molecular biochem Flashcards
Chromatin structure
DNA exist in the condensed, chromatin form
DNA loops 2x around the histone octomer to form a nucleoSOME
H1 binds the nucleosone and to linker DNA and stabilize the chromatin fiber
Phosphate groups give DNA a negative charge
Lysine and argininge give histone a + charge
DNA and histone synthesis occurs in S phase
mito have their own DNA which is circular and doesnt utilize histones
Heterochromatin
condensed, darker, inaccessible and inactive, increased methylation makes DNA mute
decreased acetylation that makes the DNA active
Barr bodies (inactive x chromosome in the periphery of nucleus)
Euchromatin
less condensed, appears lighter on EM
transcriptionally active, stericallu accessible
Euchromatin is expressed
DNA methylation
Changes the expression of a DNA segment without changing the sequence, involved with aging, carcinogenesis, genomic imprinting, transposabl eelement repression and inactivation of the X chromosome
impriming – dna methylation,
Methylation is within a gene promoter (CpG islands)
typically silences gene transcription
CpG islands for methylating the DNA segment
Histone methylation is reversible, can also cause activation in the right spot
histone acetylation removes the histones positive charge–> relaxed DNA coiling,
nucleotides
Nucleoside = base + deoxy ribose (sugar) NucleoTide= base + deoxyribose + phosphaTe, linked by 3'-5' phosphodiester bond
5’ of incoming base what joins the regular 3’ end
Pur As Gold (adenin, Guanin are purines and double ringed) CUT the Py (pyrimidines -cytosine, adenin guanine
CG triple bonds, AT only double bongs (increased C-G content–> melting temp increases )
Amino acids necessary for purine synthesis (cats purrr untile they GAG)
Glycine, Aspartate, Glutamine
Purine synthesis
PRPP synthase is the rate limiting step of both purine and pyrimidine (ribose 5 P to PRPP)
PRPP -> IMP is inhibited by 6MP (Azathioprine) inhibit denovo purine synthesis
PRPP-> IMP -> AMP
PRPP-> IMP -> GMP (mycophenolate and ribavirin - inhibit Inosine monophosphate dehydrogenase)
Pyrimidine production
needs Aspartate
Glutamine+CO2 –> Carbamyl phosphate synthetase 2 CPS2)
Carbamoyl phosphate–> orotic acid (with PRPP)
UMP synthase (orotic aciduria-> UDP Ribonucleotide reductase->dUDP ->dUMP -> dTMP (thymidylate synthase)
DHF to THF (DHFr)
methotrexate, TMP and pyrimethamine inhibit dihydrofolate reductase (deoxy
DNA repplication
single in prokaryotes and multiple in eukaryotes
Helicase unzips DNA, deficient in Bloom syndrome (BLM gene mutation
SS-binding proteins- proteins that prevent from reannealing
DNA topoisomerases- Create single or ds breats (1 and 2)- in eukaryotes irinotecan and topotecan inhibit topoisomerase TOP 1, etoposide/teniposide inhibit TOP2, In prokaryotes: fluoroquinolones inhibit TOP 2 (DNA gyrase and TOP 4)
Primase- Makes an RNA primer on which DNA polymerase 3 can initiate replication
DNA polymerase 3
Prokaryotes only, elongates leading strand by adding deoxy nucleotides to the 3’ end, elongates lagging strand until it reaches primer of precedign fragment
DNA polymerase 3 has 5’–> 3’ synthesis and proofreads with 3’–> 5’ exonuclease
Drugs blocking DNA replicaiton often have a modified 3’ OH, thereby preventing addition of the next nucleotide (chain termination)
DNA Polymerase 1
Prokaryotes only Degrades RNA primer, replaces it with DNA
Same functions as DNA polymerase 3 also excises RNA primer with 5’-> 3’ exonuclease
DNA ligase
Catalyzes the formation of a phosphodiester bond within a strand of ds DNA
Joins Okazaki fragments, Ligase Links DNA
Telomerase
Eukaryotes only, A reverse transcriptase (RNA dependent DNA polymerase) that adds DNA (TTAGGGO to 3’ ends
Lac operon
Glucose is the preferred metabolic substrate in E coli, but when glucose is absent and lactose is present, the lac operon is activated to switch to lactose metabolism
Low glucose–> increased adenylate cyclase activity–> generation of cAMP from ATP–> activation of catabolite activator protein (CAP)–> increased transcription
High lactose–> unbinds repressor protein from repressor/operator site–> increased transcription
Nucleotide exicision repair
