Cells In Their Social Context

Question 1

Pilus

Answer 1

A hairlike appendage found on the surface of many bacteria(short pili that are used to attach the bacterium to a surface are fimbriae)

Question 2

How many architectural regions does a prokaryotic cell have?

Answer 2

On the outside, flagella and pili project from the cells surface. These are structures(not present in all prokaryotes) made of proteins that facilitate movement and communication between cells Enclosing the cell is the cell envelope, consisting of a cell wall covering a plasma membrane though some bacteria may also have a further covering layer called a capsule

Question 3

Purpose of the cell envelope

Answer 3

Gives rigidity to cell and separates the interior of the cell from its environment serving as a protective filter

Question 4

Although most prokaryotes have cell walls which bacteria and archaea have exceptions?

Answer 4

Mycoplasma(baceteria) and Thermoplasma(archaea). The cell walls consist of peptidoglycan in bacteria which acts an additional barrier against exterior forces. It prevents cell from expanding and bursting from osmotic pressure due to hypotonic environment. Some eukaryotic cells like plant and fungal cells also have a cell wall.

Question 5

Theories of origin of small molecules that led to life on Earth

Answer 5

They may have been carried to Earth by meteorites, created at deep sea vents or synthesized by lightning in a reducing atmosphere

Question 6

Why is RNA thought to be the self-replicating molecule?

Answer 6

RNA is capable of both storing genetic information and catalyzing chemical reactions(RNA world hypothesis)

Question 7

What is the current belief of the earliest cells?

Answer 7

The earliest cells were heterotrophs. The early cell membranes were more simple and permeable than modern ones with only a single fatty acid chain per lipid. Lipids are known to spontaneously form bilayered vesicles in water and could have preceded RNA but the first cell membranes could also have been produced by catalytic RNA or even have required structural proteins before they could form.

Question 8

Main distinguishing feature of Eukaryotes in comparison to Prokaryotes

Answer 8

Compartmentalization - the presence of membrane bound compartments in which specific metabolic activity takes place. Most important among these is the cell nucleus a membrane delineates compartment that houses the Eukaryotic cell’s DNA.

Question 9

Differences between prokaryotes and eukaryotes

Answer 9

The plasma membrane resembles that of prokaryotic in function with minor differences in the setup. Cell walls may or may not be present. The eukaryotic DNA is organized into one or more linear molecules called chromosomes which are associated with histone proteins. All chromosomal DNA is stored in the cell nucleus separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria also contain some DNA. Many eukaryotic cells are ciliated with primary cilia. Primary cilia plays an important roles in chemosensation, mechasensation and thermosensation. Cilia may thus be viewed as a sensory cellular antennae that coordinates a large number of cellular signaling pathways sometimes coupling the signaling to ciliary mobility or alternatively to cell division and differentiation Eukaryotes can move using motile cilia or flagella. Eukaryotic flagellas are less complex than those of prokaryotes

Question 10

What are proteins responsible for?

Answer 10

Responsible for most memebrane functions, serving as specific receptors, enzymes transport proteins and so on.

Question 11

What does lipid bilayer determine?

Answer 11

the basic structure in biological membranes

Question 12

Describe membrane proteins(in general)

Answer 12

They extend across the lipid bilayer in some of these transmembrane proteins the polypeptide chain crosses the bilayer as a single helix(single pass proteins) while in others including those for the transmembrane transport of the ions ans other small water soluble molecules, the polypeptide chain crosses the bilayer multiple times either as a series of a helices or as beta sheet in the form of a closed barrel(multipass proteins).

