Biochemistry Flashcards
What is the charge of DNA double helix?
Negative
What is the charge of nucleosome?
Positive charge
what are histones?
Amino acid lysine and arginine (Histones bind to nucleosomes and to linker DNA)
what phase does DNA and histone synthesis occur?
During the S phase
what are the characteristics of heterochromatin?
Condensed DNA, transcriptional inactive, and sterically inaccessible
What is Euchromatin?
Less condesned,lighter on EM, and transcriptionally active
What is DNA methylation?
Template strands (Cytosine and adenine) are methylated in DNA replication, so mismatch repair enzymes can distinguish between old and new strands.
what happens in histone methylation?
usually suppresses DNA transcription, can can activate it in some cases
what does histone ACETYLATION do?
Relaxes DNA coiling and allows for transcription
What are the differences between nucloetides?
Nucloside
Nucleotide?
Nucloside: base + deoxyribose (sugar)
Nucleotide: base + deoxyribose +phosphate (linkare 3-5 phosphodiester bond)
What is the difference between a purine and pyrimidine?
PURines (A, G) has 2 rings
Pyrimidines (C, U, T) 1 ring
where is Uracil found?
Where is thymine found?
Uracil is RNA
Thymine is in DNA
What determines the melting temperature of DNA?
Number of C-G bonds (3- H bonds so stronger) then A-T (2 H bonds)
What amino acids are needed for purine synthesis?
GAG (gycine, aspartate, glutamine)
What are medications that disrupt pyrimidine synthesis?
1) Leflunomide: dihydroorotate dehydroxygenase
2) Methrotrexate, trimethoprim (TMP), pyrimethamine (dihydrofolate reductase)
3) 5-flurocil: forms 5-F-dUMP inhibits thymidylate synthase
What disrupts purine synthesis?
6-mercaptopurine and azathioprine: de novo purine synthesis
Mycophenolate and ribavirin: inhibits inosine monophospahte dehydrogenase
What disrupts purine and pyrimidine synthesis?
Hydroxyurea: ribonucleotide reductase
what are two medications that act on purine slavage pathways?
Which step do they act on?
1) Allopurinol and febuxostat, Probenecid
2) Allopurinol/febuxostat: Act on X0 (which is enzyme) prevents formation of Xanthine to Uric acid)
3) Probenecid: increases the transformation of Uric acid to urine
All these medications are used for gout
what does adenosine deaminase deficiency cause?
1) SCID (severe combined immunodeficiency syndrome)
2) Increases dATP, which is toxic to lymphocytes.
What is Lesch-Nyhan Syndrome?
What are the signs?
Deficiency in HGPRT enzyme
Symtoms match abbreviation (HyperuricemisGoutPissed off aggresionRetrardation DysTonia
What are features of the genetic code?
1) Unambiguous: each codon is 1 amino acid
2) Degenerate/ redundant: most amino acids are coded by mutiple codons (except mehtionin and tryptophan)
3) Comaless/nonoverlapping: read from a fixed point, continuous sequence of bases (except virus)
4) Universal: genetic code is conserved throughout evolution, except in human mitochrondria.
Where does origin of replication of DNA occur?
What is the difference between prokaryotes and eukaryotes promotor?
Base pairs, usually promoters (A-T rich segments)
2) Eukaryotes may have more then one promoter
What is the replication fork?
Y shaped region where the leading and lagging strands are synthesized
what is the function of helicase?
Unwinds the DNA at replication fork
What are the function of single stranded binding proteins?
Prevents strands from reannealing
What is function of DNA topoisomerase?
Create single or double stranded breaks in the helix to add or remove supercoils
What medications are DNA toposiomerase inhibitors?
fluroquinones
What is the function of primase?
Makes RNA primer on which DNA polymerase III can initiater replication
What is DNA polymerase III?
Prokaryote only, elongates the leading strand by adding deoxynucleotides to the 3’ end.
Synthesis occurs in 5’ to 3’
Proofreads with 3’ to 5’ exonuclease
what does DNA polymerase 1 do?
Prokaryote, degrades RNA primer, and replaces with DNA
(has same functions as DNA polymerase III but also excises RNA primer with 5’ to 3’ exonuclase
Is DNA replication semiconservative?
Yes
Is DNA replication continuous or discontinuous?
It is both. Discontinuous fragments called Okazaki fragments
What is the use of DNA ligase?
Catalyzes the formation of phosphdiesterase bond within double stranded DNA
What is function of telomerase?