Specific endonucleases release the oligonucleotides containing damaged bases, DNA polymerase and Ligase fill and reseal the gap, respectively, Repairs bulky helix distorting lesions, Occurs in G1 phase of cell cycle
Defective in xeroderma pigmentosum (inability to repair DNA pyrimidine dimers caused by UV exposure)
Dry skin extreme light sensitivity, skin cancer
Base excision repair
base specific Glycosylase removes altered base and creates AP site (Apurinic/apyrimidic )
One or more nucleotides are removed by AP-Endonuclease, which cleaves 5’end
AP lyase cleaves 3’ end
Glycosylase-> Endonuclease-> lyase-> Polymerase-> ligase
Mismatch repair
mismatched nucleotides in newly synthesized unmethylated strand are removed and gap filled and resealed, occurs predominantly in S phase
Defective in lynch syndrome (hereditary nonpolyposis colorectal cancer)
Non homologous end joining
brings together 2 ends of DNA fragments to repair double stranded breaks
Defective in ataxia-telangiectasia
No requirement for homology, some DNA may be lost
Homologous recombination
requires 2 homologous DNA duplexes, A strand from damaged dsDNA is repaired using a complementary strand from intact homologous dsDNA as a template
Defective in breast/ovarian cancers with BRCA1 mutation and in Fanconi anemia
does not lose nucleotides
regulation of gene expression
Promoter- where RNA polymerase 2 and multiple other transcription factors bind to DNA upstream from gene locus (AT rich upstream sequence with TATA and CAAT boxes
Promoter mutation commonly results in dramatic decrease in level of gene transcription
Enhancer- DNA locus where regulatory proteins (activators bind increasing expression of a gene on the same chromosome
Silencers where regulatory prototeins repressors bind, decreasing expression of a genen on the sm
RNA processing
initial transcripts is called heterogenous nuclear RNA (hnRNA) then modified and becomes mRNA
Capping of the 5’end (addition of 7 methylguanisine cap)
Polyadenylation of 3’ end (200 As on 3’)
Splicing out of introns
Capped, tailed, and spliced transcript is called mRNA
mRNA quality control occurs at cytoplasmic processign bodies (P-bodies) which contain exonucleases, decapping enzymes, and microRNAs, mRNAs
Poly A polymerase does not require a template AAUAAA - polyadenylation signal
RNA polymerase
RNA polymerase 1 makes rRNA (nucleolus)
RNA polymerase 2 makes mRNA, microRNA, snRNA
RNA polymerase 3 makes 5S rRNA, tRNA (tiny)
No proofreeding,
a-amanitin- found in amantina phalloides (death cap mushrooms) inhibits RNApolymerase 2 –> severe hepatotoxicity
Actinomycin D- also called dactinomycin, inhibits RNA polymerase in both prokaryotes and eukaryotes
Prokaryotes 1 RNA pol (mutisubunit complex) makes all 3 kinds of RNA - Rifampin inhibits DNA dependent RNA polymerase in prokaryotes
tRNA
<100 nucleotides, anticodon end is opposite 3’ aminoacyl end. All tRNAs both eukaryotes and prokaryotic, have CCA at 3’ end along with a high percentage of chemically modified bases, the amino acid is covalently bound to the 3’ end of the tRNA, CCA Can carry Amino acids
t- arm- contains the TC site for tRNA- ribosome binding, T arm, Tethers tRNA molecule to ribosome
D-arm- contains Dihydrouridine residues necessary for tRNA recognition by the correct aminoacyl-tRNA synthetase, D-arm allows Detection of the tRNA by aminoacyl tRNA synthetase
Charging- aminoacyl tRNA synthease uses ATP
Start and stop codons
AUG, inAUGurates protein synthesis
codes for methionine
stop UGA, UAA, UAG
Protein synthesis
initiation- eukaryotic initiation factors (eIFs) identify the 5’ cap , eIFs assemble the 40s ribosomal subunit with the initiator tRNA, eIFs released when the mRNA and the ribosomal 60s subunit assemble with the complex, Requires GTP
elongation- Aminoacyl-tRNA binds to A site, rRNA,
Permanent vs stable vs Labile cells
Permanent- Remain in G0 regenerate from stem cells
Stable- Enter G1 from G0 when stimulated
Labile- never go to G0 divide rapidly with short G1 , most affected by chemo
Cell trafficking
Golgi is distribution center for proteins and lipids from ER to vesicles and plasma membrane, Post translational events in Golgi inculde modifying N-oligosaccharieds on asparagine, adding O-oligosaccharides on serine and threonin, and adding mannose 6 P to proteins
