By F. Aldo. Massachusetts College of Art.
Two molecules of If histones contain large amounts each of four histone classes (histones H2A lexapro 20 mg with mastercard anxiety symptoms bloating, H2B purchase lexapro 5 mg without a prescription anxiety symptoms night sweats, H3, and H4) form the center of of arginine and lysine, will their net the core around which approximately 140 base pairs of double-stranded DNA are charge be positive or negative? The DNA wrapped around the nucleosome core is continuous and joins one DNA consists of a double helix, with the two strands of DNA wrapping around each other to form a helical structure. To compact, the DNA molecule coils about itself to form a structure called a supercoil. A telephone cord, which con- nects the handpiece to the phone, displays supercoiling when the coiled cord wraps about itself. When the strands of a DNA molecule separate and unwind over a small local region (which occurs during DNA replication), supercoils are introduced into the remain- ing portion of the molecule, thereby increasing stress on this portion. Enzymes known as topoisomerases relieve this stress so that unwinding of the DNA strands can occur. CHAPTER 12 / STRUCTURE OF THE NUCLEIC ACIDS 215 nucleosome core to the next. The DNA joining the cores is complexed with the fifth At physiologic pH, arginine and type of histone, H1. Further compaction of chromatin occurs as the strings of nucle- lysine carry positive charges on osomes wind into helical, tubular coils called solenoid structures. The argi- Although complexes of DNA and histones form the nucleosomal substructures nine and lysine residues are clustered in of chromatin, other types of proteins are also associated with DNA in the nucleus. These pos- These proteins were given the unimaginative name of “non-histone chromosomal itively charged regions of the histones inter- proteins. The Human Genome The genome, or total genetic content, of a human haploid cell (a sperm or an egg) is distributed in 23 chromosomes. Haploid cells contain one copy of each chromo- some. The haploid egg and haploid sperm cells combine to form the diploid zygote, which continues to divide to form our other cells (mitosis), which are diploid. Diploid cells thus contain 22 pairs of autosomal chromosomes, with each pair com- posed of two homologous chromosomes containing a similar series of genes (Fig. In addition to the autosomal chromosomes, each diploid cell has two sex chromosomes, designated X and Y. A female has two X chromosomes, and a male has one X and one Y chromosome. The total number of chromosomes per diploid cell is 46. A gene, in genetic terms, is the fundamental unit of heredity. In structural terms, a gene encom- passes the DNA sequence encoding the structural components of the gene prod- uct (whether it be a polypeptide chain or RNA molecule) along with the DNA Fig. Chromatin showing “beads on a sequences adjacent to the 5´ end of the gene which regulates its expression. Each gene on a chromosome in a diploid cell is matched by an alternate version of the gene at the same genetic locus on the homologous chromosome (Fig. These alternate versions of a gene are called alleles. We thus have two alleles of each DNA Nucleosome core Linker DNA Histone H1 The solenoid Core histones (H2A, H2B, H3, and H4) Fig. A polynucleosome, indicating the histone cores and linker DNA. A set of homologous chromosomes is shown diagrammatically. Each diploid cell contains 22 CC), or they may differ (e. Thus the corresponding protein diploid cell contains two X chromosomes. Each haploid cell contains chromosomes 1 products may be identical or they may differ in through 22 plus either an X or a Y. If the alleles are identical in base sequence, we are homozygous for this gene. If the alleles differ, we are het- erozygous for this gene and may produce two versions of the encoded protein Will Sichel has sickle cell anemia that differ somewhat in primary structure. He has two The genomes of prokaryotic and eukaryotic cells differ in size.