Question 13

Describe other membrane associated proteins that do not span the bilayer

Answer 13

These proteins do not span the bilayer but they are attached to one or the other site of the membrane. Many of these are bound via covalently attaches lipid groups. Like the lipid molecules in the bilayer, many membrane proteins are able to diffuse rapidly in the plane of the membrane. Cells also have ways of immobilizing specific membrane proteins and confining both membrane protein and lipid molecules to particular domains in a continuous lipid bilayer

Question 14

Describe Cystic Fibrosis(Mucoviscidosis)

Answer 14

An autosomal recessive genetic disorder that affects the lungs but also the pancreas, liver, and intestine. Difficulty breathing is the most serious symptom. Other symptoms include:sinus infection, poor growth and infertility affecting other parts of the body

Question 15

What mutation causes Cystic Fibrosis

Answer 15

Caused by different mutations of the gene for protein cystic fibrosis transmembrane conductance regulator (CFTR). This protein is requires to regulate the components of, digestive fluids, and mucus.

Question 16

How many working copies of CFTR gene do healthy people have? Carriers?People with CF?

Answer 16

2-healthy people 1-carriers 0-people with CF CF has autosomal recessive inheritance

Question 17

Underlying mechanism of CF

Answer 17

Abnormal transport of chloride and sodium across the epithelium, which is the cell layer that covers membranes over organs. This leads to thick viscous secretions.

Question 18

What is the role of ER?

Answer 18

ER plays a central part in lipid and protein biosynthesis. Its membrane is the site of production of a transmembrane proteins and lipids for most of the cells organelles, including the ER itself, the Golgi apparatus, lysosomes, endosomes,secretory vesciles, and the plasma membrane.

Question 19

What is the other major contribution of ER membrane to mitochondrila and peroxisomal membranes?

Answer 19

ER produces most of the lipids. Almost all of the proteins that will be secreted to the cell exterior. As well as those destined for the lumen of the ER, Golgi apparatus, or lysosomes are initially delivered to the ER lumen.

Question 20

The two types of ER

Answer 20

Rough Endoplasmic Reticulum(RER) and Smooth Endoplasmic Reticulum (SER). he outer (cytosolic) face of the rough ER is studded with ribososmes that are the sites of protein synthessi. The rough endoplasmic reticulum is especially prominenet in cells such as hepatocytes where active smooth endoplasmic reticulum lacks ribososmes and functions in lipid metabolism, carbohydrate metabolism and detoxification.

Question 21

The function of Golgi apparatus?

Answer 21

It receives newly synthesized proteins and lipids from the ER and distributes them to the plasma membrane, lysosomes and secretory vesicles.

Question 22

Strucute of Golgi aparatus

Answer 22

Polarized structure containing one or more stacks of disk shaped cisternae which are organized as a series of atleast 3 biochemically and functinallydistinct compartments termed cis, medial, and trans cisternae. Both cis and the trans cisternae are connected to sorting stations called the cis Golgi network and the trans Golgi respectively.

Question 23

Where are the correctly folded proteins transferred?

Answer 23

Transferred indiscriminately from the lumen and membrane of the ER to the cis Golgi network, but the resident ER proteins are returned. Proteins destined for secretory vesicles, the plasma membrane and lysosmes move through the Golgi stack in the cis to trans direction passing from one cisterna to the next until finally they reach the trans Golgi network from which each type of protein departs for its specific destination. Each of these many transport steps is mediated by transport vesicles which bud off from one membrane and then fuse with another.

Question 24

What are lysosomes

Answer 24

Lysosomes are membranous bags of hydrolysis enzymes used for the controlled intracellular digestion of macro-molecules. They contain about 40 types of hydrolytic enzymes including proteases, nucleases, glycosidases, lipases,phospholipases , phosphatases and sulphatases all are acid hydrolases

Question 25

What disease does defects in lysosomal function lead to?

Answer 25

Lysosomal storage disease(LSDs)

Question 26

What are Mucopolysaccharidoses (MPss)?

Answer 26

Group of metabolic disorders caused by the absenceor malfunctioning of lysosomal enzymes needed to break down molecules of glycosaminoglycans. They include MPS IH-Hurler Syndrome, MPS IS- Scheie syndrome and MPS II-Hunter syndrome

Question 27

Define glycosaminoglycans

Answer 27

long chains of sugar carbohydrates that help build bone, cartilage,tendons,corneas,skin and connective tissue. They are fornerly called mucopolysaccharides and are also found in the fluid that lubricates the joints

Question 28

How does Mucopolysaccharidoses affect people?