I cell diseasep- inherited lysosomal storage disorder autosomal recessive defect in N-acetylglucosaminyl –< failure of the golgi to phosphorylate mannose residues on glycoproteins, –> proteins are secreted extracellulary rather than delivered to lysosomes, results in coarse facial features, gingival hyperplasia, clouded corneas, restricted joint movements–> claw hand, fatal in kids
SRP (signal recognition particles)
abundant, cytosolic ribonucleoprotein that traffics polypeptide-ribosome complex from the cytosol to the RER . Absent or dysfunctional SRP–> accumulation of protein in cytosol
Vesicular trafficking proteins- COPI- golgi –> cis Golgi–> ER
COP2 ER–> cis golgi
Clarthrin- trans golgi–> lysosomes, plasma membrane–> endosomes (receptor-mediated endocytosis) LDL receptor
Peroxisomes
B-ox of VLCFA, a ox of Bchain FA, catabolism of amino acids and ethanol, synthesis of cholesterol, bile acids, and plasma logen, important membrane phospholipid, especially in white matter of brain
Adrenoleukodystrophy- X linked recessive disorder of B-oxidation due to mutation in ABCD1 gene–> VLCFA buildup in adrenal glands, white (leuko matter of brain testes, progressive disease that can lead to adrenal gland crisis coma, and death
Microtubules
cylindrical outer structure composed of a helical array of polymerized heterodimers of a-B tubulin, each dimer has 2 GTP bound, incorporated into flagella, cilia, mitotic spindle, grows slowly collapses quickly
C tetani- HSV, Polio, rabies use dynein for retrograde transport to the neuronal cell body
Microtubule drugs- Mebendazole, Griseofulvin, Colchicine, Vincristine, paclitaxel
Negative near nucleus
Positive poits to periphery
cilia structure
9 doublet and 2 singlet arrangement of microtubules
Base body- below cell membrane, with 9 microtubyle triplets and no central microtubules
Axonemal dynein- ATPase that links peripheral 9 doublets and causes bending of cilium by sliding
Gap junctions enaple fordinated ciliary movement
Kartagner syndrome- immotile cilia due to dynein arm defect- autosomal recessive, dysfunctional sperm and fallopian tubes, increased risk of ectopic pregnancy
Bronchiectasis, recurrent sinusitis, ear infection, conductive hearing loss, and situs inversus, nasal nitric oxide,
Collagen
most abundant proteins in human body, extensively modified by posttranslational modification, organizes and strengthens extracellular matrix
Type one- Bone, skin, tendon, dentin, fascia, cornea, late wound repair, made by osteoblasts,, decreased production in osteogenesis imperfecta type 1
Type 2- Cartwolige (including hyaline), vitresous body, nucleus pulposus
Type 3- reticulin, skin, blood vessels, uterus, fetal tissue, early wound repain,
Type 4- basement membrane- basal lamina- lens, floos, defective in ALport syndrome, and AB against in good pasture syndrome
Synthesis
Translation of collagen a chains (Preprocollagen) GLy xy, collagen is mosly Glycine
Hydroxylation fof specific proline and lysine residues, requires vitamin C, deficiency –> scurvy
Glycosylation- of pro a chain hydroxylysine, residues and formation of procollagen via hydrogen and disulfide bonds (triple helixes of 3 collagen a chains), problems forming triple helix–> osteogenesis imperfecta
Exocytosis of procollagen into extracellular space
Proteolytic processing- cleavage of disulfide rich terminal regions of procollagen–> insoluble tropocollagen
Cross linking- reinforcing staggered tropocollagen molecules by covalent lysine-hydroxylysine cross linkage by copper lysul oxidase to make collagen fibrils, problems with cross linking–> Menkes disease
Osteogenesis imperfecta
COL1A1/2 autosomal dominant with decreased production of otherwise normal type 1 collagen, manifestation include
Blue sclera- connective translucent cT over choroid
Abnormalities
hearing loss
treat with bisphosphonates to decreased fracture risk, BITe
Bones, I eyes, teeth, ear
Ehlers Danlos syndrome
Faulty collagen sunthesiso
skin, hyper mobile easy bruising
berry aneurysms
Type 5 collagen
vascular type 3 gives vessles issuew
Elastin
Stretchy protein within skin, lungs, large arteries, elastic ligaments, vocal cords, ligamenta flava (connect vertebrae–> relaxed and stretched conformations)
Rich in nonhydroxylated proline glycine, and lysine (vs collagen that needs to have hydroxylation)