In 1937 discount lexapro 20 mg on-line anxiety quiz, Allen (25) detailed an additional 25 families with inherited parkinsonism and speculated that in approximately two thirds of these kindreds the inheritance was autosomal dominant and probably the result of a ‘‘single autosomal gene cheap lexapro 10 mg anxiety chest tightness. In the levodopa era, a number of reports described families with PD and PPS (22), including two very large multigenerational kindreds known as Contursi and Family C (German-American) (27,28). With progress in molecular genetic techniques, the importance of collecting data from parkinsonian families with PD and PPS phenotypes has grown exponentially. Table 1 summarizes the status of current knowledge of the genetics of PD and related conditions. It shows the types of inheritance and the location of known chromosomal loci and mutations. ASSOCIATION STUDIES Despite substantial progress in identiﬁcation, the number of known large pedigrees with PD or PPS is still small. Furthermore, genetic linkage studies, which use ‘‘identity-by-descent’’ mapping, have been hampered because the amount of DNA available from affected pedigree members is limited, generally as a result of death, lack of consent, or geographic dispersion. Association or ‘‘identity-by-state’’ mapping is an alternate approach employing groups of unrelated individuals. Association studies measure differences in genetic variability between a group with the disease in question and a group of matched, normal individuals. This method is most powerful in implicating genes for multigenic traits in homogeneous population isolates. However, many past studies have been confounded by misconceived, a priori notions of disease etiology and by clinical, locus, and allelic heterogeneity. Studies must be reproducible, preferably in different ethnic populations, and the genetic variability should have some functional consequence (either directly or in disequilibrium) that alters gene expression or the resultant protein. The genes for a-synuclein, ubiquitin C-terminal hydrolase, parkin, and tau harbor mutations that segregate with parkinsonism in large multiply affected kindreds (31,33,34,37,43) (Fig. Although the relevance of these ﬁndings for sporadic PD is unclear, there is no doubt that these genes mark a pathway that is perturbed in both familial and sporadic PD. Under- standing the components of this pathway and its regulation is the ﬁrst step in elucidating the molecular etiology of parkinsonism (48). In some studies, common genetic variability in genes for a-synuclein (49,50), ubiquitin C- terminal hydrolase (51–53), and tau (54–56) has now been implicated in sporadic PD by association methods. It is clear that these genes contribute to risk in at least a subset of patients with idiopathic PD. Other contributing genes are likely to be identiﬁed through family studies, ultimately facilitating molecular rather than clinicopathological diagnosis. Mutations in genes implicated in parkinsonism have already been used to create in vivo models that are providing powerful insights into neuronal degeneration (57–61). Much as in Alzheimer’s disease, these new tools bring the hope of novel therapies designed to address the causes rather than merely the symptoms of disease (62). T am i li alPar i nsoni sm w i th R eported utati ons/ L oci A g e atonset rang e, R esponse C h rom osom e ene ocus y( ean) Ph enotype to lev odopa R ef A utosom al dom i nant 1 p nk now n PA R PD path olog y unk now n ood 2 p nk now n PA R –8 PD w i th s ood 4 p –1 PA R –5 PD path olog y unk now n ood m utati ons) 4 p nk now n PA R –4 PD and w i th s ood 4 q S ynuclei n ( PA R –8 PD and w i th s ood m utati ons) 1 p q nk now n PA R –6 PD path olog y unk now n ood aseg aw a, personal com uni cati on, 1 q ataxi n- S –6 PD PD and w i th out ai r 2 s 1 q ataxi n- S –5 PD and w i th out s ood 3 1 q T D P- –7 T D PD PS P, Poor m utati ons) S w i th tau path olog y 1 q nk now n Y T 1 –4 R api d- onsetdystoni a— Poor par i nsoni sm path olog y unk now n Copyright 2003 by Marcel Dekker, Inc. T conti nued) A g e atonset rang e, R esponse C h rom osom e ene ocus y( ean) Ph enotype to lev odopa R ef A utosom al recessi v e 1 p nk now n PA R –6 PD probably w i th s ood 1 p nk now n PA R –4 PD probably w i th s ood 6 q –2 PA R –5 PD som et es w i th ood rev i ew ed i n R ef m utati ons) s X li nk ed recessi v e X q nk now n Y T 3 –4 ystoni a- par i nsoni sm Poor w i th out s M i toch ondri al C om plex 1 nk now n PD dystoni a, and ai r oph th al opleg i a w i th out s C om plex 1 nk now n nk now n –7 PD path olog y unk now n ood A ataxi a; autosom aldom i nant S , am yotroph i c lateralsclerosi s; R autosom alrecessi v e; corti cobasalg ang li oni c deg enerati on; D dem enti a; T D frontotem poraldem enti a; T D P- 1 frontotem poraldem enti a and par i nsoni sm li nk ed onch rom osom e 1 s, ew y bodi es; N notav ai lable; PD Par i nson’ s di sease; PS P, prog ressi v e supranuclearpalsy; ubi qui ti n carboxy- ter i nalh ydrolase L Copyright 2003 by Marcel Dekker, Inc. FIGURE 1 Genes and mutations associated with parkinsonism. Gene names are indicated in italics with their chromosomal assignment. Coding mutations are indicated above; splice-site mutations and exonic and nucleotide deletions are represented below (not to scale). CLINICAL MOLECULAR GENETIC TESTING At present, diagnostic molecular genetic testing is not commercially available and not clinically recommended for patients with sporadic PD or for those with a positive family history of PD. However, if patients express interest in research, they may be directed to centers where molecular genetic screening for PD is conducted. There are many such centers in the United States, Europe, Asia, and Australia. SUMMARY It is apparent that the genetics of PD and related conditions is complex, even in monogenic parkinsonism. The discovery of mutations in the genes for a- synuclein, ubiquitin C-terminal hydrolase, parkin, and tau has created a unique glimpse into the basic mechanisms responsible for neurodegenerative processes (43). Further genetic studies of already known PD/PPS loci will undoubtedly uncover more mutations.