Answer 28

Either does not produce enough of one of the 11 enzymes required to break down these sugars chains into simpler molecules or they produce enymes that do not work properly. Over time these glycosaminoglycans collect in the cells, blood an d connective tissues. The result is permanent progressive cellular damage which affects appearance, physical abilities, organ and system functioning and in most cases mental development.

Question 29

The function of peroxisomes

Answer 29

involved in the catabolism of very long chain fatty acids branched chain fatty acids, D-amino acids and polyamines and biosynthesis of plasmalogens ex: ether phospholipids critical for the normal function of mammalian rains and lungs. Other functions include the glyoxylate cycle in germinating seeds(glycxysomes), photorespiration in leaves, glycolyisi in trypanosomes(glycosomes) and methanol and or amine oxidation in some yeasts.

Question 30

What do Peroxisomes contain for the total activity of 2 enzymes?

Answer 30

They also contain 10% of the total activity of 2 enzymes in the pentose phosphate pathway which is important for the energy metabolism. This is a function of peroxisome

Question 31

What are lysosomes responsible for?

Answer 31

responsible for cellular homeostasis for their involvements in secretion, plasma membrane repair, cell signaling and energy metabolism which are related to health and diseases

Question 32

Explain peroxisomal disorders

Answer 32

They represent a class of medical conditions caused by defects in peroxisome funcions. May include defects in single enzymes important for peroxisome function or in peroxins, proteins encoded by PEX genes that are critical for normal peroxisome assembly and biogenesis.

Question 33

Zellweger Syndrome

Answer 33

aka cerebrohepatorenal syndrome is a rare congenital disorder characterized by the reduction or absence of functional peroxisomes in the cells of an individual. It is one of a family of disorders called leukodystrophies

Question 34

What is Zellweger syndrome associated with?

Answer 34

Impaired neuronalmigration, neuronal positioning,and brain development. Individuals can show a reduction in CNS myelin(particularly cerebral). Patients can also show postdevelopmental sensorineuronal degeneration that leads to a progressive loss of hearing and vision.

Question 35

Define Myelin

Answer 35

critical for normal CNS functions and insulates nerve fibers in the brain

Question 36

Prominent roles of mitochondria

Answer 36

To produce energy currency of the cell, ATP (Ex: phosphorylation of ADP) through respiration and to regulate cellular metabolism

Question 37

What tasks are mitochondria involved in

Answer 37

signaling, cellular differentiation, cell death, control of cell cycle and cell growth

Question 38

Mitochondrial diseases

Answer 38

Mitochondrial disorders and cardiac dysfunction and plays a role in the aging process Recent research: autism, especially sever autism is correlated with mitochondrial defects

Question 39

What is vigourously debated about peroxisomes

Answer 39

whether they are involved in isoprenoid and cholesterol synthesis in animals

Question 40

What is an important factor for cell metabolism in the range of human diseases?

Answer 40

Damage and subsequent dysfunction in mitochondria. Mitochondrial disorders often represent themselves as neurological disorders including autism. They can also manifest myopathy, diabetes, multiple endocrinopathy and a variety of other systemic disorders

Question 41

Lebers Hereditary Optic Neuropathy(LHON)

Answer 41

Aka Leber Optic Atrophy is a mitochondrially inherited (transmitted from mother to offspring) degeneration of retinal ganglion cells and their axons that leads to an acute or subacute loss of central vision.

Question 42

How is LHON transmitted?

Answer 42

Through a mother, occurs due to mutatons in the mitochondiral(not nuclear) genome and only the egg contributes mitochondria to the embryo. LHON also occurs due to one of 3 pathogenic mitochondrial DNA(mtDNA) point mutations

Question 43

LHON evolves to….