An RNA dependent DNA polymerase that adds DNA to 3’ end of chromosome to prevent lose of genetic material with each replication (eukaryotes only)
Which DNA component is often desregulated within cancer?
Telomerase.
What are the severity of DNA damage?
silent
What is a transition DNA mutation?
Purine to purine (A to G, or C to T)
or pyrimidine to pyrimidine
What is a transversion mutation?
Purine to pyfrimidine (A to T) or pyrimidine to purine (C to G)
What is a silent mutation?
Nucleotide subsitution, but same amino acid base coded
What is missense mutation?
Nucleotide substitution in changed amino acid but with similar chemical structure
(sickle cell)
What is a nonsense mutation?
Results in nucelotide with early stop
What is a frameshift?
what are some diseases?
Deletion and insertion that causes misreading of all nucloetides downstream
1) Tay sachs, Duchesse muscular dystrophy
What is splice site?
Retrained intron in the mRNA (protein is imparied)
Cancer, dementia, epilepsy, B thalasemmia
What is the Lac operon?
1) Genetic responses to environmental changes
2) Ecoli prefers glucose metabolism, when no glucose, switches to lactose metabolism
High lactose, unbinds the repressor protein from reprressor/operator site and has transcription.
The LAC genes are expressed when there is no glucose and lactose available.
LAC genes are low basal when high glucose, lactose available
LAC genes not expressed if high glucose, and no lactose
what are the types of DNA repair, and when in cell cycle do they occur?
1) Nucleotide excision
2) Base Excisions
3) Mismatch repair
What is base excision repair?
When is this type of repair important?
Base specific glycosylase removes altered bases
Occurs throughout the cell cycle
Spontaneous or toxic deamination
what is nucleotide excision repair?
What diseases are caused by defective?
1) Endonucleases release the oligonucleotides and DNA polymerase ligase and fill, and reseal gap
Occurs in the G1 phase
Xeroderma pigmentosum
What is a mismatch repair?
What diseases?
Looks are the strand, and mismatched nucloetides are removed the gap is filled in.
Occurs during the G2 phase
Diseases: HNPCC
(also called Lynch syndrome)
What are mechanism of repairing double stranded DNA?
1) Non homologous end joining (2 ends of DNA fragments to repair double stranded breaks) some DNA maybe lost
2) DNA, RNA protein synthesis direction (if have drugs that attack the 3’ end hydroxyl attack
what are the mRNA start codons?
AUG or GUG
what is difference between eukaryotes and prokaryotes codons?
Eukaroates code for methionine which may be removed before translation is completed
Prokaryotes: n-formylmethionine
What are mRNA stop codons?
UGA (u go away)
UAA (u are away)
UAG (u are gone)
What are the regulators of gene transcription?
1) Promoter (site were RNA polymerase II and transcription factors bind to DNA upstream from AT CAAT or TATA boxes
2) Enhancer: stretch of DNA factors that alter gene expression by binding to transcription factors
3) Silencer: site where negative regulators bind
What are the different types of RNA polymerase?
RNA polymerase 1 (makes mRNA, most rampant)
RNA polymerase 2 (makes mRNA, largest, MASSIVE)
RNA polymerase 3 (makes 5s, rRNA, tRNA): t is the smallest..TINY
what disease associated with RNA polymerase II?
alpha-amanitin (death cap mushrooms and causes heptotoxicity)
What medication is associated with inhibition of RNA polymerase?
Rifampin
what are the steps of RNA production?
1) Transcript is heterogenous (nuclear) becomes hmRNA when modified
2) Capping of 5’ end with 7 methylguanosine cap
3) Polyadenylation of 3’ end (200A)
4) Splicing out introns
CAPPED, SPLICED, and TAILED is MRNA
5) Transported out of nucleus into cytosol
6) P-bodies: exonuclease, and enzymes and stored for future use.
How does splicing of pre-mRNA occur?
1) Transcript combines with snRNP and other proteins to form spliceosome
2) Lariat shaped intermediate is formed
3) Lariat removed intron to join the two exons
What are the differences, intron vs exons?
Exons contain genetic information for coding of the protein.
Introns are intervening non coding segments of DNA
what are micro RNA?
Non coding portions of mRNA that regulate protein expression
(introns can contain the microRNA genes)
They can cause degredation, ot inactivation of target mRNA
what is the shape of tRNA?