All studies reported a small number of patients lexapro 5mg for sale anxiety symptoms brain fog, and follow-up has ranged from days to a maximum of 30 months order lexapro 10mg without a prescription anxiety symptoms 50. The patients have been implanted unilaterally and bilaterally. The improvement in the off medication state in activities of daily living ranged from 19 to 68%, and the UPDRS Motor score improvement ranged from 24 to 50%. The improvement in activities of daily living in the on medication state ranged from 22 to 60%, and UPDRS Motor scores ranged from 1 to 60%. All studies reported signiﬁcant reductions in dyskinesias, resulting in improvement in on time during the day. Three patients had bilateral implants, and two had unilateral implants. Four patients were markedly improved, and one was moderately improved after surgery. The activities of daily living subscores of the UPDRS improved by 19% in the off-medication state and by 42% in the on- TABLE 2 Selected Studies of Deep Brain Stimulation of the Globus Pallidus Author Number of patients Follow-up UPDRS improvement Pahwa et al. Patient diaries demonstrated an increase in on-time with a decrease in both off-time and on-time with dyskinesias. A review by the American Academy of Neurology identiﬁed reports on 64 patients who had undergone DBS of the globus pallidus (23). An approximately equal number of patients underwent unilateral and bilateral implantations. Beneﬁt was reported in all aspects of PD with a marked attenuation of motor ﬂuctuations and dyskinesias. In unilateral implants, the beneﬁts were most pronounced on the contralateral side. Evaluations performed in the off-medication state at 6 months reported a 32% improvement in UPDRS motor scores, 40% improvement in UPDRS activities of daily living scores, and 23% improvement in dyskinesias. When the evaluations were repeated in the medication ‘‘on state,’’ UPDRS motor scores improved by 1%, UPDRS activities of daily living scores improved by 30%, and dyskinesias improved by 68%. The Deep Brain Stimulation for Parkinson’s Disease Study Group reported a multinational, prospective study of bilateral GPi stimulation in PD (25). Forty-one patients were enrolled; electrodes were implanted in 38 patients (two patients had cerebral hemorrhage and one patient had intraoperative confusion). In comparison to baseline, there was a signiﬁcant improvement in the UPDRS motor scores in the off-medication state and a smaller improvement in the on-medication state. In the off-medication state, all the subscales of the UPDRS also improved. Tremor scores improved by 59%, rigidity improved by 31%, bradykinesia improved by 26%, gait by 35%, and postural instability by 36%. In the on-medication state, tremor scores improved by 85%, rigidity and bradykinesia by 22%, gait by 33%, and postural instability by 50%. Patient diaries revealed that the percentage of on time without dyskinesias during the awake time increased from 28 to 64%, and the off time reduced from 37 to 24%. The mean daily dose in levodopa equivalents was unchanged between baseline and 6 months. Long-term results of DBS of the globus pallidus have been lacking. The mean improvement in the UPDRS motor ‘‘off’’ scores and the ADL scores was more than 50%. The mean ‘‘off’’ time decreased from 40 to 10%,and the dyskinesia scores were reduced by 30%. Although the improvements persisted beyond 2 years after surgery, signs of decreased efﬁcacy were seen after 12 months. In summary, DBS of the globus pallidus results in improvement of the cardinal features of PD including tremor, bradykinesia, rigidity, and gait and a marked reduction of levodopa-induced dyskinesias. The daily levodopa dosage or antiparkinsonian medication dosage is not reduced. Optimal Pallidal Electrode Location Studies of GPi stimulation have reported variable and sometimes opposite effects by using different electrode contacts (27–29). Stimulation in the dorsal GP (upper contact) signiﬁcantly improved gait, akinesia, and rigidity and could induce dyskinesia when the patients were in the off-state. In contrast, stimulation of the posteroventral GP (lower contact) signiﬁcantly worsened gait and akinesia.