Answer 43

Severe Optic atrophy and permanent decrease of visual acuity.

Question 44

Diabetes Mellitus and Deafness(DAD) Maternally Inherited Diabetes and Deafness(MIDD)

Answer 44

A subtype of diseases caused from a point mutation at position 3243 in human mitochondrial DNA. It affects the gene encoding tRNALeu. MIDD is characterized by diabetes and sensorineural hearing loss

Question 45

Define ribosome

Answer 45

a large and complex molecular machine found within all living cells that serves as priary site of biological protein synthesis(translation). They link amino acids together in the order specified by messenger(mRNA) molecules.

Question 46

2 major components of ribosomes

Answer 46

the small ribosomal subunit which reads RNA, the large subunit which joins amino acids to form a polypeptide chain. Each subunit is composed of oneor more ribosomal RNA(rRNA) molecules and a variety of proteins

Question 47

Define Nucleus

Answer 47

Contains most of cell’s genetic material organized as mutiple long linear DNA molecules in coplex with a large variety of proteins such as histones to from chromosomes. The genes with the chromosomes are the cell’s nuclear genome,

Question 48

Function of nucleus

Answer 48

to maintain the integrity of the genes and to control the activites of the cell by regulating gene expression which is why the nucleus is the control center of the cell.

Question 49

Structure of the nucleus

Answer 49

Nuclear envelope - a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm Nucleoskeleton- a network within the nucleus that adds mechanical support much like the cytoskeleton which supports the cell as a whole

Question 50

Renewal by Simple Duplification

Answer 50

• Most populations of differentiated cells in vertebrates are subject to turnover through cell death and cell division.
• In some cases, such as that of hepatocytes in the liver, the fully differentiated cells simply divide to produce daughter cells of the same type.
• Both the proliferation and the survival of hepatocytes are controlled to maintain appropriate total cell numbers. If a large part of the liver is destroyed, the remaining hepatocytes increase their division rate to restore the loss; and if hepatocyte proliferation is transiently increased by drug treatment, the increase in cell numbers is soon compensated for by an increase in cell death, returning cell numbers to normal.
• Such control mechanisms normally keep the numbers of cells of each type in a tissue in appropriate balance. In response to unusual damage, however, repair may be unbalanced, as when the fibroblasts in a repeatedly damaged liver grow too rapidly in relation to the hepatocytes and replace them with connective tissue.
• Endothelial cells form a single cell layer that lines all blood vessels and regulates exchanges between the bloodstream and the surrounding tissues.
• New blood vessels develop from the walls of existing small vessels by the outgrowth of endothelial cells, which have the capacity to form hollow capillary tubes even when isolated in culture.
• In the living animal anoxic, damaged, or growing tissues stimulate angiogenesis by releasing angiogenic growth factors.
• These factors attract nearby endothelial cells and stimulate them to secrete proteases, to proliferate, and to form new capillaries.
• Angiogenesis. A new blood capillary forms by the sprouting of an endothelial cell from the wall of an existing small vessel

Question 51

Renewal by Stem Cells

Answer 51

• Many tissues, especially those with a rapid turnover - such as the lining of the gut, the epidermal layer of the skin, and the blood-forming tissues - are renewed by means of stem cells.
• Stem cells, by definition, are not terminally differentiated and have the ability to divide throughout the lifetime of the organism, yielding some progeny that differentiate and others that remain stem cells.
• In the skin the stem cells of the epidermis lie in the basal layer, attached to the basal lamina.
• The progeny of the stem cells differentiate on leaving this layer and, as they move outward, synthesize a succession of different types of keratin until, eventually, their nuclei degenerate, producing an outer layer of dead keratinized cells that are continually shed from the surface.
• Only a minority of basal cells are stem cells. The fate of the daughters of a stem cell is controlled in part by interactions with the basal lamina and in part by other poorly understood factors.
• These factors allow two stem cells to be generated from one during repair processes, and they regulate the rate of basal cell proliferation according to the thickness of the epidermis.
• Glands connected to the epidermis, such as the mammary glands, have their own stem cells and their own distinct of cell renewal.