1) Cloverleaf form
2) Long 3’ end
3) T arm: ribosome binding
4) D arm: tRNA recognition for tRNA synthetase
what is the wobble?
Accurate base pairing is usually required in 2 first nucloetide positions of an mRNA, the 3rd wobble may code for the same amino acid (degeneracy of the genetic code).
How does initiation of protein synthesis from mRNA?
1) GTP hydrolysis that causes 40S + 60S and 80S to assemble
How does elongation of the protein occur?
1) Aminoacryl site: incoming
2) P site: accommodates growing peptide
3) E site holds empty tRNA as it exits.
rRNA catylizes peptide bond
Ribosomes advance nucleotide toward 3’end
How does termination occur?
Stop codon is recongized and the polypetide is released
What are some modifications that can occur in post translation of rNA?
Removal of N and C terminal peptides
What are some covalent alterations?
1) Phosporylation, glycosylation, hydroxylation, methylation, acetylation, ubiqitation
What are chaperone proteines?
Intracellular proteins (yeast, HSP 60) that are expressed at high temperatures to prevent denaturing and misfolding
what are parts of M phase?
prophase, prometaphase, metaphase, anaphase, telophase
what are the steps of cell cycle?
Synthesis Mitaosis G1 (growth) G2 G0
Where do tumor suppressors act?
p53 induces p21 which inhibits cyclin dependent kinases (these are checkpoints) inactivates E2F
Mutations lead to Li-Fraumani syndrome
what cell types (in terms of divison)?
1) Permenent (remain in GO and regenerate from stem cells) cardiac, neurons, skeletal, muscles, RBX
2) Stable enter into G1 when stimulated: heptocytes, lymphocytes
3) Labile never have Go, keep dividing (bone marrow, gut epithelium, skin, hair, germ cells)
What is I-cell disease and features?
1) Lysosome storage disease.
Golgi apparatus does not phosporylate mannose residue, and proteins are secreted extracellular rather then to lysosomes
Clinical features: Coarse facial features Clouded corneas Restircted joint movememt High lysosomal enzymes
What defects in proteosomes have been linked to disease?
Ubiquitin-proteosome system have been implicated in Parkinsons (do not tag protein properly)
What diseases do the following stains identify? Vimentin DesMin Cytokeratin GFAP Neurofilaments
Vimentin: mesnchymal tumors (sarcoma, endometrail carcinoma, renal cell carcinoma)
DesMin (muscle tumor, rhabdomyosarcoma)
Cytokeratin (epithelial tumors squamous cell carcinoma)
GFAP: astrocytoma, glioblastoma
Neurofilatments: neuronal tumors: neuroblastoma
What are drugs that act on microtubules?
1) Mebendazole : antihelminthic
2) Griseofulvin: antifungal
3) Cholchicine: antigout
4) Vincristine/ Vinblastine: anticancer
5) Paclitaxel: anticancer
What is the cilia structure?
9+2 microtubules doublets
What is Kartagner syndrome?
cilia dyskinesia (immotile cilia due to dynein arm defect, results in male and female infertility, increases risk of ectopic pregnancy.
What is the cellular mechanism of Ouabin, and Digoxin?
Ouabin (for hypotension and arrythmias) inhibits by binding to the K+ site
Digoxin: Inhibits Na-K ATPase which leads to Na/Ca inhibition
What diseases are associated with the following types of collagen defects?
Type 1: Bone (osteogenesis imperfecta type 1)
Type 2: Cartwolage
Type 3: Ehlers Danlos
Type 4: Alport syndrome, Goodpasture
What steps of collagen synthesis are specifically associated with diseases?
Collagen hydroxylation deficiency:scruvy
Glycosylation deficiency: osteogenesis imperfecta
Crosslinking: Ehlers Danlos, Menkes Disease
What are features of osteogenesis imperfecta?
1) Multiple fractures with little trauma
2) Blue sclera
3) Hearing loss
4) Opalescent teeth that wear easilt.
what are characteristics of Ehlers Danlos syndrome?
Inheritance is either dominenet or recessive
Classical (joint/skin) mutation in type 5 collagen
Vascular: Type 3 collagen (vascular and organ rupture)
Characteristics of Menkes disease?
1) Kinky hair
2) Growth retardation
3) Hypotonia
Impaired copper absorption (ATP74, Menkes protein is defective)
What disorders are linked to elastin?
