USMLE (Fach) / Biochemistry - Molecular, Cellular, Techniques (Lektion)
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- Nonhomologous end joining Double strand DNA repair - Brings together 2 ends of DNA fragments to replair double-stranded breaks. - No requirement for homology. - Some DNA may be lost. Defective in ataxia telangiectasia and Fanconi ...
- Homologous recombination Double strand DNA repair - Requires two homologous DNA duplexes.- A strand from the damaged dsDNA is repaired using a complementary strand from the intact homologous dsDNA as a template. - Restores ...
- Regulation of gene expression Promoter: Site where RNA polymerase II and multiple other transcription factors bind to DNA upstream from gene locus (AT-rich upstream sequence with TATA and CAAT boxes).- Promotor mutation commonly results ...
- Introns vs exons Exons contain the actual genetic information coding for protein.Introns are intervening noncoding segments of DNA. Different exons are frequently combined by alternative splicing to produce a larger number ...
- microRNAs MicroRNAs (miRNAs) are small, conserved, noncoding RNA molecules that posttranscriptionally regulate gene expression by targeting the 3' untranslated region of specific mRNAs for degradation or translational ...
- tRNA 75-90 nucleotides, 2° structure, cloverleaf form, anticodon end is opposite 3' aminoacyl end.All tRNAs, both eukaryotic and prokaryotic, have CCA at 3' end along with a high percentage of chemically ...
- Posttranslational modifications Trimming: Removal of N- or C-terminal propeptides from zymogen to generate mature protein (eg, trypsinogen to trypsin). Covalent alterations: Phosphorylation, glycosylation, hydroxylation, methylation, ...
- Chaperone protein Intracellular protein involved in facilitating and/or maintaining protein folding. Eg, in yeast, heat shock proteins (eg, HSP60) are expressed at high temperatures to prevent protein denaturing/misfolding. ...
- Cell cycle phases Checkpoints control transitions between phases of cell cycle. This process is regulated by cyclins, cyclin-dependent kinases (CDKs), and tumor suppressors. M phase (shortest phase of cell cycle) includes ...
- Cell types Permanent: Remian in G0, regenerate from stem cells.- Neurons, skeletal and cardiac muscle, RBCs. Stable (quiescent): Enter G1 from G0 when stimulated.- Hepatocytes, lymphocytes, PCT, periosteal cells. ...
- Rough endoplasmic reticulum Site of synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition to many proteins. Nissl bodies (RER in neurons) – synthesize peptide neurotransmitters for secretion.Free ...
- Smooth endoplasmic reticulum Site of steroid synthesis and detoxification of drugs and poisons. Lacks surface ribosomes. Liver hepatocytes and steroid hormone-producing cells of the adrenal cortex and gonads are rich in SER.
- Cell trafficking Golgi is the distribution center for proteins and lipids from the ER to the vesicles and plasma membrane. - Modifies N-oligosaccharides on aspargine. - Adds O-oligosaccharides on serine and threonine. ...
- Signal recognition particle (SRP) Abundant, cytosolic ribonucleoprotein that traffics proteins from the ribosome to the RER. Absent or dysfunctional SRP → proteins accumulate in the cytosol.
- Vesicular trafficking proteins COPII: ER → cis-Golgi (anterograde). COPI: Golgi → Golgi (retrograde); cis-Golgi → ER Clathrin: trans-Golgi → lysosomes; plasma membrane → endosomes (receptor-mediated endocytosis [eg, ...
- Proteasome Barrel-shaped protein complex that degrades damaged or ubiquitin-tagged proteins. Defects in ubiquitin-proteasome system have been implicated in some cases of Parkinson disease.
- Microtubule Cylindrical outer structure composed of a helical array of polymerized heterodimers of α- and β-tubulin. - Each dimer hase 2 GTP bound. - Incorporated into flagella, cilia, mitotic spindles.- Also ...
- Cilia structure 9 doublet + 2 singlet arrangement of microtubules. Basal body (base of cilium below cell membrane) consists of 9 microtubule triplets with no central microtubules. Axonemal dynein – ATPase that links ...
- Disorders of collagen biosynthesis Scurvy: Deficient hydroxylation secondary to ascorbate deficiency.- Petechiae, ecchymoses, loose teeth, bleeding gums, poor wound healing, poor bone development Osteogenesis imperfecta: Mutations in collagen ...
- Marfan syndrome Autosomal-dominant connective tissue disorder affecting skeleton, heart, and eyes. FBN1 gene mutation on chromosome 15 results in defective fibrillin, a glycoprotein that forms a sheath around elastin.- ...
- Polymerase chain reaction Molecular biology lab procedure used to amplify a desired fragment of DNA. 1. Denaturation – DNA is heated to ~95°C to separate the strands.2. Annealing – Sample is cooled to ~55°C. DNA primers, ...
- CRISPR/Cas9 A genome editing tool, derived from bacteria. Composed of an endonuclease (Cas9, which cleaves dsDNA) and a guide RNA (gRNA) sequence that binds to a complementary target DNA sequence. Cell DNA repair ...
- Blotting procedures Southern blot:1. DNA sample is enzymatically cleaved into smaller pieces, which are separated on a gel by electrophoresis, and then transferred to a filter.2. Filter is exposed to radiolabeled DNA probe ...
- Flow cytometry Laboratory technique to assess size, granularity, and protein expression (immunophenotype) of individual cells in a sample. Cells are tagged with antibodies specific to surface or intracellular proteins. ...
- Microarrays Thousands of nucleic acid sequences are arranged in grids on glass or silicon. DNA or RNA probes are hybridized to the chip, and a scanner detects the relative amounts of complementary binding. Used to ...
- Enzyme-linked immunosorbent assay Immunologic test used to detect the presence of either a specific antigen (eg, HBsAg) or antibody (eg, anti-HBs) in a patient's blood sample. Detection involves the use of an antibody linked to an enzyme. ...
- Karyotyping A process in which metaphase chromosomes are stained, ordered, and numbered according to morphology, size, arm-length raio, and banding pattern. Can be performed on a sample of blood, bone marrow, amniotic ...
- Fluorescence in situ hybridization Fluorescent DNA or RNA probe binds to specific gene site of interest on chromosomes. Used for specific localization of genes and direct visualization of chromosomal anomalies at the molecular level. - ...
- Molecular cloning Production of a recombinant DNA molecule in a bacterial host. 1. Isolate eukaryotic mRNA (post-RNA processing) of interest.2. Add reverse transcriptase (an RNA-dependent DNA polymerase) to produce complementary ...
- Gene expression modifications Transgenic strategies in mice involve:- Random insertion of gene into mouse genome. Random insertion = constitutive.- Targeted insertion or deletion of gene through homologous recombination with mouse ...
- Genetic code features Unambiguous: Each codon specifies only 1 amino acid. Degenerate/redundant: Most amino acids are coded by multiple codons.- Wobble – codons that differ in 3rd, "wobble" position may code for the same ...
- Lac operion Classic example of a genetic response to an environmental change. Glucose is the preferred metabolic substrate in E coli, but when glucose is absent and lactose is available, the lac operon is activated ...
- Pyrimethamine Disrupt pyrimidine synthesis Inhibit dihydrofolate reductase (↓ deoxythymidine monophosphate [dTMP]) in humans, bacteria, and protozoa, respectively