigment” or “wear and tear pigment”. Lipofuscin has been observed in mature neurons and muscle cells, and it has been implicated in the aging process

Question 103

Lysosome functions (2)

Answer 103

1. Apoptosis
2. Cellular digestion- hydrolysis of proteins, carbohydrates, lipids, and nucleic acids

Question 104

Gout

Answer 104

Uric acid is formed by catabolism of purines, which are heterocyclic compounds containing nitrogen that are found in nucleic acids. Uric acid is normally excreted in the urine. In gout patients, excess uric acid is produced, which causes uric acid to increase in the blood. Urate crystals are also deposited in the joints. Symptoms include inflammation, pain, swelling, and increased warmth of some joints, especially the big toe

Question 105

How are lysosomal enzymes related to gout?

Answer 105

Some of the symptoms of gout are caused by urate crystals, which are phagocytized by cells in the joint under normal circumstances. With gout, they accumulate in intracellular digestive vacuoles that contain lysosomal enzymes. The crystals cause physical damage to the vacuoles, releasing lysosomal hydrolases into the cytosol. The hydrolases are optimally active at an acidic pH, so their activity is decreased in cytosol. However, they still have some hydrolytic activity, causing digestion of cellular components and cellular autolysis

Question 106

Human lysosomal acid lipase (hLAL)

Answer 106

An enzyme that hydrolyzes triacylglycerol to form free fatty acids and glycerol. It also hydrolyzes cholesterol esters to cholesterol and fatty acids. hLAL is a very important enzyme to cholesterol metabolism and makes cholesterol available for cells to use. There are two rare autosomal recessive diseases resulting from genetic deficiency of LAL: Cholesteryl Ester Storage Disease (CESD) and Wolman Disease

Question 107

Cholesteryl Ester Storage Disease (CESD)

Answer 107

Autosomal recessive disease of hLAL enzyme dysfunction- it is usually diagnosed in adulthood and is characterized by hypercholesterolemia, hepatomegaly, and early onset of severe atherosclerosis. Patients do have hLAL activity, but at a level much lower than normal. They are able to hydrolyze triacylglycerol, but not cholesteryl esters

Question 108

Wolman Disease

Answer 108

Autosomal recessive disease of hLAL enzyme dysfunction. This disease is diagnosed in infants, most of which do not survive to age 1. Patients have no hLAL activity. Both triacylglycerol and cholesteryl esters accumulate in tissues

Question 109

Peroxisomes

Answer 109

An organelle with a single membrane that has the ability to produce and utilize hydrogen peroxide (H2O2). In the matrix of some peroxisomes, there is a high protein concentration, which leads to crystalline inclusions. They are used to oxidize long chain fatty acids, and for synthesis of glycerolipids, glycerol ether lipids, and isoprenoids. Over 50 enzymes catalyzing oxidative and biosynthetic reactions have been identified in peroxisomes from different tissues. More than 25 genetic diseases involve peroxisomes; grouped as disorders of peroxisome biogenesis.

Question 110

How do cells protect themselves from hydrogen peroxide produced by peroxisomes?

Answer 110

Cells protect themselves from the toxicity of H2O2 by having peroxide producing and peroxide utilizing enzymes in one compartment.

Question 111

Catalase

Answer 111

A heme enzyme that is present in peroxisomes. It catalyzes the conversion of hydrogen peroxide to water and oxygen. It also catalyzes the oxidation of different compounds by hydrogen peroxide

Question 112

Zellweger syndrome

Answer 112

The most severe peroxisome biogenesis disorder. It is due to the absence of functional peroxisomes, which usually causes death by 6 months. Patients with this disease have a genetic defect in the mechanism for importing enzymes into the matrix of peroxisomes

Question 113

Peroxisome biogenesis disorders

Answer 113

Peroxisomes are responsible for many important metabolic reactions. There are more than 25 disorders involving the enzymatic activities of peroxisomes. They are rare autosomal recessive diseases characterized by decreased levels of glycerol-ether lipids, and increased levels of long chain fatty acids and cholestanoic acid derivatives. These diseases can affect the liver, kidneys, brain, and the skeletal system. Some PBD conditions are caused by donor splice or missense mutations. In some, there is the absence of a single metabolic enzyme or a defect in a membrane transport component. Some of these diseases can be diagnosed prenatally by an assay of the amniotic fluid

Question 114

Peroxisome functions (3)

Answer 114

1. Lipid oxidation
2. Oxidative reactions involving oxygen
3. Utilization of hydrogen peroxide

Question 115

Microtubules, intermediate filaments, and microfilament functions (4)

Answer 115

1. Cell cytoskeleton
2. Cell morphology
3. Cell motility
4. Intracellular movements

Question 116

Cytosol functions (3)

Answer 116

1. Metabolism of carbohydrates, amino acids, and nucleotides
2. Synthesis of fatty acids
3. Protein synthesis

Question 117

Cytoskeleton

Answer 117

Made of microtubules, intermediate filaments, and actin filaments (microfilaments) which form a scaffolding in the cytoplasm. The cytoskeleton plays roles in intracellular transport of vesicles and organelles, and cell morphology and motility

Question 118

Microtubules

Answer 118

Consists of multimers of tubulin- microtubules make up the cytoskeleton. The tubulin protein assembles rapidly into tubular structures and disassembles depending on the needs of the cell. Actin and myosin are also important filaments in skeletal muscles