Tropoelatin with fibrillin scaffolding
Crosslinking takes place extracellularly and gives elastin its properties
a1 antitrypsin, an elastase inhibitor, (a1 antitrypsin deficiency–> unopposed elastase activity)
Changes with aging- decreased dermal collagen and elastin, decreased synthesis of collagen fibrils, crosslingking remains normal
Marfans–> AD skeleton, heartm eyes Fibrillin 1 gene mutation in chromosome 15 (FiFteen) no sheath around elastin, tall with long extremities, pectus carnitum and excavatum, cystic medial necrosis of aorta, mitral valve prolapse, subluxation of lenses upward and temporally (downward and medially in homocystinuria)
codominance
both alleles contribute to the phenotype of the heterozygote
blood groups , a1 antitrypsin deficiency, HLA groups
variable expression vs incomplete penetrance vs pleiotropy
variable expressivity- same genotype diffrent phenotypes (severity)
incomplete penetrance- not all individuals with the gene get the disease (Brca1 doesnt=cancer)
pleiotropy- one gene contributes to multiple phenotypic effects
loss of heterozygosity
mutation in a tumor supressor gene
the complemenatry gene needs to be mutated
RB, Lynch syndrome, Li fraumeni
dominant negative mutation
exerts a dominant effect
a heterozygote==> nonfunctional altered protein that also prevents the normal gene from frunctioning
p53
linkage disequilibrium
tendency for certain alleles at 2 linked loci occure together more or less oftern than expected by change
in populations not in families (brown hair and brown eyes in asia)
Mosaicism
presence of genetically distinctly cell lines in teh same individual
Somatic mosaicism- mutation arises from mitotic errors after fertilization and propagates through multiple tissues or organs
Gonadal mosaicism- mutation only in egg or sperm, if parents and relatives do not have the disease, suspect gonadal (or germline mosaicism)
McCune-Albright syndrome- due to Gs protein activating mutation, presents with unilateral CAL spots with ragged edges, polyostotic fibrous dysplasia (bone is replaced by collagen, fibroblasts) and at least one endocrinopathy, lethal if mutation occurs before fertilization affecting all cells, but survivable in pts with mosaicism
Locus heterogeneity, Allelic heterogeneity, heteroplasmy, uniparental disomy
Locus heterogeneity- mutations at different loci can produce a similar phenotype (albinism)
Allelic heterogeneity- Different mutations in the same locus produce the smae phenotype (b-thalassemia)
Heteroplasmy- both normal and mutated mtDNA resulting in variable expression in mitochondrially intherited disease
Uniparental disomy- offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent, heterod1somy (heterozygous) indicates a meiosis 1 erroe, IsoIsomy (homozygous) indicates a meiosis 2 error or postzygotic chromosomal duplication of one of a pair chromosomal
disorders of imprinting
imprinting one gene copy is silenced by methylation, and only the other copy is expressed–> parent of origin effects
Prader Willi syndrome
Maternally derived genes are silenced, Disease occurs when the Paternal allele is deleted or mutated
Hyperphagia, obesity , intellectual disability, hypogonadism, hypotonoa
Chromosome 15 of paternal origin
Prader has no Dad
Angel Man syndroem
Paternally derived UBE3A is silenced, Disease occurs when Mom allele is deleted or mutated
Seizures, Ataxia, severe intellectual disbility , inappropriate Laughter (happy puppet), set SAIL for angel Island
UBE3A on maternal copy of chromosome 15
MD are angels (maternal Deletion)
cystic fibrosis
encodes ATP Cl- that secretes CL in lungs and GIT
Reabsorbs CL in sweat glands
No Cl (with H20) in Lungss and GIT- thinck mucus
with increased CL in sweat
S aureus as kids, P aeruginosa in adults
Rett syndrome
Sporadic disorder seen in girls ( affected males die in utero)
De novo mutation of MECCP2 on X chromosome,
ages 1-4
regression, in motor, verbal and cognitive abilities, ataxia, seizures, growth failure hand wringing
Fragile X syndrome
Trinucleotide repeat in FMR 1 gene- hypermethylation –> decreased expression
down syndrome is most common genetic cause, but mostcases occurs sporadically
post pubertal macroorchidism, long face jaw, everted ears, mitral valve prolapse