1) Fibrillin 1( glycoprotein forms sheath around elastin) Marfan
2) Emphysema alpha antitrypsin defeciency (lack of elastase)
3) Wrinkles due to collagen and elastin decrease
How to polymerase cahin reaction work, and what diseases can be tested?
1) Amplifies a specific desired fragment of DNA
2) Good for neonatal HIV and herpes encephalitis
What types of blotting techniques are used? What are the diseases which are identified?
1) Southern blot DNA
2) Northern blot RNA (gene expression levels)
3) Western blot: protein (HIV)
4) Southwestern blot (DNA binding proteins)
what is flow cytometry used for, and what diseases?
1) Assess size, granularity, and protein expression
2) Hemtological abnormalities: paraxymal nocturnal hemoglobinuria, fetal RBC, CD4 count HIV
When are microarrays used?
Genetic testing, cancer mutations. DNA probes sent to thousands of nucleic acid sequences to identify specific mutations.
what are enzyme linked immunosrbent assay?
detects presence of antigen or antibody in the blood
HBsAg or anti HB
what and when karytype is done?
1) Can be done on the sample of blood
2) For trisomies or sex chromosome disorder
3)
when you do flurosecence in situ hybridization, where does flourescence sighting indicate?
1) Microdeletion: no fluo at site compared to other chromosome
2) Translocation: fluo outside of the original chromosome
3) duplication: extra fluo on one chromosome relative to homologous
What are steps to cloning?
1) Isolate mRNA of interest
2) Expose mRNA to reverse transcriptase cDNA
3) Insert cDNA fragments into bacterial plasmids
4) Transform recombinant plasmids into bactera
5) Surviving bacterial on antibiotics produce cloned DNA
What is codiminece?
Both alleles contribute to phenotype (blood type, alpha antitrypsin deficiency)
Variable expressivity?
Same gentoype, but the expression of phenotype leads to different seriousness of disease ( neurofibrmatosis type 1)
Incomplete penetrance?
Not all the same mutant genotype show the mutant phenotype
BRACA1 does not always results in breast and ovarian cancer
Pleiotrophy?
One gene contributes to multiple phenotypes
Phenylketonuria (light skin, intellectual disability and musky body odor)
Anticipation?
Increased severity and earlier onset with generations
1) Huntington’s disease
Loss of heteroziosity ?
1) Need mutation of the gene, and of the suppressor gene to get disease (2 hit)
2) Retinoblastoma
3) Lynch syndrome HNPCC
What is mosaicism and the disease associated?
1) Presence of gentically distinct cell lines within individual
2) Somatic: through multiple cell lines
3) Gonadal: only in egg and sperm cells
McCune-Albright syndrome: mutation of G protein (cafe au lait sports, early puberty, multiple endocrine abnormalities)
Locus heterogeneity?
Mutations in different loci, lead to similar disease: Albino
Allelic heterogenity?
Different loci mutations lead to the SAME disease
B-thalasssemia
What are assumptions of HArdy-Weinberg genetics?
1) No mutation at the locus
2) Natural selection not occuring
3) Random mating
4) No net migration
What is the equation and meaning of HArdy Winberg?
PP= homozygous for p allele
qq= homozygous for q allele
2pq: heterozygous
pp+2pq+ qq= 1
What is imprinting?
At some loci, only 1 allele is active
If that only allele is inactivated, causes disease
Parder-Willi syndrome Angelman syndromes (chromosome 15)
Clinical effects of Prader-Willi syndrome?
1) Hyperphagia
2) Obesity
3) Intellectual disability
4) Hypogonadism
5) Hypotnia
25% cases due to 2 maternal imprinted genes and no father gene (the maternal is silent)
What is AngelMan syndrome?
Paternal imprinting (silent) and maternal one is defective
5% due to paternal uniparental disomy (the gene from mother not received)
What are modes of inhertiance and the disorders associated?
1) Autosomal dominant (many generations, male +female)
2) Autosomal recessive (usually only 1 generation)
3) X linked recessive (son of mother have 50% chance)
4)
X linked dominent (50% males and 50% daugthers) : hypophospatemic rickets, fragile X, Alport Syndrome
Mitochondrial inheritance?
All female offspring will have
Rare syndromes: MELAS (mitochrondrial encephalopathy), lactic acidosis
Achondroplasia?
Autosomal dominenet
FGFR3 mutation
Dwarf, limbs affected more
Autosomal polycystic kidney?
Autosomal dominent
PKD1 orPKD2, have large cysts on kidney