Question 52

Renewal by Pluripotent Stem Cells

Answer 52

The many types of blood cells all derive from a common pluripotent stem cell. In the adult the stem cells are found mainly in bone marrow, where they normally divide infrequently to produce more stem cells (self-renewal) and various committed progenitor cells, each able to give rise to only one or a few types of blood cells. The committed progenitor cells divide profusely under the influence of various protein signaling molecules (called colony-stimulating factors, or CSFs) and then differentiate into mature blood cells, which usually die after several days or weeks. Studies of hemopoiesis have been greatly aided byin vitro assays in which stem cells or committed progenitor cells form clonal colonies when cultured in a semisolid matrix. The progeny of stem cells appear to make their choices among alternative developmental pathways in a partly random manner. Cell death, controlled by the availability of CSFs, also plays a central part in regulating the numbers of mature differentiated blood cells; it depends on activation of an intracellular suicide program and is thought to help regulate cell numbers in many other tissues and in other kinds of animals.

Question 53

Tissues with Permanent Cells

Answer 53

Some cells in mammals - including nerve cells, heart muscle cells, sensory receptor cells for light and sound, and lens fibers - persist throughout life without dividing and without being replaced. In mature lens fibers the cell nuclei have degenerated and protein synthesis has stopped, so that the core of the adult lens consists of lens proteins laid down early in embryonic life. In most other permanent cells biosynthetic activity continues, and there is a steady turnover of cell components. In the rod cells of the retina, for example, new layers of photoreceptive membrane are synthesized close to the nucleus and are steadily displaced outward until they are eventually engulfed and digested by cells of the pigment epithelium.

Question 54

Molecular Genetics of Cancer

Answer 54

Two classes of genes are critical in the causation of cancer - tumor suppressor genes and protooncogenes. Loss-of-function mutations of tumor suppressor genes relieve cells of inhibitions that normally hold their numbers in check; gain-of-function mutations of proto-oncogenes stimulate cells to increase their numbers when they should not. These latter mutations have a dominant effect, and the mutant genes, known as oncogenes, can be identified by their ability to transform the behavior of cells into which they are introduced. Many oncogenes have been tracked down by their presence in transforming retroviruses, which can pick up such dangerously corrupted versions of host cell genes and carry them into other host cells. A large proportion of protooncogenes code for components of the pathways by which external signals stimulate cells to divide. Mutations in tumor suppressor genes are usually recessive in their effects on the individual cell: there is no loss of control until both gene copies are put out of action. People who inherit one defective and one functional gene copy, however, are often strongly predisposed to cancer, since a single somatic mutation is enough, with the inherited mutation, to create a cell that totally lacks the tumor suppressor gene function. Cancers that run in families in this way are rare, but they provide one means to identify tumor suppressor genes whose loss turns out to be a feature of many common cancers. DNA viruses such as papillomaviruses and SV40 can promote the development of cancer by sequestering the products of tumor suppressor genesin particular, the Retinoblastoma protein, which regulates progress through the cell division cycle in normal circumstances, and the p53 protein, which is thought to act as an emergency brake on cell division in cells that have suffered genetic damage. The steps of tumor progression can be correlated with mutations that activate specific oncogenes and inactivate specific tumor suppressor genes. A loss of p53 function, for example, is a common late event and may be responsible for the genetic instability of many full-blown metastasizing cancers. Different combinations of mutations are found in different forms of cancer and even in patients that nominally have the same form of the disease, reflecting the random way in which mutations occur. Nevertheless, many of the same types of genetic lesions are encountered repeatedly, suggesting that there is only a limited number of ways in which our defenses against cancer can be breached

Question 55

Apoptosis: Programmed Cell Death