A particularly important O-linked sugar is N-acetylneuraminic acid culation lexapro 5 mg on-line anxiety symptoms in 8 year old, thereby contributing to hepatic encephalopathy (brain toxicity due to ele- (NANA or sialic acid) cheap lexapro 5 mg fast delivery anxiety for dogs, a nine-carbon sugar that is synthesized from fructose- vated ammonia levels). A Partial List of Proteins Synthesized in the Liver Type of Protein Examples Blood coagulation Blood coagulation factors: fibrinogen, prothrombin, Factors V, VII, IX and X. Metal-binding proteins Transferrin (iron), ceruloplasmin (copper), haptoglobin (heme), hemopexin (heme) Lipid transport Apoprotein B-100, apoprotein A-1 Protease inhibitor 1-Antitrypsin 852 SECTION EIGHT / TISSUE METABOLISM A. N-linked O CH2 HOCH2 O C O O O C O HO H H H H NH C CH2 CH O 2 CH NH H OH H O OH H H NH H NH H NH C O C O CH3 CH3 GalNAc Serine GlcNAc Asparagine Fig. The general configuration of O-linked and N-linked glycoproteins. NANA (sialic acid) residues are lost from the serum proteins. This change signals their removal from the circulation and their eventual degradation. An asialoglyco- protein receptor on the liver cell surface binds such proteins, and the receptor–- ligand complex is endocytosed and transported to the lysosomes. The amino acids from the degraded protein are then recycled within the liver. The Pentose Phosphate Pathway The major functions of the pentose phosphate pathway (see Chapter 29) are the gen- eration of NADPH and five-carbon sugars. All cell types, including the red blood cell, can carry out this pathway because they need to generate NADPH so that the activity of glutathione reductase, the enzyme that catalyzes the conversion of oxi- dized glutathione (GSSG) back to reduced glutathione (GSH) can be maintained. Without the activity of this enzyme, the protection against free radical injury is lost. All cells also need this pathway for the generation of ribose, especially those cells that are dividing rapidly or have high rates of protein synthesis. The liver has a much greater demand for NADPH than do most other organs. It uses NADPH for the biosynthesis of fatty acids and cholesterol, which the liver must make to produce phospholipids, and for the synthesis of VLDL and bile salts. It also uses NADPH for other biosynthetic reactions, such as that of proline syn- thesis. NADPH is also used by mixed-function oxidases such as cytochrome P450 that are involved in the metabolism of xenobiotics and of a variety of pharmaceuti- cals. Because the liver participates in so many reactions capable of generating free radicals, the liver uses more glutathione and NADPH to maintain glutathione reduc- tase and catalase activity than any other tissue. Consequently, the concentration of glucose-6-phosphate dehydrogenase (the rate-limiting and regulated enzyme in the pentose phosphate pathway) is high in the liver, and the rate of flux through this pathway may be as high as 30% of the rate of flux through glycolysis. FUELS FOR THE LIVER The reactions used to modify and inactivate dietary toxins and waste metabolites are energy requiring, as are the reactions used by anabolic (biosynthetic) pathways such as gluconeogenesis and fatty acid synthesis. Thus, the liver has a high energy requirement and consumes approximately 20% of the total oxygen used by the body. The principle forms in which energy is supplied to these reactions is the high- energy phosphate bonds of adenosine triphosphate (ATP), uridine triphosphate (UTP), and guanosine triphosphate (GTP), reduced NADPH, and acyl-CoA thioesters. The energy for the formation of these compounds is obtained directly CHAPTER 46 / LIVER METABOLISM 853 Table 46. Major Fates of Carbohydrates in the Liver • Storage as Glycogen • Glycolysis to pyruvate • Followed by oxidation to carbon dioxide in the TCA cycle • Precursors for the synthesis of glycerol-3-phosphate (the backbone of triacylglycerols and other glyceolipids), sialic acid, and serine • Entry into the TCA cycle and exit as citrate, followed by conversion to acetyl CoA, mal- onyl CoA, and entry into fatty acid synthesis and secretion as VLDL I Synthesis of phospholipids and other lipids from triacylglycerols • Conversion to mannose, sialic acid, and other sugars necessary for the synthesis of oligosaccharides for glycoproteins, including those secreted into blood • Synthesis of acid sugars for proteoglycan synthesis and formation of glucuronides • Oxidation in the pentose phosphate pathway for the formation of NADPH (necessary for biosynthetic reactions such as fatty acid synthesis, glutathione reduction, and other NADPH-utilizing detoxification reactions) from oxidative metabolism, the TCA cycle, or the electron transport chain and oxidative phosphorylation. After a mixed meal containing carbohydrate, the major fuels used by the liver are glucose, galactose, and fructose. If ethanol is consumed, the liver is the major site of ethanol oxidation, yielding principally acetate and then acetyl CoA. During an overnight fast, fatty acids become the major fuel for the liver. They are oxidized to carbon dioxide or ketone bodies. The liver also can use all of the amino acids as fuels, converting many of them to glucose. The urea cycle dis- poses of the ammonia that is generated from amino acid oxidation. Carbohydrate Metabolism in the Liver After a carbohydrate-containing meal, glucose, galactose, and fructose enter the Why would you expect fructose 1- portal circulation and flow to the liver.